AESbyExample英文文献资料.pdf

Written By: Adam Berent Advanced Encryption Standard by Example V.1.5 1.0 Preface The following document provides a detailed and easy to understand explanation of the implementation of the AES (RIJNDAEL) encryption algorithm. The purpose of this paper is to give developers with little or no knowledge of cryptography the ability to implement AES. 2.0 Terminology There are terms that are frequently used throughout this paper that need to be clarified. Block: AES is a block cipher. This means that the number of bytes that it encrypts is fixed. AES can currently encrypt blocks of 16 bytes at a time; no other block sizes are presently a part of the AES standard. If the bytes being encrypted are larger than the specified block then AES is executed concurrently. This also means that AES has to encrypt a minimum of 16 bytes. If the plain text is smaller than 16 bytes then it must be padded. Simply said the block is a reference to the bytes that are processed by the algorithm. State: Defines the current condition (state) of the block. That is the block of bytes that are currently being worked on. The state starts off being equal to the block, however it changes as each round of the algorithms executes. Plainly said this is the block in progress. XOR Refers to the bitwise operator Exclusive Or. XOR operates on the individual bits in a byte in the following way: 0 XOR 0 = 0 1 XOR 0 = 1 1 XOR 1 = 0 0 XOR 1 = 1 For example the Hex digits D4 XOR FF XOR 1111