C语言源代码RSA对任意长度的消息进行消息的分割及加密，并完成相应的解密

以下是使用C语言实现RSA加密和解密的示例代码，其中包括了对任意长度的消息进行消息的分割及加密和解密的实现。需要注意的是，RSA加密的安全性与密钥长度有关，建议使用1024位或以上的密钥长度。

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

#define MAX_LENGTH 1000 // 最大消息长度

unsigned long long gcd(unsigned long long a, unsigned long long b) {
    if (b == 0) {
        return a;
    }
    return gcd(b, a % b);
}

unsigned long long mod_pow(unsigned long long base, unsigned long long exponent, unsigned long long modulus) {
    unsigned long long result = 1;
    while (exponent > 0) {
        if (exponent % 2 == 1) {
            result = (result * base) % modulus;
        }
        base = (base * base) % modulus;
        exponent = exponent / 2;
    }
    return result;
}

int is_prime(unsigned long long n) {
    if (n <= 1 || n % 2 == 0) {
        return 0;
    }
    for (unsigned long long i = 3; i <= sqrt(n); i += 2) {
        if (n % i == 0) {
            return 0;
        }
    }
    return 1;
}

unsigned long long generate_prime() {
    unsigned long long p;
    do {
        p = rand() % (1 << 10) + (1 << 9);
    } while (!is_prime(p));
    return p;
}

unsigned long long generate_public_key(unsigned long long phi_n) {
    unsigned long long e = 65537; // 一般采用65537作为公钥指数
    while (gcd(e, phi_n) != 1) {
        e++;
    }
    return e;
}

unsigned long long generate_private_key(unsigned long long e, unsigned long long phi_n) {
    unsigned long long d = 0;
    unsigned long long k = 1;
    while (1) {
        d = (k * phi_n + 1) / e;
        if (d * e == k * phi_n + 1) {
            break;
        }
        k++;
    }
    return d;
}

void split_message(char* message, int message_length, int block_size, unsigned long long* blocks, int* block_count, unsigned long long n) {
    int i = 0;
    int j = 0;
    while (i < message_length) {
        unsigned long long block = 0;
        for (int k = 0; k < block_size && i < message_length; k++) {
            block = block * 256 + message[i];
            i++;
        }
        blocks[j] = mod_pow(block, 65537, n);
        j++;
    }
    *block_count = j;
}

void join_message(unsigned long long* blocks, int block_count, int block_size, char* message) {
    int i = 0;
    for (int j = 0; j < block_count; j++) {
        unsigned long long block = mod_pow(blocks[j], 937447, 1000000007); // 解密时采用的私钥指数和模数
        for (int k = block_size - 1; k >= 0; k--) {
            message[i] = block % 256;
            block = block / 256;
            i++;
        }
    }
}

int main() {
    srand(123456789);

    unsigned long long p = generate_prime();
    unsigned long long q = generate_prime();
    unsigned long long n = p * q;
    unsigned long long phi_n = (p - 1) * (q - 1);
    unsigned long long e = generate_public_key(phi_n);
    unsigned long long d = generate_private_key(e, phi_n);

    printf("p: %llu\n", p);
    printf("q: %llu\n", q);
    printf("n: %llu\n", n);
    printf("phi_n: %llu\n", phi_n);
    printf("e: %llu\n", e);
    printf("d: %llu\n", d);

    char message[MAX_LENGTH];
    printf("请输入要加密的消息：");
    fgets(message, MAX_LENGTH, stdin);
    int message_length = strlen(message) - 1; // 去掉换行符

    int block_size = floor(log(n) / log(256)); // 每个消息块的大小
    unsigned long long blocks[MAX_LENGTH / block_size + 1];
    int block_count;

    split_message(message, message_length, block_size, blocks, &block_count, n);

    printf("\n加密后的消息：\n");
    for (int i = 0; i < block_count; i++) {
        printf("%llu ", blocks[i]);
    }

    unsigned long long decrypted_blocks[MAX_LENGTH / block_size + 1];
    join_message(blocks, block_count, block_size, message);

    printf("\n解密后的消息：\n");
    printf("%s", message);

    return 0;
}

在上面的代码中，我们实现了以下几个功能：

- 生成随机的质数p和q，并计算n和phi_n。
- 根据phi_n生成公钥e和私钥d。
- 将消息分割成长度为block_size的块，并将每个块加密为一个整数。
- 将加密后的整数块解密，并将解密后的块拼接成原始消息。

需要注意的是，在实际应用中，我们需要采用更加严密的安全措施，如使用更长的密钥、使用随机数生成器生成随机数、使用密码学安全的哈希函数等。