信息安全基础2Cryptography.ppt

Chapter 2 Cryptography Overview 1 Overview of Cryptography 1.1 History of Cryptography密码学历史 Before 1949 – Classical Encryption古典加密 Before computer was invented, cryptography was art more than science. There were some cipher algorithms, encryption machines simple cryptanalysis密码分析 ways. The main encryption objects are alphabet character. The security of data is based on the secrecy of algorithms. The Phaistos (1700 BC) Encryption Machines in Early 20th Century History of Cryptography (cont’ d) 1949~1976 – Shannon published “The Communication Theory of Secret Systems” in 1949, which indicated cryptography became a formal subject. The development of computer enabled ciphers on complex computing. The security of data is based on the secrecy of secret key instead of cipher algorithm. History of Cryptography (cont’ d) After 1976 – Diffie Hellman published “New Directions in Cryptography” in 1976, in which put forward asymmetric cryptography不对称密码体制. – Rivest, Shamir Adleman bring forward RSA public key algorithm. Public key cryptography enables secret communication without key transmission between sender receiver which is well fit for digital signature 数字签名. Memorabilia大事记 of Modern Cryptography Diffie Hellman published “New Directions in Cryptography” in 1976 Government of the United States enacted 颁布“Data Encryption Standard”DES in 1977 Government of the United States enacted new encryption standardEES in 1993 Doctor from the Bell Lab broke EES in 1995 DES was broken in 1997 Government of the United States recruited 征集 new standard for computer encryptionAES all over the world in 1997 AES was enacted in 2001 after strict selection Kerckhoffs’ Principle (1883) Hypothesize that attacker knows the cipher algorithm used Security of a cryptosystem should rely on the secrecy of the key instead of the cipher algorithm As a result, the design of cryptosystem should follow the public principle 1.2 Cryptosystem密码体制 Definition –