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57 lines
2.2 KiB
C
57 lines
2.2 KiB
C
// Copyright 2015 The go-ethereum Authors
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// This file is part of the go-ethereum library.
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//
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// The go-ethereum library is free software: you can redistribute it and/or modify
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// it under the terms of the GNU Lesser General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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//
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// The go-ethereum library is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU Lesser General Public License for more details.
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//
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// You should have received a copy of the GNU Lesser General Public License
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// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
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/** Multiply point by scalar in constant time.
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* Returns: 1: multiplication was successful
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* 0: scalar was invalid (zero or overflow)
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* Args: ctx: pointer to a context object (cannot be NULL)
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* Out: point: the multiplied point (usually secret)
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* In: point: pointer to a 64-byte bytepublic point,
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encoded as two 256bit big-endian numbers.
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* scalar: a 32-byte scalar with which to multiply the point
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*/
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int secp256k1_pubkey_scalar_mul(const secp256k1_context* ctx, unsigned char *point, const unsigned char *scalar) {
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int ret = 0;
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int overflow = 0;
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secp256k1_fe feX, feY;
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secp256k1_gej res;
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secp256k1_ge ge;
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secp256k1_scalar s;
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ARG_CHECK(point != NULL);
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ARG_CHECK(scalar != NULL);
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(void)ctx;
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secp256k1_fe_set_b32(&feX, point);
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secp256k1_fe_set_b32(&feY, point+32);
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secp256k1_ge_set_xy(&ge, &feX, &feY);
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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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secp256k1_ecmult_const(&res, &ge, &s);
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secp256k1_ge_set_gej(&ge, &res);
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/* Note: can't use secp256k1_pubkey_save here because it is not constant time. */
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secp256k1_fe_normalize(&ge.x);
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secp256k1_fe_normalize(&ge.y);
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secp256k1_fe_get_b32(point, &ge.x);
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secp256k1_fe_get_b32(point+32, &ge.y);
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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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