密码学课件英文.ppt

1Authentication Protocols 2IntroductionCryptographic protocolDistributed algorithmBased on cryptographic building blocksTo achieve a security related goalExamples:Entity AuthenticationKey Establishment:Key Distribution(Key enveloping, Key transport), Key agreementElectronic Payment… 3authenticationAliceBobHow does Bob know that Alice is Alice, not Eve?insecure channelEve(Eve owns the channel!)Hi! I’m Alice 4authenticationAuthentication is a means by which identity is established.It allows one party to gain assurances about the identity of another party in a protocol, and that the second has actively participated.The goal of authentication is to achieve all this over an insecure channel with an active attacker and no shared secrets.Note: authentication must be combined with key exchange to avoid session hijacking (after authentication). 5objectives of identification protocolsIf Alice and Bob are both honest, A is able to successfully authenticate herself to Bob, i.e. Bob will complete the protocol having accepted Alice’s identity.Bob cannot reuse an identification exchange with Alice so as to impersonate her in conversations with others.The probability that Eve can successfully impersonate Alice to Bob is negligible (e.g. computationally difficult).All the above remain true even if Eve has seen many previous authentication sessions between Alice and Bob, has had experience in authenticating herself with both, and multiple authentication sessions are run simultaneously. 6basis of identificationSomething you knowPasswords, PINs, secret keys, your mother’s maiden name Something you haveMagnetic cards, smart cards, physical keys, handheld password generators.Something you arebiometrics (DNA, signatures, fingerprints, voice, retinal patterns, hand geometries, typing dialect/profiling). 7basis of identificationBiometrics have major problems in real world situationsHow do you revoke keys? Biology is messy We leave DNA, fingerprints everywhere - just ask OJHow do you give a