aSSURE Data Security
draft-lucas-assure-data-security-00

Versions: 00                                                            
opsawg                                                          Lucas
Internet Draft                            Cisco International Limited
Intended status: Standards track                   September 13, 2017
Expires: March 17, 2018

                          aSSURE Data Security
                draft-lucas-assure-data-security-00.txt


Abstract

   aSSURE uses industry standards and best practice to provide a
   secure communications platform for device configuration and life
   cycle management across the entire range of smart devices, from
   the largest servers through to more constrained devices, with
   minimal human involvement. Based on extensions to current standard
   methods, aSSURE also provides secure end to end communication
   across any network type.

   A new approach allows key distribution and encrypted channels to
   be established between devices that support RSA, EC and/or simple
   shared secrets. For devices that only support shared secrets, key
   derivation algorithms ensure that forward and backward compatible
   secrecy is supported so that secure change of ownership can be
   obtained. Owners prove ownership via a "case ID" known by the
   manufacturer and the "Trusted Authority" ID Server but not known
   by the device.

   aSSURE defines end-to-end encryption links, called "channels", so
   that pairs of devices communicate with a unique set of encryption
   keys. These unique keys, coupled with the end-to-end encryption,
   mean communication is both secure and private.

   DTLS supports both certificates and pre-shared keys, but does not
   cover key distribution or management. DTLS does not support
   client-specific pre-shared keys because the client cannot identify
   itself during the handshake. Herein are all the APIs required to
   support key distribution and management as well as an extension to
   the DTLS handshake that allows the client identity to be provided.

   aSSURE cleanly integrates with the Open Interconnect Consortium
   (OIC) architecture. Both use CBOR encoded data with CoAP over UDP
   and DTLS. aSSURE URIs do not collide with OIC URIs and aSSURE
   channels can be used as a secure transport for OIC requests.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF). Note that other groups may also distribute
   working documents as Internet-Drafts. The list of current
   Internet-

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   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six
   months and may be updated, replaced, or obsoleted by other
   documents at any time. It is inappropriate to use Internet-Drafts
   as reference material or to cite them other than as "work in
   progress."

   This Internet-Draft will expire on March 17, 2018.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors. All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   (http://trustee.ietf.org/license-info) in effect on the date of
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   warranty as described in the Simplified BSD License.

































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Table of Contents

1. INTRODUCTION..................................................... 7
2. THE ROLE OF ASSURE IN AN IOT ENVIRONMENT......................... 8
2.1. Background..................................................... 8
2.2. Who am I allowed to talk to?................................... 8
2.3. How can I authenticate them?................................... 9
2.4. What am I allowed to tell them?................................ 9
2.5. What are they allowed to tell me?.............................. 9
2.6. How can I ensure that our communication is private?............ 9
3. TERMINOLOGY..................................................... 10
4. THE ROLE OF THE MANAGEMENT SYSTEM IN ASSURE..................... 10
4.1. Overview...................................................... 10
4.2. Creation of Communication Topologies.......................... 10
4.3. Examples of communication topologies.......................... 11
4.3.1. A "star" topology........................................... 11
4.3.2. A "ring" topology........................................... 11
4.3.3. A "tree" topology........................................... 12
4.3.4. A "fully connected" topology................................ 12
5. ASSURE ARCHITECTURE............................................. 13
5.1. Internet Accessible Deployments............................... 13
5.2. Walled Garden Deployments..................................... 14
6. SECURITY CONSIDERATIONS......................................... 15
6.1. Overview...................................................... 15
6.2. Guidelines for manufacturers.................................. 17
6.2.1. Device UUID................................................. 17
6.2.2. Device Asymmetric Key....................................... 17
6.2.3. Device Shared Secret........................................ 17
6.2.4. Case ID..................................................... 17
6.2.5. QR Code..................................................... 17
7. DATA STRUCTURES................................................. 18
7.1. Overview...................................................... 18
7.2. Key Definition................................................ 18
7.3. Signature Definition.......................................... 20
7.4. Authenticated Key Definition.................................. 21
7.5. Content Type IDs.............................................. 22
7.6. Key Format IDs................................................ 23
7.7. Identity Class IDs............................................ 23
7.8. Cipher Suite IDs.............................................. 24
7.9. Signature Format IDs.......................................... 24
7.10. Authenticated Key Metadata................................... 25
7.11. aSSURE timestamps............................................ 25
7.11.1. Simple timestamps.......................................... 25
7.11.2. Precision timestamps....................................... 25
8. DTLS WITH ASSURE KEY IDENTITIES................................. 26
8.1. Overview...................................................... 26
8.2. Extension to (D)TLS........................................... 26
8.2.1. Peer Name Indication........................................ 26
8.3. Proof of identity by public key clients....................... 27
8.4. Proof of identity by shared secret clients.................... 28
9. TRUSTED AUTHORITY APIS.......................................... 29
9.1. Overview...................................................... 29

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9.2. Manufacturer API.............................................. 29
9.2.1. PUT /v1/devices/<uuid>...................................... 30
9.2.2. POST /v1/parametersets...................................... 31
9.2.3. PUT /v1/parametersets/<uuid>................................ 31
9.2.4. GET /v1/parametersets/<uuid>................................ 31
9.3. Owner API..................................................... 32
9.3.1. POST /v1/managementsystems.................................. 32
9.3.2. PUT /v1/devices/<uuid>/owner?case_string=<string>........... 33
9.3.3. PUT /v1/devices/<uuid>/owner?mgmtid=<string>................ 33
9.3.4. PUT /v1/devices/<uuid>/owner?case_string=................... 34
                                         <string>&mgmtid=<string>  34
9.3.5. PUT /v1/devices/<uuid>/owner?mgmtid=NULL.................... 34
9.3.6. GET /v1/devices/<uuid>/parameterset......................... 34
9.3.7. PUT /v1/devices/<uuid>/bootstrap............................ 35
9.3.8. GET /v1/devices/<uuid>/bootstrap............................ 35
9.4. Bootstrap API................................................. 36
9.4.1. GET /v1/devices/<uuid>/bootstrap............................ 36
10. DEVICE MANAGEMENT API.......................................... 36
10.1.1. PUT /v1/keys/<uuid>........................................ 37
10.1.2. POST /v1/keys/generate?type=<key_type>&persistent=<boolean> 37
10.1.3. GET /v1/keys/<uuid>........................................ 38
10.1.4. DELETE /v1/keys/<uuid>..................................... 38
10.1.5. GET /v1/keys............................................... 39
10.1.6. PUT /v1/channels........................................... 39
10.1.7. PUT /v1/channels/<id>...................................... 40
10.1.8. PUT /v1/channels/<channel_id>/open......................... 41
10.1.9. PUT /v1/channels/<channel_id>/close........................ 41
10.1.10. DELETE /v1/channels/<channel_id>.......................... 41
10.1.11. GET /v1/channels/<id>..................................... 42
10.1.12. GET /v1/channels.......................................... 43
10.1.13. PUT /v1/reboot............................................ 44
10.1.14. PUT /v1/shutdown.......................................... 44
10.1.15. PUT /v1/bootstrap......................................... 44
10.1.16. GET /v1/ping.............................................. 45
10.1.17. GET /v1/info.............................................. 45
11. MANAGEMENT SERVER API.......................................... 46
11.1. Overview..................................................... 46
11.2. Registration API............................................. 46
11.2.1. POST /v1/devices/<uuid>?case_string=<case_string>.......... 46
11.2.2. POST /v1/devices/<old_uuid>/replace?uuid=<new_uuid>........ 47
11.2.3. GET /v1/devices/<uuid>/status.............................. 47
11.2.4. GET /v1/devices/<uuid>/info................................ 47
11.3. Presence API................................................. 48
11.3.1. PUT /v1/devices/<uuid>/info................................ 48
11.3.2. PUT /v1/devices/<uuid>/goodbye............................. 49
11.4. Miscellaneous................................................ 49
11.4.1. GET /v1/timestamp.......................................... 49
12. PHYSICAL / NETWORK LAYER IMPLEMENTATIONS....................... 50
12.1. BACnet....................................................... 50
12.1.1. aSSURE Bootstrap........................................... 50
12.1.2. aSSURE Secure Management Channels.......................... 52
12.1.3. aSSURE Secure Data Channels................................ 52

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12.2. IP........................................................... 52
12.2.1. Bootstrap Server FQDN...................................... 53
12.3. Bluetooth.................................................... 53
12.4. Assigned address types....................................... 53
13. DTLS CONNECTION CONFIGURATION EXAMPLES......................... 54
13.1. Example Topology............................................. 54
13.2. Elliptic Curve device . Elliptic Curve device................ 55
13.3. Elliptic Curve device . RSA device........................... 55
13.3.1. Option 1 - Issue EC key to RSA device...................... 55
13.3.2. Option 2 - Issue RSA key to EC device...................... 55
13.3.3. Option 3 - Issue Shared Secret to both devices............. 55
13.4. Elliptic Curve device . Shared Secret device................. 55
13.5. RSA device . RSA device...................................... 55
13.6. RSA device . Shared Secret device............................ 56
13.7. Shared Secret device . Shared Secret device.................. 56
14. MESSAGE SEQUENCE DIAGRAMS...................................... 57
14.1. Manufacturing Flow........................................... 57
14.2. Management System Preparation................................ 58
14.3. Device Registration.......................................... 59
14.4. Device Ownership State Machine............................... 60
14.5. Device Configuration and Bootstrap........................... 61
14.6. Device Configuration and Bootstrap (Walled Garden)........... 62
14.7. Device Change Owner.......................................... 63
15. CONFIGURATION AND BOOTSTRAP DATA FORMATS....................... 65
15.1. Overview..................................................... 65
15.2. Configuration data format.................................... 65
15.3. Device connection to the bootstrap server using DTLS using... 66
      pre-shared secrets........................................... 66
15.4. Device connection to the bootstrap server using DTLS using... 66
      public keys.................................................. 66
15.5. Bootstrap data format........................................ 66
15.5.1. Payload protected by Elliptic Curve keys................... 67
15.5.2. Payload protected by RSA keys.............................. 68
15.5.3. Payload protected by shared secrets........................ 68
15.5.4. Decrypted payload content.................................. 68
16. SECURITY CONSIDERATIONS........................................ 69
17. IANA CONSIDERATIONS............................................ 69
18. CONCLUSIONS.................................................... 69
19. REFERENCES..................................................... 69
19.1. Normative References......................................... 69
19.2. Informative References....................................... 70
20. ACKNOWLEDGMENTS............................................... 711












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Table of Figures

               Star Topology  11
               Ring Topology  11
               Tree Topology  12
               Fully Connected Topology   12
               Internet-accessible architecture 13
               Walled-garden architecture 14
               DTLS Connection Example Topology 55
               Manufacturing Flow Sequence Diagram 57
               Management System Preparation Sequence Diagram  58
               Device Registration Sequence Diagram   59
               Device Ownership State Machine   60
               Device Configuration and Bootstrap Sequence Diagram 61
               Device Configuration and Bootstrap Sequence Diagram
                                                (Walled Garden)   62
               Device Change Owner Sequence Diagram (first part)  63
               Device Change Owner Sequence Diagram (second part) 64






































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Glossary of Terms

   API      Application Programming Interface
   CA       Certificate Authority
   CBOR     Concise Binary Object Representation, RFC-7049
   CoAP     Constrained Application Protocol, RFC-7252
   DHCP     Dynamic Host Configuration Protocol
   DNS      Domain Name System
   DTLS     Datagram Transport Layer Security (v1.2), RFC-6347
   EC       Elliptic Curve
   ECDSA    E C Digital Signature Algorithm, NIST FIPS   186-4
   ECIES    Elliptic Curve Integrated Encryption Scheme, ANSI X9.63
   FQDN     Fully Qualified Domain Name
   PKCS     Public Key Cryptography Service
   PKI      Public Key Infrastructure
   TA       Trusted Authority
   TLS      Transport Layer Security (v1.2), RFC-5246

1. Introduction

   This document provides the reference technical specification for
   aSSURE.

   aSSURE uses industry standards and best practice to provide a
   secure communications platform for device configuration and life
   cycle management. Where possible, a minimal approach is taken to
   standards implementation so that the complexity and code footprint
   for implementation is kept to a minimum.

   The underlying standards are:
  o Transport Layer Security, TLS v1.2, RFC-5246
  o Datagram Transport Layer Security, DTLS v1.2, RFC-6347
  o Constrained Application Framework, CoAP, RFC-7252
  o Concise Binary Object Representation, CBOR, RFC-7049
  o CoAP Block-wise Transfers, https://www.ietf.org/id/draft-ietf
  o core-block-21.txt


   The additional functionality provided by aSSURE is intended to
   work within existing communications frameworks. This allows aSSURE
   to provide an upgrade path to add a common security approach that
   provides both secure communications and lifecycle management
   including change of ownership. aSSURE uses a "Trusted Authority"
   (TA), similar to the role that a Certificate Authority (CA) plays
   in a Public Key Infrastructure (PKI) today, to track the
   manufacture and ownership of devices. Any number of Trusted
   Authorities may exist but each device will be assigned to a
   specific TA during its manufacture and will remain assigned to
   this TA for its entire life.

   Device owners communicate with the various Trusted Authorities to
   assert ownership of individual devices and upload the initial

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   configuration for the device. When the device powers up, it will
   contact the Trusted Authority to obtain its initial configuration
   - this process is called "bootstrap". The initial configuration
   will provide sufficient information for the device to establish a
   secure communications channel to the system that will be managing
   it. Once this channel is established, additional configuration
   will be provided from the management system directly to the device
   and the device can enter "normal service".

   The detailed device lifecycle flow is described elsewhere.

   Note
   aSSURE is designed to cleanly integrate with the Open Interconnect
   Consortium (OIC) architecture. Both OIC and aSSURE use CBOR
   encoded data with CoAP over UDP and DTLS. aSSURE URIs have been
   deliberately chosen not to collide with OIC URIs and aSSURE
   channels can be used as a secure transport for OIC requests.

2. The role of aSSURE in an IoT environment

2.1. Background

   In any secure environment, there are five basic questions that any
   device must ask:

  1. Who am I allowed to talk to?
  2. How can I authenticate them?
  3. What am I allowed to tell them?
  4. What are they allowed to tell me?
  5. How can I ensure that our communication is private?

   If these basic questions can all be answered with confidence,
   there is the foundation for a secure system. If any of the above
   are uncertain then the system has weaknesses that may be exploited
   by an attacker.

   The aSSURE standard provides an answer to all these questions in a
   way that allows devices to communicate across different network
   architectures and device capabilities yet still providing end-to
   end security at a level that is appropriate to the abilities of
   the devices that are communicating.

   Furthermore, aSSURE provides this with a solution that involves
   minimal human involvement.

   The following sections will address each of these questions in
   turn.

2.2. Who am I allowed to talk to?

   In many ways, this is one of the biggest hurdles to overcome. If
   we want to be able to manufacture and sell "generic" product that

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   has no pre-configuration, how does that device know that we own
   it?  There are a lot of different approaches to this with "Trusted
   On First Use" (TOFU) being an obvious one, but with all of them
   they either have weaknesses in the initial security or rely on
   public key cryptography.

   Public key cryptography is fine in more powerful devices, but not
   an option in the smallest ones, so for a universally secure
   solution, a different approach is required.

   The aSSURE standard uses a Trusted Authority (TA) as the reference
   for the device. The device is programmed with the identity and
   credentials of the TA during manufacture and, on first power up,
   will only talk to the TA. The user will register ownership of the
   device with the TA and securely upload the initial configuration
   data for the device to the TA. The TA will then forward that
   configuration to the device. That configuration includes the
   location and security parameters for the device to connect to the
   owner's systems, so now the device knows that it can trust its
   owner.

