As a replacement for username and
password authentication, Personal Cards provide a new level of
security, along with usability. In addition, the convenience of
providing common data to websites can signi?¬?cantly lower the
likelihood of ???drop-off??? on new account sign-up. It also makes it
easy for users to keep information current at sites where they use
cards. If users update their home phone numbers, the next time
they use a card at a site it will automatically get this new information,
without users having to remember to ???update their pro-
?¬?le.??? Finally, with users able to create as many cards as they
want, each different persona that they want to have is easily
accommodated.
Personal Cards can
be an easy way to
improve security on
most sites
195 A Deeper Look at Information Cards
How Is the Site-Speci?¬?c Card ID Calculated?
The purpose of the site-speci?¬?c card ID is to provide a user-friendly form of the
bytes in the PPID. To create the site-speci?¬?c card ID, ?¬?rst the PPID bytes are
hashed with a SHA1 hash function. Next, the ?¬?rst 10 bytes of the hash are taken
and each is divided by 32. The remainder of each division is saved, yielding 10
numbers, ranging between 0 and 31.
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