Paper 2023/653

Muckle+: End-to-End Hybrid Authenticated Key Exchanges

Sonja Bruckner, University of Applied Sciences Upper Austria
Sebastian Ramacher, AIT Austrian Institute of Technology
Christoph Striecks, AIT Austrian Institute of Technology

End-to-end authenticity in public networks plays a significant role. Namely, without authenticity, the adversary might be able to retrieve even confidential information straight away by impersonating others. Proposed solutions to establish an authenticated channel cover pre-shared key-based, password-based, and certificate-based techniques. To add confidentiality to an authenticated channel, authenticated key exchange (AKE) protocols usually have one of the three solutions built in. As an amplification, hybrid AKE (HAKE) approaches are getting more popular nowadays and were presented in several flavors to incorporate classical, post-quantum, or quantum-key-distribution components. The main benefit is redundancy, i.e., if some of the components fail, the primitive still yields a confidential and authenticated channel. However, current HAKE instantiations either rely on pre-shared keys (which yields inefficient end-to-end authenticity) or only support one or two of the three above components (resulting in reduced redundancy and flexibility). In this work, we present an extension of a modular HAKE framework due to Dowling, Brandt Hansen, and Paterson (PQCrypto'20) that does not suffer from the above constraints. While their instantiation, dubbed Muckle, requires pre-shared keys (and hence yields inefficient end-to-end authenticity), our extended instantiation called Muckle+ utilizes post-quantum digital signatures. While replacing pre-shared keys with digital signatures is rather straightforward in general, this turned out to be surprisingly non-trivial when applied to HAKE frameworks (resulting in a significant model change with adapted proof techniques).

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Cryptographic protocols
Publication info
Published elsewhere. Minor revision. PQCrypto 2023
end-to-end securityhybrid authenticated key exchangepost-quantum cryptography
Contact author(s)
sebastian ramacher @ ait ac at
christoph striecks @ ait ac at
2023-08-07: last of 2 revisions
2023-05-08: received
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      author = {Sonja Bruckner and Sebastian Ramacher and Christoph Striecks},
      title = {Muckle+: End-to-End Hybrid Authenticated Key Exchanges},
      howpublished = {Cryptology ePrint Archive, Paper 2023/653},
      year = {2023},
      doi = {10.1007/978-3-031-40003-2_22},
      note = {\url{}},
      url = {}
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