The mcTLS protocol is designed to enable secure communication between a client, server, and 1 or more middleboxes in series between the client and server. The protocol is built as an extension to the TLSv1.2 protocol. This document extends and modifieds the TLSv1.2 specification in RFC 5246. Where details are omitted here, the reader should assume that no changes are made from the TLSv1.2 specification.