6.cryptographic-protocols

6.cryptographic-protocols - Cryptographic Protocols Entity...

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Cryptographic Protocols ■ Entity Authentication ■ Key Agreement ■ Fiat-Shamir Identification Schemes ■ Zero-Knowledge Proof Systems ■ Shnorr’s Identification/Signature Scheme ■ Commitment Schemes ■ Secret Sharing ■ Electronic Election
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Click to edit Master subtitle style Entity Authentication Problem: Alice wants to prove to Bob that she is Alice and/or vice versa. Private-key based schemes Public-key based schemes Integrated with key agreement Zero-knowledge identification schemes
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( ): 1. Bo Protoco b Alice: a random challenge . 2. Bob Alice: Alice and Bob share MAC ( ) a secret key . insec . 3. Bob computes M ure AC ( ) and c l Challenge-and-response using a private key k k r y r y r k = = hecks if . 1. Bob Alice: a random challenge . 2. Bob Alice: ( ). 3. O Bob checks if ( r ) . k k y y r y E r D y r = = =
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MA C ( ) Parall el sessio Ev n attack Bob e k r y r y r = ←  → → ←
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M Bob MAC ( Ali A ( ) ce)? C Countermeasure Bo ve b E k k r y r y r r = = → ←    P P
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( ): 1. Bob Alic Alice and Bob share a secret key . sec Protocol ID e: a random challenge . 2. Bob Alice: MAC ( ). 3. Bob comput (Alic u e) es MAC ( re Challenge-and-response using a private key k k r k y r y = = P ) and checks if . 1. Bob Alice: a random challenge . 2. Bob Alice: (ID(Alice) ). 3. Bob checks if ( ) I ID(Alice) D(Alice) . Or k k r y y r y E r D y r = = = P P P
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1 2 1 1 Alice and Bob share a secret key . : 1. a random challeng Bob Alice: . 2. Bob Alice: 3. Bob Ali Pr ce: insecure and o e MAC tocol ( (ID(Alice) ) ) . Mutual authentication using a private key k y k r r r = P 2 2 4. Alice and Bob verify each M other's response AC (ID(Bob) ) . . k y r = P
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1 3 2 2 2 1 MAC (B ), MAC (A ), MA Man-in- the-middle attack Eve A lice Bob k k r r r r r r ← → → ← P P 2 C (B ) k r ← P
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2 1 1 3 2 2 3 2 MAC (A ) MAC (B ), MAC , (B C ountermeasure A Bo lic b E e ve k k k r r r r r r r r ← → → ← P P P P 2 )? r ← P
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1 2 2 1 1 ( ): 1. Bob Alice: a r Alice and Bob share a secret key . secure andom challenge . 2. Bob Alice: MAC (ID(Alice) ) and . 3. Bob Al P i rotocol ce: Mutual authentication using a private key k k r y r r r = P P 2 2 2 2 1 MAC (ID(Bob) ). 4. Alice and Bob verify each other's response. 3 . Bob Alice: Alternati MAC (ID(Bob) ). vely: k k y r y r r = = P P P
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1 (Allice) (Bob 1 1 2 ) 2 2 2 ( ): 1. Bob Alice: a random challenge . 2.
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6.cryptographic-protocols - Cryptographic Protocols Entity...

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