SCITT Reference APIs
draft-ietf-scitt-scrapi-02
The information below is for an old version of the document.
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| Authors | Henk Birkholz , Orie Steele , Jon Geater | ||
| Last updated | 2024-07-08 (Latest revision 2024-03-04) | ||
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draft-ietf-scitt-scrapi-02
SCITT H. Birkholz
Internet-Draft Fraunhofer SIT
Intended status: Standards Track O. Steele
Expires: 9 January 2025 Transmute
J. Geater
DataTrails Inc.
8 July 2024
SCITT Reference APIs
draft-ietf-scitt-scrapi-02
Abstract
This document describes a REST API that supports the normative
requirements of the SCITT Architecture. Optional key discovery and
query interfaces are provided to support interoperability issues with
Decentralized Identifiers, X509 Certificates and Artifact
Repositories.
About This Document
This note is to be removed before publishing as an RFC.
Status information for this document may be found at
https://datatracker.ietf.org/doc/draft-ietf-scitt-scrapi/.
Discussion of this document takes place on the SCITT Working Group
mailing list (mailto:scitt@ietf.org), which is archived at
https://mailarchive.ietf.org/arch/browse/scitt/. Subscribe at
https://www.ietf.org/mailman/listinfo/scitt/.
Source for this draft and an issue tracker can be found at
https://github.com/ietf-wg-scitt/draft-ietf-scitt-scrapi.
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
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 9 January 2025.
Copyright Notice
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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Endpoints . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Mandatory . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1.1. Transparency Configuration . . . . . . . . . . . . . 5
2.1.2. Signed Statement Registration . . . . . . . . . . . . 6
2.2. Optional Endpoints . . . . . . . . . . . . . . . . . . . 9
2.2.1. Issue Signed Statement . . . . . . . . . . . . . . . 10
2.2.2. Resolve Statement . . . . . . . . . . . . . . . . . . 11
2.2.3. Resolve Signed Statement . . . . . . . . . . . . . . 11
2.2.4. Resolve Receipt . . . . . . . . . . . . . . . . . . . 12
2.2.5. Resolve Issuer . . . . . . . . . . . . . . . . . . . 13
2.2.6. Request Nonce . . . . . . . . . . . . . . . . . . . . 14
2.2.7. Resolve Issuer DID . . . . . . . . . . . . . . . . . 15
3. Privacy Considerations . . . . . . . . . . . . . . . . . . . 17
4. Security Considerations . . . . . . . . . . . . . . . . . . . 17
4.1. General scope . . . . . . . . . . . . . . . . . . . . . . 17
4.2. Applicable Environment . . . . . . . . . . . . . . . . . 17
4.3. User-host authentication . . . . . . . . . . . . . . . . 18
4.4. Primary threats . . . . . . . . . . . . . . . . . . . . . 18
4.4.1. In scope . . . . . . . . . . . . . . . . . . . . . . 18
4.4.2. Out of scope . . . . . . . . . . . . . . . . . . . . 20
5. TODO . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21
6.1. URN Sub-namespace for SCITT (urn:ietf:params:scitt) . . . 21
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6.2. Well-Known URI for Issuers . . . . . . . . . . . . . . . 21
6.3. Well-Known URI for Transparency Configuration . . . . . . 21
6.4. Media Type Registration . . . . . . . . . . . . . . . . . 22
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 23
7.1. Normative References . . . . . . . . . . . . . . . . . . 23
7.2. Informative References . . . . . . . . . . . . . . . . . 24
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24
1. Introduction
The SCITT Architecture [I-D.draft-ietf-scitt-architecture] defines
the core operations necessary to support supply chain transparency
using COSE (CBOR Object Signing and Encryption).
* Issuance of Signed Statements
* Verification of Signed Statements
* Registration of Signed Statements
* Issuance of Receipts
* Verification of Receipts
* Production of Transparent Statements
* Verification of Transparent Statements
In addition to defining concrete HTTP endpoints for these operations,
this specification defines support for the following endpoints which
support these operations:
* Resolving Verification Keys for Issuers
* Retrieving Receipts Asynchronously
* Retrieving Signed Statements from an Artifact Repository
* Retrieving Statements from an Artifact Repository
1.1. 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.
