| נשלח בתאריך: 13 February 2008 בשעה 12:42 | | IP רשוּם
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Hi
I have a question from an exam that I'm not sure about
the solution:
Let's say that two stations, A and B, have an algorithm E
for symmetric encryption and an algorithm D for decryption
(with common long lived key K). The two stations want to start
a conversation. The protocol starts with four messages
which ensure mutual authentication between the two stations.
1. A sends B: A,R1 (A's name and a random number R1)
2. B sends A: B,R2 (B's name and a random number R2)
3. A sends B: Ek(R2) (the encryption of R2 using the algorithm E
and the symmetric long lived key K)
4. B sends A: Ek(R1) (the same as above)
Now the two stations want to calculate a conversation key for
the current conversation.
which of the following suggestions are not good for this purpose:
1. Ek(R1+R2+1)
2. Dk(R1+R2+1)
3. K xor R1 xor R2
4. Ek(K xor R1 xor R2)
5. Dk(K xor R1 xor R2)
6. Ek(R1 xor R2)
7. Dk(R1 xor R2)
thanks
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