 Cryptography is the science of using mathematics to encrypt and decrypt data.  Cryptography enables you to store sensitive information or transmit it across insecure networks (like the Internet) so that it cannot be read by anyone except the intended recipient.  While cryptography is the science of securing data, cryptanalysis is the science of analyzing and breaking secure communication. Cryptanalysts are also called attackers.  Cryptology embraces both cryptography and cryptanalysis.

AliceBob Plaintext Cipher text Key EncryptionDecryption

 The Advanced Encryption Standard (AES) is a symmetric-key block cipher published by the National Institute of Standards and Technology (NIST) in December  AES is a non-Feistel cipher that encrypts and decrypts a data block of 128 bits. It uses 10, 12, or 14 rounds. The key size, which can be 128, 192, or 256 bits, depends on the number of rounds.  To provide security, AES uses four types of transformations: substitution, permutation, mixing, and key-adding.

 Convert to state array  Transformations (and their inverses)  AddRoundKey  SubBytes  ShiftRows  MixColumns  Key Expansion

Input block: S 0,0 S 0,1 S 0,2 S 0,3 S 1,0 S 1,1 S 1,2 S 1,3 S 2,0 S 2,1 S 2,2 S 2,3 S 3,0 S 3,1 S 3,2 S 3,3 =

 XOR each byte of the round key with its corresponding byte in the state array S 0,0 S 0,1 S 0,2 S 0,3 S 1,0 S 1,1 S 1,2 S 1,3 S 2,0 S 2,1 S 2,2 S 2,3 S 3,0 S 3,1 S 3,2 S 3,3 S’ 0,0 S ’ 0,1 S’ 0,2 S’ 0,3 S’ 1,0 S’ 1,1 S’ 1,2 S’ 1,3 S’ 2,0 S’ 2,1 S’ 2,2 S’ 2,3 S’ 3,0 S’ 3,1 S’ 3,2 S’ 3,3 S 0,1 S 1,1 S 2,1 S 3,1 S’ 0,1 S’ 1,1 S’ 2,1 S’ 3,1 R 0,0 R 0,1 R 0,2 R 0,3 R 1,0 R 1,1 R 1,2 R 1,3 R 2,0 R 2,1 R 2,2 R 2,3 R 3,0 R 3,1 R 3,2 R 3,3 R 0,1 R 1,1 R 2,1 R 3,1 XOR

 Replace each byte in the state array with its corresponding value from the S-Box CC DD 2266AAEE 3377BBFF 55

 Last three rows are cyclically shifted S 0,0 S 0,1 S 0,2 S 0,3 S 1,0 S 1,1 S 1,2 S 1,3 S 2,0 S 2,1 S 2,2 S 2,3 S 3,0 S 3,1 S 3,2 S 3,3 S 1,0 S 3,0 S 3,1 S 3,2 S 2,0 S 2,1

 Apply MixColumn transformation to each column S 0,0 S 0,1 S 0,2 S 0,3 S 1,0 S 1,1 S 1,2 S 1,3 S 2,0 S 2,1 S 2,2 S 2,3 S 3,0 S 3,1 S 3,2 S 3,3 S’ 0,0 S ’ 0,1 S’ 0,2 S’ 0,3 S’ 1,0 S’ 1,1 S’ 1,2 S’ 1,3 S’ 2,0 S’ 2,1 S’ 2,2 S’ 2,3 S’ 3,0 S’ 3,1 S’ 3,2 S’ 3,3 S 0,1 S 1,1 S 2,1 S 3,1 S’ 0,1 S’ 1,1 S’ 2,1 S’ 3,1 MixColumns() S’ 0,c = ({02}  S 0,c )  ({03}  S 1,c )  S 2,c  S 3,c S’ 1,c = S 0,c  ({02}  S 1,c )  ({03}  S 2,c )  S 3,c S’ 2,c = S 0,c  S 1,c  ({02}  S 2,c )  ({03}  S 3,c ) S’ 3,c = ({03}  S 0,c )  S 1,c  S 2,c  ({02}  S 3,c

 Expands the key material so that each round uses a unique round key  Generates Nb(Nr+1) words Filled with just the key Filled with a combination of the previous work and the one Nk positions earlier

Encryption AddRoundKey SubBytes ShiftRows MixColumns AddRoundKey SubBytes ShiftRows AddRoundKey Decryption AddRoundKey InvShiftRows InvSubBytes AddRoundKey InvMixColumns InvShiftRows InvSubBytes AddRoundKey