RISE SICS AB RISE SICS AB ENCS Universitaet Bremen TZI This document describes an extension for TLS and DTLS to protect the server from Denial of Service attacks against the handshake protocol, carried out by an on-path adversary. The extension includes a nonce and a Message Authentication Code (MAC) over that nonce, encoded as a Handshake Token that a Trust Anchor entity computes and provides to the client. The server registered at the Trust Anchor verifies the MAC to determine whether continuing or aborting the handshake.