git / moonbite-core / src/secp256k1-zkp/src/ecmult_gen_impl.h · raw

/********************************************************************** * Copyright (c) 2013, 2014, 2015 Pieter Wuille, Gregory Maxwell      * * Distributed under the MIT software license, see the accompanying   * * file COPYING or http://www.opensource.org/licenses/mit-license.php.* **********************************************************************/#ifndef SECP256K1_ECMULT_GEN_IMPL_H#define SECP256K1_ECMULT_GEN_IMPL_H#include "scalar.h"#include "group.h"#include "ecmult_gen.h"#include "hash_impl.h"#ifdef USE_ECMULT_STATIC_PRECOMPUTATION#include "ecmult_static_context.h"#endifstatic void secp256k1_ecmult_gen_context_init(secp256k1_ecmult_gen_context *ctx) {    ctx->prec = NULL;}static void secp256k1_ecmult_gen_context_build(secp256k1_ecmult_gen_context *ctx, const secp256k1_callback* cb) {#ifndef USE_ECMULT_STATIC_PRECOMPUTATION    secp256k1_ge prec[1024];    secp256k1_gej gj;    secp256k1_gej nums_gej;    int i, j;#endif    if (ctx->prec != NULL) {        return;    }#ifndef USE_ECMULT_STATIC_PRECOMPUTATION    ctx->prec = (secp256k1_ge_storage (*)[64][16])checked_malloc(cb, sizeof(*ctx->prec));    /* get the generator */    secp256k1_gej_set_ge(&gj, &secp256k1_ge_const_g);    /* Construct a group element with no known corresponding scalar (nothing up my sleeve). */    {        static const unsigned char nums_b32[33] = "The scalar for this x is unknown";        secp256k1_fe nums_x;        secp256k1_ge nums_ge;        int r;        r = secp256k1_fe_set_b32(&nums_x, nums_b32);        (void)r;        VERIFY_CHECK(r);        r = secp256k1_ge_set_xo_var(&nums_ge, &nums_x, 0);        (void)r;        VERIFY_CHECK(r);        secp256k1_gej_set_ge(&nums_gej, &nums_ge);        /* Add G to make the bits in x uniformly distributed. */        secp256k1_gej_add_ge_var(&nums_gej, &nums_gej, &secp256k1_ge_const_g, NULL);    }    /* compute prec. */    {        secp256k1_gej precj[1024]; /* Jacobian versions of prec. */        secp256k1_gej gbase;        secp256k1_gej numsbase;        gbase = gj; /* 16^j * G */        numsbase = nums_gej; /* 2^j * nums. */        for (j = 0; j < 64; j++) {            /* Set precj[j*16 .. j*16+15] to (numsbase, numsbase + gbase, ..., numsbase + 15*gbase). */            precj[j*16] = numsbase;            for (i = 1; i < 16; i++) {                secp256k1_gej_add_var(&precj[j*16 + i], &precj[j*16 + i - 1], &gbase, NULL);            }            /* Multiply gbase by 16. */            for (i = 0; i < 4; i++) {                secp256k1_gej_double_var(&gbase, &gbase, NULL);            }            /* Multiply numbase by 2. */            secp256k1_gej_double_var(&numsbase, &numsbase, NULL);            if (j == 62) {                /* In the last iteration, numsbase is (1 - 2^j) * nums instead. */                secp256k1_gej_neg(&numsbase, &numsbase);                secp256k1_gej_add_var(&numsbase, &numsbase, &nums_gej, NULL);            }        }        secp256k1_ge_set_all_gej_var(prec, precj, 1024, cb);    }    for (j = 0; j < 64; j++) {        for (i = 0; i < 16; i++) {            secp256k1_ge_to_storage(&(*ctx->prec)[j][i], &prec[j*16 + i]);        }    }#else    (void)cb;    ctx->prec = (secp256k1_ge_storage (*)[64][16])secp256k1_ecmult_static_context;#endif    secp256k1_ecmult_gen_blind(ctx, NULL);}static int secp256k1_ecmult_gen_context_is_built(const secp256k1_ecmult_gen_context* ctx) {    return ctx->prec != NULL;}static void secp256k1_ecmult_gen_context_clone(secp256k1_ecmult_gen_context *dst,                                               const secp256k1_ecmult_gen_context *src, const secp256k1_callback* cb) {    if (src->prec == NULL) {        dst->prec = NULL;    } else {#ifndef USE_ECMULT_STATIC_PRECOMPUTATION        dst->prec = (secp256k1_ge_storage (*)[64][16])checked_malloc(cb, sizeof(*dst->prec));        memcpy(dst->prec, src->prec, sizeof(*dst->prec));#else        (void)cb;        dst->prec = src->prec;#endif        dst->initial = src->initial;        dst->blind = src->blind;    }}static void secp256k1_ecmult_gen_context_clear(secp256k1_ecmult_gen_context *ctx) {#ifndef USE_ECMULT_STATIC_PRECOMPUTATION    free(ctx->prec);#endif    secp256k1_scalar_clear(&ctx->blind);    secp256k1_gej_clear(&ctx->initial);    ctx->prec = NULL;}static void secp256k1_ecmult_gen(const secp256k1_ecmult_gen_context *ctx, secp256k1_gej *r, const secp256k1_scalar *gn) {    secp256k1_ge add;    secp256k1_ge_storage adds;    secp256k1_scalar gnb;    int bits;    int i, j;    memset(&adds, 0, sizeof(adds));    *r = ctx->initial;    /* Blind scalar/point multiplication by computing (n-b)G + bG instead of nG. */    secp256k1_scalar_add(&gnb, gn, &ctx->blind);    add.infinity = 0;    for (j = 0; j < 64; j++) {        bits = secp256k1_scalar_get_bits(&gnb, j * 4, 4);        for (i = 0; i < 16; i++) {            /** This uses a conditional move to avoid any secret data in array indexes.             *   _Any_ use of secret indexes has been demonstrated to result in timing             *   sidechannels, even when the cache-line access patterns are uniform.             *  See also:             *   "A word of warning", CHES 2013 Rump Session, by Daniel J. Bernstein and Peter Schwabe             *    (https://cryptojedi.org/peter/data/chesrump-20130822.pdf) and             *   "Cache Attacks and Countermeasures: the Case of AES", RSA 2006,             *    by Dag Arne Osvik, Adi Shamir, and Eran Tromer             *    (http://www.tau.ac.il/~tromer/papers/cache.pdf)             */            secp256k1_ge_storage_cmov(&adds, &(*ctx->prec)[j][i], i == bits);        }        secp256k1_ge_from_storage(&add, &adds);        secp256k1_gej_add_ge(r, r, &add);    }    bits = 0;    secp256k1_ge_clear(&add);    secp256k1_scalar_clear(&gnb);}/* Setup blinding values for secp256k1_ecmult_gen. */static void secp256k1_ecmult_gen_blind(secp256k1_ecmult_gen_context *ctx, const unsigned char *seed32) {    secp256k1_scalar b;    secp256k1_gej gb;    secp256k1_fe s;    unsigned char nonce32[32];    secp256k1_rfc6979_hmac_sha256 rng;    int retry;    unsigned char keydata[64] = {0};    if (seed32 == NULL) {        /* When seed is NULL, reset the initial point and blinding value. */        secp256k1_gej_set_ge(&ctx->initial, &secp256k1_ge_const_g);        secp256k1_gej_neg(&ctx->initial, &ctx->initial);        secp256k1_scalar_set_int(&ctx->blind, 1);    }    /* The prior blinding value (if not reset) is chained forward by including it in the hash. */    secp256k1_scalar_get_b32(nonce32, &ctx->blind);    /** Using a CSPRNG allows a failure free interface, avoids needing large amounts of random data,     *   and guards against weak or adversarial seeds.  This is a simpler and safer interface than     *   asking the caller for blinding values directly and expecting them to retry on failure.     */    memcpy(keydata, nonce32, 32);    if (seed32 != NULL) {        memcpy(keydata + 32, seed32, 32);    }    secp256k1_rfc6979_hmac_sha256_initialize(&rng, keydata, seed32 ? 64 : 32);    memset(keydata, 0, sizeof(keydata));    /* Retry for out of range results to achieve uniformity. */    do {        secp256k1_rfc6979_hmac_sha256_generate(&rng, nonce32, 32);        retry = !secp256k1_fe_set_b32(&s, nonce32);        retry |= secp256k1_fe_is_zero(&s);    } while (retry); /* This branch true is cryptographically unreachable. Requires sha256_hmac output > Fp. */    /* Randomize the projection to defend against multiplier sidechannels. */    secp256k1_gej_rescale(&ctx->initial, &s);    secp256k1_fe_clear(&s);    do {        secp256k1_rfc6979_hmac_sha256_generate(&rng, nonce32, 32);        secp256k1_scalar_set_b32(&b, nonce32, &retry);        /* A blinding value of 0 works, but would undermine the projection hardening. */        retry |= secp256k1_scalar_is_zero(&b);    } while (retry); /* This branch true is cryptographically unreachable. Requires sha256_hmac output > order. */    secp256k1_rfc6979_hmac_sha256_finalize(&rng);    memset(nonce32, 0, 32);    secp256k1_ecmult_gen(ctx, &gb, &b);    secp256k1_scalar_negate(&b, &b);    ctx->blind = b;    ctx->initial = gb;    secp256k1_scalar_clear(&b);    secp256k1_gej_clear(&gb);}#endif /* SECP256K1_ECMULT_GEN_IMPL_H */