A hash search is a very accurate, computationally efficient technique for testing whether a computer contains illicit material. Although police have been running hash searches for many years, case law is scarce regarding whether and to what extent the Fourth Amendment permits their use. Some commentators have argued that because hash searches reveal information concerning only the presence or absence of contraband, courts shouldn’t consider them Fourth Amendment searches. Rather, courts should treat hash searches as a sort of digital dog sniff.

This Note disagrees. It argues first that even accepting the analogy to digital dog sniffs, hash searches nevertheless violate the Fourth Amendment under Florida v. Jardines whenever they are used to look for evidence outside the scope of a search warrant or other permissive mechanism. It then argues that there is no limiting principle that would permit the use of hash searches but not more sophisticated algorithms—algorithms that would constitute the modern equivalents of general warrants. Accordingly, it proposes a rule that covers not only the hash searches that are being used now but also the more sophisticated forensic techniques that will be used in the near future: Police conduct a Fourth Amendment search whenever they use an algorithm to perform a task that would be a search if conducted manually by a human.

* J.D. Candidate, Stanford Law School, 2018; M.S. in Computer Science Candidate, Stanford University, 2020.