EST over secure CoAP (EST-coaps)
draft-vanderstok-ace-coap-est-01
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft whose latest revision state is "Replaced".
|
|
|---|---|---|---|
| Authors | Sandeep S. Kumar , Peter Van der Stok , Panos Kampanakis , Martin Furuhed , Shahid Raza | ||
| Last updated | 2017-03-09 | ||
| Replaced by | draft-ietf-ace-coap-est, RFC 9148 | ||
| RFC stream | (None) | ||
| Formats | |||
| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
| RFC Editor Note | (None) | ||
| IESG | IESG state | I-D Exists | |
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-vanderstok-ace-coap-est-01
ACE S. Kumar
Internet-Draft Philips Lighting Research
Intended status: Standards Track P. van der Stok
Expires: September 10, 2017 Consultant
P. Kampanakis
Cisco Systems
M. Furuhed
Nexus Group
S. Raza
RISE SICS
March 9, 2017
EST over secure CoAP (EST-coaps)
draft-vanderstok-ace-coap-est-01
Abstract
Low-resource devices in a Low-power and Lossy Network (LLN) can
operate in a mesh network using the IPv6 over Low-power Wireless
Personal Area Networks (6LoWPAN) and IEEE 802.15.4 link-layer
standards. Provisioning these devices in a secure manner with keys
(often called secure bootstrapping) used to encrypt and authenticate
messages is the subject of Bootstrapping of Remote Secure Key
Infrastructures (BRSKI) [I-D.ietf-anima-bootstrapping-keyinfra] and
6tisch Secure Join [I-D.ietf-6tisch-dtsecurity-secure-join].
Enrollment over Secure Transport (EST) [RFC7030], based on TLS and
HTTP, is used in BRSKI. Low-resource devices often use the
lightweight Constrained Application Protocol (CoAP) [RFC7252] for
message exchanges. This document defines how low-resource devices
are expected to use EST over secure CoAP (EST-coaps) for secure
bootstrapping and certificate enrollment. 6LoWPAN fragmentation
management and minor extensions to CoAP are needed to enable EST-
coaps.
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
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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 September 10, 2017.
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
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
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. EST operational differences . . . . . . . . . . . . . . . . . 4
3. Conformance to RFC7925 profiles . . . . . . . . . . . . . . . 5
4. Protocol Design and Layering . . . . . . . . . . . . . . . . 6
4.1. Discovery and URI . . . . . . . . . . . . . . . . . . . . 7
4.2. Payload format . . . . . . . . . . . . . . . . . . . . . 8
4.3. Message Bindings . . . . . . . . . . . . . . . . . . . . 8
4.4. CoAP response codes . . . . . . . . . . . . . . . . . . . 8
4.5. Message fragmentation . . . . . . . . . . . . . . . . . . 9
5. Transport Protocol . . . . . . . . . . . . . . . . . . . . . 10
5.1. DTLS . . . . . . . . . . . . . . . . . . . . . . . . . . 10
5.2. 6tisch approach . . . . . . . . . . . . . . . . . . . . . 11
6. Proxying . . . . . . . . . . . . . . . . . . . . . . . . . . 12
7. Parameters . . . . . . . . . . . . . . . . . . . . . . . . . 12
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
9. Security Considerations . . . . . . . . . . . . . . . . . . . 16
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 16
11. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 16
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
12.1. Normative References . . . . . . . . . . . . . . . . . . 16
12.2. Informative References . . . . . . . . . . . . . . . . . 17
Appendix A. EST messages to EST-coaps . . . . . . . . . . . . . 19
A.1. cacerts . . . . . . . . . . . . . . . . . . . . . . . . . 20
A.2. enroll / reenroll . . . . . . . . . . . . . . . . . . . . 21
A.3. csrattr . . . . . . . . . . . . . . . . . . . . . . . . . 22
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A.4. enrollstatus . . . . . . . . . . . . . . . . . . . . . . 22
A.5. voucher_status . . . . . . . . . . . . . . . . . . . . . 22
A.6. requestvoucher . . . . . . . . . . . . . . . . . . . . . 22
A.7. requestlog . . . . . . . . . . . . . . . . . . . . . . . 22
Appendix B. EST-coaps Block message examples . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 25
1. Introduction
IPv6 over Low-power Wireless Personal Area Networks (6LoWPANs)
[RFC4944] on IEEE 802.15.4 [ieee802.15.4] wireless networks is
becoming common in many industry application domains such as lighting
controls. However, commissioning of such networks suffers from a
lack of standardized secure bootstrapping mechanisms for these
networks.
Although IEEE 802.15.4 defines how security can be enabled between
nodes within a single mesh network, it does not specify the
provisioning and management of the keys. Therefore, securing a
6LoWPAN network with devices from multiple manufacturers with
different provisioning techniques is often tedious and time
consuming.
Bootstrapping of Remote Secure Infrastructures (BRSKI)
[I-D.ietf-anima-bootstrapping-keyinfra] addresses the issue of
bootstrapping networked devices in the context of Autonomic
Networking Integrated Model and Approach (ANIMA).
