We describe a secure transformation of stateful connections or parts of them into stateless ones by attaching the state information to the messages. Secret-key cryptography is used for protection of integrity and con dentiality of the state data and the connections. The stateless protocols created in this way are more robust against denial of service resulting from high loads and resource exhausting attacks than their stateful counterparts. In particular, stateless authentication resists attacks that leave connections in a half-open state.