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Squashed 'src/secp256k1/' changes from 1897b8e..22f60a6

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22f60a6 Merge pull request #245
61c1b1e Merge pull request #190
d227579 Add scalar blinding and a secp256k1_context_randomize() call.
c146b4a Add bench_internal to gitignore.
9c4fb23 Add a secp256k1_fe_cmov unit test.
426fa52 Merge pull request #243
d505a89 Merge pull request #244
2d2707a travis: test i686 builds with gmp
cf7f702 travis: update to new build infrastructure
bb0ea50 Replace set/add with cmov in secp256k1_gej_add_ge.
f3d3519 Merge pull request #241
5c2a4fa Fix memory leak in context unit test
14aacdc Merge pull request #239
93226a5 secp256k1.c: Add missing DEBUG_CHECKs for sufficiently capable contexts
6099220 Merge pull request #237
6066bb6 Fix typo: avg -> max
9688030 Merge pull request #236
d899b5b Expose ability to deep-copy a context
3608c7f Merge pull request #208
a9b6595 [API BREAK] Introduce explicit contexts
a0d3b89 Merge pull request #233
9e8d89b Merge pull request #234
65e70e7 Merge pull request #235
5098f62 Improve documentation formatting consistency
4450e24 Add a comment about the avoidance of secret data in array indexes.
6534ee1 initialize variable
d5b53aa Merge pull request #232
c01df1a Avoid some implicit type conversions to make C++ compilers happy.
bfe96ba Merge pull request #231
33270bf Add a couple comments pointing to particular sections of RFC6979.
41603aa Merge pull request #230
2632019 Brace all the if/for/while.

git-subtree-dir: src/secp256k1
git-subtree-split: 22f60a62801a8a49ecd049e7a563f69a41affd8d
This commit is contained in:
Pieter Wuille
2015-04-22 14:03:10 -07:00
parent 9d09322b41
commit a591d98c32
26 changed files with 1160 additions and 474 deletions
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140
src/ecmult_gen_impl.h
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@@ -1,5 +1,5 @@
/**********************************************************************
* Copyright (c) 2013, 2014 Pieter Wuille *
* 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.*
**********************************************************************/
@@ -10,36 +10,23 @@
#include "scalar.h"
#include "group.h"
#include "ecmult_gen.h"
#include "hash_impl.h"
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_consts_t;
static void secp256k1_ecmult_gen_context_init(secp256k1_ecmult_gen_context_t *ctx) {
ctx->prec = NULL;
}
static const secp256k1_ecmult_gen_consts_t *secp256k1_ecmult_gen_consts = NULL;
static void secp256k1_ecmult_gen_start(void) {
static void secp256k1_ecmult_gen_context_build(secp256k1_ecmult_gen_context_t *ctx) {
secp256k1_ge_t prec[1024];
secp256k1_gej_t gj;
secp256k1_gej_t nums_gej;
secp256k1_ecmult_gen_consts_t *ret;
int i, j;
if (secp256k1_ecmult_gen_consts != NULL)
return;
/* Allocate the precomputation table. */
ret = (secp256k1_ecmult_gen_consts_t*)checked_malloc(sizeof(secp256k1_ecmult_gen_consts_t));
if (ctx->prec != NULL) {
return;
}
ctx->prec = (secp256k1_ge_storage_t (*)[64][16])checked_malloc(sizeof(*ctx->prec));
/* get the generator */
secp256k1_gej_set_ge(&gj, &secp256k1_ge_const_g);
@@ -85,42 +72,113 @@ static void secp256k1_ecmult_gen_start(void) {
}
for (j = 0; j < 64; j++) {
for (i = 0; i < 16; i++) {
secp256k1_ge_to_storage(&ret->prec[j][i], &prec[j*16 + i]);
secp256k1_ge_to_storage(&(*ctx->prec)[j][i], &prec[j*16 + i]);
}
}
/* Set the global pointer to the precomputation table. */
secp256k1_ecmult_gen_consts = ret;
secp256k1_ecmult_gen_blind(ctx, NULL);
}
static void secp256k1_ecmult_gen_stop(void) {
secp256k1_ecmult_gen_consts_t *c;
if (secp256k1_ecmult_gen_consts == NULL)
return;
c = (secp256k1_ecmult_gen_consts_t*)secp256k1_ecmult_gen_consts;
secp256k1_ecmult_gen_consts = NULL;
free(c);
static int secp256k1_ecmult_gen_context_is_built(const secp256k1_ecmult_gen_context_t* ctx) {
return ctx->prec != NULL;
}
static void secp256k1_ecmult_gen(secp256k1_gej_t *r, const secp256k1_scalar_t *gn) {
const secp256k1_ecmult_gen_consts_t *c = secp256k1_ecmult_gen_consts;
static void secp256k1_ecmult_gen_context_clone(secp256k1_ecmult_gen_context_t *dst,
const secp256k1_ecmult_gen_context_t *src) {
if (src->prec == NULL) {
dst->prec = NULL;
} else {
dst->prec = (secp256k1_ge_storage_t (*)[64][16])checked_malloc(sizeof(*dst->prec));
memcpy(dst->prec, src->prec, sizeof(*dst->prec));
dst->initial = src->initial;
dst->blind = src->blind;
}
}
static void secp256k1_ecmult_gen_context_clear(secp256k1_ecmult_gen_context_t *ctx) {
free(ctx->prec);
secp256k1_scalar_clear(&ctx->blind);
secp256k1_gej_clear(&ctx->initial);
ctx->prec = NULL;
}
static void secp256k1_ecmult_gen(const secp256k1_ecmult_gen_context_t *ctx, secp256k1_gej_t *r, const secp256k1_scalar_t *gn) {
secp256k1_ge_t add;
secp256k1_ge_storage_t adds;
secp256k1_scalar_t gnb;
int bits;
int i, j;
secp256k1_gej_set_infinity(r);
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(gn, j * 4, 4);
bits = secp256k1_scalar_get_bits(&gnb, j * 4, 4);
for (i = 0; i < 16; i++) {
secp256k1_ge_storage_cmov(&adds, &c->prec[j][i], i == bits);
/** 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_t *ctx, const unsigned char *seed32) {
secp256k1_scalar_t b;
secp256k1_gej_t gb;
secp256k1_fe_t s;
unsigned char nonce32[32];
secp256k1_rfc6979_hmac_sha256_t rng;
int retry;
if (!seed32) {
/* 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.
*/
secp256k1_rfc6979_hmac_sha256_initialize(&rng, seed32 ? seed32 : nonce32, 32, nonce32, 32, NULL, 0);
/* 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);
/* 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);
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