A federal grand jury subpoena required John Doe to decrypt and produce the contents of encrypted laptops and external hard drives seized during a child-pornography investigation. Doe invoked the Fifth Amendment, but the district court granted immunity limited to his act of production, allowed the government to use the contents, and held him in civil contempt when he refused. The Eleventh Circuit reversed. It held that decryption and production would communicate facts from Doe’s mind— including his control over the drives, the existence and location of files, and his ability to access them—and therefore would be testimonial and potentially incriminating. The government could not invoke the foregone-conclusion doctrine because it had not shown with reasonable particularity that files existed, that Doe possessed or controlled them, or that he could decrypt them; the encrypted drives might contain nothing. The court also held that § 6002 requires immunity from both use and derivative use. Immunizing only the act of production while preserving the government’s ability to use the contents did not remove the danger against which the Fifth Amendment protects. Doe therefore could not be compelled to decrypt the drives, and the contempt judgment was reversed.