[ec/ecp_nistp*.c] remove flip_endian()

Replace flip_endian() by using the little endian specific
BN_bn2lebinpad() and BN_lebin2bn().

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Bernd Edlinger <bernd.edlinger@hotmail.de>
(Merged from https://github.com/openssl/openssl/pull/9511)

1 files changed, 21 insertions, 28 deletions

diff --git a/crypto/ec/ecp_nistp521.c b/crypto/ec/ecp_nistp521.c
index 285639333f..24dd96b519 100644
--- a/crypto/ec/ecp_nistp521.c
+++ b/crypto/ec/ecp_nistp521.c
@@ -169,32 +169,21 @@ static void felem_to_bin66(u8 out[66], const felem in)
     (*((limb *) & out[58])) = in[8];
 }
 
-/* To preserve endianness when using BN_bn2bin and BN_bin2bn */
-static void flip_endian(u8 *out, const u8 *in, unsigned len)
-{
-    unsigned i;
-    for (i = 0; i < len; ++i)
-        out[i] = in[len - 1 - i];
-}
-
 /* BN_to_felem converts an OpenSSL BIGNUM into an felem */
 static int BN_to_felem(felem out, const BIGNUM *bn)
 {
-    felem_bytearray b_in;
     felem_bytearray b_out;
-    unsigned num_bytes;
+    int num_bytes;
 
-    num_bytes = BN_num_bytes(bn);
-    if (num_bytes > sizeof(b_out)) {
+    if (BN_is_negative(bn)) {
         ECerr(EC_F_BN_TO_FELEM, EC_R_BIGNUM_OUT_OF_RANGE);
         return 0;
     }
-    if (BN_is_negative(bn)) {
+    num_bytes = BN_bn2lebinpad(bn, b_out, sizeof(b_out));
+    if (num_bytes < 0) {
         ECerr(EC_F_BN_TO_FELEM, EC_R_BIGNUM_OUT_OF_RANGE);
         return 0;
     }
-    num_bytes = BN_bn2binpad(bn, b_in, sizeof(b_in));
-    flip_endian(b_out, b_in, num_bytes);
     bin66_to_felem(out, b_out);
     return 1;
 }
@@ -202,10 +191,9 @@ static int BN_to_felem(felem out, const BIGNUM *bn)
 /* felem_to_BN converts an felem into an OpenSSL BIGNUM */
 static BIGNUM *felem_to_BN(BIGNUM *out, const felem in)
 {
-    felem_bytearray b_in, b_out;
-    felem_to_bin66(b_in, in);
-    flip_endian(b_out, b_in, sizeof(b_out));
-    return BN_bin2bn(b_out, sizeof(b_out), out);
+    felem_bytearray b_out;
+    felem_to_bin66(b_out, in);
+    return BN_lebin2bn(b_out, sizeof(b_out), out);
 }
 
 /*-
@@ -1873,8 +1861,8 @@ int ec_GFp_nistp521_points_mul(const EC_GROUP *group, EC_POINT *r,
     felem_bytearray *secrets = NULL;
     felem (*pre_comp)[17][3] = NULL;
     felem *tmp_felems = NULL;
-    felem_bytearray tmp;
-    unsigned i, num_bytes;
+    unsigned i;
+    int num_bytes;
     int have_pre_comp = 0;
     size_t num_points = num;
     felem x_in, y_in, z_in, x_out, y_out, z_out;
@@ -1975,10 +1963,16 @@ int ec_GFp_nistp521_points_mul(const EC_GROUP *group, EC_POINT *r,
                         ECerr(EC_F_EC_GFP_NISTP521_POINTS_MUL, ERR_R_BN_LIB);
                         goto err;
                     }
-                    num_bytes = BN_bn2binpad(tmp_scalar, tmp, sizeof(tmp));
-                } else
-                    num_bytes = BN_bn2binpad(p_scalar, tmp, sizeof(tmp));
-                flip_endian(secrets[i], tmp, num_bytes);
+                    num_bytes = BN_bn2lebinpad(tmp_scalar,
+                                               secrets[i], sizeof(secrets[i]));
+                } else {
+                    num_bytes = BN_bn2lebinpad(p_scalar,
+                                               secrets[i], sizeof(secrets[i]));
+                }
+                if (num_bytes < 0) {
+                    ECerr(EC_F_EC_GFP_NISTP521_POINTS_MUL, ERR_R_BN_LIB);
+                    goto err;
+                }
                 /* precompute multiples */
                 if ((!BN_to_felem(x_out, p->X)) ||
                     (!BN_to_felem(y_out, p->Y)) ||
@@ -2021,10 +2015,9 @@ int ec_GFp_nistp521_points_mul(const EC_GROUP *group, EC_POINT *r,
                 ECerr(EC_F_EC_GFP_NISTP521_POINTS_MUL, ERR_R_BN_LIB);
                 goto err;
             }
-            num_bytes = BN_bn2binpad(tmp_scalar, tmp, sizeof(tmp));
+            num_bytes = BN_bn2lebinpad(tmp_scalar, g_secret, sizeof(g_secret));
         } else
-            num_bytes = BN_bn2binpad(scalar, tmp, sizeof(tmp));
-        flip_endian(g_secret, tmp, num_bytes);
+            num_bytes = BN_bn2lebinpad(scalar, g_secret, sizeof(g_secret));
         /* do the multiplication with generator precomputation */
         batch_mul(x_out, y_out, z_out,
                   (const felem_bytearray(*))secrets, num_points,