Can't check signature, DSA key 9C973C92 requires a 256 bit or larger hash

[Werner Koch]

On Mon, 17 Mar 2014 15:39, dkg at fifthhorseman.net said:

> So gpg's behavior seems to be non-uniform here.  That said, i'd love to

As required by FIPS-186-3, 4.2: 

   This Standard specifies the following choices for the pair L and N
   (the bit lengths of p and q, respectively):

   L = 1024, N = 160
   L = 2048, N = 224
   L = 2048, N = 256
   L = 3072, N = 256

and RFC-4880:

  13.6.  DSA

   An implementation SHOULD NOT implement DSA keys of size less than
   1024 bits.  It MUST NOT implement a DSA key with a q size of less
   than 160 bits.  DSA keys MUST also be a multiple of 64 bits, and the
   q size MUST be a multiple of 8 bits.  The Digital Signature Standard
   (DSS) [FIPS186] specifies that DSA be used in one of the following
   ways:

     * 1024-bit key, 160-bit q, SHA-1, SHA-224, SHA-256, SHA-384, or
       SHA-512 hash

     * 2048-bit key, 224-bit q, SHA-224, SHA-256, SHA-384, or SHA-512
       hash

     * 2048-bit key, 256-bit q, SHA-256, SHA-384, or SHA-512 hash

     * 3072-bit key, 256-bit q, SHA-256, SHA-384, or SHA-512 hash

   The above key and q size pairs were chosen to best balance the
   strength of the key with the strength of the hash.  Implementations
   SHOULD use one of the above key and q size pairs when generating DSA
   keys.  If DSS compliance is desired, one of the specified SHA hashes
   must be used as well.  [FIPS186] is the ultimate authority on DSS,
   and should be consulted for all questions of DSS compliance.

> be able to tell gpg to ignore or explicitly reject signatures made by
> strong keys with MD5 digests.

Run in enforced FIPS mode ;-)


Salam-Shalom,

   Werner

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