diff options
Diffstat (limited to 'crypto/secp256k1/libsecp256k1/src/ecmult_impl.h')
| -rw-r--r-- | crypto/secp256k1/libsecp256k1/src/ecmult_impl.h | 389 |
1 files changed, 389 insertions, 0 deletions
diff --git a/crypto/secp256k1/libsecp256k1/src/ecmult_impl.h b/crypto/secp256k1/libsecp256k1/src/ecmult_impl.h new file mode 100644 index 000000000..e6e5f4718 --- /dev/null +++ b/crypto/secp256k1/libsecp256k1/src/ecmult_impl.h @@ -0,0 +1,389 @@ +/********************************************************************** + * Copyright (c) 2013, 2014 Pieter Wuille * + * Distributed under the MIT software license, see the accompanying * + * file COPYING or http://www.opensource.org/licenses/mit-license.php.* + **********************************************************************/ + +#ifndef _SECP256K1_ECMULT_IMPL_H_ +#define _SECP256K1_ECMULT_IMPL_H_ + +#include "group.h" +#include "scalar.h" +#include "ecmult.h" + +/* optimal for 128-bit and 256-bit exponents. */ +#define WINDOW_A 5 + +/** larger numbers may result in slightly better performance, at the cost of + exponentially larger precomputed tables. */ +#ifdef USE_ENDOMORPHISM +/** Two tables for window size 15: 1.375 MiB. */ +#define WINDOW_G 15 +#else +/** One table for window size 16: 1.375 MiB. */ +#define WINDOW_G 16 +#endif + +/** The number of entries a table with precomputed multiples needs to have. */ +#define ECMULT_TABLE_SIZE(w) (1 << ((w)-2)) + +/** Fill a table 'prej' with precomputed odd multiples of a. Prej will contain + * the values [1*a,3*a,...,(2*n-1)*a], so it space for n values. zr[0] will + * contain prej[0].z / a.z. The other zr[i] values = prej[i].z / prej[i-1].z. + * Prej's Z values are undefined, except for the last value. + */ +static void secp256k1_ecmult_odd_multiples_table(int n, secp256k1_gej *prej, secp256k1_fe *zr, const secp256k1_gej *a) { + secp256k1_gej d; + secp256k1_ge a_ge, d_ge; + int i; + + VERIFY_CHECK(!a->infinity); + + secp256k1_gej_double_var(&d, a, NULL); + + /* + * Perform the additions on an isomorphism where 'd' is affine: drop the z coordinate + * of 'd', and scale the 1P starting value's x/y coordinates without changing its z. + */ + d_ge.x = d.x; + d_ge.y = d.y; + d_ge.infinity = 0; + + secp256k1_ge_set_gej_zinv(&a_ge, a, &d.z); + prej[0].x = a_ge.x; + prej[0].y = a_ge.y; + prej[0].z = a->z; + prej[0].infinity = 0; + + zr[0] = d.z; + for (i = 1; i < n; i++) { + secp256k1_gej_add_ge_var(&prej[i], &prej[i-1], &d_ge, &zr[i]); + } + + /* + * Each point in 'prej' has a z coordinate too small by a factor of 'd.z'. Only + * the final point's z coordinate is actually used though, so just update that. + */ + secp256k1_fe_mul(&prej[n-1].z, &prej[n-1].z, &d.z); +} + +/** Fill a table 'pre' with precomputed odd multiples of a. + * + * There are two versions of this function: + * - secp256k1_ecmult_odd_multiples_table_globalz_windowa which brings its + * resulting point set to a single constant Z denominator, stores the X and Y + * coordinates as ge_storage points in pre, and stores the global Z in rz. + * It only operates on tables sized for WINDOW_A wnaf multiples. + * - secp256k1_ecmult_odd_multiples_table_storage_var, which converts its + * resulting point set to actually affine points, and stores those in pre. + * It operates on tables of any size, but uses