The Electronic Frontier Foundation has filed a brief in the case of Leon Gelfgatt, arguing that forcing the accused to decrypt a file violates the Fifth Amendment, which makes you secure against self-incrimination.
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.