55 lines
1.9 KiB
C
55 lines
1.9 KiB
C
/**********************************************************************
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* Copyright (c) 2015 Andrew Poelstra *
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* Distributed under the MIT software license, see the accompanying *
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* file COPYING or http://www.opensource.org/licenses/mit-license.php.*
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**********************************************************************/
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#ifndef SECP256K1_MODULE_ECDH_MAIN_H
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#define SECP256K1_MODULE_ECDH_MAIN_H
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#include "secp256k1_ecdh.h"
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#include "ecmult_const_impl.h"
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int secp256k1_ecdh(const secp256k1_context* ctx, unsigned char *result, const secp256k1_pubkey *point, const unsigned char *scalar) {
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int ret = 0;
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int overflow = 0;
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secp256k1_gej res;
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secp256k1_ge pt;
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secp256k1_scalar s;
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VERIFY_CHECK(ctx != NULL);
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ARG_CHECK(result != NULL);
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ARG_CHECK(point != NULL);
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ARG_CHECK(scalar != NULL);
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secp256k1_pubkey_load(ctx, &pt, point);
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secp256k1_scalar_set_b32(&s, scalar, &overflow);
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if (overflow || secp256k1_scalar_is_zero(&s)) {
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ret = 0;
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} else {
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unsigned char x[32];
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unsigned char y[1];
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secp256k1_sha256 sha;
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secp256k1_ecmult_const(&res, &pt, &s);
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secp256k1_ge_set_gej(&pt, &res);
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/* Compute a hash of the point in compressed form
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* Note we cannot use secp256k1_eckey_pubkey_serialize here since it does not
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* expect its output to be secret and has a timing sidechannel. */
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secp256k1_fe_normalize(&pt.x);
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secp256k1_fe_normalize(&pt.y);
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secp256k1_fe_get_b32(x, &pt.x);
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y[0] = 0x02 | secp256k1_fe_is_odd(&pt.y);
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secp256k1_sha256_initialize(&sha);
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secp256k1_sha256_write(&sha, y, sizeof(y));
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secp256k1_sha256_write(&sha, x, sizeof(x));
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secp256k1_sha256_finalize(&sha, result);
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ret = 1;
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}
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secp256k1_scalar_clear(&s);
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return ret;
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}
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#endif /* SECP256K1_MODULE_ECDH_MAIN_H */
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