Reserve option to use BN_mod_exp_mont_consttime in ECDSA.

Submitted by Shay Gueron, Intel Corp.
RT: 3149

Reviewed-by: Rich Salz <rsalz@openssl.org>
(cherry picked from commit f54be179aa4cbbd944728771d7d59ed588158a12)

diff --git a/crypto/ec/ec.h b/crypto/ec/ec.h
index 7ae8e8ad58d19b91f357b95e6026b8c5e9443b22..b8551c527e5b2b580f3d785ef0a62f3bf56b5035 100644 (file)
--- a/crypto/ec/ec.h
+++ b/crypto/ec/ec.h
@@ -243,6 +243,12 @@ int EC_GROUP_set_generator(EC_GROUP *group, const EC_POINT *generator, const BIG
  */
 const EC_POINT *EC_GROUP_get0_generator(const EC_GROUP *group);
 
  */
 const EC_POINT *EC_GROUP_get0_generator(const EC_GROUP *group);
 

+/** Returns the montgomery data for order(Generator)
+ *  \param  group  EC_GROUP object
+ *  \return the currently used generator (possibly NULL).
+*/
+BN_MONT_CTX *EC_GROUP_get_mont_data(const EC_GROUP *group);
+

 /** Gets the order of a EC_GROUP
  *  \param  group  EC_GROUP object
  *  \param  order  BIGNUM to which the order is copied
 /** Gets the order of a EC_GROUP
  *  \param  group  EC_GROUP object
  *  \param  order  BIGNUM to which the order is copied

diff --git a/crypto/ec/ec_lcl.h b/crypto/ec/ec_lcl.h
index b0d48b6b5cc7f8a8af66523b24feda6cfaf6cd60..22b53d28a9f33a0b458ba26027501481d77f9b88 100644 (file)
--- a/crypto/ec/ec_lcl.h
+++ b/crypto/ec/ec_lcl.h
@@ -235,6 +235,8 @@ struct ec_group_st {
        void *field_data1; /* method-specific (e.g., Montgomery structure) */
        void *field_data2; /* method-specific */
        int (*field_mod_func)(BIGNUM *, const BIGNUM *, const BIGNUM *, BN_CTX *); /* method-specific */
        void *field_data1; /* method-specific (e.g., Montgomery structure) */
        void *field_data2; /* method-specific */
        int (*field_mod_func)(BIGNUM *, const BIGNUM *, const BIGNUM *, BN_CTX *); /* method-specific */

+
+       BN_MONT_CTX *mont_data;    /* data for ECDSA inverse */

 } /* EC_GROUP */;
 
 struct ec_key_st {
 } /* EC_GROUP */;
 
 struct ec_key_st {


@@ -444,3 +446,12 @@ void ec_GFp_nistp_points_make_affine_internal(size_t num, void *point_array,
        void (*felem_contract)(void *out, const void *in));
 void ec_GFp_nistp_recode_scalar_bits(unsigned char *sign, unsigned char *digit, unsigned char in);
 #endif
        void (*felem_contract)(void *out, const void *in));
 void ec_GFp_nistp_recode_scalar_bits(unsigned char *sign, unsigned char *digit, unsigned char in);
 #endif

+int ec_precompute_mont_data(EC_GROUP *);
+
+#ifdef ECP_NISTZ256_ASM
+/** Returns GFp methods using montgomery multiplication, with x86-64 optimized
+ * P256. See http://eprint.iacr.org/2013/816.
+ *  \return  EC_METHOD object
+ */
+const EC_METHOD *EC_GFp_nistz256_method(void);
+#endif

diff --git a/crypto/ec/ec_lib.c b/crypto/ec/ec_lib.c
index e2c4741b5b77ca7a0e55492deaf64ba239127bef..7fe31157cafe0742ab0e2410280c8c373a1a0613 100644 (file)
--- a/crypto/ec/ec_lib.c
+++ b/crypto/ec/ec_lib.c
@@ -98,6 +98,7 @@ EC_GROUP *EC_GROUP_new(const EC_METHOD *meth)
        ret->meth = meth;
 
        ret->extra_data = NULL;
        ret->meth = meth;
 
        ret->extra_data = NULL;

+       ret->mont_data = NULL;

 
        ret->generator = NULL;
        BN_init(&ret->order);
 
        ret->generator = NULL;
        BN_init(&ret->order);


@@ -129,6 +130,9 @@ void EC_GROUP_free(EC_GROUP *group)
 
        EC_EX_DATA_free_all_data(&group->extra_data);
 
 
        EC_EX_DATA_free_all_data(&group->extra_data);
 

