Internet-Draft                                       Thomas Gindin
PKIX WG                                                IBM Corp.
Intended Category: Informational
Expires: 28 February 2000                          28 August, 1999



                 Internet X.509 Public Key Infrastructure
                Technical Requirements for a non-Repudiation Service
                 <draft-gindin-pkix-technr-00.txt>


STATUS OF THIS MEMO

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ABSTRACT

This document describes those features of a service which processes
signed doucments which must be present in order for that service to
constitute a "technical non-repudiation" service.  A technical
non-repudiation service must permit an independent verifier to
determine whether a given signature was applied to a given data object
by the private key associated with a given valid certificate, at a time
later than the signature.  The features of a technical non-repudiation
service are expected to be necessary for a full non-repudiation service,
although they may not be sufficient.

This document is intended to clarify the definition of the
"non-repudiation" service in RFC 2459.  It should thus serve as a guide
to when the nonRepudiation bit of the keyUsage extension should be used
and to when a Certificate Authority is required to archive CRL's.


 Introduction

RFC 2459 [1] specifies a bit within the KeyUsage extension called the
nonRepudiation bit which is "asserted when the subject public key is
used to verify digital signatures used to provide a non-repudiation
service which protects against the signing entity falsely denying some
action, excluding certificate or CRL signing."  Extensive discussions
in the PKIX WG have revealed that the description of the non-repudiation
service contained in this passage is not widely enough understood or
agreed upon to characterize any given service as providing or not
providing a non-repudiation service.  Two major categories of service
have been proposed as potentially providing a non-repudiation service:
the technical non-repudiation service, which this draft attempts to
define with greater precision, and a full non-repudiation service
which is intended to prevent all possible repudiations of a signed
object or document.  Since a full non-repudiation service is required
to meet all the requirements of this technical non-repudiation service
as a prerequisite, the technical non-repudiation service's definition
is necessary for both.


1.1     Definitions

Signing Certificate:    A certificate containing the key pair whose
private key was used to create the signature being verified.

Signer:         The party who created the signature being verified.  It
is outside the scope of these requirements to distinguish between the
actual signer and the holder of the signing certificate.

Relying Party:  The party who received the signature being verified, and
initially verified it.

Verifier:       An entity independent of both the signer and the relying
party who is verifying that the supplied signature, data object, and
certificate are consistent with each other.

1-way NR:       A service in which the relying party preserves
sufficient evidence to permit the verifier to perform a verification,
and may submit it for verification by his or her own action.

2-way NR:       A service in which the relying party submits
sufficient evidence to permit the verifier to perform a verification
o a third party, known as the "escrow holder".

Escrow holder:  The party responsible for preserving signature evidence
in 2-way NR.  The escrow holder may also be, but need not be, the
verifier.

Escrow package: The data submitted from the relying party to the escrow
holder, in 2-way NR.  The escrow holder may add certain auditing and
tracking information to this package before storage.

NR service:     The technical nonRepudiation service referenced above.

keyUsage extension: A standard extension within X.509v3 certificates
with object identifier { 2 5 29 15 }, consisting of a series of
enumerated bits.

NR bit:         The nonRepudiation bit (offset 1) of the keyUsage
extension.


1.2     Scope and caveats

        The NR service is expected to provide evidence that a given
object was signed by the private key corresponding to a given
certificate which was valid at the time of signature.  It is not
anticipated that the use of the NR service will ordinarily constitute
execution of a contract, or acceptance of any other legal obligation.
It is anticipated that the use of this service in accepting legal
obligations will be the subject of legislation or judicial decision
in various jurisdictions, which are likely to lay additional technical
burdens upon the provision of such a service to such an extent as to
constitute another, larger service which need not be the same in all
jurisdictions.  It is outside the scope of the definition of this
service to provide evidence that the signer and the holder of the
signing certificate are the same, that the signer has been adequately
informed of the content which is signed, that the signer is not acting
under duress, etc.

       Requirements for both 1-way and 2-way NR

2.1     The signer must submit, with the signature, the signing
certificate or an unambiguous identifier of that certificate.
Unambiguous identifiers of certificates include the combination of a
certificate serial number with an issuer name.

2.2     The signer must submit, with the signature, the content being
signed or an unambiguous reference to that content.  It is explicitly
contemplated that a URI constitutes an unambiguous reference to its
content.

2.3     The signer must include, in the base over which the signature
is calculated, the time at which the signature was created.

2.4     The relying party must, before accepting the signature, verify
that the signing certificate is valid.  This verification should include
a CRL check.

2.5     The relying party must, before accepting the signature, verify
the signature of the data object being submitted.

       Requirements for 1-way NR

3.1     The relying party must save a copy of the content being signed.

3.2     The relying party must save the identity of the signing
certificate, along with the content of the signature.

3.3     The relying party must check that the signing certificate
contains a keyUsage extension.  If the extension is not present or does
not contain the nonRepudiation bit, and the version of the certificate
is v3 or higher, the submission must be rejected.

       Requirements for 2-way NR

4.1     The relying party must submit to the escrow holder a copy of
the content being signed, the identity of the signing certificate, and
the signature.

4.2     The relying party must sign the submission to the escrow holder.
The relying party SHOULD include, in the base over which that signature
is calculated, the current time.  This time will be between the time
when the signer submitted the signature and the time when the package
is submitted.  The signed object submitted is known as the escrow
package.

4.3     The relying party must check whether or not the signing
certificate contains a keyUsage extension.  If the keyUsage extension
is present and the nonRepudiation bit is not set the submission must be
rejected.

 Copyright

Copyright (C) The Internet Society (date). All Rights Reserved.

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The limited permissions granted above are perpetual and will not be
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 References

[] R. Housley, W. Ford, W. Polk, and D. Solo "Internet X.509 Public Key
Infrastructure Certificate and CRL Profile", RFC 2459, January 1999
[2] X.509(97)


 Author's Address

Thomas Gindin
IBM Corporation
 North Frederick Ave.
Gaithersburg, MD 20879
USA

Email: tgindin@us.ibm.com

Internet-Draft  Technical Requirements for a non-Repudiation Service
Expires: 28 February 2000