Privacy Enabled Immunity Credential System on Blockchain

Immunity credentials for individuals are essential to ensure safety and security of communities in the current pandemic-stricken world. Immunity credentials can be employed to permit movement of only a certain class of individuals that are least prone to spreading infections, thus reducing the risk for the society as a whole. While the authenticity of the immunity credentials is extremely critical, it is also important to guarantee privacy and confidentiality of the individuals’ personal health information. In this paper, we present a blockchain based immunity credential system that allows users to authenticate immunity credentials in a verifiable manner. We leverage BLS aggregate signature that facilitates credential holders to selectively disclose credentials in a privacy preserving manner. Blockchain acts as single source of trust and ensures authenticity of claims. Our system enables users to reuse the tamper-evident verification status recorded on blockchain to authenticate to same verifiers without need for repeated cryptographic proof verification process. The protocol restricts any intermediaries/third-parties to use the identity or proof without authorization of the user. The protocol is fully automated through smart contracts and makes sure that credential verification is settled in near real time. We chose permissioned blockchain, Hyperledger Fabric (HLF) to implement our protocol as it befits the requirements of this problem and ensures smart contract development that supports user privacy, confidentiality, automated proof generation and verification of immunity credentials.