Symmetric key algorithm

With a secret or symmetric key algorithm, the key is a shared secret between two communicating parties. Encryption and decryption both use the same key. The Data Encryption Standard (DES) and the Advanced Encryption Standard (AES) are examples of symmetric key algorithms and typical key sizes are 64, 128, or 192 bits.

There are two types of symmetric key algorithms:

Block ciphers: In a block cipher, the actual encryption code works on a fixed-size block of data. Normally, the user's interface to the encrypt/decrypt operation will handle data longer than the block size by repeatedly calling the low-level encryption function. If the length of data is not on a block size boundary, it must be padded.

Stream ciphers: Stream ciphers do not work on a block basis, but convert 1 bit (or 1 byte) of data at a time.