Research Briefs on Information & Communication Technology Evolution (Oct 2020)
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 circumvented the problem of double spending that existed in the prior digital currencies, through validation. Particularly permissioned blockchain framework became popular with organizations forming consortium that allowed only authorized entities to participate in the network. Hyperledger Fabric, a popular distributed ledger technology hosted by Linux Foundation has remarkable features because of the fact that it is open source. It stands out from other frameworks as it focuses on the privacy-preserving requirements of the enterprises. Apart from only allowing authenticated organizations to participate in the network it implements channels that allows a subset of organizations to communicate concealing the existence of such a channel to other members. Optionally fabric also provides anonymity and unlinkability of the participating clients through a cryptographic protocol suite called Idemix that operates based on zero-knowledge proofs. Fabric follows the execute-order-validate transaction flow as opposed to order-execute flow that had certain limitations in other platforms. For executing the transactions submitted by the clients, fabric has designated endorsing peers which holds the smart contract - programmable business logic. Endorsing peers or endorsers execute the transactions and attach their signatures to the results for validation purpose. But revealing the endorser identities may be a problem when there is conflict of interest among the enterprises. Hence to have an unbiased flow of work it is important to conceal the endorser identity. According to [1] anonymization of endorsing peers is still a open problem in fabric community. We propose a solution to this problem which uses linkable threshold ring signatures that conceals the identity of endorsers. Ring signatures are known for preserving the privacy of the signer in a group. Threshold ring signature allows t-out-of-n signers to collaborate on the signing procedure. Employing threshold ring signature implicitly addresses one more problem stated in [10] where the verifiers need to manually count the valid ring signature that increases the verification time. This process of separately verifying each of the signatures and checking if the number of signatures is more than the threshold value is replaced by having just one threshold signature collaboratively signed by the required endorsers.
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