[gnutls-devel] priority string DHE parameter acceptance

[Nikos Mavrogiannopoulos]

On 11/05/2013 04:57 AM, Daniel Kahn Gillmor wrote:
> I'm having some difficulty following the logic behind the way the GnuTLS
> priority strings set what the minimum number of bits are required for
> the group used for DHE key exchange.
> 
> I notice that if i set up a server using 1024-bit DHE, i get a different
> response from these two priority strings:
> 
>         SECURE256:+VERS-TLS-ALL:+DHE-RSA:+MAC-ALL:+COMP-NULL
> 
>   NONE:+SECURE256:+VERS-TLS-ALL:+DHE-RSA:+MAC-ALL:+COMP-NULL
> 
> Using the former priority string, connections complete, but using the
> latter priority string makes gnutls-cli refuse the connection at
> 1024-bit DHE.  If the DHE group is larger (2048 bits), both strings
> allow connections to complete.
> 
> My understanding of the priority string mechanism suggests that the two
> strings should have the same behavior.  What am i missing?

Nothing, that doesn't make sense. It's a bug. I've figure it out, but it
seems a test case is needed there to avoid such issues.

regards,
Nikos



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