monkeysphere - ssh and TLS authentication framework using OpenPGP Web
Monkeysphere is a framework to leverage the OpenPGP web of trust for
OpenSSH and TLS key-based authentication. OpenPGP keys are tracked via
GnuPG, and added to the authorized_keys and known_hosts files used by
OpenSSH for connection authentication. Monkeysphere can also be used
by a validation agent to validate TLS connections (e.g. https).
Each host that uses the Monkeysphere to authenticate its remote users
needs some way to determine that those users are who they claim to be.
SSH permits key-based authentication, but we want instead to bind
authenticators to human-comprehensible user identities. This switch
from raw keys to User IDs makes it possible for administrators to see
intuitively who has access to an account, and it also enables end users
to transition keys (and revoke compromised ones) automatically across
all Monkeysphere-enabled hosts. The User IDs and certifications that
the Monkeysphere relies on are found in the OpenPGP Web of Trust.
However, in order to establish this binding, each host must know whose
cerifications to trust. Someone who a host trusts to certify User
Identities is called an Identity Certifier. A host must have at least
one Identity Certifier in order to bind User IDs to keys. Commonly,
every ID Certifier would be trusted by the host to fully identify any
User ID, but more nuanced approaches are possible as well. For
example, a given host could specify a dozen ID certifiers, but assign
them all "marginal" trust. Then any given User ID would need to be
certified in the OpenPGP Web of Trust by at least three of those
It is also possible to limit the scope of trust for a given ID
Certifier to a particular domain. That is, a host can be configured to
fully (or marginally) trust a particular ID Certifier only when they
certify identities within, say, example.org (based on the e-mail
address in the User ID).
The monkeysphere commands work from a set of user IDs to determine
acceptable keys for ssh and TLS authentication. OpenPGP keys are
considered acceptable if the following criteria are met:
The key must have the ‘authentication’ (‘a’) usage flag set.
The key itself must be valid, i.e. it must be well-formed, not
expired, and not revoked.
The relevant user ID must be signed by a trusted identity
The OpenPGP keys for hosts have associated ‘service names‘ (OpenPGP
user IDs) that are based on URI specifications for the service. Some
Written by: Jameson Rollins <email@example.com>, Daniel Kahn
monkeysphere(1), monkeysphere-host(8), monkeysphere-authentication(8),
openpgp2ssh(1), pem2openpgp(1), gpg(1),