Redactable Blockchain using Enhanced Chameleon Hash Function

Immutability is a core principle of blockchain platforms that help all participants to have an exact global log of transactions. Immutability is easier to achieve in permissioned blockchain platforms where a trusted group are the validators. In public platforms, this vital property of blockchain can be achieved only through decentralized economic mechanisms like Proof-of-Work(PoW). Blockchain along with the concept of asset tokenization provides liquidity to markets like stock trading and exchange other intangible objects. With changes in regulatory policies and/or government laws, there could be a requisite to alter the contents in such markets. We propose an idea of using Chameleon hash functions that will enable modification of a block without changing other block contents. In our proposal, the trapdoor key used to redact a block is split among major validators and is reconstructed using Multi-Party Computation(MPC). Redaction happens when the major validators agree the suggested changes by digitally signing the proposal. This eliminates the need to rely on a trusted party. We also propose an idea of using second trapdoor key that will be with the creator of the block. This can be used in scenarios where the block redaction should not happen without the consent of the creator.