Electronic signatures have a limited lifespan with respect to the time period that they can be validated and determined to be authentic. The Signature Validation Token (SVT) defined in this specification provides evidence that asserts the validity of an electronic signature. The SVT is provided by a trusted authority, which asserts that a particular signature was successfully validated according to defined procedures at a certain time. Any future validation of that electronic signature can be satisfied by validating the SVT without any need to also validate the original electronic signature or the associated digital certificates. The SVT supports electronic signatures in Cryptographic Message Syntax (CMS), XML, PDF, and JSON documents.

This document is not an Internet Standards Track specification; it is published for informational purposes. This is a contribution to the RFC Series, independently of any other RFC stream. The RFC Editor has chosen to publish this document at its discretion and makes no statement about its value for implementation or deployment. Documents approved for publication by the RFC Editor are not candidates for any level of Internet Standard; see Section 2 of RFC 7841. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at https://www.rfc-editor.org/info/rfc9321.

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Electronic signatures have a limited lifespan regarding when they can be validated and determined to be authentic. Many factors make it more difficult to validate electronic signatures over time. For example:

• Trusted information about the validity of the certificate containing the signer's public key is not available.
• Trusted information about the time when the signature was actually created is not available.
• Algorithms used to create the electronic signature may no longer be considered secure at the time of validation and may therefore no longer be available in software libraries.
• Services necessary to validate the signature are no longer available at the time of validation.
• Supporting evidence such as certification authority (CA) certificates, Online Certificate Status Protocol (OCSP) responses, Certificate Revocation Lists (CRLs), or timestamps is not available or can't be validated.

The challenges to validation of an electronic signature increase over time, and eventually it may simply be impossible to verify the signature with a sufficient level of assurance. Existing standards, such as the ETSI XAdES [XADES] profile for XML signatures [XMLDSIG11], ETSI PAdES [PADES] profile for PDF signatures [ISOPDF2], and ETSI CAdES [CADES] profile for CMS signatures [RFC 5652], can be used to extend the time within which a signature can be validated at the cost of significant complexity, which involves storing and validating significant amounts of external evidence data such as revocation data, signature time stamps, and archival time stamps. The Signature Validation Token (SVT) defined in this specification takes a trusted signature validation process as an input and preserves the validation result for the associated signature and signed document. The SVT asserts that a particular electronic signature was successfully validated by a trusted authority according to defined procedures at a certain time. Those procedures MUST include checks that the signature match the signed document, checks that the signature can be validated by the signing certificate, and checks that the signing certificate pass certificate path validation [RFC 5280]. Those procedures MAY also include checks associated with a particular trust policy such as that an acceptable certificate policy [RFC 5280] [RFC 3647] was used to issue the signer's certificate and checks that an acceptable signature policy was used by the signer [RFC 3125]. Once the SVT is issued by a trusted authority, any future validation of that electronic signature can be satisfied by validating the SVT without any need to also revalidate the original electronic signature. As the SVT is used to preserve validation results obtained through applying existing standards for signature validation, it is complementary to and not a replacement for such standards, including the ETSI standards for long-term validation listed above. The SVT does, however, have the potentially positive effect that it may significantly reduce the need to apply complex long-term validation and preservation techniques for signature validation if an SVT is issued and applied to the signed document at an early stage where the signature can be validated without support of large amounts of external evidence. The use of SVTs may therefore drastically reduce the complexity of revalidation of old archived electronic signatures. The SVT can be signed with private keys and algorithms that provide confidence for a considerable time period. In fact, multiple SVTs can be used to offer greater assurance. For example, one SVT could be produced with a large RSA private key, a second one with a strong elliptic curve, and a third one with a quantum safe digital signature algorithm to protect against advances in computing power and cryptanalytic capabilities. Further, the trusted authority can add additional SVTs in the future using fresh private keys and signatures to extend the lifetime of the SVTs if necessary.

