U4.7 Protocols for Key Agreement

U4.7 Protocols for Key Agreement

1. Entity Authentication is limited by the point in time. Authentication happens at a point in time and you cant guarantee that the entity is still online once auth has taken place

   • Some form of security is then required for information exchanged on that connection
     • A combination of confidentiality, integrity and data origin auth services

2. To communicate securely for an entire session

   • Encryption
     • Confidentiality
   • MAC
     • Integrity
   • Encryption and MAC both require keys
     • If keys are agreed as part of the authentication protocol, they can be used to secure the rest of the session

3. If the agreed keys are bound to that 1st particular run of the authentication protocol

   • And 1 keys is used to MAC all messages, and entities continually check the MAC
     • They can be sure they are still in contact with each other
       • Then the auth protocol has been extended to the entire session
         • The auth protocol is then called the Authenticated Key Agreement protocol AKE

4. If keys are only used for a particular session

   • they are called session keys
     • Having session keys benefits key management
       • session keys can be used for shorter periods and then disgarded
         • The main key is only used to encrypt a single message per session meaning exposure is reduced and its better protected

5. We want to link the remainder of a secure session to the run of the authentication protocol at the start of the session in such a way that the entities who authenticate one another at the start of the session

   • To ensure that entities are communicating securely for the duration of that session
     • and still communicating with each other over the course of the session, no hijack has occured

6. Public-key encryption can also be used to create authenticated session keys

7. Use of Diffie-Hellman key exchange

   • Because its only key exchange and not authentication it is prone to Man in the middle attack
     • Use of a Station to Station protocol required to combat it.
       • STS adds authentication by using signatures
         • All messages in STS are encrypted to ensure each participant that the other really does know the key