RC4运行过程
步骤
RC4为一种流密码加密机制，遵循一次一密。
- 初始化$S$向量
- 根据输入的密钥初始化$T$向量
- 用$T$向量打乱$S$向量，得到向量$S’$
- 传入待加密的文本
TEXT，按照字节，分别与$S`$表中的某一值进行异或。可以得到加密后的文本以及与待加密文本异或的字节串 - 若要解密，则将加密后的文本与字节串进行异或即可
RC4用C++实现：
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#include <iostream>
class RC4 {
public:
static const int s_size = 256;
RC4(std::string &key) {
inputKey = key;
init();
}
/// 加密text，引用text直接被加密，返回的std::string为密钥流
std::string encryption(std::string &text);
/// 解密text，引用encrypted_text直接被解密，返回的为状态码
int decryption(std::string &encrypted_text, std::string &key);
private:
void init();
void _init_t(); //初始化
void _init_s();
int swap(int l_index, int r_index); // 交换s盒
void transform();
std::string inputKey;
char s[s_size]{}; //S盒子
const char *t{}; //临时向量T
char k; //当前生成的k
};
void RC4::_init_s() {
for (int i = 0; i < RC4::s_size; ++i) {
s[i] = char(i);
}
}
void RC4::_init_t() {
auto length = inputKey.length();
if (length == s_size) {
//则将K赋给T
t = inputKey.c_str();
} else if (length > s_size) {
inputKey = inputKey.substr(0, s_size);
t = inputKey.c_str();
} else {
auto tmp = (char *) malloc(sizeof(char) * s_size);
for (int i = 0; i < s_size; ++i) {
tmp[i] = inputKey[i % s_size];
}
t = tmp;
}
}
void RC4::init() {
_init_s();
_init_t();
transform();
}
/// 使用T向量打乱S向量
void RC4::transform() {
int j = 0;
for (int i = 0; i < s_size; ++i) {
j = (j + s[i] + t[i]) % s_size;
swap(i, j);
}
}
int RC4::swap(int l, int r) {
if (l >= 0 && r >= 0 && l < s_size && r < s_size && l != r) {
char tmp = s[l];
s[l] = s[r];
s[r] = tmp;
}
return 0;
}
/// 生成密钥流，text直接被加密，return密钥流
std::string RC4::encryption(std::string &text) {
std::string key;
auto length = text.length();
int i = 0, j = 0, index = 0;
int en_index = 0;
while (--length) {
i = (i + 1) % s_size;
j = (j + s[i]) % s_size;
swap(i, j);
index = (s[i] + s[j]) % s_size;
k = s[index];
text[en_index] ^= k;
key += k;
en_index += 1;
}
return key;
}
int RC4::decryption(std::string &encrypted_text, std::string &key) {
auto length = encrypted_text.length();
int en_index = 0;
while (--length) {
encrypted_text[en_index] ^= key[en_index];
en_index += 1;
}
return 0;
}
int main(int argc, char *argv[]) {
std::string inputKey = "n92tU+3m52wcyRBjvpJygCM9G53nETMzaSMALMyzxFo=";
RC4 rc4(inputKey);
std::string text = "hello";
std::cout << "origin: " << text << std::endl;
std::string key = rc4.encryption(text);
std::cout << "encrypted: " << text << std::endl;
rc4.decryption(text, key);
std::cout << "decrypted: " << text << std::endl;
return 0;
}
执行结果
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origin: hello
encrypted: �e?lo
decrypted: hello
