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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.
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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
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 read across fill down Ciphertext: LTROEAYNABEPEONTNUCI
Caesar Block Cipher • Try writing and encrypting your own message! • Remember: <25 characters (including spaces) read across • Pass it to a friend to decrypt fill down
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