What is Encryption?• Information is often stored and transmitted in a file• A plaintext file uses a common encoding format such as ASCII or Unicode to represent the characters of the file.• Encryption is a translation of a file into a format that hides the content from selected parties; a secret code; ciphertext.
What Is Cryptography?• Cryptography -- from the Greek for “secret writing” -- is the mathematical “scrambling” of data so that only someone with the necessary key can “unscramble” it.• Cryptography allows secure transmission of private information over insecure channels (for example packet-switched networks).• Cryptography also allows secure storage of sensitive data on any computer.
Technology and Risk• Technological advances created new risks ▫ electronic communication makes information more easily available to more parties ▫ long-term storage of sensitive data requires stronger encryption techniques• Some technologies actually reduce risk ▫ fiber optic cable ▫ strong encryption
German Enigma Cipher Machine•In 1918, Arthur Scherbius filed for apatent for Enigma Cipher Machineand offered it to the German Navy.• In 1926, German navy begins usingEnigma Machine, lightly modifiedfrom a commercial model.•In 1930, German armed forcesintroduced asignificantly modified military model.
Goals of Cipher:• Diffussion: ▫ Small change in plaintext, changes lots of ciphertext ▫ Statistical properties of plaintext hidden in ciphertext• Confusion: ▫ Statistical relationship between key and ciphertext as complex as possible ▫ So, need to design functions that produce output that is diffuse and confused
General Principles• Longer keys make better ciphers• Random keys make better ciphers• Good ciphers produce “random” ciphertext• Best keys are used once and thrown away
Public Key Cryptography• Your turn….. ▫ What is it? ▫ How does it work? ▫ Include an analogy ▫ Any weaknesses? ▫ If you come across digital signatures, what are they? ▫ Use MS Word