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This specification uses the terms "Signed Statement", "Receipt",
"Transparent Statement", "Artifact Repositories", "Transparency
Service", "Append-Only Log" and "Registration Policy" as defined in
[I-D.draft-ietf-scitt-architecture].
This specification uses "payload" as defined in [RFC9052].
2. Endpoints
Authentication is out of scope for this document. If Authentication
is not implemented, rate limiting or other denial of service
mitigations MUST be applied to enable anonymous access.
NOTE: '' line wrapping per [RFC8792] in HTTP examples.
All messages are sent as HTTP GET or POST requests.
If the Transparency Service cannot process a client's request, it
MUST return an HTTP 4xx or 5xx status code, and the body SHOULD be a
JSON problem details object ([RFC9457]) containing:
* type: A URI reference identifying the problem. To facilitate
automated response to errors, this document defines a set of
standard tokens for use in the type field within the URN namespace
of: "urn:ietf:params:scitt:error:".
* detail: A human-readable string describing the error that
prevented the Transparency Service from processing the request,
ideally with sufficient detail to enable the error to be
rectified.
Error responses SHOULD be sent with the Content-Type: application/
problem+json HTTP header.
As an example, submitting a Signed Statement with an unsupported
signature algorithm would return a 400 Bad Request status code and
the following body:
{
"type": "urn:ietf:params:scitt:error:badSignatureAlgorithm",
"detail": "Signing algorithm not support"
}
Most error types are specific to the type of request and are defined
in the respective subsections below. The one exception is the
"malformed" error type, which indicates that the Transparency Service
could not parse the client's request because it did not comply with
this document:
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* Error code: malformed (The request could not be parsed).
Clients SHOULD treat 500 and 503 HTTP status code responses as
transient failures and MAY retry the same request without
modification at a later date. Note that in the case of a 503
response, the Transparency Service MAY include a Retry-After header
field per [RFC9110] in order to request a minimum time for the client
to wait before retrying the request. In the absence of this header
field, this document does not specify a minimum.
2.1. Mandatory
The following HTTP endpoints are mandatory to implement to enable
conformance to this specification.
2.1.1. Transparency Configuration
Authentication SHOULD NOT be implemented for this endpoint. This
endpoint is used to discovery the capabilities of a transparency
service implementing this specification.
Request:
GET /.well-known/transparency-configuration HTTP/1.1
Host: transparency.example
Accept: application/json
Response:
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HTTP/1.1 200 Ok
Content-Type: application/json
{
"issuer": "https://transparency.example",
"registration_endpoint": "https://transparency.example/entries",
"nonce_endpoint": "https://transparency.example/nonce",
"registration_policy": \
"https://transparency.example\
/statements/urn:ietf:params:scitt:statement\
:sha-256:base64url:5i6UeRzg1...qnGmr1o",
"supported_signature_algorithms": ["ES256"],
"jwks": {
"keys": [
{
"kid": "urn:ietf:params:oauth:\
jwk-thumbprint:sha-256:DgyowWs04gfVRim5i1WlQ-HFFFKI6Ltqulj1rXPagRo",
"alg": "ES256",
"use": "sig",
"kty": "EC",
"crv": "P-256",
"x": "p-kZ4uOASt9IjQRTrWikGnlbGb-z3LU1ltwRjZaOS9w",
"y": "ymXE1yltJPXgjQSRe9NweN3TLlSUALYZTzy83NVfdg0"
},
{
"kid": "urn:ietf:params:oauth:\
jwk-thumbprint:sha-256:4Fzx5HO1W0ob9CZNc3RJx28Ixpgy9JAFM8jyXKW0ClE",
"alg": "HPKE-Base-P256-SHA256-AES128GCM",
"use": "enc",
"kty": "EC",
"crv": "P-256",
"x": "Vreuil95vzR6ixutgBBf2ota-rj97MvKfuJWB4qqp5w",
"y": "NkUTeaoNlLRRsVRxHGDA-RsA0ex2tSpcd3G-4SmKXbs"
}
]
}
}
Additional fields may be present. Fields that are not understood
MUST be ignored.
2.1.2. Signed Statement Registration
Authentication MUST be implemented for this endpoint.
