DES和IDEA的CPP实现

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DES

数据加密标准（Data Encryption Standard，DES）能够依赖64位密钥加密64位明文，将64位密文反向使用64位密钥生成的子密钥可以按照完全相同的步骤把密文解密为明文，加密步骤如下：

  1. 输入准备
  • 明文：64 位分组（若不足64位则进行填充）。 (cnblogs.com)
  • 密钥：64 位（其中有效56 位，8 位用于奇偶校验）用于生成子密钥。 (维基百科)
  1. 初始置换（Initial Permutation，IP）
  • 将64 位明文按照固定表进行重排，得到一个置换后的64 位数据。 (CSDN博客)
  • 将置换结果分成左右两个32 位部分：L₀ 和 R₀。 (Echo Blog)
  1. 子密钥生成（密钥调度）
  • 对主密钥执行「选择置换 PC-1」从64 位中选出56 位。 (Pion1eer)
  • 将56 位分为两个28 位半密钥，分别左旋移位（每轮移位量由轮次决定）。 (维基百科)
  • 再通过「选择置换 PC-2」从移位后的56 位中选出48 位，作为第1轮子密钥 K₁。重复共生成16 个子密钥 K₁…K₁₆。 (Pion1eer)
  1. 16 轮 Feistel 结构迭代

对于 i = 1 到 16 轮，进行以下操作：

  • $L_{i}$= $R_{i - 1}$
  • $R_{i}$ = $L_{i - 1} \bigoplus f(R_{i - 1}, K_{i}) $ (Echo Blog1)
    其中 f 函数包含：
    1. 扩展置换 E：将32 位 $R_{i - 1}$ 扩展至48 位。 (cnblogs.com)
    2. 与子密钥 Kᵢ 做 XOR。 (知乎专栏)
    3. 分为8块，每块6 位，输入各自 S‐盒，输出4 位。总输出32 位。 (Pion1eer)
    4. 最后通过固定 P 置换将32 位再重排。 (Echo Blog)
  1. 轮结束后的交换与末置换
  • 完成第16轮后，将 L₁₆ 和 R₁₆ 交换，得到新 L₁₇ = R₁₆， R₁₇ = L₁₆。 (Echo Blog)
  • 将 L₁₇ ∥ R₁₇ （合并成64 位）输入「最终置换 FP （IP⁻¹）」进行重排，输出密文。 (cnblogs.com)
  1. 解密流程
  • 解密时流程与加密相同，但子密钥的使用顺序为 K₁₆ → K₁₅ → … → K₁；其余步骤一致。 (cnblogs.com)

