Opening Pandora's Box: An Analysis of the Usage of the Data Field in Blockchains

Since the proposal of Bitcoin in 2009 and with the inclusion of the first transaction in its genesis block, Blockchains (BC) have been used to store arbitrary data, including texts, images, and documents. However, such data is often not easily discoverable in BCs and is embedded within their binary data structures. Thus, this paper presents the design and implementation of a solution to analyze BC transactions searching for “media” content. This solution, called blockchain-parser, is capable of detecting ASCII strings and files (e.g., PDF, GIF, and SVG) embedded in BC's transactions. To evaluate such a solution, Bitcoin, Monero, and Ethereum cryptocurrencies were examined to find commonalities and differences between different BCs regarding their arbitrary data storage usage. Conclusions from such an evaluation indicate that Ethereum has been the most used BC for media data storage compared to Bitcoin and Monero.