No. There are no back doors into your server.
For VMware users only, there is an emergency remote support feature, but you must turn this on for us to gain access.
CrashPlan uses 448-bit Blowfish to encrypt your files.
Blowfish is an encryption algorithm. It's a freely available, documented and open method of encrypting data. Open is very important. This means that the processes it uses are public and can be tested by everyone and are proven to be secure. More information is available online here: http://www.schneier.com/blowfish.html.
448-bit is the length of the key. The longer the key, the harder it is to decrypt data. Online banking uses 128-bit keys so we're much stronger than online banking.
Put simply, if someone ever got a hold of your backup archive, you wouldn't need to worry about it. They would need your password and encryption key to decrypt your data. The methods we use to encrypt your data are superior to those used in online banking and most businesses.
Yes. All data is encrypted before leaving the client computer.
Yes. Data is backed up symmetrically at the source and cannot be decrypted at the destination without the user's password.