S-DES加密

Simplified Data Encryption Standard S-DES 是一个供教学的非安全的加密算法，它与DES的特性和结构类似，但参数小，明文分组为8位，主密钥分组为10位，采用两轮迭代。

S-DES加密过程包含两个重要部分：子密码生成过程，f函数结构。

S-DES加密原理：

S-DES的子密码生成过程：

S-DES的f函数结构：

S-DES的S盒：

通过对主加密过程进行翻转来解密。

实现代码：

#include <cstdio>
#include <iostream>
#include <fstream>
#include <algorithm>
#include <vector>
#include <string>

class S_DES {
private:
    typedef unsigned int uint;
    typedef unsigned char uchar;
    typedef std::pair<unsigned int, unsigned int> PII;
    typedef std::pair<PII, PII> PPI;
    typedef std::vector<unsigned int> VI;
    typedef std::vector<VI> VVI;
    typedef std::vector<unsigned char> VC;
    typedef std::string String;

    const static VI P_10;
    const static VI P_8;
    const static VI P_4;
    const static VI IP;
    const static VI IP_1;
    const static VI EP;
    const static VVI S_1;
    const static VVI S_2;

    // MakePII
    inline PII MakePII(uint L, uint R) {
        return std::make_pair(L, R);
    }

    // MakePPI
    inline PPI MakePPI(uint A, uint B, uint C, uint D) {
        return std::make_pair(std::make_pair(A, B), std::make_pair(C, D));
    }

    // 置换，长度为X
    uint Permutation(uint Bit, int X, const VI &P) {
        uint res = 0;
        int n = P.size();
        for (int i = 0; i < n; i++) {
            res <<= 1;
            if (Bit & (1 << (X - P[i]))) res |= 1;
        }
        return res;
    }

    // 逆置换
    uint InversePermutation(uint Bit, int X, const VI &P) {
        uint res = 0;
        int n = P.size();
        for (int i = 0; i < n; i++) {
            if (Bit&(1 << (n - i - 1))) {
                res |= 1 << (X - P[i]);
            }
        }
        return res;
    }

    // 以X为单位分割二进制数为两份
    PII Split(uint Bit, int X) {
        uint L = 0, R = 0;
        uint mask = (1 << X) - 1;
        R = Bit & mask;
        L = Bit >> X;
        return MakePII(L, R);
    }
    
    // 将四位二进制数转化为S-BOX的坐标
    PII GetBoxXY(uint Bit) {
        uint x = 0, y = 0;
        if (Bit&(1 << 3)) x |= 1;
        if (Bit&(1 << 2)) y |= 1;
        x <<= 1;
        y <<= 1;
        if (Bit&(1 << 0)) x |= 1;
        if (Bit&(1 << 1)) y |= 1;
        return MakePII(x, y);
    }

    // 将八位二进制数转化为S-BOX的坐标
    PPI GetExBox(uint Bit) {
        PII pii = Split(Bit,4);
        PII xy1 = GetBoxXY(pii.first);
        PII xy2 = GetBoxXY(pii.second);
        return MakePPI(xy1.first, xy1.second, xy2.first, xy2.second);
    }

    // 合并两个长度为X的二进制数
    uint Merge(uint lBit, uint rBit, int X) {
        return (lBit << X) | rBit;
    }

    // 将长度为L的二进制数，循环左移X次
    uint LS(uint Bit, int L, int X) {
        X %= L;
        uint mask = (1 << L) - 1;
        uint ans = ((Bit << X) & mask) | (Bit >> (L - X));
        return ans;
    }

    // S-DES 子密码生成过程，MasterKey是10位的主密钥。
    PII GetSubPsw(uint MasterKey) {
        uint K = Permutation(MasterKey, 10, P_10);// 主密钥K进行P10置换
        PII pii = Split(K, 5);                    // 分成左5位右5位
        uint L = pii.first;                          // 
        uint R = pii.second;                      // 
        L = LS(L, 5, 1);                          // 分别进行LS-1操作
        R = LS(R, 5, 1);                          // 其结果一方面作为下一轮的初始值
        uint K_1 = Merge(L, R, 5);                // 另一方面进行P8置换
        K_1 = Permutation(K_1, 10, P_8);          // 得到K1
        L = LS(L, 5, 2);                          // 再分别左循环2位
        R = LS(R, 5, 2);                          // 
        uint K_2 = Merge(L, R, 5);                  // 
        K_2 = Permutation(K_2, 10, P_8);          // 经过P8置换，得到K2
        return MakePII(K_1, K_2);
    }

