1. Chapt. 10 – Key Management Dr. Wayne Summers Department of Computer Science Columbus State University Summers_wayne@colstate.edu http://csc.colstate.edu/summers

2. 2 10.1 Session and Interchange Keys  Key management – distribution of cryptographic keys, mechanisms used to bind an identity to a key, and the generation, maintenance, and revoking of such keys  Solves problem of propagating authentication  Interchange key – cryptographic key associated with a principal to a communication  Session key - cryptographic key associated with the communication

3. 3 10.2 Key Exchange  Goal is two allow two parties to communicate secretly using a shared cryptographic key 1.Key cannot be transmitted in the clear (must be encipher when sent or derived without an exchange of data used to derive the key) 2.Sender and receiver may decide to trust a third party 3.Cryptosystems and protocols are publicly known. The only secret data is the keys involved.

4. 4 10.4 Cryptographic Key Infrastructures  Certificate- token that binds an identity to a cryptographic key  X.509: Directory Authentication Framework – defines certificate formats and certification validation (see Bishop pg. 257 for details)  Certification authority (CA) – entity that issues certificates  PGP (Pretty Good Privacy) – enchipherment program widely used to provide privacy for electronic mail (see Bishop pg. 259 for details)

5. 5 10.5 Storing and Revoking Keys  If stored in a file, easy to compromise, even if enchiphered  Store on one or more smart cards (ROM)  Key escrow system – system where a third party can recover a cryptographic key –Should not depend on encipherment algorithm –Privacy protections must work throughout, including the user interface –Requirements (legal/business) must map to the key exchange protocol –All parties must authenticate themselves –System must ensure that keys are valid while message is observable

6. 6 10.6 Digital Signatures  Digital signatures – authenticates both the origin and content of a message  Uses public key cryptography  Provides nonrepudiation  RSA Digital Signature (some problems)  El Gamal Digital Signature (similar to Diffie- Hellman)