CBOR Object Signing and Encryption (COSE): Header parameters for carrying and referencing X.509 certificates
draft-ietf-cose-x509-06
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 9360.
|
|
|---|---|---|---|
| Author | Jim Schaad | ||
| Last updated | 2020-08-28 (Latest revision 2020-03-09) | ||
| Replaces | draft-schaad-cose-x509 | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Formats | |||
| Reviews |
IOTDIR Telechat review
(of
-07)
by Carsten Bormann
Ready w/issues
GENART Last Call review
(of
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by Vijay Gurbani
Ready w/nits
|
||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | Submitted to IESG for Publication | |
| Document shepherd | Ivaylo Petrov | ||
| Shepherd write-up | Show Last changed 2020-05-12 | ||
| IESG | IESG state | Became RFC 9360 (Proposed Standard) | |
| Consensus boilerplate | Yes | ||
| Telechat date | (None) | ||
| Responsible AD | Barry Leiba | ||
| Send notices to | Ivaylo Petrov <ivaylo@ackl.io> |
draft-ietf-cose-x509-06
Network Working Group J. Schaad
Internet-Draft August Cellars
Intended status: Informational 9 March 2020
Expires: 10 September 2020
CBOR Object Signing and Encryption (COSE): Header parameters for
carrying and referencing X.509 certificates
draft-ietf-cose-x509-06
Abstract
The CBOR Signing And Encrypted Message (COSE) structure uses
references to keys in general. For some algorithms, additional
properties are defined which carry parts of keys as needed. The COSE
Key structure is used for transporting keys outside of COSE messages.
This document extends the way that keys can be identified and
transported by providing attributes that refer to or contain X.509
certificates.
Contributing to this document
This note is to be removed before publishing as an RFC.
The source for this draft is being maintained in GitHub. Suggested
changes should be submitted as pull requests at https://github.com/
cose-wg/X509. Instructions are on that page as well. Editorial
changes can be managed in GitHub, but any substantial issues need to
be discussed on the COSE mailing list.
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 https://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 10 September 2020.
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Copyright Notice
Copyright (c) 2020 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 (https://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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Terminology . . . . . . . . . . . . . . . . 3
2. X.509 COSE Header Parameters . . . . . . . . . . . . . . . . 3
3. X.509 certificates and static-static ECDH . . . . . . . . . . 6
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
4.1. COSE Header Parameter Registry . . . . . . . . . . . . . 7
4.2. COSE Header Algorithm Parameter Registry . . . . . . . . 7
5. Security Considerations . . . . . . . . . . . . . . . . . . . 8
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
6.1. Normative References . . . . . . . . . . . . . . . . . . 8
6.2. Informative References . . . . . . . . . . . . . . . . . 9
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
In the process of writing [RFC8152] discussions were held on the
question of X.509 certificates [RFC5280] and if there was a needed to
provide for them. At the time no use cases were presented that
appeared to have a sufficient need for these attributes. Since that
time a number of cases have been defined in which X.509 certificate
support is necessary, and by implication, applications will need a
documented and consistent way to handle such certificates. This
document defines a set of attributes that will allow applications to
transport and refer to X.509 certificates in a consistent manner.
In some of these cases, a constrained device is being deployed in the
context of an existing X.509 PKI: for example, in the 6TiSCH
environment [I-D.richardson-enrollment-roadmap], describes a device
enrollment solution that relies on the presence in the device of a
factory-installed certificate. The [I-D.selander-ace-cose-ecdhe]
draft was also written with the idea that long term certificates
could be used to provide for authentication of devices, and uses them
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to establish session keys. A third scenario is the use of COSE as
the basis for a secure messaging application. This scenario assumes
the presence of long term keys and a central authentication
authority. Basing such an application on public key certificates
allows it to make use of well established key management disciplines.
Example COSE messages for the various header parameters defined below
can be found at https://github.com/cose-wg/Examples.
