Internet Draft P. Urien
Intended status: Experimental Telecom Paris
Expires: April 2022 October 4 2021
Internet of Secure Elements
draft-urien-coinrg-iose-04.txt
Abstract
This draft defines an infrastructure for secure elements over
internet, and features needed for their secure remote use.
It describes a network architecture based on the TLS 1.3 protocol,
which enables remote calls of cryptographic procedures, identified
by Unified Resource Identifier (URI) such as
schemeS://sen@server.com:443/?query
The Internet of Secure Element (IoSE) is a set of secure elements
providing TLS servers, communication interfaces, and identified by
their name (Secure Element Name, sen).
Requirements Language
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.
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-
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 April 2022
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Copyright Notice
Copyright (c) 2021 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
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with
respect to this document. Code Components extracted from this
document must include Simplified BSD License text as described in
Section 4.e of the Trust Legal Provisions and are provided without
warranty as described in the Simplified BSD License.
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Table of Contents
Abstract........................................................... 1
Requirements Language.............................................. 1
Status of this Memo................................................ 1
Copyright Notice................................................... 2
1 Overview......................................................... 4
2. About Secure Elements........................................... 5
3. Network Architecture............................................ 6
4 Unified Resource Identifier (URI)................................ 7
5 URI Example...................................................... 7
6 Overview of Internet Of Secure Elements Framework................ 8
7 Functional Entities.............................................. 9
8 Attestation Procedure............................................ 9
8.1 Service Request............................................ 11
8.2 SE-App Downloading......................................... 11
8.3 SE-App Certificate......................................... 11
8.4 User Notification.......................................... 12
8.5 User Enrollment............................................ 12
9 IANA Considerations............................................. 12
10 Security Considerations........................................ 12
11 References..................................................... 12
11.1 Normative References...................................... 12
11.2 Informative References.................................... 13
12 Authors' Addresses............................................. 13
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1 Overview
This draft defines an infrastructure for the deployment of secure
elements over internet, and features needed for their secure remote
use.
Secure elements [ISO7816] are tamper resistant micro-controllers,
whose security Evaluation Assurance Levels (EAL) are in the range
EAL5+/EAL6+ according to Common Criteria standards [CC], which
define up to 7 levels.
This draft describes a network architecture based on the TLS 1.3
[RFC8446] protocol, which enables remote calls of cryptographic
procedures, identified by Unified Resource Identifier (URI)
[RFC3986].
We believe that internet should provide to its users open computing
resources, with high security and trust levels. Many applications,
such as blockchain, require on-line trusted computing resources,
running cryptographic algorithms.
TLS SNI SEN
+--------+ +----------------+
| TCP/IP | Communication | Application |
server.com:443---+ Server +---------------+ TLS |
SNI=SEN | | Interface | Secure Element |
+--------+ +----------------+
server.com TLS Server
schemeS://sen@server.com:port/?query
The network architecture comprises the following elements:
- Secure elements, identified by their name (Secure Element Name,
SEN) running embedded TLS servers and applications.
- TCP/IP servers, able to parse TLS ClientHello message, in order to
extract SNI (Server Name Indication) extension [RFC6066]. If the SNI
value matches the SEN value, the TLS packets are routed toward the
selected secure element.
The secure element URI [RFC3986] is
schemeS://sen@server.com:443/?query, in which:
- scheme indicates the application data interchange format,
- S means secured by TLS,
- sen is the secure element name included in the TLS SNI extension,
- server.com:port is a TCP/IP node and associated port
- query is the command to be executed by the secure element
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TLS sessions MUST use mutual authentication between client and
server, either based either on pre-shared-key (PSK) or X509
certificates.
The TCP/IP server MAY manage multiple secure elements. As an
illustration, according to the IETF draft [RACS] a grid of Secure
Elements (GoSE) is a server hosting a set of secure elements.
In summary the Internet of Secure Element (IoSE) is a set of secure
elements providing TLS servers, communication interfaces, and
identified by their SEN name.
2. About Secure Elements
Secure elements are defined according to [ISO7816] standards. Most
of them use 8 bits Micro Controller Unit (MCU) and embedded
cryptographic accelerator. Non volatile memory size is up to 100KB,
and RAM size is up to 10KB. Open software can be written thanks to
the JavaCard (JC) programming language, and associated API
frameworks such as JC3.04, JC3.05, JC3.1.
