[277] in Kerberos
timestamps in Kerberos: a question
daemon@TELECOM.MIT.EDU (steiner@ATHENA.MIT.EDU)
Mon Dec 7 14:06:01 1987
From: steiner@ATHENA.MIT.EDU
To: kerberos@ATHENA.MIT.EDU
Timestamps are used in the Kerberos protocol to help
detect replays of messages. The current status of
timestamps in Kerberos is: they are described in the
Technical Plan. They are partially implemented.
Partially implemented means that the timestamps are
inserted into messages from the user to Kerberos and
in Kerberos' reply back to the user. (I haven't looked
carefully at how they're used in the user->server exchange
yet.) Although the timestamps are sent back and forth
from user to Kerberos and back, no one ever looks at them.
My question is this: use of timestamps to preclude replays
is described inconsistently in the Technical Plan and I
wonder which way it should be.
1. On page 8, 4 paragraphs into the "4. The Kerberos Authentication
Model" section, it is stated that, in the part of the message
which Kerberos returns to the user, which is encrypted in the
user's private key, a "copy of the timestamp that was in the
original request" is inserted. In other words, a copy of the
timestamp which the client sent in the request, which the
client keeps a copy of.
2. On the other hand, on page 24, in the Protocol description of
the KKDS (section 7.1.2), it is stated that, in the reply from
Kerberos back to the user, one of the components of the "cipher"
(the part of the message encrypted in the user's private key,
as above) is
time_sec[kkds]
or the time of day according to the Kerberos server.
In the implementation, the second method is used. Could someone
shed some light; which one is correct, and what is the rationale
behind it?
Thanks,
Jennifer
