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Authentication (Distributed computing)
1. Authentication Protocols Paul Krzyzanowski [email_address] [email_address] Distributed Systems Except as otherwise noted, the content of this presentation is licensed under the Creative Commons Attribution 2.5 License.
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14. Challenge-Response authentication “ alice” Alice network host look up alice’s key, K generate random challenge number C R ’ = f( K , C ) R = f( K , C ) R = R ’ ? “ alice” C R ’ “ welcome” an eavesdropper does not see K
20. SKID2/SKID3 authentication R A Bob R B , H K (R A , R B ,”bob”) Alice Bob chooses a random number (nonce): R B. He computes H K (R A , R B ,”bob”) and sends it to Alice with R B Bob shows that he can encrypt Alice’s nonce
21. SKID2/SKID3 authentication R A Bob R B , H K (R A , R B ,”bob”) Alice Alice receives R B and has R A . Computes: H K (R A , R B ,”bob”) compares result to verify that Bob was able to encrypt data with key K . Authentication is complete as far as Alice is concerned (Bob knows the key).
22. SKID2/SKID3 authentication R A Bob R B , H K (R A , R B ,”bob”) Alice Now Alice has to convince Bob ( mutual authentication ) H K (R B , “alice”) Bob Alice demonstrates that she can encrypt Bob’s nonce
23. SKID2/SKID3 authentication R A Bob R B , H K (R A , R B ,”bob”) Alice Bob computes H K (R B , “alice”) and compares Alice’s message. If they match, he trusts Alice’s identity Key point : Each party permutes data generated by the other. Challenge the other party with data that will be different each time. H K (R B , “alice”) Bob
54. Secure Sockets Layer (SSL) client server 3. Establish session key (for symmetric cryptography) encrypt with server’s public key server decrypts with server’s public key pick a session key E(session key) set cipher mode [optional]
55. Secure Sockets Layer (SSL) client server E S (data) 4. Exchange data (symmetric encryption) encrypt and decrypt with session key and symmetric algorithm (e.g. RC4)
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