Common symmetric ciphers


Two major types:
"Block" ciphers
Fixed transformations on large (64 or 128 bits) chunks of data
e.g. DES, 3DES, RC2, RC5, IDEA, CAST, Blowfish, Twofish, AES

"Stream" ciphers
Time-varying transformations on small (1 or 8 bits) chunks of data
e.g. RC4, OFB-mode, CTR-mode

Block ciphers are the more widely used; stream ciphers are really hard to use correctly!
PPTP, 802.11 are examples of misuses of stream ciphers