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, 13 insertions, 3 deletions

diff --git a/tests/basic.c b/tests/basic.c
index 88ae1316..46e213cb 100644
--- a/tests/basic.c
+++ b/tests/basic.c
@@ -3073,6 +3073,14 @@ check_pubkey_sign_ecdsa (int n, gcry_sexp_t skey, gcry_sexp_t pkey)
     int dummy;
   } datas[] =
     {
+      { 192,
+        "(data (flags raw)\n"
+        " (value #00112233445566778899AABBCCDDEEFF0001020304050607#))",
+        0,
+        "(data (flags raw)\n"
+        " (value #80112233445566778899AABBCCDDEEFF0001020304050607#))",
+        0
+      },
       { 256,
         "(data (flags raw)\n"
         " (value #00112233445566778899AABBCCDDEEFF"
@@ -3083,12 +3091,14 @@ check_pubkey_sign_ecdsa (int n, gcry_sexp_t skey, gcry_sexp_t pkey)
         /* */    "000102030405060708090A0B0C0D0E0F#))",
         0
       },
-      { 192,
+      { 256,
         "(data (flags raw)\n"
-        " (value #00112233445566778899AABBCCDDEEFF0001020304050607#))",
+        " (hash sha256 #00112233445566778899AABBCCDDEEFF"
+        /* */          "000102030405060708090A0B0C0D0E0F#))",
         0,
         "(data (flags raw)\n"
-        " (value #80112233445566778899AABBCCDDEEFF0001020304050607#))",
+        " (hash sha256 #80112233445566778899AABBCCDDEEFF"
+        /* */          "000102030405060708090A0B0C0D0E0F#))",
         0
       },
       { 0, NULL }