   Once the device has connected to the owner's management system,
   this system can deliver additional configuration parameters,
   encryption keys, etc. to the device. This allows the management
   system to tell devices to set up secure peer-to-peer connections,
   connect to additional management systems and perform other
   actions.

2.3. How can I authenticate them?

   The same sequence as for 2.2.  above is used to provide the
   authentication details to the device. This information allows the
   device to authenticate the owner's systems and allows the owner's
   systems to authenticate the device.

2.4. What am I allowed to tell them?

   The same sequence as for 2.2.  above is used to provide the access
   control rules for access to the device data. This allows the
   device to know what information it can disclose.

2.5. What are they allowed to tell me?

   The same sequence as for 2.2.  above is used to provide the access
   control rules for commands and configuration sent to the device.
   This allows the device to know what parameters and commands it
   will accept from the owner's systems.

2.6. How can I ensure that our communication is private?

   The aSSURE standard defines end-to-end encryption links, called
   "channels", that ensure each pair of devices communicate with a

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   unique set of encryption keys. These unique keys, coupled with the
   end-to-end encryption, means that their communication is both
   secure and private.

3. Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
   NOT","SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL"
   in this document are to be interpreted as described in RFC 2119
   [RFC2119].

   In this document, these words will appear with that interpretation
   only when in ALL CAPS. Lower case uses of these words are not to
   be interpreted as carrying significance described in RFC 2119.

   In this document, the characters ">>" preceding an indented
   line(s) indicates a statement using the key words listed above.
   This convention aids reviewers in quickly identifying or finding
   The portions of this RFC covered by these keywords.


4. The role of the Management System in aSSURE

4.1. Overview

   The Management System is a key part in the trust relationship that
   the device creates. The root of trust is the Trusted Authority.
   The Trusted Authority tells the device which management systems(s)
   it can trust. The Management Systems tell the device which other
   management systems and devices it can trust (if any) and what
   their permissions are on the device.

4.2. Creation of Communication Topologies

   The Management System can instruct the aSSURE devices to form any
   topology that is within their capabilities. The limits on the
   topology types and complexity are only:

  o Limitations set by the underlying network architecture
  o Limitations set by the device memory and/or processing power
  o and/or software
  o Limitations set by the management software

   In aSSURE terminology, each connection between devices is called a
   channel. The rules about how channel keys are determined and
   assigned is described in detail in section 13.  below.








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4.3. Examples of communication topologies

4.3.1. A "star" topology
                                        _______
                                       /       \
                                       | Device|
                             _______   \_______/   ______
                            /       \      |      /      \
                            | Device|      |      |Device|
                            \_______/\     |     /\______/
                                      \ ___|___ /
                                       /       \
                                       | Device|
                                       \_______/
                             _______  /    |    \  _______
                            /       \/     |     \/       \
                            | Device|      |      | Device|
                            \_______/   ___|___   \_______/
                                       /       \
                                       | Device|
                                       \_______/

                                  Star Topology

4.3.2. A "ring" topology
                                        _______
                                       /       \
                                       | Device|
                             _______  /\_______/\  ______
                            /       \/           \/      \
                            | Device|             |Device|
                            \_______/             \______/
                                |                     |
                                |                     |
                             ___|___               ___|___
                            /       \             /       \
                            | Device|             | Device|
                            \_______/\  _______  /\_______/
                                      \/       \/
                                       | Device|
                                       \_______/

                                  Ring Topology










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4.3.3. A "tree" topology
                                        _______
                                       /       \
                                       | Device|
                             _______   \_______/   ______
                            /       \      |      /      \
                            | Device|      |      |Device|
                            \_______/\     |     /\______/
                                      \ ___|___ /
                                       /       \
                                       | Device|
                                       \_______/
                             _______       |       _______
                            /       \      |      /       \
                            | Device|      |      | Device|
                            \_______/\  ___|___  /\_______/
                                      \/       \/
                                       | Device|
                                       \_______/

                                  Tree Topology

4.3.4. A "fully connected" topology

   The fully connected topology shows four devices where each device
   has a connector to all of the other three devices. If there are
   "n" devices they each have "n-1" connectors.
                             _______           _______
                            /       \         /       \
                            | Device|<------->| Device|
                            \_______/         \_______/
                               ^  ^            ^    ^
                               |   \          /     |
                               |    \      --/      |
                               |     \    /         |
                               |      ------        |
                               |        /   \       |
                               |     --/     \      |
                               |    /         \     |
                             __v_ _v_          v____v_
                            /       \         /       \
                            | Device|<------->| Device|
                            \_______/         \_______/


                            Fully Connected Topology







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5. aSSURE Architecture

5.1. Internet Accessible Deployments

     TRUSTED AUTHORITY                    MANUFACTURER
+-------------------------+       +--------------------------+
|                         |       |                          |
|+----------------------+ |       |    +--------------+      |
||  MANUFACTURER        |<--(-)--------|MANUFACTURING |--    |
||   GATEWAY            | |Manufacturer| SYSTEM       |  |   |
|+--------------------!-+ | Interface  +--------------+  |   |
|  |                  !   |       |                      V   |
|  |                  !   |       |                +-------+ |
|  |                  !   |       |  Short-Lived   | DEVICE| |
|  |   +--A-I-R-G-A-P-!---|       |  Make & Delete +-------+ |
|  |   |              !   |       |                    !     |
|  |   A     LOCK     !   |       +--------------------!-----+
|  |   I  +-----------V-+ |                            !
|  |   R  | IDENTITY    | |                            !
|  |   G  |  SERVER     | |                            !
|  |   A  +-----------!-+ |               OWNER        !
|  |   P              !   |   +------------------------!-----+
|  |   |              !   |   |                        !     |
|  |   +---A-I-R-G-A-P!---|   | Bootstrap Interface+---v---+ |
|  v                  !   |   |     -----(-)-------| DEVICE| |
|+-----------------+  !   |   |    /               +-------+ |
||  REGISTRATION   |  !   |   |   /               /|QR CODE| |
||   SERVER        |  !   |   |  /               / +-------+ |
|+-----------------+  !   |   | /               /      |     |
|  ^       ^          !   |   |/              (/)      |     |
|  |       |          !   |   /        Management      v     |
|  |     +------------V-+ | (/)        Interface   +-------+ |
|  |     |  BOOTSTRAP   |<--/ |            (/)     INSTALLER |
|  |     |   SERVER     | |   |            /       +-------+ |
|  |     +--------------+ |   |           /           /      |
|  |       ^              |   |          /          (/)      |
|  |       |              |   |  +------v----+  Registration |
|  |       |              |   |  |           |   Interface   |
|  |       |              |   |  | MANAGEMENT|   (/)         |
|+-------------+          |   |  |  SYSTEM   |   /           |
||  OWNER      |          |   |  |           |  /            |
||   GATEWAY   |<--------(-)-----|           | /             |
|+-------------+       Owner  |  |           |v              |
|                    Interface|  +-----------+               |
|                         |   |                              |
|                         |   |                              |
+-------------------------+   +------------------------------+

                        Internet-accessible architecture




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5.2. Walled Garden Deployments

TRUSTED AUTHORITY                      MANUFACTURER
+----------------------+       +----------------------------+
|                      |       |                            |
|+-------------------+ |       |    +----------------+      |
|| MANUFACTURER      |<----(-)------|  MANUFACTURING |--    |
||  GATEWAY          | |Manufacturer|   SYSTEM       |  |   |
|+-----------------!-+ | Interface  +----------------+  |   |
| |                !   |       |                        V   |
| |                !   |       |     Short-lived  +-------+ |
| |                !   |       |    Make & Delete | DEVICE| |
| | +--A-I-R-G-A-P-!---|       |                  +-------+ |
| | |              !   |       |                      !     |
| | A     LOCK     !   |       +----------------------!-----+
| | I  +-----------V-+ |                              !
| | R  | IDENTITY    | |                              !
| | G  |  SERVER     | |                              !
| | A  +-----------!-+ |               OWNER          !
| | P              !   | +----------------------------!-----+
| | |              !   | |                            !     |
| | +---A-I-R-G-A-P!---| |+-----------+ Bootstrap +---v---+ |
| v                !   | ||  Bootstrap|<--(-)-----| DEVICE| |
|+--------------+  !   | ||   Server  | Interface +-------+ |
|| REGISTRATION |  !   | |+-----------+        /  |QR CODE| |
||  SERVER      |  !   | | ^                 (/)  +-------+ |
|+--------------+  !   | | ! +----------+ Management  |     |
| ^     ^          !   | | ! |Management| Interface   |     |
| |     |          !   | | ! |  Server  |<-/          |     |
| |   +------------V-+ | | ! +----------+             |     |
| |   |  BOOTSTRAP   | | | !   ^                      |     |
| |   |   SERVER     | | +=!===!===WALLED=GARDEN======|=====|
| |   +--------------+ | | !   !                      v     |
| |     ^              | | !  /                 +---------+ |
| |     |              | | ! /                  |INSTALLER| |
| |     |              | | !/                   +---------+ |
| |     |              | |+----------+           /          |
|+----------+          | ||INTERNET  |         (/)          |
|| OWNER    |          | || FACING   |    Registration      |
||  GATEWAY |<----(-)-----|MANAGEMENT|     Interface        |
|+----------+    Owner | || SYSTEM   |      (/)             |
|             Interface| ||          |<-----/               |
|                      | |+----------+                      |
|                      | |                                  |
+----------------------+ +----------------------------------+

                           Walled-garden architecture







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6. Security Considerations

6.1. Overview

   The aSSURE framework is intended to be usable across the entire
   range of smart devices - from the largest servers through to more
   constrained devices (as defined in RFC-7228). This is a very
   challenging goal and means that some security approaches in common
   use today are not universally suitable.

   Examples of approaches that are not universally suitable include:

  o Public Key Cryptography, e.g. RSA, DSA, EC
       o This is computationally intensive and may take too long to
          be acceptable on devices with minimal processing ability.
       o This is computationally intensive and the necessary
          additional processing load may have an unacceptable impact
          on battery life.
       o This requires reasonably large code size to implement in
          software and this may not be available on the more
          constrained devices.
  o X.509 certificates
       o These use time stamps and small devices may not have a real
          time clock.
       o These assume public key cryptography (RSA, DSA or EC) and
          constrained devices may not be able to support this as
          explained above.
       o These have a fixed lifetime, thus requiring them to be
          reissued before they expire.
       o These require a certificate authority to issue (and
          reissue) them.
       o Due to their complexity, these have been the target of
          various attacks in the past, so removing them reduces the
          attack surface.
  o Complex text-based data representations such as ASN.1, HTML,
     XML, YAML or JSON
       o These are difficult to parse, requiring larger code
          libraries and more processing power than simpler formats
          such as CBOR.
       o Due to their complexity, these have been the target of
          various attacks in the past, so removing them reduces the
          attack surface.
  o Complex protocols such as SOAP, HTML, etc.
       o Again, these are more difficult to parse, requiring larger
          code libraries and more processing power than simpler
          protocols such as CoAP.
  o Full standards implementation
       o Lots of industry standards are large and have a lot of
          different options, most of which are unnecessary for a new
          implementation with no legacy support requirements.
       o For example, TLS supports over 200 different cipher suites
          and this list continues to grow.

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       o Due to their complexity, these have been the target of
          various attacks in the past, so reducing the scope of the
          implementation also reduces the attack surface.

   Support for shared secrets

   Very constrained devices that cannot support public key
   cryptography have to fall back on "shared secrets" (also known as
   "pre-shared keys") to identify themselves. Typical approaches
   using shared secrets require the secret to be disclosed to both
   parties to set up the secure connection. Once a secret has been
   disclosed, it can never be proved to have been forgotten. This
   makes transfer of device ownership problematic, as the previous
   owner of the device may still know the shared secret even after
   the device has been transferred to a new owner. In this scenario,
   the previous owner would be able to decrypt all traffic between
   the device and its new owner, making the device untrustworthy to
   the new owner.

   aSSURE offers a new approach using shared secrets that allows the
   original secret to be concealed from the peer involved in the
   connection.

   In the aSSURE scenario, a shared secret can be distributed to a
   device (or multiple devices) with one or two derivation functions.
   These derivation functions allow a device with the correct
   reference key to derive the shared secret. Different derivation
   functions exist to derive the shared secret from an Elliptic Curve
   key, an RSA key or another shared secret.

   This ability to derive shared secrets is used to secure the
   ownership lifecycle for devices that do not support public key
   cryptography. With this approach, the device owner is provided
   with the parameters for the hashing function and the derived
   shared secret but not the original shared secret programmed into
   the device during manufacture. When the owner wishes to
   communicate with the device, the owner provides the device with
   the derived secret parameters, thus allowing the device to derive
   the new secret from the original secret. The owner is provided
   with a second derivation function that uses the owner key, so they
   can also derive the same secret and hence establish a secure
   communication link to the device. When the device changes owner,
   the new owner is given a different derived secret, not the
   original secret. The new owner can communicate with the device
   using the new parameters and the knowledge of the new derived
   secret. The previous owner, however, does not have the new owner's
   key nor the device key, so cannot derive the new shared secret and
   so is unable to decrypt the communications with the new owner.

   The only entities that know the original device secret are the
   device itself and the Identity server within the Trusted Authority
   (this is described in more detail later).

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   Shared secrets are described more in 7.2. and 8.4.  below.

6.2. Guidelines for manufacturers

6.2.1. Device UUID

   All device UUIDs should be truly randomly generated. This means
   that they are completely unpredictable and knowledge of the UUID
   does not disclose any information about what the device is, who
   manufactured it or when.

6.2.2. Device Asymmetric Key

   If a device uses an RSA or EC asymmetric key, this should be
   securely generated within the device and the private key must
   never be disclosed outside of the device. The device should have
   access to a suitable entropy source to ensure that the key is
   truly randomly generated.

6.2.3. Device Shared Secret

   If a device uses a shared secret, this should be truly randomly
   generated and at least 128 bits in size. It may be generated
   inside the device or on the local manufacturing station but, if
   generated outside the device, must never be stored in an
   unencrypted form and must be wiped from RAM as soon as it is no
   longer needed. The device secret can only ever be stored in non
   volatile storage AFTER it has been formed into the device identity
   structure and encrypted as described in 9.2.1.  below.

6.2.4. Case ID

   The aSSURE solution needs a method for an owner to prove that a
   device is in their possession. This is done through knowledge of a
   "case ID", an identification string that is printed on the outside
   of the case. This number is NOT known to the device - it is only
   known to the manufacturer and the Trusted Authority's Identity
   Server. The case ID should be a randomly generated number that is
   at least 128 bits.

6.2.5. QR Code

   The device ID and case ID should be printed in a QR Code on the
   side of the device. The data should be encoded in CBOR as follows:

   ARRAY {
     INTEGER version    // Set to 1 for aSSURE v1
     BYTE STRING device_uuid
     BYTE STRING case_id
   }


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   If the device UUID and case UUID are both 128 bits then this will
   encode in 36 bytes. This can be encoded in a type 3 QR code (27 x
   27 pixels) with "M" level of error correction, a type 4 QR code
   (33 x 33 pixels) with a "Q" level of error or a type 5 QR code (37
   x 37 pixels) with "H" level of error correction.

   The manufacturer may choose any of these QR formats, but the type
   5 is recommended as it has a higher level of error correction and
   is therefore less susceptible to damage.

7. Data Structures

7.1. Overview

   Where possible, common data structures are used across the system.
   This simplifies the development and allows better code reuse.

