academic papers Archives - Page 71 of 86

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Page 71 of 86

Secret Questions

Interesting research:

Analysing our data for security, though, shows that essentially all human-generated names provide poor resistance to guessing. For an attacker looking to make three guesses per personal knowledge question (for example, because this triggers an account lock-down), none of the name distributions we looked at gave more than 8 bits of effective security except for full names. That is, about at least 1 in 256 guesses would be successful, and 1 in 84 accounts compromised. For an attacker who can make more than 3 guesses and wants to break into 50% of available accounts, no distributions gave more than about 12 bits of effective security. The actual values vary in some interesting ways-South Korean names are much easier to guess than American ones, female first names are harder than male ones, pet names are slightly harder than human names, and names are getting harder to guess over time.

I’ve written about this problem.

EDITED TO ADD (4/13): xkcd on the secret question.

Posted on March 16, 2010 at 6:44 AM • View Comments

Typosquatting

“Measuring the Perpetrators and Funders of Typosquatting,” by Tyler Moore and Benjamin Edelman:

Abstract. We describe a method for identifying “typosquatting”, the intentional registration of misspellings of popular website addresses. We estimate that at least 938 000 typosquatting domains target the top 3 264 .com sites, and we crawl more than 285 000 of these domains to analyze their revenue sources. We find that 80% are supported by pay-per-click ads often advertising the correctly spelled domain and its competitors.Another 20% include static redirection to other sites. We present an automated technique that uncovered 75 otherwise legitimate websites which benefited from direct links from thousands of misspellings of competing websites. Using regression analysis, we find that websites in categories with higher pay-per-click ad prices face more typosquatting registrations, indicating that ad platforms such as Google AdWords exacerbate typosquatting. However, our investigations also confirm the feasibility of signicantly reducing typosquatting. We find that typosquatting is highly concentrated: Of typo domains showing Google ads, 63% use one of five advertising IDs, and some large name servers host typosquatting domains as much as four times as often as the web as a whole.

The paper appeared at the Financial Cryptography conference this year.

Posted on March 15, 2010 at 6:13 AM • View Comments

The Limits of Identity Cards

Good legal paper on the limits of identity cards: Stephen Mason and Nick Bohm, “Identity and its Verification,” in Computer Law & Security Review, Volume 26, Number 1, Jan 2010.

Those faced with the problem of how to verify a person’s identity would be well advised to ask themselves the question, ‘Identity with what?’ An enquirer equipped with the answer to this question is in a position to tackle, on a rational basis, the task of deciding what evidence will be useful for the purpose. Without the answer to the question, the verification of identity becomes a sadly familiar exercise in blind compliance with arbitrary rules.

Posted on March 10, 2010 at 7:09 AM • View Comments

De-Anonymizing Social Network Users

Interesting paper: “A Practical Attack to De-Anonymize Social Network Users.”

Abstract. Social networking sites such as Facebook, LinkedIn, and Xing have been reporting exponential growth rates. These sites have millions of registered users, and they are interesting from a security and privacy point of view because they store large amounts of sensitive personal user data.

In this paper, we introduce a novel de-anonymization attack that exploits group membership information that is available on social networking sites. More precisely, we show that information about the group memberships of a user (i.e., the groups of a social network to which a user belongs) is often sufficient to uniquely identify this user, or, at least, to significantly reduce the set of possible candidates. To determine the group membership of a user, we leverage well-known web browser history stealing attacks. Thus, whenever a social network user visits a malicious website, this website can launch our de-anonymization attack and learn the identity of its visitors.

The implications of our attack are manifold, since it requires a low effort and has the potential to affect millions of social networking users. We perform both a theoretical analysis and empirical measurements to demonstrate the feasibility of our attack against Xing, a medium-sized social network with more than eight million members that is mainly used for business relationships. Our analysis suggests that about 42% of the users that use groups can be uniquely identified, while for 90%, we can reduce the candidate set to less than 2,912 persons. Furthermore, we explored other, larger social networks and performed experiments that suggest that users of Facebook and LinkedIn are equally vulnerable (although attacks would require more resources on the side of the attacker). An analysis of an additional five social networks indicates that they are also prone to our attack.

News article. Moral: anonymity is really, really hard—but we knew that already.

Posted on March 8, 2010 at 6:13 AM • View Comments

Man-in-the-Middle Attack Against Chip and PIN

Nice attack against the EMV—Eurocard Mastercard Visa—the “chip and PIN” credit card payment system. The attack allows a criminal to use a stolen card without knowing the PIN.

The flaw is that when you put a card into a terminal, a negotiation takes place about how the cardholder should be authenticated: using a PIN, using a signature or not at all. This particular subprotocol is not authenticated, so you can trick the card into thinking it’s doing a chip-and-signature transaction while the terminal thinks it’s chip-and-PIN. The upshot is that you can buy stuff using a stolen card and a PIN of 0000 (or anything you want). We did so, on camera, using various journalists’ cards. The transactions went through fine and the receipts say “Verified by PIN”.

[…]

So what went wrong? In essence, there is a gaping hole in the specifications which together create the “Chip and PIN” system. These specs consist of the EMV protocol framework, the card scheme individual rules (Visa, MasterCard standards), the national payment association rules (UK Payments Association aka APACS, in the UK), and documents produced by each individual issuer describing their own customisations of the scheme. Each spec defines security criteria, tweaks options and sets rules—but none take responsibility for listing what back-end checks are needed. As a result, hundreds of issuers independently get it wrong, and gain false assurance that all bases are covered from the common specifications. The EMV specification stack is broken, and needs fixing.

Read Ross Anderson’s entire blog post for both details and context. Here’s the paper, the press release, and a FAQ. And one news article.

