Era of Electronic
• Electronic communication• Electronic Banking
Terminology
• Cryptology: Discipline • Cryptography: Design & Implementation• Cryptoanalysis: Breaking the system
Terminology
• Plaintext: secret message • Cipher: method to alter the plaintext• Cybertext: message has been altered
Terminology
• encryption/enciphering: process• decryption/deciphering: process
CAESAR CIPHERCharacter Cipher
AFFINE TRANSFORMATIONCharacter Cipher
• Complete system of residue!
Secure?
• Character cipher is not safe
VIGENERE CIPHERBlock Cipher
DIGRAPHIC CIPHERBlock Cipher
VERNAM CIPHERStream Cipher
AUTOKEY VERNAM CIPHERStream Cipher
EXPONENTIATION CIPHERCryptology
PUBLIC KEY CRYPTOLOGYCryptology
Factorizing prime?
• n=pq• What is the factor of following number?•
1522605027922533360535618378132637429718068114961380688657908494580122963258952897654000350692006139
• 37975227936943673922808872755445627854565536638199
× 40094690950920881030683735292761468389214899724061