base

只接受16进制的16位密钥输出和16进制的16位明文输入

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#include<bits/stdc++.h>
using namespace std;
vector<string> Key0(16);
vector<int> LS = {1, 1, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2, 1},
			EX_K1 = {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},
		    EX_K2 = {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},
			IP = { 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 },
			IPR = {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},
			E = {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},
		    P = {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};
int SBOX[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}}
};		 
string EX(string s, vector<int> & ex) {
	string s2;
	for(auto & x : ex) s2 += s[x - 1];
	return s2;
}
string movel(string s, int i) {
	return s.substr(LS[i]) + s.substr(0, LS[i]);
}
void make_key(string key) {
	string key2 = EX(key, EX_K1);
	for(int i = 0; i < 16; i ++) {
		string l = key2.substr(0, 28), r = key2.substr(28);
		l = movel(l, i);
		r = movel(r, i);
		key2 = l + r;
		Key0[i] = EX(key2, EX_K2);
	}
}
string XOR(string s1, string s2) {
	string s;
	for(int i = 0; i < (int)s1.size(); i ++) s += '0' + (s1[i] != s2[i]);
	return s;
}
string S(string s) {
	string s2;
	for(int i = 0; i < 48; i += 6) {
		int x = ((s[i] - '0') << 1) + (s[i + 5] - '0'), y = 0;
		for(int j = i + 4, base = 1; j > i; j --, base *= 2) y += (s[j] - '0') * base;
		int z = SBOX[i / 6][x][y];
		for(int j = 3; j >= 0; j --) s2 += '0' + ((z >> j) & 1);
	}
	return s2;
}
string F(string s, string key) {
	s = EX(s, E);
	s = XOR(s, key);
	s = S(s);
	s = EX(s, P);
	return s;
}
string DES(string con, bool f) {
	con = EX(con, IP);
	string l0 = con.substr(0, 32), r0 = con.substr(32), mid;
	for(int i = 0; i < 16; i ++) {
		mid = r0;
		if(f) r0 = XOR(l0, F(r0, Key0[i]));
		else r0 = XOR(l0, F(r0, Key0[15 - i]));
		l0 = mid;
	}
	con = EX(r0 + l0, IPR);
	return con;
}
string H2B(string s) {
	string s2 = "";
	vector<string> base = {"0000","0001","0010","0011","0100","0101","0110","0111","1000","1001","1010","1011","1100","1101","1110","1111" };
	for (int i = 0; i < (int)s.size(); i++) {
		if (s[i] >= 'A' && s[i] <= 'F') s2 += base[s[i] - 'A' + 10];
		else s2 += base[s[i] - '0'];
	}
	return s2;
}
string B2H(string s) {
	string s2 = "";
	int temp = 0;
	while (s.size() % 4 != 0) s = "0" + s;
	for (int i = 0; i < (int)s.size(); i += 4) {
		temp = (s[i] - '0') * 8 + (s[i + 1] - '0') * 4 + (s[i + 2] - '0') * 2 + (s[i + 3] - '0') * 1;
		if (temp < 10) s2 += '0' + temp;
		else s2 += 'A' + (temp - 10);
	}
	return s2;
}
int main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	string key, con;
	cin >> key >> con;
	string key1 = H2B(key), con1 = H2B(con);
	make_key(key1);
	string mi = DES(con1, 1);
	string con2 = DES(mi, 0);
	cout << "key: " << key << "\n" << "content: " << con << "\n" << "content_key: " << B2H(mi) << "\n";
	cout << "content: " << B2H(con2) << "\n";
	return 0;
}

std

示例输入：

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/*
enc
jielycat
Hello! DES!
*/

程序：

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#include <bits/stdc++.h>
using namespace std;
using u64 = uint64_t;
using u32 = uint32_t;
using u8  = uint8_t;

// ---- 常量与置换表 ----
static const int LS[16] = {1, 1, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2, 1}; // 每轮左移位数

// 密钥置换 PC-1（64->56，去奇偶校验位）
static const int PC1[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};
// 压缩置换 PC-2（56->48）
static const int PC2[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};

// 初始/逆初始置换
static const int IP[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};
static const int FP[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};

// E 扩展（32->48）
static const int E_tab[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};

// P 置换（F 函数输出置换）
static const int P_tab[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};

// 8 个 S 盒
static const int SBOX[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}}};

// ---- 通用置换：按表抽取位 ----
template <int N>
static inline u64 permute(u64 input, const int (&tbl)[N]) {
    u64 out = 0;
    for (int i = 0; i < N; ++i) {
        int src = tbl[i] - 1;                     // 表索引从 1 开始
        u64 bit = (input >> (64 - 1 - src)) & 1u; // 统一按 64 位视角取位
        out = (out << 1) | bit;
    }
    return out;
}

// 指定输入宽度的置换（E/PC2/P 使用）
static inline u64 permute_n(u64 input, const int *tbl, int n, int in_width) {
    u64 out = 0;
    for (int i = 0; i < n; ++i) {
        int src = tbl[i] - 1;
        u64 bit = (input >> (in_width - 1 - src)) & 1u;
        out = (out << 1) | bit;
    }
    return out;
}

// 28 位循环左移（仅低 28 位有效）
static inline u32 rol28(u32 v, int r) {
    v &= 0x0FFFFFFFu;
    return ((v << r) | (v >> (28 - r))) & 0x0FFFFFFFu;
}

