Cyber Security

ECE509 Cyber Security :Concept, Theory, and PracticeKey ManagementSpring 20141Key Managementaddresses key distribution problems

Two issues are handleddistribution of public keysusing public-key encryption to distribute secret keys

Distribution of Public KeysPublic announcementPublicly available directoryPublic-key authorityPublic-key certificates

Public AnnouncementUsers distribute public keys to recipients

Problems:Authentication: anyone can create a key claiming to be someone elsePublic-Key DirectoryRegistering keys to a public directoryRequired Properties:Continuous UpdateAuthentication before adding or changing keysIdentification {ID, public-key} entryAllow to change key at any timeAPI to access the directoryProblems:Tampering or forgeryPublic-Key AuthorityThis is an improvement on the public key-directory. It constricts the access to the distribution of public keys. Users access in real-time the directory and obtain the public keys by securely interacting with it and by using the directorys public key.Public-Key CertificatesSimilar to the Public-Key Authority but not in real-time. It uses certificates to allow public key exchange. The authority for certificates is called Certificate Authority(CA).A certificate is binds an identity to a public key. It may also have other information.The certificate can be checked by any one who has the public key of the CA.Public-Key Distribution MethodsThey are used to obtain public-key

The rarely are used for encryption because public-key algorithms are slow

Symmetric key encryption are used to protect message contents. And those are changed based on the concept of sessions.Simple Secret Key DistributionMerkle in 1979Alice generates a new temporary public key pairAlice sends Bob the public key and its identityBob generates a session key K sends it to Alice encrypted using the supplied public keyAlice decrypts the session key and both useProblem:The adversary can intercept and impersonate any of the participants.Diffie-Hellman Key ExchangeThe first public-key technique that was proposed by Diffie & Hellman in 1976.

It is a very practical method for public exchange of a secret key

It is commercially used10The idea of public key schemes, and the first practical scheme, which was for key distribution only, was published in 1977 by Diffie & Hellman. The concept had been previously described in a classified report in 1970 by James Ellis (UK CESG) - and subsequently declassified in 1987. See History of Non-secret Encryption (at CESG).Diffie-Hellman Key ExchangeIt is used for public-key distribution

The value of the key depends on the participants

It is based on exponentiation in a Galois field (modulo a prime or a polynomial)

It is depends on time and on the difficulty of computing discrete logarithmsSource: [ https://www.youtube.com/watch?v=3QnD2c4Xovk ]