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des_algo_lib.c
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des_algo_lib.c
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/*****************************************************************************
* *
* --------------------------------- des.c -------------------------------- *
* *
*****************************************************************************/
#include <math.h>
#include <stdlib.h>
#include <string.h>
#include <stdio.h>
/*****************************************************************************
* *
* -------------------------------- bit_get ------------------------------- *
* *
*****************************************************************************/
int bit_get(const unsigned char *bits, int pos) {
unsigned char mask;
int i;
/*****************************************************************************
* *
* Set a mask for the bit to get. *
* *
*****************************************************************************/
mask = 0x80;
for (i = 0; i < (pos % 8); i++)
mask = mask >> 1;
/*****************************************************************************
* *
* Get the bit. *
* *
*****************************************************************************/
return (((mask & bits[(int)(pos / 8)]) == mask) ? 1 : 0);
}
/*****************************************************************************
* *
* -------------------------------- bit_set ------------------------------- *
* *
*****************************************************************************/
void bit_set(unsigned char *bits, int pos, int state) {
unsigned char mask;
int i;
/*****************************************************************************
* *
* Set a mask for the bit to set. *
* *
*****************************************************************************/
mask = 0x80;
for (i = 0; i < (pos % 8); i++)
mask = mask >> 1;
/*****************************************************************************
* *
* Set the bit. *
* *
*****************************************************************************/
if (state)
bits[pos / 8] = bits[pos / 8] | mask;
else
bits[pos / 8] = bits[pos / 8] & (~mask);
return;
}
/*****************************************************************************
* *
* -------------------------------- bit_xor ------------------------------- *
* *
*****************************************************************************/
void bit_xor(const unsigned char *bits1, const unsigned char *bits2, unsigned
char *bitsx, int size) {
int i;
/*****************************************************************************
* *
* Compute the bitwise XOR (exclusive OR) of the two buffers. *
* *
*****************************************************************************/
for (i = 0; i < size; i++) {
if (bit_get(bits1, i) != bit_get(bits2, i))
bit_set(bitsx, i, 1);
else
bit_set(bitsx, i, 0);
}
return;
}
/*****************************************************************************
* *
* ----------------------------- bit_rot_left ----------------------------- *
* *
*****************************************************************************/
void bit_rot_left(unsigned char *bits, int size, int count) {
int fbit,
lbit,
i,
j;
/*****************************************************************************
* *
* Rotate the buffer to the left the specified number of bits. *
* *
*****************************************************************************/
if (size > 0) {
for (j = 0; j < count; j++) {
for (i = 0; i <= ((size - 1) / 8); i++) {
/********************************************************************
* *
* Get the bit about to be shifted off the current byte. *
* *
********************************************************************/
lbit = bit_get(&bits[i], 0);
if (i == 0) {
/*****************************************************************
* *
* Save the bit shifted off the first byte for later. *
* *
*****************************************************************/
fbit = lbit;
}
else {
/*****************************************************************
* *
* Set the rightmost bit of the previous byte to the leftmost *
* bit about to be shifted off the current byte. *
* *
*****************************************************************/
bit_set(&bits[i - 1], 7, lbit);
}
/********************************************************************
* *
* Shift the current byte to the left. *
* *
********************************************************************/
bits[i] = bits[i] << 1;
}
/***********************************************************************
* *
* Set the rightmost bit of the buffer to the bit shifted off the *
* first byte. *
* *
***********************************************************************/
bit_set(bits, size - 1, fbit);