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The following is a non-normative example of a HTTP request to
register a Signed Statement:
Request:
POST /entries HTTP/1.1
Host: transparency.example
Accept: application/json
Content-Type: application/cose
Payload (in CBOR diagnostic notation)
18([ / COSE Sign1 /
h'a1013822', / Protected Header /
{}, / Unprotected Header /
null, / Detached Payload /
h'269cd68f4211dffc...0dcb29c' / Signature /
])
The Registration Policy for the Transparency Service MUST be applied
to the payload bytes, before any additional processing is performed.
If the payload is detached, the Transparency Service depends on the
authentication context of the client in the Registration Policy. If
the payload is attached, the Transparency Service depends on both the
authentication context of the client, and the verification of the
Signed Statement in the Registration Policy. The details of
Registration Policy are out of scope for this document.
If registration succeeds the following identifier MAY be used to
refer to the Signed Statement that was accepted:
urn:ietf:params:scitt:signed-statement:sha-
256:base64url:5i6UeRzg1...qnGmr1o
If the payload was attached, or otherwise communicated to the
Transparency Service, the following identifier MAY be used to refer
to the payload of the Signed Statement:
urn:ietf:params:scitt:statement:sha-256:base64url:5i6UeRzg1...qnGmr1o
Response:
One of the following:
2.1.2.1. Status 201 - Registration is successful
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HTTP/1.1 201 Ok
Location: https://transparency.example/receipts\
/urn:ietf:params:scitt:signed-statement\
:sha-256:base64url:5i6UeRzg1...qnGmr1o
Content-Type: application/cose
Payload (in CBOR diagnostic notation)
18([ / COSE Sign1 /
h'a1013822', / Protected Header /
{}, / Unprotected Header /
null, / Detached Payload /
h'269cd68f4211dffc...0dcb29c' / Signature /
])
The response contains the Receipt for the Signed Statement. Fresh
receipts may be requested through the resource identified in the
Location header.
2.1.2.2. Status 202 - Registration is running
HTTP/1.1 202 Ok
Location: https://transparency.example/receipts\
/urn:ietf:params:scitt:signed-statement\
:sha-256:base64url:5i6UeRzg1...qnGmr1o
Content-Type: application/json
Retry-After: <seconds>
{
"receipt": "urn:ietf:params:scitt:receipt\
:sha-256:base64url:5i6UeRzg1...qnGmr1o",
}
The response contains a reference to the receipt which will
eventually be available for the Signed Statement.
If 202 is returned, then clients should wait until Registration
succeeded or failed by polling the receipt endpoint using the receipt
identifier returned in the response.
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2.1.2.3. Status 400 - Invalid Client Request
One of the following errors:
{
"type": "urn:ietf:params:scitt:error\
:signed-statement:algorithm-not-supported",
"detail": \
"Signed Statement contained an algorithm that is not supported."
}
{
"type": "urn:ietf:params:scitt:error\
:signed-statement:payload-missing",
"detail": \
"Signed Statement payload must be attached (must be present)"
}
{
"type": "urn:ietf:params:scitt:error\
:signed-statement:payload-forbidden",
"detail": \
"Signed Statement payload must be detached (must not be present)"
}
{
"type": "urn:ietf:params:scitt:error\
:signed-statement:rejected-by-registration-policy",
"detail": \
"Signed Statement not accepted by the current Registration Policy"
}
{
"type": "urn:ietf:params:scitt:error\
:signed-statement:confirmation-missing",
"detail": \
"Signed Statement did not contain proof of possession"
}
TODO: other error codes
2.2. Optional Endpoints
The following HTTP endpoints are optional to implement.
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2.2.1. Issue Signed Statement
Authentication MUST be implemented for this endpoint.
This endpoint enables a Transparency Service to be an issuer of
Signed Statements on behalf of authenticated clients. This supports
cases where a client lacks the ability to perform complex
cryptographic operations, but can be authenticated and report
statements and measurements.
