1. ECE509 Cyber Security : Concept, Theory, and Practice Key Management Spring 2014

2. Key Management addresses key distribution problems Two issues are handled –distribution of public keys –using public-key encryption to distribute secret keys

3. Distribution of Public Keys –Public announcement –Publicly available directory –Public-key authority –Public-key certificates

4. Public Announcement Users distribute public keys to recipients Problems: –Authentication: anyone can create a key claiming to be someone else

5. Public-Key Directory Registering keys to a public directory Required Properties: –Continuous Update –Authentication before adding or changing keys –Identification {ID, public-key} entry –Allow to change key at any time –API to access the directory Problems: –Tampering or forgery

6. Public-Key Authority This 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 directory’s public key.

7. Public-Key Certificates Similar 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.

8. Public-Key Distribution Methods They 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.

9. Simple Secret Key Distribution Merkle in 1979 –Alice generates a new temporary public key pair –Alice sends Bob the public key and its identity –Bob generates a session key K sends it to Alice encrypted using the supplied public key –Alice decrypts the session key and both use Problem: –The adversary can intercept and impersonate any of the participants.

10. Diffie-Hellman Key Exchange The 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 used

11. Diffie-Hellman Key Exchange It 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 logarithms

12. Source: [ https://www.youtube.com/watch?v=3QnD2c4Xovk ]