// 8 字节大端装载/存储
static inline u64 load64_be(const u8 *b) {
    return ((u64)b[0] << 56) | ((u64)b[1] << 48) | ((u64)b[2] << 40) | ((u64)b[3] << 32) |
           ((u64)b[4] << 24) | ((u64)b[5] << 16) | ((u64)b[6] << 8) | ((u64)b[7]);
}
static inline void store64_be(u64 v, u8 *b) {
    b[0] = (u8)(v >> 56);
    b[1] = (u8)(v >> 48);
    b[2] = (u8)(v >> 40);
    b[3] = (u8)(v >> 32);
    b[4] = (u8)(v >> 24);
    b[5] = (u8)(v >> 16);
    b[6] = (u8)(v >> 8);
    b[7] = (u8)(v);
}

// ---- 密钥安排：生成 16 轮 48 位子密钥 ----
static inline void des_key_schedule(const u8 key8[8], u64 subkey[16]) {
    u64 key64 = load64_be(key8);              // 原始 64 位密钥
    u64 k56 = permute<56>(key64, PC1);        // PC-1 去校验位
    u32 C = (u32)((k56 >> 28) & 0x0FFFFFFFu); // 左 28 位
    u32 D = (u32)(k56 & 0x0FFFFFFFu);         // 右 28 位
    for (int r = 0; r < 16; ++r) {
        C = rol28(C, LS[r]); // 左移
        D = rol28(D, LS[r]);
        u64 CD = (((u64)C) << 28) | (u64)D;   // 合并 56 位
        u64 k48 = permute_n(CD, PC2, 48, 56); // 压缩到 48 位
        subkey[r] = k48;
    }
}

// ---- 轮函数 F(R, K) ----
static inline u32 des_f(u32 R, u64 k48) {
    u64 ER = permute_n((u64)R, E_tab, 48, 32); // 扩展 32->48
    u64 x  = ER ^ k48;                         // 与子密钥异或
    u32 out32 = 0;
    for (int i = 0; i < 8; ++i) { // 8 个 S 盒
        int shift = 42 - 6 * i;
        u8 six = (u8)((x >> shift) & 0x3Fu);
        int row = ((six & 0x20) >> 4) | (six & 0x01);
        int col = (six >> 1) & 0x0F;
        u8 s = (u8)SBOX[i][row][col];
        out32 = (out32 << 4) | s;
    }
    u64 Pout = permute_n((u64)out32, P_tab, 32, 32); // P 置换
    return (u32)Pout;
}

// ---- 单块加密（ECB 基元）----
static inline void des_encrypt_block(const u8 in[8], u8 out[8], const u64 subkey[16]) {
    u64 B   = load64_be(in);
    u64 IPB = permute<64>(B, IP);           // 初始置换
    u32 L   = (u32)(IPB >> 32), R = (u32)IPB; // 拆成 L/R
    for (int r = 0; r < 16; ++r) { // 16 轮 Feistel
        u32 f    = des_f(R, subkey[r]);
        u32 newL = R;
        u32 newR = L ^ f;
        L = newL;
        R = newR;
    }
    u64 preout = (((u64)R) << 32) | L; // 交换 L/R
    u64 C      = permute<64>(preout, FP);   // 逆初始置换
    store64_be(C, out);
}

// ---- 单块解密（子密钥逆序）----
static inline void des_decrypt_block(const u8 in[8], u8 out[8], const u64 subkey[16]) {
    u64 rev[16];
    for (int i = 0; i < 16; ++i)
        rev[i] = subkey[15 - i]; // 反向子密钥
    des_encrypt_block(in, out, rev);
}

// ---- PKCS#7 填充/去填充 ----
static inline vector<u8> pkcs7_pad_vec(const vector<u8> &data, size_t block = 8) {
    size_t n   = data.size();
    size_t pad = block - (n % block);
    if (pad == 0) pad = block;
    vector<u8> out;
    out.reserve(n + pad);
    out.insert(out.end(), data.begin(), data.end());
    out.insert(out.end(), pad, (u8)pad);
    return out;
}
static inline bool pkcs7_unpad_inplace(vector<u8> &buf, size_t block = 8) {
    if (buf.empty() || (buf.size() % block) != 0)
        return false;
    u8 p = buf.back();
    if (p == 0 || p > block || p > buf.size())
        return false;
    for (size_t i = 0; i < p; ++i)
        if (buf[buf.size() - 1 - i] != p)
            return false;
    buf.resize(buf.size() - p);
    return true;
}

