In the case of the United States v. John Doe, a subpoena duces tecum was issued to an individual (named John Doe) during a child pornography investigation. That subpoena ordered Doe to appear before a grand jury and produce unencrypted contents of laptop computers and external hard drives.
Even though the prosecutor gave Doe what is called "act-of-production immunity," Doe still invoked his Fifth Amendment privilege against self-incrimination and refused to decrypt the hard drives. When he did that, the judge overseeing the case held Doe in contempt of court. So Doe appealed.
The appellate court agreed with Doe for two reasons:
1. The decryption and production of the hard drives would have required the use of the contents of Doe’s mind; it would not have been merely a physical, nontestimonial act. It would instead have been tantamount to testimony by Doe of his knowledge of the existence and location of potentially incriminating files; of his possession, control, and access to the encrypted portions of the drives; and of his capability to decrypt the files.
2. Doe’s testimony would not have been a “foregone conclusion” because there was no evidence that the prosecutor knew whether any files existed and were located on the hard drives. In fact, there was no evidence that the prosecutor knew whether Doe was even capable of accessing the encrypted portions of the hard drives.