heap-allocated temporaries. + * + * To compute a*P + b*G, we compute a table for P using the first function, + * and for G using the second (which requires an inverse, but it only needs to + * happen once). + */ +static void secp256k1_ecmult_odd_multiples_table_globalz_windowa(secp256k1_ge *pre, secp256k1_fe *globalz, const secp256k1_gej *a) { + secp256k1_gej prej[ECMULT_TABLE_SIZE(WINDOW_A)]; + secp256k1_fe zr[ECMULT_TABLE_SIZE(WINDOW_A)]; + + /* Compute the odd multiples in Jacobian form. */ + secp256k1_ecmult_odd_multiples_table(ECMULT_TABLE_SIZE(WINDOW_A), prej, zr, a); + /* Bring them to the same Z denominator. */ + secp256k1_ge_globalz_set_table_gej(ECMULT_TABLE_SIZE(WINDOW_A), pre, globalz, prej, zr); +} + +static void secp256k1_ecmult_odd_multiples_table_storage_var(int n, secp256k1_ge_storage *pre, const secp256k1_gej *a, const secp256k1_callback *cb) { + secp256k1_gej *prej = (secp256k1_gej*)checked_malloc(cb, sizeof(secp256k1_gej) * n); + secp256k1_ge *prea = (secp256k1_ge*)checked_malloc(cb, sizeof(secp256k1_ge) * n); + secp256k1_fe *zr = (secp256k1_fe*)checked_malloc(cb, sizeof(secp256k1_fe) * n); + int i; + + /* Compute the odd multiples in Jacobian form. */ + secp256k1_ecmult_odd_multiples_table(n, prej, zr, a); + /* Convert them in batch to affine coordinates. */ + secp256k1_ge_set_table_gej_var(n, prea, prej, zr); + /* Convert them to compact storage form. */ + for (i = 0; i < n; i++) { + secp256k1_ge_to_storage(&pre[i], &prea[i]); + } + + free(prea); + free(prej); + free(zr); +} + +/** The following two macro retrieves a particular odd multiple from a table + * of precomputed multiples. */ +#define ECMULT_TABLE_GET_GE(r,pre,n,w) do { \ + VERIFY_CHECK(((n) & 1) == 1); \ + VERIFY_CHECK((n) >= -((1 << ((w)-1)) - 1)); \ + VERIFY_CHECK((n) <= ((1 << ((w)-1)) - 1)); \ + if ((n) > 0) { \ + *(r) = (pre)[((n)-1)/2]; \ + } else { \ + secp256k1_ge_neg((r), &(pre)[(-(n)-1)/2]); \ + } \ +} while(0) + +#define ECMULT_TABLE_GET_GE_STORAGE(r,pre,n,w) do { \ + VERIFY_CHECK(((n) & 1) == 1); \ + VERIFY_CHECK((n) >= -((1 << ((w)-1)) - 1)); \ + VERIFY_CHECK((n) <= ((1 << ((w)-1)) - 1)); \ + if ((n) > 0) { \ + secp256k1_ge_from_storage((r), &(pre)[((n)-1)/2]); \ + } else { \ + secp256k1_ge_from_storage((r), &(pre)[(-(n)-1)/2]); \ + secp256k1_ge_neg((r), (r)); \ + } \ +} while(0) + +static void secp256k1_ecmult_context_init(secp256k1_ecmult_context *ctx) { + ctx->pre_g = NULL; +#ifdef USE_ENDOMORPHISM + ctx->pre_g_128 = NULL; +#endif +} + +static void secp256k1_ecmult_context_build(secp256k1_ecmult_context *ctx, const secp256k1_callback *cb) { + secp256k1_gej gj; + + if (ctx->pre_g != NULL) { + return; + } + + /* get the generator */ + secp256k1_gej_set_ge(&gj, &secp256k1_ge_const_g); + + ctx->pre_g = (secp256k1_ge_storage (*)[])checked_malloc(cb, sizeof((*ctx->pre_g)[0]) * ECMULT_TABLE_SIZE(WINDOW_G)); + + /* precompute the tables with odd multiples */ + secp256k1_ecmult_odd_multiples_table_storage_var(ECMULT_TABLE_SIZE(WINDOW_G), *ctx->pre_g, &gj, cb); + +#ifdef USE_ENDOMORPHISM + { + secp256k1_gej g_128j; + int i; + + ctx->pre_g_128 = (secp256k1_ge_storage (*)[])checked_malloc(cb, sizeof((*ctx->pre_g_128)[0]) * ECMULT_TABLE_SIZE(WINDOW_G)); + + /* calculate 2^128*generator */ + g_128j = gj; + for (i = 0; i < 