Reserve option to use BN_mod_exp_mont_consttime in ECDSA.

[openssl.git] / crypto / ecdsa / ecs_ossl.c

diff --git a/crypto/ecdsa/ecs_ossl.c b/crypto/ecdsa/ecs_ossl.c
index f8b5d4ed6a2e53f4116dc1621f5c98f0bcff1a7a..c23343b64d885c3e9a7e4852c6ce21574737f9c0 100644 (file)
--- a/crypto/ecdsa/ecs_ossl.c
+++ b/crypto/ecdsa/ecs_ossl.c
@@ -144,6 +144,14 @@ static int ecdsa_sign_setup(EC_KEY *eckey, BN_CTX *ctx_in, BIGNUM **kinvp,
                        }
                while (BN_is_zero(k));
 
+               /* We do not want timing information to leak the length of k,
+                * so we compute G*k using an equivalent scalar of fixed
+                * bit-length. */
+
+               if (!BN_add(k, k, order)) goto err;
+               if (BN_num_bits(k) <= BN_num_bits(order))
+                       if (!BN_add(k, k, order)) goto err;
+
                /* compute r the x-coordinate of generator * k */
                if (!EC_POINT_mul(group, tmp_point, k, NULL, NULL, ctx))
                {
@@ -159,6 +167,7 @@ static int ecdsa_sign_setup(EC_KEY *eckey, BN_CTX *ctx_in, BIGNUM **kinvp,
                                goto err;
                        }
                }
+#ifndef OPENSSL_NO_EC2M
                else /* NID_X9_62_characteristic_two_field */
                {
                        if (!EC_POINT_get_affine_coordinates_GF2m(group,
@@ -168,6 +177,7 @@ static int ecdsa_sign_setup(EC_KEY *eckey, BN_CTX *ctx_in, BIGNUM **kinvp,
                                goto err;
                        }
                }
+#endif
                if (!BN_nnmod(r, X, order, ctx))
                {
                        ECDSAerr(ECDSA_F_ECDSA_SIGN_SETUP, ERR_R_BN_LIB);
@@ -177,11 +187,37 @@ static int ecdsa_sign_setup(EC_KEY *eckey, BN_CTX *ctx_in, BIGNUM **kinvp,
        while (BN_is_zero(r));
 
        /* compute the inverse of k */
-       if (!BN_mod_inverse(k, k, order, ctx))
-       {
-               ECDSAerr(ECDSA_F_ECDSA_SIGN_SETUP, ERR_R_BN_LIB);
-               goto err;       
-       }
+       if (EC_GROUP_get_mont_data(group) != NULL)
+               {
+               /* We want inverse in constant time, therefore we utilize the
+                * fact order must be prime and use Fermats Little Theorem
+                * instead. */
+               if (!BN_set_word(X, 2) )
+                       {
+                       ECDSAerr(ECDSA_F_ECDSA_SIGN_SETUP, ERR_R_BN_LIB);
+                       goto err;
+                       }
+               if (!BN_mod_sub(X, order, X, order, ctx))
+                       {
+                       ECDSAerr(ECDSA_F_ECDSA_SIGN_SETUP, ERR_R_BN_LIB);
+                       goto err;
+                       }
+               BN_set_flags(X, BN_FLG_CONSTTIME);
+               if (!BN_mod_exp_mont_consttime(k, k, X, order, ctx, EC_GROUP_get_mont_data(group)))
+                       {
+                       ECDSAerr(ECDSA_F_ECDSA_SIGN_SETUP, ERR_R_BN_LIB);
+                       goto err;
+                       }
+               }
+       else
+               {
+               if (!BN_mod_inverse(k, k, order, ctx))
+                       {
+                       ECDSAerr(ECDSA_F_ECDSA_SIGN_SETUP, ERR_R_BN_LIB);
+                       goto err;       
+                       }
+               }
+
        /* clear old values if necessary */
        if (*rp != NULL)
                BN_clear_free(*rp);
@@ -212,7 +248,7 @@ 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 +287,19 @@ 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 +379,7 @@ 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;
@@ -400,11 +433,23 @@ 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))
        {
@@ -437,6 +482,7 @@ static int ecdsa_do_verify(const unsigned char *dgst, int dgst_len,
                        goto err;
                }
        }
+#ifndef OPENSSL_NO_EC2M
        else /* NID_X9_62_characteristic_two_field */
        {
                if (!EC_POINT_get_affine_coordinates_GF2m(group,
@@ -446,7 +492,7 @@ static int ecdsa_do_verify(const unsigned char *dgst, int dgst_len,
                        goto err;
                }
        }
-       
+#endif 
        if (!BN_nnmod(u1, X, order, ctx))
        {
                ECDSAerr(ECDSA_F_ECDSA_DO_VERIFY, ERR_R_BN_LIB);