Symmetric encryption - options?

Robert J. Hansen rjh at
Tue Mar 13 13:14:35 CET 2012

On 3/13/2012 5:01 AM, jpemail2001-321 at wrote:
> What does mean CAST5 and is it a safe alghorithmus? Why not RSA?

CAST5 is the default symmetric algorithm for GnuPG and PGP.  It is
generally accepted to be secure against cryptanalysis.

Broadly speaking, ciphers can be broken down into either "symmetric" or
"asymmetric" algorithms.  A symmetric algorithm uses the same key to
encrypt and decrypt.  If you choose to use a passphrase, for instance,
the same passphrase is used to encrypt and decrypt, therefore a
symmetric algorithm is used.

If you choose to use someone's public certificate to encrypt a message,
they use the private part of that certificate to decrypt it -- different
things for encryption and decryption, thus a different kind of
algorithm, an asymmetric one, is used.

CAST5 is a symmetric algorithm.

RSA is an asymmetric algorithm.

Hope this helps.  :)

> Can I set more than one passphrase?

Not really.

> And why was the message not integrity protected and how to protect it?

Integrity protection is only available when using newer symmetric
algorithms.  For instance, if you had selected Twofish or AES256 the
integrity protection feature would be used.  For almost all uses,
though, this is not a big deal to lose sleep over.

More information about the Gnupg-users mailing list