[I-D.ietf-6tisch-minimal-security] and
[I-D.ietf-6tisch-dtsecurity-secure-join] also address secure
bootstrapping in the 6tisch context targeted to low-resource devices.
BRSKI has not been developed specifically for low-resource devices in
constrained networks. Constrained networks use DTLS [RFC6347], CoAP
[RFC7252], and UDP instead of TLS [RFC5246], HTTP [RFC7230] and TCP.
BRSKI relies on Enrollment over Secure Transport (EST) [RFC7030] for
the provisioning of the operational domain certificates.
EST-coaps provides a subset of EST functionality and extends EST with
BRSKI functions. EST-coaps replaces the invocations of TLS and HTTP
by DTLS and CoAP invocations thus enabling EST and BRSKI for CoAP-
based low-resource devices.
Although EST-coaps paves the way for the utilization of EST for
constrained devices on constrained networks, some devices will not
have enough resources to handle the large payloads that come with
EST-coaps. The specification of EST-coaps is intended to ensure that
bootstrapping works for less constrained devices that choose to limit
their communications stack to UDP/CoAP. It is up to the network
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designer to decide which devices execute the EST protocol and which
not.
EST-coaps is designed for use in professional control networks such
as Building Control. The autonomic bootstrapping is interesting
because it reduces the manual intervention during the commissioning
of the network. Typing in passwords is contrary to this wish.
Therefore, the HTTP Basic authentication of EST is not supported in
EST-coaps.
In the constrained devices context it is very unlikely that full PKI
request messages will be used. For that reason, full PKI messages
are not supported in EST-coaps.
Because the relatively large EST messages cannot be readily
transported over constrained (6LoWPAN, LLN) wireless networks, this
document specifies the use of CoAP Block-Wise Transfer ("Block")
[RFC7959] to fragment EST messages at the application layer.
Support for Observe CoAP options [RFC7641] with BRSKI is not
supported in the current BRSKI/EST message flows and is thus out-of-
scope for this discussion. Observe options could be used by the
server to notify clients about a change in the cacerts or csr
attributes (resources) and might be an area of future work.
1.1. 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 [RFC2119].
Many of the concepts in this document are taken over from [RFC7030].
Consequently, much text is directly traceable to [RFC7030]. The same
document structure is followed to point out the differences and
commonalities between EST and EST-coaps.
The following terms are defined in the BRSKI protocol
[I-D.ietf-anima-bootstrapping-keyinfra]: pledge, Join proxy, Join
Registrar, and Manufacturer Authorized Signing Authorities (MASA).
2. EST operational differences
Only the differences to EST with respect to operational scenarios are
described in this section. EST-coaps server differs from EST server
as follows:
o Replacement of TLS by DTLS and HTTP by CoAP, resulting in:
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* DTLS-secured CoAP sessions between EST-coaps client and EST-
coaps server.
o Only certificate-based client authentication is supported, which
results in:
* The EST-coaps client does not support HTTP Basic authentication
(as described in Section 3.2.3 of [RFC7030])
* The EST-coaps client does not support authentication at the
application layer (as described in Section 3.2.3 of [RFC7030]).
o EST-coaps does not support full PKI request messages[RFC5272].
o EST-coaps specifies the BRSKI extensions over CoAP as specified in
section 5 of [I-D.ietf-anima-bootstrapping-keyinfra].
3. Conformance to RFC7925 profiles
This section shows how EST-coaps fits into the profiles of low-
resource devices as described in [RFC7925]. Within the bootstrap
context a Public Key Infrastructure (PKI) is used, where the client
is called "pledge", the Registration Authority (RA) is called Join
Registrar, which acts at the front-end for the Certificate Authority
(CA) and receives voucher feedback from as many Manufacturer
Authorized Signing Authorities (MASA) as there are manufacturers. A
Join-Proxy is placed between client and RA to receive join requests
over a 1-hop unsecured channel and transmitted over the secure
network to the EST-server. The EST-server of EST-coaps is placed
between proxy and RA or is part of RA.
EST-coaps transports Public keys and certificates. Private keys can
be transported as response to a request to a server-side key
generation as described in section 4.4 of [RFC7030]. In the
bootstrapping context, EST-coaps transport is limited to the EST
certificate transport conformant to section 4.4 of [RFC7925]. For
BRSKI, outside the profiles of [RFC7925], EST-coaps transports
vouchers, which are YANG files specified in [I-D.ietf-anima-voucher].
The mandatory cipher suite for DTLS is
TLS_ECDHE_ECDSA_WITH_AES_128_CCM_8 defined in [RFC7251] which is the
mandatory-to-implement cipher suite in CoAP. Additionally the curve
secp256r1 MUST be supported [RFC4492]; this curve is equivalent to
the NIST P-256 curve. The hash algorithm is SHA-256. DTLS
implementations MUST use the Supported Elliptic Curves and Supported
Point Formats Extensions [RFC4492]; the uncompressed point format
MUST be supported; [RFC6090] can be used as an implementation method.
