Filed under Measurement

Is Instacart Deceptive?

A few weeks ago, a Stanford colleague stormed into my office. He had ordered some groceries from Instacart, a buzzy get-it-now startup that recently raised $44 million. My friend thought he had paid a flat $3.99 for delivery from a local store. In fact, he had paid about $20 net of store prices. How, he fumed, could this be legal? From a quick Googling, he isn’t the only one steamed about Instacart’s subtle surcharge.

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MetaPhone: The Sensitivity of Telephone Metadata

Co-authored by Patrick Mutchler.

Is telephone metadata sensitive? The debate has taken on new urgency since last summer’s NSA revelations; all three branches of the federal government are now considering curbs on access. Consumer privacy concerns are also salient, as the FCC assesses telecom data sharing practices.

President Obama has emphasized that the NSA is “not looking at content.” “[T]his is just metadata,” Senator Feinstein told reporters. In dismissing the ACLU’s legal challenge, Judge Pauley shrugged off possible sensitive inferences as a “parade of horribles.”

On the other side, a number of computer scientists have expressed concern over the privacy risks posed by metadata. Ed Felten gave a particularly detailed explanation in a declaration for the ACLU: “Telephony metadata can be extremely revealing,” he wrote, “both at the level of individual calls and, especially, in the aggregate.” Holding the NSA’s program likely unconstitutional, Judge Leon credited this view and noted that “metadata from each person’s phone ‘reflects a wealth of detail about her familial, political, professional, religious, and sexual associations.’”

This is, at base, a factual dispute. Is it easy to draw sensitive inferences from phone metadata? How often do people conduct sensitive matters by phone, in a manner reflected by metadata?
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MetaPhone: The NSA’s Got Your Number

Co-authored with Patrick Mutchler.

MetaPhone is a crowdsourced study of phone metadata. If you own an Android smartphone, please consider participating. In earlier posts, we reported how automated analysis of call and text activity can reveal private relationships, as well as how phone subscribers are closely interconnected.

“You have my telephone number connecting with your telephone number,” explained President Obama in a PBS interview. “[T]here are no names . . . in that database.”

Versions of this argument have appeared frequently in debates over the NSA’s domestic phone metadata program. The factual premise is that the NSA only compels disclosure of numbers, not names. One might conclude, then, that there isn’t much cause for privacy concern.
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MetaPhone: The NSA Three-Hop

Co-authored with Patrick Mutchler.

MetaPhone is a crowdsourced study of phone metadata. If you own an Android smartphone, please consider participating. In an earlier post, we reported how automated analysis of call and text activity can detect private relationships.

Does the National Security Agency have court authority to pore over your phone records? Quite possibly.
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MetaPhone: Seeing Someone?

Co-authored with Patrick Mutchler.

Two weeks ago we kicked off the MetaPhone project, a crowdsourced study of phone metadata. Our aim is to inform policy and legal debates surrounding dragnet surveillance programs. We are exceedingly grateful to the hundreds of users who have joined. If you have not yet participated, you can still grab the MetaPhone app for Android.

Today we are excited to share some preliminary results: We can predict many romantic relationships. Automatically. Using solely phone metadata.
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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.

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.
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Presidential Identifying Information

Sunday’s New York Times included a story about how the presidential campaigns are making extensive use of third-party web trackers. In response to privacy concerns, “[o]fficials with both campaigns emphasize[d] that [tracking] data collection is ‘anonymous.’”1

The campaigns are wrong: tracking data is very often identified or identifiable. Arvind Narayanan has previously written a comprehensive and accessible explanation of why web tracking is hardly anonymous; my survey paper on web tracking provides more extensive discussion.

One of the ways in which web tracking data can become identified or identifiable is “leakage”—data flowing to trackers from the websites that users interact with. Leakage most commonly occurs when a website includes identifying information in a page URL or title. Embedded third parties receive the identifying information if they receive the URL (e.g. referrer headers) or the title (e.g. document.title). Even a little identifying information leakage thoroughly undermines the privacy properties of web tracking: once a user’s identity leaks to a tracker, all of the tracker’s past, present, and future data about the user becomes identifiable.

Web services frequently fail to account for information leakage in their design and testing; a study I conducted last year found that over half of popular websites were leaking identifying information.2 More than a few website operators have made inaccurate representations about the information they share with third parties; in just the past year the Federal Trade Commission settled deception claims against both Facebook and Myspace for falsely disclaiming identifying information leakage.

The Times coverage piqued my curiosity: Are the campaigns identifying their supporters to third-party trackers? Are they directly undermining the anonymity properties that they are so quick to invoke?

Yes, they are. I tested the two leading candidate websites using the methodology from my prior study of identifying information leakage. Both leak. The following sections describe my observations from the Barack Obama and Mitt Romney campaign websites.
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Setting the Record Straight on Google’s Safari Tracking

Our recent research on Google’s circumvention of the Safari cookie blocking feature has led to some confusion, in part owing to the company’s statement in response (reproduced in its entirety below). This post is an attempt to elucidate the central issues. As with the original writeup, I aim for a neutral viewpoint in the interest of establishing a common factual understanding.

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Safari Trackers

Apple’s Safari web browser is configured to block third-party cookies by default. We identified four advertising companies that unexpectedly place trackable cookies in Safari. Google and Vibrant Media intentionally circumvent Safari’s privacy feature. Media Innovation Group and PointRoll serve scripts that appear to be derived from circumvention example code.

In the interest of clearly establishing facts on the ground, this post provides technical analysis of Safari’s cookie blocking feature and the four companies’ practices. It does not address policy or legal issues. (More on that soon.)

Before proceeding further, I want to thank the countless friends and colleagues who provided invaluable feedback on this project. In particular: ★★★★★, whose insights have been vital at every step, and Ashkan Soltani, whose crawling data was instrumental in uncovering PointRoll’s practices and understanding the prevalence of cookie blocking circumvention.

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