1. Ch. 11 – Cipher Techniques Dr. Wayne Summers
Department of Computer Science
Columbus State University

2. Networks and Cryptography

3. Networks and Cryptography
Top four layers use end-to-end protocols (e.g. telnet) only requiring that intermediate hosts forward messages
Bottom three layers use point-to-point or link protocols (e.g. IP)
In end-to-end encryption, each host shares a cryptographic key with each destination
In link encryption, each host shares a cryptographic key with its neighbor(s).
Distinction useful for traffic analysis

4. Secure E-mail: PEM User enters e-mail using a User Agent (UA)
UA hands message to Message Transfer Agent (MTA)
MTA sends message to destination host via other MTAs
Attacker can read/modify/forge/delete at any of the intermediary MTAs

5. Secure E-mail: PEM Goal:
Confidentiality (message should be unreadable except by sender and recipient(s)
Origin authentication
Data integrity
Nonrepudiation of origin
Requires two types of keys
Data encipherment key (DEK): session key
Interchange key