Consider the following encryption scheme to provide confiden

Consider the following encryption scheme to provide confidentiality. 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 56-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 56-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? Give a YES/NO answer. If you said NO explain what you think is the single biggest weakness of the scheme.

Solution

Solution ::

(i) No, the given scheme was not good.
(ii) The given Scheme is under the \"Symmetric Key Cryptography\". Because both sender A and receiver B share a common key.

Symmetric key Cryptography ::

Encryption system in which sender and receiver of a message share single and common key that is used for both encrypt and decrypt message.Symmetric key cryptography

is sometimes also called \"secret key cryptography\". Popular symmetric key system is Data Encryption Standard (DES).

Given that A and B want to communicate with each other. Both A and B share the same two bit nummber T.So the Scheme is not good.

Disadvantages of Symmetric key cryptography ::
-> Symmetric cryptosystems have the problem of \"key transportation\". Secret
key is to transmitted to the receiving system before actual message is to
be transmitted to the receiver. Every means of the electronic communication is \'insecure\' as it is
impossible to guarantee that the no one will able to tap the communication
channels. The only secure way of the exchanging keys would be the exchanging
them personally.
-> Symmetric key cryptography cannot provide the digital signatures which cannot be repudiated.

*So the given scheme was not good.

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