f_parity.c   [plain text]

/*
 * These routines check and fix parity of encryption keys for the DES
 * algorithm.
 *
 * They are a replacement for routines in key_parity.c, that don't require
 * the table building that they do.
 *
 * Mark Eichin -- Cygnus Support
 */


#include "des_int.h"

/*
 * des_fixup_key_parity: Forces odd parity per byte; parity is bits
 *                       8,16,...64 in des order, implies 0, 8, 16, ...
 *                       vax order.
 */
#define smask(step) ((1<<step)-1)
#define pstep(x,step) (((x)&smask(step))^(((x)>>step)&smask(step)))
#define parity_char(x) pstep(pstep(pstep((x),4),2),1)

void
mit_des_fixup_key_parity(mit_des_cblock key)
{
    int i;
    for (i=0; i<sizeof(mit_des_cblock); i++) 
      {
	key[i] &= 0xfe;
	key[i] |= 1^parity_char(key[i]);
      }
  
    return;
}

/*
 * des_check_key_parity: returns true iff key has the correct des parity.
 *                       See des_fix_key_parity for the definition of
 *                       correct des parity.
 */
int
mit_des_check_key_parity(mit_des_cblock key)
{
    int i;
    
    for (i=0; i<sizeof(mit_des_cblock); i++) 
      {
	if((key[i] & 1) == parity_char(0xfe&key[i])) 
	  {
	    return 0;
	  }
      }

    return(1);
}