RCon

A recursive function that generates a Column Vector. For a given round, we XOR the current vector with the current round constant column vector we get.

Generation

• Note that this diagram above is all that is needed for AES-128’s 11 rounds

$$rco{n}_i=\left[\begin{array}{c}r{c}_i\\ \text{0x0}\\ \text{0x0}\\ \text{0x0}\end{array}\right]$$

Round constant is generated with the recursive function:

$$r{c}_i=\{\begin{array}{ll}rc(1)=1& \\ rc(i)=2\cdot rc(i-1)& \text{if }rc(i-1)<\text{0x80}\\ rc(i)=(2\cdot rc(i-1))\oplus \text{0x11B}& \text{if }rc(i-1)\ge \text{0x80}\end{array}$$