Encryption

To enable an efficient encryption of posts (also files) for groups (aspects) the following is applied:

1. a random key (RK) is generated
2. the post is encrypted with the random key: enc(RK, msg)
3. for each recipient Rn, RK is encrypted with their public key: enc(pub(Rn), RK)
4. the encrypted key is sent to each recipient

If a friend is added to the group, RK is encrypted once more. If a friend is removed from a group, we don't generate a new RK to re-encrypt everything.