Handed out: October 18, 2005
Due back: October 28 11:59pm (by submission
timestamp).
Submission: Electronic upload submission (see
instruction online at the course webpage)
Notes: 1. To be
done individually.
2. Please do not give a
simple yes/no as results to some of the questions. Briefly explain why and how you achieve that
result.
3. KPS stands for the
book “Network
Security - Private Communication in a Public World”, by Charlie
Kaufman, Radia Perlman and Mike Speciner, 2nd Edition, Prentice Hall, 2002
1.
KPS
problem 5-2
Message digests are reasonably fast, but
here’s a much faster function to compute. Take your message,
divide it into 128-bit chunks, and all the chunks together to get a 128-bit result. Do the standard message digest on the result. Is this a good
message digest function?
2.
KPS
problem 5-3
We discuss the devious secretary Bob having an automatic means of generating
many messages that
3.
KPS
problem 5-4
In the lectures, we described a hash algorithm in which a constant was
successively encrypted with blocks of the message. We showed that you could
find two messages with the same hash value in about 232 operations.
So we suggested doubling the hash size by using the message twice, first in
forward order to make up the first half of the hash, and then in reverse order
for the second half of the hash. Assuming a 64-bit encryption block, how could
you find two messages with the same hash value in about 232 iterations? Hints: consider blockwise palindromic
messages.
4.
KPS
problem 9-2
In the lectures, we found that it is extremely difficult, without public
key cryptography, to have an authentication scheme which protects against both
eavesdropping and server database disclosure. Consider the following
authentication protocol (which is based on Novell version 3 security).
Is this an example of an authentication scheme that isn’t based on
public key cryptography and yet guards against both eavesdropping and server
database disclosure?
5.
KPS
problem 11-5
Suppose we are using a three-message mutual authentication protocol, and
Is this protocol secure?