Basic HTML version of Foils prepared August 4 1997

Foil 35 Introduction to Cryptography

From Remarks on Java and Internet Security Web Certificate CPS616 Enhancement -- Summer 1997 . by Geoffrey C. Fox
1 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)
2 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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