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The EST-coaps client MUST be configured with an explicit TA database
or at least an implicit TA database from its manufacturer. The
authentication of the EST-coaps server by the EST-coaps client is
based on Certificate authentication in the DTLS handshake.
The authentication of the EST-coaps client is based on client
certificate in the DTLS handshake. This can either be
o DTLS with a previously issued client certificate (e.g., an
existing certificate issued by the EST CA); this could be a common
case for simple re-enrollment of clients;
o DTLS with a previously installed certificate (e.g., manufacturer-
installed certificate or a certificate issued by some other
party);
4. Protocol Design and Layering
EST-coaps uses CoAP to transfer EST messages, aided by Block-Wise
Transfer [RFC7959] to transport CoAP messages in blocks thus avoiding
(excessive) 6LoWPAN fragmentation of UDP datagrams. The use of
"Block" for the transfer of larger EST messages is specified in
Section 4.5. The Figure 1 below shows the layered EST-coaps
architecture.
+------------------------------------------------+
| EST request/response messages |
+------------------------------------------------+
| CoAP for message transfer and signaling |
+------------------------------------------------+
| DTLS for transport security |
+------------------------------------------------+
| UDP for transport |
+------------------------------------------------+
Figure 1: EST-coaps protocol layers
The EST-coaps protocol design follows closely the EST design,
excluding some aspects that are not relevant for automatic
bootstrapping of constrained devices within a professional context.
The parts supported by EST-coaps are identified by their message
types:
o Simple enroll and reenroll.
o CA certificate retrieval.
o CSR Attributes request messages.
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o Server-side key generation messages.
4.1. Discovery and URI
EST-coaps is targeted to low-resource networks with small packets.
Saving header space is important and the EST-coaps URI is shorter
than the EST URI.
The presence and location of (path to) the management data are
discovered by sending a GET request to "/.well-known/core" including
a resource type (RT) parameter with the value "core.est" [RFC6690].
Upon success, the return payload will contain the root resource of
the EST resources. It is up to the implementation to choose its root
resource, but it is recommended that the value "/est" is used, where
possible. The example below shows the discovery of the presence and
location of management data.
REQ: GET /.well-known/core?rt=core.est
RES: 2.05 Content </est>; rt="core.est"
The EST-coaps server URIs differ from the EST URI by replacing the
scheme https by coaps and by specifying shorter resource path names:
coaps://www.example.com/est/short-name
Figure 5 in section 3.2.2 of [RFC7030] enumerates the operations and
corresponding paths which are supported by EST. Table 1 provides the
mapping from the EST and BRSKI URI path to the EST-coaps URI path.
+------------------+------------------+-----------+
| BRSKI | EST | EST-coaps |
+------------------+------------------+-----------+
| | /cacerts | /crts |
| | /simpleenroll | /sen |
| | /simplereenroll | /sren |
| | /csrattrs | /att |
| | /serverkeygen | /skg |
| /requestvoucher | | /rv |
| /voucherstatus | | /vs |
| /enrollstatus | | /es |
+------------------+------------------+-----------+
Table 1
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/requestvoucher and /enrollstatus are needed between pledge and
Registrar.
4.2. Payload format
The content-format (media type equivalent) of the CoAP message
determines which EST message is transported in the CoAP payload. The
media types specified in the HTTP Content-Type header(see section
3.2.2 of [RFC7030]) are in EST-coaps specified by the Content-Format
Option (12) of CoAP. The combination of URI path-suffix and content-
format used for coap MUST map to an allowed combination of path-
suffix and media type as defined for EST. The required content-
formats for these request and response messages are defined in
Section 8. The CoAP response codes are defined in Section 4.4.
EST-coaps is designed for use between low-resource devices using CoAP
and hence does not need to send base64-encoded data. Simple CBOR
byte string is more efficient (30% less payload compared to base64)
and well supported by CoAP. Therefore, the content formats
specification in Section 8 requires the use of CBOR byte string
(h'xxxx' in Diagnostic JSON) for all EST-coaps CoAP payloads.
4.3. Message Bindings
This section describes BRSKI to CoAP message mappings.
All /crts, /sen, /sren, /att, /skg, /rv, /vs, and /es EST-coaps
messages expect a response, so they are all CoAP CON messages.
The Ver, TKL, Token, and Message ID values of the CoAP header are not
influenced by EST.
CoAP options are used to convey Uri-Host, Uri-Path, Uri-Port,
Content-Format and more in CoAP. The CoAP Options are used to
communicate the HTTP fields specified in the BRSKI REST messages.
BRSKI URLs are HTTPS based (https:// ), in CoAP these will be assumed
to be transformed to coaps (coaps://)
Appendix A includes some practical examples of EST messages
translated to CoAP.
