The Key Expansion Module is used to replicate the round keys generated from the last tutorial. An array of constants are added or blended
with the round keys to generate an expanded key equal to the number of rounds.
For example, the size of the round key is 128 Bits and we have to go ten rounds. Therefore, we will have an array of ten constants which will blend with the 128its round key to generate 10 different keys making it a total of 1280bits, each of the newly generated keys will be fed into each rounds. watch the video below.
`timescale 1 ns/1 ps module KeyExpantion # ( parameter DATA_W = 128, //data width parameter KEY_L = 128, //key length parameter NO_ROUNDS = 10 //number of rounds ) ( input clk, //system clock input reset, //async reset input valid_in, //input valid in input [KEY_L-1:0] cipher_key, //cipher key output [(NO_ROUNDS*DATA_W)-1:0] W, //contains all generated round keys output [NO_ROUNDS-1:0] valid_out //output valid signal ); wire [31:0] RCON [0:9]; //round constant array of words wire [NO_ROUNDS-1:0] keygen_valid_out; //every bit represens output valid signal for every RoundKeyGen module wire [DATA_W-1:0] W_array [0:NO_ROUNDS-1]; //array of round keys to form W output //round connstant values assign RCON[0] = 32'h01000000; assign RCON[1] = 32'h02000000; assign RCON[2] = 32'h04000000; assign RCON[3] = 32'h08000000; assign RCON[4] = 32'h10000000; assign RCON[5] = 32'h20000000; assign RCON[6] = 32'h40000000; assign RCON[7] = 32'h80000000; assign RCON[8] = 32'h1b000000; assign RCON[9] = 32'h36000000; //instantiate number RounkeyGen modules = number of rounds to get number of roundkeys = number of rounds RoundKeyGen #(KEY_L)RKGEN_U0(clk,reset,RCON[0],valid_in,cipher_key,W_array[0],keygen_valid_out[0]); genvar i; generate for (i=1 ;i<NO_ROUNDS;i=i+1) begin : ROUND_KEY_GEN RoundKeyGen #(KEY_L)RKGEN_U(clk,reset,RCON[i],keygen_valid_out[i-1],W_array[i-1],W_array[i],keygen_valid_out[i]); end endgenerate //assigning all the round keys to one output assign W = { W_array[0], W_array[1], W_array[2], W_array[3], W_array[4], W_array[5], W_array[6], W_array[7], W_array[8], W_array[9] }; assign valid_out = keygen_valid_out; endmodule
