When EFF preaches about the benefits of using device encryption on smartphones, one of the most frequent questions we get is whether the police can force you to turn over your passcode or unlock the device. The answer should be no. The Fifth Amendment states that no one can be forced to be “a witness against himself,” and we argue that the constitutional protection applies to forced decryption. Last week, we filed a brief making that case to the Indiana Supreme Court.

The case began when Katelin Eunjoo Seo reported to law enforcement outside of Indianapolis that she had been the victim of a rape and allowed a detective to examine her iPhone for evidence. But the state never filed charges against Seo’s alleged rapist, identified by the court as “D.S.” (Courts often refer to minors using their initials.) Instead, the detective suspected that Seo was harassing D.S. with spoofed calls and texts, and she was ultimately arrested and charged with felony stalking. The state not only sought a search warrant to go through Seo's phone, but a court order to force her to unlock it. Seo refused, invoking her Fifth Amendment rights. The trial court held her in contempt, but an intermediate appeals court reversed.

When the Indiana Supreme Court agreed to get involved, it took the somewhat rare step of inviting amicus briefs. EFF got involved because, as we say in our brief filed along with the ACLU and the ACLU of Indiana, the issue in Seo is “no technicality; it is a fundamental protection of human dignity, agency, and integrity that the Framers enshrined in the Fifth Amendment.”

In recent years, courts have struggled with how to apply the Fifth Amendment’s privilege against self-incrimination to compelled decryption of encrypted devices. It’s well settled that the privilege protects against “testimonial” communications, which a 1957 Supreme Court case describes as those that require a person to disclose “the contents of his own mind.” It’s also clear that nonverbal acts can be testimonial, such as being forced to respond truthfully to police questioning with a “nod or headshake,” or to produce a gun that police believe was used in a crime. Even responding to a subpoena for documents can be a testimonial “act of production” because it reveals information about the existence and authenticity of the documents, and the subject’s possession of them.

So what about being forced to tell police your password, or to unlock an iPhone?

Our argument to the Indiana Supreme Court is that compelling Seo to enter her memorized passcode would be inherently testimonial because it reveals the contents of her mind. Obviously, if she were forced to verbally tell a prosecutor her password, it would be a testimonial communication.

By extension, the act of forced unlocking is also testimonial. First, it would require a modern form of written testimony, the entry of the passcode itself. Second, it would rely on Seo’s mental knowledge of the passcode and require her to implicitly acknowledge other information such as the fact that it was under her possession and control. The lower appellate court in Seo added an intriguing third reason:

In a very real sense, the files do not exist on the phone in any meaningful way until the passcode is entered and the files sought are decrypted. . . . Because compelling Seo to unlock her phone compels her to literally recreate the information the State is seeking, we consider this recreation of digital information to be more testimonial in nature than the mere production of paper documents.

Because entering a passcode is testimonial, that should be the end of it, and no one should be ordered to decrypt their device, at least absent a grant of immunity that satisfies the Fifth Amendment.

But there is an additional wrinkle. In a case from 1976 called Fisher v. United States, the Supreme Court recognized an exception to the Fifth Amendment privilege for testimonial acts of production. The case involved responding to a subpoena for tax documents, and the government could show to a “foregone conclusion” that it already knew all of the information it would otherwise learn from the production—i.e. the existence, authenticity, and possession of the responsive documents.

Although the Supreme Court has never again relied on this foregone conclusion exception, the government has built it into a full-blown “doctrine.” State and federal prosecutors have invoked it in nearly every forced decryption case to date. In Seo, the State argued that all that compelling the defendant to unlock her phone would reveal is that she knows her own passcode, which would be a foregone conclusion once it “has proven that the phone belongs to her.”

As we argue in our amicus brief, this would be a dangerous rule for the Indiana Supreme Court to adopt. If all the government has to do to get you to unlock your phone is to show you know the password, it would have immense leverage to do so in any case where it encounters encryption. The Fifth Amendment is intended to avoid putting people to a “cruel trilemma”: self-incriminate, lie about knowing the password, or risk being held in contempt for refusing to cooperate.

Thankfully that’s not the law. Instead, it’s clear from Fisher and later Supreme Court cases that the foregone conclusion exception was intended to be very narrow. It has only been applied in a case involving business records, and only where the testimonial communication at issue was the act of providing specified documents. The Court has made clear there is no foregone conclusion exception where a person is required to use the contents of their mind, even in responding to a more open-ended document subpoena. So there should be no exception to the Fifth Amendment when the government compels disclosure or use of a passcode to unlock and decrypt a digital device.

The Indiana Supreme Court is set to hold argument in Seo on April 18. We’ll be watching for its ruling.