用C语言求rsa加密过程代码

RSA（Rivest-Shamir-Adleman）是一种非对称加密算法，用于保护数据的安全传输。在C语言中实现RSA加密需要涉及到大数运算、模幂运算等复杂操作，这里提供一个简化的示例，展示了如何生成密钥对、加密和解密的基本流程。请注意，这只是一个基础版本，实际应用中你需要处理更复杂的错误检查和边界情况。

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

// RSA参数设置
#define RSA_MODULUS_BITS 4096
#define MAX_NUM_DIGITS 10

typedef struct {
    unsigned long int e;
    unsigned long int n; // 公钥 (p * q)
} RSAKey;

// 大数乘法
unsigned long int mulmod(unsigned long int a, unsigned long int b, unsigned long int m) {
    unsigned long int result = 0;
    while (b > 0) {
        if (b % 2 == 1) {
            result = (result + a) % m;
        }
        a = (a * 2) % m;
        b /= 2;
    }
    return result;
}

// 加密函数
void rsa_encrypt(RSAKey* key, char* plaintext, char* ciphertext) {
    int len = strlen(plaintext);
    for (int i = 0; i < len; ++i) {
        ciphertext[i] = (plaintext[i] + key->e) % key->n;
    }
}

// 示例RSA密钥生成
RSAKey generate_rsa_key() {
    RSAKey key;
    unsigned long int p, q, phi_n, e, d;

    // Generate two large prime numbers
    do {
        p = rand() % ((1ull << RSA_MODULUS_BITS) - 2) + 2;
        q = rand() % ((1ull << RSA_MODULUS_BITS) - 2) + 2;
    } while (gcd(p, q) != 1);

    phi_n = (p - 1) * (q - 1); // Totient of n
    do {
        e = rand() % phi_n + 1;
    } while (gcd(e, phi_n) != 1);

    // Compute the modular multiplicative inverse of e (d)
    d = modinv(e, phi_n);

    key.e = e;
    key.n = p * q;

    return key;
}

// 密钥对显示
void show_keys(const RSAKey* pub_key, const RSAKey* priv_key) {
    printf("Public Key (e = %lu, n = %lu):\n", pub_key->e, pub_key->n);
    printf("Private Key (d = %lu)\n", priv_key->d);
}

// 主函数
int main() {
    RSAKey pub_key, priv_key;
    char input[50];
    char encrypted[50];

    // Generate keys
    pub_key = generate_rsa_key();
    priv_key = generate_rsa_key();

    printf("Enter text to encrypt:\n");
    fgets(input, sizeof(input), stdin);
    input[strcspn(input, "\n")] = '\0';

    // Encrypt and display
    rsa_encrypt(&pub_key, input, encrypted);
    printf("Encrypted Text: ");
    for (const char c : encrypted) {
        printf("%c", c);
    }

    return 0;
}

// 辅助函数：计算最大公约数和模逆
unsigned long int gcd(unsigned long int a, unsigned long int b) {
    if (b == 0) return a;
    return gcd(b, a % b);
}

unsigned long int modinv(unsigned long int a, unsigned long int m) {
    // Extended Euclidean algorithm
    int x0 = 0, x1 = 1, y0 = 1, y1 = 0, r0 = m, r1 = a;
    while (r1 != 0) {
        int q = r0 / r1;
        int temp = r0;
        r0 = r1;
        r1 = temp % r1;
        temp = x0;
        x0 = x1 - q * x0;
        x1 = temp;
        temp = y0;
        y0 = y1 - q * y0;
        y1 = temp;
    }
    if (r0 < 0) r0 += m;
    return y0;
}

注意，这个例子仅用于教学目的，实际生产环境中应使用专门的库（如openssl），因为上述代码可能无法处理所有边缘情况，并且效率较低。同时，密钥的生成和安全性也比这个简单示例复杂得多。