4.4. CoAP response codes
Section 5.9 of [RFC7252] specifies the mapping of HTTP response codes
to CoAP response codes. Every time the HTTP response code 200 is
specified in [RFC7030] in response to a GET request, in EST-coaps the
equivalent CoAP response code 2.05 MUST be used. Response code HTTP
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202 in EST is mapped to CoAP 2.06 as specified in
[I-D.hartke-core-pending]. All other HTTP 2xx response codes are not
used by EST. For the following HTTP 4xx error codes that may occur:
400, 401, 403, 404, 405, 406, 412, 413, 415 ; the equivalent CoAP
response code for EST-coaps is 4.xx. For the HTTP 5xx error codes:
500, 501, 502, 503, 504 the equivalent CoAP response code is 5.xx.
Appendix A includes some practical examples of HTTP response codes
from EST translated to CoAP.
4.5. Message fragmentation
DTLS defines fragmentation only for the handshake part and not for
secure data exchange (DTLS records). [RFC6347] states "Each DTLS
record MUST fit within a single datagram". In order to avoid using
IP fragmentation, which is not supported by 6LoWPAN, invokers of the
DTLS record layer MUST size DTLS records so that they fit within any
Path MTU estimates obtained from the record layer. In addition,
invokers residing on a 6LoWPAN over IEEE 802.15.4 network SHOULD
attempt to size CoAP messages such that each DTLS record will fit
within one or two IEEE 802.15.4 frames.
That is not always possible. Even though ECC certificates are small
in size, they can vary greatly based on signature algorithms, key
sizes, and OID fields used. For 256-bit curves, common ECDSA cert
sizes are 500-1000 bytes which could fluctuate further based on the
algorithms, OIDs, SANs and cert fields. For 384-bit curves, ECDSA
certs increase in size and can sometimes reach 1.5KB. Additionally,
there are times when the EST cacerts response from the server can
include multiple certs that amount to large payloads. CoAP
[RFC7252]'s section 4.6 describes the possible payload sizes: "if
nothing is known about the size of the headers, good upper bounds are
1152 bytes for the message size and 1024 bytes for the payload size".
Also "If IPv4 support on unusual networks is a consideration,
implementations may want to limit themselves to more conservative
IPv4 datagram sizes such as 576 bytes; per [RFC0791], the absolute
minimum value of the IP MTU for IPv4 is as low as 68 bytes, which
would leave only 40 bytes minus security overhead for a UDP payload".
Thus, even with ECC certs, EST-coaps messages can still exceed sizes
in MTU of 1280 for IPv6 or 60-80 bytes for 6LoWPAN [RFC4919] as
explained in section 2 of [RFC7959]. EST-coaps needs to be able to
fragment EST messages into multiple DTLS datagrams with each DTLS
datagram. Fine-grained fragmentation of EST messages is essential.
To perform fragmentation in CoAP, [RFC7959] specifies the "Block1"
option for fragmentation of the request payload and the "Block2"
option for fragmentation of the return payload of a CoAP flow.
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The BLOCK draft defines SZX in the Block1 and block2 option fields.
These are used to convey the size of the blocks in the requests or
responses.
The CoAP client MAY specify the Block1 size and MAY also specify the
Block2 size. The CoAP server MAY specify the Block2 size, but not
the Block1 size. As explained in Section 1 of [RFC7959]), blockwise
transfers SHOULD be used in Confirmable CoAP messages to avoid the
exacerbation of lost blocks.
The Size1 response MAY be parsed by the client as a size indication
of the Block2 resource in the server response or by the server as a
request for a size estimate by the client. Similarly, Size2 option
defined in BLOCK should be parsed by the server as an indication of
the size of the resource carried in Block1 options and by the client
as a maximum size expected in the 4.13 (Request Entity Too Large)
response to a request.
Examples of fragmented messages are shown in Appendix B.
5. Transport Protocol
EST-coaps depends on a secure transport mechanism over UDP that can
secure (confidentiality, authenticity) the CoAP messages exchanged.
5.1. DTLS
DTLS is one such secure protocol. Within BRSKI and EST when "TLS" is
referred to, it is understood that in EST-coaps, security is provided
using DTLS instead. No other changes are necessary (all provisional
modes etc are the same as for TLS).
CoAP was designed to avoid fragmentation. DTLS is used to secure
CoAP messages. However, fragmentation is still possible at the DTLS
layer during the DTLS handshake when using ECC ciphersuites. If
fragmentation is necessary, "DTLS provides a mechanism for
fragmenting a handshake message over a number of records, each of
which can be transmitted separately, thus avoiding IP fragmentation"
[RFC6347].
EST-coaps does not support full PKI Requests. Consequently, the
fullcmc request of section 4.3 of [RFC7030] and response MUST NOT be
supported by EST-coaps.
Channel-binding information for linking proof-of-identity with
message-based proof-of-possession is optional for EST-coaps. Given
that CoAP and DTLS can provide proof of identity for EST-coaps
clients and server, simple PKI messages can be used conformant to
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section 3.1 of [RFC5272]. EST-coaps supports the certificate types
and Trust Anchors (TA) that are specified for EST in section 3 of
[RFC7030].
