HashCloak Newsletter January 2023
Welcome to the brand new HashCloak Newsletter. In contrast with the previous iteration, now that HashCloak has grown into a leading R&D privacy lab, we will be posting links to interesting readings and findings, in addition to short form content around what we’ve been working on at HashCloak!
Stuff We’ve been reading
Fuzzers for stateful systems: Survey and Research Directions
Functional Commitments: ZK under a different lens - Geometry Research
Circom-Pairing: A Million-Dollar ZK Bug Caught Early | by Veridise
Stuff We’ve been playing with
GitHub - keep-starknet-strange/garaga: Efficient pairing library, written in Cairo 🐺.
GitHub - daira/jubjub: Supporting evidence for security of the Jubjub curve to be used in Zcash
Stuff We’ve been watching
Interesting HashCloak Research Project of the Month
As part of our research into adding privacy to Flashbots architecture, we have writing up simple prototypes of ideas around how to potentially use MPC. Our work can be found here on Github.
In particular, we have been doing research on variants of the knapsack problems and knapsack auctions and implementing them in MPC. The main use case we see this being useful for is for building distributed builder networks. At a basic level, constructing a block is an instance of the knapsack problem. MPC is a tool that can be used in order for individual builders to contribute sets of transactions only known to them but return a block satisfying the usual Ethereum constraints e.g. the block gas limit.
We presented our work at this year’s IC3 Winter Retreat. We will be writing more about this in the coming months, so stay tuned.
Bonus Project!
We also spun up this quick cheat sheet for using MP-SPDZ that came out of our frustration with using the tool through both our flashbots-privacy work and other consulting and research engagements. You can find it here https://github.com/hashcloak/mp-spdz-cheatsheet
Special Purpose Cryptography Protocol of the Month
As part of our consulting practice, we notice that many of our clients try to shoehorn general purpose cryptography such as ZK-SNARKs in problems for which there are well-studied, understood and implemented special purpose protocols. In this section, every month, we hope to give you a taste of a useful special purpose protocol in order to better educate you on good composable cryptographic design principles.This month, we will provide a short summary of BBS+ signatures, a pairing-based signature scheme that allows for selective disclosures.
BBS+ signatures are a signature scheme based on the BBS signature scheme by Boneh-Boyen-Shacham designed to be used to construct short group signatures. However, its particular construction provides several unique properties. Namely, that one can sign multiple messages using a single signature. Using this fact, it enables a signer to provide a proof of knowledge that they signed a particular message or sets of messages without revealing the underlying signature. They are able to do this without compromising the authenticity and integrity of the messages. As such, this is a zero-knowledge proof and naturally provides us with a way to do selective disclosures.
BBS+ signatures are an improvement over the original BBS signature scheme. Not only do they have an improved security proof, closing many holes in the original BBS signature scheme’s security proofs, but they also come with additional features. These additional features include
If you want to read more and play with an implementation, we recommend the following resources:
JSON-LD BBS+ Signatures over BLS12-381: GitHub - mattrglobal/jsonld-signatures-bbs: A linked data proof suite for BBS+ signatures
Papers that introduce BBS+ signatures and improvements:
Constant-Size Dynamic k-TAA* ** by Au, Susilo and Mu
Anonymous Attestation Using the Strong Diffie Hellman Assumption Revisited | SpringerLink by Camenisch, Drijvers and Lehmann
Completed engagements
We recently completed an audit of MACI v1.1.1!
You can read more about the announcement on the Privacy and Scaling Explorations blog.
That’s it for this month! Hope you enjoyed the first edition of the revamped HashCloak Newsletter. Be sure to subscribe to the newsletter if you are interested. If you would like to stay up to date on what we are up to, follow us on Twitter.
Lastly, if you or your company needs security audits, R&D around privacy and cryptography or any other consulting services, you can reach out by scheduling a call with us here: https://calendly.com/d/hhc-dnq-wfd/hashcloak-services-inquiries