MOVE ONLY: move Pedersen commitment stuff to generator module from rangeproof module
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This commit is contained in:
Andrew Poelstra
committed by
sanket1729
sanket1729
parent
b1f1675375
commit
87373f5145
@@ -14,6 +14,29 @@
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#include "../../hash.h"
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#include "../../scalar.h"
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#include "modules/generator/pedersen_impl.h"
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/** Alternative generator for secp256k1.
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* This is the sha256 of 'g' after standard encoding (without compression),
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* which happens to be a point on the curve. More precisely, the generator is
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* derived by running the following script with the sage mathematics software.
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import hashlib
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F = FiniteField (0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEFFFFFC2F)
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G = '0479be667ef9dcbbac55a06295ce870b07029bfcdb2dce28d959f2815b16f81798483ada7726a3c4655da4fbfc0e1108a8fd17b448a68554199c47d08ffb10d4b8'
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H = EllipticCurve ([F (0), F (7)]).lift_x(F(int(hashlib.sha256(G.decode('hex')).hexdigest(),16)))
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print('%x %x' % H.xy())
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*/
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static const secp256k1_generator secp256k1_generator_h_internal = {{
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0x50, 0x92, 0x9b, 0x74, 0xc1, 0xa0, 0x49, 0x54, 0xb7, 0x8b, 0x4b, 0x60, 0x35, 0xe9, 0x7a, 0x5e,
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0x07, 0x8a, 0x5a, 0x0f, 0x28, 0xec, 0x96, 0xd5, 0x47, 0xbf, 0xee, 0x9a, 0xce, 0x80, 0x3a, 0xc0,
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0x31, 0xd3, 0xc6, 0x86, 0x39, 0x73, 0x92, 0x6e, 0x04, 0x9e, 0x63, 0x7c, 0xb1, 0xb5, 0xf4, 0x0a,
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0x36, 0xda, 0xc2, 0x8a, 0xf1, 0x76, 0x69, 0x68, 0xc3, 0x0c, 0x23, 0x13, 0xf3, 0xa3, 0x89, 0x04
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}};
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const secp256k1_generator *secp256k1_generator_h = &secp256k1_generator_h_internal;
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static void secp256k1_generator_load(secp256k1_ge* ge, const secp256k1_generator* gen) {
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int succeed;
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succeed = secp256k1_fe_set_b32(&ge->x, &gen->data[0]);
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@@ -219,4 +242,200 @@ int secp256k1_generator_generate_blinded(const secp256k1_context* ctx, secp256k1
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return secp256k1_generator_generate_internal(ctx, gen, key32, blind32);
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}
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static void secp256k1_pedersen_commitment_load(secp256k1_ge* ge, const secp256k1_pedersen_commitment* commit) {
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secp256k1_fe fe;
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secp256k1_fe_set_b32(&fe, &commit->data[1]);
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secp256k1_ge_set_xquad(ge, &fe);
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if (commit->data[0] & 1) {
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secp256k1_ge_neg(ge, ge);
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}
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}
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static void secp256k1_pedersen_commitment_save(secp256k1_pedersen_commitment* commit, secp256k1_ge* ge) {
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secp256k1_fe_normalize(&ge->x);
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secp256k1_fe_get_b32(&commit->data[1], &ge->x);
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commit->data[0] = 9 ^ secp256k1_fe_is_quad_var(&ge->y);
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}
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int secp256k1_pedersen_commitment_parse(const secp256k1_context* ctx, secp256k1_pedersen_commitment* commit, const unsigned char *input) {
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secp256k1_fe x;
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secp256k1_ge ge;
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VERIFY_CHECK(ctx != NULL);
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ARG_CHECK(commit != NULL);
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ARG_CHECK(input != NULL);
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(void) ctx;
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if ((input[0] & 0xFE) != 8 ||
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!secp256k1_fe_set_b32(&x, &input[1]) ||
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!secp256k1_ge_set_xquad(&ge, &x)) {
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return 0;
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}
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if (input[0] & 1) {
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secp256k1_ge_neg(&ge, &ge);
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}
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secp256k1_pedersen_commitment_save(commit, &ge);
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return 1;
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}
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int secp256k1_pedersen_commitment_serialize(const secp256k1_context* ctx, unsigned char *output, const secp256k1_pedersen_commitment* commit) {
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secp256k1_ge ge;
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VERIFY_CHECK(ctx != NULL);
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ARG_CHECK(output != NULL);
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ARG_CHECK(commit != NULL);
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secp256k1_pedersen_commitment_load(&ge, commit);
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output[0] = 9 ^ secp256k1_fe_is_quad_var(&ge.y);
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secp256k1_fe_normalize_var(&ge.x);
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secp256k1_fe_get_b32(&output[1], &ge.x);
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return 1;
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}
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/* Generates a pedersen commitment: *commit = blind * G + value * G2. The blinding factor is 32 bytes.*/
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int secp256k1_pedersen_commit(const secp256k1_context* ctx, secp256k1_pedersen_commitment *commit, const unsigned char *blind, uint64_t value, const secp256k1_generator* gen) {
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secp256k1_ge genp;
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secp256k1_gej rj;
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secp256k1_ge r;
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secp256k1_scalar sec;
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int overflow;
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int ret = 0;
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VERIFY_CHECK(ctx != NULL);
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ARG_CHECK(secp256k1_ecmult_gen_context_is_built(&ctx->ecmult_gen_ctx));
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ARG_CHECK(commit != NULL);
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ARG_CHECK(blind != NULL);
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ARG_CHECK(gen != NULL);
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secp256k1_generator_load(&genp, gen);
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secp256k1_scalar_set_b32(&sec, blind, &overflow);
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if (!overflow) {
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secp256k1_pedersen_ecmult(&ctx->ecmult_gen_ctx, &rj, &sec, value, &genp);
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if (!secp256k1_gej_is_infinity(&rj)) {
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secp256k1_ge_set_gej(&r, &rj);
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secp256k1_pedersen_commitment_save(commit, &r);
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ret = 1;
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}
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secp256k1_gej_clear(&rj);
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secp256k1_ge_clear(&r);
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}
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secp256k1_scalar_clear(&sec);
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return ret;
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}
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/** Takes a list of n pointers to 32 byte blinding values, the first negs of which are treated with positive sign and the rest
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* negative, then calculates an additional blinding value that adds to zero.
