The key used to
sign the token must
also be checked
194 Windows CardSpace
security. The token produced by CardSpace for Personal Cards is
a SAML1.1 assertion, which contains the public key of the card
for that RP. Like the PPID, the public key is unique to the relationship
between the RP and the card. The security token is
digitally signed by the private key. This signature provides strong
cryptographic proof that the token was really created by the
owner of the card. The PPID is a weaker form of identi?¬?cation. If
somebody somehow sneaks a peek at the contents of the security
token, he will ?¬?nd out the PPID of the user, and he could
create his own token that contains that PPID. When the attacker
saw the original token, he would also discover the public key in
the token. But it is of no real value to the attacker because it is
the private key used for the signing, so the attacker would be
unable to generate an imposter token if the RP veri?¬?es the PPID
and the public key of the incoming tokens. If the system only
uses the PPID, the security of the system is based only on
a shared symmetric key, rather than a much stronger asymmetric
key.
Uses of Personal Cards
Personal Cards can be used in a wide variety of situations that
exist on the Internet today.
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