7.authen-key

# 7.authen-key - Entity Authentication and Key Agreement CSE...

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Entity Authentication and Key Agreement CSE 651

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Entity Authentication Problem: Alice wants to prove to Bob that she is Alice and/or vice versa. Basic idea: Alice shows that she knows some secrecy which is presumably known only to Alice (and Bob). That secrecy could be, for example: - Alice’s password or PIN - a MAC or encryption key shared by Alice and Bob, or - Alice’s RSA private key.
: 0. Alice Bob: "I'm Alice" 1. Alice Bob: "What's your password?" 2. Alice Bob: Alice's password 3. Bob verifies the passw Protoc ord ol Is it secure against an eavesdropper?

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( ): (0. Alic Alice and Bob share a secret key . ins e Bob: "I'm Alice") 1. Alice Bob: a random challenge . Proto 2. c Alice Bob: MAC ( ). 3 ecure . ol Challenge-and-response using a secrete key k r y k r = Bob computes MAC ( ) and checks if . 1. Alice Bob: a random challenge . 2. Alice Bob: ( ). 3. Bob checks if ( . Or ) k k k y r y y r y E r D y r = = = =
MAC ( ) Parallel sessions attack Alice Bob Eve k r y r r = ← → ←  MAC ( ) k y r = →

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MAC ( ) Bob M Count ermeasu r e Ev A o e lice B b k r r r y y = = ←      → ←       P AC ( Alice) k r     → P
): 1. Alice Alice and Bob share a secret key . se Protocol ID(Alic Bob: a random challenge . 2. Alice Bob: MAC ( ). 3. Bob c e) omputes M cure AC I ( Challenge-and-response using a secret key k k r k r y y = = P ) and checks if . 1.

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7.authen-key - Entity Authentication and Key Agreement CSE...

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