GnuPG is freely available together with all source code under the GNU General Public License ( GPL ) and is maintained separately faraway from several Graphical User Interfaces ( GUIs ) that interact with the GnuPG library for encryption , decryption and signing functions ( see KGPG , Seahorse , MacGPG ) . GnuPG is freely available together with all source code under the GNU General Public License ( GPL ) and is maintained separately from several Graphical User Interfaces ( GUIs ) that interact with the GnuPG library for encryption , decryption and signing functions ( see KGPG , Seahorse , MacGPG ) .