Ch. 11 – Cipher Techniques

Dr. Wayne Summers

Department of Computer Science

Columbus State University

Summers_wayne@colstate.edu

http://csc.colstate.edu/summers

2Networks and Cryptography

3Networks 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

4Secure 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 e-mail at any of the intermediary MTAs

5Secure 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