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*/
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int secp256k1_pedersen_blind_sum(const secp256k1_context* ctx, unsigned char *blind_out, const unsigned char * const *blinds, size_t n, size_t npositive) {
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secp256k1_scalar acc;
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secp256k1_scalar x;
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size_t i;
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int overflow;
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VERIFY_CHECK(ctx != NULL);
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ARG_CHECK(blind_out != NULL);
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ARG_CHECK(blinds != NULL);
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ARG_CHECK(npositive <= n);
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(void) ctx;
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secp256k1_scalar_set_int(&acc, 0);
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for (i = 0; i < n; i++) {
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secp256k1_scalar_set_b32(&x, blinds[i], &overflow);
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if (overflow) {
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return 0;
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}
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if (i >= npositive) {
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secp256k1_scalar_negate(&x, &x);
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}
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secp256k1_scalar_add(&acc, &acc, &x);
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}
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secp256k1_scalar_get_b32(blind_out, &acc);
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secp256k1_scalar_clear(&acc);
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secp256k1_scalar_clear(&x);
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return 1;
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}
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/* Takes two lists of commitments and sums the first set and subtracts the second and verifies that they sum to excess. */
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int secp256k1_pedersen_verify_tally(const secp256k1_context* ctx, const secp256k1_pedersen_commitment * const* commits, size_t pcnt, const secp256k1_pedersen_commitment * const* ncommits, size_t ncnt) {
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secp256k1_gej accj;
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secp256k1_ge add;
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size_t i;
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VERIFY_CHECK(ctx != NULL);
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ARG_CHECK(!pcnt || (commits != NULL));
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ARG_CHECK(!ncnt || (ncommits != NULL));
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(void) ctx;
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secp256k1_gej_set_infinity(&accj);
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for (i = 0; i < ncnt; i++) {
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secp256k1_pedersen_commitment_load(&add, ncommits[i]);
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secp256k1_gej_add_ge_var(&accj, &accj, &add, NULL);
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}
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secp256k1_gej_neg(&accj, &accj);
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for (i = 0; i < pcnt; i++) {
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secp256k1_pedersen_commitment_load(&add, commits[i]);
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secp256k1_gej_add_ge_var(&accj, &accj, &add, NULL);
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}
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return secp256k1_gej_is_infinity(&accj);
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}
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int secp256k1_pedersen_blind_generator_blind_sum(const secp256k1_context* ctx, const uint64_t *value, const unsigned char* const* generator_blind, unsigned char* const* blinding_factor, size_t n_total, size_t n_inputs) {
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secp256k1_scalar sum;
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secp256k1_scalar tmp;
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size_t i;
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VERIFY_CHECK(ctx != NULL);
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ARG_CHECK(n_total == 0 || value != NULL);
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ARG_CHECK(n_total == 0 || generator_blind != NULL);
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ARG_CHECK(n_total == 0 || blinding_factor != NULL);
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ARG_CHECK(n_total > n_inputs);
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(void) ctx;
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if (n_total == 0) {
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return 1;
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}
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secp256k1_scalar_set_int(&sum, 0);
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/* Here, n_total > 0. Thus the loop runs at least once.
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Thus we may use a do-while loop, which checks the loop
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condition only at the end.
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The do-while loop helps GCC prove that the loop runs at least
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once and suppresses a -Wmaybe-uninitialized warning. */
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i = 0;
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do {
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int overflow = 0;
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secp256k1_scalar addend;
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secp256k1_scalar_set_u64(&addend, value[i]); /* s = v */
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secp256k1_scalar_set_b32(&tmp, generator_blind[i], &overflow);
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if (overflow == 1) {
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secp256k1_scalar_clear(&tmp);
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secp256k1_scalar_clear(&addend);
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secp256k1_scalar_clear(&sum);
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return 0;
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}
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secp256k1_scalar_mul(&addend, &addend, &tmp); /* s = vr */
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secp256k1_scalar_set_b32(&tmp, blinding_factor[i], &overflow);
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if (overflow == 1) {
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secp256k1_scalar_clear(&tmp);
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secp256k1_scalar_clear(&addend);
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secp256k1_scalar_clear(&sum);
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return 0;
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}
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secp256k1_scalar_add(&addend, &addend, &tmp); /* s = vr + r' */
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secp256k1_scalar_cond_negate(&addend, i < n_inputs); /* s is negated if it's an input */
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secp256k1_scalar_add(&sum, &sum, &addend); /* sum += s */
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secp256k1_scalar_clear(&addend);
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i++;
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} while (i < n_total);
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/* Right now tmp has the last pedersen blinding factor. Subtract the sum from it. */
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secp256k1_scalar_negate(&sum, &sum);
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secp256k1_scalar_add(&tmp, &tmp, &sum);
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secp256k1_scalar_get_b32(blinding_factor[n_total - 1], &tmp);
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secp256k1_scalar_clear(&tmp);
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secp256k1_scalar_clear(&sum);
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return 1;
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}
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#endif
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