7.2. Key Definition

   A key is defined using one of the following CBOR formats depending
   on its type. All keys are identified by their ID, which is a 128
   bit randomly assigned UUID.

   Keys have a format which may be Elliptic Curve, RSA or derived
   secret. Elliptic Curve and RSA keys must include the public key
   part and may optionally also include the associated private key.

   If the key is an Elliptic Curve key, the definition is:

   ARRAY {
     INTEGER       content  // "Key Content Type", see 7.5. below
     INTEGER       format  // "EC key", see 7.6.  below
     BYTE STRING   key_id  // UUID
     BYTE STRING   public_key  // ASN.1 DER encoded string
     BYTE STRING   private_key  // ASN.1 DER encoded string
   }

   The private_key  BYTE STRING must be zero length if only a public
   key is provided.

   Note that the private key definition is not encrypted so if the
   private key is provided, the definition must be transferred over
   an encrypted channel and stored in a protected store.

   If the key is an RSA key, the definition is:

   ARRAY {
     INTEGER      content  // "Key Content Type", see 7.5. below
     INTEGER      format   // "RSA key", see 7.6.  below
     BYTE STRING  key_id   // UUID
     BYTE STRING  public_key  // ASN.1 DER encoded string
     BYTE STRING  private_key  // ASN.1 DER encoded string

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   }
   The private_key  BYTE STRING must be zero length if only a public
   key is provided.

   Note that the private key definition is not encrypted so if the
   private key is provided, the definition must be transferred over
   an encrypted channel and stored in a protected store.

   If the key is a derived secret, the definition is:

   ARRAY {
     INTEGER         content  // "Key Content Type", see 7.5. below
     INTEGER         format   // "Derived shared secret", see 7.6.
   below
                              // below
     BYTE STRING     key_id   // UUID
     ARRAY {
       // Derivation definition
       BYTE STRING     reference_A_key // UUID
       BYTE STRING     salt
       INTEGER         iterations_or_cipher
       BYTE_STRING     encrypted_secret
     }
     // Additional derivation definitions may be present in
     // the same format as above
   }

   The derived secret has one or more derivation definitions.   All
   derivations can be disclosed publicly and all derivations must
   produce the same secret. A device may use any of the derivations
   for which it already knows the reference key.

   If the reference key is a shared secret then the PBKDF2 algorithm
   is used with SHA2 as the digest function, the reference key shared
   secret used as the passphrase, the "iterations_or_cipher" used as
   the iteration count, salt and a length value determined by the
   length of the "encrypted_secret". After the PBKDF2 is completed,
   the result is XOR'd against the "encrypted_secret". This allows
   secure generation of any byte sequence.

   If the reference key is an elliptic curve key, then the "salt" and
   "iterations_or_cipher" fields are ignored (and should be zero
   length and value zero respectively). The "encrypted_secret"
   contains the shared secret protected by the Cryptographic Message
   Syntax with "enveloped-data" as the ContentInfo (see RFC 5652 and
   RFC 5753) using the "Standard" variation of Ephemeral Static ECDH
   (see RFC 5753 section 3.1). The default choices for encryption
   cipher and hash function should be AES-128 and SHA-256
   respectively.

   If the reference key is an RSA key, then the "salt" and
   "iterations_or_cipher" fields are ignored (and should be zero

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   length and value zero respectively). The "encrypted_secret"
   contains the shared secret protected by the Cryptographic Message
   Syntax with "enveloped-data" as the ContentInfo (see RFC 5652)
   using RSAES-OAEP (see RFC 8017 section 7.1). The default choices
   for encryption cipher and hash function should be AES-128 and SHA
   256 respectively. The SHA-1 hash should not be used.

7.3. Signature Definition

   Rather than use X.509 signatures, which require public key
   cryptography and ASN.1 encoding, aSSURE uses a simpler approach
   using CBOR that can also be used with derived secrets as well as
   public keys.

   If the signature is generated by an Elliptic Curve private key,
   the signature structure is:

   ARRAY {
       INTEGER     content // "Signature Content Type", see
                           // 7.5. below
       INTEGER     format // Signature format, see 7.9. below
       INTEGER     created_at
       INTEGER     valid_until
       BYTE STRING key_id
       BYTE STRING r
       BYTE STRING s
   }
   Here, "r" and "s" are the signature values as defined in the
   Elliptic Curve Digital Signature Algorithm (ECDSA).

   If the signature is generated by an RSA private key, the signature
   structure is:

   ARRAY {
       INTEGER     content // "Signature Content Type", see
                           // 7.5.  below
       INTEGER     format  // Signature format, see 7.9. below
       INTEGER     created_at
       INTEGER     valid_until
       BYTE STRING key_id
       BYTE STRING s
   }
   Here, "s" are the signature values as defined in the RSA Digital
   Signature Algorithm (PKCS #1 v1.5).


   If the signature is generated by a derived secret, the signature
   structure is:

   ARRAY {
       INTEGER     content // "Signature Content Type", see
                           // 7.5. below

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       INTEGER     format  // Signature format, see 7.9. below
       INTEGER     created_at
       INTEGER     valid_until
       BYTE STRING key_id
       BYTE STRING hmac
   }

   In all cases, the signature covers the original data structure and
   the signature structure with the "r", "s" and/or "hmac" fields
   being treated as zero length when performing the sign or
   validation actions (i.e. the BYTE STRING definition is considered
   to be the value 0b010_00000).

   Two timestamps are part of each signature:

  o The timestamp of when the signature was created ("created_at")
  o The timestamp after which the signature invalid ("valid_until")
  o
   Each signing authority is free to choose its own validity duration
   for the signatures that it issues. The authority can therefore
   balance the rate of re-issue of signatures against the time that a
   signature or a compromised key would remain valid. These fields
   can be set to zero to indicate a signature that is always valid
   and never expires. These fields may also be zero if the signature
   authority knows that the signature is being issued to a device
   with no real-time clock capability. If a device has no knowledge
   of the true time, these fields should be ignored when performing
   signature validation.

7.4. Authenticated Key Definition

   Rather than use X.509 certificates which require public key
   cryptography, ASN.1 encoding and knowledge of real time, aSSURE
   uses a simpler yet more flexible structure to authenticate a
   public key or a key derived from a shared secret.

   An authenticated key definition combines a header, key definition
   as in 7.2.  above, optional metadata and signature as in 7.3.
   above.

   ARRAY {
       INTEGER content  // "Identity Content Type", see 7.5. below
       INTEGER class    // Identity class, see 7.7.  below
       ARRAY {
           // Key definition, see 7.2.  above
           INTEGER content // "Key Content Type", see 7.5. below
       }
       MAP {
           // Metadata (key + value pairs), see 7.10.  below
       }
       ARRAY {
           // Signature definition, see 7.3.  above

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           INTEGER content  // "Signature Content Type", see
                            // 7.5.  below
       }
   }

   The device should validate an "authenticated key" as follows:

  1. Check that the key used to generate its signature is already
     present in the device
  2. Check that current time is within the timestamp range for the
     signature
  3. For each key in the hierarchy of keys required to validate this
     signature, check that current time is within the timestamp range
     for that key's signature
  4. Check that the class of the key used to generate the signature
     is allowed to sign the class of the new authenticated key. The
     rules for this are in 7.7.  below.
  5. Check that the signature matches the authenticated key data

   If all the above checks pass, the authenticated key can be
   accepted.

7.5. Content Type IDs

   +-------+------------------------------+
   | Value | Meaning                      |
   +-------+------------------------------+
   | 0     | Identity Content Type        |
   | 1     | Key Content Type             |
   | 2     | Configuration Content Type   |
   | 3     | Encrypted Key Content Type   |
   | 4     | Signature Content Type       |
   | 5     | Owner Content Type           |
   +-------+------------------------------+

   +-------+------------------------------+
   | Value | Meaning                      |
   +-------+------------------------------+
   | 0     | Identity Content Type        |
   +--------------------------------------+
   | 1     | Key Content Type             |
   +--------------------------------------+
   | 2     | Configuration Content Type   |
   +--------------------------------------+
   | 3     | Encrypted Key Content Type   |
   +--------------------------------------+
   | 4     | Signature Content Type       |
   +--------------------------------------+
   | 5     | Owner Content Type           |
   +-------+------------------------------+



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7.6. Key Format IDs

   +-------+-------------------------------------+
   | Value | Meaning                             |
   +-------+-------------------------------------+
   | 0     | Elliptic Curve Key (ASN1.DER encoded|
   |       |   following industry standards)     |
   | 1     | RSA Key (ASN1.DER encoded              |
   |       |   following industry standards)     |
   | 2     | Configuration Content Type          |
   +-------+-------------------------------------+

7.7. Identity Class IDs

   +---+------------+---------------------------------------+
   |                |                    Signing Permissions|
   +                +----+----+----+----+----+----+    |    +
   |                |      Identity Classes       |    |    |
   +                +----+----+----+----+----+----+    |    +
   |                | M  |    |    |    |    |    |    |    |
   |                | a  |    |    |    |    |    |    |    |
   |                | n  |    |M S |    |    |    |    |    |
   |                | u  |T A |a y |B S |    |    |    |B D |
   |                | f  |r u |n s |o e |    |    |    |o a |
   |                | a  |u t |a t |o r |    | C  |    |o t |
   |---+------------| c  |s h |g e |t v | D  | h  | C  |t a |
   | V |            | t  |t o |e m |s i | e  | a  | o  |s   |
   | a |            | u  |e r |m   |t c | v  | n  | n  |t   |
   | l |            | r  |d i |e   |r e | i  | n  | f  |r   |
   + u +            | e  |  t |n   |a   | c  | e  | i  |a   |
   | e |Name        | r  |  y |t   |p   | e    l    g   p   |
   +---+------------+----+----+----+----+----+----+----+----+
   | 0 |Manufacturer|  Y |  Y |  N |  N |  Y |  N |  N |  N |
   |   |            |    |    |    |    |    |    |    |    |
   +---+------------+----+----+----+----+----+----+----+----+
   | 1 |Trusted     |  N |  Y |  Y |  Y |  Y |  N |  N |  N |
   |   |Authority   |    |    |    |    |    |    |    |    |
   +---+------------+----+----+----+----+----+----+----+----+
   | 2 |Management  |  N |  N |  Y |  Y |  Y |  Y |  Y |  Y |
   |   |System      |    |    |    |    |    |    |    |    |
   +---+------------+----+----+----+----+----+----+----+----+
   | 3 |Bootstrap   |  N |  N |  N |  N |  N |  N |  N |  N |
   |   |Service     |    |    |    |    |    |    |    |    |
   +---+------------+----+----+----+----+----+----+----+----+
   | 4 |Device      |  N |  N |  N |  N |  N |  Y |  N |  N |
   |   |            |    |    |    |    |    |    |    |    |
   +---+------------+----+----+----+----+----+----+----+----+
   | 5 |Channel     |  N |  N |  N |  N |  N |  N |  N |  N |
   |   |            |    |    |    |    |    |    |    |    |
   +--------------------------------------------------------+

   The Manufacturer is the manufacturer of the device. A manufacturer

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   may install Device identification keys at the factory to allow the
   device to authenticate itself. If the device is public key
>> capable, the manufacturer MUST install the identity for the
   Trusted Authority.

   The Trusted Authority refers to all systems running within the
   Trusted Authority. A Trusted Authority is only allowed to
   authenticate other systems running within the Trusted Authority,
   the Bootstrap Service, the owner's Management Systems or the
   Device. It is not allowed to authenticate Bootstrap data or
   device communications Channels.

   The Management System is not allowed to authenticate Manufacturers
   or Trusted Authorities but it can authenticate all other
   identities used by the device.

   The Bootstrap Service is not allowed to authenticate anything else
   - it is only able to deliver bootstrap data to the device.

   The Device is only allowed to authenticate channels.

   The Channel is not allowed to authenticate anything else - it is
   only allowed to transport data.

7.8. Cipher Suite IDs

   +-------+-------------------------------------------------+
   | Value | Meaning                                         |
   +-------+-------------------------------------------------+
   | 0     | "AES-128 CBC" (OID 2.16.840.1.101.3.4.2)"       |
   | 1     | "AES-192 CBC" (OID 2.16.840.1.101.3.4.22)"      |
   | 2     | "AES-256 CBC" (OID 2.16.840.1.101.3.4.42)"      |
   | 3     | "AES-128 CCM" (OID 2.16.840.1.101.3.4.7)"       |
   | 4     | "AES-192 CCM" (OID 2.16.840.1.101.3.4.27)"      |
   | 5     | "AES-256 CCM" (OID 2.16.840.1.101.3.4.47)"      |
   | 6     | "AES-128 GCM" (OID 2.16.840.1.101.3.4.6)"       |
   | 7     | "AES-192 GCM" (OID 2.16.840.1.101.3.4.26)"      |
   | 8     | "AES-256 GCM" (OID 2.16.840.1.101.3.4.46)"      |
   +-------+-------------------------------------------------+

7.9. Signature Format IDs

   +-------+-------------------------------------------------+
   | Value | Meaning                                         |
   +-------+-------------------------------------------------+
   | 0     | ecdsa-with-SHA256 (OID 1.2.840.10045.4.3.2)     |
   +---------------------------------------------------------+
   | 1     | ecdsa-with-SHA384 (OID 1.2.840.10045.4.3.3)     |
   +---------------------------------------------------------+
   | 2     | ecdsa-with-SHA512 (OID 1.2.840.10045.4.3.4)     |
   +---------------------------------------------------------+
   | 3-7   | Reserved..future expansion of ECDSA signatures  |

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   +---------------------------------------------------------+
   | 8     | sha256-with-rsa-signature                       |
   |       | (OID 1.2.840.113549.1.1.11)                     |
   +---------------------------------------------------------+
   | 9     | sha384-with-rsa-signature                       |
   |       | (OID 1.2.840.113549.1.1.12)                     |
   +----------------------------------------------------------
   | 10    | sha512-with-rsa-signature                       |
   |       | (OID 1.2.840.113549.1.1.13)                     |
   +---------------------------------------------------------+
   | 11-15 | Reserved..future expansion of RSA signatures    |
   +---------------------------------------------------------+
   | 16    | hmacWithSHA256 (OID 1.2.840.113549.2.9)         |
   +---------------------------------------------------------+
   | 17    | hmacWithSHA384 (OID 1.2.840.113549.2.10)        |
   +---------------------------------------------------------+
   | 18    | hmacWithSHA512 (OID 1.2.840.113549.2.11)        |
   +---------------------------------------------------------+

7.10. Authenticated Key Metadata

   +----------+------------------+---------------------------+
   | Key      | Value            | Usage                     |
   +----------+------------------+---------------------------+
   |INTEGER(0)| BYTE STRING      | Indicates the device      |
   |          | (<device uuid>)  |    owning the key         |
   +----------+------------------+---------------------------+

7.11. aSSURE timestamps

7.11.1. Simple timestamps

   aSSURE uses a variant of the Unix time format for all its
   timestamps. An aSSURE simple timestamp is an integer that tracks
   the number of seconds since midnight on Friday January 1st 2010
   GMT rather than midnight on January 1st 1970 GMT. This allows a
   signed 32-bit number to provide a valid timestamp until 2078
   rather than 2038.

       aSSURE_timestamp_secs = unix_timestamp_secs - 1262304000

   A simple timestamp is defined in CBOR as:

   INTEGER timestamp_secs

7.11.2. Precision timestamps

   If more precision is required, a fractional part may also be
   provided. This holds the fractional part of the second as a 32-bit
   value (so the precision is ~233ps).

