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PGP 8.0
User’s Guide
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Twofish. Twofish is a 256-bit block cipher, symmetric algorithm. Twofish
was one of five algorithms that the U.S. National Institute of Standards and
Technology (NIST) considered for the Advanced Encryption Standard (AES).
Rijndael was the chosen algorithm.
For more information about these algorithms, see An Introduction to Cryptography.
The Preferred Algorithm choice affects the following:
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When using conventional encryption, the preferred cipher is used to encrypt.
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When creating a key, the preferred cipher is recorded as part of the key so that
other people will use that algorithm when encrypting to you.
The Allowed Algorithms are recorded as part of the key so that other people will
use one of those algorithms when encrypting to you if the preferred algorithm is
not available to them.
Caution:
Clear the Allowed Algorithms check boxes only if you have suddenly
learned that a particular algorithm is insecure. For example, if you become
aware that IDEA has been broken, you can deselect that check box and all
new keys you generate will have a record that IDEA may not be used when
encrypting to you.
Encrypting to a public key will fail if neither the Preferred Algorithm nor any of
the Allowed Algorithms are available to the person encrypting the message.
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Display marginal validity level. Use this check box to specify whether to display
marginally valid keys as such, or simply to show validity as on or off. Marginal
validity appears as bar icons having differing shading patterns. On/off validity
appears as circle icons; green for valid, gray for invalid (the key has not been validated; it has not been signed by either a trusted introducer or by you)
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Treat marginally valid keys as invalid. Use this check box to specify whether to
treat all marginally valid keys as invalid. Selecting this option causes the Key Selection dialog box to appear whenever you encrypt to marginally valid keys.
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Warn when encrypting to keys with ADKs. Use this check box to specify
whether to issue a warning whenever an encrypt-to key has an associated Additional Decryption Key.
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Export Format. The options are:
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Compatible: Exports keys in a format compatible with previous versions of
PGP.
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Complete: Exports the new key format, which includes photographic IDs and
X.509 certificates.