// ---- ECB 模式（演示用，不安全）----
static inline vector<u8> des_ecb_encrypt_vec(const vector<u8> &plain, const u8 key8[8]) {
    u64 subkey[16];
    des_key_schedule(key8, subkey);
    vector<u8> in  = pkcs7_pad_vec(plain, 8);
    vector<u8> out(in.size());
    for (size_t i = 0; i < in.size(); i += 8)
        des_encrypt_block(&in[i], &out[i], subkey);
    return out;
}
static inline bool des_ecb_decrypt_vec(const vector<u8> &cipher, const u8 key8[8], vector<u8> &plain_out) {
    if (cipher.size() % 8)
        return false;
    u64 subkey[16];
    des_key_schedule(key8, subkey);
    plain_out.assign(cipher.size(), 0);
    for (size_t i = 0; i < cipher.size(); i += 8)
        des_decrypt_block(&cipher[i], &plain_out[i], subkey);
    return pkcs7_unpad_inplace(plain_out, 8);
}

// ---- hex 编解码（调试可用）----
static inline string to_hex(const vector<u8> &v) {
    static const char *H = "0123456789abcdef";
    string s;
    s.resize(v.size() * 2);
    for (size_t i = 0; i < v.size(); ++i) {
        u8 b = v[i];
        s[2 * i]     = H[b >> 4];
        s[2 * i + 1] = H[b & 0xF];
    }
    return s;
}
static inline vector<u8> from_hex(const string &h) {
    auto hexv = [](char c) -> int {
        if ('0' <= c && c <= '9')
            return c - '0';
        if ('a' <= c && c <= 'f')
            return c - 'a' + 10;
        if ('A' <= c && c <= 'F')
            return c - 'A' + 10;
        return -1;
    };
    vector<u8> v;
    if (h.size() % 2)
        return v;
    v.resize(h.size() / 2);
    for (size_t i = 0; i < v.size(); ++i) {
        int hi = hexv(h[2 * i]), lo = hexv(h[2 * i + 1]);
        if (hi < 0 || lo < 0) {
            v.clear();
            return v;
        }
        v[i] = (u8)((hi << 4) | lo);
    }
    return v;
}

// ---- 输入读取：支持 @path 文件或直接 stdin ----
static inline bool is_space_le(char c) { return static_cast<unsigned char>(c) <= ' '; }

vector<u8> get_plain() {
    string all((istreambuf_iterator<char>(cin)), istreambuf_iterator<char>());
    size_t i = 0;
    while (i < all.size() && is_space_le(all[i]))
        ++i;
    if (i < all.size() && all[i] == '@') { // @ 路径读取文件
        size_t j = i + 1;
        while (j < all.size() && is_space_le(all[j]))
            ++j;
        size_t k = all.size();
        while (k > j && is_space_le(all[k - 1]))
            --k;
        string path = all.substr(j, k - j);
        FILE *fp = fopen(path.c_str(), "rb");
        if (!fp)
            return {};
        fseek(fp, 0, SEEK_END);
        long n = ftell(fp);
        if (n < 0) {
            fclose(fp);
            return {};
        }
        fseek(fp, 0, SEEK_SET);
        vector<u8> buf(static_cast<size_t>(n));
        if (n > 0)
            fread(buf.data(), 1, static_cast<size_t>(n), fp);
        fclose(fp);
        return buf;
    }
    return vector<u8>(all.begin(), all.end()); // 直接返回全部字节
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    // 第一行：模式
    string mode;
    if (!getline(cin, mode))
        return 0;