   A precision timestamp is defined in CBOR as:

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   ARRAY {
     INTEGER timestamp_secs
     INTEGER timestamp_frac
   }

8. DTLS with aSSURE key identities

8.1. Overview

   aSSURE uses DTLS for all secure connections due to its low
   overhead both in code and operation. DTLS supports both
   certificates and pre-shared keys, but does not cover how the
   certificate authorities or pre-shared keys are to be securely
   distributed.

   This section shows how we extend the basic DTLS standard with
   additional RFC to provide the functionality required for aSSURE.
   It also shows how to setup DTLS connections in an aSSURE
   environment.

8.2. Extension to (D)TLS

   aSSURE needs to be able to provide the client identity to the
   server during the DTLS handshake. This would normally be done
   using X.509 certificates, but aSSURE avoids the complexity and
   overhead of X.509 certificates so an alternative approach is
   required.
   aSSURE provides the client identity to the server using a new TLS
   extension, "Peer Name Indication" that is lightweight and similar
   to the "Server Name Indication" extension.

8.2.1. Peer Name Indication

   TLS does not provide a mechanism for a client to tell a server the
   name of the client that is connecting before the ServerHello is
   returned. It may be desirable for clients to provide this
   information to facilitate secure connections to servers where the
   ServerHello should vary according to the client identity.

   In order to provide any of the names, clients MAY include an
   extension of type "peer_name" in the (extended) client hello. The
   "extension_data" field of this extension SHALL contain
   "PeerNameList" where:

   struct {
       NameType name_type;
       select (name_type) {
           case uuid: UUID;
       } name;
   } PeerName;


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   enum {
       uuid(0), (255)
   } NameType;

   opaque UUID[16];

   struct {
       PeerName peer_name_list<1..2^16-1>
   } PeerNameList;

   This allows the client to provide its UUID in a compact format to
   the server. It also allows other client formats to be used in the
   future.

8.3. Proof of identity by public key clients

   A typical DTLS handshake uses X.509 certificates to allow both
   mutual authentication of identity and key exchange to set up the
   secure connection.  aSSURE does not use X.509 certificates for the
   reasons explained in section 6.1.  above so an alternative
   approach is required to allow mutual authentication and key
   exchange.

   aSSURE uses the device API calls to allow the management system to
   securely provide identity credentials for other peers to the
   device. An aSSURE device WILL NOT communicate with any peer that
   has not had the peer identity credentials provided to it by an
   authorised management system over a secured connection.

   aSSURE uses the Peer Name Indication extension (see 8.2.1.  above)
   to allow a device to indicate its ID to the peer during the
   initial connection request. This allows the peer to check that the
   device is in its list of trusted devices. If the device is not in
   the list, the peer refuses the connection.

   Similarly, the server uses the Peer Name Indication extension to
   provide its ID to the client in the initial connection response.
   This allows the client to quickly check its database to check that
   the server is in its list of trusted peers. If the server is not
   in the list, the client aborts the connection attempt.

   aSSURE then uses the Raw Public Key Extension defined in RFC-7250
   to allow just the public keys to be exchanged between device and
   peer. Both the device and the peer cross-check the public keys
   provided in the DTLS handshake against the expected public keys
   their list of trusted devices. If either device or peer detect a
   public key mismatch, they abort the handshake.

   If all checks complete without error, the handshake is allowed to
   continue normally and the secure connection is established.



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8.4. Proof of identity by shared secret clients

   When establishing a secure connection, if either device cannot
   support public keys, they must use the derived shared secret
   method of authentication. Derived shared secrets are a weaker
   form of security than public keys, but if used carefully, can
   still provide a reasonable level of security.

   DTLS connections protected by derived shared secrets differ from
   public key cryptography in that both parties must know the same
   secret to allow the DTLS handshake to complete. Hence, a derived
   shared secret can be used to prove a link relationship but not an
   endpoint identity.

   The management system will have been provided with a unique
   derived shared secret for each device - this is provided to the
   device in the bootstrap configuration so that the device can trust
   the link relationship from itself to the management system.

   The management system will then generate a unique derived shared
   secret for each link that the device needs to establish using its
   knowledge of the available keys on the devices at each end of the
   link. The management system will then push that derived shared
   secret to both devices indicating the peer device ID to which the
   derived shared secret relates and instruct one of them to act as
   the client to establish the channel.

   The client will then attempt to connect to the peer using DTLS.

   aSSURE uses the Peer Name Indication extension (see 8.2.1.  above)
   to allow a device to indicate its ID to the peer during the
   initial connection request. This allows the peer to check that the
   device is in its list of trusted devices. If the device is not in
   the list, the peer refuses the connection.

   Similarly, the server uses the Peer Name Indication extension to
   provide its ID to the client in the initial connection response.
   This allows the client to quickly check its database to check that
   the server is in its list of trusted peers. If the server is not
   in the list, the client aborts the connection attempt.

   aSSURE then uses the Pre-shared Key Identity Hint Extension
   defined in RFC-4279 to allow the server to provide the necessary
   key information to the client. The key information is encoded in
   Base64 because RFC-4279 recommends that the key information only
   contains printable characters. The key information will be one of:

  o The UUID of a key known to both client and server. The UUID is
     provided as a CBOR BYTE STRING of 16 bytes.
  o A key definition as in 7.2.  above.

   The client can determine which is provided by inspecting the data.

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   A simple UUID is a CBOR BYTE STRING whilst a key definition is a
   CBOR ARRAY.

   The client checks that the indicated (or reference) key is
   available and appropriate for this connection, derives the secret
   as appropriate and uses this as the pre-shared key for the DTLS
   session. The server also derives the secret from the key and uses
   this as the pre-shared key for the DTLS session.

   The DTLS handshake then continues as normal and the session is
   established.

9. Trusted Authority APIs

9.1. Overview

   The Trusted Authority provides three distinct APIs as follows:
  o Manufacturer API
  o Owner API
  o Bootstrap API

   The Manufacturer API is used by the manufacturer to upload
   manufacturing details about each device when it is created. Only
   the minimum amount of information about the device is uploaded and
   this information is stored in One-Time Programmable (OTP) memory
   on the device, so can never be changed. For this reason, the
   Manufacturing API has no requirement to allow device information
   to be updated after manufacture, such as during Return Merchandise
   Authorisation (RMA), because this information can never be
   changed.

   The Owner API is used by the device owner to assert ownership of
   the device, update the device bootstrap configuration and change
   device ownership.

   The Bootstrap API is used by the devices themselves to download
   their bootstrap configuration so that they can connect to their
   management systems and enter service.

9.2. Manufacturer API

   The Manufacturer API is used by the manufacturer to upload data
   about the device when it is manufactured. The manufacturer API is
   a RESTful interface using JSON over HTTPS with client
   authentication. Generation of the client key and issuing of the
   client certificate is out of scope for this document (this
   information could easily be exchanged via email). Similarly,
   delivery of the Trusted Authority "Identity Service" certificate
   to the manufacturer and disclosure of the Manufacturer API URL is
   also out of scope (again, this information could easily be
   provided via email).


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9.2.1. PUT /v1/devices/<uuid>

   After a device is manufactured, the manufacturer builds the device
   data into a JSON data structure as follows:

   {
     "id": "<device UUID>",
     "bootstrap_server": <bootstrap server ID used by device>,
     "case_string": "<string printed on case>",
     "shared_secret": "<Device shared secret as HEX>"
     "public_key": "<X.509 PEM encoded device public key>"
     "parameter_set": "<parameter set UUID>"
     "capabilities": {  // Device bootstrap capabilities
       "ec_capable": <boolean>,
       "rsa_capable": <boolean>,
       "sha384_capable": <boolean>,
       "sha512_capable": <boolean>,
       "aes256_capable": <boolean>,
       // Additional capabilities may be added in the future
     }
   }

   If the device uses an RSA or EC key as its device key, the
   "shared_secret" will not present. If the device is only shared
   secret capable then the "public_key" will not be present. The JSON
   data will NEVER have both "shared_secret" and "public_key" fields.

   All devices must support SHA-256, AES-128 and shared secrets. If
   the device can support other keys, hashing algorithms or ciphers
   during bootstrap, these should be indicated here.

   The manufacturer's production line will have encrypted the device
   data immediately after the device has been tested. The device data
   is encrypted using ECIES and the Identity Service public key
   (which must be a strong Elliptic Curve key). The ECIES
   configuration uses SHA512 and AES-256. The encrypted data is then
   provided as a binary payload in the request.

   No payload is returned. The response code will be one of:
   +--------------+------------------------------------------+
   | Response     | Description                              |
   +--------------+------------------------------------------+
   |201 Created   | The new device has been created          |
   +--------------+------------------------------------------+
   |403 Forbidden | The manufacturer cannot update the       |
   |              | device because it already exists         |
   +--------------+------------------------------------------+
   | 503 Service  | The device cannot be created at          |
   | Unavailable  | this time                                |
   +--------------+------------------------------------------+
   Only a single device is uploaded in each PUT request, but the
   client may re-use the HTTPS session to send additional requests.

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9.2.2. POST /v1/parametersets

   This allows a manufacturer to upload a parameter set definition.
   The format of the parameter set definition is TBD. The parameter
   set is defined in CBOR and provided as the request payload. The
   parameter set is provided in the configuration data to the
   Management System to guide the bootstrap data definition as
   described in 15.2.  below.

   The payload will contain the assigned UUID as a simple ASCII
   string. The response code will be one of:
   +--------------+------------------------------------------+
   | Response     | Description                              |
   +--------------+------------------------------------------+
   |201 Created   | The new parameter set has been created   |
   +--------------+------------------------------------------+
   | 503 Service  | The parameter set cannot be created at   |
   | Unavailable  | this time                                |
   +--------------+------------------------------------------+


9.2.3. PUT /v1/parametersets/<uuid>

   This allows a manufacturer to replace a parameter set definition.
   The format of the parameter set definition is TBD. The parameter
   set is defined in CBOR and provided as the request payload. The
   parameter set is provided in the configuration data to the
   Management System to guide the bootstrap data definition as
   described in 15.2.  below.

   No payload is returned. The response code will be one of:
   +--------------+------------------------------------------+
   | Response     | Description                              |
   +--------------+------------------------------------------+
   |201 Created   | The new parameter set has been created   |
   +--------------+------------------------------------------+
   |403 Forbidden | The manufacturer cannot update the       |
   |              | parameter set because it does not exist  |
   |              | or belongs to a different manufacturer   |
   +--------------+------------------------------------------+
   | 503 Service  | The parameter set cannot be created at   |
   | Unavailable  | this time                                |
   +--------------+------------------------------------------+

   Only a single parameter set is uploaded in each POST request, but
   the client may re-use the HTTPS session to send additional
   requests.

9.2.4. GET /v1/parametersets/<uuid>

   This allows a manufacturer to download a parameter set definition.

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   The format of the parameter set definition is TBD and is exactly
   the data as provided in 9.2.2.  above.

   The returned payload is the parameter set data. The response code
   will be one of:
   +--------------+------------------------------------------+
   | Response     | Description                              |
   +--------------+------------------------------------------+
   |200 OK        | The parameter set has been returned      |
   +--------------+------------------------------------------+
   |403 Forbidden | The parameter set does not exist or was  |
   |              | provided by a different manufacturer     |
   +--------------+------------------------------------------+

9.3. Owner API

   The Owner API is used to take ownership of a device, set the
   bootstrap data for the device and transfer ownership of the
   device.

   As with the Manufacturer API, the Owner API is a RESTful interface
   using JSON over HTTPS with client authentication.

9.3.1. POST /v1/managementsystems

   This is used by management systems to register with the Owner API.
   The connection does not require client authentication.

   Before making this request, the management system should generate
   a new Elliptic Curve key and associated X.509 certificate signing
   request (CSR). The management system provides the CSR in DER
   format as the request payload. The Owner API will immediately
   issue a certificate for this CSR and return it as the response
   payload in DER format.

   All management systems must support both Elliptic Curve and RSA
   public keys, SHA-256, SHA-512, AES-128 and AES-256 so that they
   can correctly interoperate with all devices irrespective of the
   device abilities (or lack of abilities).

   The response code will be one of:
   +--------------+------------------------------------------+
   | Response     | Description                              |
   +--------------+------------------------------------------+
   |201 Created   | The new management system ID             |
   |              | has been created                         |
   +--------------+------------------------------------------+
   | 503 Service  | The management system ID cannot be       |
   | Unavailable  | created at this time                     |
   +--------------+------------------------------------------+



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   Note: Some Trusted Authorities may require a username and password
   to be provided to authenticate this request to prevent attackers
   trying to overload the system with requests. Alternative
   validation approaches are also possible. Such extensions are out
   of scope of this document.

   Note: The serial number of the issued certificate is used as the
   "manufacturer ID" in owner management API requests (9.3.4.  below
   and 9.3.5.  below). For security reasons, the manufacturer ID
   should not be predictable so ought to be a large random number (>=
   64 bits).

9.3.2. PUT /v1/devices/<uuid>/owner?case_string=<string>

   This is used by management systems to take ownership of a device.
   The connection must be authenticated with the issued client
   certificate.

   The case identification string from the QR code must be provided
   as the "case_string" parameter. No payload is provided.
   No payload is returned and the response code will be one of:
   +--------------+------------------------------------------+
   | Response     | Description                              |
   +--------------+------------------------------------------+
   |204 Changed   | Ownership has been assigned to this      |
   |              | management system                        |
   +--------------+------------------------------------------+
   |403 Forbidden | The device is owned by a different       |
   |              | management system, the wrong case string |
   |              | was provided or the device does not exist|
   +--------------+------------------------------------------+

9.3.3. PUT /v1/devices/<uuid>/owner?mgmtid=<string>

   This is a variant of 9.3.2.  above and used by management systems
   to transfer ownership of a device to a different management
   system. The connection must be authenticated with the issued
   client certificate.
   The serial number of the certificate issued to the new management
   system must be provided as the "mgmtid" parameter. No payload is
   provided.

   No payload is returned and the response code will be one of:
   +--------------+------------------------------------------+
   | Response     | Description                              |
   +--------------+------------------------------------------+
   |204 Changed   | Ownership has been assigned to the new   |
   |              | owner                                    |
   +--------------+------------------------------------------+
   |403 Forbidden | The device is owned by a different       |
   |              | management system, or the device         |
   |              | does not exist                           |

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   +--------------+------------------------------------------+

9.3.4. PUT /v1/devices/<uuid>/owner?case_string=
                                            <string>&mgmtid=<string>

   This is a combination of 9.3.2.  and 9.3.3.  above. It is used by
   management systems to take ownership of a device and immediately
   assign it to a different management system. The connection must be
   authenticated with the issued client certificate.

   The case identification string must be provided as the
   "case_string" parameter and the serial number of the certificate
   issued to the new management system must be provided as the
   "mgmtid" parameter. No payload is provided.

   No payload is returned and the response code will be one of:
   +--------------+------------------------------------------+
   | Response     | Description                              |
   +--------------+------------------------------------------+
   |204 Changed   | Ownership has been assigned to the new   |
   |              | owner                                    |
   +--------------+------------------------------------------+
   |403 Forbidden | The device is owned by a different       |
   |              | management system, or the device         |
   |              | does not exist                           |
   +--------------+------------------------------------------+

9.3.5. PUT /v1/devices/<uuid>/owner?mgmtid=NULL

   This is a variant of 9.3.2.  above and used by management systems
   to release ownership of a device. Once a device has been released
   from ownership, any management system may take ownership of the
   device if knows the device UUID and case string. The connection
   must be authenticated with the issued client certificate.

