Internet DRAFT - draft-ftbs-rats-msg-wrap
draft-ftbs-rats-msg-wrap
Remote ATtestation ProcedureS H. Birkolz
Internet-Draft Fraunhofer SIT
Intended status: Standards Track N. Smith
Expires: 8 September 2023 Intel
T. Fossati
arm
H. Tschofenig
7 March 2023
RATS Conceptual Messages Wrapper
draft-ftbs-rats-msg-wrap-02
Abstract
This document defines two encapsulation formats for RATS conceptual
messages (i.e., evidence, attestation results, endorsements and
reference values.)
The first format uses a CBOR or JSON array with two members: one for
the type, another for the value. The other format wraps the value in
a CBOR byte string and prepends a CBOR tag to convey the type
information.
Discussion Venues
This note is to be removed before publishing as an RFC.
Discussion of this document takes place on the Remote ATtestation
ProcedureS Working Group mailing list (rats@ietf.org), which is
archived at https://mailarchive.ietf.org/arch/browse/rats/.
Source for this draft and an issue tracker can be found at
https://github.com/thomas-fossati/draft-ftbs-rats-msg-wrap.
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/.
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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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This Internet-Draft will expire on 8 September 2023.
Copyright Notice
Copyright (c) 2023 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/
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 3
3. Conceptual Message Wrapper Encodings . . . . . . . . . . . . 4
3.1. CMW Array . . . . . . . . . . . . . . . . . . . . . . . . 4
3.2. CMW CBOR Tags . . . . . . . . . . . . . . . . . . . . . . 5
3.2.1. Use of Pre-existing CBOR Tags . . . . . . . . . . . . 5
3.3. Decapsulation Algorithm . . . . . . . . . . . . . . . . . 5
4. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.1. JSON Array . . . . . . . . . . . . . . . . . . . . . . . 6
4.2. CBOR Array . . . . . . . . . . . . . . . . . . . . . . . 6
4.3. CBOR Tag . . . . . . . . . . . . . . . . . . . . . . . . 6
5. Registering a Media Type for Evidence . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 7
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1. Normative References . . . . . . . . . . . . . . . . . . 7
8.2. Informative References . . . . . . . . . . . . . . . . . 8
Appendix A. RFC9193 ABNF . . . . . . . . . . . . . . . . . . . . 9
Appendix B. Open Issues . . . . . . . . . . . . . . . . . . . . 10
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
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1. Introduction
The RATS architecture defines a handful of conceptual messages (see
Section 8 of [RFC9334]), such as evidence and attestation results.
Each conceptual message can have multiple claims encoding and
serialization formats (Section 9 of [RFC9334]). Such serialized
messages may have to be transported via different protocols - for
example, evidence using an EAT [I-D.ietf-rats-eat] encoding
serialized as a CBOR payload in a "background check" topological
arrangement, or attestation results as Attestation Results for Secure
Interactions (AR4SI) [I-D.ietf-rats-ar4si] payloads in "passport"
mode.
In order to minimize the cost associated with registration and
maximize interoperability, it is desirable to reuse their typing
information across such boundaries.
This document defines two encapsulation formats for RATS conceptual
messages that aim to achieve the goals stated above.
These encapsulation formats are designed to be:
* Self-describing - which removes the dependency on the framing
provided by the embedding protocol (or the storage system) to
convey exact typing information.
* Based on media types [RFC6838] - which allows amortising their
registration cost across many different usage scenarios.
A protocol designer could use these formats, for example, to convey
evidence, endorsements or reference values in certificates and CRLs
extensions ([DICE-arch]), to embed attestation results or evidence as
first class authentication credentials in TLS handshake messages
[I-D.fossati-tls-attestation], to transport attestation-related
payloads in RESTful APIs, or for stable storage of attestation
results in form of file system objects.
2. Conventions and Definitions
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.
In this document, CDDL [RFC8610] [RFC9165] is used to describe the
data formats.
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The reader is assumed to be familiar with the vocabulary and concepts
defined in [RFC9334].
This document reuses the terms defined in Section 2 of [RFC9193]
(e.g., "Content-Type").
3. Conceptual Message Wrapper Encodings
Two types of RATS Conceptual Message Wrapper (CMW) are specified in
this document:
1. A CMW using a CBOR or JSON array (Section 3.1);
2. A CMW based on CBOR tags (Section 3.2).
3.1. CMW Array
The CMW array format is defined in Figure 1. (To improve clarity,
the Content-Type ABNF is defined separately in Appendix A.)
cmw-array = cmw-array-cbor / cmw-array-json
cmw-array-cbor = [ type, bytes ]
cmw-array-json = [ type, base64-string ]
type = coap-content-format / media-type
coap-content-format = uint .size 2
media-type = text .abnf ("Content-Type" .cat Content-Type-ABNF)
base64-string = text .regexp "[A-Za-z0-9_-]+"
Figure 1: CDDL definition of the Array format
It is composed of two members:
type:
Either a text string representing a Content-Type (e.g., an EAT
media type [I-D.ietf-rats-eat-media-type]) or an unsigned Integer
corresponding to a CoAP Content-Format number (Section 12.3 of
[RFC7252].
value:
The RATS conceptual message serialized according to the value
defined in the type member.
