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.

翻译：在确保不可否认性的前提下交换数据是一项挑战，尤其是在缺乏可信第三方的情况下。区块链承诺提供许多所需的保障，因此已被用于多种具有不可否认性的数据交换协议中。具体而言，部分研究者提出将数据追加到区块链以达成接收的不可否认性。在本立场论文中，我们证明该方法是不充分的。尽管将数据追加到区块链在某些情况下能保证来源的不可否认性，但不足以实现接收的不可否认性。对于机密数据，我们发现了无法解决的"第22条军规"式困境；而对于非机密数据，则仍存在可否认性。我们探讨了潜在解决方案，并认为智能合约是一种有前景的方法。