A significant amount of media attention about the Playpen cases has focused on a curious argument. A minority of the judges have held that the the Playpen searches were constitutional because they weren’t searches at all. According to this argument, a person has no Fourth Amendment rights in IP addresses. Because the most important information obtained by the NIT was IP addresses, use of the NIT was not a search and no Fourth Amendment rights were violated. As far as I can tell, the government has not actually made this argument. Rather, it is a position introduced by one judge and then adopted by some others.

This argument is clearly wrong, though. Individuals have Fourth Amendment rights in information stored inside their computers unless they voluntarily share the information. A person using Tor has not voluntarily shared his IP address with the websites he visits. Indeed, the absence of voluntarily sharing is precisely what led the government to surreptitiously obtain the information using the NIT. Given that a Tor user has not voluntarily shared his IP address, it doesn’t matter that obtaining an IP address from a third party or a visited website would not be a search in other circumstances that did involve voluntarily sharing.

Put another way, it’s the way of obtaining information that makes the act a search, not the information itself in the abstract. This point is obvious in the physical world. See Arizona v. Hicks, 480 U.S. 321 , 325 (1987) (“A search is a search, even if it happens to disclose nothing but the bottom of a turntable.”). It should be equally obvious with computers. If the police want to read today’s newspaper, they can’t break into my house and open my desk drawer to find my copy without committing a search. The fact that they could have read the newspaper by finding a copy in public doesn’t mean they can break into my house to read mine. Similarly, the fact that IP addresses may be available without searching a target in some cases doesn’t mean they can break into his computer to find the IP address without committing a search.