[tor-dev] Key Blinding Secrets

[Bellebaum, Thomas]

Hello everyone,

I am a researcher currently looking into different schemes for what you call Keyblinding in the rendevouz spec.

https://spec.torproject.org/rend-spec/keyblinding-scheme.html

I noticed that your description there mentiones a secret `s` to be hashed into the blinding factor, and have a few questions about it:

1. Is this secret currently being used / intended to be used? If so, how?

2. What kinds of security (formally or informally) would you expect from using a secret in the derivation process? For example, do you just require that someone without `s` cannot look up the service, or is this also meant as a way of ensuring that HSDir nodes cannot find correlations between services and descriptors (amounting to some sort of additional censorship resistance)?

The reason I am asking is because my research has identified some potentially post quantum secure schemes which for unknown identity keys results in uncorrelatable blinded keys, but where for known public keys you can efficiently determine whether a blinded key is its derivative, even if you do not know the blinding factor. I am wondering for which kinds of applications (with TOR being a major one) this would be relevant.

If you have any insights, please let me know. Also I am new to the TOR-Dev world, so feel free to send me to a different mailing list, should I have chosen the wrone one for this topic :)

Thanks in advance,
Thomas

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M.Sc. Thomas Bellebaum
Applied Privacy Technologies
Fraunhofer Institute for Applied and Integrated Security AISEC

Lichtenbergstraße 11, 85748 Garching near Munich (Germany)
Tel. +49 89 32299 86 1039
thomas.bellebaum at aisec.fraunhofer.de
https://www.aisec.fraunhofer.de

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