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surjection proof: Reject proofs with too many used inputs in reduced mode

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This commit is contained in:
Tim Ruffing 2019-06-05 11:15:11 +02:00
parent 112edb2c6a
commit f7e4d08dae
3 changed files with 20 additions and 3 deletions
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5
src/modules/surjection/main_impl.h
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@ -373,6 +373,11 @@ int secp256k1_surjectionproof_verify(const secp256k1_context* ctx, const secp256
return 0;
}
/* Reject proofs with too many used inputs in USE_REDUCED_SURJECTION_PROOF_SIZE mode */
if (n_used_pubkeys > SECP256K1_SURJECTIONPROOF_MAX_USED_INPUTS) {
return 0;
}
if (secp256k1_surjection_compute_public_keys(ring_pubkeys, n_used_pubkeys, ephemeral_input_tags, n_total_pubkeys, proof->used_inputs, ephemeral_output_tag, 0, NULL) == 0) {
return 0;
}

8
src/modules/surjection/surjection_impl.h
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@ -69,6 +69,9 @@ SECP256K1_INLINE static int secp256k1_surjection_compute_public_keys(secp256k1_g
secp256k1_ge tmpge;
secp256k1_generator_load(&tmpge, &input_tags[i]);
secp256k1_ge_neg(&tmpge, &tmpge);
VERIFY_CHECK(j < SECP256K1_SURJECTIONPROOF_MAX_USED_INPUTS);
VERIFY_CHECK(j < n_pubkeys);
secp256k1_gej_set_ge(&pubkeys[j], &tmpge);
secp256k1_generator_load(&tmpge, output_tag);
@ -77,11 +80,10 @@ SECP256K1_INLINE static int secp256k1_surjection_compute_public_keys(secp256k1_g
*ring_input_index = j;
}
j++;
if (j > n_pubkeys || j > SECP256K1_SURJECTIONPROOF_MAX_USED_INPUTS) {
return 0;
}
}
}
/* Caller needs to ensure that the number of set bits in used_tags (which we counted in j) equals n_pubkeys. */
VERIFY_CHECK(j == n_pubkeys);
return 1;
}

10
src/modules/surjection/tests_impl.h
View File

@ -427,6 +427,7 @@ static void test_gen_verify(size_t n_inputs, size_t n_used) {
CHECK(secp256k1_surjectionproof_parse(ctx, &proof, serialized_proof, serialized_len));
result = secp256k1_surjectionproof_verify(ctx, &proof, ephemeral_input_tags, n_inputs, &ephemeral_input_tags[n_inputs]);
CHECK(result == 1);
/* various fail cases */
if (n_inputs > 1) {
result = secp256k1_surjectionproof_verify(ctx, &proof, ephemeral_input_tags, n_inputs, &ephemeral_input_tags[n_inputs - 1]);
@ -441,6 +442,15 @@ static void test_gen_verify(size_t n_inputs, size_t n_used) {
n_inputs += 1;
}
for (i = 0; i < n_inputs; i++) {
/* flip bit */
proof.used_inputs[i / 8] ^= (1 << (i % 8));
result = secp256k1_surjectionproof_verify(ctx, &proof, ephemeral_input_tags, n_inputs, &ephemeral_input_tags[n_inputs]);
CHECK(result == 0);
/* reset the bit */
proof.used_inputs[i / 8] ^= (1 << (i % 8));
}
/* cleanup */
for (i = 0; i < n_inputs + 1; i++) {
free(input_blinding_key[i]);