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44 lines
2.2 KiB
44 lines
2.2 KiB
9 years ago
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/**********************************************************************
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* Copyright (c) 2013, 2014 Pieter Wuille *
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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_ECMULT_GEN_
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#define _SECP256K1_ECMULT_GEN_
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#include "scalar.h"
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#include "group.h"
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typedef struct {
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/* For accelerating the computation of a*G:
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* To harden against timing attacks, use the following mechanism:
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* * Break up the multiplicand into groups of 4 bits, called n_0, n_1, n_2, ..., n_63.
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* * Compute sum(n_i * 16^i * G + U_i, i=0..63), where:
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* * U_i = U * 2^i (for i=0..62)
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* * U_i = U * (1-2^63) (for i=63)
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* where U is a point with no known corresponding scalar. Note that sum(U_i, i=0..63) = 0.
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* For each i, and each of the 16 possible values of n_i, (n_i * 16^i * G + U_i) is
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* precomputed (call it prec(i, n_i)). The formula now becomes sum(prec(i, n_i), i=0..63).
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* None of the resulting prec group elements have a known scalar, and neither do any of
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* the intermediate sums while computing a*G.
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*/
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secp256k1_ge_storage_t (*prec)[64][16]; /* prec[j][i] = 16^j * i * G + U_i */
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secp256k1_scalar_t blind;
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secp256k1_gej_t initial;
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} secp256k1_ecmult_gen_context_t;
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static void secp256k1_ecmult_gen_context_init(secp256k1_ecmult_gen_context_t* ctx);
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static void secp256k1_ecmult_gen_context_build(secp256k1_ecmult_gen_context_t* ctx, const callback_t* cb);
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static void secp256k1_ecmult_gen_context_clone(secp256k1_ecmult_gen_context_t *dst,
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const secp256k1_ecmult_gen_context_t* src, const callback_t* cb);
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static void secp256k1_ecmult_gen_context_clear(secp256k1_ecmult_gen_context_t* ctx);
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static int secp256k1_ecmult_gen_context_is_built(const secp256k1_ecmult_gen_context_t* ctx);
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/** Multiply with the generator: R = a*G */
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static void secp256k1_ecmult_gen(const secp256k1_ecmult_gen_context_t* ctx, secp256k1_gej_t *r, const secp256k1_scalar_t *a);
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static void secp256k1_ecmult_gen_blind(secp256k1_ecmult_gen_context_t *ctx, const unsigned char *seed32);
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#endif
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