If 3D printing companies and government agencies hope to police the spread of dangerous or pirated digital shapes, their task is about to get much more complicated.
Late last month Matthew Plummer-Fernandez, the 31-year-old creative technologist for Goldsmith College's Interaction Research Studio at the University of London, released what he's calling 'Disarming Corruptor,' a piece of free software designed to distort 3D-printable blueprints such that only another user with the app and the knowledge of a certain key combination can reverse the distortion and print the object. That means any controversial file--say, a figurine based on Mickey Mouse or another copyrighted or patented shape, or the 3D-printable gun created earlier this year known as the Liberator--could be 'encrypted' and made available on a public repository for 3D-printing blueprints like the popular site Thingiverse without tipping off those who would try to remove the file.
Plummer-Fernandez says the idea for obscuring 3D-printable objects came to him when the 3D-printing firm iMaterialize refused to print an object he'd designed as an artistic variation on Mickey Mouse, and again when he observed Thingiverse's decision to ban weapons files from the site in late 2012. "I was confronting all these taboos showing up in 3D-printing around copyrighted material and 3D-printed weapons, and I think these services are leaving their users out to dry," says Plummer-Fernandez. "I wanted to think of a way to circumvent these problems."
His answer was Disarming Corruptor, which distorts shapes based on seven input values from zero to 100, such that the changes can be reversed by anyone who knows those values. "When patent trolls and law enforcement agencies find these files on sharing sites they will only see abstract contortions, but within the trusting community these files will still represent the objects they are looking for, purposely in need of repair," he writes on his website.
Plummer-Fernandez encourages users to upload disguised files to Thingiverse, tagging them with the letters "DC" to show that they've been altered with his tool. (He's uploaded at least two such objects himself, though he wouldn't tell me what they are.) "You're still sharing them on sites like Thingiverse but you can subvert that web service's control," he says. "It's like physical encryption."
Any file has around 100 triillion possible different keys that would need to be guessed to reverse its distortion, and Plummer-Fernandez points out that the technique can be repeated on the same shape to make it even more difficult to crack the code. (See my correction below regarding the number of possible keys.)
But he admits that his tool isn't meant to securely encrypt shapes as much as to obscure and disguise them. Even so, it would pose a significant problem for a service like Thingiverse--now owned by the 3D-printing company Stratays following its acquisition of Makerbot--if it hopes to filter files for weapons components or intellectual property infringement.
"It's still quite entry level encryption. But if there is going to be an arms race between hacktivists sharing files and people trying to control them, it's important to make that first move," he says. "I wanted to show that if these things are going to be monitored, we as a community have the technology to circumvent that."
Cody Wilson, the founder of the group Defense Distributed whose 3D-printable gun files were targeted with a takedown order from the State Department in May for possible weapons export control violations, says Disarming Corruptor proves that attempting to censor 3D-printable objects will be a losing battle.
"It explodes the idea that there will be certain shapes we can guard against. Information itself is plastic, and it can be molded and changed," says Wilson, who also runs the 3D-printing file repository site Defcad.com. "There will be liquid markets of contraband files, and you won't even know what they are."
Correction: An earlier version of this story stated that a single value between zero and 100 was used to encrypt Disarming Corruptor's files, when in fact seven such values are used for any file. Apologies for the error.
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