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/*
* 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_cbc_encrypt.c - an implementation of the DES cipher function in cbc mode
*/
#include "des_int.h"
#include "f_tables.h"
/*
* des_cbc_encrypt - {en,de}crypt a stream in CBC mode
*/
/*
* This routine performs DES cipher-block-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
mit_des_cbc_encrypt(in, out, length, schedule, ivec, enc)
const mit_des_cblock FAR *in;
mit_des_cblock FAR *out;
unsigned long length;
const mit_des_key_schedule schedule;
const mit_des_cblock ivec;
int enc;
{
register unsigned DES_INT32 left, right;
register unsigned DES_INT32 temp;
const unsigned DES_INT32 *kp;
const unsigned char *ip;
unsigned char *op;
/*
* Get key pointer here. This won't need to be reinitialized
*/
kp = (const unsigned DES_INT32 *)schedule;
/*
* Deal with encryption and decryption separately.
*/
if (enc) {
/*
* 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 more input, xor it in. If the length is
* greater than or equal to 8 this is straight
* forward. Otherwise we have to fart around.
*/
if (length >= 8) {
left ^= ((*ip++) & FF_UINT32) << 24;
left ^= ((*ip++) & FF_UINT32) << 16;
left ^= ((*ip++) & FF_UINT32) << 8;
left ^= (*ip++) & FF_UINT32;
right ^= ((*ip++) & FF_UINT32) << 24;
right ^= ((*ip++) & FF_UINT32) << 16;
right ^= ((*ip++) & FF_UINT32) << 8;
right ^= (*ip++) & FF_UINT32;
length -= 8;
} else {
/*
* Oh, shoot. We need to pad the
* end with zeroes. Work backwards
* to do this.
*/
ip += (int) length;
switch(length) {
case 7:
right ^= (*(--ip) & FF_UINT32) << 8;
case 6:
right ^= (*(--ip) & FF_UINT32) << 16;
case 5:
right ^= (*(--ip) & FF_UINT32) << 24;
case 4:
left ^= *(--ip) & FF_UINT32;
case 3:
left ^= (*(--ip) & FF_UINT32) << 8;
case 2:
left ^= (*(--ip) & FF_UINT32) << 16;
case 1:
left ^= (*(--ip) & FF_UINT32) << 24;
break;
}
length = 0;
}
/*
* Encrypt what we have
*/
DES_DO_ENCRYPT(left, right, temp, kp);
/*
* Copy the results out
*/
PUT_HALF_BLOCK(left, op);
PUT_HALF_BLOCK(right, op);
}
} 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, temp, 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;
ocipherr = cipherr;
} 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;
}
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