ME: TOPICWISE : COMPUTER NETWORKS-1 (GATE - 2019) Q5

Question

Which of the following risk may arise, when same key is used to encrypt directions of a communication channel, that are not present if using different keys in both direction?
A  Reflection attack

B Denial of service

C Eavesdropping attack

D None of these

Comments

The answer is reflection attack
About reflection attack
In computer security, a reflection attack is a method of attacking a challenge-response authentication system that uses the same protocol in both directions. That is, the same challenge-response protocol is used by each side to authenticate the other side. The essential idea of the attack is to trick the target into providing the answer to its own challenge.
 

The general attack outline is as follows:

1. The attacker initiates a connection to a target.
2. The target attempts to authenticate the attacker by sending it a challenge.
3. The attacker opens another connection to the target, and sends the target this challenge as its own.
4. The target responds to the challenge.
5. The attacker sends that response back to the target on the original connection.
   
   The real doubt is :-
   How does  when same key is used to encrypt directions of a communication channel it's a risk?
   How and when reflection attack is possible ? It's not given in the question  that the systems are challenge-response authentication system.

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anyone?

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For How does  when same key is used to encrypt directions of a communication channel it's a risk? ->

https://crypto.stackexchange.com/questions/586/why-is-public-key-encryption-so-much-less-efficient-than-secret-key-encryption