Confidential Certified Notification Protocol Using Rejectable Soulbound Tokens and Identity-Based Cryptography

Blockchain technology can be used in several e-commerce applications, like the creation of certified notifications. This kind of service allows a user, who acts as the sender, to prove that he has sent some data to a receiver. With the use of blockchain technology, we can take advantage of the fact that it offers a transparent and decentralized way to certify the authenticity and integrity of notifications. In this proposal, we combine the use of Soulbound tokens (SBTs), a special kind of Non-Fungible Tokens (NFTs) whose owners cannot transfer or trade to other users, with an improvement of the ERC-721 standard to include the possibility that the receiver could reject a token, allowing the selective reception of SBTs. Representing the certified notifications as Rejectable SBTs (RejSBT), we can track when the sender sends a notification, and when the receiver accepts it, providing both non-repudiation of origin (NRO) and reception (NRR) proofs. The notification process requires only two steps. Once the receiver has accepted the RejSBT that represents the ownership of a notification, we will use Identity-Based Cryptography to let the owner decrypt the confidential information represented by the RejSBT.