When proof-of-possession is desired, a set of actions are required
regarding the use of tls-connect, described in section 3.5 in
[RFC7030] -- Linking Identity and POP Information. The tls-unique
information translates to the contents of the first "Finished"
message in the TLS handshake between server and client. The client
is then supposed to add this "Finished" message as a
ChallengePassword to the PKCS#10 to prove that the client is indeed
in control of the private key at the time of the TLS session when
performing a /simpleenroll, for example. In the case of EST-coaps,
the same operations can be performed during the DTLS handshake.
In a constrained CoAP environment, endpoints can't afford to
establish a DTLS connection for every EST transaction.
Authenticating and negotiating DTLS keys requires resources on low-
end endpoints and consumes valuable bandwidth. The DTLS connection
SHOULD remain open for persistent EST connections. For example, an
EST cacerts request that is followed by a simpleenroll request can
use the same authenticated DTLS connection. Given that after a
successful enrollment, it is more likely that a new EST transaction
will take place after a significant amount of time, the DTLS
connections SHOULD only be kept alive for EST messages that are
relatively close to each other.
5.2. 6tisch approach
The 6tisch bootstrapping is targeted to the "imprinting" of the
"pledge" with layer 2 keys. The content formats for the transport
are being defined and may be expressed in a YANG module.
Instead of using transport security, the 6tisch approach relies on
application security provided by OSCOAP
[I-D.ietf-core-object-security].
It is suggested that the EST-coaps communication between pledge and
registrar, specified in this document, can be freely exchanged with
the same communication specified in
[I-D.ietf-6tisch-dtsecurity-secure-join] and
[I-D.ietf-6tisch-minimal-security].
[EDNOTE: The evolution of this section depends on the directions
taken by 6tisch and anima and the possible commonality that will be
provided.]
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6. Proxying
[EDNOTE: This section to be populated. It will address how proxying
can take place by an entity that resides at the edge of the CoAP
network, such as the Registrar, and can reach the BRSKI server
residing in a traditional "TCP setting". It makes sense to mention
the properties that the proxy has to fulfill.]
7. Parameters
[EDNOTE: This section to be populated. It will address transmission
parameters for BRSKI described in sections 4.7 and 4.8 of the CoAP
draft. BRSKI does not impose any unique parameters that affect the
CoAP parameters in Table 2 and 3 in the CoAP draft but the ones in
CoAP could be affecting BRSKI. For example the processing delay of
CAs could be less then 2s, but in this case they should send a CoAP
ACK every 2s while processing.]
8. IANA Considerations
Additions to the sub-registry "CoAP Content-Formats", within the
"CoRE Parameters" registry are needed for the below media types.
These can be registered either in the Expert Review range (0-255) or
IETF Review range (256-9999).
1.
* application/pkcs7-mime
* Type name: application
* Subtype name: pkcs7-mime
* smime-type: certs-only
* ID: TBD1
* Required parameters: None
* Optional parameters: None
* Encoding considerations: CBOR byte string
* Security considerations: As defined in this specification
* Published specification: [RFC5751]
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* Applications that use this media type: ANIMA Bootstrap (BRSKI)
and EST
2.
* application/pkcs8
* Type name: application
* Subtype name: pkcs8
* ID: TBD2
* Required parameters: None
* Optional parameters: None
* Encoding considerations: CBOR byte string
* Security considerations: As defined in this specification
* Published specification: [RFC5958]
* Applications that use this media type: ANIMA Bootstrap (BRSKI)
and EST
3.
* application/csrattrs
* Type name: application
* Subtype name: csrattrs
* ID: TBD3
* Required parameters: None
* Optional parameters: None
* Encoding considerations: CBOR byte string
* Security considerations: As defined in this specification
* Published specification: [RFC7030]
* Applications that use this media type: ANIMA Bootstrap (BRSKI)
and EST
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4.
* application/pkcs10
* Type name: application
* Subtype name: pkcs10
* ID: TBD4
* Required parameters: None
* Optional parameters: None
* Encoding considerations: CBOR byte string
* Security considerations: As defined in this specification
* Published specification: [RFC5967]
* Applications that use this media type: ANIMA bootstrap (BRSKI)
and EST
*
+ application/pkcs12
+ Type name: application
+ Subtype name: pkcs12
+ ID: TBD5
+ Required parameters: None
+ Optional parameters: None
+ Encoding considerations: CBOR byte string
+ Security considerations: As defined in this specification
+ Published specification: IETF
+ Applications that use this media type: ANIMA bootstrap
(BRSKI) and EST
*
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+ application/auditnonce
+ Type name: application
+ Subtype name: auditnonce
+ ID: TBD6
+ Required parameters: None
+ Optional parameters: None
+ Encoding considerations: CBOR byte string
+ Security considerations: As defined in this specification
+ Published specification: BRSKI??
