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AES

A basic description of AES can be obtained from Wikipedia, and if you are new to AES, you should definitely do some research to understand the implementation. The description below is from Wikipedia:

In cryptography, a block cipher is a symmetric key cipher which operates on fixed-length groups of bits, termed blocks, with an unvarying transformation. When encrypting, a block cipher might take a (for example) 16-bit block of plaintext as input, and output a corresponding 16-bit block of ciphertext. The exact transformation is controlled using a second input - the secret key. Decryption is similar: the decryption algorithm takes, in this example, a 16-bit block of ciphertext together with the secret key, and yields the original 16-bit block of plaintext.

To encrypt messages longer than the block size, a mode of operation is used. Block ciphers can be contrasted with stream ciphers; a stream cipher operates on individual digits one at a time, and the transformation varies during the encryption. The distinction between the two types is not always clear-cut: a block cipher, when used in certain modes of operation, acts effectively as a stream cipher.

This example demonstrates how to use the AES key, encryption, and decryption function calls on a 16 byte block of data. Since AES is a block cipher, all data must be encrypted in 16 byte blocks. If you have more than 16 bytes to transfer, you must break the data into 16 byte blocks, encrypt them (you can use the same key for all blocks), send them, then decrypt them in 16 byte blocks on the other end.