Ch' 11 Cipher Techniques

1
Ch. 11 Cipher Techniques

• Dr. Wayne Summers
• Department of Computer Science
• Columbus State University
• Summers_wayne_at_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