In Proof-of-Stake (PoS) and permissioned blockchains, a committee of verifiers agrees and sign every new block of transactions. These blocks are validated, propagated, and stored by all users in the network. However, posterior corruptions pose a common threat to these designs, because the adversary can corrupt committee verifiers after they certified a block and use their signing keys to certify a different block. Designing efficient and secure digital signatures for use in PoS blockchains can substantially reduce bandwidth, storage and computing requirements from nodes, thereby enabling more efficient applications.

We present Pixel, a pairing-based forward-secure multi-signature scheme optimized for use in blockchains, that achieves substantial savings in bandwidth, storage requirements, and verification effort. Pixel signatures are also forward-secure and let signers evolve their keys over time, such that new keys cannot be used to sign on old blocks, protecting against posterior corruptions attacks on blockchains. We show how to integrate Pixel into any PoS blockchain.

We will also discuss the recent standardization progress of Boneh–Lynn–Shacham (BLS) signatures and how they can significantly improve storage and bandwidth for blockchain transactions.

Bio:

Sergey is an Assistant Professor at the University of Waterloo (2016 - present) and the Head of Cryptography at Algorand. He is interested in building cryptographic primitives, protocols, and systems that enable new applications in untrusted and distributed environments. He received a PhD from MIT, where he was a Microsoft PhD fellow and MSc and BSc from UToronto. His PhD dissertation was on designing cryptographic tools for the cloud using lattice-based cryptography for which he received Sprowls Doctoral Thesis Prize for best thesis in CS at MIT. He was the founder and CTO at Stealthmine, the founding team member at Algorand (on academic leave in 2018-2019), and spent some time at IBM T.J. Watson Research Centre.