实现AES-256-CBC的C语言代码

下面是一个使用C语言实现AES-256-CBC加密和解密的例子：

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

void encryptAES_CBC(const unsigned char *plaintext, const unsigned char *key, const unsigned char *iv, unsigned char *ciphertext, size_t length) {
    AES_KEY aesKey;
    AES_set_encrypt_key(key, 256, &aesKey);
    AES_cbc_encrypt(plaintext, ciphertext, length, &aesKey, iv, AES_ENCRYPT);
}

void decryptAES_CBC(const unsigned char *ciphertext, const unsigned char *key, const unsigned char *iv, unsigned char *plaintext, size_t length) {
    AES_KEY aesKey;
    AES_set_decrypt_key(key, 256, &aesKey);
    AES_cbc_encrypt(ciphertext, plaintext, length, &aesKey, iv, AES_DECRYPT);
}

int main() {
    const unsigned char *plaintext = (unsigned char *)"Hello World!";
    const unsigned char *key = (unsigned char *)"0123456789abcdef0123456789abcdef";
    const unsigned char *iv = (unsigned char *)"1234567890abcdef";
    size_t length = strlen((const char *)plaintext);

    unsigned char ciphertext[length];
    encryptAES_CBC(plaintext, key, iv, ciphertext, length);
    printf("Ciphertext: ");
    for (size_t i = 0; i < length; i++) {
        printf("%02x", ciphertext[i]);
    }
    printf("\n");

    unsigned char decrypted[length];
    decryptAES_CBC(ciphertext, key, iv, decrypted, length);
    printf("Decrypted: %s\n", decrypted);

    return 0;
}

请确保您已经安装了OpenSSL库，并使用以下命令编译和运行代码：

gcc -o aes aes.c -lssl -lcrypto
./aes

这段代码使用了OpenSSL库中的函数来实现AES-256-CBC加密和解密。它首先定义了两个函数`encryptAES_CBC`和`decryptAES_CBC`，分别用于加密和解密操作。然后在`main`函数中，设置了明文、密钥、初始化向量（IV）和明文长度，并调用`encryptAES_CBC`函数进行加密，并打印出密文。接着，调用`decryptAES_CBC`函数进行解密，并打印出解密后的明文。

注意：这只是一个简单的示例，实际应用中需要更多的错误处理和安全考虑。