Abstract away EC_SCALAR operations.

Just a little bit cleaner.

Change-Id: I0ed192a531b5aa853ba082caa6088e838f12c863
Reviewed-on: https://boringssl-review.googlesource.com/27587
Reviewed-by: Adam Langley <alangley@gmail.com>

crypto/fipsmodule/bcm.c

@@ -63,6 +63,7 @@
 #include "ec/p224-64.c"
 #include "../../third_party/fiat/p256.c"
 #include "ec/p256-x86_64.c"
+#include "ec/scalar.c"
 #include "ec/simple.c"
 #include "ec/util.c"
 #include "ec/wnaf.c"

crypto/fipsmodule/ec/ec.c

@@ -955,30 +955,3 @@ size_t EC_get_builtin_curves(EC_builtin_curve *out_curves,
 
   return OPENSSL_NUM_BUILT_IN_CURVES;
 }
-
-int ec_bignum_to_scalar(const EC_GROUP *group, EC_SCALAR *out,
-                        const BIGNUM *in) {
-  if (!ec_bignum_to_scalar_unchecked(group, out, in)) {
-    return 0;
-  }
-  if (!bn_less_than_words(out->words, group->order.d, group->order.width)) {
-    OPENSSL_PUT_ERROR(EC, EC_R_INVALID_SCALAR);
-    return 0;
-  }
-  return 1;
-}
-
-int ec_bignum_to_scalar_unchecked(const EC_GROUP *group, EC_SCALAR *out,
-                                  const BIGNUM *in) {
-  if (!bn_copy_words(out->words, group->order.width, in)) {
-    OPENSSL_PUT_ERROR(EC, EC_R_INVALID_SCALAR);
-    return 0;
-  }
-  return 1;
-}
-
-int ec_random_nonzero_scalar(const EC_GROUP *group, EC_SCALAR *out,
-                             const uint8_t additional_data[32]) {
-  return bn_rand_range_words(out->words, 1, group->order.d, group->order.width,
-                             additional_data);
-}

crypto/fipsmodule/ec/internal.h

@@ -193,6 +193,28 @@ int ec_bignum_to_scalar_unchecked(const EC_GROUP *group, EC_SCALAR *out,
 int ec_random_nonzero_scalar(const EC_GROUP *group, EC_SCALAR *out,
                              const uint8_t additional_data[32]);
 
+// ec_scalar_add sets |r| to |a| + |b|.
+void ec_scalar_add(const EC_GROUP *group, EC_SCALAR *r, const EC_SCALAR *a,
+                   const EC_SCALAR *b);
+
+// ec_scalar_to_montgomery sets |r| to |a| in Montgomery form.
+void ec_scalar_to_montgomery(const EC_GROUP *group, EC_SCALAR *r,
+                             const EC_SCALAR *a);
+
+// ec_scalar_to_montgomery sets |r| to |a| converted from Montgomery form.
+void ec_scalar_from_montgomery(const EC_GROUP *group, EC_SCALAR *r,
+                               const EC_SCALAR *a);
+
+// ec_scalar_mul_montgomery sets |r| to |a| * |b| where inputs and outputs are
+// in Montgomery form.
+void ec_scalar_mul_montgomery(const EC_GROUP *group, EC_SCALAR *r,
+                              const EC_SCALAR *a, const EC_SCALAR *b);
+
+// ec_scalar_mul_montgomery sets |r| to |a|^-1 where inputs and outputs are in
+// Montgomery form.
+void ec_scalar_inv_montgomery(const EC_GROUP *group, EC_SCALAR *r,
+                              const EC_SCALAR *a);
+
 // ec_point_add_mixed behaves like |EC_POINT_add|, but |&b->Z| must be zero or
 // one.
 int ec_point_add_mixed(const EC_GROUP *group, EC_POINT *r, const EC_POINT *a,

crypto/fipsmodule/ec/scalar.c

@@ -0,0 +1,80 @@
+/* Copyright (c) 2018, Google Inc.
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
+ * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
+ * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
+ * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
+
+#include <openssl/ec.h>
+
+#include "internal.h"
+#include "../bn/internal.h"
+
+
+int ec_bignum_to_scalar(const EC_GROUP *group, EC_SCALAR *out,
+                        const BIGNUM *in) {
+  if (!ec_bignum_to_scalar_unchecked(group, out, in)) {
+    return 0;
+  }
+  if (!bn_less_than_words(out->words, group->order.d, group->order.width)) {
+    OPENSSL_PUT_ERROR(EC, EC_R_INVALID_SCALAR);
+    return 0;
+  }
+  return 1;
+}
+
+int ec_bignum_to_scalar_unchecked(const EC_GROUP *group, EC_SCALAR *out,
+                                  const BIGNUM *in) {
+  if (!bn_copy_words(out->words, group->order.width, in)) {
+    OPENSSL_PUT_ERROR(EC, EC_R_INVALID_SCALAR);
+    return 0;
+  }
+  return 1;
+}
+
+int ec_random_nonzero_scalar(const EC_GROUP *group, EC_SCALAR *out,
+                             const uint8_t additional_data[32]) {
+  return bn_rand_range_words(out->words, 1, group->order.d, group->order.width,
+                             additional_data);
+}
+
+void ec_scalar_add(const EC_GROUP *group, EC_SCALAR *r, const EC_SCALAR *a,
+                   const EC_SCALAR *b) {
+  const BIGNUM *order = &group->order;
+  BN_ULONG tmp[EC_MAX_SCALAR_WORDS];
+  bn_mod_add_words(r->words, a->words, b->words, order->d, tmp, order->width);
+  OPENSSL_cleanse(tmp, sizeof(tmp));
+}
+
+void ec_scalar_to_montgomery(const EC_GROUP *group, EC_SCALAR *r,
+                             const EC_SCALAR *a) {
+  const BIGNUM *order = &group->order;
+  bn_to_montgomery_small(r->words, a->words, order->width, group->order_mont);
+}
+
+void ec_scalar_from_montgomery(const EC_GROUP *group, EC_SCALAR *r,
+                               const EC_SCALAR *a) {
+  const BIGNUM *order = &group->order;
+  bn_from_montgomery_small(r->words, a->words, order->width, group->order_mont);
+}
+
+void ec_scalar_mul_montgomery(const EC_GROUP *group, EC_SCALAR *r,
+                              const EC_SCALAR *a, const EC_SCALAR *b) {
+  const BIGNUM *order = &group->order;
+  bn_mod_mul_montgomery_small(r->words, a->words, b->words, order->width,
+                              group->order_mont);
+}
+
+void ec_scalar_inv_montgomery(const EC_GROUP *group, EC_SCALAR *r,
+                              const EC_SCALAR *a) {
+  const BIGNUM *order = &group->order;
+  bn_mod_inverse_prime_mont_small(r->words, a->words, order->width,
+                                  group->order_mont);
+}