Request:
POST /signed-statements/issue HTTP/1.1
Host: transparency.example
Accept: application/json
Content-Type: application/vc+ld+json
Payload
{
"@context": [
"https://www.w3.org/ns/credentials/v2",
"https://www.w3.org/ns/credentials/examples/v2"
],
"id": "https://transparency.example/credentials/1872",
"type": ["VerifiableCredential", "SensorCredential"],
"issuer": "https://transparency.example/device/1234",
"validFrom": "2010-01-01T19:23:24Z",
"credentialSubject": {
"type": "Feature",
"geometry": {
"type": "Point",
"coordinates": [125.6, 10.1]
},
"properties": {
"name": "Dinagat Islands"
}
}
}
Response:
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HTTP/1.1 200 Ok
Content-Type: application/cose
Payload (in CBOR diagnostic notation)
18([ / COSE Sign1 /
h'a1013822', / Protected Header /
{}, / Unprotected Header /
null, / Detached Payload /
h'269cd68f4211dffc...0dcb29c' / Signature /
])
2.2.2. Resolve Statement
Authentication SHOULD be implemented for this endpoint.
This endpoint enables Transparency Service APIs to act like Artifact
Repositories, and serve payload values directly, instead of
indirectly through Receipts.
Request:
GET /statements/urn...qnGmr1o HTTP/1.1
Host: transparency.example
Accept: application/pdf
Response:
HTTP/1.1 200 Ok
Content-Type: application/pdf
Payload (pdf bytes)
2.2.3. Resolve Signed Statement
Authentication SHOULD be implemented for this endpoint.
This endpoint enables Transparency Service APIs to act like Artifact
Repositories, and serve Signed Statements directly, instead of
indirectly through Receipts.
Request:
GET /signed-statements/urn...qnGmr1o HTTP/1.1
Host: transparency.example
Accept: application/cose
Response:
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HTTP/1.1 200 Ok
Content-Type: application/cose
Payload (in CBOR diagnostic notation)
18([ / COSE Sign1 /
h'a1013822', / Protected Header /
{}, / Unprotected Header /
null, / Detached Payload /
h'269cd68f4211dffc...0dcb29c' / Signature /
])
2.2.4. Resolve Receipt
Authentication SHOULD be implemented for this endpoint.
Request:
GET /receipts/urn...qnGmr1o HTTP/1.1
Host: transparency.example
Accept: application/cose
Response:
If the Signed Statement requested is already included in the Append-
Only Log:
HTTP/1.1 200 Ok
Location: https://transparency.example/receipts/urn...qnGmr1o
Content-Type: application/cose
Payload (in CBOR diagnostic notation)
18([ / COSE Sign1 /
h'a1013822', / Protected Header /
{}, / Unprotected Header /
null, / Detached Payload /
h'269cd68f4211dffc...0dcb29c' / Signature /
])
If the Signed Statement requested is not yet included in the Append-
Only Log:
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HTTP/1.1 202 Ok
Location: https://transparency.example/receipts/urn...qnGmr1o
Content-Type: application/json
Retry-After: <seconds>
{
"receipt": "urn:ietf:params:scitt:receipt\
:sha-256:base64url:5i6UeRzg1...qnGmr1o",
}
Additional eventually consistent operation details MAY be present.
Support for eventually consistent Receipts is implementation
specific, and out of scope for this specification.
2.2.5. Resolve Issuer
This endpoint is inspired by [I-D.draft-ietf-oauth-sd-jwt-vc].
Authentication SHOULD NOT be implemented for this endpoint. This
endpoint is used to discover verification keys, which is the reason
that authentication is not required.
The following is a non-normative example of a HTTP request for the
Issuer Metadata configuration when iss is set to
https://transparency.example/tenant/1234:
Request:
GET /.well-known/issuer/tenant/1234 HTTP/1.1
Host: transparency.example
Accept: application/json
Response:
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HTTP/1.1 200 Ok
Content-Type: application/json
{
"issuer": "https://transparency.example/tenant/1234",
"jwks": {
"keys": [
{
"kid": "urn:ietf:params:oauth\
:jwk-thumbprint:sha-256:DgyowWs04gfVRim5i1WlQ-HFFFKI6Ltqulj1rXPagRo",
"alg": "ES256",
"use": "sig",
"kty": "EC",
"crv": "P-256",
"x": "p-kZ4uOASt9IjQRTrWikGnlbGb-z3LU1ltwRjZaOS9w",
"y": "ymXE1yltJPXgjQSRe9NweN3TLlSUALYZTzy83NVfdg0"
},
{
"kid": "urn:ietf:params:oauth\
:jwk-thumbprint:sha-256:4Fzx5HO1W0ob9CZNc3RJx28Ixpgy9JAFM8jyXKW0ClE",
"alg": "HPKE-Base-P256-SHA256-AES128GCM",
"use": "enc",
"kty": "EC",
"crv": "P-256",
"x": "Vreuil95vzR6ixutgBBf2ota-rj97MvKfuJWB4qqp5w",
"y": "NkUTeaoNlLRRsVRxHGDA-RsA0ex2tSpcd3G-4SmKXbs"
}
]
}
}
2.2.6. Request Nonce
This endpoint in inspired by
[I-D.draft-demarco-oauth-nonce-endpoint].
