DES加密算法的一种实现

从现象上来讲，DES加密算法是对8个字节明文加密，加密时需要一个8个字节的密钥，加密后生成一个8个字节的密文；解密过程也需要8个字节的密钥，将八个字节的密文解密成明文。具体的实现过程可以在网上搜索一篇名为《DES算法原理及实现》的论文，这里只给出算法的代码供参考。

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

typedef unsigned char     uint8_t;
typedef unsigned short    uint16_t;
typedef unsigned int    uint32_t;
typedef char            int8_t;
typedef short            int16_t;
typedef int                int32_t;

const uint8_t DATA_IP_Table[64] =
{
    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,
    56,48,40,32,24,16,8,0,
    58,50,42,34,26,18,10,2,
    60,52,44,36,28,20,12,4,
    62,54,46,38,30,22,14,6
};

const uint8_t DATA_IP_1_Table[64] =
{
    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,
    32,0,40,8,48,16,56,24
};

const uint8_t DATA_E_Table[48] =
{
    31, 0, 1, 2, 3, 4,
    3, 4, 5, 6, 7, 8,
    7, 8,9,10,11,12,
    11,12,13,14,15,16,
    15,16,17,18,19,20,
    19,20,21,22,23,24,
    23,24,25,26,27,28,
    27,28,29,30,31, 0
};

const uint8_t DATA_P_Table[32] =
{
    15,6,19,20,28,11,27,16,
    0,14,22,25,4,17,30,9,
    1,7,23,13,31,26,2,8,
    18,12,29,5,21,10,3,24
};

const uint8_t DATA_S_Table[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}
    }
};

const uint8_t KEY_PC_1[56] =
{
    56,48,40,32,24,16,8,
    0,57,49,41,33,25,17,
    9,1,58,50,42,34,26,
    18,10,2,59,51,43,35,
    62,54,46,38,30,22,14,
    6,61,53,45,37,29,21,
    13,5,60,52,44,36,28,
    20,12,4,27,19,11,3
};

const uint8_t KEY_PC_2[48] =
{
    13,16,10,23,0,4,2,27,
    14,5,20,9,22,18,11,3,
    25,7,15,6,26,19,12,1,
    40,51,30,36,46,54,29,39,
    50,44,32,46,43,48,38,55,
    33,52,45,41,49,35,28,31
};

const uint8_t KEY_Shift[16] = {1,1,2,2,2,2,2,2,1,2,2,2,2,2,2,1};

/************************************************************
 * 8 bytes to 64 bits                                        *
 ***********************************************************/
static void Bytes8ToBits64(uint8_t res[8], uint8_t *dst)
{
    int32_t i, j;
    uint8_t temp;

    for (i = 0; i < 8; i++)
    {
        temp = res[i];
        for (j = 0; j < 8; j++)
        {
            *dst = temp & 0x01;
            temp >>= 1;
            dst++;
        }
    }
}

/************************************************************
 * 64 bits to 8 bytes                                        *
 ***********************************************************/
static void Bits64ToBytes8(uint8_t dst[8], uint8_t *src)
{
    int32_t i, j;
    uint8_t temp;

    for (i = 0; i < 8; i++)
    {
        temp = 0;
        for (j = 0; j < 8; j++)
        {
            temp >>= 1;
            if ((*src) & 0x01)
            {
                temp |= 0x80;
            }

            src++;
        }

        dst[i] = temp;
    }
}

/************************************************************
 * IP transfer                                                *
 ***********************************************************/
void DES_IP_Transfer(uint8_t data[64])
{
    uint8_t temp[64];
    int32_t i;

    for (i = 0; i < 64; i++)
    {
        temp[i] = data[DATA_IP_Table[i]];
    }

    memcpy(data, temp, 64);
}

/************************************************************
 * IP-1 transfer                                            *
 ***********************************************************/
void DES_IP_1_Transfer(uint8_t data[64])
{
    uint8_t temp[64];
    int32_t i;

    for (i = 0; i < 64; i++)
    {
        temp[i] = data[DATA_IP_1_Table[i]];
    }

    memcpy(data, temp, 64);
}

/************************************************************
 * P transfer                                                *
 ***********************************************************/
void DES_P_Transfer(uint8_t data[32])
{
    int32_t i;
    uint8_t temp[32];

    for (i = 0; i < 32; i++)
    {
        temp[i] = data[DATA_P_Table[i]];
    }

    memcpy(data, temp, 32);
}

/************************************************************
 * KEY PC-1 transfer                                        *
 ***********************************************************/
void DES_PC1_Transfer(uint8_t key[64], uint8_t pc1[56])
{
    int32_t i;

    for (i = 0; i < 56; i++)
    {
        *(pc1+i) = key[KEY_PC_1[i]];
    }
}

/************************************************************
 * KEY PC-2 transfer                                        *
 ***********************************************************/
void DES_PC2_Transfer(uint8_t pc1[56], uint8_t pc2[48])
{
    int32_t i;

    for (i = 0; i < 48; i++)
    {
        *(pc2+i) = pc1[KEY_PC_2[i]];
    }
}

/************************************************************
 * subkeys shift left                                        *
 ***********************************************************/
void DES_Shift(uint8_t subkey[56], uint8_t time)
{
    uint8_t temp[56];

    memcpy(temp, (subkey+time), 28-time);
    memcpy((temp+28-time), subkey, time);
    memcpy((temp+28), (subkey+time+28), 28-time);
    memcpy((temp+56-time), (subkey+28), time);

    memcpy(subkey, temp, 56);
}

/************************************************************
 * make sub keys                                            *
 ***********************************************************/
void DES_MakeSubKeys(uint8_t key[64], uint8_t subkeys[16][48])
{
    uint8_t temp[56];
    int32_t i;

