in reply to Encryption/Decryption Program:
If this is meant just as an exercise because you just started learning Perl, you should start by looking into the Perl documentation about how to open, read and write files. From there, processing text and binary data is limited only by your imagination.
If, on the other hand, you require actual strong and reliable encryption, I'd recommend looking into existing modules on CPAN under the Crypt:: namespace rather than try to reinvent the wheel. For instance, I've found Crypt::Blowfish very useful.
Time flies when you don't know what you're doing