1/*
2 * Copyright 2013 The Android Open Source Project
3 *
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions are met:
6 *     * Redistributions of source code must retain the above copyright
7 *       notice, this list of conditions and the following disclaimer.
8 *     * Redistributions in binary form must reproduce the above copyright
9 *       notice, this list of conditions and the following disclaimer in the
10 *       documentation and/or other materials provided with the distribution.
11 *     * Neither the name of Google Inc. nor the names of its contributors may
12 *       be used to endorse or promote products derived from this software
13 *       without specific prior written permission.
14 *
15 * THIS SOFTWARE IS PROVIDED BY Google Inc. ``AS IS'' AND ANY EXPRESS OR
16 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
17 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO
18 * EVENT SHALL Google Inc. BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
19 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
20 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
21 * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
22 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
23 * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
24 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
25 */
26
27#include <string.h>
28
29#include "mincrypt/p256_ecdsa.h"
30#include "mincrypt/p256.h"
31
32int p256_ecdsa_verify(const p256_int* key_x, const p256_int* key_y,
33                      const p256_int* message,
34                      const p256_int* r, const p256_int* s) {
35  p256_int u, v;
36
37  // Check public key.
38  if (!p256_is_valid_point(key_x, key_y)) return 0;
39
40  // Check r and s are != 0 % n.
41  p256_mod(&SECP256r1_n, r, &u);
42  p256_mod(&SECP256r1_n, s, &v);
43  if (p256_is_zero(&u) || p256_is_zero(&v)) return 0;
44
45  p256_modinv_vartime(&SECP256r1_n, s, &v);
46  p256_modmul(&SECP256r1_n, message, 0, &v, &u);  // message / s % n
47  p256_modmul(&SECP256r1_n, r, 0, &v, &v);  // r / s % n
48
49  p256_points_mul_vartime(&u, &v,
50                          key_x, key_y,
51                          &u, &v);
52
53  p256_mod(&SECP256r1_n, &u, &u);  // (x coord % p) % n
54  return p256_cmp(r, &u) == 0;
55}
56
57