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Re: [Rats] Requesting a Nonce from a Verifier

hannes.tschofenig@gmx.net Sun, 03 March 2024 10:51 UTC

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From: hannes.tschofenig@gmx.net
To: 'Watson Ladd' <watsonbladd@gmail.com>
Cc: rats@ietf.org
References: <02c501da6987$d2d64490$7882cdb0$@gmx.net> <CACsn0c=0iogM_OD-=9DyLm4=o+kcViWfU-RsDAPVE0-h1R7xCg@mail.gmail.com>
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Date: Sun, 03 Mar 2024 11:51:35 +0100
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Subject: Re: [Rats] Requesting a Nonce from a Verifier
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Hi Watson,

the nonce concept and terminology have been defined in the RATS architecture (see RFC 9334) and it is used in various attestation technologies.
The EAT specification provides a generic description in Section 4.1 of https://datatracker.ietf.org/doc/draft-ietf-rats-eat/ and there it says that the nonce claim in evidence must have at least 64 bits of entropy. This is also what attestation technologies do. For example, the PSA attestation token profiles EAT and demands in Section 4.1.1 of https://datatracker.ietf.org/doc/draft-tschofenig-rats-psa-token/  that the nonce is 32, 48, or 64 bytes in length.

As such, I believe we are using the right terminology but I have added extra text to the CMP/EST nonce draft.

Ciao
Hannes

-----Original Message-----
From: Watson Ladd <watsonbladd@gmail.com> 
Sent: Mittwoch, 28. Februar 2024 03:12
To: hannes.tschofenig@gmx.net
Cc: rats@ietf.org
Subject: Re: [Rats] Requesting a Nonce from a Verifier

On Tue, Feb 27, 2024 at 6:19 AM
<hannes.tschofenig=40gmx.net@dmarc.ietf.org> wrote:
>
> Hi all,
>
>
>
> Hendrik and I have been working on an update of the CMP/EST extensions, which allow an Attester to request a nonce via the Relying Party (in the background check model). This “nonce draft”, see draft-tschofenig-lamps-nonce-cmp-est, aims to provide freshness for the CSR attestation draft (see draft-ietf-lamps-csr-attestation).

A nonce is not what is needed. The challenge for freshness needs to be
unpredictable: it needs to be a sufficiently long random value. The terminology used here is unfortunate, and at odds with the accepted definition in the cryptographic literature.

Sincerely,
Watson Ladd

--
Astra mortemque praestare gradatim

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