    // 第二行：密钥(8 chars)
    string key_in;
    if (!getline(cin, key_in))
        return 0;
    if (key_in.size() < 8)
        key_in.append(8 - key_in.size(), '\0');
    if (key_in.size() > 8)
        key_in.resize(8);
    u8 key8[8];
    for (int i = 0; i < 8; ++i)
        key8[i] = (u8)key_in[i];

    if (mode == "enc" || mode == "ENC" || mode == "Enc") {
        // 加密模式：读取后续所有数据为明文
        vector<u8> plain  = get_plain();
        vector<u8> cipher = des_ecb_encrypt_vec(plain, key8);

        // 输出：十六进制密文 + 还原明文（和你原来类似的演示）
        vector<u8> plain2;
        bool ok = des_ecb_decrypt_vec(cipher, key8, plain2);
        if (!ok) {
            cerr << "unpad failed\n";
            return 1;
        }
        cout << to_hex(cipher) << "\n";
        cout.write((const char *)plain2.data(), (streamsize)plain2.size());
        cout << "\n";
    } else if (mode == "dec" || mode == "DEC" || mode == "Dec") {
        // 解密模式：第三行读取十六进制密文
        string cipher_hex;
        if (!getline(cin, cipher_hex)) {
            cerr << "no ciphertext\n";
            return 1;
        }
        vector<u8> cipher = from_hex(cipher_hex);
        if (cipher_hex.size() > 0 && cipher.empty()) {
            cerr << "invalid hex ciphertext\n";
            return 1;
        }
        vector<u8> plain;
        bool ok = des_ecb_decrypt_vec(cipher, key8, plain);
        if (!ok) {
            cerr << "decrypt or unpad failed\n";
            return 1;
        }
        // 只输出明文
        cout.write((const char *)plain.data(), (streamsize)plain.size());
        cout << "\n";
    } else {
        cerr << "unknown mode, use enc/dec\n";
        return 1;
    }
    return 0;
}

DEA

下面是 IDEA（International Data Encryption Algorithm）算法流程的

基本参数

关键操作（在每轮中使用的运算）

在 IDEA 中，每轮对数据块使用以下三种不同代数群的运算，以增强安全性：

  1. 异或 (XOR) 运算。 (维基百科)
  2. 模 2¹⁶ 加法（即以 2¹⁶ 为模的加法运算）。 (维基百科)
  3. 模 (2¹⁶ + 1) 乘法（并且将值 0x0000 视作 2¹⁶ ）。 (维基百科)

子密钥生成 (Key Schedule)

  • 从 128 位主密钥中，提取出若干 16 位子密钥。 (维基百科)
  • 每轮使用 6 个 16 位子密钥；输出半轮使用 4 个 16 位子密钥。 总计 52 个子密钥。 (国际期刊研究与评论)
  • 每次提取子密钥后，对主密钥执行左旋 25 位，然后继续提取。 (维基百科)

加密流程（每个分组处理流程）

  1. 将 64 位明文分为四个 16 位子块：X₁, X₂, X₃, X₄。
  2. 对于 i = 1 到 8 轮（每轮过程如下）：
    • 使用本轮的 6 个子密钥分别对 X₁–X₄ 进行模 2¹⁶ 加／模 (2¹⁶+1) 乘／XOR 等操作（具体组合见原文）。
    • 然后对中间结果做混合（例如两个子块之间做 XOR），再继续对其中两个子块做模 2¹⁶ 加／模 (2¹⁶+1) 乘。
    • 轮结束后，将四个子块位置进行某种置换（交换 X₂与 X₃）或重组，为下一轮输入。
  3. 经过 8 次上述全轮后，再执行一个“半轮”输出变换（使用 4 个子密钥，对四个16 位子块作最后的模运算和异或）。
  4. 最终将四个 16 位子块合并为 64 位密文。

解密流程

  • 解密流程与加密流程结构相同，但子密钥使用顺序为反向（而且在乘法／加法运算中使用相应的逆元素或逆运算）。 (国际期刊研究与评论)

特点 & 安全性

  • IDEA 通过“混合”三类不同代数运算（加、乘、XOR）增强了抗差分／线性分析的能力。 (维基百科)
  • 虽然 密钥空间达到 2¹²⁸ ，但随着时间推进，它在效率和标准化方面逐渐被新算法（如 AES）取代。 (NordVPN)

std

示例输入：

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/*
jielycatjielycat
Hello! IDEA!
*/

