It's Time to Drop the "Expectation of Privacy" Test
By Bruce Schneier
In the United States, the concept of "expectation of privacy" matters because it's the constitutional test, based on the Fourth Amendment, that governs when and how the government can invade your privacy.
Based on the 1967 Katz v. United States Supreme Court decision, this test actually has two parts. First, the government's action can't contravene an individual's subjective expectation of privacy; and second, that expectation of privacy must be one that society in general recognizes as reasonable. That second part isn't based on anything like polling data; it is more of a normative idea of what level of privacy people should be allowed to expect, given the competing importance of personal privacy on one hand and the government's interest in public safety on the other.
The problem is, in today's information society, that definition test will rapidly leave us with no privacy at all.
In Katz, the Court ruled that the police could not eavesdrop on a phone call without a warrant: Katz expected his phone conversations to be private and this expectation resulted from a reasonable balance between personal privacy and societal security. Given NSA's large-scale warrantless eavesdropping, and the previous administration's continual insistence that it was necessary to keep America safe from terrorism, is it still reasonable to expect that our phone conversations are private?
Between the NSA's massive internet eavesdropping program and Gmail's content-dependent advertising, does anyone actually expect their e-mail to be private? Between calls for ISPs to retain user data and companies serving content-dependent web ads, does anyone expect their web browsing to be private? Between the various computer-infecting malware, and world governments increasingly demanding to see laptop data at borders, hard drives are barely private. I certainly don't believe that my SMSes, any of my telephone data, or anything I say on LiveJournal or Facebook -- regardless of the privacy settings -- is private.
Aerial surveillance, data mining, automatic face recognition, terahertz radar that can "see" through walls, wholesale surveillance, brain scans, RFID, "life recorders" that save everything: Even if society still has some small expectation of digital privacy, that will change as these and other technologies become ubiquitous. In short, the problem with a normative expectation of privacy is that it changes with perceived threats, technology and large-scale abuses.
Clearly, something has to change if we are to be left with any privacy at all. Three legal scholars have written law review articles that wrestle with the problems of applying the Fourth Amendment to cyberspace and to our computer-mediated world in general.
George Washington University's Daniel Solove, who blogs at Concurring Opinions, has tried to capture the byzantine complexities of modern privacy. He points out, for example, that the following privacy violations -- all real -- are very different: A company markets a list of 5 million elderly incontinent women; reporters deceitfully gain entry to a person's home and secretly photograph and record the person; the government uses a thermal sensor device to detect heat patterns in a person's home; and a newspaper reports the name of a rape victim. Going beyond simple definitions such as the divulging of a secret, Solove has developed a taxonomy of privacy, and the harms that result from their violation.
His 16 categories are: surveillance, interrogation, aggregation, identification, insecurity, secondary use, exclusion, breach of confidentiality, disclosure, exposure, increased accessibility, blackmail, appropriation, distortion, intrusion and decisional interference. Solove's goal is to provide a coherent and comprehensive understanding of what is traditionally an elusive and hard-to-explain concept: privacy violations. (This taxonomy is also discussed in Solove's book, Understanding Privacy.)
Orin Kerr, also a law professor at George Washington University, and a blogger at Volokh Conspiracy, has attempted to lay out general principles for applying the Fourth Amendment to the internet. First, he points out that the traditional inside/outside distinction -- the police can watch you in a public place without a warrant, but not in your home -- doesn't work very well with regard to cyberspace. Instead, he proposes a distinction between content and non-content information: the body of an e-mail versus the header information, for example. The police should be required to get a warrant for the former, but not for the latter. Second, he proposes that search warrants should be written for particular individuals and not for particular internet accounts.
Meanwhile, Jed Rubenfeld of Yale Law School has tried to reinterpret (.pdf) the Fourth Amendment not in terms of privacy, but in terms of security. Pointing out that the whole "expectations" test is circular -- what the government does affects what the government can do -- he redefines everything in terms of security: the security that our private affairs are private.
This security is violated when, for example, the government makes widespread use of informants, or engages in widespread eavesdropping -- even if no one's privacy is actually violated. This neatly bypasses the whole individual privacy versus societal security question -- a balancing that the individual usually loses -- by framing both sides in terms of personal security.
I have issues with all of these articles. Solove's taxonomy is excellent, but the sense of outrage that accompanies a privacy violation -- "How could they know/do/say that!?" -- is an important part of the harm resulting from a privacy violation. The non-content information that Kerr believes should be collectible without a warrant can be very private and personal: URLs can be very personal, and it's possible to figure out browsed content just from the size of encrypted SSL traffic. Also, the ease with which the government can collect all of it -- the calling and called party of every phone call in the country -- makes the balance very different. I believe these need to be protected with a warrant requirement. Rubenfeld's reframing is interesting, but the devil is in the details. Reframing privacy in terms of security still results in a balancing of competing rights. I'd rather take the approach of stating the -- obvious to me -- individual and societal value of privacy, and giving privacy its rightful place as a fundamental human right. (There's additional commentary on Rubenfeld's thesis at ArsTechnica.)
The trick here is to realize that a normative definition of the expectation of privacy doesn't need to depend on threats or technology, but rather on what we -- as society -- decide it should be. Sure, today's technology make it easier than ever to violate privacy. But it doesn't necessarily follow that we have to violate privacy. Today's guns make it easier than ever to shoot virtually anyone for any reason. That doesn't mean our laws have to change.
No one knows how this will shake out legally. These three articles are from law professors; they're not judicial opinions. But clearly something has to change, and ideas like these may someday form the basis of new Supreme Court decisions that brings legal notions of privacy into the 21st century.
Schneier.com is a personal website. Opinions expressed are not necessarily those of Co3 Systems, Inc.