基于OpenSSL的AES算法

OpenSSL是一个强大的加密库，支持多种加密算法，包括AES算法。以下是使用OpenSSL库实现AES加密和解密的示例代码：

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

#define AES_BLOCK_SIZE 16

// AES加密
int aes_encrypt(const unsigned char *plaintext, int plaintext_len, const unsigned char *key, unsigned char *ciphertext)
{
    AES_KEY aes_key;
    if (AES_set_encrypt_key(key, 128, &aes_key) < 0)
        return -1;

    int num_blocks = plaintext_len / AES_BLOCK_SIZE;
    int remainder = plaintext_len % AES_BLOCK_SIZE;

    for (int i = 0; i < num_blocks; i++)
        AES_encrypt(plaintext + i * AES_BLOCK_SIZE, ciphertext + i * AES_BLOCK_SIZE, &aes_key);

    if (remainder > 0)
    {
        unsigned char block[AES_BLOCK_SIZE];
        memset(block, 0, AES_BLOCK_SIZE);
        memcpy(block, plaintext + num_blocks * AES_BLOCK_SIZE, remainder);
        AES_encrypt(block, ciphertext + num_blocks * AES_BLOCK_SIZE, &aes_key);
    }

    return 0;
}

// AES解密
int aes_decrypt(const unsigned char *ciphertext, int ciphertext_len, const unsigned char *key, unsigned char *plaintext)
{
    AES_KEY aes_key;
    if (AES_set_decrypt_key(key, 128, &aes_key) < 0)
        return -1;

    int num_blocks = ciphertext_len / AES_BLOCK_SIZE;
    int remainder = ciphertext_len % AES_BLOCK_SIZE;

    for (int i = 0; i < num_blocks; i++)
        AES_decrypt(ciphertext + i * AES_BLOCK_SIZE, plaintext + i * AES_BLOCK_SIZE, &aes_key);

    if (remainder > 0)
    {
        unsigned char block[AES_BLOCK_SIZE];
        memset(block, 0, AES_BLOCK_SIZE);
        memcpy(block, ciphertext + num_blocks * AES_BLOCK_SIZE, remainder);
        AES_decrypt(block, plaintext + num_blocks * AES_BLOCK_SIZE, &aes_key);
    }

    return 0;
}

int main()
{
    unsigned char key[] = "0123456789ABCDEF";
    unsigned char plaintext[] = "Hello, world!";
    unsigned char ciphertext[sizeof(plaintext)];
    unsigned char decrypted[sizeof(plaintext)];

    int plaintext_len = strlen((char*)plaintext);

    aes_encrypt(plaintext, plaintext_len, key, ciphertext);

    printf("Ciphertext: ");
    for (int i = 0; i < plaintext_len; i++)
        printf("%02x ", ciphertext[i]);
    printf("\n");

    aes_decrypt(ciphertext, plaintext_len, key, decrypted);

    printf("Decrypted: %s\n", decrypted);

    return 0;
}

在此例中，我们使用了128位的密钥。如果需要使用256位的密钥，只需将AES_set_encrypt_key和AES_set_decrypt_key的第二个参数改为256即可。