Authentication SHOULD NOT be implemented for this endpoint. This
endpoint is used to demonstrate proof of possession, which is the
reason that authentication is not required. Client holding signed
statements that require demonstrating proof of possession MUST use
this endpoint to obtain a nonce.
Request:
GET /nonce HTTP/1.1
Host: transparency.example
Accept: application/json
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Response:
HTTP/1.1 200 OK
Content-Type: application/json
{
"nonce": "d2JhY2NhbG91cmVqdWFuZGFt"
}
2.2.7. Resolve Issuer DID
This endpoint enables the use of the DID Web Decentralized Identifier
Method, as an alternative expression of the Issuer Metadata endpoint.
This endpoint is DEPRECATED.
The following is a non-normative example of a HTTP request for the
Issuer Metadata configuration when iss is set to
did:web:transparency.example:tenant:1234:
Request:
GET /tenant/1234/did.json HTTP/1.1
Host: transparency.example
Accept: application/did+ld+json
Response:
HTTP/1.1 200 Ok
Content-Type: application/did+ld+json
{
"@context": [
"https://www.w3.org/ns/did/v1",
{
"@vocab": "https://vocab.transparency.example#"
}
],
"id": "did:web:transparency.example:tenant:1234",
"verificationMethod": [
{
"id": "did:web:transparency.example:tenant:1234\
#urn:ietf:params:oauth:jwk-thumbprint\
:sha-256:5b30k1hBWBMcggA9GIJImUqj4pXqrJ9EOWV6MDdcstA",
"type": "JsonWebKey",
"controller": "did:web:transparency.example:tenant:1234",
"publicKeyJwk": {
"kid": "urn:ietf:params:oauth:jwk-thumbprint\
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:sha-256:5b30k1hBWBMcggA9GIJImUqj4pXqrJ9EOWV6MDdcstA",
"alg": "ES256",
"use": "sig",
"kty": "EC",
"crv": "P-256",
"x": "9ptuW0PBHSTN7bVexWd7xM5kmSPGRaCu-K3SLtJyvNc",
"y": "l7NvF6QbovicSciZqu_W_xy4JTZwtnUbn2SNdMKoaAk"
}
},
{
"id": "did:web:transparency.example:tenant:1234\
#urn:ietf:params:oauth:jwk-thumbprint\
:sha-256:DgyowWs04gfVRim5i1WlQ-HFFFKI6Ltqulj1rXPagRo",
"type": "JsonWebKey",
"controller": "did:web:transparency.example:tenant:1234",
"publicKeyJwk": {
"kid": "urn:ietf:params:oauth:jwk-thumbprint\
:sha-256:DgyowWs04gfVRim5i1WlQ-HFFFKI6Ltqulj1rXPagRo",
"alg": "ES256",
"use": "sig",
"kty": "EC",
"crv": "P-256",
"x": "p-kZ4uOASt9IjQRTrWikGnlbGb-z3LU1ltwRjZaOS9w",
"y": "ymXE1yltJPXgjQSRe9NweN3TLlSUALYZTzy83NVfdg0"
}
},
{
"id": "did:web:transparency.example:tenant:1234\
#urn:ietf:params:oauth:jwk-thumbprint\
:sha-256:4Fzx5HO1W0ob9CZNc3RJx28Ixpgy9JAFM8jyXKW0ClE",
"type": "JsonWebKey",
"controller": "did:web:transparency.example:tenant:1234",
"publicKeyJwk": {
"kid": "urn:ietf:params:oauth:jwk-thumbprint\
:sha-256:4Fzx5HO1W0ob9CZNc3RJx28Ixpgy9JAFM8jyXKW0ClE",
"alg": "HPKE-Base-P256-SHA256-AES128GCM",
"use": "enc",
"kty": "EC",
"crv": "P-256",
"x": "Vreuil95vzR6ixutgBBf2ota-rj97MvKfuJWB4qqp5w",
"y": "NkUTeaoNlLRRsVRxHGDA-RsA0ex2tSpcd3G-4SmKXbs"
}
}
],
"assertionMethod": [
"did:web:transparency.example:tenant:1234\
#urn:ietf:params:oauth:jwk-thumbprint\
:sha-256:5b30k1hBWBMcggA9GIJImUqj4pXqrJ9EOWV6MDdcstA",
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"did:web:transparency.example:tenant:1234\
#urn:ietf:params:oauth:jwk-thumbprint\
:sha-256:DgyowWs04gfVRim5i1WlQ-HFFFKI6Ltqulj1rXPagRo"
],
"authentication": [
"did:web:transparency.example:tenant:1234\
#urn:ietf:params:oauth:jwk-thumbprint\
:sha-256:5b30k1hBWBMcggA9GIJImUqj4pXqrJ9EOWV6MDdcstA",
"did:web:transparency.example:tenant:1234\
#urn:ietf:params:oauth:jwk-thumbprint\
:sha-256:DgyowWs04gfVRim5i1WlQ-HFFFKI6Ltqulj1rXPagRo"
],
"keyAgreement": [
"did:web:transparency.example:tenant:1234\
