Entries Tagged "academic papers"

Page 63 of 86

Cryptanalysis of Satellite Phone Encryption Algorithms

From the abstract of the paper:

In this paper, we analyze the encryption systems used in the two existing (and competing) satphone standards, GMR-1 and GMR-2. The first main contribution is that we were able to completely reverse engineer the encryption algorithms employed. Both ciphers had not been publicly known previously. We describe the details of the recovery of the two algorithms from freely available DSP-firmware updates for satphones, which included the development of a custom disassembler and tools to analyze the code, and extending prior work on binary analysis to efficiently identify cryptographic code. We note that these steps had to be repeated for both systems, because the available binaries were from two entirely different DSP processors. Perhaps somewhat surprisingly, we found that the GMR-1 cipher can be considered a proprietary variant of the GSM A5/2 algorithm, whereas the GMR-2 cipher is an entirely new design. The second main contribution lies in the cryptanalysis of the two proprietary stream ciphers. We were able to adopt known A5/2 ciphertext-only attacks to the GMR-1 algorithm with an average case complexity of 232 steps. With respect to the GMR-2 cipher, we developed a new attack which is powerful in a known-plaintext setting. In this situation, the encryption key for one session, i.e., one phone call, can be recovered with approximately 50­65 bytes of key stream and a moderate computational complexity. A major finding of our work is that the stream ciphers of the two existing satellite phone systems are considerably weaker than what is state-oft-he-art in symmetric cryptography.

Press release. And news stories.

Posted on February 16, 2012 at 12:22 PM • View Comments

Lousy Random Numbers Cause Insecure Public Keys

There’s some excellent research (paper, news articles) surveying public keys in the wild. Basically, the researchers found that a small fraction of them (27,000 out of 7.1 million, or 0.38%) share a common factor and are inherently weak. The researchers can break those public keys, and anyone who duplicates their research can as well.

The cause of this is almost certainly a lousy random number generator used to create those public keys in the first place. This shouldn’t come as a surprise. One of the hardest parts of cryptography is random number generation. It’s really easy to write a lousy random number generator, and it’s not at all obvious that it is lousy. Randomness is a non-functional requirement, and unless you specifically test for it—and know how to test for it—you’re going to think your cryptosystem is working just fine. (One of the reporters who called me about this story said that the researchers told him about a real-world random number generator that produced just seven different random numbers.) So it’s likely these weak keys are accidental.

It’s certainly possible, though, that some random number generators have been deliberately weakened. The obvious culprits are national intelligence services like the NSA. I have no evidence that this happened, but if I were in charge of weakening cryptosystems in the real world, the first thing I would target is random number generators. They’re easy to weaken, and it’s hard to detect that you’ve done anything. Much safer than tweaking the algorithms, which can be tested against known test vectors and alternate implementations. But again, I’m just speculating here.

What is the security risk? There’s some, but it’s hard to know how much. We can assume that the bad guys can replicate this experiment and find the weak keys. But they’re random, so it’s hard to know how to monetize this attack. Maybe the bad guys will get lucky and one of the weak keys will lead to some obvious way to steal money, or trade secrets, or national intelligence. Maybe.

And what happens now? My hope is that the researchers know which implementations of public-key systems are susceptible to these bad random numbers—they didn’t name names in the paper—and alerted them, and that those companies will fix their systems. (I recommend my own Fortuna, from Cryptography Engineering.) I hope that everyone who implements a home-grown random number generator will rip it out and put in something better. But I don’t hold out much hope. Bad random numbers have broken a lot of cryptosystems in the past, and will continue to do so in the future.

From the introduction to the paper:

In this paper we complement previous studies by concentrating on computational and randomness properties of actual public keys, issues that are usually taken for granted. Compared to the collection of certificates considered in [12], where shared RSA moduli are “not very frequent”, we found a much higher fraction of duplicates. More worrisome is that among the 4.7 million distinct 1024-bit RSA moduli that we had originally collected, more than 12500 have a single prime factor in common. That this happens may be crypto-folklore, but it was new to us, and it does not seem to be a disappearing trend: in our current collection of 7.1 million 1024-bit RSA moduli, almost 27000 are vulnerable and 2048-bit RSA moduli are affected as well. When exploited, it could act the expectation of security that the public key infrastructure is intended to achieve.

And the conclusion:

We checked the computational properties of millions of public keys that we collected on the web. The majority does not seem to suffer from obvious weaknesses and can be expected to provide the expected level of security. We found that on the order of 0.003% of public keys is incorrect, which does not seem to be unacceptable. We were surprised, however, by the extent to which public keys are shared among unrelated parties. For ElGamal and DSA sharing is rare, but for RSA the frequency of sharing may be a cause for concern. What surprised us most is that many thousands of 1024-bit RSA moduli, including thousands that are contained in still valid X.509 certificates, offer no security at all. This may indicate that proper seeding of random number generators is still a problematic issue….

EDITED TO ADD (3/14): The title of the paper, “Ron was wrong, Whit is right” refers to the fact that RSA is inherently less secure because it needs two large random primes. Discrete log based algorithms, like DSA and ElGamal, are less susceptible to this vulnerability because they only need one random prime.

Posted on February 16, 2012 at 6:51 AM • View Comments

Evidence on the Effectiveness of Terrorism

Readers of this blog will know that I like the works of Max Abrahms, and regularly blog them. He has a new paper (full paper behind paywall) in Defence and Peace Economics, 22:6 (2011), 583–94, “Does Terrorism Really Work? Evolution in the Conventional Wisdom since 9/11”:

The basic narrative of bargaining theory predicts that, all else equal, anarchy favors concessions to challengers who demonstrate the will and ability to escalate against defenders. For this reason, post-9/11 political science research explained terrorism as rational strategic behavior for non-state challengers to induce government compliance given their constraints. Over the past decade, however, empirical research has consistently found that neither escalating to terrorism nor with terrorism helps non-state actors to achieve their demands. In fact, escalating to terrorism or with terrorism increases the odds that target countries will dig in their political heels, depriving the nonstate challengers of their given preferences. These empirical findings across disciplines, methodologies, as well as salient global events raise important research questions, with implications for counterterrorism strategy.