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 [RFC 2119] [RFC 8174] when, and only when, they appear in all capitals, as shown here. This document use the following terms:

Signed Data:

The data covered by a particular electronic signature. This is typically equivalent to the signed content of a document, and it represents the data that the signer intended to sign. In some cases, such as in some XML signatures, the Signed Data can be the collection of several data fragments each referenced by the signature. In the case of PDF, this is the data covered by the "ByteRange" parameter in the signature dictionary. In JSON Web Signature (JWS), this is the unencoded payload data (before base64url encoding).

Signed Bytes:

These are the actual bytes of data that were hashed and signed by the digital signature algorithm. In most cases, this is not the actual Signed Data but a collection of signature metadata that includes references (hash) of the Signed Data as well as information about algorithms and other data bound to a signature. In XML, this is the canonicalized SignedInfo element. In CMS and PDF signatures, this is the DER-encoded SignedAttributes structure. In JWS, this is the protected header and payload data formatted according to [RFC 7515].

When these terms are used as defined in this section, they appear with a capitalized first letter.

The Signature Validation Token (SVT) is created by a trusted service to assert evidence of successful electronic signature validation using a well-defined and trustworthy signature validation process. The SVT binds the validation result to the validated signature, the document signed by the signature, and the certificate of the signer. This allows a relying party to verify the validity of a signed document without having to revalidate the original signature or to reuse any of its associated cryptographic algorithms for as long as the SVT itself can be validated. The SVT achieves this by binding the following information to a specific electronic signature:

• A unique identification of the electronic signature.
• The data and metadata signed by the electronic signature.
• The signer's certificate that was validated as part of electronic signature verification.
• The certification path that was used to validate the signer's certificate.
• An assertion providing evidence of signature verification, the time the verification was performed, the procedures used to verify the electronic signature, and the outcome of the verification.
• An assertion providing evidence of the time at which the signature is known to have existed, the procedures used to validate the time of existence, and the outcome of the validation.

The SVT aims to support long-term validation that can be further extended into the future by applying the following strategies:

• by using secure algorithms with long life expectancy when signing the SVT
• by reissuing the SVT before it becomes insecure or is considered expired
• optionally, by issuing multiple SVTs with different algorithms to provide redundancy in case one algorithm is broken

The SVT is carried in a JSON Web Token (JWT) as defined in [RFC 7519].

The contents of claims in an SVT are specified using the following data types:

String:

JSON Data Type of string that contains an arbitrary case-sensitive string value.

Base64Binary:

JSON Data Type of string that contains a Base64-encoded byte array of binary data.

StringOrURI:

JSON Data Type of string that contains an arbitrary string or a URI as defined in [RFC 7519]. It is REQUIRED to contain the colon character (":") to be a URI.

URI:

JSON Data Type of string that contains a URI as defined in [RFC 7519].

Integer:

JSON Data Type of number that contains a 32-bit signed integer value (from-2³¹ to 2³¹-1).

Long:

JSON Data Type of number that contains a 64-bit signed integer value (from -2⁶³ to 2⁶³-1).

NumericDate:

JSON Data Type of number that contains data as defined in [RFC 7519], which is the number of seconds from 1970-01-01T00:00:00Z UTC until the specified UTC date/time, ignoring leap seconds.

Boolean:

JSON Data Type of boolean that contains the explicit value of true orfalse.

Object<Class>:

A JSON object holding a claims object of a class defined in thisspecification (see Section 3.2.2).

Map<Type>:

A JSON object with name-value pairs where the value is an object of thespecified Type in the notation. For example, Map<String> is a JSONobject with name-value pairs where all values are of type String.

Array:

A JSON array of a specific data type as defined in this section. An arrayis expressed in this specification by square brackets. For example, [String]indicates an array of String values, and [Object<DocHash>] indicates anarray of DocHash objects.

Null:

A JSON null that represents an absent value. A claim with a null value isequivalent with an absent claim.

The SVT MUST contain only JWT claims in the following list:

"jti":

A String data type that is a "JWT ID" registered claim according to [RFC 7519]. It is RECOMMENDED that the identifier holds a hexadecimal string representation of a 128-bit unsigned integer. An SVT MUST contain one "JWT ID" claim.