}
}
return;
}
/*****************************************************************************
* *
* Define a mapping for the key transformation. *
* *
*****************************************************************************/
static const int DesTransform[56] = {
57, 49, 41, 33, 25, 17, 9, 1, 58, 50, 42, 34, 26, 18,
10, 2, 59, 51, 43, 35, 27, 19, 11, 3, 60, 52, 44, 36,
63, 55, 47, 39, 31, 23, 15, 7, 62, 54, 46, 38, 30, 22,
14, 6, 61, 53, 45, 37, 29, 21, 13, 5, 28, 20, 12, 4
};
/*****************************************************************************
* *
* Define the number of rotations for computing subkeys. *
* *
*****************************************************************************/
static const int DesRotations[16] = {
1, 1, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2, 1
};
/*****************************************************************************
* *
* Define a mapping for the permuted choice for subkeys. *
* *
*****************************************************************************/
static const int DesPermuted[48] = {
14, 17, 11, 24, 1, 5, 3, 28, 15, 6, 21, 10,
23, 19, 12, 4, 26, 8, 16, 7, 27, 20, 13, 2,
41, 52, 31, 37, 47, 55, 30, 40, 51, 45, 33, 48,
44, 49, 39, 56, 34, 53, 46, 42, 50, 36, 29, 32
};
/*****************************************************************************
* *
* Define a mapping for the initial permutation of data blocks. *
* *
*****************************************************************************/
static const int DesInitial[64] = {
58, 50, 42, 34, 26, 18, 10, 2, 60, 52, 44, 36, 28, 20, 12, 4,
62, 54, 46, 38, 30, 22, 14, 6, 64, 56, 48, 40, 32, 24, 16, 8,
57, 49, 41, 33, 25, 17, 9, 1, 59, 51, 43, 35, 27, 19, 11, 3,
61, 53, 45, 37, 29, 21, 13, 5, 63, 55, 47, 39, 31, 23, 15, 7
};
/*****************************************************************************
* *
* Define a mapping for the expansion permutation of data blocks. *
* *
*****************************************************************************/
static const int DesExpansion[48] = {
32, 1, 2, 3, 4, 5, 4, 5, 6, 7, 8, 9,
8, 9, 10, 11, 12, 13, 12, 13, 14, 15, 16, 17,
16, 17, 18, 19, 20, 21, 20, 21, 22, 23, 24, 25,
24, 25, 26, 27, 28, 29, 28, 29, 30, 31, 32, 1
};
/*****************************************************************************
* *
* Define tables for the S-box substitutions performed for data blocks. *
* *
*****************************************************************************/
static const int DesSbox[8][4][16] = {
{
{14, 4, 13, 1, 2, 15, 11, 8, 3, 10, 6, 12, 5, 9, 0, 7},
{ 0, 15, 7, 4, 14, 2, 13, 1, 10, 6, 12, 11, 9, 5, 3, 8},
{ 4, 1, 14, 8, 13, 6, 2, 11, 15, 12, 9, 7, 3, 10, 5, 0},
{15, 12, 8, 2, 4, 9, 1, 7, 5, 11, 3, 14, 10, 0, 6, 13},
},
{
{15, 1, 8, 14, 6, 11, 3, 4, 9, 7, 2, 13, 12, 0, 5, 10},
{ 3, 13, 4, 7, 15, 2, 8, 14, 12, 0, 1, 10, 6, 9, 11, 5},
{ 0, 14, 7, 11, 10, 4, 13, 1, 5, 8, 12, 6, 9, 3, 2, 15},
{13, 8, 10, 1, 3, 15, 4, 2, 11, 6, 7, 12, 0, 5, 14, 9},
},
{
{10, 0, 9, 14, 6, 3, 15, 5, 1, 13, 12, 7, 11, 4, 2, 8},
{13, 7, 0, 9, 3, 4, 6, 10, 2, 8, 5, 14, 12, 11, 15, 1},
{13, 6, 4, 9, 8, 15, 3, 0, 11, 1, 2, 12, 5, 10, 14, 7},
{ 1, 10, 13, 0, 6, 9, 8, 7, 4, 15, 14, 3, 11, 5, 2, 12},
},
{
{ 7, 13, 14, 3, 0, 6, 9, 10, 1, 2, 8, 5, 11, 12, 4, 15},
{13, 8, 11, 5, 6, 15, 0, 3, 4, 7, 2, 12, 1, 10, 14, 9},
{10, 6, 9, 0, 12, 11, 7, 13, 15, 1, 3, 14, 5, 2, 8, 4},
{ 3, 15, 0, 6, 10, 1, 13, 8, 9, 4, 5, 11, 12, 7, 2, 14},
},
{
{ 2, 12, 4, 1, 7, 10, 11, 6, 8, 5, 3, 15, 13, 0, 14, 9},
{14, 11, 2, 12, 4, 7, 13, 1, 5, 0, 15, 10, 3, 9, 8, 6},
{ 4, 2, 1, 11, 10, 13, 7, 8, 15, 9, 12, 5, 6, 3, 0, 14},
{11, 8, 12, 7, 1, 14, 2, 13, 6, 15, 0, 9, 10, 4, 5, 3},
},
{
{12, 1, 10, 15, 9, 2, 6, 8, 0, 13, 3, 4, 14, 7, 5, 11},
{10, 15, 4, 2, 7, 12, 9, 5, 6, 1, 13, 14, 0, 11, 3, 8},
{ 9, 14, 15, 5, 2, 8, 12, 3, 7, 0, 4, 10, 1, 13, 11, 6},
{ 4, 3, 2, 12, 9, 5, 15, 10, 11, 14, 1, 7, 6, 0, 8, 13},
},
{
{ 4, 11, 2, 14, 15, 0, 8, 13, 3, 12, 9, 7, 5, 10, 6, 1},
{13, 0, 11, 7, 4, 9, 1, 10, 14, 3, 5, 12, 2, 15, 8, 6},
{ 1, 4, 11, 13, 12, 3, 7, 14, 10, 15, 6, 8, 0, 5, 9, 2},
{ 6, 11, 13, 8, 1, 4, 10, 7, 9, 5, 0, 15, 14, 2, 3, 12},
},
{
{13, 2, 8, 4, 6, 15, 11, 1, 10, 9, 3, 14, 5, 0, 12, 7},
{ 1, 15, 13, 8, 10, 3, 7, 4, 12, 5, 6, 11, 0, 14, 9, 2},
{ 7, 11, 4, 1, 9, 12, 14, 2, 0, 6, 10, 13, 15, 3, 5, 8},
{ 2, 1, 14, 7, 4, 10, 8, 13, 15, 12, 9, 0, 3, 5, 6, 11},
},
};
/*****************************************************************************
* *
* Define a mapping for the P-box permutation of data blocks. *
* *
*****************************************************************************/
static const int DesPbox[32] = {
16, 7, 20, 21, 29, 12, 28, 17, 1, 15, 23, 26, 5, 18, 31, 10,
2, 8, 24, 14, 32, 27, 3, 9, 19, 13, 30, 6, 22, 11, 4, 25
};
/*****************************************************************************
