Appending Data to Blockchain is not Sufficient for Non-repudiation of Receipt

TL;DR

Appending data to blockchain alone does not ensure non-repudiation of receipt, especially for confidential data, and requires additional mechanisms like smart contracts for stronger guarantees.

Contribution

This paper demonstrates the limitations of using blockchain solely for non-repudiation of receipt and proposes smart contracts as a potential solution.

Findings

Appending data to blockchain guarantees non-repudiation of origin in some cases.

For confidential data, non-repudiation of receipt is impossible due to a catch-22.

Smart contracts are suggested as a promising approach to improve non-repudiation.

Abstract

Exchanging data while ensuring non-repudiation is a challenge, especially if no trusted third party exists. Blockchain promises to provide many of the required guarantees, which is why it has been used in many non-repudiable data exchange protocols. Specifically, some authors propose to append data to blockchain to achieve non-repudiation of receipt. In this position paper, we show that this approach is insufficient. While appending data to blockchain can guarantee non-repudiation of origin in some cases, it is not sufficient for non-repudiation of receipt. For confidential data, we find a catch-22 that makes it impossible. For non-confidential data, meanwhile, plausible deniability remains. We discuss potential solutions and suggest smart contracts as a promising approach.