3DES 概述
3DES（Triple Data Encryption Standard）是DES算法的加强版本，通过三次DES加密提升安全性。由于DES的56位密钥易受暴力破解，3DES采用两或三个不同的密钥进行多次加密，有效增加密钥长度至112或168位，兼顾兼容性和安全性。
加密模式
3DES支持多种加密模式，常见以下两种：
EDE模式（Encrypt-Decrypt-Encrypt）
使用三个不同密钥（K1、K2、K3），流程如下：
- 用K1加密明文
- 用K2解密上一步结果
- 用K3加密上一步结果
若K1=K3，则为双密钥模式（密钥长度112位）。
EEE模式（Encrypt-Encrypt-Encrypt）
三次均使用加密操作，需三个独立密钥（密钥长度168位）。
安全性分析
- 优点：兼容现有DES系统，密钥空间扩大抗暴力破解。
- 缺点：计算效率低于AES，64位分组易受重放攻击。NIST已建议逐步替换为AES。
应用场景
3DES常见于金融支付（如EMV芯片卡）、旧系统升级等对兼容性要求高的领域。
DES3.h
#ifndef _DES3_H_
#define _DES3_H_
#include <stdint.h>
/* 工作模式实现 */
typedef enum { ECB, CBC, CFB, OFB } DES3CipherMode;
void des3_crypt(uint8_t* data, size_t* len,
const uint8_t* key, // 24字节密钥
const uint8_t* iv, // 8字节IV (CBC/CFB/OFB需要)
int encrypt, // 0=解密, 1=加密
DES3CipherMode mode, // 工作模式
int padding); // 0=无填充, 1=PKCS7
#endif
DES3.cpp
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>
#include "DES3.h"
/* 类型定义 */
typedef uint64_t des_block;
/* DES 核心算法实现 */
// 初始置换表 (IP)
static const int 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
};
// 逆初始置换表 (IP^-1)
static const int FP[] = {
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
};
// 扩展置换表 (E)
static const int 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
};
// S-Boxes (6位输入 -> 4位输出)
static const uint8_t SBOX[8][64] = {
{ // 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
}
};
// 轮函数P置换
static const int 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
};
// 密钥置换表 (PC1)
static const int PC1[] = {
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
};
// 密钥压缩置换表 (PC2)
static const int PC2[] = {
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
};
// 轮数移位表
static const int SHIFTS[] = {1, 1, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2, 1};
// 通用置换函数
static uint64_t permute(const uint8_t *input, const int *table, int size, int input_size) {
uint64_t result = 0;
for (int i = 0; i < size; i++) {
int pos = table[i] - 1;
int byte_idx = pos / 8;
int bit_idx = 7 - (pos % 8);
uint8_t bit = (input[byte_idx] >> bit_idx) & 1;
result = (result << 1) | bit;
}
return result;
}
// 生成轮密钥
static void generate_subkeys(uint64_t key, uint64_t *subkeys) {
uint8_t key_bytes[8] = { 0 };
for (int i = 0; i < 8; i++) {
key_bytes[7-i] = (key >> (i * 8)) & 0xFF;
}
// PC1置换
uint64_t permuted = permute(key_bytes, PC1, 56, 64);
uint32_t left = (permuted >> 28) & 0xFFFFFFF;
uint32_t right = permuted & 0xFFFFFFF;
for (int round = 0; round < 16; round++) {
// 循环左移
left = ((left << SHIFTS[round]) | (left >> (28 - SHIFTS[round]))) & 0xFFFFFFF;
right = ((right << SHIFTS[round]) | (right >> (28 - SHIFTS[round]))) & 0xFFFFFFF;
// 合并左右部分
uint64_t combined = ((uint64_t)left << 28) | right;
// PC2置换生成子密钥
uint8_t combined_bytes[7] = { 0 };
for (int i = 0; i < 7; i++) {
combined_bytes[i] = (combined >> (42 - i*6)) & 0x3F;
}
subkeys[round] = permute(combined_bytes, PC2, 48, 56);
}
}
// Feistel轮函数
static uint32_t feistel(uint32_t right, uint64_t subkey) {
// 扩展置换 (32位 -> 48位)