"iss":

A StringOrURI data type that is an "Issuer" registered claim according to [RFC 7519], which is an arbitrary unique identifier of the SVT issuer. This value SHOULD have the value of a URI based on a domain owned by the issuer. An SVT MUST contain one "Issuer" claim.

"iat":

A NumericDate data type that is an "Issued At" registered claim according to [RFC 7519], which expresses the time when this SVT was issued. An SVT MUST contain one "Issued At" claim.

"aud":

A [StringOrURI] data type or a StringOrURI data type that is an "Audience" registered claim according to [RFC 7519]. The audience claim is an array of one or more identifiers, identifying intended recipients of the SVT. Each identifier MAY identify a single entity, a group of entities, or a common policy adopted by a group of entities. If only one value is provided, it MAY be provided as a single StringOrURI data type value instead of as an array of values. Inclusion of the "Audience" claim in an SVT is OPTIONAL.

"exp":

A NumericDate data type that is an "Expiration Time" registered claim according to [RFC 7519], which expresses the time when services and responsibilities related to this SVT are no longer provided by the SVT issuer. The precise meaning of the expiration time claim is defined by local policies. See implementation note below. Inclusion of the "Expiration Time" claim in an SVT is OPTIONAL.

"sig_val_claims":

An Object<SigValidation> data type that contains signature validation claims for this SVT extending the standard registered JWT claims above. An SVT MUST contain one sig_val_claims claim.

Note: An SVT asserts that a particular validation process was undertaken at a stated time. This fact never changes and never expires. However, some other aspects of the SVT such as liability for false claims or service provision related to a specific SVT may expire after a certain period of time, such as a service where an old SVT can be upgraded to a new SVT signed with fresh keys and algorithms.

The sig_val_claims JWT claim uses the SigValidation object class. A SigValidation object holds all custom claims, and a SigValidation object contains the following parameters:

"ver":

A String data type representing the version. This parameter MUST be present and the version in this specification indicated by the value "1.0".

"profile":

A StringOrURI data type representing the name of a profile that defines conventions followed for specific claims and any extension points used by the SVT issuer. This parameter MUST be present.

"hash_algo":

A URI data type that identifies the hash algorithm used to compute the hash values within the SVT. The URI identifier MUST be one defined in [RFC 9231] or in the IANA registry defined by this specification. This parameter MUST be present.

"sig":

An [Object<Signature>] data type that gives information aboutvalidated electronic signatures as an array of Signature objects. If the SVTcontains signature validation evidence for more than one signature, then eachsignature is represented by a separate Signature object. At least oneSignature object MUST be present.

"ext":

A Map<String> data type that provides additional claims related tothe SVT. Extension claims are added at the discretion of the SVT issuer;however, extension claims MUST follow any conventions definedin a profile of this specification (see Section 4). Inclusionof this parameter is OPTIONAL.

The sig parameter in the SigValidation object class uses the Signature object class. The Signature object contains claims related to signature validation evidence for one signature, and it contains the following parameters:

"sig_ref":

An Object<SigReference> data type that contains referenceinformation identifying the target signature. This parameterMUST be present.

"sig_data_ref":

An [Object<SignedDataReference>] data type that contains an array ofreferences to Signed Data that was signed by the target electronicsignature. At least one SignedDataReference object MUST bepresent.

"signer_cert_ref":

An Object<CertReference> data type that references the signer'scertificate and optionally references a supporting certification path thatwas used to verify the target electronic signature. This parameterMUST be present.

"sig_val":

An [Object<PolicyValidation>] data type that contains an array ofresults of signature verification according to defined procedures. At leastone PolicyValidation object MUST be present.

"time_val":

An [Object<TimeValidation>] data type that contains an array of timeverification results showing that the target signature has existed at a specifictime in the past. Inclusion of this parameter is OPTIONAL.

"ext":

A MAP<String> data type that provides additional claims related tothe target signature. Extension claims are added at the discretion of the SVTissuer; however, extension claims MUST follow any conventionsdefined in a profile of this specification (see Section 4). Inclusion of this parameter is OPTIONAL.

