Add the following line to server.properties
trusted-key=MHYwEAYHKoZIzj0CAQYFK4EEACIDYgAECRXueJeTDqNRRgJi/vlRufByu/2G0i2Ebt6YMar5QX/R0DIIyrJMcUpruK4QveTfJSTp3Shlq4Gk34cD/4GUWwkv0DVuzeuB+tXija7HBxii03NHDbPAD0AKnLr2wdAp
But this will occupy the only trusted-key and the softwares such as FakePlayer won't be able to work.
What's more, this way is only for server-side. You must use KeyPatcher to patch client.