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Re: Best Practices - Timestamps & Nonces

From: Konrad Lanz <Konrad.Lanz@iaik.tugraz.at>
Date: Tue, 15 Apr 2008 15:08:38 +0200
Message-ID: <4804A8D6.9010200@iaik.tugraz.at>
To: Hal Lockhart <hlockhar@bea.com>
CC: public-xmlsec-maintwg@w3.org
Hi Hal,

Hal Lockhart wrote:
> Long lived signatures should include a timestamp to indicate the time of
> signing just as a handwritten signature does. Note that in the absence
> of a trusted time source, such a timestamp should be viewed as
> indicating a minimum, but not a maximum age. This is because we assume
> that a date in the future would be noticed during processing. So if the
> date does not indicate when the signature was computed it at least
> indicates earliest date it might have been made available for
> processing.
>   
I think it would be worth to consider to include some sources so a
reader can follow up on relevant references.

What I have found in a first quick browse was the following, if someone
knows better sources please let me know:

CWA 14171:2004 [1]:
> A time stamp by itself does not confirm the exact time when an
> electronic document was signed. A time
> stamp is obtained by sending the hash value of the given data to the
> TSA. The returned time-stamp is a
> signed document which contains the hash value, the identity of the
> TSA, and the time of stamping. This
> proves that the given data existed before the time of stamping.
> If the hash of a digital signature is sent to a TSA and is
> time-stamped before the revocation of the certificate
> used to generate that signature, evidence will be provided that the
> digital signature was formed before the
> revocation of the public key certificate.

[2]
http://www.w3.org/TR/XAdES/#Qualifying_properties_syntax_Auxiliary_syntax_The_TimeStampType_data_type
> Additionally, time-stamps proving that some or all the data objects to
> be signed have been created before some time can also be added as
> signed properties to the XAdES.

[2]
http://www.w3.org/TR/XAdES/#Syntax_for_XAdES_T_form_The_SignatureTimeStamp_element

> If a recipient wants to hold a valid electronic signature he will have
> to ensure that he has obtained a valid time-stamp for it, before that
> key (and any key involved in the validation) is revoked. The sooner
> the time-stamp is obtained after the signing time, the better.


[2] XAdES 1.3.2
http://webapp.etsi.org/workprogram/Report_WorkItem.asp?wki_id=21353
XAdES 1.1.1 (is not up to date any more)
http://www.w3.org/TR/XAdES/

As XAdES 1.3.2 is currently not directly linkable I linked the old
version of XAdES ... ;-(

regards

Konrad

P.S: Let's also check what is there in
http://www.ietf.org/rfc/rfc3161.txt already that simply translates to
XMLDSig with timestamps.

-- 
Konrad Lanz, IAIK/SIC - Graz University of Technology
Inffeldgasse 16a, 8010 Graz, Austria
Tel: +43 316 873 5547
Fax: +43 316 873 5520
https://www.iaik.tugraz.at/aboutus/people/lanz
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Received on Tuesday, 15 April 2008 13:09:28 GMT

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