C语言怎样实现数据加密

在C语言中实现数据加密，你可以使用一些现有的加密库，如OpenSSL、Crypto++等。下面是一个使用OpenSSL库进行简单数据加密和解密的例子。

首先，确保你已经安装了OpenSSL库。在Linux系统上，你可以使用以下命令安装：

sudo apt-get install libssl-dev

然后，创建一个名为encrypt.c的文件，并添加以下代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <openssl/aes.h>
#include <openssl/rand.h>

void handleErrors(void) {
    ERR_print_errors_fp(stderr);
    abort();
}

int encrypt(unsigned char *plaintext, int plaintext_len, unsigned char *key,
            unsigned char *iv, unsigned char *ciphertext) {
    AES_KEY enc_key;
    int len;
    int ciphertext_len;

    if (!(len = AES_set_encrypt_key(key, 128, &enc_key)))
        handleErrors();

    ciphertext_len = 0;
    AES_cbc_encrypt(plaintext, ciphertext, plaintext_len, &enc_key, iv, AES_ENCRYPT);
    ciphertext_len = strlen((char *)ciphertext);

    return ciphertext_len;
}

int decrypt(unsigned char *ciphertext, int ciphertext_len, unsigned char *key,
            unsigned char *iv, unsigned char *plaintext) {
    AES_KEY dec_key;
    int len;
    int plaintext_len;

    if (!(len = AES_set_decrypt_key(key, 128, &dec_key)))
        handleErrors();

    plaintext_len = 0;
    AES_cbc_encrypt(ciphertext, plaintext, ciphertext_len, &dec_key, iv, AES_DECRYPT);
    plaintext_len = strlen((char *)plaintext);

    return plaintext_len;
}

int main(int argc, char *argv[]) {
    unsigned char key[] = "abcdefghijklmnop";
    unsigned char iv[AES_BLOCK_SIZE];
    unsigned char plaintext[] = "This is a secret message";
    unsigned char ciphertext[128];
    unsigned char decryptedtext[128];
    int decryptedtext_len, ciphertext_len;

    if (argc != 3) {
        printf("Usage: %s <encrypt|decrypt> <text>\n", argv[0]);
        return 1;
    }

    if (!RAND_bytes(iv, AES_BLOCK_SIZE)) handleErrors();

    if (strcmp(argv[1], "encrypt") == 0) {
        ciphertext_len = encrypt(plaintext, strlen((char *)plaintext), key, iv, ciphertext);
        printf("Encrypted text:\n");
        for (int i = 0; i < ciphertext_len; i++)
            printf("%x", ciphertext[i]);
        printf("\n");
    } else if (strcmp(argv[1], "decrypt") == 0) {
        decryptedtext_len = decrypt(ciphertext, strlen((char *)ciphertext), key, iv, decryptedtext);
        decryptedtext[decryptedtext_len] = '\0';
        printf("Decrypted text:\n%s\n", decryptedtext);
    } else {
        printf("Error: %s\n", argv[1]);
        printf("Usage: %s <encrypt|decrypt> <text>\n", argv[0]);
        return 1;
    }

    return 0;
}

编译并运行这个程序：

gcc encrypt.c -lcrypto -o encrypt
./encrypt encrypt "Hello, World!"
./encrypt decrypt <encrypted_text>

这个例子使用了AES-128-CBC加密算法。你可以根据需要选择其他加密算法和密钥长度。注意，这个例子仅用于演示目的，实际应用中需要考虑更多的安全因素。