Or to
put it another way, when Scott goes to buy his beer, why does
this clerk believe the ID card proves Scott can legally purchase
alcohol (and that the ID card isn??™t borrowed from a friend) and
that it was actually issued by the department of motor vehicles?
This demonstrates a brokering of trust, where the RP can believe
the statements made about a subject without directly contacting
the IP. The following must be proven to be true for the transfer of
trust to succeed:
The information on the card is truly being provided by a
trusted party.
The information applies to the subject presenting the card.
What CardSpace Provides
It is essential that
the source of the
information on a
card can be veri?¬?ed
182 Windows CardSpace
In Scott??™s case, the watermarking and other details on the card
make it hard to reproduce, so it can be trusted that it really was
created by the department of motor vehicles, which satis?¬?es the
?¬?rst condition. The second condition is met by the picture of
Scott on the card, which the clerk can use to identify that the
card does apply to Scott. The other usage scenarios previously
listed show the variety of ways that these conditions can be met.
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