EDITED TO ADD (2/14): The paper.

Posted on January 26, 2012 at 10:36 AM • View Comments

Studying Airport Security

Alan A. Kirschenbaum, Michele Mariani, Coen Van Gulijk, Sharon Lubasz, Carmit Rapaport, and Hinke Andriessen, “Airport Security: An Ethnographic Study,” Journal of Air Transport Management, 18 (January 2012): 68-73 (full article is behind a paywall).

Abstract: This paper employs a behavioral science perspective of airport security to, examine security related decision behaviors using exploratory ethnographic observations. Sampling employees from a broad spectrum of departments and occupations in several major airports across Europe, over 700 descriptive items are transcribed into story scripts that are analyzed. The results demonstrate that both formal and informal behavioral factors are present when security decisions are made. The repetitive patterns of behavior allowed us to develop a generic model applicable to a wide range of security related situations. What the descriptions suggest is that even within the formal regulatory administrative framework of airports, actual real-time security behaviors may deviate from rules and regulations to adapt to local situations.

Posted on December 30, 2011 at 6:11 AM • View Comments

Multiple Protocol Attacks

In 1997, I wrote about something called a chosen-protocol attack, where an attacker can use one protocol to break another. Here’s an example of the same thing in the real world: two different parking garages that mask different digits of credit cards on their receipts. Find two from the same car, and you can reconstruct the entire number.

I have to admit this puzzles me, because I thought there was a standard for masking credit card numbers. I only ever see all digits except the final four masked.

Posted on December 20, 2011 at 6:24 AM • View Comments

Feeling vs. Reality of Security in Sparrows

Sparrows have fewer surviving offspring if they feel insecure, regardless of whether they actually are insecure. Liana Y. Zanette, Aija F. White, Marek C. Allen, and Michael Clinchy, “Perceived Predation Risk Reduces the Number of Offspring Songbirds Produce per Year,” Science, 9 Dec 2011:

Abstract: Predator effects on prey demography have traditionally been ascribed solely to direct killing in studies of population ecology and wildlife management. Predators also affect the prey’s perception of predation risk, but this has not been thought to meaningfully affect prey demography. We isolated the effects of perceived predation risk in a free-living population of song sparrows by actively eliminating direct predation and used playbacks of predator calls and sounds to manipulate perceived risk. We found that the perception of predation risk alone reduced the number of offspring produced per year by 40%. Our results suggest that the perception of predation risk is itself powerful enough to affect wildlife population dynamics, and should thus be given greater consideration in vertebrate conservation and management.

Seems as if the sparrows could use a little security theater.

Posted on December 14, 2011 at 1:22 PM • View Comments

Full-Disk Encryption Works

According to researchers, full-disk encryption is hampering police forensics.

The authors of the report suggest there are some things law enforcement can do, but they all must happen prior to a drive being buttoned up by encryption. Specifically, they say that law enforcement should stop turning computers off to bring them to another location for study, doing so only causes the need for a password to be entered to read the encrypted data. Also, in some cases, doing so causes the data to be automatically destroyed. Fortunately, there are some tools forensics experts can use to gather data if it sits untouched, such as copying everything in memory to a separate disk. The team also suggests that law enforcement look first to see if the drive has been encrypted before scanning it with their own software, as doing so will likely result in a lot of wasted time.

Paper, behind a paywall.

Posted on December 1, 2011 at 1:44 PM • View Comments

Journal Article on Cyberwar

From the Journal of Strategic Studies: “Cyber War Will Not Take Place“:

Abstract: For almost two decades, experts and defense establishments the world over have been predicting that cyber war is coming. But is it? This article argues in three steps that cyber war has never happened in the past, that cyber war does not take place in the present, and that it is unlikely that cyber war will occur in the future. It first outlines what would constitute cyber war: a potentially lethal, instrumental, and political act of force conducted through malicious code. The second part shows what cyber war is not, case-by-case. Not one single cyber offense on record constitutes an act of war on its own. The final part offers a more nuanced terminology to come to terms with cyber attacks. All politically motivated cyber attacks are merely sophisticated versions of three activities that are as old as warfare itself: sabotage, espionage, and subversion.

Here’s another article: “The Non-Existent ‘Cyber War’ Is Nothing More Than A Push For More Government Control.”

EDITED TO ADD (11/4): A reader complained to the publication, and they removed the paywall from the first article.

Posted on November 3, 2011 at 1:22 PM • View Comments

New Attacks on CAPTCHAs

Nice research:

Abstract: We report a novel attack on two CAPTCHAs that have been widely deployed on the Internet, one being Google’s home design and the other acquired by Google (i.e. reCAPTCHA). With a minor change, our attack program also works well on the latest ReCAPTCHA version, which uses a new defence mechanism that was unknown to us when we designed our attack. This suggests that our attack works in a fundamental level. Our attack appears to be applicable to a whole family of text CAPTCHAs that build on top of the popular segmentation-resistant mechanism of “crowding character together” for security. Next, we propose a novel framework that guides the application of our well-tested security engineering methodology for evaluating CAPTCHA robustness, and we propose a new general principle for CAPTCHA design.

Posted on October 12, 2011 at 6:57 AM • View Comments

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Sidebar photo of Bruce Schneier by Joe MacInnis.