    // S-DES的f函数
    uint Function(uint Ipt, uint K) {
        uint ex = Permutation(Ipt, 4, EP);// E/P扩展及置换。将4位R扩展为8位
        ex ^= K;                          // 扩展后的8位异或秘钥K
        PPI ppi = GetExBox(ex);           // 左边4位作为S1盒输入，右边四位作为S2盒输入
        uint x1 = ppi.first.first;          // 在S1和S2中，第一位与第四位结合形成2位代表S盒的行号
        uint y1 = ppi.first.second;       // 第二位与第三位结合形成2位代表S盒的列号
        uint x2 = ppi.second.first;       //
        uint y2 = ppi.second.second;      //
        uint s1 = S_1[x1][y1];              // 得到S盒的输出
        uint s2 = S_2[x2][y2];            //
        uint res = Merge(s1, s2, 2);      //
        res = Permutation(res, 4, P_4);   // 进行P4置换，得到f函数的输出
        return res;
    }

    // S-DES 加密
    uint S_DES_Main(uint Plaintext, uint K_1, uint K_2) {
        Plaintext = Permutation(Plaintext, 8, IP);// 初始置换IP，将8位明文按照置换顺序进行位置变化。
        PII pii = Split(Plaintext, 4);              // 置换后分
        uint L0 = pii.first;                      // 左4位L0
        uint R0 = pii.second;                      // 右4位R0
        uint L1 = R0;                              // 第一轮运算，R0作为下一轮的L1
        uint R1 = L0 ^ (Function(R0, K_1));          // R0作为f函数的输入与8位子秘钥K1参与函数运算，运算结构与L0异或，结果作为下一轮的R1
        uint R2 = R1;                              // 第二轮运算，R1作为下一轮的R2
        uint L2 = L1 ^ (Function(R1, K_2));       // R1作为f函数的输入与8位子密钥K2参与函数运算，运算结果与L1异或，结果作为下一轮的L2
        uint res = Merge(L2, R2, 4);              // 
        res = Permutation(res, 8, IP_1);          // 逆置换IP-1
        return res;
    }

    // S-DES 解密
    uint Decryption(uint Cip, uint K_1, uint K_2) {
        Cip = InversePermutation(Cip, 8, IP_1);
        PII pii = Split(Cip, 4);
        uint L2 = pii.first;
        uint R2 = pii.second;
        uint R1 = R2;
        uint L1 = L2 ^ (Function(R1, K_2));
        uint R0 = L1;
        uint L0 = R1 ^ (Function(R0, K_1));
        uint res = Merge(L0, R0, 4);
        res = InversePermutation(res, 8, IP);
        return res;
    }
public:
    // 将数字以二进制形式输出
    void PrintBinary(uint b) {
        if (b == 0) {
            printf("0
");
            return;
        }
        VI vec;
        vec.clear();
        while (b > 0) {
            if (b & 1) vec.push_back(1);
            else vec.push_back(0);
            b >>= 1;
        }
        for (auto it = vec.rbegin(); it != vec.rend(); it++) {
            printf("%d", *it);
        }
        printf("
");
    }

    // 将二进制字符串转换为数字
    uint StringToBinary(const std::string &Str) {
        uint res = 0;
        uint len = Str.length();
        for (uint i = 0; i < len; i++) {
            res <<= 1;
            if (Str[i] == '1') res |= 1;
        }
        return res;
    }

    // 加密一个单位的数据
    uint EncryptInt(uint Text, uint MasterKey) {
        auto p = GetSubPsw(MasterKey);
        uint K_1 = p.first;
        uint K_2 = p.second;
        uint res = S_DES_Main(Text, K_1, K_2);
        return res;
    }
    
