Besides recording transfers of currency, the Bitcoin blockchain is being used to save metadata — i.e. arbitrary pieces of data which do not affect transfers of bitcoins. This can be done by using different techniques, and for different purposes. For instance, a growing number of protocols embed metadata in the blockchain to certify and transfer the ownership of a variety of assets beyond cryptocurrency. A point of debate in the Bitcoin community is whether metadata negatively impact on the effectiveness of Bitcoin with respect to its primary function. This paper is a systematic analysis of the usage of Bitcoin metadata over the years. We discuss all the known techniques to embed metadata in the Bitcoin blockchain; we then extract metadata, and analyse them from different angles.

中文翻译：

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比特币元数据之旅

除了记录货币的转移，比特币区块链还用于保存元数据，即不影响比特币转移的任意数据。这可以通过使用不同的技术并出于不同的目的来完成。例如，越来越多的协议将元数据嵌入到区块链中，以认证和转移除加密货币之外的各种资产的所有权。比特币社区中的一个争论点是元数据是否对比特币的主要功能产生负面影响。本文是对多年来比特币元数据使用情况的系统分析。我们讨论了将元数据嵌入比特币区块链的所有已知技术。然后，我们提取元数据，并从不同角度分析它们。