Test by Bikram | Computer Networks | Test 1 | Question: 7

Question

Consider private key crypto-system has $3$ keys, $3$ plain-texts and $4$ cipher-texts:

$K=\{ k1,k2,k3 \}$
$M=\{m1, m2,m3 \}$
$C=\{c1,c2,c3,c4 \}$

In a valid encryption table find the key that maps two different messages to same cipher text:

• A. k1
• B. k2
• C. k3
• D. No key can map

Comments

@Arjun sir no clue about this question. 😢

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This is not in the syllabus right??

Answer 1

Encryption:
2 Messages -> 1 Key -> 1 Cipher

Decryption:
1 Cipher -> 1 Key -> 1 Message

Since decryption of 1 cipher to two messages using 1 key is not possible, so answer will be D

Comments

{ In a valid encryption table find the key that maps two different messages to same cipher text }

here we are asked for encryption i.e message to cipher but  you have given answer for decryption (although the answer will remain same i guess but explanation would be different) ...correct me if i am thinking wrong..?

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Decryption is the process of converting ciphertext back to plaintext.

Question asks if we have a same key that can be use for encrypt 2 different messages .. as encryption and decryption is done at the same table and  decryption of 1 cipher message of 2 different  messages using 1 key is not possible, no key can be use for the mapping .

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Sir please clear my doubt are you saying to encrypt two different messages with same key ? if its the case then we would have two different ciphers. So by one cipher and one key we can decrypt one message not both am i right sir?