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 ⊕ D = 1010 ⊕ 1101 = 0111 = 7 (Hexa); and RC = 7 ⊕ 6 = 0111 ⊕ 0110 = 0001 = 1 (Hexa); so Ciphertext = 71 (Hexa). To decrypt, it does the reverse operation: Given ciphertext of C=LC||RC, it finds plaintext B=LB||RB, by finding LB=LC ⊕ RK and RB = RC ⊕ LK. Alice KDC Bob KEK: kA = A6 (hexa) KEK: kA = A6 (hexa); kB = D8(hexa); KEK: kB = D8 (hexa); Alice sends a message to KDC requesting a session key between Alice and Bob Generate a random session key: kses = 7B (hexa); yA = ekA(kses) = ?? yB = ekB(kses) = ?? KDC sends yA = ?? to Alice KDC send yB = ?? to Bob Decrypt yA to derive kses using kA = Decrypt yB to derive kses using kB = Message to send, m = 45 (Hexa) Encrypyt m using session key, y = ekses(m) Alice sends y to Bob Decrypt y using session key to get m = Verify that this is the message sent by Alice
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 ⊕ D = 1010 ⊕ 1101 = 0111 = 7 (Hexa); and RC = 7 ⊕ 6 = 0111 ⊕ 0110 = 0001 = 1 (Hexa); so Ciphertext = 71 (Hexa). To decrypt, it does the reverse operation: Given ciphertext of C=LC||RC, it finds plaintext B=LB||RB, by finding LB=LC ⊕ RK and RB = RC ⊕ LK.
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KEK: kA = A6 (hexa) |
KEK: kA = A6 (hexa); kB = D8(hexa); |
KEK: kB = D8 (hexa); |
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Alice sends a message to KDC requesting a session key between Alice and Bob |
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Generate a random session key: kses = 7B (hexa); |
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yA = ekA(kses) = ?? |
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yB = ekB(kses) = ?? |
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KDC sends yA = ?? to Alice |
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KDC send yB = ?? to Bob |
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Decrypt yA to derive kses using kA = |
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Decrypt yB to derive kses using kB = |
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Message to send, m = 45 (Hexa) |
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Encrypyt m using session key, y = ekses(m) |
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Alice sends y to Bob |
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Decrypt y using session key to get m = |
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Verify that this is the message sent by Alice |
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