In Response to the Society's Threats: Our Doors Need Three Keys

As a clarification to the confused, the following message is an encoded response to a similarly encoded message I received anonymously earlier this morning. The cipher was cracked simply with a few hours time in the library and asking Chronicler for advice. To prove that the initial message is from who it claims to be, I have made my reply slightly more complex.
As a clarification to those for whom the message is intended, my keys should say as much, if not more, than what lies behind the lock.

mo vle phkxd z aqb nr ckmc vbnrjc rlqvk fu gzmjsmk jy vewo zredgih eosd inyh vnvt cssdo. xskb rsssdxo ghpb ltvd. inyh ndetvx efzqsqmg ayvk jqsk. ceeq pebc’w hohkd ghpb ld idndh, qxc skb gihydw mskp bktkx kr lu sr fhytkxd ss zerxymd. au’vk fu gzmjsmk vyq cee.

don't. test. us.

Professor Terzak Winstonshire