At the 25th Chaos Communication Congress CCC today, researchers will reveal how they utilized a collision attack against the MD5 algorithm to create a rogue certificate authority. This is pretty big news, so read on.
When you make a secured connection to a website via HTTPS, a public key certificate is sent from the server to your computer. This certificate contains a digital signature which your computer uses to verify the identify of the site to which you’re connecting. Certificates are “signed” by a Certificate Authority CA, which acts as a kind of middle-man: you trust the CA, so you can trust the certificates signed by the CA. Anyone can create a certificate authority, though, so most browsers have a list of known reputable and trustworthy CAs. When your computer gets a certificate from a server, your browser checks the CA that issued it to determine whether the CA is trustworthy. If the CA is trustworthy, your browser assumes that the certificate being presented is trustworthy.