GNU Privacy Assistant (gpa) is a GTK based GUI of GNU Privacy Guard or gpg. Signing, verification, encryption and decryption have become very easy using gpa. Execute the command gpa from rxvt or gmrun and you can see the gpa window. Create a key first. Below is my gpa.

creating a key

gpa showing key details

gpa also provides a file manager. gpa -> windows -> File Manager. You can sign and verify using this file manager.

signing a file

gpa is asking passphrase

verify the signed file

This same file manager helps to encrypt and decrypt.

file encryption

file decryption