SSL Crack Shows You Must Advance Your Security

By Larry Seltzer  |  Posted 2009-01-02 Print this article Print

The successful creation of a rogue certificate authority by security researchers using a colliding certificates attack demonstrates that if you're not moving forward with your security-related standards then you're moving backward. Everything gets cracked over time, so you have to keep improving your defenses.

It's just one embarrassment after another for the digital certificate business lately. First, lax procedures at a Comodo affiliate resulted in the sale of a "" certificate to someone unaffiliated with that group. Now a more serious technical problem has developed with the way some certificates are generated, but the real problem is still human.

It was announced at the Chaos Computer Congress in Berlin held Dec. 27 to 30: A practical collision attack on MD5 hashes, called a colliding certificates attack, allowed a group of brilliant attackers to create a signing certificate for a legitimate certificate authority. Click here for the paper they wrote on their research.

Popular Web browsers and many other applications are distributed with the root certificates of trusted certificate authorities so that the browsers can verify that Web site certificates they encounter were, in fact, issued by one of the trusted authorities. By creating their rogue certificate, the researchers were able to create certificates that would be verified by Web browsers as having been issued by the legitimate certificate authority, which, in this case, was RapidSSL, a low-cost CA owned by VeriSign. The researchers revealed enough of their research to make the problem clear and to demonstrate that they did what they claimed to do, but not enough, for now, to allow others to replicate the work quickly.

The research is brilliant and the researchers handled themselves so well that they have received nothing but applause, even from VeriSign, which acknowledged the problems that allowed the colliding certificates attack and is moving swiftly to remove them from all of their certificate products. Any customer with an affected certificate can have a new, unaffected one, issued for free by the company.

Before I get to what I believe is the main lesson of this episode, I'll talk a bit about hash functions, the target of this attack. Hash functions are used to take a block of data, potentially large, and to create a value from it on which other operations may be performed. A hash function will always create the same hash for the same block of data, but you don't want it to be practical to reverse the process and create the data block from the hash. And while it's certain that, somewhere in the world, there are two blocks of data that create the same hash, you don't want it to be practical to find them.

This last problem is what happened in the colliding certificates attack: The researchers used a cluster of 200 PlayStation 3s to find a hash collision for the RapidSSL signing certificate.

Larry Seltzer has been writing software for and English about computers ever since—,much to his own amazement—,he graduated from the University of Pennsylvania in 1983.

He was one of the authors of NPL and NPL-R, fourth-generation languages for microcomputers by the now-defunct DeskTop Software Corporation. (Larry is sad to find absolutely no hits on any of these +products on Google.) His work at Desktop Software included programming the UCSD p-System, a virtual machine-based operating system with portable binaries that pre-dated Java by more than 10 years.

For several years, he wrote corporate software for Mathematica Policy Research (they're still in business!) and Chase Econometrics (not so lucky) before being forcibly thrown into the consulting market. He bummed around the Philadelphia consulting and contract-programming scenes for a year or two before taking a job at NSTL (National Software Testing Labs) developing product tests and managing contract testing for the computer industry, governments and publication.

In 1991 Larry moved to Massachusetts to become Technical Director of PC Week Labs (now eWeek Labs). He moved within Ziff Davis to New York in 1994 to run testing at Windows Sources. In 1995, he became Technical Director for Internet product testing at PC Magazine and stayed there till 1998.

Since then, he has been writing for numerous other publications, including Fortune Small Business, Windows 2000 Magazine (now Windows and .NET Magazine), ZDNet and Sam Whitmore's Media Survey.

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