At the 25th Chaos Communication Congress in the end of December 2008, several researchers gave their presentation entitled “MD5 considered harmful today:Creating a rogue CA Certificate“. Like a new tradition in security research press release, the information in the CCC site is censored. You can find the full detail at http://www.win.tue.nl/hashclash/rogue-ca/.
Here is a little bit summary of the presentation :
Using computing power from a cluster of 200 PS3 game consoles and about $700 in test digital certificates, a group of hackers in the U.S. and Europe have found a way to target a known weakness in the MD5 algorithm to create a rogue Certification Authority (CA), a breakthrough that allows the forging of certificates that are fully trusted by all modern Web browsers.
Very scary heh. Fortunately in the reality it is not that scary. :D
Johannes Ulrich of SANS give a nice summary on this MD5 SSL thing :
So short summary: It is bad, but there isn’t much you can or need to do right now. Just stay vigilant and read the vendor announcements.
As a result, this hole is easier to close than people think. The few CAs signing certs with MD5 need to switch to SHA1 (or something stronger). That immediately gets rid of the problem for new certs.
If you use Firefox as a browser and you want to block MD5 certs, you can use an addon called SSL Blacklist.