contrib/ntp/libntp/authparity.c

   1 /*
   2  * auth_parity - set parity on a key/check for odd parity
   3  */
   4
   5 #ifdef HAVE_CONFIG_H
   6 # include <config.h>
   7 #endif
   8
   9 #ifdef DES
  10 #include "ntp_stdlib.h"
  11
  12 int
  13 DESauth_parity(
  14         u_int32 *key
  15         )
  16 {
  17         u_int32 mask;
  18         int parity_err;
  19         int bitcount;
  20         int half;
  21         int byte;
  22         int i;
  23
  24         /*
  25          * Go through counting bits in each byte.  Check to see if
  26          * each parity bit was set correctly.  If not, note the error
  27          * and set it right.
  28          */
  29         parity_err = 0;
  30         for (half = 0; half < 2; half++) {              /* two halves of key */
  31                 mask = 0x80000000;
  32                 for (byte = 0; byte < 4; byte++) {      /* 4 bytes per half */
  33                         bitcount = 0;
  34                         for (i = 0; i < 7; i++) {       /* 7 data bits / byte */
  35                                 if (key[half] & mask)
  36                                     bitcount++;
  37                                 mask >>= 1;
  38                         }
  39
  40                         /*
  41                          * If bitcount is even, parity must be set.  If
  42                          * bitcount is odd, parity must be clear.
  43                          */
  44                         if ((bitcount & 0x1) == 0) {
  45                                 if (!(key[half] & mask)) {
  46                                         parity_err++;
  47                                         key[half] |= mask;
  48                                 }
  49                         } else {
  50                                 if (key[half] & mask) {
  51                                         parity_err++;
  52                                         key[half] &= ~mask;
  53                                 }
  54                         }
  55                         mask >>= 1;
  56                 }
  57         }
  58
  59         /*
  60          * Return the result of the parity check.
  61          */
  62         return (parity_err == 0);
  63 }
  64 #else
  65 int authparity_bs;
  66 #endif /* DES */