斗 长 Symmetric Key Encryption ￥斗 ★★ o Given e -key, it is easy to find out d-key o Vice versa(i.e symmetric Sometimes d-key =e-key o Only senderand receiver know the key o Sometimes this is called"secret key encryption It must not be made public
16 Symmetric Key Encryption Given e-key, it is easy to find out d-key Vice versa (i.e. symmetric) – Sometimes d-key = e-key! Only sender and receiver know the key Sometimes this is called “secret key” encryption – It must not be made public
斗 长 Symmetric Key Cryptography ￥斗 ★★ O Ex: Mono-alphabetic substitution eachletterreplaced by differentletter 9 ABCDEFGHIKLMNOPQRSTUVWXYZ O QWERTYUIOPASDFGHJKLZXCVBNM o Given e-key QWERTYUIOPASDFGHJKLZXCVBNM. o Easy to d-key. KXVMCNOPHQRSZYDADLEGWBUFT
17 Symmetric Key Cryptography Ex: Mono-alphabetic substitution – each letter replaced by different letter ABCDEFGHIJKLMNOPQRSTUVWXYZ QWERTYUIOPASDFGHJKLZXCVBNM Given e-key – QWERTYUIOPASDFGHJKLZXCVBNM, Easy to d-key: – KXVMCNOPHQRSZYIJADLEGWBUFT
斗 长 Symmetric Key Encryption ￥斗 ★★ o How do sender and receiver get a shared secret key in the first place?
18 Symmetric Key Encryption How do sender and receiver get a shared secret key in the first place?
斗 长 Symmetric Key Encryption ￥斗 ★★ o Famous Symmetric Key encryption include: ≈DES、RC2、Rc4、IDEA D GOST、 SAFER、FEAL、 Skipjack、 Blowfish
19 Symmetric Key Encryption Famous Symmetric Key encryption include: DES、RC2、RC4、IDEA GOST、SAFER、FEAL、Skipjack、Blowfish
斗 长 Public-key Encryption ￥斗 ★★ o Also called asymmetric encryption o Given e-key, it is virtually impossible to find d-key Thus the name asymmetric o Thus, the encryption key can be made public Thus the name public
20 Public-key Encryption Also called asymmetric encryption Given e-key, it is virtually impossible to find d-key – Thus the name asymmetric Thus, the encryption key can be made public – Thus the name public