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Remote access from ubiquitous IPSec hosts


  GSM phone users on this list are probably quite familiar with
  the idea of "user mobility" v/s "device mobility". These users
  can take any generic (some prefer the term "identity-less") GSM 
  phone and "personalize" it by inserting their SIM card (a highly
  portable card about the size of a thumbprint). Assuming
  that appropriate administrative agreements are in place, users
  can roam between countries without even having to carry their
  personal device (phone).

  Now imagine if you will, ubiquitous IPSec-capable hosts at airports,
  hotels and other public places (we are not there yet with IPSec,
  but SSL in the form of HTTPS already enjoys this level of ubiquity).
  It would be really cool if mechanisms developed by the IPSec/IPSecond
  working group would allow a mobile corporate employee to walk up to
  one of these "identity-less" hosts and securely access network
  resources on his/her company's intranet (let's put aside device trust
  issues for a while ... more on those a little later).
  
  The key requirement here is that even the Phase I exchange must
  rely on a "portable" authentication mechanism, i.e. authentication
  should be based on information supplied by the user and on such 
  information alone. If authentication is based on certificates,
  there's the problem of easily transferring a user's keys into
  the IPSec host. While this is doable, it requires several 
  infrastructure changes. People have been drawn to more portable
  authentication mechanisms like token cards and OTPs for this reason.
  The current XAUTH proposal assumes that mutual authentication 
  in Phase I can be accomplished without any user-specific input.
  This is hard to ensure in the remote access scenario above.
  The hybrid authentication proposal, on the other hand, is applicable.
  This is not to say that the proposal is perfect (e.g. objections to
  its use of the NOTIFY payload are quite valid in my opinion).
  However, the ability to support IPSec-based remote access from 
  identity-less hosts is certainly worth preserving IMHO. 
 
  Some of you might be thinking: Is it really wise to trust such
  identity-less hosts for remote access? Isn't it possible for the host
  to intercept sensitive information? These are valid concerns but
  not unique to this scenario. Even if you carry your own device,
  how do you know that the IPSec stack is trustworthy (most OS vendors
  don't offer code in source form). Similar device trust issues
  also arise everytime you use a bank card to withdraw cash from
  an ATM. The trust in these cases comes from existing laws.
  
  Thanks for your time. I'd like to hear what others think about this.
  
  vipul
  
  p.s. BTW, it is possible to achieve some of this with the existing
       IPSec drafts, e.g. by using aggressive exchange with pre-shared
       keys along with the ID_KEY_ID identifier payload and letting
       the user type in the pre-shared key. The only wrinkles are:
       IPSec compliant implementations are not required to support
       aggressive mode and users are notoriously bad at remembering
       large keys (small keys are susceptible to off-line guessing
       attacks). Is anyone looking into adapting schemes like
       Bellovin-Merritt's EKE for Phase I authentication?
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