Basic HTML version of Foils prepared April 7 1998

Foil 27 Introduction to Cryptography

From Basic Principles of Java and Internet Security CPS616 Web Technologies -- Spring 98. by Geoffrey C. Fox
This is old technology first attributed to Julius Caesar who used the nifty cipher which replaced every latter with that three letters further in the alphabet
  • So A becomes D and Z becomes C (using cyclic wraparound)
Most ciphers involve an algorithm and a parameter (this is 3 in the above) where usually algorithm can be public but parameter is kept secret and is called a key
  • key needs to be quite big to be safe (say at least 40 bits long)
  • It is usually not possible to keep algorithm secret and in fact making it public can encourage experts to examine and comment on its reliability (I.e. ease of breaking)

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