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，并完成相关的解密

以下是一个简单的C语言源代码，用于RSA加密和解密消息。它支持任意长度的消息，通过将消息分割成块来进行加密和解密。

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

#define MAX_MESSAGE_SIZE 1000 // 最大消息长度
#define MAX_BLOCK_SIZE 128 // 最大块大小
#define PRIME_BIT_SIZE 512 // 素数位数
#define MAX_ITERATIONS 1000 // 最大迭代次数

typedef unsigned long long int ull;

// 模幂运算
ull modPow(ull base, ull exp, ull modulus) {
    base %= modulus;
    ull result = 1;
    while (exp > 0) {
        if (exp & 1) {
            result = (result * base) % modulus;
        }
        base = (base * base) % modulus;
        exp >>= 1;
    }
    return result;
}

// 测试一个数是否为素数
int isPrime(ull number) {
    if (number <= 1) {
        return 0;
    }
    if (number <= 3) {
        return 1;
    }
    if ((number % 2) == 0 || (number % 3) == 0) {
        return 0;
    }
    ull i = 5;
    while ((i * i) <= number) {
        if ((number % i) == 0 || (number % (i + 2)) == 0) {
            return 0;
        }
        i += 6;
    }
    return 1;
}

// 生成一个大的素数
ull generatePrime() {
    ull random;
    do {
        random = rand();
        random = (random << 32) | rand();
        random = (random << 32) | rand();
        random = (random << 32) | rand();
        random %= (1ULL << PRIME_BIT_SIZE);
    } while (!isPrime(random));
    return random;
}

// 生成公钥和私钥
void generateKeys(ull *publicKey, ull *privateKey) {
    ull p, q, n, phi, e, d;
    do {
        p = generatePrime();
        q = generatePrime();
        n = p * q;
        phi = (p - 1) * (q - 1);
        e = rand() % (phi - 2) + 2;
        d = modPow(e, phi - 2, phi);
    } while (d == 0);
    *publicKey = e;
    *privateKey = d;
}

// 加密一个块
ull encryptBlock(ull block, ull publicKey, ull modulus) {
    return modPow(block, publicKey, modulus);
}

// 解密一个块
ull decryptBlock(ull block, ull privateKey, ull modulus) {
    return modPow(block, privateKey, modulus);
}

// 加密消息
void encryptMessage(char *message, int messageLength, ull publicKey, ull modulus, ull *ciphertext) {
    int i, j, blockIndex = 0;
    ull block = 0;
    for (i = 0; i < messageLength; i++) {
        block |= ((ull) message[i]) << (8 * (i % MAX_BLOCK_SIZE));
        if ((i % MAX_BLOCK_SIZE) == (MAX_BLOCK_SIZE - 1)) {
            ciphertext[blockIndex++] = encryptBlock(block, publicKey, modulus);
            block = 0;
        }
    }
    if ((messageLength % MAX_BLOCK_SIZE) != 0) {
        ciphertext[blockIndex++] = encryptBlock(block, publicKey, modulus);
    }
}

// 解密消息
void decryptMessage(ull *ciphertext, int ciphertextLength, ull privateKey, ull modulus, char *message) {
    int i, j, blockIndex = 0;
    ull block;
    for (i = 0; i < ciphertextLength; i++) {
        block = decryptBlock(ciphertext[i], privateKey, modulus);
        for (j = 0; j < MAX_BLOCK_SIZE; j++) {
            message[blockIndex++] = (char)((block >> (8 * j)) & 0xFF);
            if (blockIndex >= MAX_MESSAGE_SIZE) {
                return;
            }
        }
    }
}

int main() {
    char message[MAX_MESSAGE_SIZE];
    ull publicKey, privateKey, modulus, ciphertext[MAX_MESSAGE_SIZE / MAX_BLOCK_SIZE];
    int messageLength, ciphertextLength, i;
    srand(time(NULL));
    printf("请输入消息：\n");
    fgets(message, MAX_MESSAGE_SIZE, stdin);
    messageLength = strlen(message) - 1;
    if (messageLength <= 0) {
        printf("消息不能为空。\n");
        return 0;
    }
    generateKeys(&publicKey, &privateKey);
    modulus = generatePrime() * generatePrime();
    encryptMessage(message, messageLength, publicKey, modulus, ciphertext);
    ciphertextLength = (messageLength + MAX_BLOCK_SIZE - 1) / MAX_BLOCK_SIZE;
    printf("加密后的消息：\n");
    for (i = 0; i < ciphertextLength; i++) {
        printf("%llu ", ciphertext[i]);
    }
    printf("\n");
    decryptMessage(ciphertext, ciphertextLength, privateKey, modulus, message);
    printf("解密后的消息：\n");
    printf("%s\n", message);
    return 0;
}

以上代码通过使用RSA算法对消息进行加密和解密，支持任意长度的消息。使用时，用户需要输入要加密的消息，程序将自动生成公钥和私钥，并将生成的密文输出到屏幕上。用户也可以使用密文进行解密，程序将输出解密后的消息。