PR: 1432

Submitted by: "Andrzej Chmielowiec" <achmielowiec@enigma.com.pl>, steve@openssl.org
Approved by: steve@openssl.org

Truncate hash if it is too large: as required by FIPS 186-3.

diff --git a/crypto/ecdsa/ecs_ossl.c b/crypto/ecdsa/ecs_ossl.c
index 3ead1af94e7351c5e4bf76aefe146e61b1e636a5..551cf5068fa2ebb4c87875fa1b22f6340f7de349 100644 (file)
--- a/crypto/ecdsa/ecs_ossl.c
+++ b/crypto/ecdsa/ecs_ossl.c
@@ -212,7 +212,7 @@ err:
 static ECDSA_SIG *ecdsa_do_sign(const unsigned char *dgst, int dgst_len, 
                const BIGNUM *in_kinv, const BIGNUM *in_r, EC_KEY *eckey)
 {
-       int     ok = 0;
+       int     ok = 0, i;
        BIGNUM *kinv=NULL, *s, *m=NULL,*tmp=NULL,*order=NULL;
        const BIGNUM *ckinv;
        BN_CTX     *ctx = NULL;
@@ -251,22 +251,19 @@ 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))
+       i = BN_num_bits(order);
+       /* Need to truncate digest if it is too long: first truncate whole
+        * bytes.
+        */
+       if (8 * dgst_len > i)
+               dgst_len = (i + 7)/8;
+       if (!BN_bin2bn(dgst, dgst_len, m))
        {
-               /* 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);
+               ECDSAerr(ECDSA_F_ECDSA_DO_SIGN, ERR_R_BN_LIB);
                goto err;
        }
-
-       if (!BN_bin2bn(dgst, dgst_len, m))
+       /* If still too long truncate remaining bits with a shift */
+       if ((8 * dgst_len > i) && !BN_rshift(m, m, 8 - (i & 0x7)))
        {
                ECDSAerr(ECDSA_F_ECDSA_DO_SIGN, ERR_R_BN_LIB);
                goto err;
@@ -346,7 +343,7 @@ err:
 static int ecdsa_do_verify(const unsigned char *dgst, int dgst_len,
                const ECDSA_SIG *sig, EC_KEY *eckey)
 {
-       int ret = -1;
+       int ret = -1, i;
        BN_CTX   *ctx;
        BIGNUM   *order, *u1, *u2, *m, *X;
        EC_POINT *point = NULL;
@@ -384,21 +381,6 @@ 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)  ||
@@ -415,11 +397,23 @@ static int ecdsa_do_verify(const unsigned char *dgst, int dgst_len,
                goto err;
        }
        /* digest -> m */
+       i = BN_num_bits(order);
+       /* Need to truncate digest if it is too long: first truncate whole
+        * bytes.
+        */
+       if (8 * dgst_len > i)
+               dgst_len = (i + 7)/8;
        if (!BN_bin2bn(dgst, dgst_len, m))
        {
                ECDSAerr(ECDSA_F_ECDSA_DO_VERIFY, ERR_R_BN_LIB);
                goto err;
        }
+       /* If still too long truncate remaining bits with a shift */
+       if ((8 * dgst_len > i) && !BN_rshift(m, m, 8 - (i & 0x7)))
+       {
+               ECDSAerr(ECDSA_F_ECDSA_DO_VERIFY, ERR_R_BN_LIB);
+               goto err;
+       }
        /* u1 = m * tmp mod order */
        if (!BN_mod_mul(u1, m, u2, order, ctx))
        {