Keyserver exercise

keyservers.txt

Keyservers:

A keyserver is a repository for cryptographic keys. A person can upload their
keys to a keyserver, and other persons can retrieve the key if they want to
send them an encrypted message.

To avoid a keyserver being compromised, several keyservers can be connected
and share their databases. So if one server has its keys changed, the other
servers can 

Each key, by the way, has a "hash" (some number) that with some probability is
the only hash for that particular key. Such hashes are useful because they can
be remembered by humans. Also, a keyserver can be asked of a key by giving its
hash.

A key has the form {key, N}, and an identity has the form {id, M}, where N is
just a big number, and M is some string (e.g. "Simon Shine <[email protected]>").

Implement the following API:

  Function name                        Return value               Blocking?
-------------------------------------------------------------------------------
  keyserver:start()                 -> {ok, ServerPid}
  keyserver:put(ServerPid, Id, Key) -> true / false
  keyserver:get(ServerPid, Id)      -> {found, Key} / notfound
  keyserver:connect(FromPid, ToPid) -> true / false
  keyserver:checkHealth(ServerPid)  -> ...