Frase larga (por ejemplo, de 80 caracteres) pero
fácil de recordar por el usuario, que realiza las mismas funciones de
autenticación que una contraseña, con la ventaja de ser más difícil de
conjeturar. [Ribagorda:1997]
A sequence of words or other
text used to control access to a computer system, program or data. A passphrase
is similar to a password in usage, but is generally longer for added security.
Passphrases are often used to control both access to, and operation of,
cryptographic programs and systems. Passphrases are particularly applicable to
systems that use the passphrase as an encryption key. The origin of the term is
by analogy with "password". The modern concept of passphrases is
believed to have been invented by Sigmund N. Porter (1) in 1982.
http://en.wikipedia.org/wiki/Passphrase