   No payload is provided or returned and the response code will be
   one of:
   +--------------+------------------------------------------+
   | Response     | Description                              |
   +--------------+------------------------------------------+
   |204 Changed   | Ownership has been released              |
   +--------------+------------------------------------------+
   |403 Forbidden | The device is owned by a different       |
   |              | management system, or the device         |
   |              | does not exist                           |
   +--------------+------------------------------------------+

9.3.6. GET /v1/devices/<uuid>/parameterset

   This is used by management systems to obtain the parameter set
   required for the device. The connection must be authenticated with
   the issued client certificate.

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   No payload is provided. If the request is successful, the
   parameter set will be returned in the payload. The format of the
   parameter set data is TBD.

   Note that this returns the same data as 9.2.4.  above but
   references the device not the parameter set UUID itself.

   The response code will be one of:
   +--------------+------------------------------------------+
   | Response     | Description                              |
   +--------------+------------------------------------------+
   |200 OK        | The device parameter set has             |
   |              | been returned                            |
   +--------------+------------------------------------------+
   |403 Forbidden | The device is owned by a different       |
   |              | management system, or the device         |
   |              | does not exist                           |
   +--------------+------------------------------------------+

9.3.7. PUT /v1/devices/<uuid>/bootstrap

   This is used by management systems to set the bootstrap data for a
   device. The connection must be authenticated with the issued
   client certificate.

   The bootstrap data is provided as a binary payload. The format of
   the device bootstrap data is device dependent and detailed in the
   device parameter set returned in 9.3.6.  above. No payload is
   returned. The response code will be one of:
   +--------------+------------------------------------------+
   | Response     | Description                              |
   +--------------+------------------------------------------+
   |204 Changed   | The device bootstrap data has been       |
   |              | accepted                                 |
   +--------------+------------------------------------------+
   |403 Forbidden | The device is owned by a different       |
   |              | management system, or the device         |
   |              | does not exist                           |
   +--------------+------------------------------------------+

9.3.8. GET /v1/devices/<uuid>/bootstrap

   This is used by management systems to return the bootstrap data
   for a device. The connection must be authenticated with the issued
   client certificate.

   No payload is provided. If successful, the bootstrap data is
   returned as a binary payload. The response code will be one of:
   +--------------+------------------------------------------+
   | Response     | Description                              |
   +--------------+------------------------------------------+

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   |200 OK        | The device bootstrap data has            |
   |              | been returned                            |
   +--------------+------------------------------------------+
   |403 Forbidden | The device is owned by a different       |
   |              | management system, or the device         |
   |              | does not exist                           |
   +--------------+------------------------------------------+

9.4. Bootstrap API

   The Bootstrap API is used by the device to download its bootstrap
   data. The Bootstrap API is a RESTful interface using CBOR and CoAP
   over DTLS with client authentication.

9.4.1. GET /v1/devices/<uuid>/bootstrap

   This is used by the device to obtain its bootstrap data. The DTLS
   connection must be authenticated with the device key as described
   in section 8.  above. The <uuid> in the URI must belong to the
   device authenticated during the DTLS handshake.

   No payload is provided. If successful, the bootstrap data is
   returned as a binary payload. The response code will be one of:
   +--------------+------------------------------------------+
   | Response     | Description                              |
   +--------------+------------------------------------------+
   |2.05          | The device bootstrap data has            |
   |              | been returned                            |
   +--------------+------------------------------------------+
   |4.03          | The device is not allowed to access the  |
   |              | requested bootstrap data, or the device  |
   |              | does not exist                           |
   +--------------+------------------------------------------+

10. Device Management API

   The device API is used by the management system to control the
   aSSURE functionality in the device. Like the Bootstrap API, the
   Device API is RESTful using CBOR and CoAP over DTLS. The transport
   of the DTLS messages will vary depending on the device type and
   installation - examples of different physical and/or network
   layers are provided in section 11.  below.

   All requests on the Device Management API must be made over
   authenticated DTLS connections, known as "channels". The
   definition of channels is in 4.2.  above.

   The Management API is used to define what privileges are assigned
   to each channel. These privileges are:

   +--------------+------------------------------------------+
   | Privilege    | Description                              |

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   +--------------+------------------------------------------+
   | Key          | The connection is allowed to create,     |
   | Management   | reconfigure and delete keys on the       |
   |              | device.                                  |
   +--------------+------------------------------------------+
   | Channel      | The connection is allowed to create,     |
   | Management   | reconfigure and delete channel           |
   |              | definitions on the device.               |
   +--------------+------------------------------------------+
   | System       | The connection is allowed to instruct    |
   | Management   | the device to perform system level       |
   |              | actions such as bootstrap or reboot.     |
   +--------------+------------------------------------------+

10.1.1. PUT /v1/keys/<uuid>

   This request requires "Key Management" privileges on the
   requesting channel.

   This instructs the device to add the indicated key to its key
   store. The key is provided in the payload as a CBOR object as
   defined in 7.4.  above.

   The response code will be one of:
   +----------+----------------------------------------------+
   | Response | Description                                  |
   +----------+----------------------------------------------+
   | 2.01     | The key has been created                     |
   +----------+----------------------------------------------+
   | 2.04     | The key already exists on the device         |
   +----------+----------------------------------------------+
   | 4.01     | The channel does not have privileges to      |
   |          | manage keys                                  |
   +----------+----------------------------------------------+
   | 4.13     | The device has no space to add more keys     |
   +----------+----------------------------------------------+

10.1.2. POST /v1/keys/generate?type=<key_type>&persistent=<boolean>

   This request requires "Key Management" privileges on the
   requesting channel.

   This instructs the device to create a new key of the indicated
   type in its key store.

   +----------+----------------------------------------------+
   | Type     | Description                                  |
   +----------+----------------------------------------------+
   | 0        | RSA 2048 bits                                |
   +----------+----------------------------------------------+
   | 1        | Elliptic Curve (NIST P-256)                  |
   +----------+----------------------------------------------+

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   | 2        | Elliptic Curve (NIST P-384)                  |
   +----------+----------------------------------------------+
   | 3        | Elliptic Curve (NIST P-521)                  |
   +----------+----------------------------------------------+

   If the persistent flag is not set, the key will only exist in RAM
   and will be lost when the device next reboots or loses power.

   If the creation is successful, the device will create an
   authenticate key as defined in 7.4.  above. The device will add
   its own ID in the MAP field and create the signature using its
   device key. The authenticate key is then returned in the response
   payload.

   The response code will be one of:
   +----------+----------------------------------------------+
   | Response | Description                                  |
   +----------+----------------------------------------------+
   | 2.01     | The key has been created                     |
   +----------+----------------------------------------------+
   | 4.01     | The channel does not have privileges to      |
   |          | manage keys                                  |
   +----------+----------------------------------------------+
   | 4.13     | The device has no space to add more keys     |
   +----------+----------------------------------------------+
   | 5.01     | Unsupported key type                         |
   +----------+----------------------------------------------+

10.1.3. GET /v1/keys/<uuid>

   This request requires "Key Management" privileges on the
   requesting channel.

   This instructs the device to return the indicated key in its key
   store. The key is returned in the payload as a CBOR object as
   defined in 7.4.  above.

   The response code will be one of:
   +----------+----------------------------------------------+
   | Response | Description                                  |
   +----------+----------------------------------------------+
   | 2.05     | The key information has been returned        |
   +----------+----------------------------------------------+
   | 4.01     | The channel does not have privileges to      |
   |          | return keys                                  |
   +----------+----------------------------------------------+
   | 4.04     | The key does not exist                       |
   +----------+----------------------------------------------+

10.1.4. DELETE /v1/keys/<uuid>
   This request requires "Key Management" privileges on the
   requesting channel.

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   This instructs the device to delete the indicated key from its key
   store. The key must not be in use by any channel nor must it be
   used as a reference key by any other keys. The device will not
   permit any key defined in the bootstrap data to be deleted.

   The response code will be one of:
   +----------+----------------------------------------------+
   | Response | Description                                  |
   +----------+----------------------------------------------+
   | 2.02     | The key has been deleted or did not exist    |
   +----------+----------------------------------------------+
   | 4.01     | The channel does not have privileges to      |
   |          | manage keys                                  |
   +----------+----------------------------------------------+
   | 4.03     | The key is in use and cannot be deleted at   |
   |          | this time or is not allowed to be deleted    |
   +----------+----------------------------------------------+

10.1.5. GET /v1/keys

   This request requires "Key Management" privileges on the
   requesting channel.

   This instructs the device to list the keys in its key store. The
   key list is returned as a CBOR array of authenticated keys as
   defined in 7.4.  above. For security reasons, no private keys will
   be disclosed. Instead, if the device has the private data for the
   key, the string "PRESENT" will be returned as the "private_key"
   byte string. If the device does not have the private data for the
   key, the "private_key" byte string will be zero length.

   The response code will be one of:
   +----------+----------------------------------------------+
   | Response | Description                                  |
   +----------+----------------------------------------------+
   | 2.05     | The key list has been returned               |
   +----------+----------------------------------------------+
   | 4.01     | The channel does not have privileges to      |
   |          | manage keys                                  |
   +----------+----------------------------------------------+

10.1.6. PUT /v1/channels

   This request requires "Channel Management" privileges on the
   requesting channel.

   This instructs the device to create a new channel. The channel
   configuration will be provided in the request payload in CBOR
   format as below:

   ARRAY {

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       BYTE STRING local_key_id
       BYTE STRING peer_key_id   // Zero length if the same as
                                 // local_key_id
       ARRAY {
           BOOLEAN   persistent_across_reboots
           BOOLEAN   open_immediately
           BOOLEAN   channel_management_privilege
           BOOLEAN   system_management_privilege
           BOOLEAN   key_management_privilege
           // Additional configuration flags may follow
       }
       ARRAY {
           INTEGER address_type
           // Address content, structure varies depending on
           // address_type
       }
   }
   The format of the address content depends on the target device
   network and physical layer. As support for additional network and
   physical layers are added, additional address types and associated
   address content format will be defined. The list of assigned
   address types is in 12.4.  below.

   The assigned channel ID will be returned in the response payload
   as a CBOR integer.

   The response code will be one of:
   +----------+----------------------------------------------+
   | Response | Description                                  |
   +----------+----------------------------------------------+
   | 2.01     | The channel has been created                 |
   +----------+----------------------------------------------+
   | 4.01     | The channel does not have privileges to      |
   |          | manage channels                              |
   +----------+----------------------------------------------+
   | 4.13     | The device has no space to add more channels |
   +----------+----------------------------------------------+

10.1.7. PUT /v1/channels/<id>

   As per 10.1.6.  above, "PUT /v1/channels" but where the channel ID
   is explicitly provided. The request and response payload formats
   are unchanged.

   Additional response codes may be:

   +----------+----------------------------------------------+
   | Response | Description                                  |
   +----------+----------------------------------------------+
   | 2.04     | The channel already exists                   |
   +----------+----------------------------------------------+


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10.1.8. PUT /v1/channels/<channel_id>/open

   This request requires "Channel Management" privileges on the
   requesting channel.

   This instructs the device to open the indicated channel. No
   request payload is provided.

   The response code will be one of:
   +----------+----------------------------------------------+
   | Response | Description                                  |
   +----------+----------------------------------------------+
   | 2.04     | The device will try to open the channel      |
   +----------+----------------------------------------------+
   | 4.01     | The channel does not have privileges to      |
   |          | manage channels                              |
   +----------+----------------------------------------------+
   | 4.04     | The channel does not exist                   |
   +----------+----------------------------------------------+

   Note that a 2.04 response DOES NOT mean that the channel has been
   successfully opened. Instead, it means that the device WILL TRY to
   open the channel. This may take some time and the status can be
   monitored with the channel status request in 10.1.11.  below.

10.1.9. PUT /v1/channels/<channel_id>/close

   This request requires "Channel Management" privileges on the
   requesting channel.

   This instructs the device to close the indicated channel. No
   request payload is provided.

   The response code will be one of:
   +----------+----------------------------------------------+
   | Response | Description                                  |
   +----------+----------------------------------------------+
   | 2.04     | The device will try to close the channel     |
   +----------+----------------------------------------------+
   | 4.01     | The channel does not have privileges to      |
   |          | manage channels                              |
   +----------+----------------------------------------------+
   | 4.04     | The channel does not exist                   |
   +----------+----------------------------------------------+

   Note that a 2.04 response DOES NOT mean that the channel has been
   successfully closed. Instead, it means that the device WILL TRY to
   close the channel. This may take some time and the status can be
   monitored with the channel status request in 10.1.11.  below.

10.1.10. DELETE /v1/channels/<channel_id>


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   This request requires "Channel Management" privileges on the
   requesting channel.

   This instructs the device to delete the indicated channel, closing
   it automatically if it is currently open. No request payload is
   provided. The device will not permit any channel defined in the
   bootstrap data to be deleted.

   The response code will be one of:
   +----------+----------------------------------------------+
   | Response | Description                                  |
   +----------+----------------------------------------------+
   | 2.02     | The channel has been deleted or does not     |
   |          | exist                                        |
   +----------+----------------------------------------------+
   | 2.04     | The channel was open so will be cleanly      |
   |          | closed then deleted                          |
   +----------+----------------------------------------------+
   | 4.01     | The channel does not have privileges to      |
   |          | manage channels                              |
   +----------+----------------------------------------------+
   | 4.03     | The channel is not allowed to be deleted     |
   +----------+----------------------------------------------+

   Note that after a 2.04 response the client can poll the channel
   status using the "GET" request as in 10.1.11. below. If the
   channel is still being closed, the response will be a 2.05 with
   status = 4. As soon as the close completes, the channel will be
   deleted and the "GET" request in 10.1.11.  below will return 4.04
   because the channel no longer exists.

10.1.11. GET /v1/channels/<id>

   This request requires "Channel Management" privileges on the
   requesting channel.

   This requests the device to return the configuration and status of
   the channel. No request payload is provided. The channel
   configuration and status will be provided in the request payload
   in CBOR format as below:

   ARRAY {
       ARRAY {
           // Configuration structure as in 10.1.6.  above
       }
       ARRAY {
           INTEGER  channel_id
           INTEGER  state
           // Additional status flags may follow
       }
   }


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   The "status" integer will be one of:
   +----------+----------------------------------------------+
   | Response | Description                                  |
   +----------+----------------------------------------------+
   | 0        | The channel is closed                        |
   +----------+----------------------------------------------+
   | 1        | The channel is requested to be opened        |
   +----------+----------------------------------------------+
   | 2        | The channel handshake is in progress         |
   +----------+----------------------------------------------+
   | 3        | The channel is open                          |
   +----------+----------------------------------------------+
   | 4        | The channel is being closed                  |
   +----------+----------------------------------------------+
   | 10       | The channel handshake failed because the     |
   |          | peer did not answer                          |
   +----------+----------------------------------------------+
   | 11       | The channel handshake failed because the     |
   |          | peer provided the wrong key ID               |
   +----------+----------------------------------------------+
   | 12       | The channel handshake failed because the     |
   |          | peer failed authentication                   |
   +----------+----------------------------------------------+
   | 13       | The channel has experienced some other error |
   +----------+----------------------------------------------+

   The response code will be one of:
   +----------+----------------------------------------------+
   | Response | Description                                  |
   +----------+----------------------------------------------+
   | 2.05     | The channel information has been returned    |
   +----------+----------------------------------------------+
   | 4.01     | The channel does not have privileges to      |
   |          | manage channels                              |
   +----------+----------------------------------------------+
   | 4.04     | The channel does not exist                   |
   +----------+----------------------------------------------+

10.1.12. GET /v1/channels

   This request requires "Channel Management" privileges on the
   requesting channel.
   This requests the device to return the configuration and status of
   all channels. No request payload is provided. The information is
   returned as a CBOR array of channel responses as defined in
   10.1.11.  above.

