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Merge pull request #8052
c36ea26
fix ge_p3_is_point_at_infinity(), which is evaluating field elements that haven't been reduced by the field order (koe)
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commit
abae63c37d
7 changed files with 111 additions and 11 deletions
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@ -3830,15 +3830,51 @@ int sc_isnonzero(const unsigned char *s) {
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s[27] | s[28] | s[29] | s[30] | s[31]) - 1) >> 8) + 1;
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}
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int ge_p3_is_point_at_infinity(const ge_p3 *p) {
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// X = 0 and Y == Z
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int n;
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for (n = 0; n < 10; ++n)
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int ge_p3_is_point_at_infinity_vartime(const ge_p3 *p) {
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// https://eprint.iacr.org/2008/522
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// X == T == 0 and Y/Z == 1
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// note: convert all pieces to canonical bytes in case rounding is required (i.e. an element is > q)
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// note2: even though T = XY/Z is true for valid point representations (implying it isn't necessary to
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// test T == 0), the input to this function might NOT be valid, so we must test T == 0
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char result_X_bytes[32];
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fe_tobytes((unsigned char*)&result_X_bytes, p->X);
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// X != 0
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for (int i = 0; i < 32; ++i)
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{
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if (p->X[n] | p->T[n])
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return 0;
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if (p->Y[n] != p->Z[n])
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if (result_X_bytes[i])
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return 0;
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}
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return 1;
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char result_T_bytes[32];
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fe_tobytes((unsigned char*)&result_T_bytes, p->T);
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// T != 0
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for (int i = 0; i < 32; ++i)
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{
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if (result_T_bytes[i])
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return 0;
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}
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char result_Y_bytes[32];
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char result_Z_bytes[32];
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fe_tobytes((unsigned char*)&result_Y_bytes, p->Y);
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fe_tobytes((unsigned char*)&result_Z_bytes, p->Z);
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// Y != Z
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for (int i = 0; i < 32; ++i)
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{
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if (result_Y_bytes[i] != result_Z_bytes[i])
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return 0;
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}
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// is Y nonzero? then Y/Z == 1
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for (int i = 0; i < 32; ++i)
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{
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if (result_Y_bytes[i] != 0)
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return 1;
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}
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// Y/Z = 0/0
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return 0;
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}
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@ -162,4 +162,4 @@ void fe_add(fe h, const fe f, const fe g);
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void fe_tobytes(unsigned char *, const fe);
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void fe_invert(fe out, const fe z);
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int ge_p3_is_point_at_infinity(const ge_p3 *p);
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int ge_p3_is_point_at_infinity_vartime(const ge_p3 *p);
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@ -235,7 +235,7 @@ rct::key bos_coster_heap_conv_robust(std::vector<MultiexpData> data)
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heap.reserve(points);
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for (size_t n = 0; n < points; ++n)
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{
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if (!(data[n].scalar == rct::zero()) && !ge_p3_is_point_at_infinity(&data[n].point))
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if (!(data[n].scalar == rct::zero()) && !ge_p3_is_point_at_infinity_vartime(&data[n].point))
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heap.push_back(n);
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}
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points = heap.size();
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@ -457,7 +457,7 @@ rct::key straus(const std::vector<MultiexpData> &data, const std::shared_ptr<str
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MULTIEXP_PERF(PERF_TIMER_START_UNIT(skip, 1000000));
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std::vector<uint8_t> skip(data.size());
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for (size_t i = 0; i < data.size(); ++i)
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skip[i] = data[i].scalar == rct::zero() || ge_p3_is_point_at_infinity(&data[i].point);
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skip[i] = data[i].scalar == rct::zero() || ge_p3_is_point_at_infinity_vartime(&data[i].point);
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MULTIEXP_PERF(PERF_TIMER_STOP(skip));
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#endif
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@ -46,4 +46,6 @@ void random_scalar(crypto::ec_scalar &res);
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void hash_to_scalar(const void *data, std::size_t length, crypto::ec_scalar &res);
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void hash_to_point(const crypto::hash &h, crypto::ec_point &res);
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void hash_to_ec(const crypto::public_key &key, crypto::ec_point &res);
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bool check_ge_p3_identity_failure(const crypto::public_key &point);
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bool check_ge_p3_identity_success(const crypto::public_key &point);
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#endif
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@ -32,6 +32,36 @@
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#include "crypto-tests.h"
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static void get_ge_p3_for_identity_test(const crypto::public_key &point, crypto::ge_p3 &result_out_p3)
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{
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// compute (K + K) - K - K to get a specific ge_p3 point representation of identity
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crypto::ge_cached temp_cache;
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crypto::ge_p1p1 temp_p1p1;
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crypto::ge_frombytes_vartime(&result_out_p3, &point); // K
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crypto::ge_p3_to_cached(&temp_cache, &result_out_p3);
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crypto::ge_add(&temp_p1p1, &result_out_p3, &temp_cache); // K + K
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crypto::ge_p1p1_to_p3(&result_out_p3, &temp_p1p1);
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crypto::ge_sub(&temp_p1p1, &result_out_p3, &temp_cache); // (K + K) - K
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crypto::ge_p1p1_to_p3(&result_out_p3, &temp_p1p1);
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crypto::ge_sub(&temp_p1p1, &result_out_p3, &temp_cache); // ((K + K) - K) - K
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crypto::ge_p1p1_to_p3(&result_out_p3, &temp_p1p1);
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}
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static int ge_p3_is_point_at_infinity_vartime_bad(const crypto::ge_p3 *p) {
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// X = 0 and Y == Z
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// bad: components of 'p' are not reduced mod q
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int n;
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for (n = 0; n < 10; ++n)
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{
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if (p->X[n] | p->T[n])
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return 0;
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if (p->Y[n] != p->Z[n])
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return 0;
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}
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return 1;
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}
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bool check_scalar(const crypto::ec_scalar &scalar) {
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return crypto::sc_check(crypto::operator &(scalar)) == 0;
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}
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@ -55,3 +85,19 @@ void hash_to_ec(const crypto::public_key &key, crypto::ec_point &res) {
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crypto::hash_to_ec(key, tmp);
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crypto::ge_p3_tobytes(crypto::operator &(res), &tmp);
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}
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bool check_ge_p3_identity_failure(const crypto::public_key &point)
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{
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crypto::ge_p3 ident_p3;
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get_ge_p3_for_identity_test(point, ident_p3);
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return ge_p3_is_point_at_infinity_vartime_bad(&ident_p3) == 1;
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}
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bool check_ge_p3_identity_success(const crypto::public_key &point)
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{
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crypto::ge_p3 ident_p3;
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get_ge_p3_for_identity_test(point, ident_p3);
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return crypto::ge_p3_is_point_at_infinity_vartime(&ident_p3) == 1;
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}
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@ -259,6 +259,16 @@ int main(int argc, char *argv[]) {
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if (expected != actual) {
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goto error;
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}
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} else if (cmd == "check_ge_p3_identity") {
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cerr << "Testing: " << cmd << endl;
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public_key point;
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bool expected_bad, expected_good, result_badfunc, result_goodfunc;
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get(input, point, expected_bad, expected_good);
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result_badfunc = check_ge_p3_identity_failure(point);
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result_goodfunc = check_ge_p3_identity_success(point);
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if (expected_bad != result_badfunc || expected_good != result_goodfunc) {
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goto error;
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}
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} else {
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throw ios_base::failure("Unknown function: " + cmd);
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}
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