/*
 * $Source: /afs/sipb.mit.edu/project/sipb-athena/repository/src/kerberos/lib/des/epc_encrypt.c,v $
 * $Author: ghudson $
 *
 * Copyright 1985, 1986, 1987, 1988 by the Massachusetts Institute
 * of Technology.
 *
 * For copying and distribution information, please see the file
 * <mit-copyright.h>.
 *
 * These routines perform encryption and decryption using the DES
 * private key algorithm, or else a subset of it-- fewer inner loops.
 * (AUTH_DES_ITER defaults to 16, may be less.)
 *
 * Under U.S. law, this software may not be exported outside the US
 * without license from the U.S. Commerce department.
 *
 * These routines form the library interface to the des facilities.
 *
 * spm	8/85	MIT project athena
 */

#ifndef	lint
static char rcsid_epc_encrypt_c[] =
"$Header: /afs/sipb.mit.edu/project/sipb-athena/repository/src/kerberos/lib/des/epc_encrypt.c,v 1.2 1996/06/02 07:36:47 ghudson Exp $";
#endif	lint

#include <mit-copyright.h>
#include <des.h>

extern int des_debug;
extern int des_debug_print();

/*
 * epc_encrypt is an "error propagation chaining" encrypt operation
 * for DES, similar to CBC.  However, CBC limits errors to 2 blocks,
 * while "epc" will propagate a single bit error anywhere in the chain
 * all the way through to the end. This is NOT an official mode of
 * operation.  It offers the cryptanalyst the same plaintext
 * ciphertext pairs for repeated plaintext, regardless of the IV.
 * However, cryptanalysis is not one of our concerns.
 */

/*
 * This routine performs the EPC error-propagation chaining operation,
 * either encrypting from cleartext to ciphertext, if encrypt != 0, or
 * decrypting from ciphertext to cleartext, if encrypt == 0.
 *
 * The key schedule is passed as an arg, as well as the cleartext or
 * ciphertext. The cleartext and ciphertext should be in host order.
 *
 * NOTE-- the output is ALWAYS an multiple of 8 bytes long.  If not
 * enough space was provided, your program will get trashed.
 *
 * For encryption, the cleartext string is null padded, at the end, to
 * an integral multiple of eight bytes.
 *
 * For decryption, the ciphertext will be used in integral multiples
 * of 8 bytes, but only the first "length" bytes returned into the
 * cleartext.
 */

int
epc_encrypt(in,out,length,key,iv,encrypt)
    des_cblock *in;		/* >= length bytes of inputtext */
    des_cblock *out;		/* >= length bytes of outputtext */
    register long length;	/* in bytes */
    int encrypt;		/* 0 ==> decrypt, else encrypt */
    des_key_schedule key;		/* precomputed key schedule */
    des_cblock *iv;		/* 8 bytes of ivec */
{
    register unsigned long *input = (unsigned long *) in;
    register unsigned long *output = (unsigned long *) out;
    register unsigned long *ivec = (unsigned long *) iv;

    unsigned long i,j;
    static unsigned long t_input[2];
    static unsigned long t_output[2];
    static unsigned char *t_in_p = (unsigned char *) t_input;
    static unsigned long xor_0, xor_1;

    if (encrypt) {
	xor_0 = *ivec++;
	xor_1 = *ivec;

	for (i = 0; length > 0; i++, length -= 8) {
	    /* get input */
	    t_input[0] = *input;
	    t_input[1] = *(input+1);
	    /* zero pad */
	    if (length < 8)
		for (j = length; j <= 7; j++)
		    *(t_in_p+j)= 0;

#ifdef DEBUG
	    if (des_debug)
		des_debug_print("clear",length,t_input[0],t_input[1]);
#endif
	    /* do the xor for cbc into the temp */
	    t_input[0] ^= xor_0 ;
	    t_input[1] ^= xor_1 ;
	    /* encrypt */
	    des_ecb_encrypt(t_input,t_output,key,encrypt);
	    /* copy temp output and save it for cbc */
	    *output++ = t_output[0];
	    *output++ = t_output[1];
	    xor_0 = *input++;
	    xor_1 = *input++;
#ifdef DEBUG
	    if (des_debug) {
		des_debug_print("xor'ed",i,t_input[0],t_input[1]);
		des_debug_print("cipher",i,t_output[0],t_output[1]);
	    }
#endif
	}
	t_output[0] = 0;
	t_output[1] = 0;
	xor_0 = 0;
	xor_1 = 0;
	return 0;
    }

    else	/* decrypt */
    {
	xor_0 = *ivec++;
	xor_1 = *ivec;

	for (i = 0; length > 0; i++, length -= 8) {
	    /* get input */
	    t_input[0] = *input++;
	    t_input[1] = *input++;
	    /* no padding for decrypt */
#ifdef DEBUG
	    if (des_debug)
		des_debug_print("cipher",i,t_input[0],t_input[1]);
#endif
	    /* encrypt */
	    des_ecb_encrypt(t_input,t_output,key,encrypt);
#ifdef DEBUG
	    if (des_debug)
		des_debug_print("out pre xor",i,t_output[0],t_output[1]);
#endif
	    /* do the xor for cbc into the output */
	    t_output[0] ^= xor_0 ;
	    t_output[1] ^= xor_1 ;
	    /* copy temp output */
	    *output++ = t_output[0];
	    *output++ = t_output[1];
	    /* save xor value for next round */
	    xor_0 = t_output[0];
	    xor_1 = t_output[1];
#ifdef DEBUG
	    if (des_debug)
		des_debug_print("clear",i,t_output[0],t_output[1]);
#endif
	}

    }
}