[Openid-specs-ab] amr vs acr

Mike Jones Michael.Jones at microsoft.com
Sat Jun 1 01:19:23 UTC 2013

I disagree with the MUSTs.  We already have language in place saying that if claims aren't understood, they should be ignored, so there's no actual problem.  (Were there a problem, it would apply to "acr" as well.)

I could see going as far as saying, in both "acr" and "amr" that "The definition of particular values to be used in the acr/amr Claim is beyond the scope of this specification.  Parties using this claim will need to agree on the meanings of the values used for it to be useful to them."

                                                                -- Mike

From: Nat Sakimura [mailto:sakimura at gmail.com]
Sent: Friday, May 31, 2013 6:06 PM
To: Mike Jones
Cc: Torsten Lodderstedt; OpenId Connect List
Subject: Re: [Openid-specs-ab] amr vs acr

Ah, that's the call in the morning of the JICS that you did in the 11th floor of NII.
I came in late, sitting at a different table that hearing to the call was a bit hard but did not mind as I was very much distracted by various things to be dealt with JICS.

I remember talking about changing 1,2,3,4 as it became non-compliant to the RFC, as well as arguing against conflating authentication method with the authentication class, on the basis that authentication method by itself is useless and harmful, as in the previous mail. I mistakingly thought that I have killed the idea of amr, which apparently was not.

Unfortunately, the discussion is not recorded in http://lists.openid.net/pipermail/openid-specs-ab/Week-of-Mon-20130304/003231.html .

Probably, we should add some warning text to amr then. At the end of the definition of arm, how about adding the following?

When using amr, the RP and OP MUST define the common context including the meaning, security characteristics, and the compliance requirement for using it and the RP MUST be able to evaluate the values according to the defined context.

That would mitigate my worries.

2013/6/1 Mike Jones <Michael.Jones at microsoft.com<mailto:Michael.Jones at microsoft.com>>
This was one of the two open issues discussed on the 4-Mar-13 working group call.  You were on that call, according to the minutes.  We had a fairly extensive discussion about the meaning of "acr" and the right way to return information about authentication methods used.  Originally the request was to allow multi-valued "acr" values.  There was a use case where an implementation wanted to communicate the actual methods used such as "password", "OTP", "code in text message", etc. and I'd originally advocated for letting "acr" be multi-valued, just like PAPE did.  John, Tony, and I think you convinced us that that conflating classes with methods would create more problems than it would solve and that it was better to define an optional claim for returning an array of methods used, when needed.

On that call we also deleted the LoA values "1", "2", "3", and "4" since as part of that discussion, it came up that they are prohibited by RFC 6711.  Instead, we replaced the example values used with real values from InCommon - urn:mace:incommon:iap:bronze and urn:mace:incommon:iap:silver.

I don't think that we should require "acr" when "amr" is used, because there may not be a class, even though there are methods.  It depends upon the business context in which the parties are communicating.  Like "acr", "amr" is only useful when the values are understood by both parties.  Nonetheless, it's better to have a standard claim for these methods than to have everyone make up a different one.  This kind of information is used in practice, in some contexts.

                                                                -- Mike

From: openid-specs-ab-bounces at lists.openid.net<mailto:openid-specs-ab-bounces at lists.openid.net> [mailto:openid-specs-ab-bounces at lists.openid.net<mailto:openid-specs-ab-bounces at lists.openid.net>] On Behalf Of Nat Sakimura
Sent: Friday, May 31, 2013 4:53 PM
To: Torsten Lodderstedt
Cc: OpenId Connect List
Subject: Re: [Openid-specs-ab] amr vs acr

s/ where acr gives more context to the values of acr. / where acr gives more context to the values of amr. /

2013/6/1 Nat Sakimura <sakimura at gmail.com<mailto:sakimura at gmail.com>>
I suppose you mean amr, not acm.

I actually was not aware of amr till now. It seems it was a fairly quick decision made between March 4 and 6.
See https://bitbucket.org/openid/connect/issue/789/make-acr-claim-values-be-arrays-of-acr
At the time, I was so busy managing JICS 2013, so it went unnoticed for me.
I also searched through the list archive, but I cannot find the topic in it. There is no record of the decision on the call notes either.

Mike, could you point us to the record how the WG decision was reached?

Apparently, amr is the list of authentication methods, while acr is the indicator of the identity proofing and authentication quality.
i.e., amr is just the list of such things like "password", "otp", etc. while acr is "InCommons Silver", "ISO29115 LoA 3", etc.

Personally, I do not see much value in amr since it does not indicate any quality information. It may even be harmful when used without context in the sense that it may create sense of false security to the relying parties. For example, "otp" by itself does not mean it is secure. An OTP system with badly managed seed will generate a predictable sequence of "one time passwords", which is not secure at all. It would only be meaningful when there is an assurance that the system is properly managed. In this respect, amr may be meaningful as an auxiliary information only when it is used with acr, where acr gives more context to the values of acr.

I might want to require acr if amr is used, or drop amr, but that is only my personal opinion.

2013/6/1 Torsten Lodderstedt <torsten at lodderstedt.net<mailto:torsten at lodderstedt.net>>

could someone please describe me the difference between the id token members acr and acm? From my understanding, they are just the same. I'm also interested to learn why the authorization request allows to specify multiple acrs but does not support to specify any authentication method (via acm). Additionally, why is there no way to indicate more than one acr in the id token?

Thanks in advance,
Openid-specs-ab mailing list
Openid-specs-ab at lists.openid.net<mailto:Openid-specs-ab at lists.openid.net>

Nat Sakimura (=nat)
Chairman, OpenID Foundation

Nat Sakimura (=nat)
Chairman, OpenID Foundation

Nat Sakimura (=nat)
Chairman, OpenID Foundation
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