Netcraft's SSL Survey shows that 14% of valid third party SSL certificates have been issued using MD5 signatures — an algorithm that has recently been demonstrated to be vulnerable to attack by producing a fake certificate authority certificate signed by a widely-trusted third party certificate authority.

The researchers achieved this by producing a hash collision — they submitted valid certificate requests to a certificate authority (CA), while producing a second certificate that had the same signature but entirely different details. When the CA signed the valid certificate, the signature applied also to the invalid certificate, allowing the researchers to spoof any secure website that they liked. This attack is the first practical use against SSL of already-known attacks against the MD5 checksum algorithm.

At Netcraft.

[ Read more ]