uint8_t right_bytes[4] = { 0 };
for (int i = 0; i < 4; i++) {
right_bytes[3-i] = (right >> (i * 8)) & 0xFF;
}
uint64_t expanded = permute(right_bytes, E, 48, 32);
// 与子密钥异或
uint64_t xored = expanded ^ subkey;
// S-Box代换 (48位 -> 32位)
uint32_t substituted = 0;
for (int i = 0; i < 8; i++) {
// 提取6位输入
uint8_t sbox_input = (xored >> (42 - i*6)) & 0x3F;
// 计算S-Box行列索引
uint8_t row = ((sbox_input & 0x20) >> 4) | (sbox_input & 1);
uint8_t col = (sbox_input >> 1) & 0x0F;
// 获取S-Box输出
uint8_t sbox_output = SBOX[i][row * 16 + col];
substituted = (substituted << 4) | sbox_output;
}
// P置换
uint8_t sub_bytes[4] = { 0 };
for (int i = 0; i < 4; i++) {
sub_bytes[3-i] = (substituted >> (i * 8)) & 0xFF;
}
return (uint32_t)permute(sub_bytes, P, 32, 32);
}
// 核心DES加密/解密函数
static void des_core(uint64_t *data, uint64_t key, int encrypt) {
uint64_t subkeys[16];
generate_subkeys(key, subkeys);
// 初始置换
uint8_t data_bytes[8] = { 0 };
for (int i = 0; i < 8; i++) {
data_bytes[7-i] = (*data >> (i * 8)) & 0xFF;
}
uint64_t permuted = permute(data_bytes, IP, 64, 64);
uint32_t left = (permuted >> 32) & 0xFFFFFFFF;
uint32_t right = permuted & 0xFFFFFFFF;
// 16轮Feistel网络
for (int round = 0; round < 16; round++) {
uint32_t next_left = right;
uint64_t round_key = encrypt ? subkeys[round] : subkeys[15 - round];
uint32_t feistel_out = feistel(right, round_key);
right = left ^ feistel_out;
left = next_left;
}
// 最终置换 (左右交换)
uint64_t combined = ((uint64_t)right << 32) | left;
uint8_t combined_bytes[8] = { 0 };
for (int i = 0; i < 8; i++) {
combined_bytes[7-i] = (combined >> (i * 8)) & 0xFF;
}
*data = permute(combined_bytes, FP, 64, 64);
}
/* 3DES 实现 (EDE模式) */
static void des3_encrypt_block(uint64_t *block, uint64_t k1, uint64_t k2, uint64_t k3) {
des_core(block, k1, 1); // Encrypt with K1
des_core(block, k2, 0); // Decrypt with K2
des_core(block, k3, 1); // Encrypt with K3
}
static void des3_decrypt_block(uint64_t *block, uint64_t k1, uint64_t k2, uint64_t k3) {
des_core(block, k3, 0); // Decrypt with K3
des_core(block, k2, 1); // Encrypt with K2
des_core(block, k1, 0); // Decrypt with K1
}
// PKCS#7填充
static size_t pkcs7_pad(uint8_t *data, size_t len, size_t block_size) {
size_t pad_len = block_size - (len % block_size);
for (size_t i = 0; i < pad_len; i++) {
data[len + i] = (uint8_t)pad_len;
}
return len + pad_len;
}
static size_t pkcs7_unpad(uint8_t *data, size_t len) {
if (len == 0) return 0;
uint8_t pad_len = data[len - 1];
if (pad_len > 0 && pad_len <= 8) {
// 验证填充是否正确
for (size_t i = 1; i <= pad_len; i++) {
if (data[len - i] != pad_len) {
return len; // 无效填充
}
}
return len - pad_len;
}
return len; // 无效填充
}
// ECB模式加密/解密
static void des3_ecb_crypt(uint8_t *data, size_t len,
uint64_t k1, uint64_t k2, uint64_t k3,
int encrypt) {
for (size_t i = 0; i < len; i += 8) {
if (encrypt) {
des3_encrypt_block((uint64_t*)(data + i), k1, k2, k3);
} else {
des3_decrypt_block((uint64_t*)(data + i), k1, k2, k3);
}
}
}
// CBC模式加密
