Paper 2021/1178

Onion Routing with Replies

Christiane Kuhn, Dennis Hofheinz, Andy Rupp, and Thorsten Strufe

Abstract

Onion routing (OR) protocols are a crucial tool for providing anonymous internet communication. An OR protocol enables a user to anonymously send requests to a server. A fundamental problem of OR protocols is how to deal with replies: ideally, we would want the server to be able to send a reply back to the anonymous user without knowing or disclosing the user's identity. Existing OR protocols do allow for such replies, but do not provably protect the payload (i.e., message) of replies against manipulation. Kuhn et al. (IEEE S&P 2020) show that such manipulations can in fact be leveraged to break anonymity of the whole protocol. In this work, we close this gap and provide the first framework and protocols for OR with protected replies. We define security in the sense of an ideal functionality in the universal composability model, and provide corresponding (less complex) game-based security notions for the individual properties. We also provide two secure instantiations of our framework: one based on updatable encryption, and one based on succinct non-interactive arguments (SNARGs) to authenticate payloads both in requests and replies. In both cases, our central technical handle is an implicit authentication of the transmitted payload data, as opposed to an explicit, but insufficient authentication (with MACs) in previous solutions. Our results exhibit a new and surprising application of updatable encryption outside of long-term data storage.

Metadata
Available format(s)
PDF
Category
Cryptographic protocols
Publication info
A major revision of an IACR publication in ASIACRYPT 2021
Keywords
PrivacyAnonymityUpdatable EncryptionSNARGsOnion RoutingMix Networks
Contact author(s)
christiane kuhn @ kit edu
History
2021-09-14: received
Short URL
https://ia.cr/2021/1178
License
Creative Commons Attribution
CC BY

BibTeX

@misc{cryptoeprint:2021/1178,
      author = {Christiane Kuhn and Dennis Hofheinz and Andy Rupp and Thorsten Strufe},
      title = {Onion Routing with Replies},
      howpublished = {Cryptology ePrint Archive, Paper 2021/1178},
      year = {2021},
      note = {\url{https://eprint.iacr.org/2021/1178}},
      url = {https://eprint.iacr.org/2021/1178}
}
Note: In order to protect the privacy of readers, eprint.iacr.org does not use cookies or embedded third party content.