Encryption splits into two main categories:

Symmetric key encryption

This type of encryption is a way of processing data with a key, storing it somewhere, and then, using the same key, reversing the process so that the original data is retreived. Algorithms which do this are RC4, DES, Rajendal (eh?) Rijndael, Blowfish, and Towfish. They are usually very easy to implement, and you can, if you need, implement them in pure perl quite easily yourself. Search for these on http://search.cpan.org and see what comes up

Asymetric key encryption

This is the heavier grade encryption. It's slower, and more complete. You have one key to encrypt, and one key to decrypt. Security is better, because you don't need a protocol to ensure that the two sides of a correspondence know the symmetric key, rather each knows the other public, or encrypting key, and encrypts data so that only the other side can decrypt it. Modules which take care of this have been mentioned. Generally this is GNUPG, and PGP stuff. The algorithms are usually still not that complicated, but the auxillery operations are - generating huge prime numbers, for example. El Gammal, RSA, and DSA are algorithms which may be of concern to you. the module Crypt::OpenPGP is a pure perl one, but unfortunately requires the non easy build Math::PARI.

For encrypting files which are stored you probably want to use a symmetric key encryption, and as the key you can use a Digest::MD5 or Digest::SHA1 hash of a passphrase, or even the passphrase itself if it suffices. Public key encryption becomes necessary when you want to pass files between two computers on an unsafe communication. If you are interested in that, perhaps a secure protocol, like https, ssh, or some other is more suitable. Public key encryption has it's use mainly in emails.

Finally i'd like to note that since your question is clear, non obstrusive, polite, and to the point (and a reasonable point too), there's no reason any community would flame you. Some communities are intolerant to newbies, but those are usually much more specific in their interests. Perlmonks is too general for snobism.

Good luck!

Updates: Fixed phonetic memory wordo to the real name of Rijndael, Fixed OpenPGP to Crypt::OpenPGP

-nuffin
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