Block and Stream Ciphers

Block and Stream Ciphers are two categories of ciphers used in classical cryptography. Block and Stream Ciphers differ in how large a piece of the message is processed in each encryption operation.

Block Ciphers

Block ciphers encrypt plaintext in chunks. Common block sizes are 64 and 128 bits.

Stream Ciphers

Stream ciphers encrypt plaintext one byte or one bit at a time. A stream cipher can be thought of as a block cipher with a really small block size.

Block Ciphers vs. Stream Ciphers

Generally speaking, block ciphers are more efficient for computers and stream ciphers are easier for humans to do by hand.

Example Block Ciphers

DES is a block cipher with a 64 bit block size. AES is a block cipher with a 128 bit block size. RSA and Diffie-Hellman are block ciphers with variable block sizes.

Example Stream Ciphers

A5, the algorithm used to encrypt GSM communications, is a stream cipher. The RC4 cipher and the one-time pad are also stream ciphers.