The sig_ref parameter in the Signature object class uses the SigReference object class. The SigReference object provides information used to match the Signature claims object to a specific target electronic signature and to verify the integrity of the target signature value and Signed Bytes, and it contains the following parameters:

"id":

A String data type that contains an identifier assigned to the targetsignature. Inclusion of this parameter is OPTIONAL.

"sig_hash":

A Base64Binary data type that contains a hash value of the targetelectronic signature value. This parameter MUST be present.

"sb_hash":

A Base64Binary data type that contains a hash value of the Signed Bytes ofthe target electronic signature. This parameter MUST bepresent.

The sig_data_ref parameter in the Signature object class uses the SignedDataReference object class. The SignedDataReference object provides information used to verify the target electronic signature references to Signed Data as well as to verify the integrity of all data that is signed by the target signature, and it contains the following parameters:

"ref":

A String data type that contains a reference identifier for the data ordata fragment covered by the target electronic signature. This parameterMUST be present.

"hash":

A Base64Binary data type that contains the hash value for the data coveredby the target electronic signature. This parameter MUST bepresent.

The sig_val parameter in the Signature object class uses the PolicyValidation object class. The PolicyValidation object provides information about the result of a validation process according to a specific policy, and it contains the following parameters:

"pol":

A StringOrURI data type that contains the identifier of the policy governing the electronic signature verification process. This parameter MUST be present.

"res":

A String data type that contains the result of the electronic signature verification process. The value MUST be one of "PASSED", "FAILED", or "INDETERMINATE" as defined by [ETSI319102-1]. This parameter MUST be present.

"msg":

A String data type that contains a message describing the result. Inclusion of this parameter is OPTIONAL.

"ext":

A MAP<String> data type that provides additional claims related to the target signature. Extension claims are added at the discretion of the SVT issuer; however, extension claims MUST follow any conventions defined in a profile of this specification (see Section 4). Inclusion of this parameter is OPTIONAL.

The time_val parameter in the Signature object class uses the TimeValidation object class. The TimeValidation claims object provides information about the result of validating evidence of time asserting that the target signature existed at a particular time in the past. Evidence of time is typically a timestamp according to [RFC 3161], but other types of evidence may be used such as a previously issued SVT for this signature. The TimeValidation claims object contains the following parameters:

"time":

A NumericDate data type that contains the verified time. This parameter MUST be present.

"type":

A StringOrURI data type that contains an identifier of the type of evidence of time. This parameter MUST be present.

"iss":

A StringOrURI data type that contains an identifier of the entity that issued the evidence of time. This parameter MUST be present.

"id":

A String data type that contains an unique identifier assigned to the evidence of time. Inclusion of this parameter is OPTIONAL.

"hash":

A Base64Binary data type that contains the hash value of the validated evidence of time. Inclusion of this parameter is OPTIONAL.

"val":

An [Object<PolicyValidation>] data type that contains an array of results of the time evidence validation according to defined validation procedures. Inclusion of this parameter is OPTIONAL.

"ext":

A MAP<String> data type that provides additional claims related to the target signature. Extension claims are added at the discretion of the SVT issuer; however, extension claims MUST follow any conventions defined in a profile of this specification (see Section 4). Inclusion of this parameter is OPTIONAL.

The signer_cert_ref parameter in the Signature object class uses the CertReference object class. The CertReference object references a single X.509 certificate or a X.509 certification path either by providing the certificate data or by providing hash references for certificates that can be located in the target electronic signature, and it contains the following parameters:

"type":

A StringOrURI data type that contains an identifier of the type of reference. The type identifier MUST be one of the identifiers defined below, an identifier specified by the selected profile, or a URI identifier. This parameter MUST be present.

"ref":

A [String] data type that contains an array of string parameters according to conventions defined by the type identifier. At least one parameter MUST be present.

The following type identifiers are defined:

"chain":

The ref contains an array of Base64-encoded X.509 certificates [RFC 5280]. The certificates MUST be provided in the order starting with the end entity certificate. Any following certificate must be able to validate the signature on the previous certificate in the array.

"chain_hash":

The ref contains an array of one or more Base64-encoded hash values where each hash value is a hash over a X.509 certificate [RFC 5280] used to validate the signature. The certificates MUST be provided in the order starting with the end entity certificate. Any following certificate must be able to validate the signature on the previous certificate in the array. This option MUST NOT be used unless all hashed certificates are present in the target electronic signature.

Note: All certificates referenced using the identifiers above are X.509 certificates. Profiles of this specification MAY define alternative types of public key containers; however, a major function of these referenced certificates is not just to reference the public key but also to provide the subject name of the signer. It is therefore important for the full function of an SVT that the referenced public key container also provides the means to identify the signer.

The SVT JWT MUST contain the following JSON Object Signing and Encryption (JOSE) header parameters in accordance with Section 5 of RFC 7519:

"typ":

This parameter MUST have the string value "JWT" (uppercase).

"alg":

This parameter identifies the algorithm used to sign the SVT JWT. Thealgorithm identifier MUST be specified in [RFC 7518] or the IANA "JSON Web Signature and Encryption Algorithms"registry [IANA-JOSE-REG]. The specified signature hashalgorithm MUST be identical to the hash algorithm specified inthe hash_algo parameter of the SigValidation object within the sig_val_claimsclaim.

The SVT header MUST contain a public key or a reference to a public key used to verify the signature on the SVT in accordance with [RFC 7515]. Each profile, as discussed in Section 4, MUST define the requirements for how the key or key reference is included in the header.

Each signed document and signature type will have to define the precise content and use of several claims in the SVT. At a minimum, each profile MUST define:

• The identifier of the profile
• How to reference the Signed Data content of the signed document
• How to reference the target electronic signature and the Signed Bytes of the signature
• How to reference certificates supporting each electronic signature
• How to include public keys or references to public keys in the SVT
• Whether each electronic signature is supported by a single SVT, or one SVT may support multiple electronic signatures of the same document

A profile MAY also define:

• Explicit information on how to perform signature validation based on an SVT
• How to attach an SVT to an electronic signature or signed document

The following profiles are defined in appendixes of this document:

XML Signature Profile

PDF Signature Profile

JWS Profile

Other documents MAY define other profiles that MAY complement, amend, or supersede these profiles.

Signature verification based on an SVT MUST follow these steps:

1. Select the most recent SVT that can be successfully validated and meets the requirement of the relying party.
2. Verify the integrity of the signature and the Signed Bytes of the target electronic signature using the sig_ref claim.
3. Verify that the Signed Data reference in the original electronic signature matches the reference values in the sig_data_ref claim.
4. Verify the integrity of referenced Signed Data using provided hash values in the sig_data_ref claim.
5. Obtain the verified certificates supporting the asserted electronic signature verification through the signer_cert_ref claim.
6. Verify that signature validation policy results satisfy the requirements of the relying party.
7. Verify that verified time results satisfy the context for the use of the signed document.

After successfully performing these steps, signature validity is established as well as the trusted signer certificate binding the identity of the signer to the electronic signature.

IANA has registered the "sig_val_claims" claim name in the "JSON Web Token Claims" registry established by Section 10.1 of RFC 7519.

Claim Name:

sig_val_claims

Claim Description:

Signature Validation Token

Change Controller:

IESG

Specification Document(s):

Section 3.2.3 of RFC 9321

IANA has registered the "svt" Header Parameter in the "JSON Web Signature and Encryption Header Parameters" registry established by [RFC 7515].

Header Parameter Name:

svt

Header Parameter Description:

Signature Validation Token

Header Parameter Usage Location(s):

JWS

Change Controller:

IESG

Specification Document(s):

Appendix C.1.1 of RFC 9321

An SVT allows a signature verifier to still validate the original signature using the original signature data and to use the information in the SVT selectively to confirm the validity and integrity of the original data, such as confirming the integrity of Signed Data or the validity of the signer's certificate, etc. Another way to use an SVT is to completely rely on the validation conclusion provided by the SVT and to omit revalidation of the original signature value and original certificate status checking data. This choice is a decision made by the verifier according to its own policy and risk assessment. However, even when relying on the SVT validation conclusion of an SVT, it is vital to still verify that the present SVT is correctly associated with the document and signature that is being validated by validating the hashed reference data in the SVT of the signature, signing certificate chain, Signed Data, and the Signed Bytes.

Even if the SVT provides protection against algorithms becoming weakened or broken over time, this protection is only valid for as long as the algorithms used to sign the SVT are still considered secure. It is advisable to reissue SVTs in cases where an algorithm protecting the SVT is getting close to its end of life. One way to increase the resistance of algorithms becoming insecure, is to issue multiple SVTs for the same signature with different algorithms and key lengths where one algorithm could still be secure even if the corresponding algorithm used in the alternative SVT is broken.

[CADES]

ETSI, "Electronic Signatures and Infrastructures (ESI); CAdES digital signatures; Part 1: Building blocks and CAdES baseline signatures", ETSI EN 319 122-1, April 2016.

[ETSI319102-1]

ETSI, "Electronic Signatures and Infrastructures (ESI); Procedures for Creation and Validation of AdES Digital Signatures; Part 1: Creation and Validation", ETSI EN 319 102-1, May 2016.

[IANA-JOSE-REG]

IANA, "JSON Object Signing and Encryption (JOSE)",
<https://www.iana.org/assignments/jose/>.

[ISOPDF2]

ISO, "Document management -- Portable document format -- Part 2: PDF 2.0", ISO 32000-2:2020, December 2020.

[PADES]

ETSI, "Electronic Signatures and Infrastructures (ESI); PAdES digital signatures; Part 1: Building blocks and PAdES baseline signatures", ETSI EN 319 142-1, April 2016.

[RFC2119]

S. Bradner, "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>.

[RFC3125]

J. Ross, D. Pinkas, and N. Pope, "Electronic Signature Policies", RFC 3125, DOI 10.17487/RFC3125, September 2001,
<https://www.rfc-editor.org/info/rfc3125>.

[RFC3161]

C. Adams, P. Cain, D. Pinkas, and R. Zuccherato, "Internet X.509 Public Key Infrastructure Time-Stamp Protocol (TSP)", RFC 3161, DOI 10.17487/RFC3161, August 2001,
<https://www.rfc-editor.org/info/rfc3161>.

[RFC3647]

S. Chokhani, W. Ford, R. Sabett, C. Merrill, and S. Wu, "Internet X.509 Public Key Infrastructure Certificate Policy and Certification Practices Framework", RFC 3647, DOI 10.17487/RFC3647, November 2003,
<https://www.rfc-editor.org/info/rfc3647>.

[RFC5035]

J. Schaad, "Enhanced Security Services (ESS) Update: Adding CertID Algorithm Agility", RFC 5035, DOI 10.17487/RFC5035, August 2007,
<https://www.rfc-editor.org/info/rfc5035>.

[RFC5280]

D. Cooper, S. Santesson, S. Farrell, S. Boeyen, R. Housley, 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>.

[RFC5652]

R. Housley, "Cryptographic Message Syntax (CMS)", STD 70, RFC 5652, DOI 10.17487/RFC5652, September 2009,
<https://www.rfc-editor.org/info/rfc5652>.

[RFC7515]

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

[RFC7518]

M. Jones, "JSON Web Algorithms (JWA)", RFC 7518, DOI 10.17487/RFC7518, May 2015,
<https://www.rfc-editor.org/info/rfc7518>.

[RFC7519]

M. Jones, J. Bradley, and N. Sakimura, "JSON Web Token (JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
<https://www.rfc-editor.org/info/rfc7519>.

[RFC8174]

B. Leiba, "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>.

[RFC9231]

D. Eastlake 3rd, "Additional XML Security Uniform Resource Identifiers (URIs)", RFC 9231, DOI 10.17487/RFC9231, July 2022,
<https://www.rfc-editor.org/info/rfc9231>.

[XADES]

ETSI, "Electronic Signatures and Infrastructures (ESI); XAdES digital signatures; Part 1: Building blocks and XAdES baseline signatures", ETSI EN 319 132-1, April 2016.

[XMLDSIG11]

D. Eastlake 3rd, J. Reagle, D. Solo, F. Hirsch, M. Nystrom, T. Roessler, and K. Yiu, "XML Signature Syntax and Processing Version 1.1", W3C Proposed Recommendation, April 2013.

[RFC8610]

H. Birkholz, C. Vigano, 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/info/rfc8610>.

This appendix defines a profile for implementing SVTs 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 an 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.

When referring to elements from the W3C XML Signature namespace (https://www.w3.org/2000/09/xmldsig#), the following syntax is used:

• <ds:Signature>

When referring to elements from the ETSI XAdES XML Signature namespace (https://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>

When SVTs are 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 Appendix A.2.1.

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. 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 does 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 a signature using signed information in the SVT itself. The <svt:SignatureValidationToken> 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:

If a new SVT is stored in a signature that already contains a previously issued SVT, implementations can choose either to 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.

When this profile is used, the SigValidation object MUST contain a "profile" claim with the value "XML".

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 generate the signature value).

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 that were identified by the corresponding <ds:Reference>element after applying all identified canonicalization and transformationalgorithms. These are the same bytes that are hashed by the hash value in the<ds:DigestValue> element inside the <ds:Reference> element.

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.

The SVT JOSE header for XML signatures must contain one of the following header parameters in accordance with [RFC 7515] for storing a reference to the public key used to verify the signature on the SVT:

"x5c":

Holds an X.509 certificate [RFC 5280] 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.

This appendix defines a profile for implementing SVTs with a signed PDF document, and it defines the following aspects of SVT usage:

• How to include reference data related to PDF signatures and PDF documents in an SVT.
• How to add an SVT token to a PDF document.

PDF document signatures are added as incremental updates to the signed PDF document and signs all data of the PDF document up until the current signature. When more than one signature is added to a PDF document the previous signature is signed by the next signature and can not be updated with additional data after this event. To minimize the impact on PDF documents with multiple signatures and to stay backwards compatible with PDF software that does not understand SVTs, PDF documents add one SVT token for all signatures of the PDF as an extension to a document timestamp added to the signed PDF as an incremental update. This SVT covers all signatures of the signed PDF.

The SVT for a signed PDF document MAY provide signature validation information about any of the present signatures in the PDF. The SVT MUST contain a separate "sig" claim (Signature object) for each signature on the PDF that is covered by the SVT. An SVT added to a signed PDF document MUST be added to a document timestamp in accordance with ISO 32000-2:2020 [ISOPDF2]. The document timestamp contains an [RFC 3161] timestamp token (TSTInfo) in EncapsulatedContentInfo of the CMS signature. The SVT MUST be added to the timestamp token (TSTInfo) as an Extension object as defined in Appendix B.1.1.

The SVT extension is an Extension suitable to be included in TSTInfo as defined by [RFC 3161]. The SVT extension is identified by the Object Identifier (OID) 1.2.752.201.5.2. This extension data (OCTET STRING) holds the bytes of SVT JWT, represented as a UTF-8-encoded string. This extension MUST NOT be marked critical. Note: Extensions in timestamp tokens according to [RFC 3161] are imported from the definition of the X.509 certificate extensions defined in [RFC 5280].

When this profile is used, the SigValidation object MUST contain a "profile" claim with the value "PDF".

The SVT Signature object MUST contain a "sig_ref" claim (SigReference object) with the following elements:

"id":

Absent or a Null value.

"sig_hash":

The hash over the signature value bytes.

"sb_hash":

The hash over the DER-encoded SignedAttributes in SignerInfo.

The SVT Signature object MUST contain one instance of the "sig_data" claim (SignedData object) with the following elements:

"ref":

The string representation of the ByteRange value of the PDF signature dictionary of the target signature. This is a sequence of integers separated by space where each integer pair specifies the start index and length of a byte range.

