Saving Your Cryptographic Front Door

Does the Fourth Amendment protect SSL keys? Not really, argues the executive branch in Lavabit’s appeal. “[A] business cannot prevent the execution of a search warrant by locking its front gate.”1

True enough. But a business does have a constitutional right to keep that gate intact. When executing a warrant, officers must ordinarily announce themselves and afford an opportunity to open up.

What’s In Your Metadata?

Original at Stanford CIS.

Co-authored with Patrick Mutchler. This is a project of the Stanford Security Lab.

We’re studying the National Security Agency, and we need your help.

The NSA has confirmed that it collects American phone records. Defenders of the program insist it has little privacy impact and is “not surveillance.”

Like many computer scientists, we strongly disagree. Phone metadata is inherently revealing. We want to rigorously prove it—for the public, for Congress, and for the courts.

That’s where you come in. We’re crowdsourcing the data for our study. We’ll measure how much of your Facebook information can be inferred from your phone records.

Participation takes just a few minutes. You’re eligible if you’re in the United States, use an Android smartphone, and have a Facebook account.

To get started, grab the MetaPhone app from Google Play.

Why Data Center Tapping is (Legally) Different

Last week the Washington Post broke news that the National Security Agency has collected international traffic between Google and Yahoo data centers. I happened to be delivering a course lecture on signals intelligence the same day, so I made brief mention of the program—and how it appears particularly aggressive under the Fourth Amendment.

A sharp student pressed for specifics. How, he asked, could data center tapping be more legally questionable than previously leaked surveillance initiatives? This post is an expanded and refined version of my response.

In short: The firms evade Fourth Amendment pitfalls of citizenship, personal interest, and metadata. They also have enough evidence to establish standing. Finally, the NSA would have difficulty demonstrating that its surveillance was reasonable.


The Web Is Flat

Consider this a bug report for the National Security Agency and its overseers. Dragnet online surveillance may be directed at international activity. But it nonetheless ensnares ordinary Americans as they browse domestic websites.

The spy outfit admits to vacuuming vast quantities of network traffic as it passes through the United States. Some taps are on the nation’s borders; others are on the domestic Internet backbone. International partner agencies, most prominently the UK’s Government Communications Headquarters, contribute to the NSA’s reach. Recent leaks have provided substantial detail: Under the Marina program, the agency appears to retain web browsing activity for a year.1 The XKeyscore system offers at least one way for analysts at the NSA and cooperating services to efficiently query both historical and realtime data.

Agency apologists are quick to point out that the snooping has limits. The NSA only acquires online communications when a sender or recipient seems international. Doing otherwise might, in their view, violate congressional restrictions or constitutional protections.

Tough luck for foreigners. But if you’re within the United States, the notion goes, you don’t have much cause for concern.

That’s wrong. Americans routinely send personal data outside the country. They just might not know it.

Do Not Track in California

Both houses of the California legislature have unanimously approved AB 370, a Do Not Track initiative that is backed by Attorney General Harris. If Governor Brown signs the bill, it will be the first Do Not Track law worldwide. So, what would it do? More and less than a casual reader might expect.

Legislating NSA Crypto Circumvention

The National Security Agency works to circumvent cryptography. In the abstract, that’s hardly objectionable—legitimate intelligence targets may adopt security measures. Concerns arise, however, when the NSA subverts the technologies that ordinary consumers and businesses rely upon. Longstanding conventional wisdom in the computer security community has been that the NSA works to insert backdoors into crypto standards and security products, and that the agency hoards vulnerabilities in popular crypto algorithms and implementations. Widely read reports recently confirmed these views.

The go-to recommendation among many security experts has been deployment of additional protective measures. That’s an appealing near-term option for sophisticated users and companies. It’s largely impractical for ordinary users, however. And adding more crypto won’t restore damaged trust, shut potentially risky backdoors, or patch vulnerable systems.

Advancing Empirical Legal Scholarship: Federal Trial Opinions and Rules

In earlier posts I have shared XML versions of certain legal materials, including federal statutes, appellate opinions, and appellate rules. My aim has been to assist empirical legal scholars by providing machine-readable government documents.

Additional legal materials accompany this post, including federal trial-level opinions and rules. Suggestions from the research community remain very much welcome.


Next Steps for the Firefox Cookie Policy

Consumers neither expect nor approve of web tracking.1 Mozilla has been a frequent advocate for its users, advancing technologies that signal preferences (Do Not Track), lend transparency (Collusion), and facilitate privacy-friendly web services (Persona and Social API). Last fall, the Mozilla community began a concerted effort in a new direction: technical countermeasures against tracking.2 One of our first projects has been a revision of the Firefox cookie policy.3

Cookie policies are inherently imprecise. Some unwanted tracking cookies might slip through, compromising user privacy (“underblocking”). And some non-tracking cookies might get blocked, breaking the web experience (“overblocking”). The challenge in designing a cookie policy is calibrating the tradeoff between underblocking and overblocking.4

The patch that I developed is an intentionally cautious first step: it aims to substantially reduce underblocking with little (if any) overblocking. The revised policy is so cautious, it isn’t even new: it’s drawn directly from Safari.5 Almost every iPhone, iPad, and iPod Touch user is already running the revised Firefox cookie policy. Web engineers are already familiar with designing to accomodate the policy. The notion is simple: start by raising Firefox to the present best practice among competing browsers, then iteratively innovate improvements.

Firefox’s revised cookie policy landed in the pre-alpha build in late February. Since then, Mozillans and I have carefully monitored bug reports. It appears that we achieved our aim: there are only two confirmations of inadvertent breakage.6 We did not hear any novel concerns when the patch advanced to alpha in early April. This past week, Mozilla’s CTO requested a hold on the revised policy for an extra release cycle to measure its performance. At the same time, he reaffirmed that Mozilla is “committed to user privacy” and “committed to shipping a version of the patch that is ‘on’ by default.”

I agree that we should be quantitatively rigorous in our approach to iterating the Firefox cookie policy. An extra six-week release cycle will allow us to further validate our hypothesis that the patch delivers improved privacy without breakage,7 as well as lay the groundwork for future updates. Going forwards, our challenge will be to understand and improve the underblocking and overblocking properties of the Firefox cookie policy.

Advancing Empirical Legal Scholarship: Federal Appellate Opinions and Rules

Last December I shared XML versions of the U.S. Code and Supreme Court opinions through early 2012. My intent was and remains to facilitate empirical legal scholarship by providing government-authored materials in a machine-readable format.

This post is accompanied by additional documents: opinions and rules of various federal appellate tribunals. As before, I welcome feedback from the academic research community.