c语言实现AES加密解密算法

C语言实现AES加密解密算法可以使用现成的库，也可以自己实现。下面是一个使用OpenSSL库实现AES加密解密的示例代码：

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

#define BLOCK_SIZE 16

int aes_encrypt(unsigned char *in, int in_len, unsigned char *key, unsigned char *out) {
    AES_KEY aes_key;
    if (AES_set_encrypt_key(key, 128, &aes_key) < 0) {
        return -1;
    }

    int len = in_len;
    unsigned char *padding = NULL;
    if (len % BLOCK_SIZE != 0) {
        padding = (unsigned char *)malloc(BLOCK_SIZE - len % BLOCK_SIZE);
        memset(padding, BLOCK_SIZE - len % BLOCK_SIZE, BLOCK_SIZE - len % BLOCK_SIZE);
        len += BLOCK_SIZE - len % BLOCK_SIZE;
    }

    int i = 0;
    while (i < len) {
        AES_encrypt(in + i, out + i, &aes_key);
        i += BLOCK_SIZE;
    }

    if (padding != NULL) {
        memcpy(out + len - BLOCK_SIZE, padding, BLOCK_SIZE - len % BLOCK_SIZE);
        free(padding);
    }

    return 0;
}

int aes_decrypt(unsigned char *in, int in_len, unsigned char *key, unsigned char *out) {
    AES_KEY aes_key;
    if (AES_set_decrypt_key(key, 128, &aes_key) < 0) {
        return -1;
    }

    int len = in_len;
    unsigned char *padding = NULL;
    if (len % BLOCK_SIZE != 0) {
        return -1;
    }

    int i = 0;
    while (i < len) {
        AES_decrypt(in + i, out + i, &aes_key);
        i += BLOCK_SIZE;
    }

    return 0;
}

int main() {
    unsigned char in[] = "Hello, world!";
    unsigned char key[] = "0123456789abcdef";

    unsigned char out[32] = {0};
    aes_encrypt(in, strlen(in), key, out);

    unsigned char dec[32] = {0};
    aes_decrypt(out, 16, key, dec);

    printf("in: %s\n", in);
    printf("out: ");
    for (int i = 0; i < 16; i++) {
        printf("%02x", out[i]);
    }
    printf("\n");

    printf("dec: %s\n", dec);

    return 0;
}

在上面的代码中，使用了OpenSSL库提供的AES加密解密函数。需要注意的是，加密的数据长度必须为16的倍数，如果不足16个字节，需要进行填充。在示例中，使用了简单的尾部填充方式。另外，密钥长度为128位，可以根据需要进行修改。