Integrating Group Signatures in Complex Decentralized Marketplace Transactions for Improved Buyer Privacy

Marketplace applications are a popular application category for blockchains because they allow the possibility for parties to transact without the need of a trusted middleman entity. Supply chain marketplaces involve buyers and sellers of goods and services that interact using complex transactional workflows rather than single, one-off transactions. Further, in some contexts, there is a need to maintain some degree of privacy about which parties are transacting and/or the nature of their transactions. Keeping such information private is often crucial for maintaining competitive advantage. However, traditional public key signature schemes do not provide strong enough privacy guarantees for such applications. On the other hand, signature schemes like Group Signatures offer more robust privacy guarantees but have not yet been adopted broadly in existing platforms. However, supporting privacy across multiple transactions in a workflow requires some extension to existing group signatures as opposed to just for a single transaction. In this paper, we present our effort on implementing some existing theoretical proposals for Group Signatures. We focus on application contexts in which it is sufficient to “hide” the originator of a transaction workflow i.e., the buyer (but is easily generalizable). Because, transaction workflows involve “multiple” related transactions which will be obfsucated by introducing privacy, we extend a group signature scheme with “linkability” of related transactions in a workflow under anonymity. We integrate our extended signature scheme into SmartChainDB - our extension of an open source blockchain platform, BigChainDB, that introduces several features for enabling complex marketplaces on blockchains.