From: Andrew Roos <andrewr@vironix.co.za>
Date: Tue, 3 Oct 95 08:40:03 PDT
To: aba@dcs.ex.ac.uk
Subject: STT Authentication
Message-ID: <9510031738.aa13031@herman.vironix.co.za>
MIME-Version: 1.0
Content-Type: text/plain


Hi All

Ramblings from a disturbed mind...

I've had a look at Microsoft's Secure Transaction Technology (STT) protocol.
The purchase order/authorization/receipt phase is authenticated using the
card holder's credential ("cred", in MS speak). The credential is similar to
a certificate except the binding is between a credit card and a public key,
rather than between an identity and a public key. What interests me is the
procedure for issuing cred's to cardholders. If I'm reading the spec right,
this is done in response to a "Cardholder Credential Request" message which
includes card details and the public keys to be associated with the card.
This data, along with a SHA hash of the data, is encrypted and sent to the
issuing bank, which then responds with a "Cardholder Credential Response"
containing the signature and key-exchange creds, also encrypted. However
there does not appear to be any authentication whatsoever on the credential
request message, presumably becuase the cardholder does not have a published
public key at the time when this message is issued. It may be that
authentication is out-of-band - e.g. the bank may phone the registered owner
of the card # before issuing a cred response message - but there is no
mention of this in the spec. If there isn't OOB authentication, then this is
a major hole in the protocol, since anyone who knew a credit card no, name
and expiry date could request a cred for that card, and then go shopping...

If someone will just tell me what I'm missing (because this is too obviously
f'd up for even Uncle Bill) then I'll go sit on top of my mountain again and
hum softly to myself.

Andrew

BTW, same apears to be true for Merchant creds.
________________________________________________________________
Andrew Roos <andrewr@vironix.co.za>

// C++ programmers have class (but not much inheritance)

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