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#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
using u64 = uint64_t;
using u32 = uint32_t;
using u8 = uint8_t;
using u16 = uint16_t;

constexpr ll ADD_MOD = 65536LL;
constexpr ll MUL_MOD = 65537LL;

u16 key[60];
u16 key2[60];
string my_key_bin_str;

static inline u16 add(u16 a, u16 b) { return a + b; }

u16 mul(u16 a, u16 b)
{
    u64 a1 = (a == 0) ? ADD_MOD : a;
    u64 b1 = (b == 0) ? ADD_MOD : b;
    u64 res = (a1 * b1) % MUL_MOD;
    return (res == ADD_MOD) ? 0 : static_cast<u16>(res);
}

static inline u16 yihuo(u16 a, u16 b) { return a ^ b; }

u16 bin_str_to_u16(string_view s)
{
    u16 res = 0;
    for (int i = 0; i < 16; ++i)
        res = (res << 1) | (s[i] - '0');
    return res;
}

// 128比特循环左移25位
string roll_left(string t)
{
    string s(128, '0');
    for (int i = 0; i < 128; i++)
        s[i] = t[(i + 25) % 128];
    return s;
}

// 生成52个子密钥
void extend(string t)
{
    int k_idx = 1;
    for (int i = 0; i < 6; i++)
    {
        key[k_idx++] = bin_str_to_u16(string_view(t.c_str() + 0, 16));
        key[k_idx++] = bin_str_to_u16(string_view(t.c_str() + 16, 16));
        key[k_idx++] = bin_str_to_u16(string_view(t.c_str() + 32, 16));
        key[k_idx++] = bin_str_to_u16(string_view(t.c_str() + 48, 16));
        key[k_idx++] = bin_str_to_u16(string_view(t.c_str() + 64, 16));
        key[k_idx++] = bin_str_to_u16(string_view(t.c_str() + 80, 16));
        key[k_idx++] = bin_str_to_u16(string_view(t.c_str() + 96, 16));
        key[k_idx++] = bin_str_to_u16(string_view(t.c_str() + 112, 16));
    }
    key[k_idx++] = bin_str_to_u16(string_view(t.c_str() + 0, 16));
    key[k_idx++] = bin_str_to_u16(string_view(t.c_str() + 16, 16));
    key[k_idx++] = bin_str_to_u16(string_view(t.c_str() + 32, 16));
    key[k_idx++] = bin_str_to_u16(string_view(t.c_str() + 48, 16));
}

void exgcd(ll a, ll b, ll &d, ll &x, ll &y)
{
    if (!b)
    {
        d = a;
        x = 1;
        y = 0;
    }
    else
    {
        exgcd(b, a % b, d, y, x);
        y -= x * (a / b);
    }
}

u16 inv(u16 a_u16, ll p)
{
    ll a = (a_u16 == 0) ? ADD_MOD : a_u16;
    ll d, x, y;
    exgcd(a, p, d, x, y);
    ll res = (d == 1) ? (x % p + p) % p : -1;
    return (res == ADD_MOD) ? 0 : static_cast<u16>(res);
}

u16 add_ni(u16 a, ll p)
{
    ll b = -static_cast<ll>(a);
    b = (b % p + p) % p;
    return static_cast<u16>(b);
}

// 生成解密子密钥
void dkey()
{
    for (int i = 1; i <= 9; i++)
    {
        for (int j = 1; j <= 4; j++)
        {
            int t = 6 * (10 - i - 1) + j;
            if (j == 1 || j == 4)
                key2[(i - 1) * 6 + j] = inv(key[t], MUL_MOD);
            else
            {
                if (i == 1 || i == 9)
                    key2[(i - 1) * 6 + j] = add_ni(key[t], ADD_MOD);
                else
                {
                    if (j == 2)
                        key2[(i - 1) * 6 + j] = add_ni(key[t + 1], ADD_MOD);
                    else
                        key2[(i - 1) * 6 + j] = add_ni(key[t - 1], ADD_MOD);
                }
            }
        }
    }
    for (int i = 1; i <= 8; i++)
    {
        key2[(i - 1) * 6 + 5] = key[(9 - i - 1) * 6 + 5];
        key2[(i - 1) * 6 + 6] = key[(9 - i - 1) * 6 + 6];
    }
}