128; i++) { + secp256k1_gej_double_var(&g_128j, &g_128j, NULL); + } + secp256k1_ecmult_odd_multiples_table_storage_var(ECMULT_TABLE_SIZE(WINDOW_G), *ctx->pre_g_128, &g_128j, cb); + } +#endif +} + +static void secp256k1_ecmult_context_clone(secp256k1_ecmult_context *dst, + const secp256k1_ecmult_context *src, const secp256k1_callback *cb) { + if (src->pre_g == NULL) { + dst->pre_g = NULL; + } else { + size_t size = sizeof((*dst->pre_g)[0]) * ECMULT_TABLE_SIZE(WINDOW_G); + dst->pre_g = (secp256k1_ge_storage (*)[])checked_malloc(cb, size); + memcpy(dst->pre_g, src->pre_g, size); + } +#ifdef USE_ENDOMORPHISM + if (src->pre_g_128 == NULL) { + dst->pre_g_128 = NULL; + } else { + size_t size = sizeof((*dst->pre_g_128)[0]) * ECMULT_TABLE_SIZE(WINDOW_G); + dst->pre_g_128 = (secp256k1_ge_storage (*)[])checked_malloc(cb, size); + memcpy(dst->pre_g_128, src->pre_g_128, size); + } +#endif +} + +static int secp256k1_ecmult_context_is_built(const secp256k1_ecmult_context *ctx) { + return ctx->pre_g != NULL; +} + +static void secp256k1_ecmult_context_clear(secp256k1_ecmult_context *ctx) { + free(ctx->pre_g); +#ifdef USE_ENDOMORPHISM + free(ctx->pre_g_128); +#endif + secp256k1_ecmult_context_init(ctx); +} + +/** Convert a number to WNAF notation. The number becomes represented by sum(2^i * wnaf[i], i=0..bits), + * with the following guarantees: + * - each wnaf[i] is either 0, or an odd integer between -(1<<(w-1) - 1) and (1<<(w-1) - 1) + * - two non-zero entries in wnaf are separated by at least w-1 zeroes. + * - the number of set values in wnaf is returned. This number is at most 256, and at most one more + * than the number of bits in the (absolute value) of the input. + */ +static int secp256k1_ecmult_wnaf(int *wnaf, int len, const secp256k1_scalar *a, int w) { + secp256k1_scalar s = *a; + int last_set_bit = -1; + int bit = 0; + int sign = 1; + int carry = 0; + + VERIFY_CHECK(wnaf != NULL); + VERIFY_CHECK(0 <= len && len <= 256); + VERIFY_CHECK(a != NULL); + VERIFY_CHECK(2 <= w && w <= 31); + + memset(wnaf, 0, len * sizeof(wnaf[0])); + + if (secp256k1_scalar_get_bits(&s, 255, 1)) { + secp256k1_scalar_negate(&s, &s); + sign = -1; + } + + while (bit < len) { + int now; + int word; + if (secp256k1_scalar_get_bits(&s, bit, 1) == (unsigned int)carry) { + bit++; + continue; + } + + now = w; + if (now > len - bit) { + now = len - bit; + } + + word = secp256k1_scalar_get_bits_var(&s, bit, now) + carry; + + carry = (word >> (w-1)) & 1; + word -= carry << w; + + wnaf[bit] = sign * word; + last_set_bit = bit; + + bit += now; + } +#ifdef VERIFY + CHECK(carry == 0); + while (bit < 256) { + CHECK(secp256k1_scalar_get_bits(&s, bit++, 1) == 0); + } +#endif + return last_set_bit + 1; +} + +static void secp256k1_ecmult(const secp256k1_ecmult_context *ctx, secp256k1_gej *r, const secp256k1_gej *a, const secp256k1_scalar *na, const secp256k1_scalar *ng) { + secp256k1_ge pre_a[ECMULT_TABLE_SIZE(WINDOW_A)]; + secp256k1_ge tmpa; + secp256k1_fe Z; +#ifdef USE_ENDOMORPHISM + secp256k1_ge pre_a_lam[ECMULT_TABLE_SIZE(WINDOW_A)]; + secp256k1_scalar na_1, na_lam; + /* Splitted G factors. */ + secp256k1_scalar ng_1, ng_128; + int wnaf_na_1[130]; + int wnaf_na_lam[130]; + int bits_na_1; + int bits_na_lam; + int wnaf_ng_1[129]; + int bits_ng_1; + int wnaf_ng_128[129]; + int bits_ng_128; +#else + int wnaf_na[256]; + int