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Signed-digit multi-comb ecmult_gen algorithm

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This introduces the signed-digit multi-comb multiplication algorithm
for constant-time G multiplications (ecmult_gen). It is based on
section 3.3 of "Fast and compact elliptic-curve cryptography" by
Mike Hamburg (see https://eprint.iacr.org/2012/309).

Original implementation by Peter Dettman, with changes by Pieter Wuille
to use scalars for recoding, and additional comments.
This commit is contained in:
Peter Dettman
2021-12-26 18:09:27 -05:00
committed by Pieter Wuille
parent 486518b350
commit fde1dfcd8d
8 changed files with 762 additions and 9876 deletions
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69
src/precompute_ecmult_gen.c
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@@ -17,10 +17,42 @@
#include "ecmult_gen.h"
#include "ecmult_gen_compute_table_impl.h"
static const int CONFIGS[1][2] = {
{11, 6}
};
static void print_table(FILE* fp, int blocks, int teeth) {
size_t points = ((size_t)1) << (teeth - 1);
int outer;
size_t inner;
secp256k1_ge_storage* table = checked_malloc(&default_error_callback, blocks * points * sizeof(secp256k1_ge_storage));
secp256k1_ecmult_gen_compute_table(table, &secp256k1_ge_const_g, blocks, teeth);
fprintf(fp, "#elif (COMB_BLOCKS == %d) && (COMB_TEETH == %d)\n", blocks, teeth);
for (outer = 0; outer != blocks; outer++) {
fprintf(fp,"{");
for (inner = 0; inner != points; inner++) {
fprintf(fp, "S(%"PRIx32",%"PRIx32",%"PRIx32",%"PRIx32",%"PRIx32",%"PRIx32",%"PRIx32",%"PRIx32
",%"PRIx32",%"PRIx32",%"PRIx32",%"PRIx32",%"PRIx32",%"PRIx32",%"PRIx32",%"PRIx32")",
SECP256K1_GE_STORAGE_CONST_GET(table[outer * points + inner]));
if (inner != points - 1) {
fprintf(fp,",\n");
}
}
if (outer != blocks - 1) {
fprintf(fp,"},\n");
} else {
fprintf(fp,"}\n");
}
}
free(table);
}
int main(int argc, char **argv) {
const char outfile[] = "src/precomputed_ecmult_gen.c";
FILE* fp;
int bits;
size_t config;
(void)argc;
(void)argv;
@@ -40,36 +72,15 @@ int main(int argc, char **argv) {
fprintf(fp, "# error Cannot compile precomputed_ecmult_gen.c in exhaustive test mode\n");
fprintf(fp, "#endif /* EXHAUSTIVE_TEST_ORDER */\n");
fprintf(fp, "#define S(a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p) SECP256K1_GE_STORAGE_CONST(0x##a##u,0x##b##u,0x##c##u,0x##d##u,0x##e##u,0x##f##u,0x##g##u,0x##h##u,0x##i##u,0x##j##u,0x##k##u,0x##l##u,0x##m##u,0x##n##u,0x##o##u,0x##p##u)\n");
fprintf(fp, "const secp256k1_ge_storage secp256k1_ecmult_gen_prec_table[ECMULT_GEN_PREC_N(ECMULT_GEN_PREC_BITS)][ECMULT_GEN_PREC_G(ECMULT_GEN_PREC_BITS)] = {\n");
for (bits = 2; bits <= 8; bits *= 2) {
int g = ECMULT_GEN_PREC_G(bits);
int n = ECMULT_GEN_PREC_N(bits);
int inner, outer;
secp256k1_ge_storage* table = checked_malloc(&default_error_callback, n * g * sizeof(secp256k1_ge_storage));
secp256k1_ecmult_gen_compute_table(table, &secp256k1_ge_const_g, bits);
fprintf(fp, "#if ECMULT_GEN_PREC_BITS == %d\n", bits);
for(outer = 0; outer != n; outer++) {
fprintf(fp,"{");
for(inner = 0; inner != g; inner++) {
fprintf(fp, "S(%"PRIx32",%"PRIx32",%"PRIx32",%"PRIx32",%"PRIx32",%"PRIx32",%"PRIx32",%"PRIx32
",%"PRIx32",%"PRIx32",%"PRIx32",%"PRIx32",%"PRIx32",%"PRIx32",%"PRIx32",%"PRIx32")",
SECP256K1_GE_STORAGE_CONST_GET(table[outer * g + inner]));
if (inner != g - 1) {
fprintf(fp,",\n");
}
}
if (outer != n - 1) {
fprintf(fp,"},\n");
} else {
fprintf(fp,"}\n");
}
}
fprintf(fp, "#endif\n");
free(table);
fprintf(fp, "const secp256k1_ge_storage secp256k1_ecmult_gen_prec_table[COMB_BLOCKS][COMB_POINTS] = {\n");
fprintf(fp, "#if 0\n");
for (config = 0; config < sizeof(CONFIGS) / sizeof(*CONFIGS); ++config) {
print_table(fp, CONFIGS[config][0], CONFIGS[config][1]);
}
fprintf(fp, "#else\n");
fprintf(fp, "# error Configuration mismatch, invalid COMB_* parameters. Try deleting precomputed_ecmult_gen.c before the build.\n");
fprintf(fp, "#endif\n");
fprintf(fp, "};\n");
fprintf(fp, "#undef S\n");