1.1. Requirements Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. X.509 COSE Header Parameters
The use of X.509 certificates allows for an existing trust
infrastructure to be used with COSE. This includes the full suite of
enrollment protocols, trust anchors, trust chaining and revocation
checking that have been defined over time by the IETF and other
organizations. The key structures that have been defined in COSE
currently do not support all of these properties although some may be
found in COSE Web Tokens (CWT) [RFC8392].
It is not necessarily expected that constrained devices themselves
will evaluate and process of X.509 certificates: it is perfectly
reasonable for a constrained device to be provisioned with a
certificate which it can then provide to a relying party - along with
a signature or encrypted message - on the assumption that the relying
party is not a constrained device, and is capable of performing the
required certificate evaluation and processing.
Certificates obtained from any of these methods MUST still be
validated. This validation can be done according to the PKIX rules
in [RFC5280] or by using a different trust structure, such as a
trusted certificate distributor for self-signed certificates. The
PKIX validation includes matching against the trust anchors
configured for the application. These rules apply to certificates of
a chain length of one as well as longer chains. If the application
cannot establish trust in the certificate, that certificate cannot be
used.
The header parameters defined in this document are:
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x5bag: This header parameter contains a bag of X.509 certificates.
The set of certificates in this header parameter is unordered and
may contain self-signed certificates. The certificate bag can
contain certificates which are completely extraneous to the
message. (An example of this would be where a signed message is
being used to transport a certificate containing a key agreement
key.) As the certificates are unordered, the party evaluating the
signature will need to be capable of building the certificate path
as necessary. That party will also have to take into account that
the bag may not contain the full set of certificates needed to
build any particular chain.
The trust mechanism MUST process any certificates in this
parameter as untrusted input. The presence of a self-signed
certificate in the parameter MUST NOT be used as a signal to
modify the set of trust anchors. As the contents of this header
parameter are untrusted input, the header parameter can be in
either the protected or unprotected header bucket.
This header parameter allows for a single X.509 certificate or a
bag of X.509 certificates to be carried in the message.
* If a single certificate is conveyed, it is placed in a CBOR
bstr.
* If multiple certificates are conveyed, a CBOR array of bstrs is
used, with each certificate being in its own bstr.
x5chain: This header parameter contains an ordered array of X.509
certificates. The certificates are to be ordered starting with
the certificate containing the end-entity key followed by the
certificate which signed it and so on. There is no requirement
for the entire chain to be present in the element if there is
reason to believe that the relying party already has, or can
locate the missing certificates. This means that the relying
party is still required to do path building, but that a candidate
path is proposed in this attribute.
The trust mechanism MUST process any certificates in this
parameter as untrusted input. The presence of a self-signed
certificate in the parameter MUST NOT be used as a signal to
modify the set of trust anchors. As the contents of this header
parameter are untrusted input, the header parameter can be in
either the protected or unprotected header bucket.
This header parameter allows for a single X.509 certificate or a
chain of X.509 certificates to be carried in the message.
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* If a single certificate is conveyed, it is placed in a CBOR
bstr.
* If multiple certificates are conveyed, a CBOR array of bstrs is
used, with each certificate being in its own bstr.
x5t: This header parameter provides the ability to identify an X.509
certificate by a hash value. The attribute is an array of two
elements. The first element is an algorithm identifier which is
an integer or a string containing the hash algorithm identifier.
The algorithm is registered in the "COSE Algorithms" registry The
second element is a binary string containing the hash value.
As this header parameter does not provide any trust, the header
parameter can be in either a protected or unprotected header
bucket.
For interoperability, applications which use this header parameter
MUST support the hash algorithm 'SHA-256', but can use other hash
algorithms.
x5u: This header parameter provides the ability to identify an X.509
certificate by a URI [RFC3986]. The referenced resource can be
any of the following media types:
* application/pkix-cert [RFC2585]
* application/pkcs7-mime; smime-type="certs-only" [RFC8551]
As this header parameter implies a trust relationship, the
attribute MUST be in the protected attribute bucket.
The URI provided MUST provide integrity protection and server
authentication. For example, an HTTP or CoAP GET request to
retrieve a certificate MUST use TLS [RFC8446] or DTLS
[I-D.ietf-tls-dtls13]. If the certificate does not chain to an
existing trust anchor, the certificate MUST NOT be trusted unless
the server is configured as trusted to provide new trust anchors.
