Re: [TLS] DH security issue in TLS

Peter Gutmann <pgut001@cs.auckland.ac.nz> Fri, 06 December 2019 08:32 UTC

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From: Peter Gutmann <pgut001@cs.auckland.ac.nz>
To: Pascal Urien <pascal.urien@gmail.com>, Antoine Delignat-Lavaud <antoine@delignat-lavaud.fr>
CC: "tls@ietf.org" <tls@ietf.org>
Thread-Topic: [TLS] DH security issue in TLS
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Date: Fri, 6 Dec 2019 08:32:18 +0000
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Subject: Re: [TLS] DH security issue in TLS
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Pascal Urien <pascal.urien@gmail.com>; writes:

>I found in NIST Special Publication 800-56A Revision 3
>
>5.6.2.3.1 FFC Full Public-Key Validation Routine
>2. Verify  that  1 = y q mod p. 

This only works for FIPS 186-style DH values where q is present, not PKCS #3
values as used in SSH and SSL/TLS.  Only TLS-LTS sends the q value allowing
this check.

Peter.