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keyExpansion.v
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keyExpansion.v
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module keyExpansion #(parameter nk=4,parameter nr=10)(key,w);
// The first [(nk*32)-1 ]-bit key that we use to generate the rest of the keys of the other rounds.
// [(nk*32)-1 ] is the key length (128-bit key, 192-bit key or 256-bit key for nK=4,6 or 8 respectively).
input [0 : (nk * 32) - 1] key;
// w represents the array that will store all the generated keys of all rounds.
/* [(128 * (nr + 1)) - 1] this formula is meant to calculate the length of W ; so that it can store all the
generated keys of all rounds.*/
output reg [0 : (128 * (nr + 1)) - 1] w;
reg [0:31] temp;
reg [0:31] r;
reg [0:31] rot; // It stores the returned value from the function rotword().
reg [0:31] x; //It stores the returned value from the function subwordx().
reg [0:31] rconv; //It stores the returned value from the function rconx().
reg [0:31]new;
integer i;
/*
We generate all the keys needed in the encryption and decryption at the beginning of the encryption or decryption
and store them, then we use them in the AES_Encrypt and AES_Decrypt modules as needed according to the current
round.
*/
/*
The functions:
1) subwordx() applies a table lookup to all to all four bytes of the sent word. subwordx() calls the function
c() four times, each time it sends to c() 1-byte to perform the table lookup on it.
2) rconx() contains the values given by [x^(i-1),{00},{00},{00}], with x^(i-1) being powers
of x (x is denoted as {02}) in the field GF(28).
3) rotword() applies a cyclic shift of the bytes in a word. For example,{09cf4f3c} is changed into {cf4f3c09}
after applying this function.
*/
/*
The pseudo-code of the this algorithm is found in the NIST.pdf attached to the repository with some modification
in the code to fit with verilog.
*/
/*
For simplicity, We are going to explain the storing mechanism of the generated keys on an example of
128-bit key.It would be easy to apply the same concept on 192-bit and 256-bit keys. We would explain it in one
round only. The next rounds would perform the same operations.
-The example:
-Note that in case of 128-bit key w[0:1407].
1) when w=key then w= {1279*{0}:key} where 1279*{0} means that the first 1279 bits are all zero valued
and the end of the w array contains the current 128-bit key.
2) when temp = w[(128 * (nr + 1) - 32) +: 32] then temp=w[1376 +:32] so temp in the first round would contain
the last 32-bit word of the the current key.
3) After performing (temp = SubWord(RotWord(temp)) xor Rcon[i/Nk]) or (temp = SubWord(temp)), We would perform
(new = w[(128*(nr+1)-(nk*32))+:32] ^ temp) which is (new=w[1280+:32] ^ temp) in the first round,
where w[(128*(nr+1)-(nk*32))+:32] here is equivelent to w[i-Nk] in the pseudo-code. Now we have the new
generated key word (new) and we need to add it at the end of (W) array.
4) We would shift W by 32-bit to the left to empty space to the new generated key word.
5) w = {w[0 : (128 * (nr + 1) - 32) - 1], new} is w={w[0:1375],new} where w now contains w={1247*{0}:key:new}
where 1247*{0} means that the first 1247 bits are all zero valued and they are followed by the original
128-bit key, which are followed by the new generated 32-bit key.
6) Repeat this process for the rest of the rounds.At the end of all the rounds we would have all the W array
filled with all the keys.
*/
always@* begin
//The first [(nk*32)-1 ]-bit key is stored in W.
w = key;
for(i = nk; i < 4*(nr + 1); i = i + 1) begin
temp = w[(128 * (nr + 1) - 32) +: 32];
if(i % nk == 0) begin
rot = rotword(temp); // A call to the function rotword() is done and the returned value is stored in rot.
x = subwordx (rot); //A call to the function subwordx() is done and the returned value is stored in x.
rconv = rconx (i/nk); //A call to the function rconx() is done and the returned value is stored in rconv.
temp = x ^ rconv;
end
else if(nk >6 && i % nk == 4) begin
temp = subwordx(temp);
end
new = (w[(128*(nr+1)-(nk*32))+:32] ^ temp);
// We would shift W by 32 bit to the left to add the new generated key word (new) at its end.
