Ch. 11 – Cipher Techniques Dr. Wayne Summers Department of Computer Science Columbus State University Summers_wayne@colstate.edu http://csc.colstate.edu/summers
Networks and Cryptography
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
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 e-mail at any of the intermediary MTAs
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