Entries Tagged "academic papers"

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Stealing ATM PINs with a Thermal Camera

It’s easy:

Researchers from UCSD pointed thermal cameras towards plastic ATM PIN pads and metal ATM PIN pads to test how effective they were at stealing PIN numbers. The thermal cams didn’t work against metal pads but on plastic pads the success rate of detecting all the digits was 80% after 10 seconds and 60% after 45 seconds. If you think about your average ATM trip, that’s a pretty wide window and an embarrassingly high success rate for thieves to take advantage of.

Paper here. More articles.

Posted on August 24, 2011 at 7:13 AM • View Comments

New Attack on AES

“Biclique Cryptanalysis of the Full AES,” by Andrey Bogdanov, Dmitry Khovratovich, and Christian Rechberger.

Abstract. Since Rijndael was chosen as the Advanced Encryption Standard, improving upon 7-round attacks on the 128-bit key variant or upon 8-round attacks on the 192/256-bit key variants has been one of the most difficult challenges in the cryptanalysis of block ciphers for more than a decade. In this paper we present a novel technique of block cipher cryptanalysis with bicliques, which leads to the following results:

  • The first key recovery attack on the full AES-128 with computational complexity 2126.1.
  • The first key recovery attack on the full AES-192 with computational complexity 2189.7.
  • The first key recovery attack on the full AES-256 with computational complexity 2254.4.
  • Attacks with lower complexity on the reduced-round versions of AES not considered before, including an attack on 8-round AES-128 with complexity 2124.9.
  • Preimage attacks on compression functions based on the full AES versions.

In contrast to most shortcut attacks on AES variants, we do not need to assume related-keys. Most of our attacks only need a very small part of the codebook and have small memory requirements, and are practically verified to a large extent. As our attacks are of high computational complexity, they do not threaten the practical use of AES in any way.

This is what I wrote about AES in 2009. I still agree with my advice:

Cryptography is all about safety margins. If you can break n round of a cipher, you design it with 2n or 3n rounds. What we’re learning is that the safety margin of AES is much less than previously believed. And while there is no reason to scrap AES in favor of another algorithm, NST should increase the number of rounds of all three AES variants. At this point, I suggest AES-128 at 16 rounds, AES-192 at 20 rounds, and AES-256 at 28 rounds. Or maybe even more; we don’t want to be revising the standard again and again.

And for new applications I suggest that people don’t use AES-256. AES-128 provides more than enough security margin for the forseeable future. But if you’re already using AES-256, there’s no reason to change.

The advice about AES-256 was because of a 2009 attack, not this result.

Again, I repeat the saying I’ve heard came from inside the NSA: “Attacks always get better; they never get worse.”

Posted on August 18, 2011 at 6:12 AM • View Comments

Search Redirection and the Illicit Online Prescription Drug Trade

Really interesting research.

Search-redirection attacks combine several well-worn tactics from black-hat SEO and web security. First, an attacker identifies high-visibility websites (e.g., at universities) that are vulnerable to code-injection attacks. The attacker injects code onto the server that intercepts all incoming HTTP requests to the compromised page and responds differently based on the type of request:
Requests from search-engine crawlers return a mix of the original content, along with links to websites promoted by the attacker and text that makes the website appealing to drug-related queries.

  • Requests from users arriving from search engines are checked for drug terms in the original search query. If a drug name is found in the search term, then the compromised server redirects the user to a pharmacy or another intermediary, which then redirects the user to a pharmacy.
  • All other requests, including typing the link directly into a browser, return the infected website’s original content.
  • The net effect is that web users are seamlessly delivered to illicit pharmacies via infected web servers, and the compromise is kept hidden from view of the affected host’s webmaster in nearly all circumstances.

Upon inspecting search results, we identified 7,000 websites that had been compromised in this manner between April 2010 and February 2011. One quarter of the top ten search results were observed to actively redirect to pharmacies, and another 15% of the top results were for sites that no longer redirected but had previously been compromised. We also found that legitimate health resources, including authorized pharmacies, were largely crowded out of the top results by search-redirection attacks and blog and forum spam promoting fake pharmacies.

And the paper.

