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 "constrainedcrypto/p256_ecdsa.h" 30 #include "constrainedcrypto/p256.h" 31 32 int 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
