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Signed-digit multi-comb for ecmult_gen #546

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Signed-digit multi-comb for ecmult_gen #546

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75d9e97
Signed-digit multi-comb for ecmult_gen
peterdettman Aug 2, 2018
09ca146
Support static precomputation with multi-comb
peterdettman Aug 5, 2018
e8beef9
Add comments for context offset
peterdettman Sep 23, 2018
183a7ff
Reduce side-channels from single-bit reads
peterdettman Sep 24, 2018
e848342
Avoid unnecessary doublings in precomputation
peterdettman Sep 24, 2018
4c8ff9b
Add precompiler guards on comb constants
peterdettman Sep 24, 2018
9156619
Make use of negation optional via COMB_NEGATION
peterdettman Sep 24, 2018
91179c1
Add missing COMB_NEGATION for exhaustive tests
peterdettman Sep 24, 2018
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2 changes: 0 additions & 2 deletions src/ecmult_gen.h
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Original file line number Diff line number Diff line change
Expand Up @@ -10,9 +10,7 @@
#include "scalar.h"
#include "group.h"

#ifndef USE_ECMULT_STATIC_PRECOMPUTATION
#define USE_COMB 1
#endif

#if USE_COMB

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20 changes: 15 additions & 5 deletions src/ecmult_gen_impl.h
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Expand Up @@ -141,7 +141,14 @@ static void secp256k1_ecmult_gen_context_build(secp256k1_ecmult_gen_context *ctx
#endif
#else
(void)cb;
ctx->prec = (secp256k1_ge_storage (*)[64][16])secp256k1_ecmult_static_context;
#if USE_COMB
ctx->prec = (secp256k1_ge_storage (*)[COMB_BLOCKS][COMB_POINTS])secp256k1_ecmult_gen_ctx_prec;
#if COMB_OFFSET
secp256k1_ge_from_storage(&ctx->offset, &secp256k1_ecmult_gen_ctx_offset);
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secp256k1_ecmult_gen_ctx_offset is not declared except in gen_context.c, so this line doesn't compile for me when I set the parameters to 4/4/16.

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This is a build system issue; there's no dependency of gen_context on ecmult_gen.h (and presumably others). At the moment, after changing comb parameters in ecmult_gen.h, you'd need to touch gen_context.c (or just make clean).

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This has burned me multiple times while testing -- @sipa can you advise how to fix this?

#endif
#else
ctx->prec = (secp256k1_ge_storage (*)[64][16])secp256k1_ecmult_gen_ctx_prec;
#endif
#endif
secp256k1_ecmult_gen_blind(ctx, NULL);
}
Expand All @@ -158,16 +165,19 @@ static void secp256k1_ecmult_gen_context_clone(secp256k1_ecmult_gen_context *dst
#ifndef USE_ECMULT_STATIC_PRECOMPUTATION
#if USE_COMB
dst->prec = (secp256k1_ge_storage (*)[COMB_BLOCKS][COMB_POINTS])checked_malloc(cb, sizeof(*dst->prec));
#if COMB_OFFSET
dst->offset = src->offset;
#endif
#else
dst->prec = (secp256k1_ge_storage (*)[64][16])checked_malloc(cb, sizeof(*dst->prec));
#endif
memcpy(dst->prec, src->prec, sizeof(*dst->prec));
#else
(void)cb;
dst->prec = src->prec;
#endif

#if USE_COMB
#if COMB_OFFSET
dst->offset = src->offset;
#endif
#endif
dst->initial = src->initial;
dst->blind = src->blind;
Expand All @@ -177,11 +187,11 @@ static void secp256k1_ecmult_gen_context_clone(secp256k1_ecmult_gen_context *dst
static void secp256k1_ecmult_gen_context_clear(secp256k1_ecmult_gen_context *ctx) {
#ifndef USE_ECMULT_STATIC_PRECOMPUTATION
free(ctx->prec);
#endif
#if USE_COMB
#if COMB_OFFSET
secp256k1_ge_clear(&ctx->offset);
#endif
#endif
#endif
secp256k1_scalar_clear(&ctx->blind);
secp256k1_gej_clear(&ctx->initial);
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35 changes: 29 additions & 6 deletions src/gen_context.c
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Expand Up @@ -29,6 +29,18 @@ int main(int argc, char **argv) {
int inner;
int outer;
FILE* fp;
const char *SC_FORMAT = " SC(%uu, %uu, %uu, %uu, %uu, %uu, %uu, %uu, %uu, %uu, %uu, %uu, %uu, %uu, %uu, %uu)";

#if USE_COMB
const int blocks = COMB_BLOCKS;
const int points = COMB_POINTS;
#if COMB_OFFSET
secp256k1_ge_storage offset;
#endif
#else
const int blocks = 64;
const int points = 16;
#endif

(void)argc;
(void)argv;
Expand All @@ -43,21 +55,32 @@ int main(int argc, char **argv) {
fprintf(fp, "#define _SECP256K1_ECMULT_STATIC_CONTEXT_\n");
fprintf(fp, "#include \"src/group.h\"\n");
fprintf(fp, "#define SC SECP256K1_GE_STORAGE_CONST\n");
fprintf(fp, "static const secp256k1_ge_storage secp256k1_ecmult_static_context[64][16] = {\n");

secp256k1_ecmult_gen_context_init(&ctx);
secp256k1_ecmult_gen_context_build(&ctx, &default_error_callback);
for(outer = 0; outer != 64; outer++) {

#if USE_COMB
#if COMB_OFFSET
secp256k1_ge_to_storage(&offset, &ctx.offset);
fprintf(fp, "static const secp256k1_ge_storage secp256k1_ecmult_gen_ctx_offset =\n");
fprintf(fp, SC_FORMAT, SECP256K1_GE_STORAGE_CONST_GET(offset));
fprintf(fp, ";\n");
#endif
#endif

fprintf(fp, "static const secp256k1_ge_storage secp256k1_ecmult_gen_ctx_prec[%i][%i] = {\n",
blocks, points);
for(outer = 0; outer != blocks; outer++) {
fprintf(fp,"{\n");
for(inner = 0; inner != 16; inner++) {
fprintf(fp," SC(%uu, %uu, %uu, %uu, %uu, %uu, %uu, %uu, %uu, %uu, %uu, %uu, %uu, %uu, %uu, %uu)", SECP256K1_GE_STORAGE_CONST_GET((*ctx.prec)[outer][inner]));
if (inner != 15) {
for(inner = 0; inner != points; inner++) {
fprintf(fp, SC_FORMAT, SECP256K1_GE_STORAGE_CONST_GET((*ctx.prec)[outer][inner]));
if (inner != (points - 1)) {
fprintf(fp,",\n");
} else {
fprintf(fp,"\n");
}
}
if (outer != 63) {
if (outer != (blocks - 1)) {
fprintf(fp,"},\n");
} else {
fprintf(fp,"}\n");
Expand Down