Basic cleanup. Handle the possibly NULL ctx_in in ecdsa_sign_setup() with

the usual idiom. All the allocations are now handled inside conditionals as
is usually done in this part of the tree. Turn a few comments into actual
sentences and remove a few self-evident ones. Change outdated or cryptic
comments into more helpful annotations. In ecdsa_do_verify(), start
calculating only after properly truncating the message digest.  More
consistent variable names: prefer 'order_bits' and 'point' over 'i' and
'tmp_point'.

ok jsing

1 files changed, 62 insertions, 67 deletions

diff --git a/src/lib/libcrypto/ecdsa/ecs_ossl.c b/src/lib/libcrypto/ecdsa/ecs_ossl.c
index be279b34b6..eff2a5022d 100644
--- a/src/lib/libcrypto/ecdsa/ecs_ossl.c
+++ b/src/lib/libcrypto/ecdsa/ecs_ossl.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: ecs_ossl.c,v 1.13 2018/06/15 05:00:41 tb Exp $ */
+/* $OpenBSD: ecs_ossl.c,v 1.14 2018/06/15 19:24:13 tb Exp $ */
 /*
  * Written by Nils Larsch for the OpenSSL project
  */
@@ -88,9 +88,9 @@ ECDSA_OpenSSL(void)
 static int
 ecdsa_sign_setup(EC_KEY *eckey, BN_CTX *ctx_in, BIGNUM **kinvp, BIGNUM **rp)
 {
-        BN_CTX   *ctx = NULL;
-        BIGNUM   *k = NULL, *r = NULL, *order = NULL, *X = NULL;
-        EC_POINT *tmp_point = NULL;
+        BN_CTX *ctx = ctx_in;
+        BIGNUM *k = NULL, *r = NULL, *order = NULL, *X = NULL;
+        EC_POINT *point = NULL;
         const EC_GROUP *group;
         int order_bits, ret = 0;
 
@@ -99,23 +99,19 @@ ecdsa_sign_setup(EC_KEY *eckey, BN_CTX *ctx_in, BIGNUM **kinvp, BIGNUM **rp)
                 return 0;
         }
 
-        if (ctx_in == NULL) {
+        if (ctx == NULL) {
                 if ((ctx = BN_CTX_new()) == NULL) {
                         ECDSAerror(ERR_R_MALLOC_FAILURE);
                         return 0;
                 }
-        } else
-                ctx = ctx_in;
-
-        k = BN_new();   /* this value is later returned in *kinvp */
-        r = BN_new();   /* this value is later returned in *rp    */
-        order = BN_new();
-        X = BN_new();
-        if (!k || !r || !order || !X) {
+        }
+
+        if ((k = BN_new()) == NULL || (r = BN_new()) == NULL ||
+            (order = BN_new()) == NULL || (X = BN_new()) == NULL) {
                 ECDSAerror(ERR_R_MALLOC_FAILURE);
                 goto err;
         }
-        if ((tmp_point = EC_POINT_new(group)) == NULL) {
+        if ((point = EC_POINT_new(group)) == NULL) {
                 ECDSAerror(ERR_R_EC_LIB);
                 goto err;
         }
@@ -132,14 +128,13 @@ ecdsa_sign_setup(EC_KEY *eckey, BN_CTX *ctx_in, BIGNUM **kinvp, BIGNUM **rp)
                 goto err;
 
         do {
-                /* get random k */
-                do
+                do {
                         if (!BN_rand_range(k, order)) {
                                 ECDSAerror(
                                     ECDSA_R_RANDOM_NUMBER_GENERATION_FAILED);
                                 goto err;
                         }
-                while (BN_is_zero(k));
+                } while (BN_is_zero(k));
 
                 /*
                  * We do not want timing information to leak the length of k,
@@ -162,23 +157,23 @@ ecdsa_sign_setup(EC_KEY *eckey, BN_CTX *ctx_in, BIGNUM **kinvp, BIGNUM **rp)
 
                 BN_set_flags(k, BN_FLG_CONSTTIME);
 
-                /* compute r the x-coordinate of generator * k */
-                if (!EC_POINT_mul(group, tmp_point, k, NULL, NULL, ctx)) {
+                /* Compute r, the x-coordinate of G * k. */
+                if (!EC_POINT_mul(group, point, k, NULL, NULL, ctx)) {
                         ECDSAerror(ERR_R_EC_LIB);
                         goto err;
                 }
                 if (EC_METHOD_get_field_type(EC_GROUP_method_of(group)) ==
                     NID_X9_62_prime_field) {
-                        if (!EC_POINT_get_affine_coordinates_GFp(group,
-                            tmp_point, X, NULL, ctx)) {
+                        if (!EC_POINT_get_affine_coordinates_GFp(group, point,
+                            X, NULL, ctx)) {
                                 ECDSAerror(ERR_R_EC_LIB);
                                 goto err;
                         }
                 }
 #ifndef OPENSSL_NO_EC2M
                 else {  /* NID_X9_62_characteristic_two_field */
-                        if (!EC_POINT_get_affine_coordinates_GF2m(group,
-                            tmp_point, X, NULL, ctx)) {
+                        if (!EC_POINT_get_affine_coordinates_GF2m(group, point,
+                            X, NULL, ctx)) {
                                 ECDSAerror(ERR_R_EC_LIB);
                                 goto err;
                         }
@@ -190,15 +185,12 @@ ecdsa_sign_setup(EC_KEY *eckey, BN_CTX *ctx_in, BIGNUM **kinvp, BIGNUM **rp)
                 }
         } while (BN_is_zero(r));
 