+ Applications that use this media type: ANIMA bootstrap
(BRSKI)
*
+ application/authorizationvoucher
+ Type name: application
+ Subtype name: authorizationvoucher
+ ID: TBD7
+ Required parameters: None
+ Optional parameters: None
+ Encoding considerations: CBOR byte string
+ Security considerations: As defined in this specification
+ Published specification: BRSKI??
+ Applications that use this media type: ANIMA bootstrap
(BRSKI)
Additions to the sub-registry "CoAP Resource Type", within the "CoRE
Parameters" registry are needed for a new resource type.
o rt="core.est" needs registration with IANA.
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[EDNOTE: This section will be expanded to include types needed that
do not exist in CoAP.]
9. Security Considerations
[EDNOTE: This section to be populated. This document describes an
existing protocol moved to CoAP and there should not be additional
security concerns added beyond the protocol's or CoAP's specifics
security considerations. The security considerations mentioned in
EST applies also to EST-coaps. Specifically for server-side key
generation, it introduces implications for the endpoints and their
private keys, which will be covered here. ]
10. Acknowledgements
The authors are very grateful to Klaus Hartke for his detailed
explanations on the use of Block with DTLS. The authors would like
to thank Esko Dijk and Michael Verschoor for the valuable discussions
that helped in shaping the solution. They would also like to thank
Peter Panburana from Cisco for his feedback on technical details of
the solution.
11. Change Log
-01:
Merging of draft-vanderstok-ace-coap-est-00 and draft-pritikin-
coap-bootstrap-01
URI and discovery are modified
More text about 6tisch bootstrap including EDHOC and OSCOAP
mapping to DICE IoT profiles
adapted to BRSKI progress
12. References
12.1. Normative References
[I-D.hartke-core-pending]
Stok, P. and K. Hartke, "The 'Pending' Response Code for
the Constrained Application Protocol (CoAP)", draft-
hartke-core-pending-00 (work in progress), February 2017.
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[I-D.ietf-anima-bootstrapping-keyinfra]
Pritikin, M., Richardson, M., Behringer, M., Bjarnason,
S., and K. Watsen, "Bootstrapping Remote Secure Key
Infrastructures (BRSKI)", draft-ietf-anima-bootstrapping-
keyinfra-04 (work in progress), October 2016.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC5272] Schaad, J. and M. Myers, "Certificate Management over CMS
(CMC)", RFC 5272, DOI 10.17487/RFC5272, June 2008,
<http://www.rfc-editor.org/info/rfc5272>.
[RFC5751] Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet
Mail Extensions (S/MIME) Version 3.2 Message
Specification", RFC 5751, DOI 10.17487/RFC5751, January
2010, <http://www.rfc-editor.org/info/rfc5751>.
[RFC5967] Turner, S., "The application/pkcs10 Media Type", RFC 5967,
DOI 10.17487/RFC5967, August 2010,
<http://www.rfc-editor.org/info/rfc5967>.
[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>.
[RFC7030] Pritikin, M., Ed., Yee, P., Ed., and D. Harkins, Ed.,
"Enrollment over Secure Transport", RFC 7030,
DOI 10.17487/RFC7030, October 2013,
<http://www.rfc-editor.org/info/rfc7030>.
[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>.
[RFC7959] Bormann, C. and Z. Shelby, Ed., "Block-Wise Transfers in
the Constrained Application Protocol (CoAP)", RFC 7959,
DOI 10.17487/RFC7959, August 2016,
<http://www.rfc-editor.org/info/rfc7959>.
12.2. Informative References
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[I-D.ietf-6tisch-dtsecurity-secure-join]
Richardson, M., "6tisch Secure Join protocol", draft-ietf-
6tisch-dtsecurity-secure-join-01 (work in progress),
February 2017.
[I-D.ietf-6tisch-minimal-security]
Vucinic, M., Simon, J., and K. Pister, "Minimal Security
Framework for 6TiSCH", draft-ietf-6tisch-minimal-
security-01 (work in progress), February 2017.
[I-D.ietf-anima-voucher]
Watsen, K., Richardson, M., Pritikin, M., and T. Eckert,
"Voucher and Voucher Revocation Profiles for Bootstrapping
Protocols", draft-ietf-anima-voucher-00 (work in
progress), January 2017.
[I-D.ietf-core-object-security]
Selander, G., Mattsson, J., Palombini, F., and L. Seitz,
"Object Security of CoAP (OSCOAP)", draft-ietf-core-
object-security-01 (work in progress), December 2016.
[I-D.selander-ace-cose-ecdhe]
Selander, G., Mattsson, J., and F. Palombini, "Ephemeral
Diffie-Hellman Over COSE (EDHOC)", draft-selander-ace-
cose-ecdhe-04 (work in progress), October 2016.
[ieee802.15.4]
Institute of Electrical and Electronics Engineers, , "IEEE
Standard 802.15.4-2006", 2006.
[RFC4492] Blake-Wilson, S., Bolyard, N., Gupta, V., Hawk, C., and B.
Moeller, "Elliptic Curve Cryptography (ECC) Cipher Suites
for Transport Layer Security (TLS)", RFC 4492,
DOI 10.17487/RFC4492, May 2006,
<http://www.rfc-editor.org/info/rfc4492>.
