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Alice how decide to change (43) Holice and shape and Alives and 2 were What is the publicly Alice What is the public eyed by What is the computery b. Porta Matex when Alle andere har med Alice Carolruder TEO pendo we of Chooter Choose to be Alice's putihy AAN Bobby how mod med p Aloe Sandsted by Carol 3 Serde topired by Card 10 Carol Choose Computer - med p Carosends to stromice Carolconds B to iesaistrom Bob Alice derives the shared secretKey Carol derives Kimod Bob Gelive the shared Secret key P. Kºmodo K1.mod p K. A mod p Session 1 bished with key Ki Verity of Alice and Carave dorived the same key kt Session 2 established with key : verify the Cars and to have doved the same key K2
member to show your work in all the questions! 1. [6 points] Shared session key establishment using a Key Distribution Center (KDC). Using the following table, illustrate how Alice can initiate a secure session with Bob with the help of KDC. Here, KEKs are the long term key establishment keys used to transport the session keys across the network securely. Assume the encryption process to be as follows: Block (LB || RB) is 8 bits, Encryption Key (LK||RK) is 8 bits; Ciphertext=LC| RC where LC-LB RK; and RC RB LK: For example, if plaintext=A7 (Hexa) and Key = 6D, then LC-A OD-1010 011010111 = 7 (Hexa), and RC =706 = 01110110 = 0001 = 1 (Hexa), so Ciphertext = 71 (Hexa). To decrypt, it does the reverse operation: Given ciphertext of CELCIRC, it finds plaintext BƏLBIRB. by finding LB=LCORK and RB RCLK Alice KDC Bob KEK: KA=DC (hexa) KEK: KA=DC (hexa); KEK: kB = A4 (hexa); kB = A4(hexa); Alice sends a message to KDC requesting a session key between Alice and Bob Generate a random session key: kses - 7B (hexa); YA= ekakses) = ?? YB = ekbikses) = 77 KDC sends yA=?? to Alice KDC send yg = ??to Bob Decrypt yA to derive Decrypt ye to derive kses using A- kses using ke - Message to send m =E3 (Hexa) Encrypyt m using rossinn key
Encrypyt m using session key y = ekses (m) Alice sends y to Bob XC lid Decrypt y using session key to get m = Verity that this is the message sent by Alice ice a it. [3 points) Alice and Bob now decide to use DHKE exchange with certificates (P. 343). Both Alice and Bob agree on p-13 and a-5. Alice chooses a-7 and Bob chooses 6-2. Answer the following 1 What is the public key generated by Alice? ii. What is the public key generated by Bob? What is the computed shared key? b. Points 6 Mon-in-the middle attack when Alice and Bob employ Diffie-Hellman koy exchange. Hero, Carol is the intruder, Alice Carol (Intruder) Bob pa13 and a 5 are known to all Choose kpri A = = 6 Choose Kpri Bb=3 Alice's public key: kpub.A-A= Bob's public key: Kpub, Bua a mod p = mod p Alice Sends A to Bob; intercepted by Carol Bob Sends B to Alice, intercepted by Carol Carol chooses 5
Carol chooses c=5; computes A' =B'=a mod p Carol sends A' to Bob as if it is A from Alice Carol sends B'to Alice as if it is from Bob Alice derives the shared secret Carol derives K1= AC Bob derives the shared secret key as key as mod p, K2= BC mod p, K1=B'a mod p K2= Ab mod p Session 1 established with key K1: verify that Alice and Carol have derived the same key kí Session 2 established with key K2; verify that Carol and Bob have derived the same key K2 Scan your work for Question 6 (all parts from a to b) as a pdf file and attach it below: