OASIS Digital Signature Services TC
Nick Pope, Thales eSecurity
Juan Carlos Cruellas, Centre d'aplicacions avançades d’Internet (UPC)
Trevor Perrin, individual
Juan Carlos Cruellas, Centre d'aplicacions avançades d’Internet (UPC)
This specification is related to:
This document profiles the OASIS DSS core protocols for the purpose of creating and verifying XML-encoded time-stamps.
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The DSS signing and verifying protocols are defined in [DSSCore]. As defined in that document, these protocols have a fair degree of flexibility and extensibility. This document profiles these protocols to limit their flexibility and extend them in concrete ways. The resulting profile is suitable for implementation and interoperability.
The following sections describe how to understand the rest of this document.
The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”,
“SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” in this specification are to be interpreted as described in IETF RFC 2119 [RFC 2119]. These keywords are capitalized when used to unambiguously specify requirements over protocol features and behavior that affect the interoperability and security of implementations. When these words are not capitalized, they are meant in their natural-language sense.
This specification uses the following typographical conventions in text: <ns:Element>, Attribute, Datatype, OtherCode.
[Core-XSD] S. Drees et al. DSS Schema. OASIS, February 2007
[DSSCore] S. Drees et al. Digital Signature Service Core Protocols and Elements. OASIS, February 2007
[TST-XSD] T. Perrin et al. Timestamping Profile Schema, OASIS, , February 2007
[RFC 2119] S. Bradner. Key words for use in RFCs to Indicate Requirement Levels. http://www.ietf.org/rfc/rfc2396.txt, IETF RFC 2396, August 1998.
[XML-ns] T. Bray, D. Hollander, A. Layman. Namespaces in XML. http://www.w3.org/TR/1999/REC-xml-names-19990114, W3C Recommendation, January 1999.
[XMLSig] D. Eastlake et al. XML-Signature Syntax and Processing. http://www.w3.org/TR/1999/REC-xml-names-19990114, W3C Recommendation, February 2002.
The structures described in this specification are contained in the schema file [TST-XSD]. All schema listings in the current document are excerpts from the schema file. In the case of a disagreement between the schema file and this document, the schema file takes precedence.
This schema is associated with the following XML namespace:
Conventional XML namespace prefixes are used in this document:
· The prefix dss: stands for the DSS core namespace [Core-XSD].
Applications MAY use different namespace prefixes, and MAY use whatever namespace defaulting/scoping conventions they desire, as long as they are compliant with the Namespaces in XML specification [XML-ns].
This document profiles the DSS signing and verifying protocols defined in [DSSCore].
This profile is based directly on the [DSSCore].
This profile supports the creation and verification of isolated <dss:Timestamp> elements as defined in [DSSCore]. These elements can wrap different types of time-stamp tokens; this profile does not specify or constrain the internal structure of the <dss:Timestamp>, unless the <dss:SignatureType> optional input is used (see section 3.1.1).
This profile is transported using the HTTP POST Transport Binding defined in [DSSCore].
This profile is secured using the TLS X.509 Server Authentication Binding defined in [DSSCore].
The <dss:SignatureType> optional input from [DSSCore] is supported and may be sent by the client. The timestamping specific optional input <RenewTimestamp> may also be supported and may be sent by the client. No other optional inputs are supported.
The <dss:SignatureType> optional input may be one of these values, from section 7. of [DSSCore]:
Servers may support other values. However, servers are under no obligation to support any particular values. Thus, clients using the <dss:SignatureType> optional input may not interoperate with certain servers.
The <RenewTimestamp> optional input element indicates to the server that the current sign request is a request for the renewal of an existing timestamp on data that were timestamped in the past, so that the validity period of the existing timestamp is effectively extended.
If the <RenewTimestamp> optional input is present in the sign request submitted by the client to the server, and it is supported by the server, the <PreviousTimestamp> element contained in this optional input must also be present as an element of the resulting timestamp generated by the server and returned to the client. For XML timestamps of type <ds:signature>, processing rules are described in Section 3.2.3.
Before submitting the sign request, the client must verify that the <PreviousTimestamp> element corresponds to the document(s) being re-timestamped, and the client should verify the <PreviousTimestamp> element.
