A Decentralized Trusted Timestamping Based on Blockchains

Abstract

Decentralized trusted timestamping based on blockchains is used to protect a large variety of digital data. At present, in the case of trusted timestamping services, such related information is not included in the OP_RETURN field of a Bitcoin's transaction chain, which has a limited size (40 bytes). When OP_RETURN is extended, (e.g., with multiple OP_RETURN fields) the transaction is rejected by the Bitcoin network. We propose storing data in the blockchain by encoding into Bitcoin addresses. The transactions created by the proposed method are similar to the usual transactions; therefore, they will not be rejected. The proposed method expands the storage space to a maximum of N^*20 bytes, thereby enabling the storage of additional information (e.g., file names, creator names, and keywords) as well as file hashes. We performed experiments with a picture and its copyright information. We set N =3, resulting in storage of 60 bytes of data. The experimental results indicate that the proposed method can timestamp a file in an average of 24 min at a possible cost of 0.24 USD. We believe that the proposed method can prove the existence and integrity of a digital file, which is helpful in copyright protection.