Transcript ia.unm.edu
An Introduction to Cryptography What is cryptography? noun \krip-ˈtä-grə-fē\ : the process of writing or reading secret messages or codes • • “Encryption”: to put into a format that is unreadable to unauthorized individuals “Cipher”: a method of encryption, or a code Basics History 1900 B.C. Egyptians encoded messages on clay tablets 100 B.C. Julius Caesar uses simple encryption to send messages in wartime 1466 A.D. Leon Battista Alberti invents polyalphabetic cipher History 1835 Samuel Morse develops Morse Code 1940s Allies in World War II coded on enigma machines 1970s Data Encryption Standard (DES) was developed to encrypt electronic data Substitution Cipher • Substitute one value for another Substitution Cipher Common example: Cryptograms in newspapers Substitution Cipher • Original message: “plaintext”: • Encrypted message: “ciphertext” Solve this Substitution Cipher XKGTJDHI Solution SECURITY Ciphers in Popular Culture “National Treasure” (2004) Keys • They are what we use to secure the messages. (And to decrypt them!) • They are shared to decrypt the message. Keys • “Asymmetric” cryptography has two keys: – Public key: used to encrypt the message – Private key: used to decrypt the message. (This one is secret) – Mathematically matched to protect the message Vigenere Square • Polyalphabetic cipher • Column letter: plaintext • Row Letter: key Example: Vigenere Square Encrypt this word: Solution VDOZF Ciphers in Popular Culture “A Beautiful Mind” (2001) Transposition Cipher Rearranges values within a block to create ciphertext • Example: – “Caesar Block Cipher” – Uses 5X5 square – Message contains <25 characters Famously created by Julius Caesar! Caesar Block Cipher Plaintext: LEARN ABOUT ENCRYPTION fill down read across Ciphertext: L TROEA YNABEP EONT NUCI Caesar Block Cipher fill down • Try writing and encrypting your own message! • Remember: <25 characters read across (including spaces) • Pass it to a friend to decrypt Advanced Cryptography • Using the types of techniques we learned, computers can encrypt files, emails, etc. – Makes communication secure – But we still need to protect our keys and passwords! Advanced Cryptography Technology Example Real World Application • Cryptanalysts: study information systems to find hidden aspects • It’s their job to decrypt messages Why does this matter to you? • When you put your personal information on the internet, make it hard for thieves to steal Check your passwords: http://www.passwordmeter.com/ Create a strong password • Start with a weak password: Linda!Marie1207 • Come up with a secret key (4-6 characters) puppy • Encrypt text using the vigenere square: Accsy!Bugxc1207 Strong Password Jeopardy! What four aspects In what profession should your do people break password include? codes? Where does Gabe work? What is an encrypted message called? What type of What cipher cryptography uses replaces one letter public and private with another? keys? Who encoded messages on clay tablets? What machine was used to encrypt messages in World War II? What is an unencrypted message called? Questions