src/ecmult_gen.h

   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 typedef struct {
  14     /* For accelerating the computation of a*G:
  15      * To harden against timing attacks, use the following mechanism:
  16      * * Break up the multiplicand into groups of 4 bits, called n_0, n_1, n_2, ..., n_63.
  17      * * Compute sum(n_i * 16^i * G + U_i, i=0..63), where:
  18      *   * U_i = U * 2^i (for i=0..62)
  19      *   * U_i = U * (1-2^63) (for i=63)
  20      *   where U is a point with no known corresponding scalar. Note that sum(U_i, i=0..63) = 0.
  21      * For each i, and each of the 16 possible values of n_i, (n_i * 16^i * G + U_i) is
  22      * precomputed (call it prec(i, n_i)). The formula now becomes sum(prec(i, n_i), i=0..63).
  23      * None of the resulting prec group elements have a known scalar, and neither do any of
  24      * the intermediate sums while computing a*G.
  25      */
  26     secp256k1_ge_storage (*prec)[64][16]; /* prec[j][i] = 16^j * i * G + U_i */
  27     secp256k1_scalar blind;
  28     secp256k1_gej initial;
  29 } secp256k1_ecmult_gen_context;
  30
  31 static void secp256k1_ecmult_gen_context_init(secp256k1_ecmult_gen_context* ctx);
  32 static void secp256k1_ecmult_gen_context_build(secp256k1_ecmult_gen_context* ctx, const secp256k1_callback* cb);
  33 static void secp256k1_ecmult_gen_context_clone(secp256k1_ecmult_gen_context *dst,
  34                                                const secp256k1_ecmult_gen_context* src, const secp256k1_callback* cb);
  35 static void secp256k1_ecmult_gen_context_clear(secp256k1_ecmult_gen_context* ctx);
  36 static int secp256k1_ecmult_gen_context_is_built(const secp256k1_ecmult_gen_context* ctx);
  37
  38 /** Multiply with the generator: R = a*G */
  39 static void secp256k1_ecmult_gen(const secp256k1_ecmult_gen_context* ctx, secp256k1_gej *r, const secp256k1_scalar *a);
  40
  41 static void secp256k1_ecmult_gen_blind(secp256k1_ecmult_gen_context *ctx, const unsigned char *seed32);
  42
  43 #endif /* SECP256K1_ECMULT_GEN_H */