This is big. There are about a gazillion of these in circulation.

EDITED TO ADD (2/12): BBC video of the attack in action.

Posted on February 11, 2010 at 4:18 PM • View Comments

The Limits of Visual Inspection

Interesting research:

Target prevalence powerfully influences visual search behavior. In most visual search experiments, targets appear on at least 50% of trials. However, when targets are rare (as in medical or airport screening), observers shift response criteria, leading to elevated miss error rates. Observers also speed target-absent responses and may make more motor errors. This could be a speed/accuracy tradeoff with fast, frequent absent responses producing more miss errors. Disproving this hypothesis, our experiment one shows that very high target prevalence (98%) shifts response criteria in the opposite direction, leading to elevated false alarms in a simulated baggage search. However, the very frequent target-present responses are not speeded. Rather, rare target-absent responses are greatly slowed. In experiment two, prevalence was varied sinusoidally over 1000 trials as observers’ accuracy and reaction times (RTs) were measured. Observers’ criterion and target-absent RTs tracked prevalence. Sensitivity (d’) and target-present RTs did not vary with prevalence. These results support a model in which prevalence influences two parameters: a decision criterion governing the series of perceptual decisions about each attended item, and a quitting threshold that governs the timing of target-absent responses. Models in which target prevalence only influences an overall decision criterion are not supported.

This has implications for searching for contraband at airports.

Posted on February 8, 2010 at 1:54 PM • View Comments

Online Credit/Debit Card Security Failure

Ross Anderson reports:

Online transactions with credit cards or debit cards are increasingly verified using the 3D Secure system, which is branded as “Verified by VISA” and “MasterCard SecureCode”. This is now the most widely-used single sign-on scheme ever, with over 200 million cardholders registered. It’s getting hard to shop online without being forced to use it.

In a paper I’m presenting today at Financial Cryptography, Steven Murdoch and I analyse 3D Secure. From the engineering point of view, it does just about everything wrong, and it’s becoming a fat target for phishing. So why did it succeed in the marketplace?

Quite simply, it has strong incentives for adoption. Merchants who use it push liability for fraud back to banks, who in turn push it on to cardholders. Properly designed single sign-on systems, like OpenID and InfoCard, can’t offer anything like this. So this is yet another case where security economics trumps security engineering, but in a predatory way that leaves cardholders less secure. We conclude with a suggestion on what bank regulators might do to fix the problem.

Posted on February 1, 2010 at 6:26 AM • View Comments

The Power Law of Terrorism

Research result #1: “A Generalized Fission-Fusion Model for the Frequency of Severe Terrorist Attacks,” by Aaron Clauset and Frederik W. Wiegel.

Plot the number of people killed in terrorists attacks around the world since 1968 against the frequency with which such attacks occur and you’ll get a power law distribution, that’s a fancy way of saying a straight line when both axis have logarithmic scales.

The question, of course, is why? Why not a normal distribution, in which there would be many orders of magnitude fewer extreme events?

Aaron Clauset and Frederik Wiegel have built a model that might explain why. The model makes five simple assumptions about the way terrorist groups grow and fall apart and how often they carry out major attacks. And here’s the strange thing: this model almost exactly reproduces the distribution of terrorists attacks we see in the real world.

These assumptions are things like: terrorist groups grow by accretion (absorbing other groups) and fall apart by disintegrating into individuals. They must also be able to recruit from a more or less unlimited supply of willing terrorists within the population.

Research Result #2: “Universal Patterns Underlying Ongoing Wars and Terrorism,” by Neil F. Johnson, Mike Spagat, Jorge A. Restrepo, Oscar Becerra, Juan Camilo Bohorquez, Nicolas Suarez, Elvira Maria Restrepo, and Roberto Zarama.

In the case of the Iraq war, we might ask how many conflicts causing ten casualties are expected to occur over a one-year period. According to the data, the answer is the average number of events per year times 10^-2.3, or 0.005. If we instead ask how many events will cause twenty casualties, the answer is proportional to 20^-2.3. Taking into account the entire history of any given war, one finds that the frequency of events on all scales can be predicted by exactly the same exponent.

Professor Neil Johnson of Oxford University has come up with a remarkable result regarding these power laws: for several different wars, the exponent has about the same value. Johnson studied the long-standing conflict in Colombia, the war in Iraq, the global rate of terrorist attacks in non-G7 countries, and the war in Afghanistan. In each case, the power law exponent that predicted the distribution of conflicts was close to the value 2.5.

This doesn’t surprise me; power laws are common in naturally random phenomena.

Posted on January 12, 2010 at 1:46 PM • View Comments

768-bit Number Factored

News:

On December 12, 2009, we factored the 768-bit, 232-digit number RSA-768 by the number field sieve. The number RSA-768 was taken from the now obsolete RSA Challenge list as a representative 768-bit RSA modulus. This result is a record for factoring general integers. Factoring a 1024-bit RSA modulus would be about a thousand times harder, and a 768-bit RSA modulus is several thousands times harder to factor than a 512-bit one. Because the first factorization of a 512-bit RSA modulus was reported only a decade ago it is not unreasonable to expect that 1024-bit RSA moduli can be factored well within the next decade by an academic effort such as ours…. Thus, it would be prudent to phase out usage of 1024-bit RSA within the next three to four years.

[…]

Our computation required more than 10²⁰ operations. With the equivalent of almost 2000 years of computing on a single core 2.2GHz AMD Opteron, on the order of 2⁶⁷ instructions were carried out. The overall effort is sufficiently low that even for short-term protection of data of little value, 768-bit RSA moduli can no longer be recommended.

News articles.

Posted on January 11, 2010 at 8:00 AM • View Comments