This will normally be the situation when self-signed certificates
are used.
The header parameters are used in the following locations:
* COSE_Signature and COSE_Sign0 objects, in these objects they
identify the certificate to be used for validation the signature.
* COSE_recipient objects, in this location they identify the
certificate for the recipient of the message.
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+---------+-------+---------------+---------------------+
| Name | Label | Value Type | Description |
+=========+=======+===============+=====================+
| x5bag | TBD4 | COSE_X509 | An unordered bag of |
| | | | X.509 certificates |
+---------+-------+---------------+---------------------+
| x5chain | TBD3 | COSE_X509 | An ordered chain of |
| | | | X.509 certificates |
+---------+-------+---------------+---------------------+
| x5t | TBD1 | COSE_CertHash | Hash of an X.509 |
| | | | certificate |
+---------+-------+---------------+---------------------+
| x5u | TBD2 | uri | URI pointing to an |
| | | | X.509 certificate |
+---------+-------+---------------+---------------------+
Table 1: X.509 COSE Header Parameters
Below is an equivalent CDDL [RFC8610] description of the text above.
COSE_X509 = bstr / [ 2*certs: bstr ]
COSE_CertHash = [ hashAlg: (int / tstr), hashValue: bstr ]
3. X.509 certificates and static-static ECDH
The header parameters defined in the previous section are used to
identify the recipient certificates for the ECDH key agreement
algorithms. In this section we define the algorithm specific
parameters that are used for identifying or transporting the sender's
key for static-static key agreement algorithms.
These attributes are defined analogously to those in the previous
section. There is no definition for the certificate bag as the same
attribute would be used for both the sender and recipient
certificates.
x5chain-sender: This header parameter contains the chain of
certificates starting with the sender's key exchange certificate.
The structure is the same as 'x5chain'.
x5t-sender: This header parameter contains the hash value for the
sender's key exchange certificate. The structure is the same as
'x5t'.
x5u-sender: This header parameter contains a URI for the sender's
key exchange certificate. The structure and processing are the
same as 'x5u'.
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+---------------+-----+-------------+-------------------+-----------+
| Name |Label| Type | Algorithm |Description|
+===============+=====+=============+===================+===========+
| x5t-sender | TBD |COSE_CertHash| ECDH-SS+HKDF-256, |Thumbprint |
| | | | ECDH-SS+HKDF-512, | for the |
| | | | ECDH-SS+A128KW, | senders |
| | | | ECDH-SS+AES192KW, | X.509 |
| | | | ECDH-SS+AES256KW |certificate|
+---------------+-----+-------------+-------------------+-----------+
| x5u-sender | TBD | uri | ECDH-SS+HKDF-256, |URI for the|
| | | | ECDH-SS+HKDF-512, | senders |
| | | | ECDH-SS+A128KW, | X.509 |
| | | | ECDH-SS+AES192KW, |certificate|
| | | | ECDH-SS+AES256KW | |
+---------------+-----+-------------+-------------------+-----------+
|x5chain-sender | TBD | COSE_X509 | ECDH-SS+HKDF-256, |static key |
| | | | ECDH-SS+HKDF-512, | X.509 |
| | | | ECDH-SS+A128KW, |certificate|
| | | | ECDH-SS+AES192KW, | chain |
| | | | ECDH-SS+AES256KW | |
+---------------+-----+-------------+-------------------+-----------+
Table 2: Static ECDH Algorithm Values
4. IANA Considerations
4.1. COSE Header Parameter Registry
IANA is requested to register the new COSE Header parameter in
Table 1 in the "COSE Header Parameters" registry. The "Value
Registry" field is empty for all of the items. For each item, the
'Reference' field points to this document.
4.2. COSE Header Algorithm Parameter Registry
IANA is requested to register the new COSE Header Algorithm
parameters in Table 2 in the "COSE Header Algorithm Parameters"
registry. For each item, the 'Reference' field points to this
document.
