RSA数字签名C++代码

以下是一个简单的RSA数字签名C++代码示例：

#include <iostream>
#include <cmath>
#include <cstring>
#include <cstdio>

using namespace std;

const int MAXN = 10000;

int p, q, n, f, d, e;
int prime[MAXN], vis[MAXN], cnt = 0;

void create_prime() {
    memset(vis, 0, sizeof(vis));
    for (int i = 2; i < MAXN; i++) {
        if (!vis[i]) prime[++cnt] = i;
        for (int j = 1; j <= cnt && i * prime[j] < MAXN; j++) {
            vis[i * prime[j]] = 1;
            if (i % prime[j] == 0) break;
        }
    }
}

int gcd(int a, int b) {
    return b == 0 ? a : gcd(b, a % b);
}

int exgcd(int a, int b, int &x, int &y) {
    if (b == 0) {
        x = 1, y = 0;
        return a;
    }
    int gcd = exgcd(b, a % b, y, x);
    y -= a / b * x;
    return gcd;
}

int quick_pow(int a, int b, int mod) {
    int res = 1;
    while (b) {
        if (b & 1) res = (long long) res * a % mod;
        a = (long long) a * a % mod;
        b >>= 1;
    }
    return res;
}

void generate_key() {
    create_prime();
    srand(time(NULL));
    p = prime[rand() % cnt + 1];
    q = prime[rand() % cnt + 1];
    n = p * q;
    f = (p - 1) * (q - 1);
    do {
        e = rand() % f + 1;
    } while (gcd(e, f) != 1);
    exgcd(e, f, d, d);
    d = (d % f + f) % f;
}

int rsa_encrypt(int plain_text, int e, int n) {
    return quick_pow(plain_text, e, n);
}

int rsa_decrypt(int cipher_text, int d, int n) {
    return quick_pow(cipher_text, d, n);
}

int main() {
    generate_key();
    int plain_text = 123456;
    int cipher_text = rsa_encrypt(plain_text, e, n);
    int decrypted_text = rsa_decrypt(cipher_text, d, n);
    cout << "Plain Text: " << plain_text << endl;
    cout << "Cipher Text: " << cipher_text << endl;
    cout << "Decrypted Text: " << decrypted_text << endl;
    return 0;
}

这段代码使用了RSA算法进行数字签名，先通过生成私钥和公钥，然后使用私钥加密明文，再使用公钥解密密文，得到原始的明文。需要注意，为了保证安全性，实际应用中需要使用更复杂的加密算法，并使用更长的密钥长度。