Today we present an updated version of our paper examining how the ubiquitous use of online tracking cookies can allow an adversary conducting network surveillance to target a user or surveil users en masse. In the initial version of the study, summarized below, we examined the technical feasibility of the attack. Now we’ve made the attack model more complete and nuanced as well as analyzed the effectiveness of several browser privacy tools in preventing the attack. Finally, inspired by Jonathan Mayer and Ed Felten’s The Web is Flat study, we incorporate the geographic topology of the Internet into our measurements of simulated web traffic and our adversary model, providing a more realistic view of how effective this attack is in practice. [Read more...]
Today, the vulnerable state of electronic communications security dominates headlines across the globe, while surveillance, money and power increasingly permeate the ‘cybersecurity’ policy arena. With the stakes so high, how should communications security be regulated? Deirdre Mulligan (UC Berkeley), Ashkan Soltani (independent, Washington Post), Ian Brown (Oxford) and Michel van Eeten (TU Delft) weighed in on this proposition at an expert panel on my doctoral project at the Amsterdam Information Influx conference. [Read more...]
[Let's welcome new CITP blogger Pete Zimmerman, a first-year graduate student in the computer security group at Princeton. — Arvind Narayanan]
Following the revelations of wide-scale surveillance by US intelligence agencies and their allies, a myriad of services offering end-to-end encrypted communications have cropped up to take advantage of the increasing demand for privacy from surveillance. When coupled with anonymity, end-to-end encryption can prevent a central service provider from obtaining any information about its users or their communications. However, maintaining anonymity is difficult while simultaneously offering a straightforward way for users to find each other.
Enter Wickr. This startup offers a simple app featuring “military grade encryption” of text, photo, video, and voice messages as well as anonymous registration for its users. Wickr claims that it cannot identify who has registered with the service or which of its users are communicating with each other. During registration, users enter their email address and/or phone number (non-Wickr IDs). The app utilizes a cryptographic hash function (SHA-256 in this case) to obtain “anonymous” Wickr IDs from the non-Wickr IDs. Wickr IDs are then stored server-side and used for discovery. When your friends want to find you, they enter your phone number or email address, which is then put through the same hash function, resulting in the same output (Wickr ID). Wickr looks this up in its database to determine if you’ve registered with the service to facilitate message exchange. This process simplifies the discovery of other users, supposedly without Wickr having the ability to identify the users of the anonymous service.
The problem here is that while it’s not always possible to determine the input to a hash function given the output, we can leverage the fact that the same input always yields the same output. If the number of possible inputs is small, we can simply try all of them. Unfortunately, this is a recurring theme in a variety of applications as a result of misunderstanding cryptography — specifically, the fact that hash functions are not one-way if the input space is small. A great explanation on the use of cryptographic hash functions in attempts to anonymize data can be found here.
Yesterday we saw two stories that illustrate the limits of cryptography as a shield against government. In San Francisco, police arrested a man alleged to be Dread Pirate Roberts (DPR), the operator of online drug market Silk Road. And in Alexandria, Virginia, a court unsealed documents revealing the tussle between the government and secure email provider Lavabit.
On Monday, Ed wrote about Software Transparency, the idea that software is more resistant to intentional backdoors (and unintentional security vulnerabilities) if the process used to create it is transparent. Elements of software transparency include the availability of source code and the ability to read or contribute to a project’s issue tracker or internal developer discussion. He mentioned a case that I want to discuss in detail: in 2008, the Debian Project (a popular Linux distribution used for many web servers) announced that the pseudorandom number generator in Debian’s version of OpenSSL was broken and insecure.
Thanks to the recent NSA leaks, people are more worried than ever that their software might have backdoors. If you don’t believe that the software vendor can resist a backdoor request, the onus is on you to look for a backdoor. What you want is software transparency.
Transparency of this type is a much-touted advantage of open source software, so it’s natural to expect that the rise of backdoor fears will boost the popularity of open source code. [Read more...]