| Internet-Draft | RATS CMW | February 2024 |
| Birkholz, et al. | Expires 30 August 2024 | [Page] |
This document defines the RATS conceptual message wrapper (CMW) format, a type of encapsulation format that can be used for any RATS messages, such as Evidence, Attestation Results, Endorsements, and Reference Values. Additionally, the document describes a collection type that enables the aggregation of one or more CMWs into a single message.¶
This document also defines corresponding CBOR tag, JSON Web Tokens (JWT) and CBOR Web Tokens (CWT) claims, as well as an X.509 extension. These allow embedding the wrapped conceptual messages into CBOR-based protocols, web APIs, and PKIX protocols.¶
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.¶
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 30 August 2024.¶
Copyright (c) 2024 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 Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License.¶
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]). Throughout their lifetime, RATS conceptual messages are typically transported over different protocols. For example,¶
EAT [I-D.ietf-rats-eat] Evidence in a "background check" topological arrangement first flows from Attester to Relying Party, and then from Relying Party to Verifier, over separate protocol legs.¶
Attestation Results for Secure Interactions (AR4SI) [I-D.ietf-rats-ar4si] payloads in "passport" mode would be sent by the Verifier to the Attester and then, at a later point in time and over a different channel, from the Attester to the Relying Party.¶
It is desirable to reuse any typing information associated with the messages across such protocol boundaries to minimize the cost associated with type registrations and maximize interoperability. With the CMW format described in this document, protocol designers do not need to update protocol specifications to support different conceptual messages. This approach reduces the implementation effort for developers to support different attestation technologies. For example, an implementer of a Relying Party application does not need to parse attestation-related conceptual messages, such as different Evidence formats, but can instead utilize the CMW format to be agnostic to the attestation technology.¶
This document defines two encapsulation formats for RATS conceptual messages that aim to achieve the goals stated above.¶
These encapsulation formats have been specifically designed to possess the following characteristics:¶
They are self-describing, which means that they can convey precise typing information without relying on the framing provided by the embedding protocol or the storage system.¶
They are based on media types [RFC6838], which allows the cost of their registration to be spread across numerous usage scenarios.¶
A protocol designer could use these formats, for example, to convey Evidence, Endorsements and 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 the form of file system objects.¶
This document also defines corresponding CBOR tag, JSON Web Tokens (JWT) and CBOR Web Tokens (CWT) claims, as well as an X.509 extension. These allow embedding the wrapped conceptual messages into CBOR-based protocols, web APIs, and PKIX protocols.¶
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.¶
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").¶
Two types of RATS Conceptual Message Wrapper (CMW) are specified in this document:¶
A CMW using a CBOR or JSON record (Section 3.1);¶
A CMW based on CBOR tags (Section 3.2).¶
A further CMW "collection" type that holds together multiple CMW items is defined in Section 3.3.¶
A CMW "tunnel" type is also defined in Section 3.4 to allow transporting CBOR CMWs in JSON collections and vice-versa.¶
The collected CDDL is in Appendix A.¶
The format of the CMW record is shown in Figure 1.
The JSON [STD90] and CBOR [STD94] representations are provided separately.
Both the json-record and cbor-record have the same fields except for slight differences in the types discussed below.¶
json-record = [ type: media-type value: base64-string ? ind: uint .bits cm-type ] cbor-record = [ type: coap-content-format-type / media-type value: bytes ? ind: uint .bits cm-type ]
Each contains two or three 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]). The latter MUST NOT be used in the JSON serialization.¶
value:The RATS conceptual message serialized according to the value defined in the type member. When using JSON, the value field MUST be encoded as Base64 using the URL and filename safe alphabet (Section 5 of [RFC4648]) without padding. This always applies, even if the conceptual message format is already textual (e.g., a JWT EAT). When using CBOR, the value field MUST be encoded as a CBOR byte string.¶
ind:An optional bitmap that indicates which conceptual message types are
carried in the value field. Any combination (i.e., any value between
1 and 15, included) is allowed. This is useful only if the type is
potentially ambiguous and there is no further context available to the
CMW consumer to decide. For example, this might be the case if the base
media type is not profiled (e.g., application/eat+cwt), if the value
field contains multiple conceptual messages with different types (e.g.,
both Reference Values and Endorsements within the same application/signed-corim+cbor), or if the same profile identifier is
shared by different conceptual messages.