// 加密块
void IDEA_encrypt_block(u16 x[4])
{
    for (int i = 1; i <= 8; i++)
    {
        int k_idx = (i - 1) * 6 + 1;
        u16 z1 = key[k_idx++], z2 = key[k_idx++], z3 = key[k_idx++],
            z4 = key[k_idx++], z5 = key[k_idx++], z6 = key[k_idx++];

        u16 t1 = mul(x[0], z1);
        u16 t2 = add(x[1], z2);
        u16 t3 = add(x[2], z3);
        u16 t4 = mul(x[3], z4);
        u16 t5 = yihuo(t1, t3);
        u16 t6 = yihuo(t2, t4);
        u16 t7 = mul(t5, z5);
        u16 t8 = add(t6, t7);
        u16 t9 = mul(t8, z6);
        u16 t10 = add(t7, t9);

        u16 w1 = yihuo(t1, t9);
        u16 w2 = yihuo(t3, t9);
        u16 w3 = yihuo(t2, t10);
        u16 w4 = yihuo(t4, t10);

        x[0] = w1;
        x[1] = w2;
        x[2] = w3;
        x[3] = w4;
    }

    u16 y1 = mul(x[0], key[49]);
    u16 y2 = add(x[2], key[50]);
    u16 y3 = add(x[1], key[51]);
    u16 y4 = mul(x[3], key[52]);
    x[0] = y1;
    x[1] = y2;
    x[2] = y3;
    x[3] = y4;
}

// 解密块
void IDEA_decrypt_block(u16 x[4])
{
    for (int i = 1; i <= 8; i++)
    {
        int k_idx = (i - 1) * 6 + 1;
        u16 z1 = key2[k_idx++], z2 = key2[k_idx++], z3 = key2[k_idx++],
            z4 = key2[k_idx++], z5 = key2[k_idx++], z6 = key2[k_idx++];

        u16 t1 = mul(x[0], z1);
        u16 t2 = add(x[1], z2);
        u16 t3 = add(x[2], z3);
        u16 t4 = mul(x[3], z4);
        u16 t5 = yihuo(t1, t3);
        u16 t6 = yihuo(t2, t4);
        u16 t7 = mul(t5, z5);
        u16 t8 = add(t6, t7);
        u16 t9 = mul(t8, z6);
        u16 t10 = add(t7, t9);

        u16 w1 = yihuo(t1, t9);
        u16 w2 = yihuo(t3, t9);
        u16 w3 = yihuo(t2, t10);
        u16 w4 = yihuo(t4, t10);

        x[0] = w1;
        x[1] = w2;
        x[2] = w3;
        x[3] = w4;
    }

    u16 y1 = mul(x[0], key2[49]);
    u16 y2 = add(x[2], key2[50]);
    u16 y3 = add(x[1], key2[51]);
    u16 y4 = mul(x[3], key2[52]);
    x[0] = y1;
    x[1] = y2;
    x[2] = y3;
    x[3] = y4;
}

// 字节转二进制字符串
string B2b(vector<char> &block)
{
    string out;
    out.reserve(128);
    for (int i = 0; i < 16; ++i)
    {
        u8 u = static_cast<u8>(block[i]);
        for (int b = 7; b >= 0; --b)
            out.push_back(((u >> b) & 1) ? '1' : '0');
    }
    return out;
}

// 读取16字节密钥
vector<char> get_key()
{
    string key;
    getline(cin, key);
    while (key.size() < 16)
        key += "0";
    if (key.size() > 16)
        key.resize(16);
    return vector<char>(key.begin(), key.end());
}

static inline bool is_space_le(char c) { return static_cast<unsigned char>(c) <= ' '; }

