You may be better off using Rjindael encryption, which is normally used
on AG Venues when setting the 'encryption' option in the venue server
config.
A Rjindael key is passed to VIC and RAT as 'Rjindael/passphrase' where
passphrase should be something random and unguessable, and distributed
to those needing the key to enter manually. There's a program for Debian
called 'pwgen' that I've used to generate a passphrase before. For
manually entering the key, you would probably just disable the venue
encryption and manually key it in. For a DES key, just use a passphrase
that doesn't start with a string 'Rjindael/'.
Of course you can also use certificates to secure a venue too, so not
just anyone can enter and obtain the encryption key.