The purpose of the
preceding description was to show how the idea of ticket, or
token, coupled with the availability of an authority (the KDC)
can truly secure interactions andsupport identity-based decisions
directly at the resource, by propagating information otherwise
available only at a central location.
Remember when we tried to use certi?¬?cates for client authentication?
The few data we were able to embed in the certi?¬?cate
was the data available at the moment of issuance. In the
Kerberos model, in which a ticket is generated anew all the
time, we can guarantee that information is always as fresh as it
can get. Furthermore, we can embed arbitrary information or
Tickets can contain
arbitrary data and
are encrypted onthe-
?¬‚y so that only
the intended recipient
can consume
them
The Babel of Cryptography 75
even re?¬‚ect authentication and authorization decisions just by
emitting or not emitting a ticket upon request. The best part of
all this is that we didn??™t have to give up security for obtaining
such agile features. Every leg of the schema previously
described is properly secured. We can even overcome some of
the security weaknesses we encountered in the section ???Hard
Tokens.
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