#urn:ietf:params:oauth:jwk-thumbprint\
:sha-256:4Fzx5HO1W0ob9CZNc3RJx28Ixpgy9JAFM8jyXKW0ClE"
]
}
3. Privacy Considerations
TODO
4. Security Considerations
4.1. General scope
This document describes the interoperable API for client calls to,
and implementations of, a Transparency Service as specified in
[I-D.draft-ietf-scitt-architecture]. As such the security
considerations in this section are concerned only with security
considerations that are relevant at that implementation layer. All
questions of security of the related COSE formats, algorithm choices,
cryptographic envelopes,verifiable data structures and the like are
handled elsewhere and out of scope of this document.
4.2. Applicable Environment
SCITT is concerned with issues of cross-boundary supply-chain-wide
data integrity and as such must assume a very wide range of
deployment environments. Thus, no assumptions can be made about the
security of the computing environment in which any client
implementation of this specification runs.
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4.3. User-host authentication
[I-D.draft-ietf-scitt-architecture] defines 2 distinct roles that
require authentication: Issuers who sign Statements, and clients that
submit API calls on behalf of Issuers. While Issuer authentication
and signing of Statements is very important for the trustworthiness
of systems implementing the SCITT building blocks, it is out of scope
of this document. This document is only concerned with
authentication of API clients.
For those endpoints that require client authentication, Transparency
Services MUST support at least one of the following options:
* HTTP Authorization header with a bearer JWT
* domain-bound API key
* TLS client authentication
Transparency Services MUST provide a configuration surface that
allows Issuers to specify which authorized clients can submit
Statements on their behalf.
Where authentication methods rely on long term secrets, both clients
and Transparency Services implementing this specification MUST allow
for the revocation and rolling of authentication secrets.
4.4. Primary threats
4.4.1. In scope
The most serious threats to implementations on Transparency Services
are ones that would cause the failure of their main promises, to wit:
* Threats to strong identification, for example representing the
Statements from one issuer as those of another
* Threats to payload integrity, for example changing the contents of
a Signed Statement before making it transparent
* Threats to non-equivocation, for example attacks that would enable
the presentation or verification of divergent proofs for the same
Statement payload
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4.4.1.1. Denial of service attacks
While denial of service attacks are very hard to defend against
completely, and Transparency Services are unlikely to be in the
critical path of any safety-liable operation, any attack which could
cause the _silent_ failure of Signed Statement registration, for
example, should be considered in scope.
In principle DoS attacks are easily mitigated by the client checking
that the Transparency Service has registered any submitted Signed
Statement and returned a Receipt. Since verification of Receipts
does not require the involvement of the Transparency Service DoS
attacks are not a major issue.
Clients to Transparency Services SHOULD ensure that Receipts are
available for their registered Statements, either on a periodic or
needs-must basis, depending on the use case.
