aes加解密c语言实现

AES是一种高级加密标准，它是一种对称加密算法，也就是说AES加密和解密使用的是同一套算法。下面是使用C语言实现AES加解密的示例代码（使用openssl库）：

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

#define AES_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 padding_len = AES_BLOCK_SIZE - (in_len % AES_BLOCK_SIZE);
    int total_len = in_len + padding_len;

    unsigned char *padded_in = malloc(total_len);
    if (!padded_in) {
        return -1;
    }
    memcpy(padded_in, in, in_len);
    memset(padded_in + in_len, padding_len, padding_len);

    for (int i = 0; i < total_len / AES_BLOCK_SIZE; i++) {
        AES_encrypt(padded_in + i * AES_BLOCK_SIZE, out + i * AES_BLOCK_SIZE, &aes_key);
    }

    free(padded_in);
    return total_len;
}

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;
    }

    for (int i = 0; i < in_len / AES_BLOCK_SIZE; i++) {
        AES_decrypt(in + i * AES_BLOCK_SIZE, out + i * AES_BLOCK_SIZE, &aes_key);
    }

    int padding_len = out[in_len - 1];
    return in_len - padding_len;
}

int main()
{
    unsigned char key[16] = "0123456789abcdef";
    unsigned char in[] = "hello world";
    unsigned char out[256];

    int len = aes_encrypt(in, strlen(in), key, out);
    printf("encrypt: %s\n", out);

    int out_len = aes_decrypt(out, len, key, in);
    in[out_len] = '\0';
    printf("decrypt: %s\n", in);

    return 0;
}

注意，在加密时需要对输入进行padding，以保证长度是16的倍数。在解密时需要去除padding。