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Ch. 11 – Cipher Techniques

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.

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Ch. 11 – Cipher Techniques

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  1. Ch. 11 – Cipher Techniques Dr. Wayne Summers Department of Computer Science Columbus State University Summers_wayne@colstate.edu http://csc.colstate.edu/summers

  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 e-mail 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

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