DBL: Deniable Blockchain Ledger

Abstract

In this paper, we construct a deniable blockchain ledger (DBL), which enhances blockchain with a new feature, deniability. The owner of the deniable blockchain ledger can produce a new blockchain copied from the original blockchain and replace some blocks with fake blocks. So, the original transaction data are hidden and our scheme can keep transaction privacy from outside coercion. The transaction data on DBL can also be redacted or be forgotten. Our DBL construction uses the Chameleon Hash as the hash function to make a block be redactable since it is easy to find a collision with the trapdoor. So, the hash value of the redacted block is still the same to the original block and the original following block can still associated to the generated fake block. Even an attacker can collect multiple blockchains, it is impossible for the attacker to determine which blockchain is the original one. We also provide two scenarios and the corresponding algorithms of generating fake blocks. One is that every user is normal user and the other is that some users are compromised. We are currently implementing the DBL and hope that our construction can protect data privacy in the blockchain.