Future specifications may add new values to the ind field; see Section 8.4.¶
CBOR Tags used as CMW may be 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.¶
cbor-tag = #6.<0..18446744073709551615>(bytes)
Layered Attesters and composite devices (Sections 3.2 and 3.3 of [RFC9334]) generate Evidence that consists of multiple parts.¶
For example, in data center servers, it is not uncommon for separate attesting environments (AE) to serve a subsection of the entire machine. One AE might measure and attest to what was booted on the main CPU, while another AE might measure and attest to what was booted on a SmartNIC plugged into a PCIe slot, and a third AE might measure and attest to what was booted on the machine's GPU.¶
To address the composite Attester use case, this document defines a CMW "collection" as a container that holds several CMW items, each with a label that is unique within the scope of the collection.¶
The CMW collection (Figure 3) is defined as a CBOR map or JSON object with CMW values, either native or "tunnelled" (Section 3.4).
The position of a cmw entry in the cmw-collection is not significant.
Instead, the labels identify a conceptual message that, in the case of a composite Attester, should typically correspond to a component of a system.
Labels can be strings (or integers in the CBOR serialization) that serve as a mnemonic for different conceptual messages in the collection.
The "__cmwc_t" key is reserved for associating an optional type to the overall collection and MUST NOT be used for a label.
The collection type is either a Uniform Resource Identifier (URI) or an object identifier (OID).
The OID is always absolute and never relative.¶
Since the collection type is recursive, implementations may limit the allowed depth of nesting.¶
json-collection = {
? "__cmwc_t": ~uri / oid
+ text => json-CMW / c2j-tunnel
}
cbor-collection = {
? "__cmwc_t": ~uri / oid
+ (int / text) => cbor-CMW / j2c-tunnel
}
Although initially designed for the composite Attester use case, the CMW collection can be repurposed for other use cases requiring CMW aggregation.¶
The CMW tunnel type (Figure 4) allows for moving a CMW in one serialization format, either JSON or CBOR, into a collection that uses the opposite serialization format.¶
Both tunnel types are arrays with two elements.
The first element, a fixed text string starting with a #, acts as a sentinel value.
The #, which is not an acceptable start symbol for the Content-Type production (Appendix A), makes it possible to disambiguate a CMW tunnel from a CMW record.¶
c2j-tunnel = [ "#cmw-c2j-tunnel", base64-string ] j2c-tunnel = [ "#cmw-j2c-tunnel", bytes ]
The conversion algorithms are described in the following subsections.¶
The CBOR byte string of the serialised CBOR CMW is encoded as Base64 using the URL and filename safe alphabet (Section 5 of [RFC4648]) without padding.
The obtained string is added as the second element of the c2j-tunnel array.
The c2j-tunnel array is serialized as JSON.¶
The UTF-8 string of the serialized JSON CMW is encoded as a CBOR byte string (Major type 2).
The byte string is added as the second element of the j2c-tunnel array.
The j2c-tunnel array is serialized as CBOR.¶
Once any external framing is removed (for example, if the CMW is carried in a certificate extension), the CMW decoder performs a 1-byte lookahead to determine how to decode the remaining byte buffer. The following pseudo-code illustrates this process:¶
func CMWTypeSniff(b []byte) (CMW, error) {
if len(b) == 0 {
return Unknown
}
if b[0] == 0x82 || b[0] == 0x83 {
return CBORRecord
} else if b[0] >= 0xc0 && b[0] <= 0xdb {
return CBORTag
} else if b[0] == 0x5b {
return JSONRecord
} else if b[0] == 0x7b {
return JSONCollection
} else if (b[0] >= 0xa0 && b[0] <= 0xbb) || b[0] == 0xbf {
return CBORCollection
}
return Unknown
}
¶
The (equivalent) examples in Section 4.1, Section 4.2, and Section 4.3 assume that
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.¶
The example in Section 4.4 is a signed CoRIM payload with an explicit CM
indicator 0b0000_0011 (3), meaning that the wrapped message contains both
Reference Values and Endorsements.¶
[ "application/vnd.example.rats-conceptual-msg", "q82rzQ" ]¶
Note that a CoAP Content-Format number can also be used with the JSON record form. That may be the case when it is known that the receiver can handle CoAP Content-Formats and it is crucial to save bytes.¶
