[tor-reports] October - November 2016 Report for Tor Bridge Distribution
isis agora lovecruft
isis at torproject.org
Tue Dec 20 02:46:07 UTC 2016
Hello,
The following progress was made in October and November 2016:
- Began implementing the crypto needed for the social distributor, as well as
writing documentation describing it. [0] [1]
In light of the history of attacks on pairing-friendly curves combined with
the recent pseudo-MOV attack which solves discrete logarithms in the
embedding field of the pairing (where the embedding field is of small
degree), [2] I decided to avoid pairings altogether and use an
attribute-based credential scheme based on algebraic MACs. [3] The
construction of this scheme required a library for working with points on
an elliptic curve, [4] which Henry de Valence and I have implemented in
Rust, using a curve25519 in Edwards form. Henry has made more detailed
announcement of our curve25519-dalek library on the curves mailing list,
[5] and our documentation is also available online. [6]
The next steps for the social distributor are to implement:
* hashing to a point on the curve (elligator2),
* the algebraic MAC scheme,
* Schnorr-style zero-knowledge proofs of knowledge of discrete logarithms,
* a blind signature scheme, and
* (maybe) a better point (de-)compression scheme, in order to eliminate the
need to worry about the cofactor (if possible for cofactor 8).
This may sound like a lot of work, but it really shouldn't be, now that the
library is in a somewhat usable, if not HIGHLY EXPERIMENTAL AND UNREVIEWED,
state. (On that note: we'd also like to humbly request code review. If
you're up for this, please email me.)
This work is potentially applicable to other OTF and internet freedom
projects, including Tor (if we ever allow linking against Rust code) and
Signal. After a meeting with Trevor Perrin, we've also added to our todo
list (probably after this project is done, so with alternate funding) to
incorporate into curve25519-dalek some additional functionality required
for the Signal protocol.
[0]: https://bugs.torproject.org/7520
[1]: https://people.torproject.org/~isis/papers/rBridge:%20User%20Reputation%20based%20Tor%20Bridge%20Distribution%20with%20Privacy%20Preservation.copy%20with%20notes.pdf
[2]: https://arxiv.org/pdf/1605.07746.pdf
[3]: https://eprint.iacr.org/2013/516
[4]: https://github.com/isislovecruft/curve25519-dalek
[5]: https://moderncrypto.org/mail-archive/curves/2016/000830.html
[6]: https://docs.rs/curve25519-dalek/
Best Regards,
--
♥Ⓐ isis agora lovecruft
_________________________________________________________
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Current Keys: https://fyb.patternsinthevoid.net/isis.html
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