Paper 2018/1132

Ouroboros Crypsinous: Privacy-Preserving Proof-of-Stake

Thomas Kerber and Markulf Kohlweiss and Aggelos Kiayias and Vassilis Zikas

Abstract

We present Ouroboros Crypsinous, the first formally analysed privacy-preserving proof-of-stake (PoS) block\-chain protocol. To model its security we give a thorough treatment of private ledgers in the universal composition (UC) setting that might be of independent interest. To prove our protocol secure against adaptive attacks, which are particularly critical in the PoS setting, we introduce a new coin evolution technique that relies on a SNARKs mechanism and key-private forward secure encryption. The latter primitive - and the associated construction - can be of independent interest. We stress that existing approaches to private blockchains, such as the proof-of-work-based Zerocash are analyzed only against static corruptions.