crypto/fipsmodule/ecdsa/ecdsa.c

@@ -66,21 +66,6 @@
 #include "../../internal.h"
 
 
-static void scalar_add(const EC_GROUP *group, EC_SCALAR *r, const EC_SCALAR *a,
-                       const EC_SCALAR *b) {
-  const BIGNUM *order = &group->order;
-  BN_ULONG tmp[EC_MAX_SCALAR_WORDS];
-  bn_mod_add_words(r->words, a->words, b->words, order->d, tmp, order->width);
-  OPENSSL_cleanse(tmp, sizeof(tmp));
-}
-
-static void scalar_mul_montgomery(const EC_GROUP *group, EC_SCALAR *r,
-                                 const EC_SCALAR *a, const EC_SCALAR *b) {
-  const BIGNUM *order = &group->order;
-  bn_mod_mul_montgomery_small(r->words, a->words, b->words, order->width,
-                              group->order_mont);
-}
-
 // digest_to_scalar interprets |digest_len| bytes from |digest| as a scalar for
 // ECDSA. Note this value is not fully reduced modulo the order, only the
 // correct number of bits.
@@ -233,16 +218,15 @@ int ECDSA_do_verify(const uint8_t *digest, size_t digest_len,
       !ec_bignum_to_scalar_unchecked(group, &s_inv_mont, X)) {
     goto err;
   }
-  bn_to_montgomery_small(s_inv_mont.words, s_inv_mont.words, order->width,
+  ec_scalar_to_montgomery(group, &s_inv_mont, &s_inv_mont);
-                         group->order_mont);
   // u1 = m * s^-1 mod order
   // u2 = r * s^-1 mod order
   //
   // |s_inv_mont| is in Montgomery form while |m| and |r| are not, so |u1| and
   // |u2| will be taken out of Montgomery form, as desired.
   digest_to_scalar(group, &m, digest, digest_len);
-  scalar_mul_montgomery(group, &u1, &m, &s_inv_mont);
+  ec_scalar_mul_montgomery(group, &u1, &m, &s_inv_mont);
-  scalar_mul_montgomery(group, &u2, &r, &s_inv_mont);
+  ec_scalar_mul_montgomery(group, &u2, &r, &s_inv_mont);
 
   point = EC_POINT_new(group);
   if (point == NULL) {
@@ -327,10 +311,8 @@ static int ecdsa_sign_setup(const EC_KEY *eckey, BN_CTX *ctx,
 
     // Compute k^-1. We leave it in the Montgomery domain as an optimization for
     // later operations.
-    bn_to_montgomery_small(out_kinv_mont->words, k.words, order->width,
+    ec_scalar_to_montgomery(group, out_kinv_mont, &k);
-                           group->order_mont);
+    ec_scalar_inv_montgomery(group, out_kinv_mont, out_kinv_mont);
-    bn_mod_inverse_prime_mont_small(out_kinv_mont->words, out_kinv_mont->words,
-                                    order->width, group->order_mont);
 
     // Compute r, the x-coordinate of generator * k.
     if (!ec_point_mul_scalar(group, tmp_point, &k, NULL, NULL, ctx) ||
@@ -393,16 +375,15 @@ ECDSA_SIG *ECDSA_do_sign(const uint8_t *digest, size_t digest_len,
     if (!ec_bignum_to_scalar(group, &r_mont, ret->r)) {
       goto err;
     }
-    bn_to_montgomery_small(r_mont.words, r_mont.words, order->width,
+    ec_scalar_to_montgomery(group, &r_mont, &r_mont);
-                           group->order_mont);
+    ec_scalar_mul_montgomery(group, &s, priv_key, &r_mont);
-    scalar_mul_montgomery(group, &s, priv_key, &r_mont);
 
     // Compute tmp = m + priv_key * r.
-    scalar_add(group, &tmp, &m, &s);
+    ec_scalar_add(group, &tmp, &m, &s);
 
     // Finally, multiply s by k^-1. That was retained in Montgomery form, so the
     // same technique as the previous multiplication works.
-    scalar_mul_montgomery(group, &s, &tmp, &kinv_mont);
+    ec_scalar_mul_montgomery(group, &s, &tmp, &kinv_mont);
     if (!bn_set_words(ret->s, s.words, order->width)) {
       goto err;
     }