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

TL;DR

Coconut is a new credential scheme enabling threshold issuance, selective attribute disclosure, and integration with blockchains, supporting privacy, security, and availability even with malicious authorities, demonstrated through practical applications.

Contribution

We introduce Coconut, a novel cryptographic credential scheme with threshold issuance, re-randomization, and unlinkable disclosures, optimized for blockchain integration and practical deployment.

Findings

Cryptographic primitives execute in a few milliseconds.

Verification takes approximately 10 milliseconds.

Applications include anonymous payments, petitions, and censorship-resistant proxies.

Abstract

Coconut is a novel selective disclosure credential scheme supporting distributed threshold issuance, public and private attributes, re-randomization, and multiple unlinkable selective attribute revelations. Coconut integrates with blockchains to ensure confidentiality, authenticity and availability even when a subset of credential issuing authorities are malicious or offline. We implement and evaluate a generic Coconut smart contract library for Chainspace and Ethereum; and present three applications related to anonymous payments, electronic petitions, and distribution of proxies for censorship resistance. Coconut uses short and computationally efficient credentials, and our evaluation shows that most Coconut cryptographic primitives take just a few milliseconds on average, with verification taking the longest time (10 milliseconds).