Advanced Encryption Standard With Randomized Round Keys for Communication Security in IoT Networks

Advanced Encryption Standard

The Advanced Encryption Standard (AES) is a symmetric cipher which works on 128 bit block data with three key size variants of 128, 192 and 256 bits. The encryption consists of repeated iterations of four operations performed on the data over 10, 12 and 14 rounds for the 128, 192 and 256 bit key variants respectively. The four operations are Sub Bytes, Shift Rows, Mix Columns and Add Round Key. For the 128 bit key version, the single 128 bit key is broken down into 11 keys of 128 bits. One key is used in the initially to XOR with the text/data and thereafter the balance 10 keys are used for each of the 10 rounds. The last round has three operations without the Mix Columns operation. The decryption is the exact reverse of the encryption process (FIPS Publication 197, 2001;Daemen & Rijmen, 1999, 2013). The AES algorithm is the strongest known symmetric algorithm. The only known attacks against AES are the brute force attack, wherein the attacker obtains the key by trying out all possible bit combinations of the key length and the side channel attacks which makes use of the incorrect or flawed implementation of the algoithm.

The high level algorithm for AES encryption is given below:-

AES_Round (Data, RoundKey[j])
{
SubBytes (Data);
ShiftRows (Data);
MixColns (Data);
AddRoundKey (Data, RoundKey[j]);
}
AES_RoundLast (Data, RoundKey[NumofRounds])
{
SubBytes (Data);
ShiftRows (Data);
AddRoundKey (Data, RoundKey[Numof Rounds]);
}