Secure elements are dedicated to cryptographic procedures; they are
available under multiples physical form factors, such as smartcard,
NFC chip, embedded SIM (eSIM), or surface-mount devices.
Secure elements have no network resources. They exchange small
messages (up to 256 bytes) over communication interfaces such as
ISO7816 (5 wires) [ISO7816], I2C (Inter-Integrated Circuit), or SPI
(Serial Peripheral Interface) [GP-SPI-I2C].
Nevertheless they are able to process the TLS 1.3 protocol. For
example the IETF draft [TLS-SE] defines segmentation/reassembly
mechanisms over ISO7816, which enable exchange of TLS packets with
secure elements. The open project [TLS-SE-CODE] is an implementation
of [TLS-SE] for javacards. The open project [KEYSTORE-CODE] is an
implementation of secure element server. The open project [IOSE-
CODE] is a demonstrator for Internet of Secure Elements.
Therefore secure element can be used as host, providing TLS server,
and communication interface.
They are several ways to provide a host name for a secure element
(i.e. a server name), which is referred as secure element name (SEN)
by this draft,:
- The [TLS-SE] draft uses historical bytes (up to 15 bytes) inserted
in the ISO7816 ATR (Answer To Reset), which is a response triggered
by a physical reset. A javacard application may define the value of
historical bytes.
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- The [RACS] IETF draft describes Grid of Secure Elements (GoSE),
and introduces Secure Element Identifier (SEID) as unique identifier
indicating that a given SE is hosted by a GoSE. SEID also implicitly
refers the physical slot (SlotID) to which the secure element is
plugged. SEID MAY be used as SEN.
3. Network Architecture
The network architecture is based on TLS1.3 servers and future
versions.
A TCP/IP node manages a server. According to [ESNI] TLS has two
working modes, shared and split.
- In Shared Mode, the provider is the origin server for all the
domains whose DNS records point to it. In this mode, the TLS
connection is terminated by the provider
- In Split Mode, the provider is not the origin server for private
domains. Rather, the DNS records for private domains point to the
provider, and the provider's server relays the connection back to
the origin server, who terminates the TLS connection with the
client.
According to this terminology the secure element is the backend
server, identified by a server name (referred as SEN).
The client-facing server finds in the ClientHello message required
secure element name. Thereafter it performs segmentation/reassembly
operations in order to shuttle TLS packet over the communication
interface.
The client-facing server MAY also use encrypted server name
indication (ESNI) features in order to protect secure elements name.
The application-layer protocol negotiation extension (ALPN)
[RFC7301] MAY be used by secure element to select an internal
application.
TLS protocol MUST be used with mutual authentication between client
and secure element. PSK is a symmetric cryptographic scheme for one
client-to-one-secure-element, while PKI is an asymmetric
cryptographic scheme adapted to multiple-clients-to-one-secure-
element.
Nevertheless it should be noticed that secure elements have not
clock and therefore are not able to check validity date or
certificate revocation.
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4 Unified Resource Identifier (URI)
According to [RFC3986] the URI comprises a scheme name ended by the
'S' character, the secure element name, the client-facing name and
port (server.com:port), and a query.
URI= schemeS://sen@server.com:port/?query
A client software entity able to process this URI, MUST retrieves
the PSK or the certificate chain to be used within the TLS protocol.
The secure element name MUST be included in the SNI extension.
The used scheme used by the query, MAY be included in the ALPN
extension.
For PSK it is possible, but not recommended for security reasons, to
include the PSK value in the URI:
schemeS://sen:psk@server.com:port/?query
5 URI Example
A secure element implements a keystore, of which keys are identified
by an index. The secure element name is mykeystore
The secure element name is found in the historical bytes of the
ISO7816 ATR.
The client-facing server is server.com:443
The scheme used by the secure element is a shell, i.e. ASCII command
lines ended by line feed and carriage return characters.
The query
s010102030405060708090A0B0C0D0E0F101112131415161718191A1B1C1D1E1F20%
0D%0A computes a signature command ('s' prefix) with key of index
01, over the 32 bytes value 0102...1920
The URI is:
shellS://mykeystore@server.com:443/?s010102030405060708090A0B0C0D0E0
F101112131415161718191A1B1C1D1E1F20%0D%0A
The software client opens a TLS session with the server
server.com:443, with the name "mykeystore" inserted the SNI
extension. Upon success a TLS secure channel is established with the
secure element. The client sends the query, the secure element
computes the signature and returns its value encoded in hexadecimal
text.
