backtop


Print 28 comment(s) - last by ipay.. on Jan 6 at 11:55 AM

Ever wanted to be an Intermediate Certificate Authority?

Speaking at the 25th annual Chaos Communication Conference (25C3) early last week, security researchers demonstrated the first known application of a years-old theoretical attack against the MD5 hashing algorithm used by companies like Verisign and Thawte to issue SSL certificates.

SSL certificates use hash codes generated by a variety of algorithms, including MD5, to verify their issuer’s identity. The hash code is an important feature of public-key cryptography, which SSL is based upon, as it is essential to protecting the secret, private code that CAs use to sign SSL certificates.

By exploiting a weakness specific to hashes generated with the MD5 algorithm – namely, that they are prone to “collisions”, or multiple inputs producing the same output – an attacker could derive a working private key from a single, regular SSL certificate, and then use that key to sign future SSL certificates with the original CA’s signature.

Security experts have known about the possibility for MD5 collisions since at least 2004. Until now, however, the vulnerability was dismissed as a theoretical possibility due to the amount of CPU time needed to attack a single hash for collisions. The 25C3 presenters claim they were able to run the attack in only four weekends, using a network of 200 PlayStation 3 game consoles at a cost of $657.

For about $2,000, said the presenters, an attacker could pull off a similar attack using Amazon’s cloud-computing EC2 service, and the attack would take about a day.

A successful attack would allow attackers to appoint themselves as an Intermediate Certificate Authority, and then generate trusted certificates without having to contact a real CA. The spoofed certificates could then be used to add the appearance of legitimacy to a phishing site designed to steal bank account passwords, for example.

While many CAs have moved on to the more secure SHA-1 or SHA-2 algorithms, a handful of issuers have not. Of the brands still using MD5, the researchers found approximately 97% of those certificates to be signed by Verisign-owned low-cost CA RapidSSL. Other companies using MD5 include FreeSSL, Thawte, and Verisign.co.jp.

Verisign announced that it will replace RapidSSL customers’ certificates free of charge.

“This successful proof of concept shows that the certificate validation performed by browsers can be subverted and malicious attackers might be able to monitor or tamper with data sent to secure websites,” said security researcher Alexander Sotirov, who worked with others from the U.S., the Netherlands, and Switzerland.

Sotirov’s website includes a detailed explanation of the attack, as well as samples of a real certificate and the rogue signing certificate derived from it.

Extended-Validation SSL certificates are immune to the attack due to the fact that they are forbidden from using MD5.

Microsoft reportedly downplayed the threat, noting that the researchers withheld important information that renders the attack “not repeatable”.

A blog post from Verisign’s Tim Callahan says his company applauds the team’s research, noting that their work was so secret that not even Verisign had access to the information before the 25C3 presentation.

Customers holding an MD5-signed SSL certificate will need to contact their CA to acquire and install a new certificate on their servers.



Comments     Threshold


This article is over a month old, voting and posting comments is disabled

RE: 200 PS3's cost how much
By darkpaw on 1/4/2009 9:00:31 PM , Rating: 1
Yup, botnet is the biggest threat. People that would want to use this sort of thing maliciously already have networks of tens of thousands of PC's waiting to do their dirt work. It probably wouldn't take long at all to generate one of these on a 50k pc botnet.

Its good that most vendors have phased these out, but the ones that haven't account for a pretty large chunk. Especially in the small business market since the named providers are typically the ones that come with web hosting. Many of those businesses had their websites setup by another company or an employee that knows a little about web tech and don't know the first thing about maintaining them or what kind of certificate they are using.

I think overall this will be a good thing though. Its been years since it was revealed this was possible, but now that its been done it will force the companies to respond that have been dragging their feet.


"Nowadays you can buy a CPU cheaper than the CPU fan." -- Unnamed AMD executive











botimage
Copyright 2014 DailyTech LLC. - RSS Feed | Advertise | About Us | Ethics | FAQ | Terms, Conditions & Privacy Information | Kristopher Kubicki