Network Working Group S. Santesson Internet-Draft IDsec Solutions Intended status: Informational R. Housley Expires: 7 March 2022 Vigil Security 3 September 2021 XML Signature Validation Token draft-santesson-svt-xml-02 Abstract This document defines a XML profile for the Signature Validation Token defined in [SVT]. 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 7 March 2022. Copyright Notice Copyright (c) 2021 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. Santesson & Housley Expires 7 March 2022 [Page 1] Internet-Draft XML Signature Validation Token September 2021 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1. Notation . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1.1. References to XML Elements from XML Schemas . . . . . 3 3. SVT in XML Documents . . . . . . . . . . . . . . . . . . . . 3 3.1. SignatureValidationToken Signature Property . . . . . . . 3 3.2. Multiple SVT in a signature . . . . . . . . . . . . . . . 5 4. SVT Claims . . . . . . . . . . . . . . . . . . . . . . . . . 5 4.1. Signature Reference Data . . . . . . . . . . . . . . . . 5 4.2. Signed Data Reference Data . . . . . . . . . . . . . . . 6 4.3. Signer Certificate References . . . . . . . . . . . . . . 6 5. JOSE Header . . . . . . . . . . . . . . . . . . . . . . . . . 6 5.1. SVT Signing Key Reference . . . . . . . . . . . . . . . . 6 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 7. Security Considerations . . . . . . . . . . . . . . . . . . . 7 8. Normative References . . . . . . . . . . . . . . . . . . . . 7 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 1. Introduction The "Signature Validation Token" specification [SVT] defines the basic token to support signature validation in a way that can significantly extend the lifetime of a signature. This specification defines a profile for implementing SVT with a signed XML document, and defines the following aspects of SVT usage: * How to include reference data related to XML signatures and XML documents in an SVT. * How to add an SVT token to a XML signature. XML documents can have any number of signature elements, signing an arbitrary number of fragments of XML documents. The actual signature element may be included in the signed XML document (enveloped), include the signed data (enveloping) or may be separate from the signed content (detached). To provide a generic solution for any type of XML signature an SVT is added to each XML signature element within the XML signature element. Santesson & Housley Expires 7 March 2022 [Page 2] Internet-Draft XML Signature Validation Token September 2021 2. 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. The definitions in [SVT] apply also to this document. 2.1. Notation 2.1.1. References to XML Elements from XML Schemas When referring to elements from the W3C XML Signature namespace (http://www.w3.org/2000/09/xmldsig#) the following syntax is used: * When referring to elements from the ETSI XAdES XML Signature namespace (http://uri.etsi.org/01903/v1.3.2#) the following syntax is used: * When referring to elements defined in this specification (http://id.swedenconnect.se/svt/1.0/sig-prop/ns) the following syntax is used: * 3. SVT in XML Documents When SVT is provided for XML signatures then one SVT MUST be provided for each XML signature. An SVT embedded within the XML signature element MUST be placed in a element as defined in Section 3.1. 3.1. SignatureValidationToken Signature Property The element MUST be placed in a element in accordance with [XMLDSIG11]. The element MUST be placed inside a element inside a element inside a element. Santesson & Housley Expires 7 March 2022 [Page 3] Internet-Draft XML Signature Validation Token September 2021 Note: [XMLDSIG11] requires the Target attribute to be present in , referencing the signature targeted by this signature property. If an SVT is added to a signature that do not have an Id attribute, implementations SHOULD add an Id attribute to the element and reference that Id in the Target attribute. This Id attribute and Target attribute value matching is required by the [XMLDSIG11] standard, but it is redundant in the context of SVT validation as the SVT already contains information that uniquely identifies the target signature. Validation applications SHOULD not reject an SVT token because of Id and Target attribute mismatch, and MUST rely on matching against signature using signed information in the SVT itself. The element is defined by the following XML Schema: The SVT token MUST be included as a string representation of the SVT JWT. Note that this is the string representation of the JWT without further encoding. The SVT MUST NOT be represented by the Base64 encoded bytes of the JWT string. Example: Santesson & Housley Expires 7 March 2022 [Page 4] Internet-Draft XML Signature Validation Token September 2021 ... eyJ0eXAiOiJKV1QiLCJhb...2aNZ 3.2. Multiple SVT in a signature If a new SVT is stored in a signature which already contains a previously issued SVT, implementations can choose to either replace the existing SVT or to store the new SVT in addition to the existing SVT. If the new SVT is stored in addition to the old SVT, it SHOULD be stored in a new element inside the existing element where the old SVT is located. For interoperability robustness, signature validation applications MUST be able to handle signatures where the new SVT is located in a new element. 4. SVT Claims 4.1. Signature Reference Data The SVT Signature object MUST contain a "sig_ref" claim (SigReference object) with the following elements: * "id" - The Id-attribute of the XML signature, if present. * "sig_hash" - The hash over the signature value bytes. * "sb_hash" - The hash over the canonicalized element (the bytes the XML signature algorithm has signed to generated the signature value). Santesson & Housley Expires 7 March 2022 [Page 5] Internet-Draft XML Signature Validation Token September 2021 4.2. Signed Data Reference Data The SVT Signature object MUST contain one instance of the "sig_data" claim (SignedData object) for each element in the element. The "sig_data" claim MUST contain the following elements: * "ref" - The value of the URI attribute of the corresponding element. * "hash" - The hash of all bytes identified corresponding element after applying all identified canonicalization and transformation algorithms. These are the same bytes that is hashed by the hash value in the element inside the element. 4.3. Signer Certificate References The SVT Signature object MUST contain a "signer_cert_ref" claim (CertReference object). The "type" parameter of the "signer_cert_ref" claim MUST be either "chain" or "chain_hash". * The "chain" type MUST be used when signature validation was performed using one or more certificates where some or all of the certificates in the chain are not present in the target signature. * The "chain_hash" type MUST be used when signature validation was performed using one or more certificates where all of the certificates are present in the target signature. 5. JOSE Header 5.1. SVT Signing Key Reference The SVT JOSE header must contain one of the following header parameters in accordance with [RFC7515], for storing a reference to the public key used to verify the signature on the SVT: * "x5c" - Holds an X.509 certificate [RFC5280] or a chain of certificates. The certificate holding the public key that verifies the signature on the SVT MUST be the first certificate in the chain. * "kid" - A key identifier holding the Base64 encoded hash value of the certificate that can verify the signature on the SVT. The hash algorithm MUST be the same hash algorithm used when signing the SVT as specified by the "alg" header parameter. Santesson & Housley Expires 7 March 2022 [Page 6] Internet-Draft XML Signature Validation Token September 2021 6. IANA Considerations This document has no IANA actions. 7. Security Considerations The security considerations of [SVT] applies also to this document. 8. 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, . [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, . [RFC7515] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May 2015, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [SVT] Santesson, S. and R. Housley, "Signature Validation Token", IETF draft-santesson-svt-02, September 2021. [XMLDSIG11] Eastlake, D., Reagle, J., Solo, D., Hirsch, F., Nystrom, M., Roessler, T., and K. Yiu, "XML Signature Syntax and Processing Version 1.1", W3C Proposed Recommendation, 11 April 2013. Authors' Addresses Stefan Santesson IDsec Solutions AB Forskningsbyn Ideon SE-223 70 Lund Sweden Email: sts@aaa-sec.com Santesson & Housley Expires 7 March 2022 [Page 7] Internet-Draft XML Signature Validation Token September 2021 Russ Housley Vigil Security, LLC 516 Dranesville Road Herndon, VA, 20170 United States of America Email: housley@vigilsec.com Santesson & Housley Expires 7 March 2022 [Page 8]