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)
This commit is contained in:
luigi1111 2022-03-02 18:52:51 -05:00
commit abae63c37d
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GPG Key ID: F4ACA0183641E010
7 changed files with 111 additions and 11 deletions

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@ -3830,15 +3830,51 @@ int sc_isnonzero(const unsigned char *s) {
s[27] | s[28] | s[29] | s[30] | s[31]) - 1) >> 8) + 1; s[27] | s[28] | s[29] | s[30] | s[31]) - 1) >> 8) + 1;
} }
int ge_p3_is_point_at_infinity(const ge_p3 *p) { int ge_p3_is_point_at_infinity_vartime(const ge_p3 *p) {
// X = 0 and Y == Z // https://eprint.iacr.org/2008/522
int n; // X == T == 0 and Y/Z == 1
for (n = 0; n < 10; ++n) // note: convert all pieces to canonical bytes in case rounding is required (i.e. an element is > q)
// note2: even though T = XY/Z is true for valid point representations (implying it isn't necessary to
// test T == 0), the input to this function might NOT be valid, so we must test T == 0
char result_X_bytes[32];
fe_tobytes((unsigned char*)&result_X_bytes, p->X);
// X != 0
for (int i = 0; i < 32; ++i)
{ {
if (p->X[n] | p->T[n]) if (result_X_bytes[i])
return 0;
if (p->Y[n] != p->Z[n])
return 0; return 0;
} }
char result_T_bytes[32];
fe_tobytes((unsigned char*)&result_T_bytes, p->T);
// T != 0
for (int i = 0; i < 32; ++i)
{
if (result_T_bytes[i])
return 0;
}
char result_Y_bytes[32];
char result_Z_bytes[32];
fe_tobytes((unsigned char*)&result_Y_bytes, p->Y);
fe_tobytes((unsigned char*)&result_Z_bytes, p->Z);
// Y != Z
for (int i = 0; i < 32; ++i)
{
if (result_Y_bytes[i] != result_Z_bytes[i])
return 0;
}
// is Y nonzero? then Y/Z == 1
for (int i = 0; i < 32; ++i)
{
if (result_Y_bytes[i] != 0)
return 1; return 1;
} }
// Y/Z = 0/0
return 0;
}

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@ -162,4 +162,4 @@ void fe_add(fe h, const fe f, const fe g);
void fe_tobytes(unsigned char *, const fe); void fe_tobytes(unsigned char *, const fe);
void fe_invert(fe out, const fe z); void fe_invert(fe out, const fe z);
int ge_p3_is_point_at_infinity(const ge_p3 *p); 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)
heap.reserve(points); heap.reserve(points);
for (size_t n = 0; n < points; ++n) for (size_t n = 0; n < points; ++n)
{ {
if (!(data[n].scalar == rct::zero()) && !ge_p3_is_point_at_infinity(&data[n].point)) if (!(data[n].scalar == rct::zero()) && !ge_p3_is_point_at_infinity_vartime(&data[n].point))
heap.push_back(n); heap.push_back(n);
} }
points = heap.size(); points = heap.size();
@ -457,7 +457,7 @@ rct::key straus(const std::vector<MultiexpData> &data, const std::shared_ptr<str
MULTIEXP_PERF(PERF_TIMER_START_UNIT(skip, 1000000)); MULTIEXP_PERF(PERF_TIMER_START_UNIT(skip, 1000000));
std::vector<uint8_t> skip(data.size()); std::vector<uint8_t> skip(data.size());
for (size_t i = 0; i < data.size(); ++i) for (size_t i = 0; i < data.size(); ++i)
skip[i] = data[i].scalar == rct::zero() || ge_p3_is_point_at_infinity(&data[i].point); skip[i] = data[i].scalar == rct::zero() || ge_p3_is_point_at_infinity_vartime(&data[i].point);
MULTIEXP_PERF(PERF_TIMER_STOP(skip)); MULTIEXP_PERF(PERF_TIMER_STOP(skip));
#endif #endif

