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package krypto;
public class GalNumber {
public static int RIJN_MOD = 0x11B;
public static int BITWIDTH = 8;
public static int BITMASK = 0xff;
public static int DIV_POS = 0;
public static int MOD_POS = 1;
private static int[] BIT_LUT = {
0x1, 0x2, 0x4, 0x8,
0x10, 0x20, 0x40, 0x80,
0x100, 0x200, 0x400, 0x800,
0x1000, 0x2000, 0x4000, 0x8000
};
private int value;
public GalNumber() {
this.value = 0;
}
public GalNumber (int in) {
value = in & BITMASK;
}
public GalNumber (GalNumber in) {
value = in.value;
}
public GalNumber div(GalNumber rightOp) {
int[] result = new int[2];
result=this.reduce(rightOp);
return new GalNumber(result[DIV_POS]);
}
private int unstrippedMult(GalNumber rightOp) {
int result = 0x0;
int bitmask=0x0;
int ro=rightOp.toInt();
int lo=this.value;
int temp=0x0;
int actBit;
for (int i=0;i<16;i++)
{
bitmask=(0x1 << i);
actBit=ro&bitmask;
if (actBit != 0) {
temp=lo << i;
result ^= temp;
}
}
return result;
}
public GalNumber mult(GalNumber rightOp) {
int [] divmod = new int[2];
GalNumber gn_tmp = new GalNumber();
int tmp = this.unstrippedMult(rightOp);
gn_tmp.setVal(tmp);
divmod = gn_tmp.reduce(RIJN_MOD);
return new GalNumber(divmod[MOD_POS]);
}
public GalNumber mod(GalNumber rightOp) {
int[] result = new int[2];
result=this.reduce(rightOp);
return new GalNumber(result[MOD_POS]);
}
public GalNumber euklid(int modul, GalNumber toInvert) throws Exception {
GalNumber a= new GalNumber(modul);
GalNumber b=new GalNumber(toInvert);
GalNumber r1=new GalNumber(0);
GalNumber r2=new GalNumber(1);
GalNumber a_new=new GalNumber(0);
GalNumber b_new=new GalNumber(0);
GalNumber r1_new=new GalNumber(0);
GalNumber r2_new=new GalNumber(0);
//while (b.toInt() != 1) {
while (b.toInt() > 1) {
/*if (b.toInt() == 0)
{
throw new Exception("b became ZERO");
}*/
a_new = b;
b_new= a.mod(b);
r1_new=r2;
r2_new=r1.add( ( a.div(b) ).mult(r2) );
a=a_new;
b=b_new;
r1=r1_new;
r2=r2_new;
}
return r2;
}
public GalNumber inv() {
GalNumber result = new GalNumber();
try {
result = euklid(RIJN_MOD, this);
}
catch (Exception e) {
//System.out.println(e.getMessage());
result.setVal(0);
}
return result;
}
public GalNumber add(GalNumber rightOp) {
int sum=0;
sum=this.value ^ rightOp.toInt();
return new GalNumber(sum);
}
private int[] reduce(GalNumber rightOp) {
return reduce(rightOp.toInt() );
}
private int[] reduce(int rightOp) {
int [] divmod = new int[2];
divmod[DIV_POS]=0;
divmod[MOD_POS]=this.toInt();
int shift = 0;
int rightOpMSB=0;
int leftOpMSB=0;
// Search MSB in right Operand
for (int i = BIT_LUT.length - 1; i >= 0; i--)
{
if ((rightOp & BIT_LUT[i]) != 0)
{
rightOpMSB = i;
break;
}
}
if (this.toInt() == 0) {
divmod[DIV_POS]=0;
divmod[MOD_POS]=0;
return divmod;
}
if (rightOp == 0){
divmod[DIV_POS]=0;
divmod[MOD_POS]=this.toInt();
return divmod;
}
do {
// Search MSB in left Operand
for (int i = BIT_LUT.length - 1; i >= 0; i--)
{
if ((divmod[MOD_POS] & BIT_LUT[i]) != 0)
{
leftOpMSB = i;
break;
}
}
if (leftOpMSB >= rightOpMSB)
{
// Align the ro to the MSB of the lp and add this
shift = leftOpMSB - rightOpMSB;
// Save result vor integral div
divmod[DIV_POS] = divmod[DIV_POS] ^ (0x1 << shift);
// Next polynom for division
divmod[MOD_POS] = divmod[MOD_POS] ^ (rightOp << shift);
if (divmod[MOD_POS] == 0)
return divmod;
}
} while (leftOpMSB>=rightOpMSB);
return divmod;
}
public GalNumber sub(GalNumber rightOp) {
return new GalNumber(this.add(rightOp));
}
public int toInt() {
return this.value;
}
public String toHex() {
return "'"+Integer.toHexString(this.toInt()).toUpperCase()+"'";
}
public String toString() {
return Integer.toString(this.value);
}
public char toChar() {
return (char) this.toInt();
}
public void setVal(int a) {
value=a;
}
}
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