[RFC4919] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6
over Low-Power Wireless Personal Area Networks (6LoWPANs):
Overview, Assumptions, Problem Statement, and Goals",
RFC 4919, DOI 10.17487/RFC4919, August 2007,
<http://www.rfc-editor.org/info/rfc4919>.
[RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler,
"Transmission of IPv6 Packets over IEEE 802.15.4
Networks", RFC 4944, DOI 10.17487/RFC4944, September 2007,
<http://www.rfc-editor.org/info/rfc4944>.
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[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>.
[RFC5958] Turner, S., "Asymmetric Key Packages", RFC 5958,
DOI 10.17487/RFC5958, August 2010,
<http://www.rfc-editor.org/info/rfc5958>.
[RFC6090] McGrew, D., Igoe, K., and M. Salter, "Fundamental Elliptic
Curve Cryptography Algorithms", RFC 6090,
DOI 10.17487/RFC6090, February 2011,
<http://www.rfc-editor.org/info/rfc6090>.
[RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link
Format", RFC 6690, DOI 10.17487/RFC6690, August 2012,
<http://www.rfc-editor.org/info/rfc6690>.
[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing",
RFC 7230, DOI 10.17487/RFC7230, June 2014,
<http://www.rfc-editor.org/info/rfc7230>.
[RFC7251] McGrew, D., Bailey, D., Campagna, M., and R. Dugal, "AES-
CCM Elliptic Curve Cryptography (ECC) Cipher Suites for
TLS", RFC 7251, DOI 10.17487/RFC7251, June 2014,
<http://www.rfc-editor.org/info/rfc7251>.
[RFC7641] Hartke, K., "Observing Resources in the Constrained
Application Protocol (CoAP)", RFC 7641,
DOI 10.17487/RFC7641, September 2015,
<http://www.rfc-editor.org/info/rfc7641>.
[RFC7925] Tschofenig, H., Ed. and T. Fossati, "Transport Layer
Security (TLS) / Datagram Transport Layer Security (DTLS)
Profiles for the Internet of Things", RFC 7925,
DOI 10.17487/RFC7925, July 2016,
<http://www.rfc-editor.org/info/rfc7925>.
Appendix A. EST messages to EST-coaps
[EDNOTE: This section to be expanded to ensure it covers all BRSKI
edge conditions.]
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A.1. cacerts
In EST, an HTTPS cacerts message can be
GET /.well-known/est/cacerts HTTP/1.1
User-Agent: curl/7.22.0 (i686-pc-linux-gnu) libcurl/7.22.0
OpenSSL/1.0.1 zlib/1.2.3.4 libidn/1.23 librtmp/2.3
Host: 192.0.2.1:8085
Accept: */*
The corresponding secure CoAP request is
GET coaps://[192.0.2.1:8085]/est/crts
with CoAP fields
Ver = 1
T = 0 (CON)
Code = 0x01 (0.01 is GET)
Options
Option1 (Uri-Host)
Option Delta = 0x3 (option nr = 3)
Option Length = 0x9
Option Value = 192.0.2.1
Option2 (Uri-Port)
Option Delta = 0x4 (option nr = 4+3=7)
Option Length = 0x4
Option Value = 8085
Option3 (Uri-Path)
Option Delta = 0x4 (option nr = 7+4= 11)
Option Length = 0x9
Option Value = /est/crts
Payload = [Empty]
A 200 OK response with a cert in EST will then be
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200 OK
Status: 200 OK
Content-Type: application/pkcs7-mime
Content-Transfer-Encoding: base64
Content-Length: 4246 [EDNOTE: this example overflows and would
need fragmentation. Choose a better example.
Regardless we might need an CoAP option for
the content-length ie the CoAP payload?)
MIIMOQYJKoZIhvcNAQcCoIIMKjCCDCYCAQExADALBgkqhkiG9w0BBwGgggwMMIIC
+zCCAeOgAwIBAgIJAJpY3nUZO3qcMA0GCSqGSIb3DQEBBQUAMBsxGTAXBgNVBAMT
...
The corresponding CoAP response is
2.05 Content (Content-Format: application/pkcs7-mime)
{payload}
with CoAP fields
Ver = 1
T = 2 (ACK)
Code = 0x45 (2.05 Content)
Options
Option1 (Content-Format)
Option Delta = 0xC (option nr = 12)
Option Length = 0x2
Option Value = TBD1 (defined in this note)
Payload = h'123456789ABCDEF...'
A.2. enroll / reenroll
[EDNOTE: username/password authentication can be described here but
is not a primary focus for BRSKI. It is important for generic EST
exchanges but would an endpoint device with sufficient user interface
to allow username/password input from an end user be required to use
CoAP instead of a full HTTPS exchange?]
[EDNOTE: We might need a new Option for the Retry-After response
message. We might need a new Option for the WWW-Authenticate
response.]