[ 30001, h'2347da55' ]¶
with the following wire representation:¶
82 # array(2)
19 7531 # unsigned(30001)
44 # bytes(4)
2347da55 # "#G\xDAU"
¶
Note that a Media-Type-Name can also be used with the CBOR record form, for example if it is known that the receiver cannot handle CoAP Content-Formats, or (unlike the case in point) if a CoAP Content-Format number has not been registrered.¶
[ "application/vnd.example.rats-conceptual-msg", h'2347da55' ]¶
1668576818(h'2347da55')¶
with the following wire representation:¶
da 63747632 # tag(1668576818)
44 # bytes(4)
2347da55 # "#G\xDAU"
¶
[ "application/signed-corim+cbor", h'd28443a10126a1', 3 ]¶
with the following wire representation:¶
83 # array(3)
78 1d # text(29)
6170706c69636174696f6e2f7369676e65642d636f72696d2b63626f72
# "application/signed-corim+cbor"
47 # bytes(7)
d28443a10126a1 # "҄C\xA1\u0001&\xA1"
03 # unsigned(3)
¶
The following example is a CBOR collection that assembles conceptual messages from three attesters: Evidence for attesters A and B and Attestation Results for attester C. It is given an explicit collection type using the URI form.¶
{
"attester A": [
30001,
h'2347da55',
4
],
"attester B": 1668576818(h'2347da55'),
"attester C": [
"application/eat+jwt",
h'4c693475',
8
]
}
¶
with the following wire representation:¶
a3 # map(3)
6a # text(10)
61747465737465722041 # "attester A"
83 # array(3)
19 7531 # unsigned(30001)
44 # bytes(4)
2347da55 # "#G\xDAU"
04 # unsigned(4)
6a # text(10)
61747465737465722042 # "attester B"
da 63747632 # tag(1668576818)
44 # bytes(4)
2347da55 # "#G\xDAU"
6a # text(10)
61747465737465722043 # "attester C"
83 # array(3)
73 # text(19)
6170706c69636174696f6e2f6561742b6a7774 # "application/eat+jwt"
44 # bytes(4)
4c693475 # "Li4u"
08 # unsigned(8)
¶
The following example shows the use of a tunnelled type to move a JSON record to a CBOR collection:¶
{
"__cmwc_t": "tag:example.com,2024:composite-attester",
0: [
30001,
h'2347da55',
4
],
1: 1668576818(h'2347da55'),
2: [
"#cmw-j2c-tunnel",
'[ "application/eat+jwt", "Li4u", 8 ]'
]
}
¶
The following example is a JSON collection that assembles Evidence from two attesters.¶
{
"attester A": [
"application/eat-ucs+json",
"e30K",
4
],
"attester B": [
"application/eat-ucs+cbor",
"oA",
4
]
}
¶
The following example shows the use of a tunnelled type to move a CBOR record to a JSON collection:¶
{
"attester A": [
"application/eat-ucs+json",
"e30K",
4
],
"attester B (tunnelled)": [
"#cmw-c2j-tunnel",
"g3gYYXBwbGljYXRpb24vZWF0LXVjcytjYm9yQaAE"
]
}
¶
The following example shows the use of the cmw JWT claim to transport a CMW collection in a JWT [RFC7519]:¶
{
"cmw": {
"attester A": [
"application/eat-ucs+json",
"e30K",
4
],
"attester B (tunnelled)": [
"#cmw-c2j-tunnel",
"g3gYYXBwbGljYXRpb24vZWF0LXVjcytjYm9yQaAE"
]
},
"iss": "evidence collection daemon",
"exp": 1300819380
}
¶
There are cases where CMW need to be transported in PKIX messages, for example in Certificate Signing Requests (CSRs) [I-D.ietf-lamps-csr-attestation], or in X.509 Certificates and Certificate Revocation Lists (CRLs) [DICE-arch].¶
This section specifies the CMW extension to carry CMW objects.¶
The CMW extension MAY be included in X.509 Certificates, CRLs [RFC5280], and CSRs.¶
The CMW extension MUST be identified by the following object identifier:¶
id-pe-cmw-collection OBJECT IDENTIFIER ::=
{ iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-pe(1) TBD }
¶
This extension MUST NOT be marked critical.¶
The CMW extension MUST have the following syntax:¶
CMW ::= CHOICE {
json UTF8String,
cbor OCTET STRING
}
¶
The CMW MUST contain the serialized CMW object in JSON or CBOR format, using the appropriate CHOICE entry.¶
The DER-encoded CMW is the value of the OCTET STRING for the extnValue field of the extension.¶
This section provides an ASN.1 module [X.680] for the CMW extension, following the conventions established in [RFC5912] and [RFC6268].¶
CMWExtn
{ iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-cmw-collection-extn(TBD) }
DEFINITIONS IMPLICIT TAGS ::=
BEGIN
IMPORTS
EXTENSION
FROM PKIX-CommonTypes-2009 -- RFC 5912
{ iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-pkixCommon-02(57) } ;
-- CMW Extension
ext-CMW EXTENSION ::= {
SYNTAX CMW
IDENTIFIED BY id-pe-cmw-collection }
-- CMW Extension OID
id-pe-cmw-collection OBJECT IDENTIFIER ::=
{ iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-pe(1) TBD }
-- CMW Extension Syntax
CMW ::= CHOICE {
json UTF8String,
cbor OCTET STRING
}
END
¶
ConceptualMessageWrapper
Section 6.1.8 of [DICE-arch] defines the ConceptualMessageWrapper format and the associated object identifier. The CMW format defined in [DICE-arch] allows only a subset of the CMW grammar defined in this document. Specifically, the tunnel and collection formats cannot be encoded using DICE CMWs.¶
This section records the status of known implementations of the protocol defined by this specification at the time of posting of this Internet-Draft, and is based on a proposal described in [RFC7942]. The description of implementations in this section is intended to assist the IETF in its decision processes in progressing drafts to RFCs. Please note that the listing of any individual implementation here does not imply endorsement by the IETF. Furthermore, no effort has been spent to verify the information presented here that was supplied by IETF contributors. This is not intended as, and must not be construed to be, a catalog of available implementations or their features. Readers are advised to note that other implementations may exist.¶
According to [RFC7942], "this will allow reviewers and working groups to assign due consideration to documents that have the benefit of running code, which may serve as evidence of valuable experimentation and feedback that have made the implemented protocols more mature. It is up to the individual working groups to use this information as they see fit".¶
The organization responsible for this implementation is Project Veraison, a Linux Foundation project hosted at the Confidential Computing Consortium.¶
The software, hosted at https://github.com/veraison/cmw, provides a Golang package that allows encoding and decoding of CMW payloads. The implementation covers all the features presented in this draft. The maturity level is alpha. The license is Apache 2.0. The developers can be contacted on the Zulip channel: https://veraison.zulipchat.com/#narrow/stream/383526-CMW/.¶
This document introduces two encapsulation formats for RATS conceptual messages. RATS conceptual messages are typically secured using cryptography. If the messages are already protected, then there are no additional security requirements imposed by the introduction of this encapsulation. If an adversary tries to modify the payload encapsulation, it will result in incorrect processing of the encapsulated message and lead to an error. If the messages are not protected, additional security must be added at a different layer. As an example, a CMW record containing an UCCS [I-D.ietf-rats-uccs] can be signed using COSE Sign1 [STD96].¶
This document introduces a format for holding multiple CMW items in a collection. If the collection is not protected from tampering by external security measures (such as object security primitives) or internal mechanisms (such as intra-item binding), an attacker could easily manipulate the collection's contents.¶
RFC Editor: replace "RFCthis" with the RFC number assigned to this document.¶
cmw Claim Registration
IANA is requested to add a new cmw claim to the "CBOR Web Token (CWT) Claims" registry [IANA.cwt] as follows:¶
Claim Name: cmw¶
Claim Description: A RATS Conceptual Message Wrapper¶
Claim Key: TBD¶
Claim Value Type(s): CBOR Map, CBOR Array, or CBOR Tag¶
Change Controller: IETF¶
Specification Document(s): Section 3.1 and Section 3.2 of RFCthis¶
The suggested value for the Claim Key is 299.¶
cmw Claim Registration
IANA is requested to add a new cmw claim to the "JSON Web Token Claims" sub-registry of the "JSON Web Token (JWT)" registry [IANA.jwt] as follows:¶
IANA is requested to add the following tag to the "CBOR Tags" [IANA.cbor-tags] registry.¶
| CBOR Tag | Data Item | Semantics | Reference |
|---|---|---|---|
| TBD | CBOR map, CBOR array, CBOR tag | RATS Conceptual Message Wrapper | Section 3.1, Section 3.2 and Section 3.3 of RFCthis |
This specification defines a new "RATS Conceptual Message Wrapper (CMW) Indicators" registry, with the policy "Expert Review" (Section 4.5 of [BCP26]).¶
The objective is to have Indicators values registered for all RATS Conceptual Messages (Section 8 of [RFC9334]).¶
The expert is instructed to add the values incrementally.¶
