Difference between revisions of "Kernel/XcDESKeyParity"

Latest revision as of 00:03, 3 October 2018

The XcDESKeyParity function turns a key into a DES key which requires odd-parity per byte.

^[FIXME]

@@ Line 1: / Line 1: @@
-=== Pseudocode ===
+The ''XcDESKeyParity'' function turns a key into a DES key which requires odd-parity per byte.
-<pre>
+{{FIXME|reason=Mention crypto vector}}
-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.
+=== Links ===
-  const uint8_t parity_table[] = {
-x00, 0x01, 0x01, 0x02, 0x01, 0x02, 0x02, 0x03,
-x01, 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.
+* [https://github.com/Cxbx-Reloaded/Cxbx-Reloaded/blob/f73114df61d943ba73b329a6e4bd6805254af243/src/CxbxKrnl/EmuKrnlXc.cpp#L234 XcDESKeyParity implementation in Cxbx-Reloaded]
-  // 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;
-}
-</pre>