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RE: [higgins-dev] PPID generation

 
so if the master key and salt value was known, then you could generate the unique ppid for a rp with a utility pgm, how does the master key and salt value get initially populated, and is it in the card itself, or the card store
From: higgins-dev-bounces@xxxxxxxxxxx [mailto:higgins-dev-bounces@xxxxxxxxxxx] On Behalf Of Andrew Hodgkinson
Sent: Thursday, May 10, 2007 3:05 PM
To: Higgins (Trust Framework) Project developer discussions
Subject: Re: [higgins-dev] PPID generation

Unless the "AppliesTo" element is passed to the STS, the client is required to provide a PPID value in the RST message.  The STS can return the PPID unmodified in the RSTR or it can use the PPID as input to a custom PPID function (section 4.3.4).


When the client generates the PPID, the algorithm requires the use of a master key and a salt value.  Both of these values are contained within the "information card private data" area of the card store.  In order to generate the same unique PPID for a given card and relying party, the master key must be known to the client.  It is the relying party's responsibility to verify, for a given user, that the PPID matches a PPID previously used or registered at the RP by the user.


>>> "Broberg, Jeffrey C" <Jeffrey.Broberg@xxxxxx> 05/10/07 12:28 PM >>>

In the MS infocard doco, they talk about how a ppid is generated and made unique for a particular RP


the doco


<start>

7.5.2. PPID

The PPID MUST be computed as follows using the card identifier (value of the ic:CardId

element in the information card) and the RP identifier (constructed as in Section 160H7.5.1):

• Encode the value of the ic:CardId element of the information card into a sequence

of bytes, call it CardIdBytes, using Unicode encoding.

• Hash CardIdBytes using the SHA256 hash function to obtain the canonical card

identifier CanonicalCardId.

CanonicalCardId = SHA256 (CardIdBytes)

• Hash the RP identifier with the CanonicalCardId using the SHA256 hash function to

obtain the PPID.

PPID = SHA256 (RP identifier + CanonicalCardId)

<end>


my question is this, can a rp be tricked by someone trying to generate a PPID for someone elses card.  Is it all dependent on the unique cardid ?  it seems like this algorithem could easily replicate a PPID if you know the RP you are going to, and the cardid naming scheme used by the users card provider.  I must be wrong...


Jeffrey C. Broberg


CA
Director, Senior Architect


Security Systems


Advanced Technology Group
Tel: +1-508-628-8490
Jeffrey.Broberg@xxxxxx


=

jeff.broberg




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