static void des3_cbc_encrypt(uint8_t *data, size_t len,
uint64_t k1, uint64_t k2, uint64_t k3,
const uint8_t *iv) {
uint64_t prev_block = *(uint64_t*)iv;
for (size_t i = 0; i < len; i += 8) {
uint64_t block = *(uint64_t*)(data + i);
block ^= prev_block;
des3_encrypt_block(&block, k1, k2, k3);
*(uint64_t*)(data + i) = block;
prev_block = block;
}
}
// CBC模式解密
static void des3_cbc_decrypt(uint8_t *data, size_t len,
uint64_t k1, uint64_t k2, uint64_t k3,
const uint8_t *iv) {
uint64_t prev_block = *(uint64_t*)iv;
for (size_t i = 0; i < len; i += 8) {
uint64_t block = *(uint64_t*)(data + i);
uint64_t save_block = block;
des3_decrypt_block(&block, k1, k2, k3);
block ^= prev_block;
*(uint64_t*)(data + i) = block;
prev_block = save_block;
}
}
// CFB模式加密
static void des3_cfb_encrypt(uint8_t *data, size_t len,
uint64_t k1, uint64_t k2, uint64_t k3,
const uint8_t *iv) {
uint64_t shift_register = *(uint64_t*)iv;
for (size_t i = 0; i < len; i++) {
// 加密移位寄存器
uint64_t encrypted = shift_register;
des3_encrypt_block(&encrypted, k1, k2, k3);
// 加密1字节数据
data[i] ^= (uint8_t)(encrypted >> 56);
// 更新移位寄存器
shift_register = (shift_register << 8) | data[i];
}
}
// CFB模式解密
static void des3_cfb_decrypt(uint8_t *data, size_t len,
uint64_t k1, uint64_t k2, uint64_t k3,
const uint8_t *iv) {
uint64_t shift_register = *(uint64_t*)iv;
for (size_t i = 0; i < len; i++) {
// 加密移位寄存器
uint64_t encrypted = shift_register;
des3_encrypt_block(&encrypted, k1, k2, k3);
// 保存当前密文字节用于更新寄存器
uint8_t cipher_byte = data[i];
// 解密1字节数据
data[i] ^= (uint8_t)(encrypted >> 56);
// 更新移位寄存器
shift_register = (shift_register << 8) | cipher_byte;
}
}
// OFB模式加密/解密
static void des3_ofb_crypt(uint8_t *data, size_t len,
uint64_t k1, uint64_t k2, uint64_t k3,
const uint8_t *iv) {
uint64_t shift_register = *(uint64_t*)iv;
for (size_t i = 0; i < len; i++) {
// 加密移位寄存器
des3_encrypt_block(&shift_register, k1, k2, k3);
// 加密/解密1字节数据
data[i] ^= (uint8_t)(shift_register >> 56);
// 更新移位寄存器
shift_register = (shift_register << 8) | (data[i] & 0xFF);
}
}
/* 完整3DES接口 */
void des3_crypt(uint8_t *data, size_t *len,
const uint8_t *key, // 24字节密钥
const uint8_t *iv, // 8字节IV (CBC/CFB/OFB需要)
int encrypt, // 0=解密, 1=加密
DES3CipherMode mode, // 工作模式
int padding) { // 0=无填充, 1=PKCS7
uint64_t k1 = *(uint64_t*)key;
uint64_t k2 = *(uint64_t*)(key + 8);
uint64_t k3 = *(uint64_t*)(key + 16);
// 处理填充
if (encrypt && padding) {
*len = pkcs7_pad(data, *len, 8);
}
// 分块处理
switch (mode) {
case ECB:
des3_ecb_crypt(data, *len, k1, k2, k3, encrypt);
break;
case CBC:
if (encrypt) {
des3_cbc_encrypt(data, *len, k1, k2, k3, iv);
} else {
des3_cbc_decrypt(data, *len, k1, k2, k3, iv);
}
break;
case CFB:
if (encrypt) {
des3_cfb_encrypt(data, *len, k1, k2, k3, iv);
} else {
des3_cfb_decrypt(data, *len, k1, k2, k3, iv);
}
break;
case OFB:
des3_ofb_crypt(data, *len, k1, k2, k3, iv);
break;
default:
fprintf(stderr, "Unsupported cipher mode\n");
break;
}
// 去除填充
if (!encrypt && padding) {
*len = pkcs7_unpad(data, *len);
}
}