+       if (group->mont_data)
+               BN_MONT_CTX_free(group->mont_data);
+

        if (group->generator != NULL)
                EC_POINT_free(group->generator);
        BN_free(&group->order);
        if (group->generator != NULL)
                EC_POINT_free(group->generator);
        BN_free(&group->order);


@@ -152,6 +156,9 @@ void EC_GROUP_clear_free(EC_GROUP *group)
 
        EC_EX_DATA_clear_free_all_data(&group->extra_data);
 
 
        EC_EX_DATA_clear_free_all_data(&group->extra_data);
 

+       if (group->mont_data)
+               BN_MONT_CTX_free(group->mont_data);
+

        if (group->generator != NULL)
                EC_POINT_clear_free(group->generator);
        BN_clear_free(&group->order);
        if (group->generator != NULL)
                EC_POINT_clear_free(group->generator);
        BN_clear_free(&group->order);


@@ -197,6 +204,25 @@ int EC_GROUP_copy(EC_GROUP *dest, const EC_GROUP *src)
                        return 0;
                }
 
                        return 0;
                }
 

+       if (src->mont_data != NULL)
+               {
+               if (dest->mont_data == NULL)
+                       {
+                       dest->mont_data = BN_MONT_CTX_new();
+                       if (dest->mont_data == NULL) return 0;
+                       }
+               if (!BN_MONT_CTX_copy(dest->mont_data, src->mont_data)) return 0;
+               }
+       else
+               {
+               /* src->generator == NULL */
+               if (dest->mont_data != NULL)
+                       {
+                       BN_MONT_CTX_free(dest->mont_data);
+                       dest->mont_data = NULL;
+                       }
+               }
+

        if (src->generator != NULL)
                {
                if (dest->generator == NULL)
        if (src->generator != NULL)
                {
                if (dest->generator == NULL)


@@ -306,6 +332,11 @@ int EC_GROUP_set_generator(EC_GROUP *group, const EC_POINT *generator, const BIG
        else
                BN_zero(&group->cofactor);
 
        else
                BN_zero(&group->cofactor);
 

+       /* We ignore the return value because some groups have an order with
+        * factors of two, which makes the Montgomery setup fail.
+        * |group->mont_data| will be NULL in this case. */
+       ec_precompute_mont_data(group);
+

        return 1;
        }
 
        return 1;
        }
 


@@ -315,6 +346,10 @@ const EC_POINT *EC_GROUP_get0_generator(const EC_GROUP *group)
        return group->generator;
        }
 
        return group->generator;
        }
 

+BN_MONT_CTX *EC_GROUP_get_mont_data(const EC_GROUP *group)
+       {
+       return group->mont_data;
+       }

 
 int EC_GROUP_get_order(const EC_GROUP *group, BIGNUM *order, BN_CTX *ctx)
        {
 
 int EC_GROUP_get_order(const EC_GROUP *group, BIGNUM *order, BN_CTX *ctx)
        {


@@ -1094,3 +1129,39 @@ int EC_GROUP_have_precompute_mult(const EC_GROUP *group)
        else
                return 0; /* cannot tell whether precomputation has been performed */
        }
        else
                return 0; /* cannot tell whether precomputation has been performed */
        }

+
+/* ec_precompute_mont_data sets |group->mont_data| from |group->order| and
+ * returns one on success. On error it returns zero. */
+int ec_precompute_mont_data(EC_GROUP *group)
+       {
+       BN_CTX *ctx = BN_CTX_new();
+       int ret = 0;
+
+       if (group->mont_data)
+               {
+               BN_MONT_CTX_free(group->mont_data);
+               group->mont_data = NULL;
+               }
+
+       if (ctx == NULL)
+               goto err;
+
+       group->mont_data = BN_MONT_CTX_new();
+       if (!group->mont_data)
+               goto err;
+
+       if (!BN_MONT_CTX_set(group->mont_data, &group->order, ctx))
+               {
+               BN_MONT_CTX_free(group->mont_data);
+               group->mont_data = NULL;
+               goto err;
+               }
+
+       ret = 1;
+
+err:
+
+       if (ctx)
+               BN_CTX_free(ctx);
+       return ret;
+       }

diff --git a/crypto/ecdsa/ecs_ossl.c b/crypto/ecdsa/ecs_ossl.c
index 7725935610ed2e7fb149f97532cb9704e07d9b8d..c23343b64d885c3e9a7e4852c6ce21574737f9c0 100644 (file)
--- a/crypto/ecdsa/ecs_ossl.c
+++ b/crypto/ecdsa/ecs_ossl.c
@@ -187,11 +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 */
        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);
        /* clear old values if necessary */
        if (*rp != NULL)
                BN_clear_free(*rp);