
Kleopatra is an open-source certificate manager and graphical front-end for
cryptographic services, primarily designed to handle OpenPGP and S/MIME (X.509)
certificates. Part of the KDE ecosystem, it provides an accessible interface
for managing encryption keys, signing and verifying data, and encrypting or
decrypting files and emails.
A complete GUI that supports all functionalities. Easy key management and easy to use encryption/decryption/verification. German languange pack is available. I was unable to delete a secret key and had to switch to the CLI to do that.