Archive for 2013

Karsten Nohl visits UVa

Friday, November 1st, 2013

Karsten Nohl, who complete a PhD in our group in 2009, is visiting UVa this week. UVa Today has an article: Renowned ‘White Hat Hacker’ to Speak on Real-World Security Holes:

University of Virginia graduate Karsten Nohl, one of the world’s most famous “white hat computer hackers,” will speak Friday at 3:30 p.m. in Rice Hall, room 130, about lessons learned from the security holes that he and fellow researchers have uncovered in mobile phones, wireless car keys and other technology used by billions of people everyday.

Nohl first made international headlines in 2008, while still a computer engineering doctoral student at U.Va., for research that exposed vulnerabilities in the world’s most popular smartcard, used by millions of people to pay fares on several major mass-transit systems around the world, including the London Underground and the Boston subway.

Such cards utilize miniscule wireless computer chips, about the size of a grain of rice, called RFIDs, short for “radio-frequency identification.” They send and receive information over short distances (generally 10 feet or less) via very low-power radio waves.

As an ethical security researcher, often called a “white hat hacker,” Nohl exposes vulnerabilities to spur improvements in the systems that he researches. He now does such work around the world as the founder and director of research at Security Research Labs in Berlin.

To prevent those with nefarious purposes from exploiting security holes he uncovers, Nohl typically withholds key details of the exploit and discloses his findings only months after sharing his research with the relevant manufacturers or trade organizations to allow them to roll out upgrades or countermeasures to mitigate the security risk.

Since graduating from U.Va. in August 2008, Nohl has gone on to discover and demonstrate two key security vulnerabilities in mobile phones – encryption flaws in both the GSM protocol that most cell phones use to communicate with cell towers, and in SIM cards, the tiny “subscriber identity module” chip in every phone that identifies and authenticates the phone.

Both discoveries generated worldwide media coverage.

As just one example of possible ramifications, the latter security hole could allow a malicious hacker to send a virus through a text message, which could then allow the hacker to eavesdrop on calls or make purchases through mobile payment systems.

“Karsten has had an outstanding impact in analyzing how cryptography gets used in the real world and demonstrating what goes wrong when important engineering principles are not followed carefully,” said computer science professor David Evans, Nohl’s former doctoral adviser and a co-organizer of Friday’s talk. “The vulnerabilities he has identified in RFID algorithms, GSM encryption and SIM cards impact billions of devices most of us use every day, and it’s really important that people understand the security weaknesses in these systems and that vendors work to improve them. Karsten’s work is a fundamental step toward those goals.”

Nohl’s talk will discuss how security exploits with real-world implications are usually enabled by not just one design flaw, but by deviations from best practices on multiple design layers. Protection designs that focus on a single security function and neglect complementary layers are more prone to compromise, Nohl will argue, with examples from his own research on three widely deployed technologies – cell phones, car keys and smartcards.

“Real-world cryptographic systems rarely meet academic expectations, with most systems being shown ‘insecure’ at some point,” Nohl said in an email description of his talk. “At the same time, our IT-driven world has not yet fallen apart, suggesting that many protection mechanisms are ‘secure enough’ for how they are employed.”

The talk will be followed by a reception in the fourth-floor atrium of Rice Hall.

The event is co-sponsored by the departments of Computer Science and Electrical and Computer Engineering, which jointly administer U.Va.’s computer engineering Program in the School of Engineering and Applied Science.

Engineering Cryptosystems

Wednesday, October 30th, 2013

I gave a four-session “mini-course” for Microstrategy on Engineering Cryptosystems. It ended up attracting enough interest to be moved from their offices to a nearby movie theater!

The course was targeted to engineers at Microstrategy with no prior experience with cryptography, and designed to give them some ideas of the power of modern cryptography, and to provide enough stories about cryptosystems going bad to convince them not do try to develop their own cryptosystems, and to know enough to ask the right questions of people who do.

The four main topics were:

Since it was in a movie theater, it also provided an opportunity to officially screen this trailer in a real movie theater:

Explicating SDKs

Thursday, June 27th, 2013

Security exploits nearly always stem from attackers finding ways to violate assumptions system implementers relied upon. As a simple example, consider a classic buffer overflow attack which is possible because the implementers assumed (perhaps implicitly) that the size of some data could not exceed the buffer size, but an attacker found a way to create an input that violates that assumption.