Posted on August 16, 2011 at 10:47 AM • View Comments

Security Flaws in Encrypted Police Radios

“Why (Special Agent) Johnny (Still) Can’t Encrypt: A Security Analysis of the APCO Project 25 Two-Way Radio System,” by Sandy Clark, Travis Goodspeed, Perry Metzger, Zachary Wasserman, Kevin Xu, and Matt Blaze.

Abstract: APCO Project 25a (“P25”) is a suite of wireless communications protocols used in the US and elsewhere for public safety two-way (voice) radio systems. The protocols include security options in which voice and data traffic can be cryptographically protected from eavesdropping. This paper analyzes the security of P25 systems against both passive and active adversaries. We found a number of protocol, implementation, and user interface weaknesses that routinely leak information to a passive eavesdropper or that permit highly efficient and difficult to detect active attacks. We introduce new selective subframe jamming attacks against P25, in which an active attacker with very modest resources can prevent specific kinds of traffic (such as encrypted messages) from being received, while emitting only a small fraction of the aggregate power of the legitimate transmitter. We also found that even the passive attacks represent a serious practical threat. In a study we conducted over a two year period in several US metropolitan areas, we found that a significant fraction of the “encrypted” P25 tactical radio traffic sent by federal law enforcement surveillance operatives is actually sent in the clear, in spite of their users’ belief that they are encrypted, and often reveals such sensitive data as the such sensitive data as the names of informants in criminal investigations.

I’ve heard Matt talk about this project several times. It’s great work, and a fascinating insight into the usability problems of encryption in the real world.

News article.

Posted on August 11, 2011 at 6:19 AM • View Comments

Identifying People by their Writing Style

The article is in the context of the big Facebook lawsuit, but the part about identifying people by their writing style is interesting:

Recently, a team of computer scientists at Concordia University in Montreal took advantage of an unusual set of data to test another method of determining e-mail authorship. In 2003, the Federal Energy Regulatory Commission, as part of its investigation into Enron, released into the public domain hundreds of thousands of employee e-mails, which have become an important resource for forensic research. (Unlike novels, newspapers or blogs, e-mails are a private form of communication and aren’t usually available as a sizable corpus for analysis.)

Using this data, Benjamin C. M. Fung, who specializes in data mining, and Mourad Debbabi, a cyber-forensics expert, collaborated on a program that can look at an anonymous e-mail message and predict who wrote it out of a pool of known authors, with an accuracy of 80 to 90 percent. (Ms. Chaski claims 95 percent accuracy with her syntactic method.) The team identifies bundles of linguistic features, hundreds in all. They catalog everything from the position of greetings and farewells in e-mails to the preference of a writer for using symbols (say, “$” or “%”) or words (“dollars” or “percent”). Combining all of those features, they contend, allows them to determine what they call a person’s “write-print.”

It seems reasonable that we have a linguistic fingerprint, although 1) there are far fewer of them than finger fingerprints, 2) they’re easier to fake. It’s probably not much of a stretch to take that software that “identifies bundles of linguistic features, hundreds in all” and use the data to automatically modify my writing to look like someone else’s.

EDITED TO ADD (8/3): A good criticism of the science behind author recognition, and a paper on how to evade these systems.

Posted on August 3, 2011 at 6:08 AM • View Comments

Breaking the Xilinx Virtex-II FPGA Bitstream Encryption

It’s a power-analysis attack, which makes it much harder to defend against. And since the attack model is an engineer trying to reverse-engineer the chip, it’s a valid attack.

Abstract: Over the last two decades FPGAs have become central components for many advanced digital systems, e.g., video signal processing, network routers, data acquisition and military systems. In order to protect the intellectual property and to prevent fraud, e.g., by cloning an FPGA or manipulating its content, many current FPGAs employ a bitstream encryption feature. We develop a successful attack on the bitstream encryption engine integrated in the widespread Virtex-II Pro FPGAs from Xilinx, using side-channel analysis. After measuring the power consumption of a single power-up of the device and a modest amount of o-line computation, we are able to recover all three different keys used by its triple DES module. Our method allows extracting secret keys from any real-world device where the bitstream encryption feature of Virtex-II Pro is enabled. As a consequence, the target product can be cloned and manipulated at will of the attacker. Also, more advanced attacks such as reverse engineering or the introduction of hardware Trojans become potential threats. As part of the side-channel attack, we were able to deduce certain internals of the hardware encryption engine. To our knowledge, this is the first attack against the bitstream encryption of a commercial FPGA reported in the open literature.