-        /* compute the inverse of k */
         if (!BN_mod_inverse_ct(k, k, order, ctx)) {
                 ECDSAerror(ERR_R_BN_LIB);
                 goto err;
         }
-        /* clear old values if necessary */
         BN_clear_free(*rp);
         BN_clear_free(*kinvp);
-        /* save the pre-computed values  */
         *rp = r;
         *kinvp = k;
         ret = 1;
@@ -211,7 +203,7 @@ ecdsa_sign_setup(EC_KEY *eckey, BN_CTX *ctx_in, BIGNUM **kinvp, BIGNUM **rp)
         if (ctx_in == NULL)
                 BN_CTX_free(ctx);
         BN_free(order);
-        EC_POINT_free(tmp_point);
+        EC_POINT_free(point);
         BN_clear_free(X);
         return (ret);
 }
@@ -228,7 +220,7 @@ ecdsa_do_sign(const unsigned char *dgst, int dgst_len,
         const EC_GROUP *group;
         ECDSA_SIG  *ret;
         ECDSA_DATA *ecdsa;
-        int     ok = 0, i;
+        int ok = 0, order_bits;
 
         ecdsa = ecdsa_check(eckey);
         group = EC_KEY_get0_group(eckey);
@@ -239,8 +231,7 @@ ecdsa_do_sign(const unsigned char *dgst, int dgst_len,
                 return NULL;
         }
 
-        ret = ECDSA_SIG_new();
-        if (!ret) {
+        if ((ret = ECDSA_SIG_new()) == NULL) {
                 ECDSAerror(ERR_R_MALLOC_FAILURE);
                 return NULL;
         }
@@ -258,18 +249,21 @@ ecdsa_do_sign(const unsigned char *dgst, int dgst_len,
                 ECDSAerror(ERR_R_EC_LIB);
                 goto err;
         }
-        i = BN_num_bits(order);
+
         /* Truncate digest if it is too long: first truncate whole bytes. */
-        if (8 * dgst_len > i)
-                dgst_len = (i + 7)/8;
+        order_bits = BN_num_bits(order);
+        if (8 * dgst_len > order_bits)
+                dgst_len = (order_bits + 7) / 8;
         if (!BN_bin2bn(dgst, dgst_len, m)) {
                 ECDSAerror(ERR_R_BN_LIB);
                 goto err;
         }
         /* If it is still too long, truncate the remaining bits with a shift. */
-        if ((8 * dgst_len > i) && !BN_rshift(m, m, 8 - (i & 0x7))) {
-                ECDSAerror(ERR_R_BN_LIB);
-                goto err;
+        if (8 * dgst_len > order_bits) {
+                if (!BN_rshift(m, m, 8 - (order_bits & 0x7))) {
+                        ECDSAerror(ERR_R_BN_LIB);
+                        goto err;
+                }
         }
 
         do {
@@ -359,7 +353,7 @@ ecdsa_do_sign(const unsigned char *dgst, int dgst_len,
         ok = 1;
 
  err:
-        if (!ok) {
+        if (ok == 0) {
                 ECDSA_SIG_free(ret);
                 ret = NULL;
         }
@@ -379,22 +373,20 @@ static int
 ecdsa_do_verify(const unsigned char *dgst, int dgst_len, const ECDSA_SIG *sig,
     EC_KEY *eckey)
 {
-        int ret = -1, i;
-        BN_CTX   *ctx;
-        BIGNUM   *order, *u1, *u2, *m, *X;
+        BN_CTX *ctx;
+        BIGNUM *order, *u1, *u2, *m, *X;
         EC_POINT *point = NULL;
         const EC_GROUP *group;
         const EC_POINT *pub_key;
+        int order_bits, ret = -1;
 
-        /* check input values */
         if (eckey == NULL || (group = EC_KEY_get0_group(eckey)) == NULL ||
             (pub_key = EC_KEY_get0_public_key(eckey)) == NULL || sig == NULL) {
                 ECDSAerror(ECDSA_R_MISSING_PARAMETERS);
                 return -1;
         }
 