Acceptable values are those corresponding to RATS Conceptual Messages defined by the RATS architecture [RFC9334] and any of its updates.¶
Each entry in the registry must include:¶
A number corresponding to the bit position in the cm-ind bitmap.¶
A text string describing the RATS conceptual message this indicator corresponds to.¶
A reference to a document, if available, or the registrant.¶
The initial registrations for the registry are detailed in Table 2.¶
| Indicator value | Conceptual Message name | Reference |
|---|---|---|
| 0 | Reference Values | RFCthis |
| 1 | Endorsements | RFCthis |
| 2 | Evidence | RFCthis |
| 3 | Attestation Results | RFCthis |
IANA is requested to add the following media types to the "Media Types" registry [IANA.media-types].¶
| Name | Template | Reference |
|---|---|---|
cmw+cbor
|
application/cmw+cbor
|
Section 3.1, Section 3.2 and Section 3.3 of RFCthis |
cmw+json
|
application/cmw+json
|
Section 3.1 and Section 3.3 of RFCthis |
application/cmw+cbor
application¶
cmw+cbor¶
n/a¶
cmwc_t (CMW collection type in string format. The parameter value is case-insensitive. It MUST NOT be used for CMW that are not collections.)¶
binary (CBOR)¶
n/a¶
RFCthis¶
Attesters, Verifiers, Endorsers and Reference-Value providers, Relying Parties that need to transfer CMW payloads over HTTP(S), CoAP(S), and other transports.¶
The syntax and semantics of fragment identifiers are as specified for "application/cbor". (No fragment identification syntax is currently defined for "application/cbor".)¶
RATS WG mailing list (rats@ietf.org)¶
COMMON¶
none¶
IETF¶
no¶
application/cmw+json
application¶
cmw+json¶
n/a¶
cmwc_t (CMW collection type in string format. The parameter value is case-insensitive. It MUST NOT be used for CMW that are not collections.)¶
binary (JSON is UTF-8-encoded text)¶
n/a¶
RFCthis¶
Attesters, Verifiers, Endorsers and Reference-Value providers, Relying Parties that need to transfer CMW payloads over HTTP(S), CoAP(S), and other transports.¶
The syntax and semantics of fragment identifiers are as specified for "application/json". (No fragment identification syntax is currently defined for "application/json".)¶
RATS WG mailing list (rats@ietf.org)¶
COMMON¶
none¶
IETF¶
no¶
IANA is requested to assign an object identifier (OID) for the CMW extension defined in Section 5 in the "Certificate Extension" sub-registry of the "SMI Numbers" [IANA.smi-numbers] registry.¶
IANA is requested to assign an object identifier (OID) for the ASN.1 Module defined in Section 5.1 in the "Module Identifier" sub-registry of the "SMI Numbers" [IANA.smi-numbers] registry.¶
start = cmw
cmw = json-CMW / cbor-CMW
json-CMW = json-record / json-collection
cbor-CMW = cbor-record / cbor-collection / cbor-tag
json-record = [
type: media-type
value: base64-string
? ind: uint .bits cm-type
]
cbor-record = [
type: coap-content-format-type / media-type
value: bytes
? ind: uint .bits cm-type
]
cbor-tag = #6.<0..18446744073709551615>(bytes)
json-collection = {
? "__cmwc_t": ~uri / oid
+ text => json-CMW / c2j-tunnel
}
cbor-collection = {
? "__cmwc_t": ~uri / oid
+ (int / text) => cbor-CMW / j2c-tunnel
}
c2j-tunnel = [ "#cmw-c2j-tunnel", base64-string ]
j2c-tunnel = [ "#cmw-j2c-tunnel", bytes ]
media-type = text .abnf ("Content-Type" .cat Content-Type-ABNF)
base64-string = text .regexp "[A-Za-z0-9_-]+"
cm-type = &(
reference-values: 0
endorsements: 1
evidence: 2
attestation-results: 3
)
coap-content-format-type = uint .size 2
oid = text .regexp "([0-2])((\\.0)|(\\.[1-9][0-9]*))*"
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)
'
¶
Figure 5 describes the registration preconditions for using CMWs in either CMW record or CBOR tag forms. When using CMW collection, the preconditions apply for each entry in the collection.¶
The list of currently open issues for this documents can be found at https://github.com/thomas-fossati/draft-ftbs-rats-msg-wrap/issues.¶
Note to RFC Editor: please remove before publication.¶
The authors would like to thank Carl Wallace, Carsten Bormann, Dionna Glaze, Laurence Lundblade, Russ Housley, and Tom Jones for their reviews and suggestions.¶
The definition of a CMW collection has been modelled on a proposal originally made by Simon Frost for an EAT-based Evidence collection type. The CMW collection intentionally attains binary compatibility with Simon's design and aims at superseding it by also generalizing on the allowed Evidence formats.¶