Computer Science 322
Operating Systems

Mount Holyoke College
Spring 2008

Lecture 33: Encryption; Wrapup
Date: Monday, May 5, 2008

Agenda

Announcements
- Project presentations tonight, 6:30, here
Encryption
- May want to encrypt some data (in storage or for network transmission) for privacy or security
- Original data is "clear text", encrypted is "cipher text"
- Conventional encryption:
  - brute-force attack expensive, but not as much as in the past
  - Data Encryption Standard (DES): 56-bit secret key. Selected by US Gov't in 1977, broken in 1998.
  - Advanced Encryption Standard (AES): 168-bit key - Rijndael selected in 2000 as new standard
- Problem: how to distribute the keys? Solution: use Public-Key encryption
  - keys are generated as public/private pairs
  - public keys are freely distributed
  - only the holder of the private key can decrypt messages encrypted using the corresponding public key
- Is it OK if someone listens in on the encrypted conversation?
- ssh uses public key encryption
- Most popular: Rivest-Shamir-Adleman (RSA)
Other topics: networks, distributed systems, multiprocessors

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