   The response code will be one of:
   +----------+----------------------------------------------+
   | Response | Description                                  |
   +----------+----------------------------------------------+
   | 2.05     | The configuration and status for all         |

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   |          | channels has been returned                   |
   +----------+----------------------------------------------+
   | 4.01     | The channel does not have privileges to      |
   |          | manage channels                              |
   +----------+----------------------------------------------+

10.1.13. PUT /v1/reboot

   This request requires "System Management" privileges on the
   requesting channel.

   This instructs the device to reboot. The device will reboot after
   returning the response. No request payload is provided and no
   response payload is returned.

   The response code will be one of:
   +----------+----------------------------------------------+
   | Response | Description                                  |
   +----------+----------------------------------------------+
   | 2.04     | The device is about to reboot                |
   +----------+----------------------------------------------+
   | 4.01     | The channel does not have privileges to      |
   |          | manage the system                            |
   +----------+----------------------------------------------+

10.1.14. PUT /v1/shutdown

   This request requires "System Management" privileges on the
   requesting channel.

   This instructs the device to shut down. The device will shut down
   after returning the response. No request payload is provided and
   no response payload is returned.

   The response code will be one of:
   +----------+----------------------------------------------+
   | Response | Description                                  |
   +----------+----------------------------------------------+
   | 2.04     | The device is about to shutdown              |
   +----------+----------------------------------------------+
   | 4.01     | The channel does not have privileges to      |
   |          | manage the system                            |
   +----------+----------------------------------------------+

10.1.15. PUT /v1/bootstrap

   This request requires "System Management" privileges on the
   requesting channel.

   This instructs the device to perform an aSSURE bootstrap. The
   device will bootstrap after returning the response. No request
   payload is provided and no response payload is returned.

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   The response code will be one of:
   +----------+----------------------------------------------+
   | Response | Description                                  |
   +----------+----------------------------------------------+
   | 2.04     | The device is about to bootstrap             |
   +----------+----------------------------------------------+
   | 4.01     | The channel does not have privileges to      |
   |          | manage the system                            |
   +----------+----------------------------------------------+

10.1.16. GET /v1/ping

   This request requires no privileges on the requesting channel.
   This is used to check that the device is online and able to
   respond to requests.

   A payload may be provided. The device will respond with the same
   payload (or as much of the payload as the device can return if it
   is a constrained device). The response code will be:

   +----------+----------------------------------------------+
   | Response | Description                                  |
   +----------+----------------------------------------------+
   | 2.05     | Ping response                                |
   +----------+----------------------------------------------+

10.1.17. GET /v1/info

   This request requires no privileges on the requesting channel.

   This is used to return basic information about the device. The
   device will return the CBOR structure below:

   ARRAY {
       BYTE STRING  device_id
       BYTE STRING  device_mac_address
       TEXT STRING  device_manufacturer
       TEXT STRING  device_product_code
       TEXT STRING  device_serial_number
       TEXT STRING  device_build_date
       TEXT STRING  software_manufacturer
       TEXT STRING  software_product_code
       TEXT STRING  software_version
   }

   The only field that must be present is the device_id. All other
   fields may be zero length if the device is unable to provide them
   for any reason.

   The response code will be:


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   +----------+----------------------------------------------+
   | Response | Description                                  |
   +----------+----------------------------------------------+
   | 2.05     | Information returned                         |
   +----------+----------------------------------------------+


11. Management Server API

11.1. Overview

   The management server must support the registration and presence
   APIs. The registration API is used to allow devices to be
   registered with the management system. The presence API is used by
   devices after bootstrap to inform the management system of their
   presence on the network.

11.2. Registration API

   The Registration API is used to register the device with the
   management system when it is installed. The Registration API is a
   RESTful interface using JSON over HTTPS. The authentication
   behaviour is determined by the Management Server implementation
   but either username + passphrase or client certificates are
   recommended.

11.2.1. POST /v1/devices/<uuid>?case_string=<case_string>

   This is used to register the indicated device UUID with the
   management system. The case string is provided to prove the device
   is physically present. The UUID and case string would normally
   come from a QR code or similar attached to the device (use of an
   RFID is not recommended as the source for obvious security
   reasons).

   No payload is returned. The response code will be one of:
   +--------------+------------------------------------------+
   | Response     | Description                              |
   +--------------+------------------------------------------+
   |201 Created   | The new device has been registered       |
   +--------------+------------------------------------------+
   | 401          | The device cannot be registered because  |
   | Unauthorised | it already exists                        |
   +--------------+------------------------------------------+
   | 503 Service  | The device cannot be registered          |
   | Unavailable  | at this time                             |
   +--------------+------------------------------------------+

   Only a single device is uploaded in each POST request, but the
   client may re-use the HTTPS session to send additional requests.



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11.2.2. POST /v1/devices/<old_uuid>/replace?uuid=<new_uuid>

   This is used to tell the management system that the indicated
   device with UUID <old_uuid> has been replaced by the device with
   UUID <new_uuid>. For example, this would occur when a device has
   failed and a maintenance engineer has replaced it. The management
   system can then update its database, etc. to allow the new device
   to "seamlessly replace" the old device (e.g. by applying the old
   device configuration to the new device). For security reasons, the
   management system should immediately disable the old device as
   this call indicates that the old device is no longer in use.

   The new device must be registered with the call in 11.2.1.  above
   before performing this call to replace the old device.

   No payload is returned. The response code will be one of:
   +--------------+------------------------------------------+
   | Response     | Description                              |
   +--------------+------------------------------------------+
   | 201 Created  | The new device has replaced the old one  |
   +--------------+------------------------------------------+
   | 401          | The old device does not exist, the client|
   |              | is not allowed to update the state of the|
   |              | old device, the new device does not exist|
   |              | or the client is not allowed to update   |
   |              | the state of the new device.             |
   +--------------+------------------------------------------+
   | 503 Service  | The device cannot be replaced            |
   | Unavailable  | at this time                             |
   +--------------+------------------------------------------+

11.2.3. GET /v1/devices/<uuid>/status

   This is used to get the status of the device. The registration,
   configuration, bootstrap and presence of a device may take some
   time. A registration client may obtain the status of the device
   here to check if the device has entered service.

   If successful, the payload is a JSON structure:

   {
       status: <value>,
       description: "<helpful_text>"
   }

11.2.4. GET /v1/devices/<uuid>/info

   This is used to get the information for the device. This is only
   available after the device has sent is presence message to the
   management system.

   If successful, the payload is a JSON structure with the same

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   information as in 10.1.17.  above:

   {
       "device_id": "<device uuid>",
       "device_mac_address": "<device MAC address>",
       "device_manufacturer": "...",
       "device_product_code": "...",
       "device_serial_number": "...",
       "device_build_date": "...",
       "software_manufacturer": "...",
       "software_product_code": "...",
       "software_version": "..."
   }

   The response code will be one of:
   +--------------+------------------------------------------+
   | Response     | Description                              |
   +--------------+------------------------------------------+
   | 200 OK       | The device information has been returned |
   +--------------+------------------------------------------+
   | 401          | The client is not authorised to access   |
   | Unauthorised | this device                              |
   +--------------+------------------------------------------+
   | 503 Service  | Device information cannot be returned at |
   | Unavailable  | this time                                |
   +--------------+------------------------------------------+

   Only a single device response is permitted per GET request, but
   the client may re-use the HTTPS session to send additional
   requests.

11.3. Presence API

   The Presence API is used by the device to indicate to the
   management system that its bootstrap process has completed and it
   is now online in the network. Like the Bootstrap API and Device
   Management APIs, the Presence API is RESTful using CBOR and CoAP
   over DTLS.

11.3.1. PUT /v1/devices/<uuid>/info

   This is used by the device to confirm it is active and has
   completed its bootstrap.

   The device provides the same CBOR structure as in 10.1.17.  above
   as the request payload.

   No payload is returned. The response code will be one of:
   +-------------+-------------------------------------------+
   | Response    | Description                               |
   +-------------+-------------------------------------------+
   | 2.01 Created| The device presence has been acknowledged |

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   +-------------+-------------------------------------------+
   | 4.01        | The device has attempted to provide       |
   |Unauthorized | information for a different device        |
   +-------------+-------------------------------------------+

11.3.2. PUT /v1/devices/<uuid>/goodbye

   This is used by the device to indicate it is deliberately going
   offline. It will send this to all connected management systems.

   The device will provide a single INTEGER in CBOR format to
   indicate the reason.

   +---------+-----------------------------------------------+
   | Value   | Reason                                        |
   +---------+-----------------------------------------------+
   | 0       | Device is shutting down                       |
   +---------+-----------------------------------------------+
   | 1       | Device has been instructed to reboot by       |
   |         | Management System                             |
   +---------+-----------------------------------------------+
   | 2       | Device has been instructed to bootstrap by    |
   |         | Management System                             |
   +---------+-----------------------------------------------+
   | 3       | Device has been instructed to reboot by       |
   |         | local controls (e.g. button)                  |
   +---------+-----------------------------------------------+
   | 4       | Device has been instructed to bootstrap by    |
   |         | local controls (e.g. button)                  |
   +---------+-----------------------------------------------+

   No payload is returned. The response code will be one of:
   +-------------+-------------------------------------------+
   | Response    | Description                               |
   +-------------+-------------------------------------------+
   | 2.04 Changed| The device goodbye has been acknowledged  |
   +-------------+-------------------------------------------+
   | 4.01        | The device has attempted to provide       |
   |Unauthorized | information for a different device        |
   +-------------+-------------------------------------------+

11.4. Miscellaneous

11.4.1. GET /v1/timestamp

   This is used to get the current time from a trusted source. A
   device may use this to set its clock without having to include
   support for other protocols such as NTP. This request may be made
   by any client with or without authentication.

   No payload is provided. The response is a timestamp in CBOR as
   defined in 7.11.  above (both integer and fractional parts).

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   The response code will be one of:
   +--------------+------------------------------------------+
   | Response     | Description                              |
   +--------------+------------------------------------------+
   | 200 OK       | The timestamp has been returned          |
   +--------------+------------------------------------------+
   | 503 Service  | Device information cannot be returned at |
   | Unavailable  | this time                                |
   +--------------+------------------------------------------+

12. Physical / Network Layer Implementations

12.1. BACnet

   aSSURE traffic is fully compatible with existing BACnet traffic
   and is identified as Network Control messages using Message Types
   0x80 - 0x82 and Vendor ID 0x_TBD_.

   Message Types 0x80 through 0x82 are used to identify the aSSURE
   traffic as belonging to one of three logical groups.

   +-------------+-------------------------------------------+
   | Message Type| Description                               |
   +-------------+-------------------------------------------+
   | 0x80        | aSSURE Bootstrap                          |
   +-------------+-------------------------------------------+
   | 0x81        | aSSURE Secure Management Channels         |
   +-------------+-------------------------------------------+
   | 0x82        | aSSURE Secure Data Channels               |
   +-------------+-------------------------------------------+

   When an address is indicated in a CBOR message, the address format
   is:

   ARRAY {
       INTEGER     0        // Address type 1 = BACnet
       INTEGER     net
       BYTE STRING addr      // "len" is the BYTE STRING length
   }

   If the "net" field is a NULL (CBOR Major: 7, Value: 22 => 0xF6)
   rather than an INTEGER (CBOR Major: 0), this indicates a local
   network address. When creating the BACnet NPDU, the NPDU
   destination specifier for that address would not be present.

12.1.1. aSSURE Bootstrap

   The aSSURE Bootstrap messages are used to identify the bootstrap
   gateways on the BACnet network and assign a secure data channel
   for communication with the bootstrap server. This traffic cannot
   be secured because it happens BEFORE the bootstrap data has been

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   received so the device has no keys for communicating with peers on
   the local network.

   All Insecure Control Messages are RESTful using CoAP in the NSDU
   part of an NPDU frame. They are therefore independent of any
   specific BACnet LLC such as BACnet IP or BACnet MS/TP.

12.1.1.1. GET /v1/gateway/<bootstrap_server_id>

   This message is broadcast on BACnet to discover the best gateway
   capable of routing traffic to the indicated bootstrap server. No
   payload is provided.

   All gateways capable of routing traffic to the broadcast server
   should respond with their assigned priority for handling traffic
   (or zero if it has not been explicitly set). This means that a
   device may receive multiple replies to its GET message and it
   should be able to handle this. The device should wait a reasonable
   time (e.g. 5 seconds) for all replies to be received and should
   pick the gateway with the lowest priority value. If multiple
   gateways respond with the same lowest priority value, a gateway
   should be chosen at random.

   If no gateways respond, the device should backoff and retry.

   The gateway response should be a 2.00 status code with a CBOR
   payload containing the following content:

   INTEGER priority

12.1.1.2. POST /v1/gateway/channel?server=<bootstrap_server_id>

   This message is sent to the chosen gateway that responded to the
   discovery message described in 12.1.1.1.  above. The gateway
   should assign a channel that routes messages to the indicated
   bootstrap server. No payload is provided. If successful, the
   gateway response should be a CBOR payload with the following
   content:

   INTEGER channel_id
   BYTE STRING token

   The cookie should be a random string of at least 4 bytes. The
   device must provide this token when closing the channel.

   The status code will be one of:
   +----------+----------------------------------------------+
   | Response | Description                                  |
   +----------+----------------------------------------------+
   | 2.01     | The channel has been created                 |
   +----------+----------------------------------------------+
   | 4.04     | The gateway cannot find a route to the       |

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   |          | indicated bootstrap server                   |
   +----------+----------------------------------------------+
   | 5.03     | The gateway cannot create the channel at     |
   |          | this time                                    |
   +----------+----------------------------------------------+

12.1.1.3. DELETE/v1/gateway/channel/<channel_id>?token=<token_in_hex>

   This message is sent to the chosen gateway that responded to the
   discovery message described in 12.1.1.1.  above. The gateway
   should assign a channel that routes messages to the indicated
   bootstrap server. No payload is provided and no payload is
   returned. The device must offer the token returned by the gateway
   in the channel assign request in 12.1.1.2.  above and the DELETE
   request must come from the same network address as the POST
   request.

   The status code will be one of:
   +----------+----------------------------------------------+
   | Response | Description                                  |
   +----------+----------------------------------------------+
   | 2.02     | The channel has been deleted                 |
   +----------+----------------------------------------------+
   | 4.01     | The device is not allowed to delete this     |
   |          | channel                                      |
   +----------+----------------------------------------------+


12.1.2. aSSURE Secure Management Channels

   These messages are used for encrypted aSSURE-protected DTLS
   sessions accessing the Device Management API defined in 10.
   above. All messages on the aSSURE Secure Management Channel have
   the following CBOR structure:

   INTEGER channel_id
   BYTE STRING dtls_data

12.1.3. aSSURE Secure Data Channels

   These messages are used for all other aSSURE-protected DTLS
   session such as secure bootstrap or peer-to-peer channels. All
   messages on the aSSURE Secure Data Channel have the following CBOR
   structure:

   INTEGER channel_id
   BYTE STRING dtls_data

12.2. IP

   When deployed on IP networks, aSSURE traffic uses UDP port TBD for
   Secure Management Channels and UDP port TBD for Secure Data

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   Channels. The UDP payload is the DTLS data. The channel ID is
   inferred from the local port and remote address and port.

