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