A CMW array can be encoded as CBOR [STD94] or JSON [RFC8259].
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When using JSON, the value field is encoded as Base64 using the URL
and filename safe alphabet (Section 5 of [RFC4648]) without padding.
When using CBOR, the value field is encoded as a CBOR byte string.
3.2. CMW CBOR Tags
CBOR Tags used as CMW are derived from CoAP Content-Format numbers.
If a CoAP content format exists for a RATS conceptual message, the
TN() transform defined in Appendix B of [RFC9277] can be used to
derive a corresponding CBOR tag in range [1668546817, 1668612095].
The RATS conceptual message is first serialized according to the
Content-Format number associated with the CBOR tag and then encoded
as a CBOR byte string, to which the tag is prepended.
The CMW CBOR Tag is defined in Figure 2.
cmw-cbor-tag<bytes> = #6.<coap-cf-tag-number>(bytes)
coap-cf-tag-number = 1668546817..1668612095
Figure 2: CDDL definition of the CBOR Tag format
3.2.1. Use of Pre-existing CBOR Tags
If a CBOR tag has been registered in association with a certain RATS
conceptual message independently of a CoAP content format (i.e., it
is not obtained by applying the TN() transform), it can be readily
used as an encapsulation without the extra processing described in
Section 3.2.
A consumer can always distinguish tags that have been derived via
TN(), which all fall in the [1668546817, 1668612095] range, from tags
that are not, and therefore apply the right decapsulation on receive.
3.3. Decapsulation Algorithm
After removing any external framing (for example, the ASN.1 OCTET
STRING if the CMW is carried in a certificate extension [DICE-arch]),
the CMW decoder does a 1-byte lookahead, as illustrated in the
following pseudo code, to decide how to decode the remainder of the
byte buffer:
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func CMWDecode(b []byte) (CMW, error) {
if len(b) < CMWMinSize {
return CMW{}, errors.New("CMW too short")
}
switch b[0] {
case 0x82:
return cborArrayDecode(b)
case 0x5b:
return jsonArrayDecode(b)
default:
return cborTagDecode(b)
}
}
4. Examples
The (equivalent) examples below assume the Media-Type-Name
application/vnd.example.rats-conceptual-msg has been registered
alongside a corresponding CoAP Content-Format number 30001. The CBOR
tag 1668576818 is derived applying the TN() transform as described in
Section 3.2.
4.1. JSON Array
[
"application/vnd.example.rats-conceptual-msg",
"q82rzQ"
]
4.2. CBOR Array
[
30001,
h'abcdabcd'
]
with the following wire representation:
82 # array(2)
19 7531 # unsigned(30001)
44 # bytes(4)
abcdabcd # "\xABͫ\xCD"
4.3. CBOR Tag
1668576818(h'abcdabcd')
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with the following wire representation:
da 63747632 # tag(1668576818)
44 # bytes(4)
abcdabcd # "\xABͫ\xCD"
5. Registering a Media Type for Evidence
// Note: Not sure whether this advice should go.
When registering a new media type for evidence, in addition to its
syntactical description, the author SHOULD provide a public and
stable description of the signing and appraisal procedures associated
with the data format.
6. Security Considerations
This document defines two encapsulation formats for RATS conceptual
messages. The messages themselves and their encoding ensure security
protection. For this reason there are no further security
requirements raised by the introduction of this encapsulation.
Changing the encapsulation of a payload by an adversary will result
in incorrect processing of the encapsulated messages and this will
subsequently lead to a processing error.
7. IANA Considerations
This document does not make any requests to IANA.
8. References
8.1. 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/rfc/rfc2119>.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
<https://www.rfc-editor.org/rfc/rfc4648>.
[RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type
Specifications and Registration Procedures", BCP 13,
RFC 6838, DOI 10.17487/RFC6838, January 2013,
<https://www.rfc-editor.org/rfc/rfc6838>.
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[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014,
<https://www.rfc-editor.org/rfc/rfc7252>.
[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/rfc/rfc8174>.
[RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", STD 90, RFC 8259,
DOI 10.17487/RFC8259, December 2017,
<https://www.rfc-editor.org/rfc/rfc8259>.
[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/rfc/rfc8610>.
[RFC9165] Bormann, C., "Additional Control Operators for the Concise
Data Definition Language (CDDL)", RFC 9165,
DOI 10.17487/RFC9165, December 2021,
<https://www.rfc-editor.org/rfc/rfc9165>.
