24、数据加密-DES

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最新推荐文章于 2024-09-25 23:49:25 发布

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分类专栏：笔记-算法精解C语言实现文章标签：数据加密 des加密对称加密

本文链接：https://blog.youkuaiyun.com/qq_23084801/article/details/77532910

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本文深入解析了DES（数据加密标准）算法的工作原理和技术细节，包括密钥生成、数据加密及解密过程，并提供了具体的实现流程和关键步骤。

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1、密码的安全性不依赖算法的保密性，而依赖于密钥。加密算法分类：对称加密算法，加密和解密使用同一个密钥；非对称加密算法，加密使用公钥，解密使用私钥。
ECB：电子码本，把数据分组，每组都各自生成码文，然后组合。
CBC：密码分组连接，加密时把前一个输出密文与当前明文异或再加密；解密时前一个解好的明文异或当前密文，再解密。
2、DES（Data Encryption Standard）：最流行对称加密算法。明文64bit为一组进行加密。加密过程根据64bit初始密钥生成的16个48位子密钥K1-K16进行。
这里写图片描述
一、生成子密钥
（1）初始密钥K0，根据密钥转换表64bit->56bit。第一个57表示原数据第57位为现在的第一位。

（2）把56bit分成2组，每组左移下图位数（最终要形成K1-K16），合并后置换56bit->48bit，形成子密钥K1-K16
这里写图片描述

二、加密，解密对称K16-K1，其它顺序不变

（1）一组数据根据置换表初始置换，64bit->64bit

（2）数据分成两组Li、Ri，Ri根据查表32bit扩展到48bit

（3）Ri异或Ki得到Rin
（4）Rin的48bit分成8组，每组6bit，这n组对应第n个盒Sn（8组8个盒），把6bit转换成4bit。如：第3组为101011，取第1位和最后一位对应S3中第4行，中间四位对应S3第6列，找到一个数字（4bit）。此时R又变为32bit
这里写图片描述
（5）P盒查表置换，32bit->32bit

（6）循环从（2）开始，Li = Ri-1，Ri = Li-1 异或 Rin
（7）循环16次后合并，最后在置换一次得到加密后的密文。

3、各种表

//初始秘钥64bit到56bit转换表
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
}; 

//产生K1-K16的旋转表
static const int SesRotations[16] =
{
    1,  1,  2,  2,  2,  2,  2,  2,  1,  2,  2,  2,  2,  2,  2,  1   
};

//K1-K16 56bit到48bit转换表
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 
};

//原文数据组64bit初始转换表
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
};

//Ri 32bit到48bit扩展表
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     
};

//8个4行16列盒子S，48bit到32bit
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}
    }   
};

//P盒子，32bit到32bit
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
};

//最后转换表64bit到64bit
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
};

4、根据表进行转换

//bits为源数据；mapping为转换表； n为源数据bit数 
static void permute(unsigned char *bits, const int *mapping, int n)
{
    unsigned char temp[8];
    int i;

    //ceil取 >= 指定表达式的整数 
    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;
}

5、编码、解码处理函数

//key为密钥， direction选择解码还是译码 
static int des_main(const unsigned char *source, unsigned char *target, const unsigned char *key, DesEorD direction)
{
    //K1-K16, 56bit还需要转换到48bit 
    static unsigned char subkeys[16][7];
    unsigned char temp[8];

    //K0分成左右32bit 
    unsigned char lkey[4], rkey[4];

    unsigned char lblk[6], rblk[6];
    unsigned char fblk[6], xblk[6], sblk;
    int row, col, i, j, k, p;

    //生成子密钥 
    if(key != NULL)
    {
        memcpy(temp, key, 8);

        //K0 64bit->56bit
        permute(temp, DesTransform, 56);

        //分成左右28bit 
        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));

        //得到K1-K16 旋转，56bit->48bit  
        for(i = 0; i < 16; i++)
        {
            bit_rot_left(lkey, 28, DesRotations[i]);
            bit_rot_left(rkey, 28, DesRotations[i]);

            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(lkey, j));

            permute(subkeys[i], DesPermuted, 48);
        }
    } 

    //取64bit数据 
    memcpy(temp, source, 8);

    //数据初始转换 
    permute(temp, DesInitial, 64);

    //分左右
    memcpy(lblk, &temp[0], 4); 
    memcpy(rblk, &temp[4], 4);

    for(i = 0; i < 16; i++)
    {
        //右32bit扩展到48bit 
        memcpy(fblk, rblk, 4);
        permute(fblk, DesExpansion, 48);

        //编码处理过程是K1-K16，解码处理过程是K16-K1 
        if(direction == encipher)
        {
            bit_xor(fblk, subkeys[i], xblk, 48);
            memset(fblk, xblk, 6);
        }
        else
        {
            bit_xor(fblk, subkeys[16 - i], xblk, 48);
            memset(fblk, xblk, 6);
        }

        p = 0;

        //8组6bit处理 
        for(j = 0; j < 8; j++)
        {
            //找到每6bit对应的盒子Sj中的数字 
            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);
            sblk = (unsigned char)DesSbox[j][row][col];
            for(k = 4; k < 8; k++)
            {
                bit_set(fblk, p, bit_get(&sblk, k));
                p++;
            }
        }   
            //P盒子转换
            permute(fblk, DesPermuted, 32);

            bit_xor(lblk, fblk, xblk, 32);
            memset(lblk, rblk, 4);
            memset(rblk, xblk, 4); 

    }

    //最后合并转换
    memset(&target[0], rblk, 4);
    memset(&target[4], lblk, 4);

    permute(target, DesFinal, 64);

    return 0;
}