// 获取明文
vector<u8> get_plain()
{
    string all((istreambuf_iterator<char>(cin)), (istreambuf_iterator<char>()));
    size_t i = 0;
    while (i < all.size() && is_space_le(all[i]))
        ++i;
    if (i < all.size() && all[i] == '@')
    {
        size_t j = i + 1;
        while (j < all.size() && is_space_le(all[j]))
            ++j;
        size_t k = all.size();
        while (k > j && is_space_le(all[k - 1]))
            --k;
        string path = all.substr(j, k - j);
        FILE *fp = fopen(path.c_str(), "rb");
        if (!fp)
            return {};
        fseek(fp, 0, SEEK_END);
        long n = ftell(fp);
        if (n < 0)
        {
            fclose(fp);
            return {};
        }
        fseek(fp, 0, SEEK_SET);
        vector<u8> buf(static_cast<size_t>(n));
        if (n > 0)
            fread(buf.data(), 1, static_cast<size_t>(n), fp);
        fclose(fp);
        return buf;
    }
    return vector<u8>(all.begin(), all.end());
}

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    vector<char> key0 = get_key();
    my_key_bin_str = B2b(key0);
    extend(my_key_bin_str);
    dkey();

    vector<u8> plain = get_plain();
    size_t original_len = plain.size();
    size_t padding = (8 - (original_len % 8)) % 8;
    for (size_t i = 0; i < padding; ++i)
        plain.push_back(padding);

    size_t num_blocks = plain.size() / 8;
    vector<u8> encrypted_bytes(plain.size());
    vector<u8> decrypted_bytes(plain.size());
    u16 x[4];

    // 加密
    for (size_t i = 0; i < num_blocks; ++i)
    {
        u8 *p_in = plain.data() + i * 8;
        x[0] = (p_in[0] << 8) | p_in[1];
        x[1] = (p_in[2] << 8) | p_in[3];
        x[2] = (p_in[4] << 8) | p_in[5];
        x[3] = (p_in[6] << 8) | p_in[7];
        IDEA_encrypt_block(x);
        u8 *p_out = encrypted_bytes.data() + i * 8;
        p_out[0] = (x[0] >> 8);
        p_out[1] = (x[0] & 0xFF);
        p_out[2] = (x[1] >> 8);
        p_out[3] = (x[1] & 0xFF);
        p_out[4] = (x[2] >> 8);
        p_out[5] = (x[2] & 0xFF);
        p_out[6] = (x[3] >> 8);
        p_out[7] = (x[3] & 0xFF);
    }

    // 解密
    for (size_t i = 0; i < num_blocks; ++i)
    {
        u8 *p_in = encrypted_bytes.data() + i * 8;
        x[0] = (p_in[0] << 8) | p_in[1];
        x[1] = (p_in[2] << 8) | p_in[3];
        x[2] = (p_in[4] << 8) | p_in[5];
        x[3] = (p_in[6] << 8) | p_in[7];
        IDEA_decrypt_block(x);
        u8 *p_out = decrypted_bytes.data() + i * 8;
        p_out[0] = (x[0] >> 8);
        p_out[1] = (x[0] & 0xFF);
        p_out[2] = (x[1] >> 8);
        p_out[3] = (x[1] & 0xFF);
        p_out[4] = (x[2] >> 8);
        p_out[5] = (x[2] & 0xFF);
        p_out[6] = (x[3] >> 8);
        p_out[7] = (x[3] & 0xFF);
    }

    // cout << "明文：" << string(plain.begin(), plain.begin() + original_len) << endl;
    // cout << "密文 (hex)：";
    // cout << hex << setfill('0');
    // for (size_t i = 0; i < encrypted_bytes.size(); ++i)
        // cout << setw(2) << static_cast<int>(encrypted_bytes[i]);
    // cout << dec << endl;
    // string mingwen1(decrypted_bytes.begin(), decrypted_bytes.begin() + original_len);
    // cout << "解密后的明文：" << mingwen1 << endl;
    return 0;
}

参考资料

DES_CSDN.

IDEA_CSDN.

IDEA_GitHub.