You want to sign and encrypt a file, with the results not human-readable.

To sign myfile:

$ gpg -s myfile

To sign and encrypt myfile:

gpg -e -s myfile

In either case you must provide your passphrase. Add the -r option to encrypt the file with an intended recipient’s public key, so only he or she can decrypt it. [Recipe 7.11]

If you want the result to be an ASCII text file—say, for mailing—add the -a (armor) option.

This signature confirms to a recipient that the file is authentic: that the claimed signer really signed it.

gpg(1).