Requiring Pseudonymous Identifier

John Bradley jbradley at
Thu May 14 03:16:49 UTC 2009

Sorry I am playing catchup on this thread.

There may be use cases where you want to rotate the users PPID URI.
That is only practical if you have a per user salt.

Are you talking about letting groups of RP's in a close federation  
generate the same PPID?

We solved this two ways in info-card:
1 For RP's with Class 2 certificates the "Client Pseudonym" is based  
on a subset of the fields in the DN.
	Or, Locality, State/Prov, and Country.   This allows the CN for SSL  
to differ but generate the same PPID for sites within the same  
2. We have something called a RP/STS that allows multiple RPs that  
have a trust relationship say inside a company to proxy trust through  
a common authentication point.

2 would be difficult for openID but 1 is certainly worth considering.

If the RP has a cert the CN or other fields could be used to calculate  
the "Client Psyudonim" rather than the realm.

John Bradley

On 13-May-09, at 12:07 PM, specs-request at wrote:

> Date: Wed, 13 May 2009 16:00:25 +0900
> From: Nat Sakimura <sakimura at>
> Subject: Re: Requiring Pseudonymous Identifier
> To: Dick Hardt <dick.hardt at>
> Cc: OpenID Specs Mailing List <specs at>
> Message-ID:
> 	<bf26e2340905130000r2adc5f09ve15e2f653ea9b7e7 at>
> Content-Type: text/plain; charset=ISO-8859-1
> Sorry for a slow response. This week is especially busy for me...
> I borrowed the notion from Austrian Citizen ID system.
> In there, the services are divided into "sectors."
> A sector may span several agencies.
> They call ID as PIN (Personal Identification Number).
> There is a secret PIN (sPIN) which is not used anywhere but in their  
> SmartCard.
> Then, sector sepcific PIN (ssPIN) is calculated in the manner of :
> SHA1(sPIN + SectorID)
> (Note, there is a bit more details but...)
> I have thrown OP secret into it.
> To avoid the analytic attack, I agree that it is better to use
> individual secret, as some of you
> points out.
> Regards,
> =nat

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