AES encryption, also known as Advanced Encryption Standard, is an encryption algorithm that is used to encrypt sensitive data. It was originally implemented in 2001 when the Secretary of Commerce in the United States specified that all unclassified documents use AES for encryption, replacing the outdated DES encryption method. Since then the US government has acknowledged that AES encryption is sufficient to protect information up to the Secret level. With a key of 192 or 256 bits, AES can be used to encrypt Top Secret data.
The cipher itself is what can be called a substitution permutation network. AES has a block size of 128 bits and the key size can vary from 128 to 256 bits. The key size is what determines the number of conversion cycles that the cipher runs through.
The cipher uses four primary steps to encrypt data. The first step is the KeyExpansion in which the keys for the rounds are selected using a key schedule. The second step is the first round the cipher will run. Each byte of the state is added to the round key using bitwise xor. The third step is when the cipher runs through the normal rounds which are dependent on the size of the key. A substitution step is followed by transposition, mixing, and another combination step. The final round of the encryption process skips the mixing operation.
AES encryption is used in many encryption applications today. Many programs that encrypt data from commercial businesses, home computer users, and government agencies use AES encryption because of its speed and realibility. The TLS security protocol uses AES encryption.