20 Security, Encryption

20 Security, Encryption - ECE 110 M.-C. Brunet Coding for...

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ECE 110 M.-C. Brunet Coding for Security: Cryptography Handout 20 Coding for Security : ryptography Cryptography = secret writing. It is a form of coding to make information ifficult to read or be understood by others Cryptography difficult to read or be understood by others. Æ Security Æ Encryption Cryptography has influenced the course of many battles, political events and decisions. Æ Julius Caesar, (~50BC) used secret writing Æ Louis XIV, “the man in e iron mask” the iron mask”. Æ WWI, politics US-Germany. Æ WWII, Enigma machine. Wordsworth Classics; 1 edition (Jun 15, 2000) M.-C. BRUNET ECE 110 UIUC 20.1 The true revolution in cryptography is the concept of public key .
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ECE 110 M.-C. Brunet Coding for Security: Cryptography Handout 20 science of unscrambling a message without knowledge of the encryption Cryptoanalysis: method. The same skills were required for: Æ Polish Rejewski’s attack on Enigma Æ Rosetta Stone. Champollion (1824) http://thinkertoy.com/ancient/ttegypt05.jpg www.royalnavalmuseum.org/CuratorschoiceMay05.htm M.-C. BRUNET ECE 110 UIUC 20. .2 An ongoing battle between “codemakers” and “codebreakers” has generated numerous codebreakers has generated numerous contributions to many subjects , Mathematics, Linguistics, Information Theory. Cryptography is an unusual science: many breakthroughs were kept secret for many years, and scientists were not recognized for their discoveries (ideas were classified confidential for political reasons). Example: lan Turing broke the Enigma cipher 940 Alan Turing broke the Enigma cipher -1940 (unknown by German for years). James Ellis is the original inventor of the public key concept – 1968 (1976, Diffie et al). M.-C. BRUNET ECE 110 UIUC 20.3
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ECE 110 M.-C. Brunet Coding for Security: Cryptography Handout 20 Definitions Cryptography refers to secret communication (by extension). Codes & Ciphers are techniques to disguise a message so that only the intended recipient can read it. Code: disguise words , Cipher: disguise letters . Key is a unique numeric or symbolic sequence used to encrypt or decrypt information. Security For a good code: Keep the key secret Have lots of potential keys. Problem of key distribution in a secure way. o code is 100% secure odebreakers) M.-C. BRUNET ECE 110 UIUC 20.4 No code is 100% secure (codebreakers). Secret Encoding Cryptography Steganography Microdot shaving head, invisible ink, digital stenography The message is hidden The message is scrambled Substitution Transposition ADFGVX cipher rail fence, Spartan scytale Each letter in a message retains its identity but Each letter in a message changes its identity but retains its position Ciphers Codes words, syllables cipher of Mary Queen of Scots, Nomenclator, Great cipher of iX I V changes its position Polyalphabetic Monoalphabetic Homophonic Vigenere cipher, Beale ciphers, t i d ih Caesar shift or Rotational encoding, h l k H l Louis XIV M.-C. BRUNET ECE 110 UIUC 20.5 Onetime pad cipher, Enigma machine, Key exchange system, Public key concept (RSA) Sherlock Holmes’ Dancing Men, Permutation encoding, Pigpen cipher
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ECE 110 M.-C. Brunet
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20 Security, Encryption - ECE 110 M.-C. Brunet Coding for...

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