Coconut: Threshold Issuance Selective Disclosure Credentials with Applications to Distributed Ledgers.

We present Coconut, a novel selective disclosure credential scheme supportingdistributed threshold issuance, public and private attributes,re-randomization, and multiple unlinkable selective attribute revelations.Coconut can be used by modern blockchains to ensure confidentiality,authenticity and availability even when a subset of credential issuingauthorities are malicious or offline. We implement and evaluate a genericCoconut smart contract library for Chainspace and Ethereum; and present threeapplications related to anonymous payments, electronic petitions, anddistribution of proxies for censorship resistance. Coconut uses short andcomputationally efficient credentials, and our evaluation shows that mostCoconut cryptographic primitives take just a few milliseconds on average, withverification taking the longest time (10 milliseconds).