Thoughts on "Initial authentication"

"If it was easy we'd have already done it!"

I've recently contributed to some work on 'Password management". Here are some of the thoughts that I've managed to condense into words. Don't be disappointed - they raise at least as many questions as they answer.

1) Looking say five years ahead I think we need to talk about 'authentication' and not just 'passwords'. Given their vulnerability to keyboard sniffing it seems to me that within five years it will be necessary at least to support (though perhaps not require) some sort(s) of non-password based authentication for some systems.

2) While there will be pressure do so, it might be better not to try to solve everyone's problems. For example in some cases it might still be best to create a shared password system for use only on a limited set of systems and not allow anyone else to use it.

3) The understandable enthusiasm for SSO by some is at variance with an equal enthusiasm, in some cases promoted by the same people, for aggressive inactivity timeouts on individual systems. Meeting everyone's individual security requirements may result in an unusable service.

4) The group developing HTML5 have adopted a policy that says "In case of conflict, consider users over authors over implementers over specifiers over theoretical purity". It might be sensible to adopt something similar in this area (suitably adapted). Or perhaps not... Discuss.

5) A critical feature of any authentication system is who is able to reset its authentication credentials (i.e. reset passwords or equivalent), because they (all of them) can subvert the security of the systems (all of them) that use it. It looks to me to be difficult to simultaneously meet the expectations of people who would like easy local reset of passwords and the operators of some 'high risk' systems who want tight control of access.

6) Given the existence of a central password verification service overloading existing protocols (LDAP, Radius, ...), I don't see any technical way to restrict the clients that can use it since clients don't identify themselves. Such use could be restricted by rules, but they would be hard to enforce, and by non-100% perfect technical restrictions (e.g. client IP address filtering). So anyone providing such a service will have to accept that in practise it will be open to anyone to use. You could implement a central password verification service using something like SAML, where clients are strongly identified, but then there wouldn't be any clients to use it.

7) Accepting that we'll at least have to accept passwords for the foreseeable future (even if we accept other things in parallel), then the not-unreasonable idea that people will only willing accept using two passwords restricts us to a maximum of two authentication systems. So how about:

• a) A 'low trust' service verifying a single password over one or more commonly used protocols (so LDAP, RADUIS, TACAS), intended for use in situations where we can't do better (3rd party service that can only do LDAP auth, WebDAV service that has to work with common clients that can only do username/password, etc).Document that this is a low trust service, that server operators can intercept passwords in transit, etc. Require good practive as a condition of using the service - don't ship passwords over unsecured networks, don't write them to disk, etc. Perhaps make token attempts to restrict client access (e.g. by IP address) but accept and document that this won't be perfect. This violates all my prerequisites for secure use of passwords, but perhaps on balance doing so is necessary to support what needs to be supported.
• b) A 'higher trust' service where credential disclosure is limited to local workstations and a logically single central server. Web redirection based protocols (i.e. Ucam_WebAuth, Shibboleth) and Kerberos (and so Windows AD) meet this requirement and provide at least some single sign-on. Web redirect, and perhaps Kerberos could both use things other than a password for initial authentication. SPNEGO holds the possibility of transparently transferring a pre-existing Kerberos session into a web redirection-based system thus widening SSO for existing Kerberos users but leaving open password or other authentication for access to web systems in situations when Kerberos isn't available.

Item (b) violates my third prerequisite for secure use of passwords ("It must be possible for password holders to decide when it is safe to divulge their password"), but I'm coming to the conclusion that the price of adhering to this principle does not warrant the cost.

8) If you can't stomach the single shared password idea, an alternative might be a 'Managed Password Service' that extended the 'token' (in the current University Computing Service sense) idea by centrally managing multiple password sets (one for each 'system'). So the administrator of a new system somewhere could mint a new password set for their system and configure their system to do password verification against it using LDAP, RADIUS or anything else supported. Users could set and reset these passwords under the authority of their web redirect/Kerberos credentials. The end-system would have to it's own authorisation since in principle anyone could create a password for any system. This doesn't give 'two passwords', but it does at least allow one password to manage all the others.