pub fn fixed_output_hash_bytes<H>(
    data: &[u8],
    iter_num: u64
) -> [u8; <H::OutputSize>::USIZE]where
    H: Digest + FixedOutput + OutputSizeUser + Write,
    GenericArray<u8, H::OutputSize>: From<[u8; <H::OutputSize>::USIZE]> + Into<[u8; <H::OutputSize>::USIZE]>,