path: root/doc/MonkeySpec

THE MONKEYSPHERE
================

Monkeysphere is authentication layer that allows the sysadmin to
perform authorization on OpenPGP user identities instead of on keys.
It also allows end users to authenticate/identify the ssh server they
are connecting to by checking the sysadmin's certification.

* GENERAL GOAL - use openpgp web-of-trust to authenticate ppl for SSH
* SPECIFIC GOAL - allow openssh to tie into pgp web-of-trust without
  modifying the openpgp spec, gpg or openssh 
* DESIGN GOALS - authentication, use the existing generic OpenSSH
  client, the admin can make it default, although end-user should be
  decide to use monkeysphere or not 
* DESIGN GOAL - use of monkeysphere should not radically change
  connecting-to-server experience

Host identity piece of monkeysphere could be used without buying into
the user authentication component.


USE CASE
========

Dramatis Personae: http://en.wikipedia.org/wiki/Alice_and_Bob
Backstory: http://www.conceptlabs.co.uk/alicebob.html

Bob wants to sign on to the computer "mangabey.example.org" via
monkeysphere framework.  He doesn't yet have access to the machine,
but he knows Alice, who is the admin of mangabey.  Alice and Bob,
being the conscientious netizens that they are, have already published
their personal gpg keys to the web of trust, and being good friends,
have both signed each other's keys and marked each others keys with
"full" ownertrust.

When Alice set up mangabey initially, she published an OpenPGP key for
the machine with the special userid of "ssh://mangabey.example.org".
She also signed mangabey's OpenPGP key and published this
certification to commonly-used keyservers.  Alice also configured
mangabey to treat her own key with full ownertrust, so that it knows
how to identify connecting users.

Now, Alice creates a user account "bob" on mangabey, and puts Bob's
userid ("Bob <bob@example.org>") in the authorized_user_ids file for
user bob on mangabey.  The monkeysphere automatically (via cron or
inotify hook) takes each userid in bob's authorized_user_ids file, and
looks on a keyserver to find all public keys associated with that user
ID, with the goal of populating the authorized_keys file for
bob@mangabey.

In particular: for each key found, the server evaluates the calculated
validity of the specified user ID based on the ownertrust rules it has
configured ("trust alice's certifications fully", in this example).
For each key for which the user ID in question is fully-valid, it
extracts all DSA- or RSA-based primary or secondary keys marked with
the authentication usage flag, and converts these OpenPGP public keys
into ssh public keys.  These keys are automatically placed into the
authorized_keys file for bob.

Bob now attempts to connect, by firing up a terminal and invoking:
"ssh bob@mangabey.example.org".  Bob's monkeysphere-enabled ssh client
notices that mangabey.example.org isn't already available in bob's
known_hosts file, and fetches the host key for mangabey from the
public keyservers, with the goal of populating Bob's local known_hosts
file.

In particular: the monkeysphere queries its configured keyservers to
find all public keys with User ID ssh://mangabey.example.org.  For
each public key found, it checks the relevant User ID's validity,
converts any authentication-capable OpenPGP public keys into ssh
public keys if the User ID validity is acceptable, and finally insert
those keys into Bob's known_hosts file.

On Bob's side, since mangabey's key had "full" validity (it was signed
by Alice, whom he fully trusts), Bob's ssh client deems mangabey
"known" and no further host key checking is required.

On mangabey's side, since Bob's key has "full" validity (it had been
signed by Alice, mangabey's trusted administrator), Bob is
authenticated and therefore authorized to log into his account.