Comment by nanomonkey

Shamir's Secret sharing allows one to store secret keys within m of n number of your peer group (where m is less than n), thus you can hand out an encrypted secret with 5 of your friends and reproduce the secret by getting 3 of them to respond back to you with the secret at a later date. None of the peers will be able to reproduce the secret by themselves.

There are other options for key storage, revoking group privileges, etc. It's an extensive topic, but the foundation is there, it just depends on your network and use cases.