Key-Value Commitments with Unlinkability

Blockchain technology enables secure transactions without requiring a centralized administrator used in various applications. Therefore, efficient verification in terms of computation and memory is desired. To reduce computational and memory costs, Agrawal et al. proposed Key-Value Commitments (KVC) with efficient data verification. KVC supports both a new pair insertions and value updates. However, their KVC outputs a key with each new pair insertion or value update, which connects transactions and leaks whether they belong to the same User. In this research, we define the feature that each transaction is independent of each other and not linked called unlinkability. Furthermore, KVC has two other issues. One is that the proof consists of three group elements, which yield the computational cost of updating proofs. The other is that the sign of the value change is leaked during value updates. This research constructs KVC that satisfies unlinkability by integrating Oblivious Accumulators (OblvAcc) into the KVC. The proposed method also resolves three issues. By processing update operations as insertions in our proposal, it reduces the computational cost for User by structuring proofs with only two elements, prevents sign leakage by outputting value changes as positive during updates. The key-binding security for the KVC in our proposal is reduced to the GRSA assumption under the random oracle model, and the SRSA assumption without random oracle. If the collision resistance, preimage resistance, and second preimage resistance of the hash function holds, KVC in our psoposal satisfies unlinkability.