Deterministic DSA

[Werner Koch]

Hi,

I just pushed the last patch to support RFC-6979 style Deterministic DSA
to master.  All prime field tests from the RFC (or well, the I-D) work
as expected.  Using it is pretty straighforward:

      const char *hashname = "sha256".
      int hashalgo;
      int digestlen;
      char digest[32];

      hashalgo = gcry_md_map_name (hashname);
      if (!hashalgo)
        die ("hash with name '%s' is not supported\n", tests[tno].hashname);
      digestlen = gcry_md_get_algo_dlen (hashalgo);
      if (digestlen > sizeof digest)
        die ("internal error: digest does not fit into our buffer\n");

      gcry_md_hash_buffer (hashalgo, digest, message, strlen (message));

      err = gcry_sexp_build (&data, NULL,
                             "(data "
                             " (flags rfc6979)"
                             " (hash %s %b))",
                             hashname, digestlen, digest);
      if (err)
        die ("building data sexp failed: %s\n", gpg_strerror (err));

      err = gcry_pk_sign (&sig, data, seckey);

You may now also use (hash ALGO BUFFER) instead of (value MPI) for
standard DSA.  In that case Libgcrypt takes care of standard conforminf
truncation


Shalom-Salam,

   Werner


-- 
Die Gedanken sind frei.  Ausnahmen regelt ein Bundesgesetz.