-        ctx = BN_CTX_new();
-        if (!ctx) {
+        if ((ctx = BN_CTX_new()) == NULL) {
                 ECDSAerror(ERR_R_MALLOC_FAILURE);
                 return -1;
         }
@@ -404,7 +396,7 @@ ecdsa_do_verify(const unsigned char *dgst, int dgst_len, const ECDSA_SIG *sig,
         u2 = BN_CTX_get(ctx);
         m = BN_CTX_get(ctx);
         X = BN_CTX_get(ctx);
-        if (!X) {
+        if (X == NULL) {
                 ECDSAerror(ERR_R_BN_LIB);
                 goto err;
         }
@@ -414,43 +406,46 @@ ecdsa_do_verify(const unsigned char *dgst, int dgst_len, const ECDSA_SIG *sig,
                 goto err;
         }
 
-        if (BN_is_zero(sig->r)          || BN_is_negative(sig->r) ||
-            BN_ucmp(sig->r, order) >= 0 || BN_is_zero(sig->s)  ||
-            BN_is_negative(sig->s)      || BN_ucmp(sig->s, order) >= 0) {
+        /* Verify that r and s are in the range [1, order-1]. */
+        if (BN_is_zero(sig->r) || BN_is_negative(sig->r) ||
+            BN_ucmp(sig->r, order) >= 0 ||
+            BN_is_zero(sig->s) || BN_is_negative(sig->s) ||
+            BN_ucmp(sig->s, order) >= 0) {
                 ECDSAerror(ECDSA_R_BAD_SIGNATURE);
-                ret = 0;        /* signature is invalid */
-                goto err;
-        }
-        /* calculate tmp1 = inv(S) mod order */
-        if (!BN_mod_inverse_ct(u2, sig->s, order, ctx)) {
-                ECDSAerror(ERR_R_BN_LIB);
+                ret = 0;
                 goto err;
         }
-        /* digest -> m */
-        i = BN_num_bits(order);
+
         /* Truncate digest if it is too long: first truncate whole bytes. */
-        if (8 * dgst_len > i)
-                dgst_len = (i + 7)/8;
+        order_bits = BN_num_bits(order);
+        if (8 * dgst_len > order_bits)
+                dgst_len = (order_bits + 7) / 8;
         if (!BN_bin2bn(dgst, dgst_len, m)) {
                 ECDSAerror(ERR_R_BN_LIB);
                 goto err;
         }
         /* If it is still too long, truncate the remaining bits with a shift. */
-        if ((8 * dgst_len > i) && !BN_rshift(m, m, 8 - (i & 0x7))) {
+        if (8 * dgst_len > order_bits) {
+                if (!BN_rshift(m, m, 8 - (order_bits & 0x7))) {
+                        ECDSAerror(ERR_R_BN_LIB);
+                        goto err;
+                }
+        }
+
+        if (!BN_mod_inverse_ct(u2, sig->s, order, ctx)) {       /* w = inv(s) */
                 ECDSAerror(ERR_R_BN_LIB);
                 goto err;
         }
-        /* u1 = m * tmp mod order */
-        if (!BN_mod_mul(u1, m, u2, order, ctx)) {
+        if (!BN_mod_mul(u1, m, u2, order, ctx)) {               /* u1 = mw */
                 ECDSAerror(ERR_R_BN_LIB);
                 goto err;
         }
-        /* u2 = r * w mod q */
-        if (!BN_mod_mul(u2, sig->r, u2, order, ctx)) {
+        if (!BN_mod_mul(u2, sig->r, u2, order, ctx)) {          /* u2 = rw */
                 ECDSAerror(ERR_R_BN_LIB);
                 goto err;
         }
 
+        /* Compute the x-coordinate of G * u1 + pub_key * u2. */
         if ((point = EC_POINT_new(group)) == NULL) {
                 ECDSAerror(ERR_R_MALLOC_FAILURE);
                 goto err;
@@ -461,16 +456,16 @@ ecdsa_do_verify(const unsigned char *dgst, int dgst_len, const ECDSA_SIG *sig,
         }
         if (EC_METHOD_get_field_type(EC_GROUP_method_of(group)) ==
             NID_X9_62_prime_field) {
-                if (!EC_POINT_get_affine_coordinates_GFp(group,
-                    point, X, NULL, ctx)) {
+                if (!EC_POINT_get_affine_coordinates_GFp(group, point, X, NULL,
+                    ctx)) {
                         ECDSAerror(ERR_R_EC_LIB);
                         goto err;
                 }
         }
 #ifndef OPENSSL_NO_EC2M
         else { /* NID_X9_62_characteristic_two_field */
-                if (!EC_POINT_get_affine_coordinates_GF2m(group,
-                    point, X, NULL, ctx)) {
+                if (!EC_POINT_get_affine_coordinates_GF2m(group, point, X, NULL,
+                    ctx)) {
                         ECDSAerror(ERR_R_EC_LIB);
                         goto err;
                 }
@@ -481,7 +476,7 @@ ecdsa_do_verify(const unsigned char *dgst, int dgst_len, const ECDSA_SIG *sig,
                 goto err;
         }
 
-        /* If the signature is correct, then u1 is equal to sig->r. */
+        /* If the signature is correct, the x-coordinate is equal to sig->r. */
         ret = (BN_ucmp(u1, sig->r) == 0);
 
  err: