What is a passphrase?
The term passphrase is often used in cryptography for what might be better known as a password in other contexts. For example, an OpenPGP private key is typically stored to disc in an file encrypted by a symmetric cypher keyed by a passphrase. This passphrase is one of the weakest elements in the system: should anyone else gain access to the file then a dictionary attack will be feasible on a weak passphrase. So, choosing a strong passphrase is very important. Passphrases are (unlike passwords) typically unlimited in length. Long passphrases are recommended. This allows sequences of (at least seven) unrelated words to be used as well as more conventional mixtures of symbols and alphanumerics. Note that even a good passphrase will offer only limited protection. Given the encrypted file and enough time, a determined cracker will be able to break any passphrase. A good passphrase will buy important time in the event of a compromise but is no substitute for keeping the private key safe and
