A Privacy-Preserving Framework for Endorsement Process in Hyperledger Fabric

Hyperledger Fabric is a permissioned flavor of blockchain which offers various privacy features to its users. It stands out from other permissioned framework by allowing only a subset of peers called endorsing peers to execute the chaincode. This subset is given in the form of logical expression called endorsement policy. During the validation phase, every peer checks the transaction for desired endorser signatures against the endorsement policy. There are various attacks and privacy risks involved in disclosing the endorser signature and endorsement policy. In this paper we provide a framework for a secure endorsement system in Hyperledger Fabric. An efficient linkable threshold ring signature scheme is constructed, with a ZK-SNARK set membership proof, to secure the endorsements made by the endorsers. The endorsement policy is obfuscated by employing a recent construction of universal RSA accumulators and the individual membership proofs are batched through a non-interactive proof of exponentiation technique for efficient validation. We provide formal security definitions and proofs for the proposed framework.