Cryptography and Network Security Chapter 7. Fourth Edition by William Stallings Lecture slides by Lawrie Brown Modified – Tom Noack, UPRM. Chapter 7 – Confidentiality Using Symmetric Encryption.
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by William Stallings
Lecture slides by Lawrie Brown
Modified – Tom Noack, UPRM
John wrote the letters of the alphabet under the letters in its first lines and tried it against the message. Immediately he knew that once more he had broken the code. It was extraordinary the feeling of triumph he had. He felt on top of the world. For not only had he done it, had he broken the July code, but he now had the key to every future coded message, since instructions as to the source of the next one must of necessity appear in the current one at the end of each month.
—Talking to Strange Men, Ruth Rendell
Note:physically vulnerable points
Vulnerable points in software
Again, note who can look at each vulnerable pointISP or monitors of ISP’ssysadmins
IDA||IDB||N1 Sent in clear – identifies A, B, and this request
E(Ka,[KS||IDA||IDB||N1])||E(Kb[Ks.IDA) – Only message sent by KDC
E(Kb,[Ks||IDA]) Retransmitted to B part of message 2
E(KS,N2) B is sending a Nonce, also says I know Ks
E(KS,f(N2)) You can’t make this with a replay
Xn+1 = (aXn + c) mod m
Xi = EKm[i]
Xi = EKm[Xi-1]