TCP and TLS are among the essential protocols in today's Internet. TCP ensures reliable data delivery while TLS secures the data transfer. Although they are very often used together, they have been designed independently following the Internet layered model. This paper demonstrates the various benefits that a closer integration between TCP and TLS would bring.By leveraging the extensible TLS 1.3 records, we combine TCP and TLS into TCPLS to build modern transport services such as multiplexing, connection migration, stream steering, and bandwidth aggregation. These services do not modify the TCP wire format and are resistant to middleboxes. TCPLS offers a powerful API enabling applications to precisely express the required transport services, ranging from a single-path single-stream connection to a multistream connection over several network paths, enabling choices between aggregated bandwidth and head-of-line blocking avoidance.Compared to MPTCP, our TCPLS prototype offers more control to the application and can be easily deployed as an extension to user-space TLS libraries, while being implemented at a low cost. Measurements demonstrate that it offers higher performance than existing QUIC libraries with a super set of transport services. CCS CONCEPTS• Networks → Transport protocols; Network protocol design.

TCP and TLS are among the most essential protocols in today's Internet. TCP ensures reliable delivery of data while TLS secures the data transfer. Following the layered model, TLS was designed to be as independent as possible from the underlying transport protocol. This paper revisits this assumption and demonstrates the various benefits that a closer integration between TCP and TLS brings. We implement a first TCPLS prototype that demonstrates the feasibility of this integration. We show its usefulness on different use cases such as the benefit of bandwidth aggregation during a connection migration, and discuss several open research directions. CCS CONCEPTS • Networks → Session protocols.

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