Beyond this, implementers of Transparency Services SHOULD implement
general good practice around network attacks, flooding, rate limiting
etc.
4.4.1.2. Eavesdropping
Since the purpose of this API is to ultimately put the message
payloads on a Transparency Log there is limited risk to
eavesdropping. Nonetheless transparency may mean 'within a limited
community' rather than 'in full public', so implementers MUST add
protections against man-in-the-middle and network eavesdropping, such
as TLS.
4.4.1.3. Message modification attacks
While most relevant modification attacks are mitigated by the use of
the Issuer signature on the Signed Statement, the Issue Statement
endpoint presents an opportunity for manipulation of messages and
misrepresentation of Issuer intent that could mislead later
Verifiers.
Transparency Services offering the Issue Statement endpoint MUST
require authentication and transport-level security for that
endpoint, MUST NOT modify anything in the message to be signed, and
MUST take steps to ensure that the party calling the endpoint is
authorized to register statements on behalf of the specified Issuer.
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4.4.1.4. Message insertion attacks
While most relevant insertion attacks are mitigated by the use of the
Issuer signature on the Signed Statement, the Issue Statement
endpoint presents an opportunity for insertion of messages and
misrepresentation of Issuer intent that could mislead later
Verifiers. There are 2 most likely avenues to this attack:
* Stolen client endpoint authentication credentials
* Stolen or misused Issuer keys held in the Transparency Service on
behalf of clients
Clients relying on the Issue Statement endpoint SHOULD take steps to
ensure their endpoint authentication credentials are securely stored
and can be rotated and/or revoked in the case of a breach.
Transparency Services offering the Issue Statement endpoint MUST
require authentication and transport-level security for that
endpoint, and MUST enable the rotation and revocation of those
credentials.
Transparency Services offering the Issue Statement endpoint MUST take
careful steps in both design and operation of their software stack to
prevent the theft or inappropriate use of the Issuer keys they use to
sign Statements on behalf of Issuers, such as HSMs for storage and
least-privilege, regularly refreshed access controls for use.
Transparency Services MAY also implement additional protections such
as anomaly detection or rate limiting in order to mitigate the impact
of any breach.
4.4.2. Out of scope
4.4.2.1. Replay attacks
Replay attacks are not particularly concerning for SCITT or SCRAPI:
once a statement is made, it is intended to be immutable and non-
repudiable, so making it twice should not lead to any particular
issues. There could be issues at the payload level (for instance,
the statement "it is raining" may true when first submitted but not
when replayed), but being payload-agnostic implementations of SCITT
services cannot be required to worry about that.
If the semantic content of the payload are time dependent and
susceptible to replay attacks in this way then timestamps MAY be
added to the payload signed by the Issuer.
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4.4.2.2. Message deletion attacks
Once registered with a Transparency Service, Registered Signed
Statements cannot be deleted. Thus, any message deletion attack must
occur prior to registration else it is indistinguishable from a man-
in-the-middle or denial-of-service attack on this interface.
5. TODO
TODO: Consider negotiation for receipt as "JSON" or "YAML". TODO:
Consider impact of media type on "Data URIs" and QR Codes.
6. IANA Considerations
6.1. URN Sub-namespace for SCITT (urn:ietf:params:scitt)
IANA is requested to register the URN sub-namespace
urn:ietf:params:scitt in the "IETF URN Sub-namespace for Registered
Protocol Parameter Identifiers" Registry [IANA.params], following the
template in [RFC3553]:
Registry name: scitt
Specification: [RFCthis]
Repository: http://www.iana.org/assignments/scitt
Index value: No transformation needed.
6.2. Well-Known URI for Issuers
The following value is requested to be registered in the "Well-Known
URIs" registry (using the template from [RFC8615]):
URI suffix: issuer Change controller: IETF Specification document(s):
RFCthis. Related information: N/A
6.3. Well-Known URI for Transparency Configuration
The following value is requested to be registered in the "Well-Known
URIs" registry (using the template from [RFC8615]):
URI suffix: transparency-configuration Change controller: IETF
Specification document(s): RFCthis. Related information: N/A
TODO: Register them from here.
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6.4. Media Type Registration
This section requests registration of the "application/
scitt.receipt+cose" media type [RFC2046] in the "Media Types"
registry in the manner described in [RFC6838].