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5. Security Considerations
Establishing trust in a certificate is a vital part of processing. A
major component of establishing trust is determining what the set of
trust anchors are for the process. A new self-signed certificate
appearing on the client cannot be a trigger to modify the set of
trust anchors, instead a well defined trust-establishment process is
required. One common way for a new trust anchor to be added (or
removed) from a device is by doing a new firmware upgrade.
In constrained systems, there is a trade-off between the order of
checking the signature and checking the certificate for validity.
Validating certificates can require that network resources be
accessed in order to get revocation information or retrieve
certificates during path building. The resulting network access can
consume power and network bandwidth. On the other hand, an oracle
can potentially be built based on detecting the network resources
which is only done if the signature validation passes. In any event,
both the signature and certificate validation MUST be completed
successfully before acting on any requests.
Before using the keys in a certificate, they MUST be checked as
described in the COSE algorithms document
[I-D.ietf-cose-rfc8152bis-algs]. These checks can include validating
that points are on curves for elliptical curve algorithms, and that
sizes of RSA keys are of an acceptable size. The use of unvalidated
keys can lead either to loss of security or excessive consumption of
resources.
6. References
6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/info/rfc5280>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
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6.2. Informative 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>.
[I-D.ietf-tls-dtls13]
Rescorla, E., Tschofenig, H., and N. Modadugu, "The
Datagram Transport Layer Security (DTLS) Protocol Version
1.3", Work in Progress, Internet-Draft, draft-ietf-tls-
dtls13-34, 19 November 2019,
<https://tools.ietf.org/html/draft-ietf-tls-dtls13-34>.
[RFC8551] Schaad, J., Ramsdell, B., and S. Turner, "Secure/
Multipurpose Internet Mail Extensions (S/MIME) Version 4.0
Message Specification", RFC 8551, DOI 10.17487/RFC8551,
April 2019, <https://www.rfc-editor.org/info/rfc8551>.
[RFC2585] Housley, R. and P. Hoffman, "Internet X.509 Public Key
Infrastructure Operational Protocols: FTP and HTTP",
RFC 2585, DOI 10.17487/RFC2585, May 1999,
<https://www.rfc-editor.org/info/rfc2585>.
[I-D.selander-ace-cose-ecdhe]
Selander, G., Mattsson, J., and F. Palombini, "Ephemeral
Diffie-Hellman Over COSE (EDHOC)", Work in Progress,
Internet-Draft, draft-selander-ace-cose-ecdhe-14, 11
September 2019, <https://tools.ietf.org/html/draft-
selander-ace-cose-ecdhe-14>.
[RFC8392] Jones, M., Wahlstroem, E., Erdtman, S., and H. Tschofenig,
"CBOR Web Token (CWT)", RFC 8392, DOI 10.17487/RFC8392,
May 2018, <https://www.rfc-editor.org/info/rfc8392>.
[RFC8152] Schaad, J., "CBOR Object Signing and Encryption (COSE)",
RFC 8152, DOI 10.17487/RFC8152, July 2017,
<https://www.rfc-editor.org/info/rfc8152>.
[RFC8610] Birkholz, H., Vigano, C., and C. Bormann, "Concise Data
Definition Language (CDDL): A Notational Convention to
Express Concise Binary Object Representation (CBOR) and
JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610,
June 2019, <https://www.rfc-editor.org/info/rfc8610>.
[I-D.ietf-cose-rfc8152bis-algs]
Schaad, J., "CBOR Object Signing and Encryption (COSE):
Initial Algorithms", Work in Progress, Internet-Draft,
draft-ietf-cose-rfc8152bis-algs-06, 4 November 2019,
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<https://tools.ietf.org/html/draft-ietf-cose-rfc8152bis-
algs-06>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/info/rfc3986>.
[I-D.richardson-enrollment-roadmap]
Richardson, M., "Device Enrollment in IETF protocols -- A
Roadmap", Work in Progress, Internet-Draft, draft-
richardson-enrollment-roadmap-02, 23 May 2018,
<https://tools.ietf.org/html/draft-richardson-enrollment-
roadmap-02>.
Author's Address
Jim Schaad
August Cellars
Email: ietf@augustcellars.com
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