Welcome to the resource topic for 2023/002
Title:
Ethical identity, ring VRFs, and zero-knowledge continuations
Authors: Jeffrey Burdges, Handan Kılınç Alper, Alistair Stewart, Sergey Vasilyev
Abstract:We introduce a new cryptographic primitive, aptly named ring verifiable random functions (ring VRF), which provides an array of uses, especially in anonymous credentials. Ring VRFs are (anonymized) ring signatures that prove correct evaluation of an authorized signer’s PRF, while hiding the specific signer’s identity within some set of possible signers, known as the ring.
We discover a family of ring VRF protocols with surprisingly efficient instantiations, thanks to our novel zero-knowledge continuation technique. Intuitively our ring VRF signers generate two linked proofs, one for PRF evaluation and one for ring membership. An evaluation proof needs only a cheap Chaum-Pedersen DLEQ proof, while ring membership proof depends only upon the ring itself. We reuse this ring membership proof across multiple inputs by expanding a Groth16 trusted setup to rehide public inputs when rerandomizing the Groth16. Incredibly, our fastest amortized ring VRF needs only eight G_1 and two G_2 scalar multiplications, making it the only ring signature with performance competitive with group signatures.
We discuss applications that range across the anonymous credential space:
As in Bryan Ford’s proof-of-personhood work, a ring VRF output acts like a unique pseudo-nonymous identity within some desired context, given as the ring VRF input, but remains unlinkable between different contexts. These unlinkable but unique pseudonyms provide a better balance between user privacy and service provider or social interests than attribute based credentials like IRMA credentials.
Ring VRFs support anonymously rationing or rate limiting resource consumption that winds up vastly more flexible and efficient than purchases via money-like protocols.
We define the security of ring VRFs in the universally composable (UC) model and show that our protocol is UC secure.
ePrint: https://eprint.iacr.org/2023/002
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