A PassPhrase is a string of text (phrase) that's used by encryption software to generate a Secret Key. PassPhrases are like passwords, but should be much longer and more difficult to guess. When using a PassPhrase to generate a Secret Key, you should be aware of the following criteria for coming up with an effective phrase:

• Length. A typical english-text PassPhrase should have about the same number of characters as there will be bits in the Secret Key to be generated. The reason for this is the weak entropy of regular English text based on the predictability of subsequent characters or words. In fact, each character can contribute about 1.2 bits for a Secret Key.

• Content. To create a really good PassPhrase, or to reduce the number of characters without sacrificing effectiveness you should use words not found in dictionaries and you should also use plenty of numbers, special characters and mix uppercase characters with lowercase characters often. You can also reverse some words and not reverse others, and maybe even throw in a word or two from other languages too.