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@ -46,4 +46,6 @@ void random_scalar(crypto::ec_scalar &res);
void hash_to_scalar(const void *data, std::size_t length, crypto::ec_scalar &res); void hash_to_scalar(const void *data, std::size_t length, crypto::ec_scalar &res);
void hash_to_point(const crypto::hash &h, crypto::ec_point &res); void hash_to_point(const crypto::hash &h, crypto::ec_point &res);
void hash_to_ec(const crypto::public_key &key, crypto::ec_point &res); void hash_to_ec(const crypto::public_key &key, crypto::ec_point &res);
bool check_ge_p3_identity_failure(const crypto::public_key &point);
bool check_ge_p3_identity_success(const crypto::public_key &point);
#endif #endif

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@ -32,6 +32,36 @@
#include "crypto-tests.h" #include "crypto-tests.h"
static void get_ge_p3_for_identity_test(const crypto::public_key &point, crypto::ge_p3 &result_out_p3)
{
// compute (K + K) - K - K to get a specific ge_p3 point representation of identity
crypto::ge_cached temp_cache;
crypto::ge_p1p1 temp_p1p1;
crypto::ge_frombytes_vartime(&result_out_p3, &point); // K
crypto::ge_p3_to_cached(&temp_cache, &result_out_p3);
crypto::ge_add(&temp_p1p1, &result_out_p3, &temp_cache); // K + K
crypto::ge_p1p1_to_p3(&result_out_p3, &temp_p1p1);
crypto::ge_sub(&temp_p1p1, &result_out_p3, &temp_cache); // (K + K) - K
crypto::ge_p1p1_to_p3(&result_out_p3, &temp_p1p1);
crypto::ge_sub(&temp_p1p1, &result_out_p3, &temp_cache); // ((K + K) - K) - K
crypto::ge_p1p1_to_p3(&result_out_p3, &temp_p1p1);
}
static int ge_p3_is_point_at_infinity_vartime_bad(const crypto::ge_p3 *p) {
// X = 0 and Y == Z
// bad: components of 'p' are not reduced mod q
int n;
for (n = 0; n < 10; ++n)
{
if (p->X[n] | p->T[n])
return 0;
if (p->Y[n] != p->Z[n])
return 0;
}
return 1;
}
bool check_scalar(const crypto::ec_scalar &scalar) { bool check_scalar(const crypto::ec_scalar &scalar) {
return crypto::sc_check(crypto::operator &(scalar)) == 0; return crypto::sc_check(crypto::operator &(scalar)) == 0;
} }
@ -55,3 +85,19 @@ void hash_to_ec(const crypto::public_key &key, crypto::ec_point &res) {
crypto::hash_to_ec(key, tmp); crypto::hash_to_ec(key, tmp);
crypto::ge_p3_tobytes(crypto::operator &(res), &tmp); crypto::ge_p3_tobytes(crypto::operator &(res), &tmp);
} }
bool check_ge_p3_identity_failure(const crypto::public_key &point)
{
crypto::ge_p3 ident_p3;
get_ge_p3_for_identity_test(point, ident_p3);
return ge_p3_is_point_at_infinity_vartime_bad(&ident_p3) == 1;
}
bool check_ge_p3_identity_success(const crypto::public_key &point)
{
crypto::ge_p3 ident_p3;
get_ge_p3_for_identity_test(point, ident_p3);
return crypto::ge_p3_is_point_at_infinity_vartime(&ident_p3) == 1;
}

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@ -259,6 +259,16 @@ int main(int argc, char *argv[]) {
if (expected != actual) { if (expected != actual) {
goto error; goto error;
} }
} else if (cmd == "check_ge_p3_identity") {
cerr << "Testing: " << cmd << endl;
public_key point;
bool expected_bad, expected_good, result_badfunc, result_goodfunc;
get(input, point, expected_bad, expected_good);
result_badfunc = check_ge_p3_identity_failure(point);
result_goodfunc = check_ge_p3_identity_success(point);
if (expected_bad != result_badfunc || expected_good != result_goodfunc) {
goto error;
}
} else { } else {
throw ios_base::failure("Unknown function: " + cmd); throw ios_base::failure("Unknown function: " + cmd);
} }

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