    // 按字符加密一个字符串
    VI EncryptString(const String &Str, uint MasterKey) {
        VI res;
        auto p = GetSubPsw(MasterKey);
        uint K_1 = p.first;
        uint K_2 = p.second;
        int len = Str.length();
        for (int i = 0; i < len; i++) {
            uint e = S_DES_Main((uint)Str[i], K_1, K_2);
            res.push_back(e);
        }
        return res;
    }

    // 加密一组vector中的数字
    VI EncryptVector(const VI &Arr, uint MasterKey) {
        VI res;
        auto p = GetSubPsw(MasterKey);
        uint K_1 = p.first;
        uint K_2 = p.second;
        int len = Arr.size();
        for (int i = 0; i < len; i++) {
            uint e = S_DES_Main(Arr[i], K_1, K_2);
            res.push_back(e);
        }
        return res;
    }

    // 加密长度为n的数组中的数字
    VI EncryptArray(const uint Arr[], int n, uint MasterKey) {
        VI res;
        auto p = GetSubPsw(MasterKey);
        uint K_1 = p.first;
        uint K_2 = p.second;
        for (int i = 0; i < n; i++) {
            uint e = S_DES_Main(Arr[i], K_1, K_2);
            res.push_back(e);
        }
        return res;
    }

    // 加密长度为n的Byte数组
    VI EncryptBytes(const uchar Arr[], int n, uint MasterKey) {
        VI res;
        auto p = GetSubPsw(MasterKey);
        uint K_1 = p.first;
        uint K_2 = p.second;
        for (int i = 0; i < n; i++) {
            uint e = S_DES_Main((uint)Arr[i], K_1, K_2);
            res.push_back(e);
        }
        return res;
    }

    // 加密一个文件中的数据
    VI EncryptFile(char FileName[], uint MasterKey) {
        VI res;
        std::ifstream fin(FileName, std::ios::binary);
        if (!fin.is_open()) return res;
        int n = (int)fin.gcount(); 
        char pc;
        for (int i = 0; i < n; i++) {
            fin.read(&pc, sizeof(uchar));
            res.push_back((uint)pc);
        }
        return res;
    }

    // 解密一个单位的数据
    uint DecryptInt(uint Cip, uint MasterKey) {
        auto p = GetSubPsw(MasterKey);
        uint K_1 = p.first;
        uint K_2 = p.second;
        uint res = Decryption(Cip, K_1, K_2);
        return res;
    }

    // 解密vector中的数据
    VI DecryptVector(const VI& Cips, uint MasterKey) {
        auto p = GetSubPsw(MasterKey);
        uint K_1 = p.first;
        uint K_2 = p.second;
        VI res;
        for (auto it = Cips.begin(); it != Cips.end(); it++) {
            uint des = Decryption(*it, K_1, K_2);
            res.push_back(des);
        }
        return res;
    }

    // 将vector中的数据转化为string类型
    String VectorToString(const VI& vec) {
        String res;
        for (auto it = vec.begin(); it != vec.end(); it++) {
            res.push_back((char)*it);
        }
        return res;
    }
};

const S_DES::VI S_DES::P_10{ 3, 5, 2, 7, 4, 10, 1, 9, 8, 6 };
const S_DES::VI S_DES::P_8{ 6, 3, 7, 4, 8, 5, 10, 9 };
const S_DES::VI S_DES::P_4{ 2, 4, 3, 1 };
const S_DES::VI S_DES::IP{ 2, 6, 3, 1, 4, 8, 5, 7 };
const S_DES::VI S_DES::IP_1{ 4, 1, 3, 5, 7, 2, 8, 6 };
const S_DES::VI S_DES::EP{ 4, 1, 2, 3, 2, 3, 4, 1 };
const S_DES::VVI S_DES::S_1{ { 1, 0, 3, 2 },
                             { 3, 2, 1, 0 },
                             { 0, 2, 1, 3 },
                             { 3, 1, 3, 2 } };
const S_DES::VVI S_DES::S_2{ { 0, 1, 2, 3 },
                             { 2, 0, 1, 3 }, 
                             { 3, 0, 1, 0 },
                             { 2, 1, 0, 3 } };