* *
* Define a mapping for the final permutation of data blocks. *
* *
*****************************************************************************/
static const int DesFinal[64] = {
40, 8, 48, 16, 56, 24, 64, 32, 39, 7, 47, 15, 55, 23, 63, 31,
38, 6, 46, 14, 54, 22, 62, 30, 37, 5, 45, 13, 53, 21, 61, 29,
36, 4, 44, 12, 52, 20, 60, 28, 35, 3, 43, 11, 51, 19, 59, 27,
34, 2, 42, 10, 50, 18, 58, 26, 33, 1, 41, 9, 49, 17, 57, 25
};
/*****************************************************************************
* *
* Define a type for whether to encipher or decipher data. *
* *
*****************************************************************************/
typedef enum DesEorD_ {encipher, decipher} DesEorD;
/*****************************************************************************
* *
* -------------------------------- permute ------------------------------- *
* *
*****************************************************************************/
static void permute(unsigned char *bits, const int *mapping, int n) {
unsigned char temp[8];
int i;
/*****************************************************************************
* *
* Permute the buffer using an n-entry mapping. *
* *
*****************************************************************************/
memset(temp, 0, (int)ceil(n / 8));
for (i = 0; i < n; i++)
bit_set(temp, i, bit_get(bits, mapping[i] - 1));
memcpy(bits, temp, (int)ceil(n / 8));
return;
}
/*****************************************************************************
* *
* ------------------------------- des_main ------------------------------- *
* *
*****************************************************************************/
static int DES_main(const unsigned char *source, unsigned char *target, const
unsigned char *key, DesEorD direction) {
static unsigned char subkeys[16][7];
unsigned char temp[8],
lkey[4],
rkey[4],
lblk[6],
rblk[6],
fblk[6],
xblk[6],
sblk;
int row,
col,
i,
j,
k,
p;
/*****************************************************************************
* *
* If key is NULL, use the subkeys as computed in a previous call. *
* *
*****************************************************************************/
if (key != NULL) {
/**************************************************************************
* *
* Make a local copy of the key. *
* *
**************************************************************************/
memcpy(temp, key, 8);
/**************************************************************************
* *
* Permute and compress the key into 56 bits. *
* *
**************************************************************************/
permute(temp, DesTransform, 56);
/**************************************************************************
* *
* Split the key into two 28-bit blocks. *
* *
**************************************************************************/
memset(lkey, 0, 4);
memset(rkey, 0, 4);
for (j = 0; j < 28; j++)
bit_set(lkey, j, bit_get(temp, j));
for (j = 0; j < 28; j++)
bit_set(rkey, j, bit_get(temp, j + 28));
/**************************************************************************
* *
* Compute the subkeys for each round. *
* *
**************************************************************************/
for (i = 0; i < 16; i++) {
/***********************************************************************
* *
* Rotate each block according to its round. *
* *
***********************************************************************/
bit_rot_left(lkey, 28, DesRotations[i]);
bit_rot_left(rkey, 28, DesRotations[i]);
/***********************************************************************
* *
* Concatenate the blocks into a single subkey. *
* *
***********************************************************************/
for (j = 0; j < 28; j++)
bit_set(subkeys[i], j, bit_get(lkey, j));
for (j = 0; j < 28; j++)
bit_set(subkeys[i], j + 28, bit_get(rkey, j));
/***********************************************************************
* *
* Do the permuted choice permutation. *
* *
***********************************************************************/
permute(subkeys[i], DesPermuted, 48);
}
}
/*****************************************************************************
* *
* Make a local copy of the source text. *
* *
*****************************************************************************/
memcpy(temp, source, 8);
/*****************************************************************************
* *
* Do the initial permutation. *
* *
*****************************************************************************/
permute(temp, DesInitial, 64);
/*****************************************************************************
* *
* Split the source text into a left and right block of 32 bits. *
* *
*****************************************************************************/
memcpy(lblk, &temp[0], 4);
