Entries Tagged "cryptography"

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Breaking Microsoft's PPTP Protocol

Some things never change. Thirteen years ago, Mudge and I published a paper breaking Microsoft’s PPTP protocol and the MS-CHAP authentication system. I haven’t been paying attention, but I presume it’s been fixed and improved over the years. Well, it’s been broken again.

ChapCrack can take captured network traffic that contains a MS-CHAPv2 network handshake (PPTP VPN or WPA2 Enterprise handshake) and reduce the handshake’s security to a single DES (Data Encryption Standard) key.

This DES key can then be submitted to CloudCracker.com—a commercial online password cracking service that runs on a special FPGA cracking box developed by David Hulton of Pico Computing—where it will be decrypted in under a day.

The CloudCracker output can then be used with ChapCrack to decrypt an entire session captured with WireShark or other similar network sniffing tools.

Posted on August 6, 2012 at 11:22 AM • View Comments

So You Want to Be a Security Expert

I regularly receive e-mail from people who want advice on how to learn more about computer security, either as a course of study in college or as an IT person considering it as a career choice.

First, know that there are many subspecialties in computer security. You can be an expert in keeping systems from being hacked, or in creating unhackable software. You can be an expert in finding security problems in software, or in networks. You can be an expert in viruses, or policies, or cryptography. There are many, many opportunities for many different skill sets. You don’t have to be a coder to be a security expert.

In general, though, I have three pieces of advice to anyone who wants to learn computer security.

  • Study. Studying can take many forms. It can be classwork, either at universities or at training conferences like SANS and Offensive Security. (These are good self-starter resources.) It can be reading; there are a lot of excellent books out there—and blogs—that teach different aspects of computer security out there. Don’t limit yourself to computer science, either. You can learn a lot by studying other areas of security, and soft sciences like economics, psychology, and sociology.
  • Do. Computer security is fundamentally a practitioner’s art, and that requires practice. This means using what you’ve learned to configure security systems, design new security systems, and—yes—break existing security systems. This is why many courses have strong hands-on components; you won’t learn much without it.
  • Show. It doesn’t matter what you know or what you can do if you can’t demonstrate it to someone who might want to hire you. This doesn’t just mean sounding good in an interview. It means sounding good on mailing lists and in blog comments. You can show your expertise by making podcasts and writing your own blog. You can teach seminars at your local user group meetings. You can write papers for conferences, or books.

I am a fan of security certifications, which can often demonstrate all of these things to a potential employer quickly and easily.

I’ve really said nothing here that isn’t also true for a gazillion other areas of study, but security also requires a particular mindset—one I consider essential for success in this field. I’m not sure it can be taught, but it certainly can be encouraged. “This kind of thinking is not natural for most people. It’s not natural for engineers. Good engineering involves thinking about how things can be made to work; the security mindset involves thinking about how things can be made to fail. It involves thinking like an attacker, an adversary or a criminal. You don’t have to exploit the vulnerabilities you find, but if you don’t see the world that way, you’ll never notice most security problems.” This is especially true if you want to design security systems and not just implement them. Remember Schneier’s Law: “Any person can invent a security system so clever that she or he can’t think of how to break it.” The only way your designs are going to be trusted is if you’ve made a name for yourself breaking other people’s designs.

One final word about cryptography. Modern cryptography is particularly hard to learn. In addition to everything above, it requires graduate-level knowledge in mathematics. And, as in computer security in general, your prowess is demonstrated by what you can break. The field has progressed a lot since I wrote this guide and self-study cryptanalysis course a dozen years ago, but they’re not bad places to start.

This essay originally appeared on “Krebs on Security,” the second in a series of answers to the question. This is the first. There will be more.

Posted on July 5, 2012 at 6:17 AM • View Comments

Al Qaeda Steganography

The reports are still early, but it seems that a bunch of terrorist planning documents were found embedded in a digital file of a porn movie.

Several weeks later, after laborious efforts to crack a password and software to make the file almost invisible, German investigators discovered encoded inside the actual video a treasure trove of intelligence—more than 100 al Qaeda documents that included an inside track on some of the terror group’s most audacious plots and a road map for future operations.

Posted on May 2, 2012 at 12:41 PM • View Comments

Alan Turing Cryptanalysis Papers

GCHQ, the UK government’s communications headquarters, has released two new—well, 70 years old, but new to us—cryptanalysis documents by Alan Turing.

The papers, one entitled The Applications of Probability to Crypt, and the other entitled Paper on the Statistics of Repetitions, discuss mathematical approaches to code breaking.

[…]

According to the GCHQ mathematician, who identified himself only as Richard, the papers detailed using “mathematical analysis to try and determine which are the more likely settings so that they can be tried as quickly as possible.”

The papers don’t seem to be online yet, but here’s their National Archives data.

EDITED TO ADD (5/12): The papers are available for download at GBP 3.50 each.

Posted on April 23, 2012 at 6:18 AM • View Comments

Can the NSA Break AES?

In an excellent article in Wired, James Bamford talks about the NSA’s codebreaking capability.

According to another top official also involved with the program, the NSA made an enormous breakthrough several years ago in its ability to cryptanalyze, or break, unfathomably complex encryption systems employed by not only governments around the world but also many average computer users in the US. The upshot, according to this official: “Everybody’s a target; everybody with communication is a target.”

Bamford has been writing about the NSA for decades, and people tell him all sorts of confidential things. Reading the above, the obvious question to ask is: can the NSA break AES?

My guess is that they can’t. That is, they don’t have a cryptanalytic attack against the AES algorithm that allows them to recover a key from known or chosen ciphertext with a reasonable time and memory complexity. I believe that what the “top official” was referring to is attacks that focus on the implementation and bypass the encryption algorithm: side-channel attacks, attacks against the key generation systems (either exploiting bad random number generators or sloppy password creation habits), attacks that target the endpoints of the communication system and not the wire, attacks that exploit key leakage, attacks against buggy implementations of the algorithm, and so on. These attacks are likely to be much more effective against computer encryption.

EDITED TO ADD (3/22): Another option is that the NSA has built dedicated hardware capable of factoring 1024-bit numbers. There’s quite a lot of RSA-1024 out there, so that would be a fruitful project. So, maybe.

EDITED TO ADD (4/13): The NSA denies everything.

Posted on March 22, 2012 at 7:17 AM • View Comments

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Sidebar photo of Bruce Schneier by Joe MacInnis.