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6 Overview of Internet Of Secure Elements Framework
+---------------------------------+
| User Application |
+---------------------------------+
| APIs |
+---------------------------------+
| TCP/IP Client |
+---------------------------------+ +----------------+
| TCP/IP Server |<--| |
+---------------------------------+ | Administration |
| Secure Element Application |<--| (RACS) |
+---------------------------------+ +----------------+
| Secure Element Hardware |
+---------------------------------+
The goal of IOSE is to provide to internet users open computing
resources, with high security and trust levels. In order to reach
this objective, the IOSE framework comprises seven layers.
- The User Application layer uses secure resources hosted in the
internet
- The APIs layer provides software interface to virtual resources.
It SHOULD provide secure storage of credentials required by TLS
sessions.
- The TCP/IP client layer manages TLS session, according to profiles
compatible with secure element computing capacities.
- The TCP/IP server layer manages one or several secure elements. It
MAY provide privacy features such as server name encryption.
- The secure element application layer defines data interchange
format and available procedures
- The secure element hardware layer defines security profile
(according to Common Criteria standards) and communication
interfaces
- The administration layer is in charge of secure elements
application deployment and lifetime. These operations are performed
locally or remotely (through the internet).
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7 Functional Entities
+---------------------------+ +-------------------+
| | | |
| Infrastructure Provider +----+ SE-App Provider |
| (Secure Element Server) | | |
| | +------+-----+------+
+------------+--------------+ | |
| | |
| | |
+------------+--------------+ | |
| +-----------+ |
| Service Provider | |
| (Cloud Infrastructure) | |
| +-------+ +------+
+------------+--------------+ | |
| | |
| | |
+------------+--------------+ +--+--+--+
| | | |
| Application Provider +----+ User +
| | | |
+---------------------------+ +--------+
The functional entities COULD involve five elements.
- The User is equipped with a connected device, executing an
application using IOSE services.
- The Application Provider (AP) designs software, using IOSE
infrastructure.
- The Service Provider (SP) manages a cloud infrastructure, and all
facilities needed to setup secure element applications. An
attestation mechanism MUST be available in order to prove SE
application authenticity.
- The Infrastructure Provider (IP) provides secure element servers.
- The SE-App Provider (SE-AppP) designs secure and trusted software
(SE-App) for secure elements.
8 Attestation Procedure
The goal of the attestation procedure is to allocate a secure
element, and to prove to its user the exclusive access to a genuine
secure element.
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SE-App Provider Infrastructure Secure
Provider Provider Element
| | |
| RACS: Download --->|----------->|Private and Public Key
| TLS-PSK App in SE | |Generation
| With PSK-Provider | |TLS-PSK Ready
| <--------------Done|<-------Done|
| | |
| RACS: Link ------>| |
| SEN to SEID | |
| <--------------Done| |
| | |
| TLS-PSK: ---------|----------->|
| Read Public Key | |
| <------------------|--------Done|
| | |
| Generate | |
| Certificate | |
| | |
| TLS-PSK: -------|----------->|
| Write Certificate | |
| <------------------|------- Done|
|
| SEND ------------------------------------------------->|
| PSK-Provider & SEN |
Secure User
Element |
|<---------Open TLS-PSK|
|Compute Compute|
|HS HS|
|<---TLS-PSK Opened--->|
| |
|<------Read Public Key|
|Done----------------->|
| |
|<-----Read Certificate|
|Done----------------->|
| |
| Check Certificate|
| |
|<-------------Send rnd|
|Compute |
|Sign(HS | rnd) |
|Send Sign------------>|
| |
| Check Sign|
| |
|<-------Write PSK-User|
|Done----------------->|
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8.1 Service Request
The User requests to an on-line Service Provider a secure element
for a specific application.
8.2 SE-App Downloading
The Service Provider requests the SE-App Provider to download the
user's application in a secure element hosted by an Infrastructure
Provider.
The SE-App Provider downloads the selected application thanks to
protocols such as [RACS].
