a journey into bitcoin metadata

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.