No, There Isn’t Child Porn on the Bitcoin Blockchain

Anyone swiping through the tech news on their tablet this week may have been startled by an unsavory story. Child pornography (CP) is permanently encoded in the bitcoin blockchain accoriding to mainstream media reports, making anyone who downloads the blockchain guilty of accessing CP. Not only is this old news, but it’s fake news. Understanding why calls for taking a quick dip into bitcoin’s code.

Bitcoin’s Boogeyman Returns

No one can really recall what bitcoin was branded as first: a tool of terrorists, drug dealers, or child pornographers. All that can be said for certain is all three canards have been trotted out regularly over the years. Only last week in the U.S. Senate, Representative Brad Sherman expressed hope that a cryptocurrency panel would reconvene immediately after there had been a terrorist attack funded by crypto. But that was last week; this week it’s all about pornography of the worst kind. CP is the topic du jour thanks to a new research paper. Its abstract explains:

Blockchains…irrevocably record arbitrary data, ranging from short messages to pictures. This does not come without risk for users as each participant has to locally replicate the complete blockchain, particularly including potentially harmful content…Our analysis shows that certain content, e.g., illegal pornography, can render the mere possession of a blockchain illegal…our analysis reveals more than 1600 files on the blockchain, over 99% of which are texts or images. Among these files there is clearly objectionable content such as links to child pornography, which is distributed to all Bitcoin participants.

This all sounds pretty damning, and given some of the alarmist headlines the paper has generated, you would have thought the FBI van was speeding its way to every address known to operate a full bitcoin node. But that’s not quite how the real story goes.

The Daily Dot cranks up the FUD.

Old News Is Old

The CP on the blockchain story isn’t news and it isn’t new either. In fact, it was first dragged up in 2013, and has been revived, six years on, purely because a new paper has given the claims an air of legitimacy. News outlets were quick to jump on the story again, which was then widely shared by attention trolls such as Brianna Wu. The false hypothesis comes from the fact that it’s possible to encode information in the blockchain. That was how Satoshi famously hid his message in the genesis block: “The Times 03/Jan/2009 Chancellor on brink of second bailout for banks”. Anyone inspecting the blockchain won’t find those words however. Instead they’ll find the following hash: 000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26. That is the block’s coinbase parameter (nothing to do with Coinbase the company), written in hex.

Media publications have had a field day with the CP non-story.

research paper published in July 2017 titled Data Insertion in Bitcoin’s Blockchain explores this topic in more detail and explains how the coinbase data “is arbitrary and can be up to 100 bytes in size”. Only miners have the ability to insert data in this manner, and it’s typically used to signal mining support for proposed protocol changes. There are five other ways in which data can be encoded on the bitcoin blockchain, and it is the OP_RETURN option that is at the center of the child pornography story. The 2017 research paper explains that “this method is appropriate for inserting small amounts of data (or transaction metadata), but it is not suitable for large quantities of data.” […]

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