diff options
Diffstat (limited to 'src/secp256k1/src/ecmult_gen.h')
-rw-r--r-- | src/secp256k1/src/ecmult_gen.h | 30 |
1 files changed, 27 insertions, 3 deletions
diff --git a/src/secp256k1/src/ecmult_gen.h b/src/secp256k1/src/ecmult_gen.h index 42f822f9ce..3745633c47 100644 --- a/src/secp256k1/src/ecmult_gen.h +++ b/src/secp256k1/src/ecmult_gen.h @@ -10,10 +10,34 @@ #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_scalar_t blind; + secp256k1_gej_t initial; +} 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_clone(secp256k1_ecmult_gen_context_t *dst, + const secp256k1_ecmult_gen_context_t* src); +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); + +static void secp256k1_ecmult_gen_blind(secp256k1_ecmult_gen_context_t *ctx, const unsigned char *seed32); #endif |