In this work, joint with colleagues at Microsoft Research, we consider the implicit assumptions upon which secure use of single sign-on SDKs depends. Our study of three important authentication and authorization SDKs (including Facebook’s) supports the need for systematically explicating SDKs to uncover these assumptions. We found assumptions that were critical to secure use of the SDKs, but that were not clearly documented and were subtle enough to be missed by the majority of tested apps.

We advocate that a systematic explication process for uncovering these assumptions should be part of the engineering process for developing security-critical SDKs.

For details, see our paper:

Rui Wang, Yuchen Zhou, Shuo Chen, Shaz Qadeer, David Evans, and Yuri Gurevich. Explicating SDKs: Uncovering Assumptions Underlying Secure Authentication and Authorization. 22nd USENIX Security Symposium, Washington DC, 14-16 August 2013. [PDF, 16 pages]

Symmetric Cut-and-Choose

Friday, June 14th, 2013

Our paper on symmetric cut-and-choose is now available. The paper will be presented at CRYPTO 2013 in August.

Abstract. Beginning with the work of Lindell and Pinkas, researchers have proposed several protocols for secure two-party computation based on the cut-and-choose paradigm. In existing instantiations of this paradigm, one party generates k garbled circuits; some fraction of those are “checked” by the other party, and the remaining fraction are evaluated. We introduce here the idea of symmetric cut-and-choose protocols, in which both parties generate k circuits to be checked by the other party. The main advantage of our technique is that k can be reduced by a factor of 3 while attaining the same statistical security level as in prior work. Since the number of garbled circuits dominates the costs of the protocol, especially as larger circuits are evaluated, our protocol is expected to run up to 3 times faster than existing schemes. Preliminary experiments validate this claim.

Full paper (16 pages): [PDF]

Congratulations SRG Graduates

Monday, May 27th, 2013

Congratulations to the 2013 SRG Graduates!

Tianhao Tong (MCS), Dr. Yan Huang (PhD)

Jonathan Burket (BACS with Highest Distinction), William Melicher (BSCS, not pictured)

Stephen Colbert on Jefferson’s Wheel!

Wednesday, May 22nd, 2013

Stephen Colbert spoke about Jefferson’s wheel cipher at his valediction speech:

Congratulations Jonathan!

Monday, May 6th, 2013

Jonathan Burket has been recognized with a CRA Outstanding Undergraduate Researcher Honorable Mention. This award recognizes outstanding research by undergraduate students in North America.

Jonathan joined our research group as a first year student (recruited from cs1120) and has done several research projects focused on web security including working on GuardRails and leading a new research project on correlating web application state and requests with behavior such as database requests.

Congratulations to Jonathan!


Thursday, May 2nd, 2013

UVa Today has an article about my talk yesterday on open education: Evans: U.Va. Should Be a Global Leader in MOOCS, Online Learning, UVaToday, 1 May 2013. The article focuses just on the last slide, which is my proposal for what UVa should do.

The full talk is available at and below:

Trusted Password Entry

Saturday, April 20th, 2013

Fraudulent mobile applications could trick users into entering sensitive passwords, and then send those passwords to rogue site operators. With current technologies, users have no way of knowing that when they enter a password it is going to the intended application. What is needed is a trusted path for password entry, so when users enter a password they can trust that it will only be visible to the trusted provider.

This paper presents a solution that does not require any modifications to existing apps or application servers, but modifies the Android kernel to establish a shared secret between the user and kernel as part of the boot process, and then uses that shared secret to provide a trusted path for password entry.

Tianhao Tong will present the paper at Moble Security Technologies (MoST) in San Francisco, CA, 23 May 2013.

Paper: Tianhao Tong and David Evans. GuarDroid: A Trusted Path for Password Entry. In Moble Security Technologies (MoST), San Francisco, CA, 23 May 2013. [PDF, 10 pages]


Circuit Structures for Improving Efficiency of Security and Privacy Tools

Monday, March 4th, 2013

Samee Zahur and I have written a paper on Circuit Structures for Improving Efficiency of Security and Privacy Tools. The paper explores ways to design static circuits (as used in garbled circuit protocols and symbolic execution, among other things) to provide reasonable efficiency for algorithms that use common data structures like arrays. By taking advantage of somewhat predictable access patterns, as well as batching, our circuit structures are able to provide operations with amortized cost that is polylogarithmic in the size of the data structure (in contrast to naive approaches that would require effectively copying the entire data structure for each operation). Samee will present the paper at the IEEE Symposium on Security and Privacy (“Oakland”) in San Francisco in May.

Full paper (15 pages): [PDF]