w = w << 32;
w = {w[0 : (128 * (nr + 1) - 32) - 1], new};
end
end
function [0:31] rotword;
input [0:31] x;
begin
rotword={x[8:31],x[0:7]};
end
endfunction
function [0:31] subwordx;
input [0:31] a;
begin
subwordx[0:7]=c(a[0:7]);
subwordx[8:15]=c(a[8:15]);
subwordx[16:23]=c(a[16:23]);
subwordx[24:31]=c(a[24:31]);
end
endfunction
function [7:0] c(input [7:0] a);
begin
case (a)
8'h00: c=8'h63;
8'h01: c=8'h7c;
8'h02: c=8'h77;
8'h03: c=8'h7b;
8'h04: c=8'hf2;
8'h05: c=8'h6b;
8'h06: c=8'h6f;
8'h07: c=8'hc5;
8'h08: c=8'h30;
8'h09: c=8'h01;
8'h0a: c=8'h67;
8'h0b: c=8'h2b;
8'h0c: c=8'hfe;
8'h0d: c=8'hd7;
8'h0e: c=8'hab;
8'h0f: c=8'h76;
8'h10: c=8'hca;
8'h11: c=8'h82;
8'h12: c=8'hc9;
8'h13: c=8'h7d;
8'h14: c=8'hfa;
8'h15: c=8'h59;
8'h16: c=8'h47;
8'h17: c=8'hf0;
8'h18: c=8'had;
8'h19: c=8'hd4;
8'h1a: c=8'ha2;
8'h1b: c=8'haf;
8'h1c: c=8'h9c;
8'h1d: c=8'ha4;
8'h1e: c=8'h72;
8'h1f: c=8'hc0;
8'h20: c=8'hb7;
8'h21: c=8'hfd;
8'h22: c=8'h93;
8'h23: c=8'h26;
8'h24: c=8'h36;
8'h25: c=8'h3f;
8'h26: c=8'hf7;
8'h27: c=8'hcc;
8'h28: c=8'h34;
8'h29: c=8'ha5;
8'h2a: c=8'he5;
8'h2b: c=8'hf1;
8'h2c: c=8'h71;
8'h2d: c=8'hd8;
8'h2e: c=8'h31;
8'h2f: c=8'h15;
8'h30: c=8'h04;
8'h31: c=8'hc7;
8'h32: c=8'h23;
8'h33: c=8'hc3;
8'h34: c=8'h18;
8'h35: c=8'h96;
8'h36: c=8'h05;
8'h37: c=8'h9a;
8'h38: c=8'h07;
8'h39: c=8'h12;
8'h3a: c=8'h80;
8'h3b: c=8'he2;
8'h3c: c=8'heb;
8'h3d: c=8'h27;
8'h3e: c=8'hb2;
8'h3f: c=8'h75;
8'h40: c=8'h09;
8'h41: c=8'h83;
8'h42: c=8'h2c;
8'h43: c=8'h1a;
8'h44: c=8'h1b;
8'h45: c=8'h6e;
8'h46: c=8'h5a;
8'h47: c=8'ha0;
8'h48: c=8'h52;
8'h49: c=8'h3b;
8'h4a: c=8'hd6;
8'h4b: c=8'hb3;
8'h4c: c=8'h29;
8'h4d: c=8'he3;
8'h4e: c=8'h2f;
8'h4f: c=8'h84;
8'h50: c=8'h53;
8'h51: c=8'hd1;
8'h52: c=8'h00;
8'h53: c=8'hed;
8'h54: c=8'h20;
8'h55: c=8'hfc;
8'h56: c=8'hb1;
8'h57: c=8'h5b;
8'h58: c=8'h6a;
8'h59: c=8'hcb;
8'h5a: c=8'hbe;
8'h5b: c=8'h39;
8'h5c: c=8'h4a;
8'h5d: c=8'h4c;
8'h5e: c=8'h58;
8'h5f: c=8'hcf;
8'h60: c=8'hd0;
8'h61: c=8'hef;
8'h62: c=8'haa;
8'h63: c=8'hfb;
8'h64: c=8'h43;
8'h65: c=8'h4d;
8'h66: c=8'h33;
8'h67: c=8'h85;
8'h68: c=8'h45;
8'h69: c=8'hf9;
8'h6a: c=8'h02;
8'h6b: c=8'h7f;
8'h6c: c=8'h50;
8'h6d: c=8'h3c;
8'h6e: c=8'h9f;
8'h6f: c=8'ha8;
8'h70: c=8'h51;
8'h71: c=8'ha3;
8'h72: c=8'h40;
8'h73: c=8'h8f;
8'h74: c=8'h92;
8'h75: c=8'h9d;
8'h76: c=8'h38;
8'h77: c=8'hf5;
8'h78: c=8'hbc;
8'h79: c=8'hb6;
8'h7a: c=8'hda;
8'h7b: c=8'h21;
8'h7c: c=8'h10;
8'h7d: c=8'hff;
8'h7e: c=8'hf3;
8'h7f: c=8'hd2;
8'h80: c=8'hcd;
