[Openid-specs-ab] amr vs acr

Nat Sakimura sakimura at gmail.com
Fri May 31 23:50:41 UTC 2013

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.
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>

> Hi,
> 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,
> Torsten.
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> Openid-specs-ab mailing list
> Openid-specs-ab at lists.openid.net
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Nat Sakimura (=nat)
Chairman, OpenID Foundation
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