Hi,

I have just concluded my Master's Thesis at ETH Zurich titled "Implementing
and Evaluating

Quantum-Safe Fully Encrypted Protocols" and I believe the content is
relevant for this mailing list.


My thesis consists mainly of the implementation of the "Drivel" protocol
[1]. Two of the authors of [1], Felix Günther ([email protected]) and
Shannon Veitch ([email protected]), supervised this thesis and are
also available for questions regarding the protocol design in this thread.


Drivel is an evolution of obfs4 [2] that:

   -

   allows for key encapsulation mechanisms, particularly the ones proposed
   as part of the NIST standardization [3],
   -

   has stronger obfuscation, providing more guarantees than obfs4 in the
   scenario that censors should get ahold of bridge information such as NodeID
   and long-term public key,
   -

   contains a thin crypto-agility layer, allowing the replacement of
   cryptographic algorithms as needed,
   -

   provides more configuration options to bridge operators regarding
   performance trade-offs by allowing for runtime-configuration of the
   cryptographic algorithms, and
   -

   allows for post-quantum traditional hybrid instantiations. Note:; my
   thesis covers the “pure” post-quantum case (i.e., non-hybrid). Due to the
   crypto agility, hybrids are relatively easy to add by implementing an
   appropriate PQ/T hybrid combiner, such as OEINC [1].

Additionally, there are proposed changes to Drivel itself, evaluations of
the implementation's performance, and some security proofs in the thesis.
The main purpose of my proposed changes is to add more flexibility in
traffic shaping (minimize “quiet periods” previously discussed on this list
[4]) and to optimize performance.


The thesis PDF is available under: https://doi.org/10.3929/ethz-b-000746588

The chapters "Implementing Drivel" and "Experimental Evaluation" should be
most relevant to this list.

I encourage everyone interested in pluggable transports to have a look if
this sounds intriguing.


The implementation is done as a fork of the lyrebird repository [5] and is
available under: https://github.com/marc-himmelberger/lyrebird-drivel

The Tor Project is more than welcome to use my work for future changes to
lyrebird, although I do believe some changes to drivel and some
optimizations to my code may be beneficial for performance reasons before
the pluggable transport is used in production.


In case of any feedback or questions, do not hesitate to reach out.


Best regards,

Marc Himmelberger


[1] https://eprint.iacr.org/2025/408.pdf

[2]
https://gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/lyrebird/-/blob/main/doc/obfs4-spec.txt

[3] https://csrc.nist.gov/projects/post-quantum-cryptography

[4]
https://archive.torproject.org/websites/lists.torproject.org/pipermail/tor-dev/2017-June/012310.html

[5]
https://gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/lyrebird
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