NACDL

If the government seizes a computer during one criminal investigation, can it go ahead and search for evidence of a completely different crime?

Because Fourth Amendment jurisprudence has evolved around traditional notions of physical property and common law trespass, its application to new technologies has been an ongoing challenge for the courts.¹ It is well-settled that people generally have a reasonable expectation of privacy in their personal computers,² but forensic examinations — a key component of many police investigations — raise some difficult questions. One common forensic technique is the use of a cryptographic hash to verify or analyze digital evidence taken from a computer. This article examines whether the Fourth Amendment applies to hashing, and suggests ways to argue that evidence should be suppressed if the government uses a hash to search a client’s computer without a warrant.

What’s a Hash?

A hash value is created when a computer program analyzes digital information an