Note: Legitimate reasons to renew a timestamp include (a) the public key certificate used to verify the digital signature in the timestamp is nearing its expiration date, or (b) the client needs to replace the hash value used for the timestamped data in the existing timestamp with a hash value using a stronger hash algorithm.
The client MAY send any component of <dss:InputDocument> element as input document. The extraction and processing of these elements MUST be carried out as indicated in the core document, with the changes mentioned in the present document.
If the client is not sending the <dss:SignatureType> optional input, then the client SHOULD only send a single input document, since some types of time-stamps (e.g. RFC 3161) can only cover one document per time-stamp.
If the client is sending the <dss:SignatureType> optional input, then the client MAY send multiple input documents, if the client knows that the specified time-stamp type can handle them.
This profile defines no additional <ResultMinor> codes.
The server MUST NOT return any optional outputs.
The server MUST return a <dss:Timestamp> signature object.
If the <RenewTimestamp> optional input is present in the sign request submitted by the client to the server, and it is supported by the server, the <PreviousTimestamp> element contained in this optional input must also be present as an element of the resulting timestamp generated by the server and returned to the client. Specifically, for XML processing rules for XML timestamps of type <ds:signature>, the server must include the <PreviousTimestamp> element contained in the optional input as a child of an additional <ds:Signature>/<ds:Object> in the newly generated timestamp (i.e. in addition to the <ds:object> containing the <TstInfo>). An additional <ds:SignedInfo>/<ds:Reference> referencing the <ds:Object>/<dss:PreviousTimestamp> must be included in the signature of the new timestamp signature.
The server generating the new timestamp in response to a request carrying the <RenewTimestamp> optional input need make no assertions about the validity of the <PreviousTimestamp> element submitted to it within this optional input.
A server that does not support the <RenewTimestamp> optional input must reject the sign request with a <ResultMajor> code of RequesterError and a <ResultMinor> code urn:oasis:names:tc:dss:1.0:resultminor:NotSupported.
The client may submit the <UseVerificationTime> optional input to instruct the server to determine the timestamp's validity at the specified time, instead of the current time. No other optional inputs are supported.
The client MUST send a <dss:Timestamp> signature object.
Note: A timestamp T2 that was generated by a server in response to a renewal request for timestamp T1, that is, in response to a sign request on the same data as for timestamp T1 and carrying timestamp T1 within the <PreviousTimestamp> element of the <RenewTimestamp> optional input, may be used to assert current time validity for timestamp T1. This situation applies when timestamp T1's current time validity can no longer be asserted independently, for example, because the cryptographic primitives in timestamp T1 are considered compromised. Specifically, the client may:
· submit a verify request for timestamp T2,
· submit a verify request for timestamp T1 and include the optional input <UseVerificationTime> with a value set to the issue time of timestamp T2 (i.e. using element <SpecificTime>).
If the result codes in the server verify responses indicate that both timestamps are valid as requested, the client may assert that timestamp T1 is currently valid, as supported by the fact that timestamp T1 is considered valid at the issue time of timestamp T2, and timestamp T2 is considered valid currently. This process may be generalized to timestamps that were generated after multiple renewal requests on the same data, that is, timestamp T1, renewed by timestamp T2, renewed by timestamp T3, and so on.
The client MAY send any component of <dss:InputDocuments> element as input documents. The extraction and processing of these elements MUST be carried out as indicated in the core document, with the changes mentioned in the present document.
This profile defines no additional <dss:ResultMinor> codes.
The server MUST return the <dss:SigningTimeInfo> optional output.
The server MUST return this optional output profiled as detailed below:
The server MUST NOT return any other optional outputs.
The following individuals have participated in the creation of this specification and are gratefully acknowledged:
Dimitri Andivahis, Surety
Frederick Hirsch, Nokia
Pieter Kasselman, Betrusted
Andreas Kuehne, individual
Paul Madsen, Entrust
John Messing, American Bar Association
Tim Moses, Entrust
Nick Pope, Thales eSecurity
Rich Salz, DataPower
Ed Shallow, Universal Postal Union