Basic HTML version of Foils prepared May 19 99

Foil 27 Introduction to Cryptography

From Remarks on Internet and Java Security Basic Information Track Computational Science Course CPS616 -- Spring Semester 1999. by Geoffrey Fox, Mehmet Sen
1 This is old technology first attributed to Julius Caesar who used the nifty cipher which replaced every letter 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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