As /u/four said, this is implemented pretty well already. Go on my profile and you can see my PGP key on the right.
I see you haven't added yours, simply go into your account settings and paste in your public key, then decrypt whatever it wants you to, and save. Tada.
My issue is decrypting the message to verify my key. I use the same key on every market (obviously) and never have an issue verifying. Although the Dread verification message wont decrypt for me. Verified my key is still working fine by decrypting messages between myself and vendors so it is obviously working as it should from a normal standpoint.
I see you haven't added yours, simply go into your account settings and paste in your public key, then decrypt whatever it wants you to, and save. Tada.