To indicate that the content is a SCITT Receipt:
* Type name: application
* Subtype name: scitt.receipt+cose
* Required parameters: n/a
* Optional parameters: n/a
* Encoding considerations: TODO
* Security considerations: TODO
* Interoperability considerations: n/a
* Published specification: this specification
* Applications that use this media type: TBD
* Fragment identifier considerations: n/a
* Additional information:
- Magic number(s): n/a
- File extension(s): n/a
- Macintosh file type code(s): n/a
* Person & email address to contact for further information: TODO
* Intended usage: COMMON
* Restrictions on usage: none
* Author: TODO
* Change Controller: IESG
* Provisional registration? No
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7. References
7.1. Normative References
[I-D.draft-ietf-scitt-architecture]
Birkholz, H., Delignat-Lavaud, A., Fournet, C., Deshpande,
Y., and S. Lasker, "An Architecture for Trustworthy and
Transparent Digital Supply Chains", Work in Progress,
Internet-Draft, draft-ietf-scitt-architecture-07, 8 July
2024, <https://datatracker.ietf.org/doc/html/draft-ietf-
scitt-architecture-07>.
[IANA.params]
IANA, "Uniform Resource Name (URN) Namespace for IETF
Use", <http://www.iana.org/assignments/params>.
[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>.
[RFC3553] Mealling, M., Masinter, L., Hardie, T., and G. Klyne, "An
IETF URN Sub-namespace for Registered Protocol
Parameters", BCP 73, RFC 3553, DOI 10.17487/RFC3553, June
2003, <https://www.rfc-editor.org/rfc/rfc3553>.
[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>.
[RFC8615] Nottingham, M., "Well-Known Uniform Resource Identifiers
(URIs)", RFC 8615, DOI 10.17487/RFC8615, May 2019,
<https://www.rfc-editor.org/rfc/rfc8615>.
[RFC9052] Schaad, J., "CBOR Object Signing and Encryption (COSE):
Structures and Process", STD 96, RFC 9052,
DOI 10.17487/RFC9052, August 2022,
<https://www.rfc-editor.org/rfc/rfc9052>.
[RFC9110] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP Semantics", STD 97, RFC 9110,
DOI 10.17487/RFC9110, June 2022,
<https://www.rfc-editor.org/rfc/rfc9110>.
[RFC9457] Nottingham, M., Wilde, E., and S. Dalal, "Problem Details
for HTTP APIs", RFC 9457, DOI 10.17487/RFC9457, July 2023,
<https://www.rfc-editor.org/rfc/rfc9457>.
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7.2. Informative References
[I-D.draft-demarco-oauth-nonce-endpoint]
De Marco, G. and O. Steele, "OAuth 2.0 Nonce Endpoint",
Work in Progress, Internet-Draft, draft-demarco-oauth-
nonce-endpoint-00, 6 February 2024,
<https://datatracker.ietf.org/doc/html/draft-demarco-
oauth-nonce-endpoint-00>.
[I-D.draft-ietf-oauth-sd-jwt-vc]
Terbu, O., Fett, D., and B. Campbell, "SD-JWT-based
Verifiable Credentials (SD-JWT VC)", Work in Progress,
Internet-Draft, draft-ietf-oauth-sd-jwt-vc-04, 8 July
2024, <https://datatracker.ietf.org/doc/html/draft-ietf-
oauth-sd-jwt-vc-04>.
[RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", RFC 2046,
DOI 10.17487/RFC2046, November 1996,
<https://www.rfc-editor.org/rfc/rfc2046>.
[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>.
[RFC8792] Watsen, K., Auerswald, E., Farrel, A., and Q. Wu,
"Handling Long Lines in Content of Internet-Drafts and
RFCs", RFC 8792, DOI 10.17487/RFC8792, June 2020,
<https://www.rfc-editor.org/rfc/rfc8792>.
Authors' Addresses
Henk Birkholz
Fraunhofer SIT
Rheinstrasse 75
64295 Darmstadt
Germany
Email: henk.birkholz@sit.fraunhofer.de
Orie Steele
Transmute
Email: orie@transmute.industries
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Jon Geater
DataTrails Inc.
United States
Email: jon.geater@datatrails.ai
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