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crypto: fix non zero scalar being 0 after reducing

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moneromooo-monero 2020-12-03 16:23:16 +00:00
parent 4f401f6fca
commit 5ed604fe5b
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2 changed files with 548 additions and 555 deletions
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10
src/crypto/crypto.cpp
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@ -123,13 +123,17 @@ namespace crypto {
void random32_unbiased(unsigned char *bytes) void random32_unbiased(unsigned char *bytes)
{ {
// l = 2^252 + 27742317777372353535851937790883648493. // l = 2^252 + 27742317777372353535851937790883648493.
// it fits 15 in 32 bytes // l fits 15 times in 32 bytes (iow, 15 l is the highest multiple of l that fits in 32 bytes)
static const unsigned char limit[32] = { 0xe3, 0x6a, 0x67, 0x72, 0x8b, 0xce, 0x13, 0x29, 0x8f, 0x30, 0x82, 0x8c, 0x0b, 0xa4, 0x10, 0x39, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xf0 }; static const unsigned char limit[32] = { 0xe3, 0x6a, 0x67, 0x72, 0x8b, 0xce, 0x13, 0x29, 0x8f, 0x30, 0x82, 0x8c, 0x0b, 0xa4, 0x10, 0x39, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xf0 };
do while(1)
{ {
generate_random_bytes_thread_safe(32, bytes); generate_random_bytes_thread_safe(32, bytes);
} while (!sc_isnonzero(bytes) && !less32(bytes, limit)); // should be good about 15/16 of the time if (!less32(bytes, limit))
continue;
sc_reduce32(bytes); sc_reduce32(bytes);
if (sc_isnonzero(bytes))
break;
}
} }
/* generate a random 32-byte (256-bit) integer and copy it to res */ /* generate a random 32-byte (256-bit) integer and copy it to res */
static inline void random_scalar(ec_scalar &res) { static inline void random_scalar(ec_scalar &res) {

1091
tests/crypto/tests.txt
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