Kernel/XcDESKeyParity
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Pseudocode
XBAPI VOID NTAPI XcDESKeyParity(IN OUT PUCHAR pbKey, IN ULONG dwKeyLength) { // For each number between 0x0 and 0xF, this tells how many set bits there are. const uint8_t parity_table[] = { 0x00, 0x01, 0x01, 0x02, 0x01, 0x02, 0x02, 0x03, 0x01, 0x02, 0x02, 0x03, 0x02, 0x03, 0x03, 0x04 }; // Count number of set bits in each byte, and flip the lowest bit if there's an even number. // This forces each byte to have odd parity, as required by DES. for(ULONG i = 0; i < dwKeyLength; i++) { high_parity = parity_table[(pbKey[i] >> 4) & 0xF]; low_parity = parity_table[(pbKey[i] >> 0) & 0xF]; if ((high_parity + low_parity) % 2) == 0 { pbKey[i] ^= 0x01; } } return; }