Question

There is a key distribution scheme as illustrated in the first Figure.

a. Describe the scheme in the first Figure.

b. Compare these two schemes in two figures. What are the pros and cons of each other?

Key Distribution Center (KD 1 IDIDg l Ni Key distribution steps LK, IDAI) 3) Ek Responder Initiator (4) E(K, N2) (5) E(K,, fN2)) Authentication steps

Answer 1

Answer

1. Scheme

Step1:A initiates communicationit sends ID of A , andNonce of A , encrypted with key of A

Step2:B sends Id’s of both A and B and also Nonce of A encrypted with Key of A , and Nonce of B encrypted with key of B

Step3: KDCresponds with sessions keys to both parties A and B

Sesssion key of B , Id of A and Nonc e of B encrypted with key of B

Session key of A, Id of B ,Nonce of A encrypted with key of A

Step4: B communicates session key of A generated by KDC

1. Step1:A sends ID of A ,B and Nonce1 without encryption

Step2:KDC generates session key for Ausing ID of A, B and Nonce N1 and encrypts with key of A

KDc generates session key of B using ID of A and encrypts with key of B

Step3: Acommunicates session key of B , encrypting with key of B

Step4:B communicates Nonce 2 with session key

Step5: Aaccepts Nonce 2 and authenticates B

In figure A3-2 step 1 communication is not encrypted , there is a vulnerability

Scheme of figure A3-1 is secure ,

Session keys are formed by exchanging ID

Key of A is formed with Id of B and Nonce of A

Key of B is formed with ID of A and Nonce of B.

In scheme 2 B is not playing role in intiating communication, in scheme 1 both parites are involving in key generation.