Encrypt data @data with key @key, skipping @skip first bytes of the
    keystream

def ARC4_encrypt(key, data, skip=0):
    """Encrypt data @data with key @key, skipping @skip first bytes of the
    keystream"""

    algorithm = algorithms.ARC4(key)
    cipher = Cipher(algorithm, mode=None, backend=default_backend())
    encryptor = cipher.encryptor()
    if skip:
        encryptor.update(b"\x00" * skip)
    return encryptor.update(data)