The technology that underpins the world’s most popular cryptocurrency, known as the blockchain, not only contains records of financial transactions but also child abuse material, links to the so-called ‘dark web’ and copies of WikiLeaks files.
The findings were published this month in a paper written by academics from Germany’s RWTH Aachen University and Goethe University. Titled A Quantitative Analysis of the Impact of Arbitrary Blockchain Content on Bitcoin, it claims to be the first “comprehensive and systematic” study conducted on the topic.
The researchers found more than 1,600 files on the blockchain—a public record of bitcoin transactions that is shared between every user—over 99 percent of which were texts or images. But there is also “clearly objectionable content,” they said.
The team found several text files that potentially infringed on copyright, two leaked cryptographic keys, and at least eight files with sexual material. While five of those linked to “mildly pornographic content” the remaining three contained content that would be “objectionable for almost all jurisdictions.” Two of the files were “backups of link lists to child pornography” that led to the dark web.
The university experts found 609 transactions containing “online public chat logs, emails, and forum posts discussing bitcoin, including topics such as money laundering” and one image showing people alongside their internet pseudonyms.
Furthermore, the blockchain was storing a backup for WikiLeaks’ “Cablegate” release from 2010, which published more than 200,000 government messages.
They found no malware encoded into the technology but said that one security researcher had inserted a piece of suspicious computer code. The experts stressed that, while alarming, only 1.4 percent of bitcoin transactions (out of roughly 251 million transactions in total) contained non-financial data.
“Since all bitcoin participants maintain a complete local copy of the blockchain, these desired and vital features put all users at risk when objectionable content is irrevocably stored on the blockchain,” the academics’ paper read.
It continued: “A plethora of fundamentally different methods to store non-financial potentially objectionable content on the blockchain exists in bitcoin.
“As of now, this can affect at least 112 countries in which possessing content such as child pornography is illegal. This especially endangers the multi-billion dollar markets powering cryptocurrencies such as bitcoin.”
It has been discussed for a number of years how the bitcoin protocol could be used to store more than just financial logs. It emerged in 2014 that the protocol contains a tribute to Nelson Mandela, texts of Catholic prayers and even Valentine’s Day messages.
In 2015, the issue caught the attention of security researchers and law enforcement. Interpol, the international police organization, warned at the time that bitcoin’s blockchain could be exploited as a potential target for malware. It said: “The design of the blockchain means there is the possibility of malware being injected and permanently hosted with no methods currently available to wipe this data.
“This could affect ‘cyber hygiene’ as well as the sharing of child sexual abuse images where the blockchain could become a safe haven for hosting such data.”