    DES_PC1_Transfer(key, temp);
    for (i = 0; i < 16; i++)
    {
        DES_Shift(temp, KEY_Shift[i]);
        DES_PC2_Transfer(temp, subkeys[i]);
    }
}

/************************************************************
 * data expand                                                *
 ***********************************************************/
void DES_DataExpand(uint8_t data[48])
{
    uint8_t temp[48];
    int32_t i;

    for (i = 0; i < 48; i++)
    {
        temp[i] = data[DATA_E_Table[i]];
    }

    memcpy(data, temp, 48);
}

/************************************************************
 * S-Box                                                     *
 ***********************************************************/
void DES_SBox(uint8_t data[48])
{
    int32_t i;
    uint8_t row, col;
    uint8_t in_p, out_p;
    uint8_t out;

    in_p = 0;
    out_p = 0;
    for (i = 0; i < 8; i++)
    {
        row = (data[in_p] << 1) + data[in_p+5];
        col = (data[in_p+1] << 3) | (data[in_p+2] << 2) | (data[in_p+3] << 1) + data[in_p+4];

        out = DATA_S_Table[i][row][col];
        in_p += 6;

        data[out_p++] = (out >> 3) & 0x01;
        data[out_p++] = (out >> 2) & 0x01;
        data[out_p++] = (out >> 1) & 0x01;
        data[out_p++] = out & 0x01;
    }
}

/************************************************************
 * DES XOR                                                     *
 ***********************************************************/
void DES_XOR(uint8_t *dst, uint8_t *src, int count)
{
    while (count--)
    {
        *dst ^= *src;
        dst++;
        src++;
    }
}

/************************************************************
 * Swap L&R                                                     *
 ***********************************************************/
void DES_Swap(uint8_t *left, uint8_t *right)
{
    uint8_t temp[32];

    memcpy(temp, left, 32);
    memcpy(left, right, 32);
    memcpy(right, temp, 32);
}

/************************************************************
 * Encrypt Block                                             *
 ***********************************************************/
void DES_EncryptBlock(uint8_t plain_data[8], uint8_t sub_keys[16][48], uint8_t cipher_data[8])
{
    uint8_t plain_bits[64];
    uint8_t temp[48];
    uint8_t i;

    Bytes8ToBits64(plain_data, plain_bits);

    DES_IP_Transfer(plain_bits);
    for (i = 0; i < 16; i++)
    {
        memcpy(temp, (plain_bits+32), 32);
        DES_DataExpand(temp);
        DES_XOR(temp, sub_keys[i], 48);
        DES_SBox(temp);
        DES_P_Transfer(temp);
        DES_XOR(plain_bits, temp, 32);
        if (i != 15)
        {
            DES_Swap(plain_bits, plain_bits+32);
        }
    }

    DES_IP_1_Transfer(plain_bits);
    Bits64ToBytes8(cipher_data, plain_bits);
}

/************************************************************
 * Dencrypt Block                                             *
 ***********************************************************/
void DES_DencryptBlock(uint8_t cipher_data[8], uint8_t sub_keys[16][48], uint8_t plain_data[8])
{
    uint8_t cipher_bits[64];
    uint8_t temp[48];
    int8_t i;

    Bytes8ToBits64(cipher_data, cipher_bits);

    DES_IP_Transfer(cipher_bits);
    for (i = 15; i >= 0; i--)
    {
        memcpy(temp, (cipher_bits+32), 32);
        DES_DataExpand(temp);
        DES_XOR(temp, sub_keys[i], 48);
        DES_SBox(temp);
        DES_P_Transfer(temp);
        DES_XOR(cipher_bits, temp, 32);
        if (i != 0)
        {
            DES_Swap(cipher_bits, cipher_bits+32);
        }
    }

    DES_IP_1_Transfer(cipher_bits);
    Bits64ToBytes8(plain_data, cipher_bits);
}

int main(int argc, char **argv)
{
    uint8_t data[8] = { 0x01, 0x02, 0x07, 0x04, 0x05, 0x06, 0x07, 0x08 }; // data tobe encrypted
    uint8_t key[8] = { 0x30, 0x30, 0x32, 0x30, 0x30, 0x37, 0x30, 0x30 }; // key for encrypt
    uint8_t cipher_data[8];
    uint8_t key_bits[64];
    uint8_t sub_keys[16][48];
    uint8_t i;

    Bytes8ToBits64(key, key_bits);
    DES_MakeSubKeys(key_bits, sub_keys);
    DES_EncryptBlock(data, sub_keys, cipher_data);

    printf("cipher data is : ");
    for (i = 0; i < 8; i++)
    {
        printf("%02x ", cipher_data[i]);
    }
    printf("\n");

    DES_DencryptBlock(cipher_data, sub_keys, data);
    printf(" plain data is : ");
    for (i = 0; i < 8; i++)
    {
        printf("%02x ", data[i]);
    }

    printf("\n");


    return 0;
}