Secret-key cryptography
Secret key ciphers provide secrecy among parties who share knowledge of a secret key
- examples include DES, IDEA, RC4, Skipjack
- all have more details than you want to know
Block ciphers - encrypt fixed-size blocks:
ciphertext = Encrypt(key,cleartext)
cleartext = Decrypt(key,ciphertext)
Stream ciphers - sequence of “mask” bits:
ciphertext[i] = cleartext[i]+stream(key,state)
cleartext[i] = ciphertext[i]-stream(key,state)