The Volokh Conspiracy has a nice article discussing District Judge William K. Sessions III ruling compelling a defendant to decrypt his hard drive for an investigation against him.  The defendant tried to invoke Fifth Amendment protection against self-incrimination however Judge Sessions ruled his prior compliance in the investigation rendered the protection invalid:

“Where the existence and location of the documents are known to the government, “no constitutional rights are touched,” because these matters are a “foregone conclusion.” Fisher, 425 U.S. at 411. The Magistrate Judge determined that the foregone conclusion rationale did not apply, because the government has not viewed most of the files on the Z drive, and therefore does not know whether most of the files on the Z drive contain incriminating material. Second Circuit precedent, however, does not require that the government be aware of the incriminatory contents of the files; it requires the government to demonstrate “with reasonable particularity that it knows of the existence and location of subpoenaed documents.”

Boucher accessed the Z drive of his laptop at the ICE agent’s request. The ICE agent viewed the contents of some of the Z drive’s files, and ascertained that they may consist of images or videos of child pornography. The Government thus knows of the existence and location of the Z drive and its files. Again providing access to the unencrypted Z drive “adds little or nothing to the sum total of the Government’s information” about the existence and location of files that may contain incriminating information. Fisher, 425 U.S. at 411.

Boucher’s act of producing an unencrypted version of the Z drive likewise is not necessary to authenticate it. He has already admitted to possession of the computer, and provided the Government with access to the Z drive. The Government has submitted that it can link Boucher with the files on his computer without making use of his production of an unencrypted version of the Z drive, and that it will not use his act of production as evidence of authentication.

Because Boucher has no act of production privilege to refuse to provide the grand jury with an unencrypted version of the Z drive of his computer, his motion to quash the subpoena . . . is denied.”

via The Volokh Conspiracy – District Court Overturns Magistrate Judge in Fifth Amendment Encryption Case:.