Design of Anonymous Endorsers in Hyperledger Fabric with Linkable Threshold Ring Signature

Abstract

Blockchain technology has gained its attention from its application in bitcoin which circumventedthe problem of double spending that existed in the prior digital currencies, through validation. Particularlypermissioned blockchain framework became popular with organizations forming consortiumthat allowed only authorized entities to participate in the network. Hyperledger Fabric, a popular distributedledger technology hosted by Linux Foundation has remarkable features because of the factthat it is open source. It stands out from other frameworks as it focuses on the privacy-preservingrequirements of the enterprises. Apart from only allowing authenticated organizations to participatein the network it implements channels that allows a subset of organizations to communicate concealingthe existence of such a channel to other members. Optionally fabric also provides anonymity andunlinkability of the participating clients through a cryptographic protocol suite called Idemix thatoperates based on zero-knowledge proofs. Fabric follows the execute-order-validate transaction flowas opposed to order-execute flow that had certain limitations in other platforms. For executing thetransactions submitted by the clients, fabric has designated endorsing peers which holds the smartcontract - programmable business logic. Endorsing peers or endorsers execute the transactions andattach their signatures to the results for validation purpose. But revealing the endorser identities maybe a problem when there is conflict of interest among the enterprises. Hence to have an unbiased flowof work it is important to conceal the endorser identity. According to [1] anonymization of endorsingpeers is still a open problem in fabric community. We propose a solution to this problem which useslinkable threshold ring signatures that conceals the identity of endorsers. Ring signatures are knownfor preserving the privacy of the signer in a group. Threshold ring signature allows t-out-of-n signersto collaborate on the signing procedure. Employing threshold ring signature implicitly addressesone more problem stated in [10] where the verifiers need to manually count the valid ring signaturethat increases the verification time. This process of separately verifying each of the signatures andchecking if the number of signatures is more than the threshold value is replaced by having just onethreshold signature collaboratively signed by the required endorsers.