pcbc_encrypt.c   [plain text]

/*
 * lib/des425/pcbc_encrypt.c
 */

/*
 * Copyright (c) 1990 Dennis Ferguson.  All rights reserved.
 *
 * Commercial use is permitted only if products which are derived from
 * or include this software are made available for purchase and/or use
 * in Canada.  Otherwise, redistribution and use in source and binary
 * forms are permitted.
 */

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

#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;
{
	register 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.  */
		register unsigned DES_INT32 plainl = 42;
		register 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;
}