$ printf 'hello\n' > foo
$ md5sum *
b1946ac92492d2347c6235b4d2611184  foo

$ gpg --symmetric foo && rm foo
Enter passphrase:
Repeat passphrase:
$ md5sum *           
fb8fb61071e4f3c5ec8ea3663ffca6d7  foo.gpg

$ gpg --decrypt-files foo.gpg && rm foo.gpg
gpg: CAST5 encrypted data
gpg: encrypted with 1 passphrase
gpg: WARNING: message was not integrity protected
$ md5sum *
b1946ac92492d2347c6235b4d2611184  foo