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
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)
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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