Difference between revisions of "Kernel/XcDESKeyParity"
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(Port from my Python code, but with added comments) |
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| + | The ''XcDESKeyParity'' function turns a key into a DES key which requires odd-parity per byte. | ||
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=== Pseudocode === | === Pseudocode === | ||
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| + | {{FIXME|reason=This should be removed from here, and instead we should just link to an actual implementation of the algorithm}} | ||
<pre> | <pre> | ||
Revision as of 23:58, 2 October 2018
The XcDESKeyParity function turns a key into a DES key which requires odd-parity per byte.
Pseudocode
[FIXME]
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;
}