bits_na; + int wnaf_ng[256]; + int bits_ng; +#endif + int i; + int bits; + +#ifdef USE_ENDOMORPHISM + /* split na into na_1 and na_lam (where na = na_1 + na_lam*lambda, and na_1 and na_lam are ~128 bit) */ + secp256k1_scalar_split_lambda(&na_1, &na_lam, na); + + /* build wnaf representation for na_1 and na_lam. */ + bits_na_1 = secp256k1_ecmult_wnaf(wnaf_na_1, 130, &na_1, WINDOW_A); + bits_na_lam = secp256k1_ecmult_wnaf(wnaf_na_lam, 130, &na_lam, WINDOW_A); + VERIFY_CHECK(bits_na_1 <= 130); + VERIFY_CHECK(bits_na_lam <= 130); + bits = bits_na_1; + if (bits_na_lam > bits) { + bits = bits_na_lam; + } +#else + /* build wnaf representation for na. */ + bits_na = secp256k1_ecmult_wnaf(wnaf_na, 256, na, WINDOW_A); + bits = bits_na; +#endif + + /* Calculate odd multiples of a. + * All multiples are brought to the same Z 'denominator', which is stored + * in Z. Due to secp256k1' isomorphism we can do all operations pretending + * that the Z coordinate was 1, use affine addition formulae, and correct + * the Z coordinate of the result once at the end. + * The exception is the precomputed G table points, which are actually + * affine. Compared to the base used for other points, they have a Z ratio + * of 1/Z, so we can use secp256k1_gej_add_zinv_var, which uses the same + * isomorphism to efficiently add with a known Z inverse. + */ + secp256k1_ecmult_odd_multiples_table_globalz_windowa(pre_a, &Z, a); + +#ifdef USE_ENDOMORPHISM + for (i = 0; i < ECMULT_TABLE_SIZE(WINDOW_A); i++) { + secp256k1_ge_mul_lambda(&pre_a_lam[i], &pre_a[i]); + } + + /* split ng into ng_1 and ng_128 (where gn = gn_1 + gn_128*2^128, and gn_1 and gn_128 are ~128 bit) */ + secp256k1_scalar_split_128(&ng_1, &ng_128, ng); + + /* Build wnaf representation for ng_1 and ng_128 */ + bits_ng_1 = secp256k1_ecmult_wnaf(wnaf_ng_1, 129, &ng_1, WINDOW_G); + bits_ng_128 = secp256k1_ecmult_wnaf(wnaf_ng_128, 129, &ng_128, WINDOW_G); + if (bits_ng_1 > bits) { + bits = bits_ng_1; + } + if (bits_ng_128 > bits) { + bits = bits_ng_128; + } +#else + bits_ng = secp256k1_ecmult_wnaf(wnaf_ng, 256, ng, WINDOW_G); + if (bits_ng > bits) { + bits = bits_ng; + } +#endif + + secp256k1_gej_set_infinity(r); + + for (i = bits - 1; i >= 0; i--) { + int n; + secp256k1_gej_double_var(r, r, NULL); +#ifdef USE_ENDOMORPHISM + if (i < bits_na_1 && (n = wnaf_na_1[i])) { + ECMULT_TABLE_GET_GE(&tmpa, pre_a, n, WINDOW_A); + secp256k1_gej_add_ge_var(r, r, &tmpa, NULL); + } + if (i < bits_na_lam && (n = wnaf_na_lam[i])) { + ECMULT_TABLE_GET_GE(&tmpa, pre_a_lam, n, WINDOW_A); + secp256k1_gej_add_ge_var(r, r, &tmpa, NULL); + } + if (i < bits_ng_1 && (n = wnaf_ng_1[i])) { + ECMULT_TABLE_GET_GE_STORAGE(&tmpa, *ctx->pre_g, n, WINDOW_G); + secp256k1_gej_add_zinv_var(r, r, &tmpa, &Z); + } + if (i < bits_ng_128 && (n = wnaf_ng_128[i])) { + ECMULT_TABLE_GET_GE_STORAGE(&tmpa, *ctx->pre_g_128, n, WINDOW_G); + secp256k1_gej_add_zinv_var(r, r, &tmpa, &Z); + } +#else + if (i < bits_na && (n = wnaf_na[i])) { + ECMULT_TABLE_GET_GE(&tmpa, pre_a, n, WINDOW_A); + secp256k1_gej_add_ge_var(r, r, &tmpa, NULL); + } + if (i < bits_ng && (n = wnaf_ng[i])) { + ECMULT_TABLE_GET_GE_STORAGE(&tmpa, *ctx->pre_g, n, WINDOW_G); + secp256k1_gej_add_zinv_var(r, r, &tmpa, &Z); + } +#endif + } + + if (!r->infinity) { + secp256k1_fe_mul(&r->z, &r->z, &Z); + } +} + +#endif |