8'h81: c=8'h0c;
8'h82: c=8'h13;
8'h83: c=8'hec;
8'h84: c=8'h5f;
8'h85: c=8'h97;
8'h86: c=8'h44;
8'h87: c=8'h17;
8'h88: c=8'hc4;
8'h89: c=8'ha7;
8'h8a: c=8'h7e;
8'h8b: c=8'h3d;
8'h8c: c=8'h64;
8'h8d: c=8'h5d;
8'h8e: c=8'h19;
8'h8f: c=8'h73;
8'h90: c=8'h60;
8'h91: c=8'h81;
8'h92: c=8'h4f;
8'h93: c=8'hdc;
8'h94: c=8'h22;
8'h95: c=8'h2a;
8'h96: c=8'h90;
8'h97: c=8'h88;
8'h98: c=8'h46;
8'h99: c=8'hee;
8'h9a: c=8'hb8;
8'h9b: c=8'h14;
8'h9c: c=8'hde;
8'h9d: c=8'h5e;
8'h9e: c=8'h0b;
8'h9f: c=8'hdb;
8'ha0: c=8'he0;
8'ha1: c=8'h32;
8'ha2: c=8'h3a;
8'ha3: c=8'h0a;
8'ha4: c=8'h49;
8'ha5: c=8'h06;
8'ha6: c=8'h24;
8'ha7: c=8'h5c;
8'ha8: c=8'hc2;
8'ha9: c=8'hd3;
8'haa: c=8'hac;
8'hab: c=8'h62;
8'hac: c=8'h91;
8'had: c=8'h95;
8'hae: c=8'he4;
8'haf: c=8'h79;
8'hb0: c=8'he7;
8'hb1: c=8'hc8;
8'hb2: c=8'h37;
8'hb3: c=8'h6d;
8'hb4: c=8'h8d;
8'hb5: c=8'hd5;
8'hb6: c=8'h4e;
8'hb7: c=8'ha9;
8'hb8: c=8'h6c;
8'hb9: c=8'h56;
8'hba: c=8'hf4;
8'hbb: c=8'hea;
8'hbc: c=8'h65;
8'hbd: c=8'h7a;
8'hbe: c=8'hae;
8'hbf: c=8'h08;
8'hc0: c=8'hba;
8'hc1: c=8'h78;
8'hc2: c=8'h25;
8'hc3: c=8'h2e;
8'hc4: c=8'h1c;
8'hc5: c=8'ha6;
8'hc6: c=8'hb4;
8'hc7: c=8'hc6;
8'hc8: c=8'he8;
8'hc9: c=8'hdd;
8'hca: c=8'h74;
8'hcb: c=8'h1f;
8'hcc: c=8'h4b;
8'hcd: c=8'hbd;
8'hce: c=8'h8b;
8'hcf: c=8'h8a;
8'hd0: c=8'h70;
8'hd1: c=8'h3e;
8'hd2: c=8'hb5;
8'hd3: c=8'h66;
8'hd4: c=8'h48;
8'hd5: c=8'h03;
8'hd6: c=8'hf6;
8'hd7: c=8'h0e;
8'hd8: c=8'h61;
8'hd9: c=8'h35;
8'hda: c=8'h57;
8'hdb: c=8'hb9;
8'hdc: c=8'h86;
8'hdd: c=8'hc1;
8'hde: c=8'h1d;
8'hdf: c=8'h9e;
8'he0: c=8'he1;
8'he1: c=8'hf8;
8'he2: c=8'h98;
8'he3: c=8'h11;
8'he4: c=8'h69;
8'he5: c=8'hd9;
8'he6: c=8'h8e;
8'he7: c=8'h94;
8'he8: c=8'h9b;
8'he9: c=8'h1e;
8'hea: c=8'h87;
8'heb: c=8'he9;
8'hec: c=8'hce;
8'hed: c=8'h55;
8'hee: c=8'h28;
8'hef: c=8'hdf;
8'hf0: c=8'h8c;
8'hf1: c=8'ha1;
8'hf2: c=8'h89;
8'hf3: c=8'h0d;
8'hf4: c=8'hbf;
8'hf5: c=8'he6;
8'hf6: c=8'h42;
8'hf7: c=8'h68;
8'hf8: c=8'h41;
8'hf9: c=8'h99;
8'hfa: c=8'h2d;
8'hfb: c=8'h0f;
8'hfc: c=8'hb0;
8'hfd: c=8'h54;
8'hfe: c=8'hbb;
8'hff: c=8'h16;
endcase
end
endfunction
function[0:31] rconx;
input [0:31] r;
begin
case(r)
4'h1: rconx=32'h01000000;
4'h2: rconx=32'h02000000;
4'h3: rconx=32'h04000000;
4'h4: rconx=32'h08000000;
4'h5: rconx=32'h10000000;
4'h6: rconx=32'h20000000;
4'h7: rconx=32'h40000000;
4'h8: rconx=32'h80000000;
4'h9: rconx=32'h1b000000;
4'ha: rconx=32'h36000000;
default: rconx=32'h00000000;
endcase
end
endfunction
endmodule