pcbc_encrypt.c   [plain text]

/*
 * lib/des425/pcbc_encrypt.c
 *
 * Copyright (C) 1990 by the Massachusetts Institute of Technology.
 * All rights reserved.
 *
 * Export of this software from the United States of America may
 *   require a specific license from the United States Government.
 *   It is the responsibility of any person or organization contemplating
 *   export to obtain such a license before exporting.
 *
 * WITHIN THAT CONSTRAINT, permission to use, copy, modify, and
 * distribute this software and its documentation for any purpose and
 * without fee is hereby granted, provided that the above copyright
 * notice appear in all copies and that both that copyright notice and
 * this permission notice appear in supporting documentation, and that
 * the name of M.I.T. not be used in advertising or publicity pertaining
 * to distribution of the software without specific, written prior
 * permission.  Furthermore if you modify this software you must label
 * your software as modified software and not distribute it in such a
 * fashion that it might be confused with the original M.I.T. software.
 * M.I.T. makes no representations about the suitability of
 * this software for any purpose.  It is provided "as is" without express
 * or implied warranty.
 *
 * DES implementation donated by Dennis Ferguson
 */

/*
 * des_pcbc_encrypt.c - encrypt a string of characters in error propagation mode
 */

#include "autoconf.h"		/* in case this defines CONFIG_SMALL */
#undef CONFIG_SMALL		/* XXX needs non-exported crypto symbols */
#include "des_int.h"
#include "des.h"
#include <f_tables.h>

/*
 * des_pcbc_encrypt - {en,de}crypt a stream in PCBC mode
 */
int KRB5_CALLCONV
des_pcbc_encrypt(in, out, length, schedule, ivec, enc)
	des_cblock *in;
	des_cblock *out;
	long length;
	const des_key_schedule schedule;
	des_cblock *ivec;
	int enc;
{
	unsigned DES_INT32 left, right;
	const unsigned DES_INT32 *kp;
	const unsigned char *ip;
	unsigned char *op;

	/*
	 * Copy the key pointer, just once
	 */
	kp = (const unsigned DES_INT32 *)schedule;

	/*
	 * Deal with encryption and decryption separately.
	 */
	if (enc) {
		/* Initialization isn't really needed here, but gcc
		   complains because it doesn't understand that the
		   only case where these can be used uninitialized is
		   to compute values that'll in turn be ignored
		   because we won't go around the loop again.  */
		unsigned DES_INT32 plainl = 42;
		unsigned DES_INT32 plainr = 17;

		/*
		 * Initialize left and right with the contents of the initial
		 * vector.
		 */
		ip = *ivec;
		GET_HALF_BLOCK(left, ip);
		GET_HALF_BLOCK(right, ip);

		/*
		 * Suitably initialized, now work the length down 8 bytes
		 * at a time.
		 */
		ip = *in;
		op = *out;
		while (length > 0) {
			/*
			 * Get block of input.  If the length is
			 * greater than 8 this is straight
			 * forward.  Otherwise we have to fart around.
			 */
			if (length > 8) {
				GET_HALF_BLOCK(plainl, ip);
				GET_HALF_BLOCK(plainr, ip);
				left ^= plainl;
				right ^= plainr;
				length -= 8;
			} else {
				/*
				 * Oh, shoot.  We need to pad the
				 * end with zeroes.  Work backwards
				 * to do this.  We know this is the
				 * last block, though, so we don't have
				 * to save the plain text.
				 */
				ip += (int) length;
				switch(length) {
				case 8:
					right ^= *(--ip) & 0xff;
				case 7:
					right ^= (*(--ip) & 0xff) << 8;
				case 6:
					right ^= (*(--ip) & 0xff) << 16;
				case 5:
					right ^= (*(--ip) & 0xff) << 24;
				case 4:
					left ^= *(--ip) & 0xff;
				case 3:
					left ^= (*(--ip) & 0xff) << 8;
				case 2:
					left ^= (*(--ip) & 0xff) << 16;
				case 1:
					left ^= (*(--ip) & 0xff) << 24;
					break;
				}
				length = 0;
			}

			/*
			 * Encrypt what we have
			 */
			DES_DO_ENCRYPT(left, right, kp);

			/*
			 * Copy the results out
			 */
			PUT_HALF_BLOCK(left, op);
			PUT_HALF_BLOCK(right, op);

			/*
			 * Xor with the old plain text
			 */
			left ^= plainl;
			right ^= plainr;
		}
	} else {
		/*
		 * Decrypting is harder than encrypting because of
		 * the necessity of remembering a lot more things.
		 * Should think about this a little more...
		 */
		unsigned DES_INT32 ocipherl, ocipherr;
		unsigned DES_INT32 cipherl, cipherr;

		if (length <= 0)
			return 0;

		/*
		 * Prime the old cipher with ivec.
		 */
		ip = *ivec;
		GET_HALF_BLOCK(ocipherl, ip);
		GET_HALF_BLOCK(ocipherr, ip);

		/*
		 * Now do this in earnest until we run out of length.
		 */
		ip = *in;
		op = *out;
		for (;;) {		/* check done inside loop */
			/*
			 * Read a block from the input into left and
			 * right.  Save this cipher block for later.
			 */
			GET_HALF_BLOCK(left, ip);
			GET_HALF_BLOCK(right, ip);
			cipherl = left;
			cipherr = right;

			/*
			 * Decrypt this.
			 */
			DES_DO_DECRYPT(left, right, kp);

			/*
			 * Xor with the old cipher to get plain
			 * text.  Output 8 or less bytes of this.
			 */
			left ^= ocipherl;
			right ^= ocipherr;
			if (length > 8) {
				length -= 8;
				PUT_HALF_BLOCK(left, op);
				PUT_HALF_BLOCK(right, op);
				/*
				 * Save current cipher block here
				 */
				ocipherl = cipherl ^ left;
				ocipherr = cipherr ^ right;
			} else {
				/*
				 * Trouble here.  Start at end of output,
				 * work backwards.
				 */
				op += (int) length;
				switch(length) {
				case 8:
					*(--op) = (unsigned char) (right & 0xff);
				case 7:
					*(--op) = (unsigned char) ((right >> 8) & 0xff);
				case 6:
					*(--op) = (unsigned char) ((right >> 16) & 0xff);
				case 5:
					*(--op) = (unsigned char) ((right >> 24) & 0xff);
				case 4:
					*(--op) = (unsigned char) (left & 0xff);
				case 3:
					*(--op) = (unsigned char) ((left >> 8) & 0xff);
				case 2:
					*(--op) = (unsigned char) ((left >> 16) & 0xff);
				case 1:
					*(--op) = (unsigned char) ((left >> 24) & 0xff);
					break;
				}
				break;		/* we're done */
			}
		}
	}

	/*
	 * Done, return nothing.
	 */
	return 0;
}