memcpy(rblk, &temp[4], 4);
/*****************************************************************************
* *
* Encipher or decipher the source text. *
* *
*****************************************************************************/
for (i = 0; i < 16; i++) {
/**************************************************************************
* *
* Begin the computation of f. *
* *
**************************************************************************/
memcpy(fblk, rblk, 4);
/**************************************************************************
* *
* Permute and expand the copy of the right block into 48 bits. *
* *
**************************************************************************/
permute(fblk, DesExpansion, 48);
/**************************************************************************
* *
* Apply the appropriate subkey for the round. *
* *
**************************************************************************/
if (direction == encipher) {
/***********************************************************************
* *
* For enciphering, subkeys are applied in increasing order. *
* *
***********************************************************************/
bit_xor(fblk, subkeys[i], xblk, 48);
memcpy(fblk, xblk, 6);
}
else {
/***********************************************************************
* *
* For deciphering, subkeys are applied in decreasing order. *
* *
***********************************************************************/
bit_xor(fblk, subkeys[15 - i], xblk, 48);
memcpy(fblk, xblk, 6);
}
/**************************************************************************
* *
* Do the S-box substitutions. *
* *
**************************************************************************/
p = 0;
for (j = 0; j < 8; j++) {
/***********************************************************************
* *
* Compute a row and column into the S-box tables. *
* *
***********************************************************************/
row = (bit_get(fblk, (j * 6)+0) * 2) + (bit_get(fblk, (j * 6)+5) * 1);
col = (bit_get(fblk, (j * 6)+1) * 8) + (bit_get(fblk, (j * 6)+2) * 4) +
(bit_get(fblk, (j * 6)+3) * 2) + (bit_get(fblk, (j * 6)+4) * 1);
/***********************************************************************
* *
* Do the S-box substitution for the current six-bit block. *
* *
***********************************************************************/
sblk = (unsigned char)DesSbox[j][row][col];
for (k = 4; k < 8; k++) {
bit_set(fblk, p, bit_get(&sblk, k));
p++;
}
}
/**************************************************************************
* *
* Do the P-box permutation to complete f. *
* *
**************************************************************************/
permute(fblk, DesPbox, 32);
/**************************************************************************
* *
* Compute the XOR of the left block and f. *
* *
**************************************************************************/
bit_xor(lblk, fblk, xblk, 32);
/**************************************************************************
* *
* Set the left block for the round. *
* *
**************************************************************************/
memcpy(lblk, rblk, 4);
/**************************************************************************
* *
* Set the right block for the round. *
* *
**************************************************************************/
memcpy(rblk, xblk, 4);
}
/*****************************************************************************
* *
* Set the target text to the rejoined final right and left blocks. *
* *
*****************************************************************************/
memcpy(&target[0], rblk, 4);
memcpy(&target[4], lblk, 4);
/*****************************************************************************
* *
* Do the final permutation. *
* *
*****************************************************************************/
permute(target, DesFinal, 64);
return 0;
}
/*****************************************************************************
* *
* ----------------------------- DES_encipher ----------------------------- *
* *
*****************************************************************************/
void DES_encipher(const unsigned char *plaintext, unsigned char *ciphertext,
const unsigned char *key) {
DES_main(plaintext, ciphertext, key, encipher);
return;
}
/*****************************************************************************
* *
* ----------------------------- DES_decipher ----------------------------- *
* *
*****************************************************************************/
void DES_decipher(const unsigned char *ciphertext, unsigned char *plaintext,
const unsigned char *key) {
DES_main(ciphertext, plaintext, key, decipher);
return;
}