pk: Allow the use of a hash element for DSA sign and verify.

* cipher/pubkey.c (pubkey_sign): Add arg ctx and pass it to the sign
module.
(gcry_pk_sign): Pass CTX to pubkey_sign.
(sexp_data_to_mpi): Add flag rfc6979 and code to alls hash with *DSA
* cipher/rsa.c (rsa_sign, rsa_verify): Return an error if an opaque
MPI is given for DATA/HASH.
* cipher/elgamal.c (elg_sign, elg_verify): Ditto.
* cipher/dsa.c (dsa_sign, dsa_verify): Convert a given opaque MPI.
* cipher/ecc.c (ecc_sign, ecc_verify): Ditto.
* tests/basic.c (check_pubkey_sign_ecdsa): Add a test for using a hash
element with DSA.
--

This patch allows the use of

  (data (flags raw)
    (hash sha256 #80112233445566778899AABBCCDDEEFF
                  000102030405060708090A0B0C0D0E0F#))

in addition to the old but more efficient

  (data (flags raw)
    (value #80112233445566778899AABBCCDDEEFF
            000102030405060708090A0B0C0D0E0F#))

for DSA and ECDSA.  With the hash element the flag "raw" must be
explicitly given because existing regression test code expects that
conflict error is return if no flags but a hash element is given.

Note that the hash algorithm name is currently not checked.  It may
eventually be used to cross-check the length of the provided hash
value.  It is suggested that the correct hash name is given - even if
a truncated hash value is used.

Finally this patch adds a way to pass the hash algorithm and flag
values to the signing module.  "rfc6979" as been implemented as a new
but not yet used flag.

Signed-off-by: Werner Koch <wk@gnupg.org>

1 files changed, 7 insertions, 1 deletions

diff --git a/cipher/rsa.c b/cipher/rsa.c
index 4787f813..c9fcebf0 100644
--- a/cipher/rsa.c
+++ b/cipher/rsa.c
@@ -700,7 +700,7 @@ stronger_key_check ( RSA_secret_key *skey )
  * Where m is OUTPUT, c is INPUT and d,n,p,q,u are elements of SKEY.
  */
 static void
-secret(gcry_mpi_t output, gcry_mpi_t input, RSA_secret_key *skey )
+secret (gcry_mpi_t output, gcry_mpi_t input, RSA_secret_key *skey )
 {
   if (!skey->p || !skey->q || !skey->u)
     {
@@ -1002,6 +1002,9 @@ rsa_sign (int algo, gcry_mpi_t *resarr, gcry_mpi_t data, gcry_mpi_t *skey,
   (void)flags;
   (void)hashalgo;
 
+  if (mpi_is_opaque (data))
+    return GPG_ERR_INV_DATA;
+
   sk.n = skey[0];
   sk.e = skey[1];
   sk.d = skey[2];
@@ -1028,6 +1031,9 @@ rsa_verify (int algo, gcry_mpi_t hash, gcry_mpi_t *data, gcry_mpi_t *pkey,
   (void)cmp;
   (void)opaquev;
 
+  if (mpi_is_opaque (hash))
+    return GPG_ERR_INV_DATA;
+
   pk.n = pkey[0];
   pk.e = pkey[1];
   result = gcry_mpi_new ( 160 );