
A block cipher works on a chunk of characters at a time. Examples of block ciphers are the popular DES, 3DES, and AES ciphers. You should also know about Cipher Block Chaining (CBC). This is where you exclusive OR (XOR) data with itself and the key table to encrypt the data.
Stream ciphers on the other hand work on one character at a time. An example of a stream cipher is RC4. Another example is the Secure Telephone Unit #3 (STU-III).
Next time I will enumerate the popular block ciphers, including DES and AES.