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Subject: Re: Representing anonymous Subjects
Hmmmm..... At FTF3 we took it as implied that we were going to have a "bearer" option in the subject specifier. However we were pretty sure that our thinking on the topic was confused; to quote from FTF3 minutes: >ISSUE:[F2F#3-35]: BobB said in an aside that there is something wrong >with at least some of the occurrences of our use of the "bearer" in >Subject specifiers in all of the above constructs. Need to get him to >elaborate in detail on what his observations are. I didn't do this, but it also appears that "bearer" has disappeared from the schema , probably because I couldn't find our whiteboard mentions of it at all in the minutes (!) We need to add it back and discuss how to get it right. I agree with Marlena that we don't currently capture the concept: >Summary: I don't think we currently have a good way of representing >either "bearer" assertions or anonymous assertions gotten via an artifact. > A possible solution is the extension of the Subject field to >include an "anonymous" type. But I'm no >XML expert. I'm hoping that if others agree that there is a need, >we can work out the XML specifics. I see three possibilities: (1) A distinguished name, to be used within the "name" field of a subject definition. (2) A distinguished public "key" field to be used with the "holder of key" (is it called "authenticator" now?) field (3) A type-distinct fourth subject option, called "bearer". I don't like either (1) or (2) -- I'd rather have (3). I don't necessarily think that bearer = anonymous, however, since in either an authentication assertion or an attribute assertion, other asserted data may in fact identify the subject. However you could USE a bearer token to implement anonymity. Now I need to think about what the issues are and how to get it right.... --bob Bob Blakley (email: blakley@us.tivoli.com phone: +1 512 436 1564) Chief Scientist, Security, Tivoli Systems, Inc. Marlena Erdos <marlena@us.ibm.com> on 08/20/2001 12:59:25 AM To: security-services@lists.oasis-open.org cc: Subject: Representing anonymous Subjects Dear SAML'ers, Recent discussions of the http binding have brought up two flows that result in assertions about (potentially) anonymous subjects. These flows either involve an artifact (or "handle" in Shibboleth) that is used to retrieve an assertion about the browser user, or involve the assertion being "redirected" (so to speak) through the user's browser (via interesting uses of javascript and "post"). Various discussions have flowed about impersonation countermeasures and other aspects of these http-based flows. I won't repeat them here. Instead, I'd like to raise up the question of the "Subject" element in the assertion. In both flows (artifact or "bearer" assertion), it is possible for the assertion to have an anonymous (or pseudonymous) subject. (Note that the assertion could be either an authN or attribute assertion.) Currently, the Subject element in the SAML schema (version 14) doesn't seem to have a graceful way of dealing with the sorts of anonymous subjects that arise from the http binding. (I'll continue to say "anonymous subjects" to refer to both anonymity and pseudonymity, and to mean the http binding case.) Here's what it does allow for (to the extent that I understand the schema correctly). I'll follow with a brief discussion on why none of the options seem to have a good fit for the anonymous subject case. The Subject element allows for 3 different types of identifiers. It allows for -- a string "name" qualified by a security domain -- an "authenticator" field (mostly related to a subject authenticating with a key) -- a reference to another assertion or inclusion ofthat assertion Why these don't really fit: - The string name could be used to convey the contents of the handle or the "assertion id" part of the artifact, but neither of these is in any way a subject 'name'. I suppose that the RP could use the fake name as a real name in its continued processing, but that is conceptually incorrect, and it feels like looking for trouble to me. (One concrete difficulty is how an RP could meaningfully have the notion of "anonymous" in an authZ policy if it can't tell the difference between a fake name referring to an anonymous user and a real user name.) - The authenticator field strikes me as being mostly related to subjects with keys, but Phill (in a phone call with me) suggested that it could be used for the anonymous browser user case. I feel reluctant about this because the association between an anonymous browser user and an assertion is just that -- an association. To refer to it as an authentication just seems like a distortion of both the term authentication and what is really going on from a processing standpoint. (That is, the RP validates the association of user and assertion rather than validating the identity of the user. ) - The reference to an assertion or inclusion of one doesn't seem to apply, because anonymous assertions in the http binding are (often) the initial ones. There is not necessarily any other assertion to refer to (and there would still be the question of representing anonymity in that assertion!). Summary: I don't think we currently have a good way of representing either "bearer" assertions or anonymous assertions gotten via an artifact. A possible solution is the extension of the Subject field to include an "anonymous" type. But I'm no XML expert. I'm hoping that if others agree that there is a need, we can work out the XML specifics. Regards, Marlena IBM/Tivoli PS My apologies if I've misunderstood the meaning of the fields in the current schema. I welcome enlightenment. ---------------------------------------------------------------- To subscribe or unsubscribe from this elist use the subscription manager: <http://lists.oasis-open.org/ob/adm.pl>
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