Posted by Chenxi Wang on February 10, 2009 In December 2008, a
group of researchers demonstrated a credible attack against MD5
signatures. Since then, Forrester received a number of client
inquiries regarding the security strength of their MD5
certificates. There seems to be much confusion over what the
attack is about and its actual consequences. To properly
understand the security consequence of this attack and the
impact on certificates, we need to understand how the attack
works. The researchers demonstrated a successful attack against
the RapidSSL certificate authority, which uses MD5 signatures to
sign certificate requests. This is how the attack worked: the
researchers first got the RapidSSL CA to sign a particular
certificate request, issued for a domain in their control. This
request and the ensuing signature are completely legitimate. The
researchers then demonstrated that they were able to create a
second certificate bearing the same signature, for a separate
made-up entity. In essence, they were a