I recently installed 11.10 on a fresh disk using entire disk encryption. Can someone tell me how secure the encryption algorithm is? Has there been any recent breaches with said algorithm? I use a 36 character random passphrase so I know thats not a weak link. What are the chances my client's data could be compromised if the hard drive was stolen?
Yes, it is secure. Ubuntu uses AES-256 to encrypt the disk volume and has a cypher feedback to help protect it from frequency attacks and others attacks that target statically encrypted data.
As an algorithm, AES is secure and this has been proved by crypt-analysis testing. The weakness actually lies within the cypher and the software to pass it the keys. Specifically lies in the keystore (which is stored in the header of the volume), the keystore is secured by a passphrase. Passphrases are of course open to some attacks such as dictionary/brute force (if this was successful, it would decrypt the keystore). Using long "complex" non-word passwords would reduce the chance of this happening.
The only other possibility to decrypt is using recording devices or social engineering to determine your passphrase.
In short, your computer is reasonably safe unless you are subject to serious organised cyber crime or Government investigation!
I have created a Windows program that will perform a dictionary attack on Luks volumes. http://code.google.com/p/luks-volume-cracker/
Its slow by design, trying around 3 keys a second. Other dictionary attacks will be similarly slow, so unless you've chosen an easy passphrase the weakness will not be the algorithm.
Be aware of key stealing from memory, and caching of files, however.