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A new approach to encryption beats attackers by presenting them with fake data.

By Tom Simonite

Ari Juels, an independent researcher who was previously chief scientist at computer security company RSA, thinks something important is missing from the cryptography protecting our sensitive data: trickery.

“Decoys and deception are really underexploited tools in fundamental computer security,” Juels says. Together with Thomas Ristenpart of the University of Wisconsin, he has developed a new encryption system with a devious streak. It gives encrypted data an additional layer of protection by serving up fake data in response to every incorrect guess of the password or encryption key. If the attacker does eventually guess correctly, the real data should be lost amongst the crowd of spoof data.

The new approach could be valuable given how frequently large encrypted stashes of sensitive data fall into the hands of criminals. Some 150 million usernames and passwords were taken from Adobe servers in October 2013, for example.

After capturing encrypted data, criminals often use software to repeatedly guess the password or cryptographic key used to protect it. The design of conventional cryptographic systems makes it easy to know when such a guess is correct or not: the wrong key produces a garbled mess, not a recognizable piece of raw data.

Juels and Ristenpart’s approach, known as Honey Encryption, makes it harder for an attacker to know if they have guessed a password or encryption key correctly or not. When the wrong key is used to decrypt something protected by their system, the Honey Encryption software generates a piece of fake data resembling the true data.

If an attacker used software to make 10,000 attempts to decrypt a credit card number, for example, they would get back 10,000 different fake credit card numbers. “Each decryption is going to look plausible,” says Juels. “The attacker has no way to distinguish a priori which is correct.” Juels previously worked with Ron Rivest, the “R” in RSA, to develop a system called Honey Words to protect password databases by also stuffing them with false passwords.

Juels and Ristenpart will present a paper on Honey Encryption at the Eurocryptcryptography conference later this year. Juels is also working on building a system based on it to protect the data stored by password manager services such as LastPass and Dashlane. These services store all of a person’s different passwords in an encrypted form, protected by a single master password, so that software can automatically enter them into websites.

Password managers are a tasty target for criminals, says Juels. He believes that many people use an insecure master password to protect their collection. “The way they’re constructed discourages the use of a strong password because you’re constantly having to type it in—also on a mobile device in many cases.”

Juels predicts that if criminals got hold of a large collection of encrypted password vaults they could probably unlock many of them without too much trouble by guessing at the master passwords. But if those vaults were protected with Honey Encryption, each incorrect attempt to decrypt a vault would yield a fake one instead.

Hristo Bojinov, CEO and founder of mobile software company Anfacto, who has previously worked on the problem of protecting password vaults as a security researcher, says Honey Encryption could help reduce their vulnerability. But he notes that not every type of data will be easy to protect this way since it’s not always possible to know the encrypted data in enough detail to produce believable fakes. “Not all authentication or encryption systems yield themselves to being ‘honeyed.’”

Juels agrees, but is convinced that by now enough password dumps have leaked online to make it possible to create fakes that accurately mimic collections of real passwords. He is currently working on creating the fake password vault generator needed for Honey Encryption to be used to protect password managers. This generator will draw on data from a small collection of leaked password manager vaults, several large collections of leaked passwords, and a model of real-world password use built into a powerful password cracker.