'Create an L{ISSHPrivateKey} checker which recognizes C{users} and add it
to C{portal}.
@param portal: A L{Portal} to which to add the checker.
@type portal: L{Portal}
@param users: The users and their keys the checker will recognize.  Keys
are byte strings giving user names.  Values are byte strings giving
OpenSSH-formatted private keys.
@type users: L{dict}'

def setupKeyChecker(self, portal, users):

    mapping = dict([(k, [Key.fromString(v).public()]) for (k, v) in iteritems(users)])
    checker = SSHPublicKeyChecker(InMemorySSHKeyDB(mapping))
    portal.registerChecker(checker)
