59 lines
1.1 KiB
C
59 lines
1.1 KiB
C
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/* authparity.c,v 3.1 1993/07/06 01:07:55 jbj Exp
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* auth_parity - set parity on a key/check for odd parity
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*/
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#include "ntp_stdlib.h"
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int
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DESauth_parity(key)
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U_LONG *key;
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{
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U_LONG mask;
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int parity_err;
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int bitcount;
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int half;
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int byte;
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int i;
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/*
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* Go through counting bits in each byte. Check to see if
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* each parity bit was set correctly. If not, note the error
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* and set it right.
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*/
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parity_err = 0;
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for (half = 0; half < 2; half++) { /* two halves of key */
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mask = 0x80000000;
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for (byte = 0; byte < 4; byte++) { /* 4 bytes per half */
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bitcount = 0;
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for (i = 0; i < 7; i++) { /* 7 data bits / byte */
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if (key[half] & mask)
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bitcount++;
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mask >>= 1;
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}
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/*
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* If bitcount is even, parity must be set. If
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* bitcount is odd, parity must be clear.
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*/
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if ((bitcount & 0x1) == 0) {
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if (!(key[half] & mask)) {
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parity_err++;
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key[half] |= mask;
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}
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} else {
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if (key[half] & mask) {
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parity_err++;
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key[half] &= ~mask;
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}
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}
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mask >>= 1;
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}
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}
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/*
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* Return the result of the parity check.
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*/
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return (parity_err == 0);
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}
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