MD5 is considered harmful

Message Digest Algorithm 5 (aka MD5) was invented by Ronald Rivest in 1991 as a replacement to the insecure MD4 algorithm. But current research has shown that MD5 is insecure, due to "collisions".

Source: http://www.win.tue.nl/hashclash/rogue-ca/

MD5 considered harmful today : Creating a rogue CA certificate
dated December 30, 2008

Authors: Alexander Sotirov, Marc Stevens, Jacob Appelbaum, Arjen Lenstra, David Molnar, Dag Arne Osvik, Benne de Weger

We have identified a vulnerability in the Internet Public Key Infrastructure (PKI) used to issue digital certificates for secure websites. As a proof of concept we executed a practical attack scenario and successfully created a rogue Certification Authority (CA) certificate trusted by all common web browsers. This certificate allows us to impersonate any website on the Internet, including banking and e-commerce sites secured using the HTTPS protocol.

Our attack takes advantage of a weakness in the MD5 cryptographic hash function that allows the construction of different messages with the same MD5 hash. This is known as an MD5 "collision". Previous work on MD5 collisions between 2004 and 2007 showed that the use of this hash function in digital signatures can lead to theoretical attack scenarios. Our current work proves that at least one attack scenario can be exploited in practice, thus exposing the security infrastructure of the web to realistic threats.

An active discussion on this issue is happening at http://www.ietf.org/mail-archive/web/saag/current/msg02348.html

Additionally, US-CERT has issued an advisory.

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