Progressive Authentication

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Full Title or Meme

When the exact nature of the user request is unknown, it is best to try Authentication in the least obtrusive manner, which is typically not at the highest level they might need later in the interchange.


Then general use case[1] is where trust elevation must occur at some time during the a long term engagement, as when as user first goes to a site to get information, investigates the options and then decides to commit to the service offering that requires stronger identity in order to qualify for access to some resource, such as a state sponsored benefit.

An anti-use case was discovered when the NSA funded the Blacker System[2] which attempted to use the Bell-LaPadula model with computer networking.

When mobile device became common it was early realized that the blacker solution was not feasible and progressive authentication was proposed[3] for mobile y devices and later specifically for Android devices.[4]

An alternative definition of progressive authentication is a suite of authentication tests which can be selected to be run at a single time with a Trust Vector that can be tested by the authorization service.


NIST in now in the third update to their Digital Identity Guidelines [5] where they still insist, against all evidence to the contrary that "digital identity is the unique representation of a subject engaged in an online transaction." It is a fact, acknowledged in that publication that user will have different personas for email versus banking. Imposition of privacy obligations makes it clear that users must not be expected to offer detailed attributes of their life which are not needed for the transaction at hand, so there can be no expectation that any online representation of a user is anything other that what they are willing to release. While any Relying Party may insist on a high level of assurance as to the validity of the attributes provided by the user, in most cases those parties are willing to accept whatever assurances the user may offer, or the user will just go elsewhere. This should not be considered as any reason to abandon the current NIST publications. As of May 2018 these publications are still the best available benchmark for authenticating users on the internet. Still it is time to move on with the next generation of solution.


The best solution is one that asks the user only for sufficient attributes to complete the simplest tasks on the relying party web site. As more verification of the user's trustworthiness are required because of the user's request to access protected information, the authentication of the user can progress as those desire of the user are made known.


  1. Tom Jones Trust Elevation Use Case
  2. Donald MacKenzie, Mechanizing Proof: Computing, Risk and Trust, MIT Press
  3. Oriana Riva +3 Progressive authentication: deciding when to authenticate on mobile phones Published in: Proceedings Security'12 Proceedings of the 21st USENIX conference on Security symposium Pages 15-15 Bellevue, WA August 08 - 10, 2012,
  4. Jeffrey Warren, +3, Progressive Authentication on Android
  5. NIST Digital Identity Guidelines