Essay About Ab Cd Ef And 128-Bit Plaintext

Advance Encryption Standard
Advance Encryption Standard (Rijndael)The Advanced Encryption Standard (Rijndael) is a symmetric-key encryption standard. It encrypts a 128-bit plaintext into 128-bit cipher text using variable key either of 128 bits, 192 bits and 256 bits, this difference of key lengths in AES is referred to: AES-128, AES-192 and AES 256.[pic 1][pic 2][pic 3]Let,Plain Text: 12 34 56 78 90 AB CD EF 12 34 56 78 90 AB CD EFKey            : 12 90 12 90 34 AB 34 AB 56 CD 56 CD 78 EF 78 EFWe will write plain text and key in state matrix form column wise as shown below.P.T. =                         Key =          [pic 4][pic 5]AES Key Expansion:AES key expansions can be understand easily with the help of the following diagram.[pic 6][pic 7]In above figure there is one unknown element which is ‘g’. Working of ‘g’ is as follow:8 Bit Left Shift/RotateSubstitution BOXXOR with round constant According to figure 2: W4 = W0 ⊕ g (W3)W5 = W4 ⊕ W1W6 = W5 ⊕ W2W7 = W6 ⊕ W3Here,W0 = 12 90 12 90W1 = 34 AB 34 ABW2 = 56 CD 56 CDW3 = 78 EF 78 EFjRC[j]10120230440851062074088091B1036For W4g (W3) = g (78 EF 78 EF )                = EF 78 EF 78                 after         8 Bit Left Circular Shift