Encryption is one of the most important ways to safeguard data from prying eyes. But what happens when those prying belong to the government? Can they force you to break your own encryption and provide them with the information they want?

In a new amicus brief, we explain that the Fifth Amendment privilege against self-incrimination prohibits the government from forcing someone to decrypt their computer when they're suspected of a crime.

Leon Gelfgatt was charged with forgery and the government, with a search warrant, seized a number of his electronic devices. Law enforcement couldn't break the encryption that protected the devices, so it went to court, asking a judge to order Gelfgatt to decrypt the devices for them. The Fifth Amendment protects a person from being forced to testify against themselves and so the government promised not to look at the encryption key—the "testimony" in their eyes—but nonetheless wanted the ability to use the unencrypted data against Gelfgatt. The judge denied the government's request, ruling that forcing Gelfgatt to decrypt the devices would violate the Fifth Amendment.

The government appealed that decision and the case is now before the Massachusetts Supreme Judicial Court, where we filed an amicus brief with the ACLU and the ACLU of Massachusetts.

Our brief argues that the lower court got it right. The Fifth Amendment protects a person from being forced to reveal the "contents of his mind" to the government, allowing law enforcement to learn facts it didn't already know. When it comes to compelled decryption, the Fifth Amendment clearly applies because the government would be learning new facts beyond simply the encryption key. By forcing Gelfgatt to translate the encrypted data it cannot read into a readable format, it would be learning what the unencrypted data was (and whether any data existed). Plus, the government would learn perhaps the most crucial of facts: that Gelfgatt had access to and dominion and control of files on the devices.

It's not the first time we've made this argument in court; we've filed amicus briefs in other cases involving forced decryption, and won big last year in the Eleventh Circuit Court of Appeals, which agreed with us that the act of decrypting a computer is protected by the Fifth Amendment.

At a time when the recent public disclosures have suggested the government has been undermining cryptography, we hope the court understands the importance of having strong technological safeguards to protect our privacy and find that our constitutional protections prohibit what the government is trying to do here.

Oral argument in the case is set for Nov. 5, 2013 in Boston.