Consider the following encryption scheme to provide confidently A and B want to

Question

Consider the following encryption scheme to provide confidently A and B want to communicate with each other. A and B share a secret two bit number T i.e. T is known only to A and B. A gets a 65-bit DES key K by repeating T 28 times. For example, if T was 01, then K would be 010101 Independently, B also gets the 65-bit DES key K in the same way. Now if a wants to send M to B, A will calculate C = E_K (M) and send C to B. B will recover the plaintext by doing M = D_K (C). Is this a good scheme? i. Give a YES/NO answer. ii. If you said NO explain what you think is the single biggest weakness of the scheme.

Explanation / Answer

Ans: The answer is NO.

Explanation:

The scenario in question is fine.But in that DES key k is used.DES key means Data Encryption Standard.Its 56 bit key very short.So it is much vulnerable to brute force seach.

DESX operates as below.

C = W *EK(P * W).

So a 56 bit DES key is always not a good thing in providing confidentiality.This is why the encryption scheme explained in the question is not a good scheme as it uses DES key which is of 56 bytes.

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