   When compared to BACnet, the "aSSURE Bootstrap" messages are not
   required because an IP network is already able to route traffic
   directly to the bootstrap servers without the explicit
   establishment of a channel. The device is assumed to be capable of
   DHCP and DNS to obtain a local IP address, determine the subnet
   gateway and resolve the bootstrap server FQDN.

   When an address is indicated in a CBOR message, the address format
   is:

   ARRAY {
       INTEGER     1           // Address type 1 = IP
       BYTE STRING remote_addr // 4 bytes for IPv4,network byte order
                               //16 bytes for IPv6,network byte order
       INTEGER     local_port  // Local UDP port, 0=any
       INTEGER     remote_port // Remote UDP port
   }

12.2.1. Bootstrap Server FQDN

   The bootstrap server ID can be converted to a Fully Qualified
   Domain Name (FQDN) by suffixing the decimal value of the ID with
   the string ".*TBD*.net". Similarly, an aSSURE bootstrap server
   FQDN can be converted to the server ID by reversing the process.

12.3. Bluetooth

   Bluetooth implementations should use the "Internet Protocol
   Support Profile" to allow the device to send and receive IPv6
   traffic.

   When an address is indicated in a CBOR message, the address format
   should be type 1 as in 12.2.  above.
   When a Bluetooth MAC address is specifically indicated in a CBOR
   message, the address format is:

   ARRAY {
       INTEGER     2       // Address type 2 = Bluetooth
       BYTE STRING mac     // MAC address, 6 bytes
   }

   In all other respects, the Bluetooth implementation follows the
   "IP" implementation as in 12.2.  above.

12.4. Assigned address types
   +-------------+-------------------------------------------+
   | Address Type| Description                               |
   +-------------+-------------------------------------------+
   | 0           | BACnet NPDU address                       |

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   +-------------+-------------------------------------------+
   | 1           | Destination IP address and UDP ports      |
   +-------------+-------------------------------------------+
   | 2           | Bluetooth MAC address                     |
   +-------------+-------------------------------------------+
13. DTLS Connection Configuration Examples

13.1. Example Topology

     ***********       ***********       +++++++++++
     +Device G +<-ec-->*Device A *<-ec-->*Device B *
     +++++++++++       ***********       ***********
      ^      ^          ^   |    ^        /       ^
      |   |   \        /    |     \      R        |
      e   e    \      e     e      s    S         R
      c   c     R    c      c       s  A          S
      |   |      SA-----RSA-------RS \/           A
      |   e        /        |       A/\           |
      e    c-ec---/-e       e       /\ \          R
      c          e   c      c      /  \ s         S
      |         c     \     |     /    \ s        A
      |        /       \    |    /      \ \       |
      v       v         v   v   v        v v      v
     ***********      OOOOOOOOOOOO       +++++++++++
     *         *      oManagemento       +         +
     *Device F *--ec->o  System  o<-RSA--+Device C +
     ***********      OOOOOOOOOOOO       +++++++++++
           ^            ^   ^  ^             ^
           |           /    |   \            |
           |          /     |    \           |
           s         /      s     \          s
           s     ss-/       s      \-ss      s
           |    /           |           \    |
           |   /            |            \   |
           |  /             |             \  |
      _____v_/_         _________         _\_v_____
     /         \       /         \       /         \
     |Device E |<--ss->|Device E |<-ss-->|Device D |
     |Service X|       |Service Y|       |         |
     \________ /       \_________/       \_________/

*** - (Device A & F) Elliptic Curve and Shared Secret Capable
+++ - (Device C) RSA and Shared Secret Capable

*** _ (Device G) Elliptic Curve, RSA and Shared Secret Capable
+++   (EC Device Key)

+++ _ (Device B) Elliptic Curve, RSA and Shared Secret Capable
***   (RSA Device Key)

___ - (device D and E) Only Shared Secret Capable
      (Shared Secret Device Key)

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"ec", "ss", "RSA" are the channels
                        DTLS Connection Example Topology

13.2. Elliptic Curve device . Elliptic Curve device

   e.g. Device A . Device F
   Both endpoints have Elliptic Curve keys so no additional keys need
   to be created. Each endpoint is sent a channel definition
   indicating the local device key, the peer device key, the peer
   address and the privileges for the channel.

13.3. Elliptic Curve device . RSA device

   We cannot use the two device keys to directly secure the DTLS
   connection. There are three possible solutions to allow a secure
   link. These are presented in the order of most to least preferred.

13.3.1. Option 1 - Issue EC key to RSA device

   e.g. Device A . Device B
   If the RSA device can support Elliptic Curve keys, then a new
   Elliptic Curve key should be created on (or issued to) the RSA
   device by the Management System. The Management System should sign
   the new key as assigned to the device.

   Now both devices have an EC key, so 13.2.  above can be followed.

13.3.2. Option 2 - Issue RSA key to EC device

   e.g. Device C . Device G
   If the EC device can support RSA keys, then a new RSA key should
   be created on (or issued to) the EC device by the Management
   System. The Management System should sign the new key as assigned
   to the device.

   Now both devices have an RSA key, so 13.5.  below can be followed.

13.3.3. Option 3 - Issue Shared Secret to both devices

   e.g. Device A . Device C
   Shared secrets must be used, so 13.7.  below is followed.

13.4. Elliptic Curve device . Shared Secret device

   e.g. Device F . Device E (Service X)
   Shared secrets must be used, so 13.7.  below is followed.

13.5. RSA device . RSA device

   e.g. Device B . Device C
   Both endpoints have RSA key so no additional keys need to be

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   created. Each endpoint is sent a channel definition indicating the
   local device key, the peer device key, the peer address and the
   privileges for the channel.

13.6. RSA device . Shared Secret device

   e.g. Device C . Device D
   Shared secrets must be used, so 13.7.  below is followed.

13.7. Shared Secret device . Shared Secret device

   e.g. Device D . Device E (Service Y)
   The management system must issue a new shared secret (called the
   "Channel Key") to both devices to identify the channel. Each
   endpoint is sent a channel definition indicating the Channel Key,
   the peer address and the privileges for the channel.










































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14. Message Sequence Diagrams

14.1. Manufacturing Flow

+------+ +--------+ +--------+ +--------+ +------------+  +---------+
|DEVICE| | MAKER  | | MAKER  | |IDENTITY| |REGISTRATION|  |BOOTSTRAP|
|      | |        | |GATEWAY | | SERVER | | SERVER     |  | SERVER  |
+------+ +--------+ +--------+ +--------+ +------------+  +---------+
  |         |             |     |                   |             |
 []<--UUID--|             |     |                   |             |
 [Key Generation]         |     |                   |             |
 []UUID+KEY->             |     |                   |             |
  |        []POST         |     |                   |             |
  |        []/v1/devices->[]    |                   |             |
  |        []             []-CheckDeviceExists()--->[]            |
  |        []             []    |                   []            |
  |        []             []<-------FALSE-----------[]            |
  |        []             []    |                   |             |
  |        []             []-----CreareDevice()---->[]            |
  |       [Key]           []    |                   []            |
  |     [Encryption]      []<--------ACK------------[]            |
  |        []             []    |                   |             |
  |        []             []--------------CreateDevice()--------->[]
  |        []             []    |                   |             []
  |        []             []<-----------------ACK-----------------[]
  |        []             []    |                   |             |
  |        []             []SUBMIT device data      |             |
  |        []             []--->|                   |             |
  |        []<201 Created-[]    []                  |             |
  |         |                [Key Decryption]       |             |
  |         |      [Bootstrap and Registration Identity]          |
  |         |                [Generation]           |             |
  |         |                   []ISSUE device bootstrap data---->|
  |         |                   []                  |             |
  |         |                   []ISSUE device      |             |
  |         |                   |   registration    |             |
  |         |                   |       data------->|             |
  |         |                   |                   |             |
  |         |                   |                   []            []
  |         |                   |                 IMPORT       IMPORT
  |         |                   |                  data         data
  |         |                   |                   []            []
  |         |                   |                   |             |
  |         |                   |             Ready for    Ready for
  |         |                   |               device     owner data
  |         |                   |           registration     upload
  |         |                   |                   |             |

                       Manufacturing Flow Sequence Diagram




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14.2. Management System Preparation

+------------+                    +-------+
| MANAGEMENT |                    | OWNER |
|   SYSTEM   |                    |GATEWAY|
+------------+                    +-------+
      |                                |
      []                               |
   Certificate                         |
   Generation                          |
      []             POST              |
      []   /v1/managementsystems       |
      []------------------------------>[]
      []                               []
      []      201 Created UUID         []
      []<------------------------------[]
      []                               |
      |                                |

Registration of the Management System with the Trusted Authority

                 Management System Preparation Sequence Diagram



































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14.3. Device Registration

+------+ +---------+ +----------+ +-------+ +---------+ +-----------+
|DEVICE| |INSTALLER| |MANAGEMENT| | OWNER | |BOOTSTRAP| REGISTRATION|
|      | |         | |  SERVER  | |GATEWAY| | SERVER  | |   SERVER  |
+------+ +---------+ +----------+ +-------+ +---------+ +-----------+
  |         |             |            |            |             |
[Installed  |             |            |            |             |
 On site  ] |             |            |            |             |
  |         |             |            |            |             |
  |------->[]             |            |            |             |
  | QR Code[]------------>[]           |            |             |
  | scanned[] Upload UUID []           |            |             |
  |        [] and case ID []           |            |             |
  |        []             []  PUT      |                          |
  |        []             []/v1/devices/<id>/owner  |             |
  |        []             []---------->[]           |             |
  |        []             []           []     Set DeviceOwner()   |
  |        []             []           []------------------------>[]
  |        []             []           []          ACK            []
  |        []             []           []<------------------------[]
  |        []             []   200 OK  []           |             |
  |        []             []<----------[]           |             |
  |        []     ACK     []           |            |             |
  |        []<------------[]           |            |             |
  |         |             |            |            |             |
  |         |             |            |            |             |

Registration of the device with the management systems

                        Device Registration Sequence Diagram

























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14.4. Device Ownership State Machine

                O
                |
                |
                |
                V
          +------------+
          |   UNOWNED  |
          |            |<-----------------
          +------------+                  |
                |                         |
                |                         |
                |POST                     |POST
                |/v1/devices/<uuid>/owner |/v1/devices/<uuid>/release
                |                         |
                V                         |
          +------------+                  |
          |   OWNED    |                  |
  ------->|            |------------------
 |        +------------+
 |          |
 |  POST    |
  ----------
    /v1/devices/<uuid>/transfer

                           Device Ownership State Machine





























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14.5. Device Configuration and Bootstrap

+------+ +----------------+ +----------+ +----------+ +------------+
|DEVICE| |  MANAGEMENT    | |OWNER     | |BOOTSTRAP | |REGISTRATION|
|      | |    SYSTEM      | |GATEWAY   | | SERVER   | |   SERVER   |
+------+ +----------------+ +----------+ +----------+ +------------+
  |         |                    |                 |             |
  |     [Device Registration     |                 |             |
  |      Completed]              |                 |             |
  |        []                    |                 |             |
  |        []     GET            |                 |             |
  |        []/v1/devices/<uuid>/configuration      |             |
  |        []------------------->[]                |             |
  |        []                    []                |             |
  |        []                    []GetDeviceData() |             |
  |        []                    []-------------->[]GetDeviceOwner()
  |        []                    []               []------------>[]
  |        []                    []               []   [Owner]   []
  |        []                    []               []<------------[]
  |        []                    []     [data]    []             |
  |        []                    []<--------------[]             |
  |        []                    []                |             |
  |        []     200 OK [data]  []                |             |
  |        []<-------------------[]                |             |
  |        []                    |                 |             |
  |         |                    |                 |             |
[Power      |                    |                 |             |
 Applied]   |                    |                 |             |
  |         |                    |                 |             |
 []       GET /v1/devices/<uuid>/bootstrap         |             |
 []---------------------------------------------->[]             |
 []         |                    |                []             |
 []         |   200 OK [image]   |                []             |
 []<----------------------------------------------[]             |
 []         |                    |                 |             |
[Validate and                    |                 |             |
 decrypt bootstrap               |                 |             |
 image]     |                    |                 |             |
 []         |                    |                 |             |
[Apply bootstrap                 |                 |             |
 Image]     |                    |                 |             |
 []         |                    |                 |             |
 []PUT /v1/devices/<uuid>/info   |                 |             |
 []------->[]                    |                 |             |
 [] <data> []                    |                 |             |
 []<-------[]                    |                 |             |
  |         |                    |                 |             |
  |         |                    |                 |             |

                Device Configuration and Bootstrap Sequence Diagram



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14.6. Device Configuration and Bootstrap (Walled Garden)
+------+  +-------+ +-------+ +-------+ +-------+ +------+ +--------+
|DEVICE|  |WALLED | |WALLED | |MANAGE | |OWNER  | |BOOT    | REG    |
|      |  |BOOT   | |MANAGE | |SYSTEM | |GATEWAY| |SERVER| |SERVER  |
+------+  +-------+ +-------+ +-------+-+-------+ +------+ +--------+
  |          |            |[Device Reg Done] |          |         |
  |          |            |      []          |          |         |
  |          |            |      [-GET------>]          |         |
  |          |            |      [] ?/config[]          []        |
  |          |            |      []         [-GetDevData ]        |
  |          |            |      []         []---------->]        |
  |          |            |      []         []          [GetDevOwner
  |          |            |      []         []          [--------->]
  |          |            |      []         []          [] owner  []
  |          |            |      []         []   data   [<---------]
  |          |            |      [] 200 OK  []<----------]        []
  |          |            |      []<---------]          []        |
  |          |            |      []         []          |         |
  |          |        (Build Bootstrap Image)|          |         |
  |          |            |      []          |          |         |
  |          |<------------------[]EXPORT device bootstrap data   |
  |          |            |<-----[]EXPORT device management data  |
  |          []           []      |          |          |         |
  |        IMPORT       IMPORT    |          |          |         |
  |   bootstrap data   management data       |          |         |
  |          []           []      |          |          |         |
  |          |            |       |          |          |         |
[Power Applied]           |       |          |          |         |
  []         |            |       |          |          |         |
  [-GET----->[]           |       |          |          |         |
  []?/bootstrap           |       |          |          |         |
  []         []           |       |          |          |         |
  [] 200 OK  []           |       |          |          |         |
  []<---------]           |       |          |          |         |
  [] (image) []           |       |          |          |         |
  []                      |       |          |          |         |
[Validate and decrypt     |       |          |          |         |
 Bootstrap image]         |       |          |          |         |
[Apply bootstrap image]   |       |          |          |         |
  []         |            |       |          |          |         |
  []         |            []      |          |          |         |
  []-POST ?/info---------->]      |          |          |         |
  []         |            []      |          |          |         |
  []<----------------------]      |          |          |         |
  []         |            []      |          |          |         |
  |          |            |       |          |          |         |

?/ is /v1/devices/<uuid>/
Configuration of the device to connect to the management system

                Device Configuration and Bootstrap Sequence Diagram
                                                     (Walled Garden)

