#include <stdio.h>
#include <stdlib.h>
#include <string.h>


static int SubKey[16][48];
typedef enum {ENCRYPT, DECRYPT}
    Operation;

const static char PC1_Table[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
};

// Left Shifts
const static char LOOP_Table[16] =
{
1, 1, 2, 2, 2, 2, 2, 2,
1, 2, 2, 2, 2, 2, 2, 1
};

// Permuted Choice 2 (PC-2)
const static char PC2_Table[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
};

// Initial Permutation (IP)
const static char IP_Table[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
};

// Expansion (E)
static const char E_Table[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
};

// The (in)famous S-boxes
const static char S_Box[8][4][16] =
{
{
   // S1 
   {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}
},
{
   // S2 
      {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}
},
{
   // S3 
      {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}
},
{
   // S4 
      { 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}
      },
      {
   // S5 
      { 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}
      },
      {
   // S6 
      {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}
      },
      {
   // S7 
      { 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}
      },
      {
   // S8 
      {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}
      }
};

// Permutation P
const static char P_Table[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
};

// Final Permutation (IP**-1)
const static char IPR_Table[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
};
void DES_SetKey(const char Key[8]);
void Des_Run(char Out[8], char In[8], Operation Type);
void F_func(int In[32], const int Ki[48]);
void S_func(int Out[32], const int In[48]);
void Transform(int *Out, int *In, const char *Table, int len);
void Xor(int *InA, const int *InB, int len);
void RotateL(int *In, int len, int loop);
void ByteToBit(int *Out, const char *In, int bits);
void BitToByte(char *Out, const int *In, int bits);

void DES_SetKey(const char Key[8])
{
    int i;
    static int K[64], *KL = &K[0], *KR = &K[28];
    ByteToBit(K, Key, 64);
    Transform(K, K, PC1_Table, 56);
    for(i=0; i<16; i++)
    {
        RotateL(KL, 28, LOOP_Table[i]);
        RotateL(KR, 28, LOOP_Table[i]);
        Transform(SubKey[i],K,PC2_Table,48);
    }
}
void Des_Run(char Out[8], char In[8], Operation Type)
{
    int i;
    static int M[64], tmp[32], *Li = &M[0], *Ri = &M[32];
    ByteToBit(M, In, 64);
    Transform(M, M, IP_Table, 64);
    if(Type==ENCRYPT)
        for(i=0; i<16; i++)
        {
            memcpy(tmp, Ri, 32);
            F_func(Ri, SubKey[i]);
            Xor(Ri, Li, 32);
            memcpy(Li, tmp, 32);
        }
    if(Type==DECRYPT)
        for(i=15; i>=0; i--)
        {
            memcpy(tmp, Li, 32);
            F_func(Li, SubKey[i]);
            Xor(Li, Ri, 32);
            memcpy(Ri, tmp, 32);
        }
    Transform(M, M, IPR_Table, 64);
    BitToByte(Out, M, 64);
}
void F_func(int In[32], const int Ki[48])
{
    static int MR[48];
    Transform(MR, In, E_Table, 48);
    Xor(MR, Ki, 48);
    S_func(In, MR);
    Transform(In, In, P_Table, 32);
}
void S_func(int Out[32], const int In[48])
{
    char j,m,n;
    for(j=0; j<8; j++,In+=6,Out+=4)
    {
        m = (In[0]<<1) + In[5];
        n = (In[1]<<3) + (In[2]<<2) + (In[3]<<1) + In[4];
        ByteToBit(Out, &S_Box[(int)j][(int)m][(int)n], 4);
    }
}
void Transform(int *Out, int *In, const char *Table, int len)
{
    int i;
    static int tmp[256];
    for(i=0; i<len; i++)
        tmp[i] = In[ Table[i]-1 ];
    memcpy(Out, tmp, len);
}
void Xor(int *InA, const int *InB, int len)
{
    int i;
    for(i=0; i<len; i++)
        InA[i] ^= InB[i];
}
void RotateL(int *In, int len, int loop)
{
    static int tmp[256];
    memcpy(tmp, In, loop);
    memcpy(In, In+loop, len-loop);
    memcpy(In+len-loop, tmp, loop);
}
void ByteToBit(int *Out, const char *In, int bits)
{
    int i;
    for(i=0; i<bits; i++)
        Out[i] = (In[i/8]>>(i%8)) & 1;
}
void BitToByte(char *Out, const int *In, int bits)
{
    int i;
    memset(Out, 0, (bits+7)/8);
    for(i=0; i<bits; i++)
        Out[i/8] |= In[i]<<(i%8);
}

int main()
{
    char i,ch,key[9],plaintext[9],ciphertext[9];
    memset(key,0,sizeof(key));
    printf("Input Key: ");
    gets(key);
    DES_SetKey(key);
    printf("Input PlainText: ");
    gets(plaintext);
    memset(ciphertext,0,sizeof(ciphertext));
    Des_Run(ciphertext,plaintext,ENCRYPT);
    printf("CipherText: ");
    for(i=0;i<8;i++)
        printf("%02X",(unsigned char)ciphertext[i]);
    putchar('\n');
    memset(plaintext,0,sizeof(plaintext));
    Des_Run(plaintext,ciphertext,DECRYPT);
    printf("Decryption: ");
    puts(plaintext);
    return 0;
}