Bruce Stephens <[email protected]> writes:
[...]
> Wouldn't it make sense for the truncation to be done in ECDSA_do_sign(),
> as it is in dsa_do_sign()?
Presuming that this is sensible, would this change be about right?
--- a/crypto/ecdsa/ecs_ossl.c
+++ b/crypto/ecdsa/ecs_ossl.c
@@ -251,26 +251,16 @@ static ECDSA_SIG *ecdsa_do_sign(const unsigned char *dgst, int dgst_len,
ECDSAerr(ECDSA_F_ECDSA_DO_SIGN, ERR_R_EC_LIB);
goto err;
}
- if (8 * dgst_len > BN_num_bits(order))
- {
- /* XXX
- *
- * Should provide for optional hash truncation:
- * Keep the BN_num_bits(order) leftmost bits of dgst
- * (see March 2006 FIPS 186-3 draft, which has a few
- * confusing errors in this part though)
- */
-
- ECDSAerr(ECDSA_F_ECDSA_DO_SIGN,
- ECDSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
- goto err;
- }
-
if (!BN_bin2bn(dgst, dgst_len, m))
{
ECDSAerr(ECDSA_F_ECDSA_DO_SIGN, ERR_R_BN_LIB);
goto err;
}
+ if (8 * dgst_len > BN_num_bits(order))
+ {
+ BN_rshift(m, m, 8 * dgst_len - BN_num_bits(order));
+ }
+
do
{
if (in_kinv == NULL || in_r == NULL)
@@ -384,21 +374,6 @@ static int ecdsa_do_verify(const unsigned char *dgst, int dgst_len,
ECDSAerr(ECDSA_F_ECDSA_DO_VERIFY, ERR_R_EC_LIB);
goto err;
}
- if (8 * dgst_len > BN_num_bits(order))
- {
- /* XXX
- *
- * Should provide for optional hash truncation:
- * Keep the BN_num_bits(order) leftmost bits of dgst
- * (see March 2006 FIPS 186-3 draft, which has a few
- * confusing errors in this part though)
- */
-
- ECDSAerr(ECDSA_F_ECDSA_DO_VERIFY,
- ECDSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
- ret = 0;
- goto err;
- }
if (BN_is_zero(sig->r) || BN_is_negative(sig->r) ||
BN_ucmp(sig->r, order) >= 0 || BN_is_zero(sig->s) ||
@@ -420,6 +395,11 @@ static int ecdsa_do_verify(const unsigned char *dgst, int dgst_len,
ECDSAerr(ECDSA_F_ECDSA_DO_VERIFY, ERR_R_BN_LIB);
goto err;
}
+ /* truncate digest if longer than order */
+ if (8 * dgst_len > BN_num_bits(order))
+ {
+ BN_rshift(m, m, 8 * dgst_len - BN_num_bits(order));
+ }
/* u1 = m * tmp mod order */
if (!BN_mod_mul(u1, m, u2, order, ctx))
{
--
1.6.5.GIT
