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1Secure ChannelsCS 161/194-1Anthony D. JosephSeptember 26, 2005September 26, 2005CS161 Fall 2005Joseph/Tygar/Vazirani/Wagner2Main Points•Applying last week’s lectures in practice•Creating Secure Channels•Example Applications – PGP: Pretty Good Privacy– TLS: Transport Layer Security– VPN: Virtual Private NetworkSeptember 26, 2005CS161 Fall 2005Joseph/Tygar/Vazirani/Wagner3What is a Secure Channel?•A stream with these security requirements:– Authentication •Ensures sender and receiver are who they claim to be– Confidentiality •Ensures that data is read only by authorized users–Data integrity •Ensures that data is not changed from source to destination–Non-repudiation (not discussed today)•Ensures that sender can’t deny message and rcvr can’t deny msgInternetEncryption /DecryptionPlaintextPlaintextCiphertext and MACEncryption /DecryptionSeptember 26, 2005CS161 Fall 2005Joseph/Tygar/Vazirani/Wagner4Creating Secure Channels•Authentication and Data Integrity– Use Public Key Infrastructure or third-party server to authenticate each end to the other– Add Message Authentication Code for integrity• Confidentiality – Exchange session key for encrypt/decrypt ops• Bulk data transfer•Key Distribution and SegmentationSeptember 26, 2005CS161 Fall 2005Joseph/Tygar/Vazirani/Wagner5Symmetric Key-based Secure Channel•Sender (A) and receiver (B) share secret keys– One key for A LB confidentiality– One for A LB authentication/integrity– Each message sent from A LB contains:• Ciphertext = E_KABencrypt(nonce + msg)•Authenticity/Integrity check = MAC_KABauth(Ciphertext)•Different keys for each direction = 4 keys– KABencrypt, KABauth, KBAencrypt, KBAauthSeptember 26, 2005CS161 Fall 2005Joseph/Tygar/Vazirani/Wagner6Symmetric Key-based Secure ChannelMessageAliceBobC = E_KABencrypt(M), MAC_KABauth(C)MACKABauthKABencryptKABauthKABencryptMAC Compare?How to exchange secret keys?EncryptionNonce + MessageMessageDecryptionNonce Check?
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