考虑以下 C++ 代码片段:
#include <iostream>
#include <openssl/aes.h>
#define AES_KEY_LENGTH 32
using namespace std;
int main()
{
AES_KEY encryption_key;
AES_KEY decryption_key;
unsigned char key[AES_KEY_LENGTH] = {'t', 'e', 's', 't', 't', 'e', 's', 't', 't', 'e', 's', 't', 't', 'e', 's', 't', 't', 'e', 's', 't', 't', 'e', 's', 't', 't', 'e', 's', 't', 't', 'e', 's', 't'};
unsigned char iv[AES_BLOCK_SIZE] = {'t', 'e', 's', 't', 't', 'e', 's', 't', 't', 'e', 's', 't', 't', 'e', 's', 't'};
unsigned char iv_enc[AES_BLOCK_SIZE];
unsigned char iv_dec[AES_BLOCK_SIZE];
memcpy(iv_enc, iv, AES_BLOCK_SIZE);
memcpy(iv_dec, iv, AES_BLOCK_SIZE);
AES_set_encrypt_key(key, AES_KEY_LENGTH * 8, &(encryption_key));
AES_set_decrypt_key(key, AES_KEY_LENGTH * 8, &(decryption_key));
char message[] = "Attack at dawn! Attack.";
unsigned char * encryption_output = new unsigned char[32];
encryption_output[31] = 3;
AES_cbc_encrypt((unsigned char *) message, encryption_output, sizeof(message), &encryption_key, iv_enc, AES_ENCRYPT);
unsigned char * decryption_output = new unsigned char[32];
AES_cbc_encrypt(encryption_output, decryption_output, 32, &decryption_key, iv_dec, AES_DECRYPT);
}
我在这里所做的是使用 openssl aes 库加密然后解密消息。我关心的是长度加密输出。据我了解,由于 AES 以大小为 AES_BLOCK_SIZE(又名 16 字节)的块进行加密,因此输出字节数应等于消息的大小,四舍五入为最接近的 AES_BLOCK_SIZE 倍数。这个对吗?特别是,如果我将消息扩展为正好 32 个字节长,会发生什么?这仍然有效,还是会添加 16 个空填充字节,从而在尝试在加密输出中写入字节 32 到 47 时导致分段错误?