def challenge_response(challenge, password_hash):
    """ChallengeResponse"""
    zpassword_hash = password_hash.ljust(21, '\0')

    response = ""
    des_obj = des.DES(zpassword_hash[0:7])
    response += des_obj.encrypt(challenge)

    des_obj = des.DES(zpassword_hash[7:14])
    response += des_obj.encrypt(challenge)

    des_obj = des.DES(zpassword_hash[14:21])
    response += des_obj.encrypt(challenge)
    return response