XML Signature Validation Token
draft-santesson-svt-xml-02

Document Type Active Internet-Draft (individual)
Authors Stefan Santesson  , Russ Housley 
Last updated 2021-09-03
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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.

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   This Internet-Draft will expire on 7 March 2022.

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   document authors.  All rights reserved.

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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
   <ds:Object> element.

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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:

   *  <ds:Signature>

   When referring to elements from the ETSI XAdES XML Signature
   namespace (http://uri.etsi.org/01903/v1.3.2#) the following syntax is
   used:

   *  <xades:CertDigest>

   When referring to elements defined in this specification
   (http://id.swedenconnect.se/svt/1.0/sig-prop/ns) the following syntax
   is used:

   *  <svt:Element>

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
   <svt:SignatureValidationToken> element as defined in Section 3.1.

3.1.  SignatureValidationToken Signature Property

   The <svt:SignatureValidationToken> element MUST be placed in a
   <ds:SignatureProperty> element in accordance with [XMLDSIG11].  The
   <ds:SignatureProperty> element MUST be placed inside a
   <ds:SignatureProperties> element inside a <ds:Object> element inside
   a <ds:Signature> element.

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   Note: [XMLDSIG11] requires the Target attribute to be present in
   <ds:SignatureProperty>, 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 <ds:Signature> 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 <svt:SignatureValidationToken> element is defined by the
   following XML Schema:

   <?xml version="1.0" encoding="UTF-8"?>
   <xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
       elementFormDefault="qualified"
       targetNamespace="http://id.swedenconnect.se/svt/1.0/sig-prop/ns"
       xmlns:svt="http://id.swedenconnect.se/svt/1.0/sig-prop/ns">

     <xs:element name="SignatureValidationToken"
         type="svt:SignatureValidationTokenType" />

     <xs:complexType name="SignatureValidationTokenType">
       <xs:simpleContent>
         <xs:extension base="xs:string">
         </xs:extension>
       </xs:simpleContent>
     </xs:complexType>

   </xs: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:

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   <ds:Signature Id="MySignatureId">
     ...
     <ds:Object>
       <ds:SignatureProperties>
         <ds:SignatureProperty Target="#MySignatureId">
           <svt:SignatureValidationToken>
                 eyJ0eXAiOiJKV1QiLCJhb...2aNZ
           </svt:SignatureValidationToken>
         </ds:SignatureProperty>
       </ds:SignatureProperties>
     </ds:Object>
   </ds:Signature>

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 <ds:SignatureProperty> element inside the existing
   <ds:SignatureProperties> 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 <ds:Object> 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 <ds:SignedInfo>
      element (the bytes the XML signature algorithm has signed to
      generated the signature value).

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4.2.  Signed Data Reference Data

   The SVT Signature object MUST contain one instance of the "sig_data"
   claim (SignedData object) for each <ds:Reference> element in the
   <ds:SignedInfo> element.  The "sig_data" claim MUST contain the
   following elements:

   *  "ref" - The value of the URI attribute of the corresponding
      <ds:Reference> element.

   *  "hash" - The hash of all bytes identified corresponding
      <ds:Reference> element after applying all identified
      canonicalization and transformation algorithms.  These are the
      same bytes that is hashed by the hash value in the
      <ds:DigestValue> element inside the <ds:Reference> 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.

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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,
              <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>.

   [RFC7515]  Jones, M., Bradley, J., and N. Sakimura, "JSON Web
              Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May
              2015, <https://www.rfc-editor.org/info/rfc7515>.

   [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>.

   [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

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   Russ Housley
   Vigil Security, LLC
   516 Dranesville Road
   Herndon, VA,  20170
   United States of America

   Email: housley@vigilsec.com

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