http://tzoz3bensgxyzs7da7lpgsn3a74h7hlbm4wa6ytq2tg6ktd57w22vqqd.onion/doc/about/openpgp_keys/signing_key_revocation/index.pt.html
Three different shares are needed to reassemble the revocation
certificate. For example, shares A1, A2, and A3, or shares A1, B, and C.
How to store your share
=======================
Please keep your share in an encrypted storage and make it as hard as you
can for untrusted people to get a copy of it.