Posted on August 1, 2011 at 12:29 PM • View Comments

Using Science Fiction to Teach Computer Security

Interesting paper: “Science Fiction Prototyping and Security Education: Cultivating Contextual and Societal Thinking in Computer Security Education and Beyond,” by Tadayoshi Kohno and Brian David Johnson.

Abstract: Computer security courses typically cover a breadth of technical topics, including threat modeling, applied cryptography, software security, and Web security. The technical artifacts of computer systems—and their associated computer security risks and defenses—do not exist in isolation, however; rather, these systems interact intimately with the needs, beliefs, and values of people. This is especially true as computers become more pervasive, embedding themselves not only into laptops, desktops, and the Web, but also into our cars, medical devices, and toys. Therefore, in addition to the standard technical material, we argue that students would benefit from developing a mindset focused on the broader societal and contextual issues surrounding computer security systems and risks. We used science fiction (SF) prototyping to facilitate such societal and contextual thinking in a recent undergraduate computer security course. We report on our approach and experiences here, as well as our recommendations for future computer security and other computer science courses.

Posted on August 1, 2011 at 6:03 AM • View Comments

Insurgent Groups Exhibit Learning Curve

Interesting research:

After analyzing reams of publicly available data on casualties from Iraq, Afghanistan, Pakistan and decades of terrorist attacks, the scientists conclude that “insurgents pretty much seemed to be following a progress curve—or a learning curve—that’s very common in the manufacturing literature,” says physicist Neil Johnson of the University of Miami in Florida and lead author of the study.

Paper here.

Posted on July 12, 2011 at 7:13 AM • View Comments

The Problem with Cyber-crime Surveys

Good paper: “Sex, Lies and Cyber-crime Surveys,” Dinei Florêncio and Cormac Herley, Microsoft Research.

Abstract: Much of the information we have on cyber-crime losses is derived from surveys. We examine some of the difficulties of forming an accurate estimate by survey. First, losses are extremely concentrated, so that representative sampling of the population does not give representative sampling of the losses. Second, losses are based on unverified self-reported numbers. Not only is it possible for a single outlier to distort the result, we find evidence that most surveys are dominated by a minority of responses in the upper tail (i.e., a majority of the estimate is coming from as few as one or two responses). Finally, the fact that losses are confined to a small segment of the population magnifies the difficulties of refusal rate and small sample sizes. Far from being broadly-based estimates of losses across the population, the cyber-crime estimates that we have appear to be largely the answers of a handful of people extrapolated to the whole population. A single individual who claims $50,000 losses, in an N=1000 person survey, is all it takes to generate a $10 billion loss over the population. One unverified claim of $7,500 in phishing losses translates into $1.5 billion.

I’ve been complaining about our reliance on self-reported statistics for cyber-crime.

Posted on June 21, 2011 at 5:58 AM • View Comments

Fourth SHB Workshop

I’m at SHB 2011, the fourth Interdisciplinary Workshop on Security and Human Behavior, at Carnegie Mellon University. This is a two-day invitational gathering of computer security researchers, psychologists, behavioral economists, sociologists, political scientists, anthropologists, philosophers, and others—all of whom are studying the human side of security—organized by Alessandro Acquisti, Ross Anderson, and me. It’s not just an interdisciplinary conference; most of the people here are individually interdisciplinary. For the past four years, this has been the most intellectually stimulating conference I have attended.

Here is the program. The list of attendees contains links to readings from each of them—definitely a good place to browse for more information on this topic.

Ross Anderson is liveblogging this event. Matt Blaze is taping the sessions; I’ll link to them if he puts them up on the Internet.

Here are links to my posts on the first, second, and third SHB workshops. Follow those links to find summaries, papers, and audio recordings of the workshops.

Posted on June 18, 2011 at 1:06 PM • View Comments

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Sidebar photo of Bruce Schneier by Joe MacInnis.