Sidekick: In-Network Assistance for Secure End-to-End Transport Protocols


Gina Yuan, Matthew Sotoudeh, and David K. Zhang, Stanford University; Michael Welzl, University of Oslo; David Mazières and Keith Winstein, Stanford University
Outstanding Paper Award and Community Award Winner!


In response to concerns about protocol ossification and privacy, post-TCP transport protocols such as QUIC and Web-RTC include end-to-end encryption and authentication at the transport layer. This makes their packets opaque to middleboxes, freeing the transport protocol to evolve but preventing some in-network innovations and performance improvements. This paper describes sidekick protocols: an approach to in-network assistance for opaque transport protocols where in-network intermediaries help endpoints by sending information adjacent to the underlying connection, which remains opaque and unmodified on the wire.

A key technical challenge is how the sidekick connection can efficiently refer to ranges of packets of the underlying connection without the ability to observe cleartext sequence numbers. We present a mathematical tool called a quACK that concisely represents a selective acknowledgment of opaque packets, without access to cleartext sequence numbers.

In real-world and emulation-based evaluations, the sidekick improved performance in several scenarios: early retransmission over lossy Wi-Fi paths, proxy acknowledgments to save energy, and a path-aware congestion-control mechanism we call PACUBIC that emulates a "split" connection.

NSDI '24 Open Access Sponsored by
King Abdullah University of Science and Technology (KAUST)

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@inproceedings {295691,
author = {Gina Yuan and Matthew Sotoudeh and David K. Zhang and Michael Welzl and David Mazi{\`e}res and Keith Winstein},
title = {Sidekick: {In-Network} Assistance for Secure {End-to-End} Transport Protocols},
booktitle = {21st USENIX Symposium on Networked Systems Design and Implementation (NSDI 24)},
year = {2024},
isbn = {978-1-939133-39-7},
address = {Santa Clara, CA},
pages = {1813--1830},
url = {},
publisher = {USENIX Association},
month = apr

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