import hashlib


def double_sha256(ba):
    """
    Perform two SHA256 operations on the input.

    Args:
        ba (bytes): data to hash.

    Returns:
        str: hash as a double digit hex string.
    """
    d1 = hashlib.sha256(ba)
    d2 = hashlib.sha256()
    d1.hexdigest()
    d2.update(d1.digest())
    return d2.hexdigest()