[EDNOTE: Include CoAP message examples. ]
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A.3. csrattr
[EDNOTE: Include CoAP message examples. ]
A.4. enrollstatus
[EDNOTE: Include CoAP message examples. ]
A.5. voucher_status
[EDNOTE: Include CoAP message examples. ]
A.6. requestvoucher
[EDNOTE: Include CoAP message examples. ]
A.7. requestlog
[EDNOTE: Include CoAP message examples. ]
[EDNOTE: More examples can be added, for server-side key generation
in CMS envelopes. ]
Appendix B. EST-coaps Block message examples
This section provides a detailed example of the messages using DTLS
and BLOCK option Block2. The minimum PMTU is 1280 bytes, which is
the example value assumed for the DTLS datagram size. The example
block length is taken as 64 which gives an SZX value of 2.
The following is an example of a valid /cacerts exchange over DTLS. .
The content length of the cacerts response in appendix A.1 of
[RFC7030] is 4246 bytes using base64. This leads to a length of 3185
bytes in binary. The CoAP message adds around 10 bytes, the DTLS
record 29 bytes. To avoid IP fragmentation, the CoAP block option is
used and an MTU of 127 is assumed to stay within one IEEE 802.15.4
packet. To stay below the MTU of 127, the payload is split in 50
packets with a payload of 64 bytes each. The client sends an IPv6
packet containing the UDP datagram with the DTLS record that
encapsulates the CoAP Request 50 times. The server returns an IPv6
packet containing the UDP datagram with the DTLS record that
encapsulates the CoAP response. The CoAP request-response exchange
with block option is shown below. Block option is shown in a
decomposed way indicating the kind of Block option (2 in this case
because used in the response) followed by a colon, and then the block
number (NUM), the more bit (M = 0 means last block), and block size
exponent (2**(SZX+4)) separated by slashes. The Length 64 is used
with SZX= 2 to avoid IP fragmentation. The CoAP Request is sent with
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confirmable (CON) option and the content format of the Response is
/application/cacerts.
GET [192.0.2.1:8085]/est/crts -->
<-- (2:0/1/64) 2.05 Content
GET URI (2:1/1/64) -->
<-- (2:1/1/64) 2.05 Content
|
|
|
GET URI (2:49/1/64) -->
<-- (2:49/0/64) 2.05 Content
For further detailing the CoAP headers of the first two blocks are
written out.
The header of the first GET looks like:
Ver = 1
T = 0 (CON)
Code = 0x01 (0.1 GET)
Options
Option1 (Uri-Host)
Option Delta = 0x3 (option nr = 3)
Option Length = 0x9
Option Value = 192.0.2.1
Option2 (Uri-Port)
Option Delta = 0x4 (option nr = 3+4=7)
Option Length = 0x4
Option Value = 8085
Option3 (Uri-Path)
Option Delta = 0x4 (option nr = 7+4=11)
Option Length = 0x9
Option Value = /est/crts
Payload = [Empty]
The header of the first response looks like:
[EDNOTE: The contents of the payload do not need to be written as
they are encoded with DTLS into something unreadable.]
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Ver = 1
T = 2 (ACK)
Code = 0x45 (2.05 Content.)
Options
Option1 (Content-Format)
Option Delta = 0xC (option 12)
Option Length = 0x2
Option Value = TBD1
Option2 (Block2)
Option Delta = 0xB (option 23 = 12 + 11)
Option Length = 0x1
Option Value = 0x0A (block number = 0, M=1, SZX=2)
Payload = h'123456789ABCDEF...' (512 bytes)
The second Block2:
Ver = 1
T = 2 (means ACK)
Code = 0x45 (2.05 Content.)
Options
Option1 (Content-Format)
Option Delta = 0xC (option 12)
Option Length = 0x2
Option Value = TBD1
Option2 (Block2)
Option Delta = 0xB (option 23 = 12 + 11)
Option Length = 0x1
Option Value = 0x1D (block number = 1, M=1, SZX=2)
Payload = = h'123456789ABCDEF...' (512 bytes)
The 49th and final Block2:
Ver = 1
T = 2 (means ACK)
Code = 0x21
Options
Option1 (Content-Format)
Option Delta = 0xC (option 12)
Option Length = 0x2
Option Value = TBD1
Option2 (Block2)
Option Delta = 0xB (option 23 = 12 + 11)
Option Length = 0x2
Option Value = 0x312 (block number = 49, M=0, SZX=2)
Payload = = h'123456789ABCDEF...' (512 bytes)
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Authors' Addresses
Sandeep S. Kumar
Philips Lighting Research
High Tech Campus 7
Eindhoven 5656 AE
NL
Email: ietf@sandeep.de
Peter van der Stok
Consultant
Email: consultancy@vanderstok.org
Panos Kampanakis
Cisco Systems
Email: pkampana@cisco.com
Martin Furuhed
Nexus Group
Email: martin.furuhed@nexusgroup.com
Shahid Raza
RISE SICS
Isafjordsgatan 22
Kista, Stockholm 16440
SE
Email: shahid@sics.se
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