I'm trying to symmetrically encrypt a file using gpg.
$ gpg --encrypt --symmetric $MYFILE
I enter and re-enter a passphrase, then gpg tells me
You did not specify a user ID. (you may use "-r") Current recipients: Enter the user ID. End with an empty line:
I don't know what to enter here. I'm symmetrically encrypting (not public key encrypting) so I don't understand why gpg wants to know who the recipient might be. I don't know what the sort of user id gpg is expecting looks like, and I don't know any gpg user ids anyway. If I just enter an empty line, gpg complains that there are "no valid addressees".
So how do I symmetrically encrypt a file using gpg?
Version: gpg (GnuPG) 1.4.11, as packaged in Ubuntu 11.10.