Using drop casting, in which a drop of liquid containing a suspension of the desired materials is deposited on a surface, dean of engineering Anantha Chandrakasan and his colleagues produced tags less than a tenth of an inch in diameter. Then they found a way to add color to silk microparticles and mix four basic types to create random patterns.
“With a minimal amount of silk, we were able to generate 128 random bits of security,” says Benedetto Marelli, a professor of civil and environmental engineering and a coauthor of the paper. The patterns can be read out by a cell-phone camera with a macro lens, processed locally to generate the PUF code, and sent to the cloud and compared against a secure database.
As Marelli says, it’s democratic—“something that you can literally read with your phone, and you can fabricate by simply drop-casting a solution, without using any advanced manufacturing technique.”