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14.7. Device Change Owner

+------+ +--------+ +--------+ +--------+ +----------+ +------------+
|DEVICE| | MAKER  | | MAKER  | |OWNER   | |BOOTSTRAP | |REGISTRATION|
|      | |SYSTEM A| |SYSTEM B| |GATEWAY | | SERVER   | |   SERVER   |
+------+ +--------+ +--------+ +--------+ +----------+ +------------+
  |         |             |           |            |             |
 []<-data->[]             []---GET--->]            |             |
 []        []             []?/configuration        |             |
 []        []             []         []            |             |
 []        []             []         []GetDeviceData()           |
 []        []             []         []----------->[]GetDeviceOwner()
 []        []             []         []            []----------->[]
 []        []             []         []            []  [Mgmt B]  []
 []        []             []         []UNAUTHORISED[]<-----------[]
 []        []             []   403   []<-----------[]            |
 []        []             []<--------[]            |             |
 []        []             |  Forbidden|            |             |
 []        []  PUT        |           |            |             |
 []        []------------------------>]            |             |
 []        []?/transfer?mgmtid=$MgmtB[] SetDeviceOwner("Mgmt B") |
 []        []             |          []------------------------->[]
 []        []             |          []            |   Reset     []
 []        []             |          []            |   Device    []
 []        []             |          []            |  Bootstrap()[]
 []        []             |          []            []<-----------[]
 []        []             |          []            []   ACK      []
 []        []             |          []            []----------->[]
 []        []             |          []     ACK    |             []
 []        []          200 OK        []<-------------------------[]
 []        []<-----------------------[]            |             |
 []<-------[]             |           |            |             |
 []  PUT /v1/bootstrap    |           |            |             |
 []        []             |           |            |             |
 []-------->]             |           |            |             |
 [] PUT ?/goodbye         |           |            |             |
 []        []             |           |            |             |
 []         |             |           |            |             |
 []-----------GET /v1/devices/<uuid>/bootstrap---->[]            |
 []         |             |           |            []            |
 []<-----------------  204 No Content--------------[]            |
 []         |             |           |            |             |
  |         |             |           |            |             |
 [sleeps]   |             |           |            |             |
  |         |             |           |            |             |
  |         |             |           |            |             |
  |         |             |           |            |             |

                 Device Change Owner Sequence Diagram (first part)




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  |         |             |           |            |             |
+------+ +--------+ +--------+ +--------+ +----------+ +------------+
|DEVICE| | MAKER  | | MAKER  | |OWNER   | |BOOTSTRAP | |REGISTRATION|
|      | |SYSTEM A| |SYSTEM B| |GATEWAY | | SERVER   | |   SERVER   |
+------+ +--------+ +--------+ +--------+ +----------+ +------------+
[sleeps]    |             |           |            |             |
  |         |             []---GET--->]            |             |
  |         |             []?/configuration        |             |
  |         |             []         []            |             |
  |         |             []         []GetDeviceData()           |
  |         |             []         []----------->[]GetDeviceOwner()
  |         |             []         []            []----------->[]
  |         |             []         []            []  [Mgmt B]  []
  |         |             []  200 OK []    [data]  []<-----------[]
  |         |             []  [data] []<-----------[]            |
  |         |             []<--------[]            |             |
  |         |             []          |            |             |
  |         | [Build bootstrap image] |            |             |
  |         |             []          |            |             |
  |         |             [] POST ?/bootstrap      |             |
  |         |             []-------->[]            |             |
  |         |             []         []SetDeviceBootstrap()      |
  |         |             []         []----------->[]            |
  |         |             []         []            []GetDeviceOwner()
  |         |             []         []            []----------->[]
  |         |             []         []            []  [Mgmt B]  []
  |         |             []         []     ACK    []<-----------[]
  |         |             []  200 OK []<-----------[]            |
  |         |             []<--------[]            |             |
[wakes up]  |             |           |            |             |
  |         |             |           |            |             |
 []         |             |           |            |             |
 []-----------GET /v1/devices/<uuid>/bootstrap---->[]            |
 []         |             |           |            []            |
 []<-----------------------[image]-----------------[]            |
 []         |             |           |            |             |
[Validate and decrypt bootstrap data] |            |             |
 []         |             |           |            |             |
[Apply bootstrap data]    |           |            |             |
 []         |             |           |            |             |
 []-PUT ?/info----------->[]          |            |             |
 []         |             []          |            |             |
 []        [data]         []          |            |             |
 []<--------------------->[]          |            |             |
  |         |              |          |            |             |

?/ is /v1/devices/<uuid>/
Device Change of Ownership
Change the management system authorized for the device

                 Device Change Owner Sequence Diagram (second part)


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15. Configuration and Bootstrap Data Formats

15.1. Overview

   The bootstrap data is critical to the device to determine
   ownership and allow authentication of the management system.
   Additional parameters may be provided to the device as part of the
   bootstrap data. The Management System uploads the bootstrap data
   for a device to the bootstrap server so that the bootstrap server
   can be provide it to the device during the bootstrap sequence. he
   Management System therefore encrypts the bootstrap data so that
   only the target device can decode it (in the case of shared secret
   devices, the Identity Service is also theoretically capable of
   this decryption). This protects the data from exposure should the
   bootstrap server be compromised.

   The Management System needs to know what information the device
   needs to complete its bootstrap and it requests this in the
   request defined in 9.3.6.  above.

15.2. Configuration data format

   The configuration data for a device provides the manufacturing
   data for the device and information about the key to use to
   encrypt the bootstrap data. The data is in JSON format as below:
   {
     "device": {
       "id": "<device UUID>",
       "bootstrap_server": <bootstrap server ID used by device>,
       "capabilities": {   // Device bootstrap capabilities
         "ec_capable": <boolean>,
         "rsa_capable": <boolean>,
         "sha384_capable": <boolean>,
         "sha512_capable": <boolean>,
         "aes256_capable": <boolean>,
         // Additional capabilities may be added in the future
       },
     },
     "authenticated_keys": [
       // Array of base-64 encoded key identity strings as in
       // 7.4.  above
     ],
     "owner_information": "<base64-encoded signed owner data
                                             in 15.3.  below>",
     "parameter_choices": [
         // List of sets of parameter choices. The Management
         // System should provide exactly one of the sets of
         // parameters, but it may choose to provide a different
         // parameter set if it has additional information about
         // what the device can support.
     ],
   }

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   The format of the "parameter_choices" array depends on the types
   of messages that are required by the device. The exact format is
   TBD at this time.

15.3. Device connection to the bootstrap server using DTLS using
                                              pre-shared secrets

   The array of "authenticated_keys" provided in the configuration
   data will include a bootstrap server key. This key and all keys
   that it relies on to derive it from the device key must be
   provided to the device by the bootstrap server during the DTLS
   handshake so that the device can establish the DTLS connection.
   The bootstrap service in the Trusted Authority will do this
   automatically. If a bootstrap service is used within the Walled
   Garden, it must be careful to include all these keys in the
   correct order (from device key to bootstrap server) so that the
   device can derive the key necessary for the DTLS session.

15.4. Device connection to the bootstrap server using DTLS using
                                                     public keys

   There is a special requirement for the device behaviour when
   establishing the DTLS connection to the bootstrap server. The DTLS
   handshake (with extensions as in RFC-7250 allowing raw public
   keys) uses public keys rather than certificates, so the device
   cannot authenticate the bootstrap server key during the DTLS
   handshake.

   The device must therefore temporarily accept the public key from
   the bootstrap server during the DTLS handshake and download the
   bootstrap data. The device must then check that the public key
   from the bootstrap server is in the list of identities in the
   bootstrap and that it has the "Bootstrap Service" identity class.

   Once the identity of the bootstrap server has been confirmed,
   validation of the bootstrap data can continue. If the identity of
   the bootstrap server cannot be confirmed, the bootstrap data
   should be discarded.

15.5. Bootstrap data format

   The bootstrap data is constructed by the management system based
   on the configuration data and the additional information that the
   management system needs to provide.

   The bootstrap data is in CBOR format comprises three sections - a
   header, the encrypted content and the signature. The header
   includes one or more authenticated keys and the owner information.
   All authenticated keys in the configuration data must be included
   in the authenticated key list in the order provided. The
   management system may then append additional keys if it wishes.

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   The order is important because the device will validate and import
   the authenticated keys in the order provided. If a key is invalid
   or depends on a key that is not yet imported, the bootstrap data
   will be rejected.

   The owner information tells the device the number of owners the
   device has had. This number starts at zero and is incremented each
   time the owner changes. The device must store this number in non
   volatile memory and only accept bootstrap data if the owner
   sequence_number in the bootstrap data is the same or higher than
   the owner_sequence_number stored in non-volatile memory. This
   prevents replay attacks of older owner data in an attempt to
   reclaim ownership of a device. The owner data must be signed by a
   manufacturer or registration identity as defined in 7.7.  above.

   ARRAY {
     // One or more authenticated key definitions in 7.4.  above
     ARRAY {
       ...  // Authenticated key definition
     }

     // Owner information
     ARRAY {
       INTEGER content  //"Owner Content Type" as in 7.5.  above
       INTEGER owner_sequence_number
       ARRAY {
         // Signature for owner data, provided by bootstrap
         // server as in 7.3.  above
       }
     }
     // End of owner information

     // Start of encryption information
     BYTE STRING decryption_key_id  // Key UUID
     BYTE STRING encrypted_payload

     // Signature for the entire bootstrap data
     ARRAY {
       // Signature as in 7.3.  above, signed by Management
       // Systems key
       // Signature covers ENCRYPTED payload, so signature
       //.validation is done before decryption
     }
   }

15.5.1. Payload protected by Elliptic Curve keys

   If the decryption key refers to an Elliptic Curve key, the
   encrypted_payload is a Cryptographic Message Syntax object
   containing an enveloped-data block (see RFC 5652 and RFC 5753).
   The enveloped-data should be encrypted using the "Standard"
   variation of Ephemeral Static ECDH (see RFC 5753 section 3.1). The

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   default choices for encryption cipher and hash function should be
   AES-128 and SHA-256 respectively.

   The "enveloped-data", after decryption, contains the payload CBOR
   structure as defined in 15.5.4.  below.

15.5.2. Payload protected by RSA keys

   If the decryption key refers to an RSA key, then the
   encrypted_payload is a Cryptographic Message Syntax object
   containing an enveloped-data block (see RFC 5652).

   The enveloped-data should be encrypted using RSAES-OAEP (see RFC
   8017 section 7.1). The default choices for encryption cipher and
   hash function should be AES-128 and SHA-256 respectively.
   The SHA-1 hash should NOT be used.

   The "enveloped-data", after decryption, contains the payload CBOR
   structure as defined in 15.5.4.  below.

15.5.3. Payload protected by shared secrets

   If the decryption key refers to a shared secret then the
   encrypted_payload contains the CBOR structure below. The salt,
   iterations_or_cipher and encrypted_secret fields are used to
   derive a decryption key for the cipher in the same way as a
   derived secret is obtained in section 7.2.  above. This key is
   then used with the indicated cipher_suite with the cipher_IV and
   optional tag to decrypt the encrypted_data.

   ARRAY {
     BYTE STRING     salt
     INTEGER         iterations_or_cipher
     BYTE_STRING     encrypted_secret
     INTEGER         cipher_suite  // As in 7.8.  above
     BYTE STRING     cipher_IV
     BYTE STRING     tag        // Zero length for CBC ciphers
     BYTE STRING     encrypted_data
   }

   The "encrypted_data", after decryption, contains the payload CBOR
   structure as defined in 15.5.4.  below.

15.5.4. Decrypted payload content

   The payload has the following CBOR format:
   ARRAY {
     BYTE STRING coap_message0
     BYTE STRING coap_message1
     ...
     BYTE STRING coap_messageN
   }

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   Each message is replayed to the local API in the order in the
   payload.

   If the device requires configuration messages to be replayed to a
   different API, a local API function should be created that
   understands how to replay the message content to the other API.
   E.g. replay of a BACnet APDU to the local device.

16. Security Considerations

   This whole draft concerns security considerations. See Chapter 6.

17. IANA Considerations

   None

18. Conclusions

   End to end certificate handling and encrypted communication using
   "channels" within the DTLS framework can easily be achieved
   without inventing new standards, just by enhancing current ones.
   This covers devices from high end servers down to resource
   constrained devices across different types of network.

   The underlying standards are:

   Transport Layer Security, TLS v1.2, RFC-5246
   Datagram Transport Layer Security, DTLS v1.2, RFC-6347
   Constrained Application Framework, CoAP, RFC-7252
   Concise Binary Object Representation, CBOR, RFC-7049
   CoAP Block-wise Transfers, https://www.ietf.org/id/draft-ietf
   core-block-21.txt

  The aSSURE specification lends itself to the industrial
  manufacture and distribution of IoT and other connected pieces of
  equipment and can serve many markets both in retrofit and new
  build. Indeed IoT is currently disgorging millions of devices in
  architectures that are not secure enough and could be repaired
  using the aSSURE framework and philosophy. This problem is better
  described by Bob Hinden in his paper "Internet of Insecure Things"
  published in the Internet Protocol Journal.

19. References

19.1. Normative References

   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
   Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4279] Eronen, P., Ed., and H. Tschofenig, Ed., "Pre-Shared Key
   Ciphersuites for Transport Layer Security (TLS)", RFC4279, DOI

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   10.17487/RFC4279, December 2005, <http://www.rfc
   editor.org/info/rfc4279>.

   [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer
   Security (TLS) Protocol Version 1.2", RFC 5246, DOI
   10.17487/RFC5246, August 2008, <http://www.rfc
   editor.org/info/rfc5246>.

   [RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD
   70, RFC 5652, DOI 10.17487/RFC5652, September 2009,
   <http://www.rfc-editor.org/info/rfc5652>.

    [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
   Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, January
   2012, <http://www.rfc-editor.org/info/rfc6347>.

   [RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object
   Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049, October
   2013, <http://www.rfc-editor.org/info/rfc7049>.

   [RFC7250] Wouters, P., Ed., Tschofenig, H., Ed., Gilmore, J.,
   Weiler, S., and T. Kivinen, "Using Raw Public Keys in Transport
   Layer Security (TLS) and Datagram Transport Layer Security
   (DTLS)", RFC 7250, DOI 10.17487/RFC7250, June 2014,
   <http://www.rfc-editor.org/info/rfc7250>.

   [RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
   Application Protocol (CoAP)", RFC 7252, DOI 10.17487/RFC7252, June
   2014, <http://www.rfc-editor.org/info/rfc7252>.

19.2. Informative References

   CoAP Block-wise Transfers, https://www.ietf.org/id/draft-ietf
   core-block-21.txt

   [RFC2898] Kaliski, B., "PKCS #5: Password-Based Cryptography
   Specification Version 2.0", RFC 2898, DOI 10.17487/RFC2898,
   September 2000, <http://www.rfc-editor.org/info/rfc2898>.

   [RFC5753] Turner, S. and D. Brown, "Use of Elliptic Curve
   Cryptography (ECC) Algorithms in Cryptographic Message Syntax
   (CMS)", RFC 5753, DOI 10.17487/RFC5753, January 2010,
   <http://www.rfc-editor.org/info/rfc5753>.

   [RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for
   Constrained-Node Networks", RFC 7228, DOI 10.17487/RFC7228, May
   2014, <http://www.rfc-editor.org/info/rfc7228>.

   "Internet of Insecure Things", Hinden, B., Internet Protocol
   Journal March 2017 Vol 20, Number 1, Page 12.
   <http://ipj.dreamhosters.com/wp-content/uploads/issues/2017/ipj20-
   1.pdf>.

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20. Acknowledgments

   This document is a byproduct of the "aSSURE" project, partially
   funded by Innovate UK. It is provided "as is" and without
   any express or implied warranties, including, without limitation,
   the implied warranties of fitness for a particular purpose. The
   views and conclusion contained herein are those of the authors and
   should not be interpreted as necessarily representing the official
   policies or endorsements, either expressed or implied, of the
   aSSURE project or Innovate UK.

Author's Address

   Roger Lucas
   c/o Cisco International Limited
   10, New Square Park
   Bedfont Lakes
   Feltham
   TW14 8HA
   United Kingdom
   Email: iot@hiddenengine.co.uk



































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