) Every principal in a realm is
assigned a symmetric key. Such a key is known only by the key
owner itself and by a central service known as the Key
Distribution Center (KDC). The KDC knows the key of every
principal. In a nutshell, the KDC is the authority that is involved
every time a principal needs to authenticate for using another
principal; the currency used in the operation is a security token,
which in Kerberos terms is called a ticket.
We can use once more the help of our friend Alice for understanding,
at least in general terms, how the Kerberos protocol
works. Alice owns an account in our Kerberos realm; she wants
to access service B, also a principal in the same realm.
1. Before everything else, Alice needs to log into the system.
She accomplishes that by sending her credentials to
the authentication service (AS), a component of the
KDC. ???Sending her credentials??? is not actually accurate,
but it should be enough for the purpose of the discussion.
Kerberos is a
widely adopted
technology
Principal, realms,
KDC, and tickets
are the basic entities
and concepts
behind Kerberos
The Babel of Cryptography 73
2. If the AS recognizes Alice as a principal in the realm, it
sends back to her two pieces of data:
A symmetric key that will work as a session key for
all future communications between Alice and the
KDC.
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