Correct way of AES NI encryption in C++

Question

I am attempting to make AES 256 bit (CBC mode) encrypt function using special instruction set (AES-NI) from Intel.

This is my code so far:

int Nb = 4;
int Nk = 8;
int Nr = 14;

unsigned int BLOCK_SIZE = 16;

void block_encryption_special(unsigned char input[], unsigned char result[], __m256i *key)
{

    __m256i block = _mm256_loadu_si256((__m256i *) input);

    block = _mm256_xor_si256(block, key[0]);

    for (int i = 1; i < Nr; i++)
    {
        block = _mm256_aesenc_epi128(block, key[i]);
    }

    block = _mm256_aesenclast_epi128(block, key[Nr]);

    _mm256_storeu_si256((__m256i *) result, block);

}

unsigned char* encrypt(unsigned char input[], unsigned int input_length, unsigned  char key[], unsigned char *iv, bool special)
{
    unsigned int i = 0;
    unsigned int total_lenght;
    unsigned int length_padded = (input_length / BLOCK_SIZE);

    if(input_length % BLOCK_SIZE)
    {
        length_padded++;
    }

    length_padded *=  BLOCK_SIZE;

    total_lenght = length_padded;

    unsigned char *align  = null_padding(input, input_length, total_lenght);
    unsigned char *result = new unsigned char[total_lenght];
    unsigned char *block = new unsigned char[BLOCK_SIZE];

    memcpy(block, iv, BLOCK_SIZE);

    for (i = 0; i < total_lenght; i += BLOCK_SIZE)
    {
        block_encryption_special(block, result + i, (__m256i *)key);
        memcpy(block, result + i, BLOCK_SIZE);
    }

    delete[] block;
    delete[] align;

    return result;
}

I think, I am doing something wrong, because I get empty output from it. Do I miss something please?

Answer 1

Please read documentation of memcpy. The first argument must be destination buffer. In your code you are copy data to block and then delete it. Also the usage of memcpy in for loop is wrong. You should increment destination buffer pointer.