"hash":

The hash of all bytes identified by the ByteRange value. This is the concatenation of all byte ranges identified by the ByteRange value.

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.

Note: The referenced signer certificate MUST match any certificates referenced using ESSCertID or ESSCertIDv2 from [RFC 5035].

The SVT JOSE header must contain one of the following header parameters in accordance with [RFC 7515] for storing a reference to the public key used to verify the signature on the SVT:

"x5c":

Holds an X.509 certificate [RFC 5280] 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. The referenced certificate SHOULD be the same certificate that was used to sign the document timestamp that contains the SVT.

This appendix defines a profile for implementing SVTs with a JWS signed payload according to [RFC 7515], and it defines the following aspects of SVT usage:

• How to include reference data related to JWS signatures in an SVT.
• How to add an SVT token to JWS signatures.

A JWS may have one or more signatures, depending on its serialization format, signing the same payload data. A JWS either contains the data to be signed (enveloping) or may sign any externally associated payload data (detached). To provide a generic solution for JWS, an SVT is added to each present signature as a JWS Unprotected Header. If a JWS includes multiple signatures, then each signature includes its own SVT.

An SVT token MAY be added to any signature of a JWS to support validation of that signature. If more than one signature is present, then each present SVT MUST provide information exclusively related to one associated signature and MUST NOT include information about any other signature in the JWS. Each SVT is stored in its associated signature's "svt" header as defined in Appendix C.1.1.

The "svt" (Signature Validation Token) Header Parameter is used to contain an array of SVT tokens to support validation of the associated signature. Each SVT token in the array has the format of a JWT as defined in [RFC 7519] and is stored using its natural string representation without further wrapping or encoding. The "svt" Header Parameter, when used, MUST be included as a JWS Unprotected Header. Note: A JWS Unprotected Header is not supported with JWS Compact Serialization. A consequence of adding an SVT token to a JWS is therefore that JWS JSON Serialization MUST be used either in the form of general JWS JSON Serialization (for one or more signatures) or in the form of flattened JWS JSON Serialization (optionally used when only one signature is present in the JWS).

If a new SVT is stored in a signature that already contains a previously issued SVT, implementations can choose either to replace the existing SVT or to store the new SVT in addition to the existing SVT. If a JWS signature already contains an array of SVTs and a new SVT is to be added, then the new SVT MUST be added to the array of SVT tokens in the existing "svt" Header Parameter.

When this profile is used, the SigValidation object MUST contain a "profile" claim with the value "JWS".

The SVT Signature object MUST contain a "sig_ref" claim (SigReference object) with the following elements:

"sig_hash":

The hash over the associated signature value (the bytes of the base64url-decoded signature parameter).

"sb_hash":

The hash over all bytes signed by the associated signature (the JWS Signing Input according to [RFC 7515]).

The SVT Signature object MUST contain one instance of the "sig_data" claim (SignedData object) with the following elements:

"ref":

This parameter MUST hold one of the following three possible values:

1. The explicit string value "payload" if the signed JWS Payload is embedded in a "payload" member of the JWS.
2. The explicit string value "detached" if the JWS signs detached payload data without explicit reference.
3. A URI that can be used to identify or fetch the detached Signed Data. The means to determine the URI for the detached Signed Data is outside the scope of this specification.

"hash":

The hash over the JWS Payload data bytes (not its base64url-encoded string representation).

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 JOSE header using the "x5c" Header Parameter.

The SVT JOSE header must contain one of the following header parameters in accordance with [RFC 7515] for storing a reference to the public key used to verify the signature on the SVT:

"x5c":

Holds an X.509 certificate [RFC 5280] 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.

The following informative CDDL [RFC 8610] expresses the structure of an SVT token:

The following informative JSON schema describes the syntax of the SVT token payload.

The following example illustrates a basic SVT according to this specification issued for a signed PDF document. Note: Line breaks in the decoded example are inserted for readability. Line breaks are not allowed in valid JSON data. Signature validation token JWT: Decoded JWT Header: Decoded JWT Claims:

Stefan Santesson

Russ Housley