There is a mutual authentication between SE-App Provider and
Infrastructure Provider. The SE-App Provider owns a set of secure
elements identified by their SEID (Secure Element Identifier). He
may erase their content and write binary image, but he can't read
binary images.
The SE-App includes a TLS 1.3 server with a pre shared key (PSK-App-
Provider) and a server name (SEN). Upon instantiation, the
downloaded SE-App generates a pair of private key (SE-App-Priv-Key)
and public key (SE-App-Pub-key).
Thanks to a dedicated [RACS] command, the SE-APP provider notifies
to the Infrastructure Provider the SEN associated to the secure
element SEID.
At this step the secure element is on-line, and may process TLS
sessions, with the right server name (SEN), and authenticated by
PSK-App-Provider.
The PSK-App provider has the exclusive knowledge of the pre-shared-
key, and consequently is the only entity able to communicate with
the secure element.
8.3 SE-App Certificate
The SE-App Provider opens a TLS (with PSK= PSK-App-Provider) session
with the SEN secure element, reads its SE-App-Pub-key, and computes
a certificate (SE-Cert) for this public key.
The SE-Cert is remotely written in the secure element
The SE-App provider forwards the secure element URI and PSK-App-
Provider to the Service Provider or to the User, according to pre-
defined agreements.
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8.4 User Notification
The User receives the secure element URI and pre-shared-key (i.e.
PSK-App-Provider).
8.5 User Enrollment
A secure element only manages a unique TLS session at a given time.
The User opens a TLS session with the secure element (with PSK-App-
Provider and SEN). According to [RFC8446] a TLS handshake secret
(HS) is computed from the Diffie-Hellman exchange.
He reads the secure element public key (SE-App-Pub-key) and its
certificate (SE-Cert)
He checks the certificate SE-Cert with the Infrastructure Provider
public key.
He performs the attestation procedure that sends a random value
(RND) to the secure element. The secure element returns a signature
of the concatenation of HS and RND values, computed with the private
key SE-App-Priv-key.
He checks the signature with the public key SE-App-Pub-key.
At this point the User has the proof that it shares an exclusive TLS
session with the secure element.
The user sets the pre-share-key value to new one: PSK-User-Provider.
At this step the User has the exclusive access to a genuine secure
element.
9 IANA Considerations
This draft does not require any action from IANA.
10 Security Considerations
This entire document is about security.
11 References
11.1 Normative References
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
https://www.rfc-editor.org/info/rfc8446.
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[RFC6066] Eastlake 3rd, D., "Transport Layer Security (TLS)
Extensions: Extension Definitions", RFC 6066, DOI 10.17487/RFC6066,
January 2011.
[RFC7301] Friedl, S., Popov, A., Langley, A., and E. Stephan,
"Transport Layer Security (TLS) Application-Layer Protocol
Negotiation Extension", RFC 7301, July 2014
[RFC3986] Berners-Lee, Tim; Fielding, Roy T.; Masinter, Larry.
Uniform Resource Identifiers (URI): Generic Syntax. Internet
Engineering Task Force. doi:10.17487/RFC3986, January 2005
[ISO7816] ISO 7816, "Cards Identification - Integrated Circuit Cards
with Contacts", The International Organization for Standardization
(ISO).
[CC] ISO/IEC 15408, "Common Criteria for Information Technology
Security Evaluation", The International Organization for
Standardization (ISO)
[GP-SPI-I2C] GlobalPlatform Technology, APDU Transport over SPI/I2C
Version 0.0.0.39", July 2019
11.2 Informative References
[ESNI] "TLS Encrypted Client Hello", draft-ietf-tls-esni-13, 2021
[RACS] "Remote APDU Call Secure (RACS)", draft-urien-core-racs-
15.txt, 2021
[TLS-SE] IETF Draft, "Secure Element for TLS Version 1.3", draft-
urien-tls-se-03.txt, 2021
[TLS-SE-CODE] "tls-se.java", https://github.com/purien/TLS-SE
[KEYSTORE-CODE] https://github.com/purien/keystore
[IOSE-CODE] https://github.com/purien/iose
12 Authors' Addresses
Pascal Urien
Telecom Paris
19 place Marguerite Perey
91120 Palaiseau Phone: NA
France Email: Pascal.Urien@telecom-paris.fr
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