The Fifth Amendment and Testimonial Searches: A Complex Intersection with Biometric Decryption

-- By JoshSidi - 07 Apr 2025

The Fifth Amendment states that “no person… shall be compelled in any criminal case to be a witness against himself.” U.S Const., Amend. V. The constitutional privilege provides citizens that the government bears the “entire burden” in building a criminal case. Therefore, to provide citizens dignity and integrity the US criminal justice system “demands that the government seeking to punish an individual produce the evidence against him by its own independent labors, rather than by the cruel, simple expedient of compelling it from his own mouth.” Miranda v. Arizona, 384 U.S. 436, 460 (1966). The privilege protects the accused from having to “reveal, directly or indirectly, his knowledge of facts relating him to the offense or from having to share his thoughts and beliefs with the Government.” Doe v. U.S., 487 U.S. 201, 213 (1988). The privilege against self-incrimination bars the state from (1) compelling a defendant; (2) to make a testimonial communication to the state; (3) that is incriminating. Fisher v. United States, 425 U.S. 391, 408 (1976). A statement is considered “testimonial” when an accused’s “communication must itself, explicitly or implicitly, relate a factual assertion or disclose information,” thereby safeguarding the accused from having to disclose oral or written evidence that reflects their personal thoughts or the product of their mind. In contrast, non-testimonial evidence refers to physical acts or objects that provide “real or physical evidence,” used to measure physical properties or exhibit physical characteristics. State v. Diamond, 905 N.W.2d 870, 874 (Minn., 2018). As such, the Fifth Amendment does not protect the accused from having to produce their body as evidence, since this involves revealing physical traits, which is classified as a non-testimonial act. Id. Examples of non testimonial acts include blood samples, standing in a lineup, voice or handwriting samples, photographs, and general appearance. Described in Doe, the court introduced a metaphor that contrasts being forced to “surrender a key to a strongbox” (which is not protected) with being compelled to provide “the combination to a wall safe” (which is protected). In the context of modern day decryption, the “key” can be likened to biometric encryption, while the “combination” refers to a phone’s passcode. Recent precedent has raised questions and concerns about the protections afforded to individuals being forced to unlock their cell phones through biometric security measures such as facial recognition or fingerprints. Courts are divided on whether the Fifth Amendment protects individuals from being compelled to unlock their cell phones using biometric decryption. In State v. Diamond, the court held that the privilege against self-incrimination shields individuals from being forced to produce a password, as it constitutes a testimonial act that requires the accused to reveal the contents of their mind. 905 N.W.2d 870, 875 (Minn., 2018). The court drew on Schmerber, where the Supreme Court made a distinction between the testimonial act of producing documents as evidence and the nontestimonial act of producing the body as evidence. Id. The Diamond court explained that unlocking a cell phone with a fingerprint involves both displaying a physical characteristic (the fingerprint) and producing documents (the contents of the device). While acknowledging the complexity of fingerprint encryption, the court concluded that the act of providing a fingerprint did not reveal any mental content but merely demonstrated the defendant's “physical characteristics.” Therefore, unlocking a phone with a fingerprint is not considered a testimonial act under the Fifth Amendment. Other courts have reached similar conclusions, as seen in Diamond, raising concerns about the potential vulnerability of citizens to searches of their cell phone contents once law enforcement obtains a search warrant and compels the accused to unlock their device. The question arises: Are citizens protected when using biometric encryption, such as facial recognition? Facial recognition, or Face ID, is potentially similar to fingerprint-based passcodes, as both rely on physical characteristics to grant access to a device's contents. As noted, law enforcement can compel an individual to provide their fingerprint to unlock a phone, an action that has been determined not to violate the Fifth Amendment. Therefore, Face ID could be treated in a similar manner. Federal and state courts across the United States remain split on this issue. It is almost paradoxical that simple alphanumeric passcodes may receive more Fifth Amendment protection compared to biometric locking mechanisms, which are widely regarded as the most unique and secure form of encryption. However, most recently, the D.C Circuit diverged from the common precedent of finding biometrics encryption as nontestimonial. In United States v. Brown, the court found that forcing the defendant to unlock his phone with his fingerprint revealed his thoughts: “I know how to open the phone,” “I have control over [the phone],” and “the print of this specific finger is the password to this phone” United States v. Brown, 125 F.4th 1186, 1202–03 (D.C. Cir. 2025). Therefore, the court held that compelling the opening of a phone with a fingerprint is the same as verbally disclosing the password. The court determined that his Fifth Amendment rights were violated, as the compelled action was testimonial. Given the ambiguity surrounding the protections offered by the Fifth Amendment in relation to biometric encryption, there are proactive measures that individuals can take to safeguard their privacy. While the convenience of using biometric authentication methods may be appealing, individuals concerned about their legal rights under the Fifth Amendment should consider using strong alphanumeric passwords. Until a clear and definitive ruling is made by the U.S. Supreme Court, individuals who value their privacy and wish to ensure robust protection against self-incrimination may find it prudent to use strong alphanumeric passwords to lock their devices. While this may be less convenient than using biometric methods, it offers greater certainty that their rights under the Fifth Amendment will be protected.