AES_cbc_encrypt 是否添加填充?

Consider the following snippet of C++ code:

#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);
}

我在这里做的是使用 openssl aes 库加密然后解密消息.我关心的是长度encryption_output.就我的理解而言，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，四舍五入到最接近的 AES_BLOCK_SIZE 倍数.这个对吗?特别是，如果我将消息扩展为恰好 32 个字节长，会发生什么情况?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?