A federal judge refused to compel a Wisconsin suspect to decrypt the contents of several hard drives because doing so would violate the man's Fifth Amendment right against self-incrimination. Judge William E. Callahan's Friday ruling ultimately labeled the issue a "close call."

Courts have wrestled with how to apply the Fifth Amendment to encrypted hard drives for several years. According to past rulings, forcing a defendant to decrypt a hard drive isn't necessarily self-incriminating, but forcing a defendant to decrypt a hard drive can amount to self-incrimination if the government can't otherwise show that the defendant has the password for the drive. In that case, forced decryption amounts to a forced confession that the defendant owns the drive.

For example, in one case a border patrol agent viewed incriminating files on a suspect's laptop during a border crossing. But the official then closed the laptop, causing the portion of the hard drive containing the files to be encrypted automatically and deprive investigators of access. The court ruled that because the government already knew the files existed and the suspect had access to them, compelling their decryption didn't force the suspect to implicitly admit the laptop was his.

The circumstances of the Wisconsin case were different. While police officers did find logs on the suspect's PC suggesting that incriminating files had been saved to an encrypted drive, the suspect had multiple encrypted hard drives in his apartment, and the government had no way of proving which specific hard drives, if any, contained the incriminating files in question. In theory, a guest might have used the man's computer to download the files and store them on a hard drive he didn't own. Or the hard drives containing the files might not be among the ones the police seized.

"Feldman’s act of production, which would necessarily require his using a password of some type to decrypt the storage device, would be tantamount to telling the government something it does not already know with 'reasonably particularity'—namely, that Feldman has personal access to and control over the encrypted storage devices," Judge Callahan wrote. "Accordingly, in my opinion, Fifth Amendment protection is available to Feldman. Stated another way, ordering Feldman to decrypt the storage devices would be in violation of his Fifth Amendment right against compelled self-incrimination."