1. Chapt. 10 – Key Management Dr. Wayne Summers
Department of Computer Science
Columbus State University

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

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. 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. 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)