Bitcoin Core  0.20.99
P2P Digital Currency
ecmult_gen.h
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1 /**********************************************************************
2  * Copyright (c) 2013, 2014 Pieter Wuille *
3  * Distributed under the MIT software license, see the accompanying *
4  * file COPYING or http://www.opensource.org/licenses/mit-license.php.*
5  **********************************************************************/
6 
7 #ifndef SECP256K1_ECMULT_GEN_H
8 #define SECP256K1_ECMULT_GEN_H
9 
10 #include "scalar.h"
11 #include "group.h"
12 
13 #if ECMULT_GEN_PREC_BITS != 2 && ECMULT_GEN_PREC_BITS != 4 && ECMULT_GEN_PREC_BITS != 8
14 # error "Set ECMULT_GEN_PREC_BITS to 2, 4 or 8."
15 #endif
16 #define ECMULT_GEN_PREC_B ECMULT_GEN_PREC_BITS
17 #define ECMULT_GEN_PREC_G (1 << ECMULT_GEN_PREC_B)
18 #define ECMULT_GEN_PREC_N (256 / ECMULT_GEN_PREC_B)
19 
20 typedef struct {
21  /* For accelerating the computation of a*G:
22  * To harden against timing attacks, use the following mechanism:
23  * * Break up the multiplicand into groups of PREC_B bits, called n_0, n_1, n_2, ..., n_(PREC_N-1).
24  * * Compute sum(n_i * (PREC_G)^i * G + U_i, i=0 ... PREC_N-1), where:
25  * * U_i = U * 2^i, for i=0 ... PREC_N-2
26  * * U_i = U * (1-2^(PREC_N-1)), for i=PREC_N-1
27  * where U is a point with no known corresponding scalar. Note that sum(U_i, i=0 ... PREC_N-1) = 0.
28  * For each i, and each of the PREC_G possible values of n_i, (n_i * (PREC_G)^i * G + U_i) is
29  * precomputed (call it prec(i, n_i)). The formula now becomes sum(prec(i, n_i), i=0 ... PREC_N-1).
30  * None of the resulting prec group elements have a known scalar, and neither do any of
31  * the intermediate sums while computing a*G.
32  */
33  secp256k1_ge_storage (*prec)[ECMULT_GEN_PREC_N][ECMULT_GEN_PREC_G]; /* prec[j][i] = (PREC_G)^j * i * G + U_i */
37 
44 
47 
48 static void secp256k1_ecmult_gen_blind(secp256k1_ecmult_gen_context *ctx, const unsigned char *seed32);
49 
50 #endif /* SECP256K1_ECMULT_GEN_H */
static void secp256k1_ecmult_gen_context_finalize_memcpy(secp256k1_ecmult_gen_context *dst, const secp256k1_ecmult_gen_context *src)
static void secp256k1_ecmult_gen(const secp256k1_ecmult_gen_context *ctx, secp256k1_gej *r, const secp256k1_scalar *a)
Multiply with the generator: R = a*G.
static void secp256k1_ecmult_gen_context_build(secp256k1_ecmult_gen_context *ctx, void **prealloc)
static void secp256k1_ecmult_gen_blind(secp256k1_ecmult_gen_context *ctx, const unsigned char *seed32)
A group element of the secp256k1 curve, in jacobian coordinates.
Definition: group.h:24
static void secp256k1_ecmult_gen_context_clear(secp256k1_ecmult_gen_context *ctx)
secp256k1_scalar blind
Definition: ecmult_gen.h:34
static secp256k1_context * ctx
Definition: tests.c:36
#define ECMULT_GEN_PREC_G
Definition: ecmult_gen.h:17
A scalar modulo the group order of the secp256k1 curve.
Definition: scalar_4x64.h:13
static void secp256k1_ecmult_gen_context_init(secp256k1_ecmult_gen_context *ctx)
#define ECMULT_GEN_PREC_N
Definition: ecmult_gen.h:18
static const size_t SECP256K1_ECMULT_GEN_CONTEXT_PREALLOCATED_SIZE
Definition: ecmult_gen.h:38
static int secp256k1_ecmult_gen_context_is_built(const secp256k1_ecmult_gen_context *ctx)