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[API BREAK] Introduce explicit contexts

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This commit is contained in:
Pieter Wuille
2015-02-03 17:27:00 -08:00
parent a0d3b89dd6
commit a9b6595ef8
14 changed files with 345 additions and 280 deletions
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24
src/ecmult_gen.h
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@@ -10,10 +10,28 @@
#include "scalar.h"
#include "group.h"
static void secp256k1_ecmult_gen_start(void);
static void secp256k1_ecmult_gen_stop(void);
typedef struct {
/* For accelerating the computation of a*G:
* To harden against timing attacks, use the following mechanism:
* * Break up the multiplicand into groups of 4 bits, called n_0, n_1, n_2, ..., n_63.
* * Compute sum(n_i * 16^i * G + U_i, i=0..63), where:
* * U_i = U * 2^i (for i=0..62)
* * U_i = U * (1-2^63) (for i=63)
* where U is a point with no known corresponding scalar. Note that sum(U_i, i=0..63) = 0.
* For each i, and each of the 16 possible values of n_i, (n_i * 16^i * G + U_i) is
* precomputed (call it prec(i, n_i)). The formula now becomes sum(prec(i, n_i), i=0..63).
* None of the resulting prec group elements have a known scalar, and neither do any of
* the intermediate sums while computing a*G.
*/
secp256k1_ge_storage_t (*prec)[64][16]; /* prec[j][i] = 16^j * i * G + U_i */
} secp256k1_ecmult_gen_context_t;
static void secp256k1_ecmult_gen_context_init(secp256k1_ecmult_gen_context_t* ctx);
static void secp256k1_ecmult_gen_context_build(secp256k1_ecmult_gen_context_t* ctx);
static void secp256k1_ecmult_gen_context_clear(secp256k1_ecmult_gen_context_t* ctx);
static int secp256k1_ecmult_gen_context_is_built(const secp256k1_ecmult_gen_context_t* ctx);
/** Multiply with the generator: R = a*G */
static void secp256k1_ecmult_gen(secp256k1_gej_t *r, const secp256k1_scalar_t *a);
static void secp256k1_ecmult_gen(const secp256k1_ecmult_gen_context_t* ctx, secp256k1_gej_t *r, const secp256k1_scalar_t *a);
#endif