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/*
* Copyright 2013 The Android Open Source Project
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* * Neither the name of Google Inc. nor the names of its contributors may
* be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY Google Inc. ``AS IS'' AND ANY EXPRESS OR
* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO
* EVENT SHALL Google Inc. BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
* OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
* WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
* OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
* ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#include <string.h>
#include "mincrypt/p256_ecdsa.h"
#include "mincrypt/p256.h"
int p256_ecdsa_verify(const p256_int* key_x, const p256_int* key_y,
const p256_int* message,
const p256_int* r, const p256_int* s) {
p256_int u, v;
// Check public key.
if (!p256_is_valid_point(key_x, key_y)) return 0;
// Check r and s are != 0 % n.
p256_mod(&SECP256r1_n, r, &u);
p256_mod(&SECP256r1_n, s, &v);
if (p256_is_zero(&u) || p256_is_zero(&v)) return 0;
p256_modinv_vartime(&SECP256r1_n, s, &v);
p256_modmul(&SECP256r1_n, message, 0, &v, &u); // message / s % n
p256_modmul(&SECP256r1_n, r, 0, &v, &v); // r / s % n
p256_points_mul_vartime(&u, &v,
key_x, key_y,
&u, &v);
p256_mod(&SECP256r1_n, &u, &u); // (x coord % p) % n
return p256_cmp(r, &u) == 0;
}
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