Suppose that someone suggests the following way to confirm that the two of you a

Q: Suppose that someone suggests the following way to confirm that the two of you a

Answer: Yes, an attacker can attend the message and find the key in next way: - Let ‘A’ and ‘B’ are the associates, and ‘K’ is the key of size ‘N’. 1> A makes random string ‘R’ 2> Computes S : = K XOR R 3> S to B 4> B computes S1:= S XOR K 5> S1 to A 6> A authenticates whether R = S1 or not? So an attacker attending the talk will have both ‘S’ and ‘S1’. So, K: = S1 XOR S

ID: 3926430 • Letter: S

Question

Suppose that someone suggests the following way to confirm that the two of you are both in possession of the same secret key. You create a random bit string the length of the key, XOR it with the key, and send the result over the channel. Your partner XORs the incoming block with the key (which should be the same as your key) and sends it back. You check, and if what you receive is your original random string, you have verified that your partner has the same secret key, yet neither of you has ever transmitted the key. Is there a flaw in this scheme?

Explanation / Answer

Answer:

Yes, an attacker can attend the message and find the key in next way: -

Let ‘A’ and ‘B’ are the associates, and ‘K’ is the key of size ‘N’.

1> A makes random string ‘R’
2> Computes S : = K XOR R
3> S to B
4> B computes S1:= S XOR K
5> S1 to A
6> A authenticates whether R = S1 or not?

So an attacker attending the talk will have both ‘S’ and ‘S1’.

So,

K: = S1 XOR S

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