2.7 ) When using the one-time pad with the key k = 0l, we have Enck(m) = k ? m =
ID: 3740760 • Letter: 2
Question
2.7 ) When using the one-time pad with the key k = 0l, we have Enck(m) = k ? m = m and the message is sent in the clear! It has therefore been suggested to modify the one-time pad by only encrypting with k ?= 0l (i.e., to have Gen choose k uniformly from the set of nonzero keys of length l). Is this modified scheme still perfectly secret? Explain.2.7 ) When using the one-time pad with the key k = 0l, we have Enck(m) = k ? m = m and the message is sent in the clear! It has therefore been suggested to modify the one-time pad by only encrypting with k ?= 0l (i.e., to have Gen choose k uniformly from the set of nonzero keys of length l). Is this modified scheme still perfectly secret? Explain.
2.7 ) When using the one-time pad with the key k = 0l, we have Enck(m) = k ? m = m and the message is sent in the clear! It has therefore been suggested to modify the one-time pad by only encrypting with k ?= 0l (i.e., to have Gen choose k uniformly from the set of nonzero keys of length l). Is this modified scheme still perfectly secret? Explain.
Explanation / Answer
Answer:
Here we can explain the followins as about OTP
OTP is a symmetric cipher( i.e. common key is used for both encryption and decryption), therefore, key sharing becomes an issue at this point. OTP is a key must be changed each time a message is sent for communication. Here the case of perfect secrecy proposed by Shannon which states that a perfect secrecy can be achieved in encryption and decryption if the key is chosen randomly for encryption and decryption from the key domain. For example, the additive cipher, instead of choosing the same key for each symbol of the plaintext, if the key can be generated randomly and uniquely for each symbol (where k != 0 and length of k = length of message), then it is impossible to break the Cipher using the Ciphertext-only attack. Also, it is impossible for other attacks to break this cipher.
Than otp is used for the security perpoes therefore, in terms of secrecy, it is a perfect cipher.But if we come to the reality, then we may understand that it is not easy to implement the Cipher. If the key is generated each time a message needs to be sent, then how the sender informs the receiver that what key she has used to encrypt the plaintext.Therefore we can conclude that, though One-time pad provides perfect secrecy, in term of key exchange still there are issues which prove it as not recommended Cipher.
Finally we conclude that OTP is used for the security reasons.
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.