[RFC9277] Richardson, M. and C. Bormann, "On Stable Storage for
Items in Concise Binary Object Representation (CBOR)",
RFC 9277, DOI 10.17487/RFC9277, August 2022,
<https://www.rfc-editor.org/rfc/rfc9277>.
[STD94] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", STD 94, RFC 8949,
DOI 10.17487/RFC8949, December 2020,
<https://www.rfc-editor.org/rfc/rfc8949>.
8.2. Informative References
[DICE-arch]
Trusted Computing Group, "DICE Attestation Architecture",
March 2021, <https://trustedcomputinggroup.org/wp-
content/uploads/DICE-Attestation-Architecture-
r23-final.pdf>.
[I-D.fossati-tls-attestation]
Tschofenig, H., Fossati, T., Howard, P., Mihalcea, I., and
Y. Deshpande, "Using Attestation in Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", Work in Progress, Internet-Draft, draft-fossati-
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tls-attestation-02, 24 October 2022,
<https://datatracker.ietf.org/doc/html/draft-fossati-tls-
attestation-02>.
[I-D.ietf-rats-ar4si]
Voit, E., Birkholz, H., Hardjono, T., Fossati, T., and V.
Scarlata, "Attestation Results for Secure Interactions",
Work in Progress, Internet-Draft, draft-ietf-rats-ar4si-
04, 2 March 2023, <https://datatracker.ietf.org/doc/html/
draft-ietf-rats-ar4si-04>.
[I-D.ietf-rats-eat]
Lundblade, L., Mandyam, G., O'Donoghue, J., and C.
Wallace, "The Entity Attestation Token (EAT)", Work in
Progress, Internet-Draft, draft-ietf-rats-eat-19, 19
December 2022, <https://datatracker.ietf.org/doc/html/
draft-ietf-rats-eat-19>.
[I-D.ietf-rats-eat-media-type]
Lundblade, L., Birkholz, H., and T. Fossati, "EAT Media
Types", Work in Progress, Internet-Draft, draft-ietf-rats-
eat-media-type-01, 19 October 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-rats-
eat-media-type-01>.
[RFC9193] Keränen, A. and C. Bormann, "Sensor Measurement Lists
(SenML) Fields for Indicating Data Value Content-Format",
RFC 9193, DOI 10.17487/RFC9193, June 2022,
<https://www.rfc-editor.org/rfc/rfc9193>.
[RFC9334] Birkholz, H., Thaler, D., Richardson, M., Smith, N., and
W. Pan, "Remote ATtestation procedureS (RATS)
Architecture", RFC 9334, DOI 10.17487/RFC9334, January
2023, <https://www.rfc-editor.org/rfc/rfc9334>.
Appendix A. RFC9193 ABNF
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; from RFC9193
Content-Type-ABNF = '
Content-Type = Media-Type-Name *( *SP ";" *SP parameter )
parameter = token "=" ( token / quoted-string )
token = 1*tchar
tchar = "!" / "#" / "$" / "%" / "&" / "\'" / "*"
/ "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
/ DIGIT / ALPHA
quoted-string = %x22 *( qdtext / quoted-pair ) %x22
qdtext = SP / %x21 / %x23-5B / %x5D-7E
quoted-pair = "\" ( SP / VCHAR )
Media-Type-Name = type-name "/" subtype-name
type-name = restricted-name
subtype-name = restricted-name
restricted-name = restricted-name-first *126restricted-name-chars
restricted-name-first = ALPHA / DIGIT
restricted-name-chars = ALPHA / DIGIT / "!" / "#" /
"$" / "&" / "-" / "^" / "_"
restricted-name-chars =/ "." ; Characters before first dot always
; specify a facet name
restricted-name-chars =/ "+" ; Characters after last plus always
; specify a structured syntax suffix
DIGIT = %x30-39 ; 0 - 9
POS-DIGIT = %x31-39 ; 1 - 9
ALPHA = %x41-5A / %x61-7A ; A - Z / a - z
SP = %x20
VCHAR = %x21-7E ; printable ASCII (no SP)
'
Appendix B. Open Issues
// Note to RFC Editor: please remove before publication.
The list of currently open issues for this documents can be found at
https://github.com/thomas-fossati/draft-ftbs-rats-msg-wrap/issues.
Acknowledgments
The authors would like to thank Carl Wallace and Carsten Bormann for
their reviews and suggestions.
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Authors' Addresses
Henk Birkolz
Fraunhofer SIT
Email: henk.birkholz@sit.fraunhofer.de
Ned Smith
Intel
Email: ned.smith@intel.com
Thomas Fossati
arm
Email: thomas.fossati@arm.com
Hannes Tschofenig
Email: hannes.tschofenig@gmx.net
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