Author: Nita Farahany Source: https://nitafarahany.substack.com/p/two-courts-one-test-one-thumb-inside Published: March 31, 2026
A Substack essay by Nita Farahany, published March 31, 2026, reconstructing the middle class of Week 10 of her Advanced Topics in AI Law and Policy course (Class 10.2 of roughly 30). The class walks the encrypted-device biometric-unlock cases through the Schmerber/Fisher/Hubbell Fifth Amendment framework, surfaces a 2024 federal circuit split, and introduces Farahany's four-category cognitive-evidence spectrum from her 2012 Stanford Law Review article as the lens that makes the split legible.
Summary
The class traces compelled-decryption doctrine across four cases and argues that the courts deciding them apply the same three-element self-incrimination test (a compelled act that is incriminating and testimonial) yet divide on what "testimonial" measures when an act is at once physical (a thumb pressed to a sensor) and communicative (the suspect's knowledge of the device). Farahany presents her four-category cognitive-evidence spectrum as the vocabulary the courts lack, and closes on what the essay frames as a cognitive-exertion paradox that the following class (10.3) takes up.
Cases discussed
U.S. v. Boucher (D. Vt., 2009). An ICE agent viewed the contents of a Z drive at the border; the government later subpoenaed Boucher to produce the decrypted Z drive. A magistrate quashed the subpoena on the ground that the foregone-conclusion exception was not satisfied. The district court reversed, reasoning that the government already knew of the drive's existence and location from the border viewing.
Commonwealth v. Jones (Mass. SJC 2019). A trafficking case involving compelled passcode disclosure. The court held that a passcode has no existence independent of the mind that holds it, and that compelling its production carries three implicit testimonial assertions: that the suspect knows the passcode, that it unlocks this device, and that the suspect controls the device contents. The foregone-conclusion exception had no foothold.
U.S. v. Payne (9th Cir. 2024). Officers forcibly grabbed Payne's thumb to unlock a phone. The court held there was no Fifth Amendment violation, reasoning that pressing the thumb "required no cognitive exertion," that Payne was physically passive, and that the thumb was used as an instrument, equivalent to fingerprinting at booking.
U.S. v. Brown (D.C. Cir. 2024). Arising from a January 6 prosecution, an FBI agent ordered the defendant to unlock a phone with a thumbprint. The court held this was a violation, identifying three implicit testimonial assertions (the defendant knew how to open the phone, had access, and that the print of that finger was the credential) and emphasizing that the defendant was ordered to actively use his hand rather than remaining physically passive.
Payne and Brown turn on nearly identical thumb-print facts and reach opposite conclusions. Both apply the same three-element test (compelled, incriminating, testimonial) but split on what "testimonial" measures when the unlocking act is simultaneously physical and communicative.
The four-category cognitive-evidence spectrum
Farahany introduces the spectrum from her 2012 Stanford Law Review article Incriminating Thoughts as the framework that makes the split legible. It sorts evidence into four categories:
- Identifying evidence — physical traits requiring no mental participation (fingerprints at booking, DNA, mug shot).
- Automatic evidence — involuntary physiological responses (blood pressure during a polygraph, galvanic skin response).
- Memorialized evidence — information stored in memory and accessed via a mental act (a passcode, a safe combination, the location of hidden documents).
- Uttered evidence — direct verbal or written testimony.
Through this lens, Payne treats the thumb-press as identifying evidence (the least protected category), while Brown treats it as memorialized-becoming-uttered (more protected). Farahany's argument is that the vocabulary the courts use does not have these distinctions built in.
The essay closes on what it frames as a cognitive-exertion paradox: Payne grounds non-protection in the absence of cognitive exertion, and Farahany argues the logical conclusion is that the more seamless the authentication interface, the less Fifth Amendment protection it carries. She offers the Meta EMG band, which reads intention before a conscious gesture, as the example, arguing that the more directly a technology reads the mind, the less protection the mind receives. The essay states that Class 10.3 takes up this paradox.
Relationships
- part-of: Nita Farahany Advanced Topics course (Class 10.2 of ~30)
- introduces: Farahany Cognitive Evidence Spectrum (4 Categories)
- related: Cognitive Liberty
- previous: Inside My Advanced Topics Class 10.1: The Government Can Take Your Blood. Can It Take Your Thoughts? (Farahany, March 2026) next: Inside My Advanced Topics Class 10.3: When the Interface Is Neural (Farahany, April 2026)