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crypto: fix non zero scalar being 0 after reducing
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parent
065bb292df
commit
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2 changed files with 548 additions and 555 deletions
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@ -123,13 +123,17 @@ namespace crypto {
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void random32_unbiased(unsigned char *bytes)
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void random32_unbiased(unsigned char *bytes)
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{
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{
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// l = 2^252 + 27742317777372353535851937790883648493.
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// l = 2^252 + 27742317777372353535851937790883648493.
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// it fits 15 in 32 bytes
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// l fits 15 times in 32 bytes (iow, 15 l is the highest multiple of l that fits in 32 bytes)
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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 };
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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 };
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do
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while(1)
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{
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{
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generate_random_bytes_thread_safe(32, bytes);
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generate_random_bytes_thread_safe(32, bytes);
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} while (!sc_isnonzero(bytes) && !less32(bytes, limit)); // should be good about 15/16 of the time
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if (!less32(bytes, limit))
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continue;
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sc_reduce32(bytes);
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sc_reduce32(bytes);
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if (sc_isnonzero(bytes))
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break;
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}
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}
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}
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/* generate a random 32-byte (256-bit) integer and copy it to res */
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/* generate a random 32-byte (256-bit) integer and copy it to res */
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static inline void random_scalar(ec_scalar &res) {
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static inline void random_scalar(ec_scalar &res) {
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