Free Cryptography Class
Dan Boneh of Stanford University is teaching a free cryptography class starting in January.
Entries Tagged "cryptography"
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Paul Kocher
Really nice article on crypotographer Paul Kocher and his company, Cryptography Research, Inc.
Cracking the Copiale Cipher
I don’t follow historical cryptography, so all of this comes as a surprise to me. But something called the Copiale Cipher from the 18th Century has been cracked.
EDITED TO ADD (11/14): Here’s the academic website.
Twofish Mentioned in Thriller Novel
I’ve been told that the Twofish encryption algorithm is mentioned in the book Abuse of Power, in the first paragraph of Chapter 3. Did the terrorists use it? Did our hero break it? I am unlikely to read it; can someone scan the page for me.
EDITED TO ADD (10/25): Google Books has it:
The line was picked up after three rings. The cell phones were encrypted using a Twofish algorithm and a 4096-bit Diffie-Hellman key exchange.
No one would be listening in.
Official Malware from the German Police
The Chaos Computer Club has disassembled and analyzed the Trojan used by the German police for legal intercept. In its default mode, it takes regular screenshots of the active window and sends it to the police. It encrypts data in AES Electronic Codebook mode with—are you ready?—a fixed key across all versions. There’s no authentication built in, so it’s easy to spoof. It sends data to a command-and-control server in the U.S., which is almost certainly against German law. There’s code to allow the controller to install additional software onto the target machine, but that’s not authenticated either, so it would be easy to fool the Trojan into installing anything.
Detailed analysis in German. F-Secure has announced it will treat the Trojan as malware. I hope all the other anti-virus companies will do the same.
EDITED TO ADD (10/12): Another story. And some good information on the malware. Germany’s Justice Minister is calling for an investigation.
Man-in-the-Middle Attack Against SSL 3.0/TLS 1.0
It’s the Browser Exploit Against SSL/TLS Tool, or BEAST:
The tool is based on a blockwise-adaptive chosen-plaintext attack, a man-in-the-middle approach that injects segments of plain text sent by the target’s browser into the encrypted request stream to determine the shared key. The code can be injected into the user’s browser through JavaScript associated with a malicious advertisement distributed through a Web ad service or an IFRAME in a linkjacked site, ad, or other scripted elements on a webpage.
Using the known text blocks, BEAST can then use information collected to decrypt the target’s AES-encrypted requests, including encrypted cookies, and then hijack the no-longer secure connection. That decryption happens slowly, however; BEAST currently needs sessions of at least a half-hour to break cookies using keys over 1,000 characters long.
The attack, according to Duong, is capable of intercepting sessions with PayPal and other services that still use TLS 1.0which would be most secure sites, since follow-on versions of TLS aren’t yet supported in most browsers or Web server implementations.
While Rizzo and Duong believe BEAST is the first attack against SSL 3.0 that decrypts HTTPS requests, the vulnerability that BEAST exploits is well-known; BT chief security technology officer Bruce Schneier and UC Berkeley’s David Wagner pointed out in a 1999 analysis of SSL 3.0 that “SSL will provide a lot of known plain-text to the eavesdropper, but there seems to be no better alternative.” And TLS’s vulnerability to man-in-the middle attacks was made public in 2009. The IETF’s TLS Working Group published a fix for the problem, but the fix is unsupported by SSL.
Another article.
EDITED TO ADD: Good analysis.
Smartphone Keystroke Logging Using the Motion Sensor
“When the user types on the soft keyboard on her smartphone (especially when she holds her phone by hand rather than placing it on a fixed surface), the phone vibrates. We discover that keystroke vibration on touch screens are highly correlated to the keys being typed.”
Applications like TouchLogger could be significant because they bypass protections built into both Android and Apple’s competing iOS that prevent a program from reading keystrokes unless it’s active and receives focus from the screen. It was designed to work on an HTC Evo 4G smartphone. It had an accuracy rate of more than 70 percent of the input typed into the number-only soft keyboard of the device. The app worked by using the phone’s accelerometer to gauge the motion of the device each time a soft key was pressed.
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.”
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.
GPRS Hacked
Just announced:
Nohl’s group found a number of problems with GPRS. First, he says, lax authentication rules could allow an attacker to set up a fake cellular base station and eavesdrop on information transmitted by users passing by. In some countries, they found that GPRS communications weren’t encrypted at all. When they were encrypted, Nohl adds, the ciphers were often weak and could be either broken or decoded with relatively short keys that were easy to guess.
The group generated an optimized set of codes that an attacker could quickly use to find the key protecting a given communication. The attack the researchers designed against GPRS costs about 10 euros for radio equipment, Nohl says.
Sidebar photo of Bruce Schneier by Joe MacInnis.