Encrypt method (from decrypt method)

[mmmmmm]

Hi,

In the code below there is a method called "decrypt". I am trying to reverse the code to implement the corresponding "encrypt":

public partial class Form1 : Form
{
private uint P;
private uint Q;
private uint[] _S;
char[] k = new char[0x80];


        public byte Crr
        {
            get
            {
                return 12;
            }
        }
        public byte Crb
        {
            get
            {
                return 16;
            }
        }
        public byte Crt
        {
            get
            {
                return 26;
            }
        }
        public byte Crc
        {
            get
            {
                return 4;
            }
        }

//Constructor
public Form1()
{
            this.P = 0xb7e15163;
            this.Q = 0x9e3779b9;
            this._S = new uint[this.Crt];
            k[0] = '\x0017';
            k[1] = '\x009b';
            k[2] = '\x0084';
            k[3] = '\x0096';
            k[4] = 'V';
            k[5] = '\x00f0';
            k[6] = '\x0011';
            k[7] = '\x00d1';
            k[8] = '\x0088';
            k[9] = '\x0082';
            k[10] = '\x00bc';
            k[11] = '\x00e4';
            k[12] = '\x0089';
            k[13] = 'C';
            k[14] = '\x00da';
            k[15] = '\x0091';

            setup_S(k)
}

        private void setup_S(char[] K)
        {
            int index = 0;
            int num2 = 0;
            int num3 = 0;
            int num4 = licBase.Crw / 8;
            uint[] numArray = new uint[this.Crc];
            uint num5 = 0;
            uint num6 = 0;
            for (int i = 0; i < numArray.Length; i++)
            {
                numArray[i] = 0;
            }
            index = this.Crb - 1;
            numArray[this.Crc - 1] = 0;
            while (index != -1)
            {
                numArray[index / num4] = (numArray[index / num4] << 8) + K[index];
                index--;
            }
            this._S[0] = this.P;
            for (index = 1; index < this.Crt; index++)
            {
                this._S[index] = this._S[index - 1] + this.Q;
            }
            num5 = num6 = 0;
            index = num2 = num3 = 0;
            while (num3 < (3 * this.Crt))
            {
                num5 = this._S[index] = rotLeft(this._S[index] + (num5 + num6), 3);
                num6 = numArray[num2] = rotLeft(numArray[num2] + (num5 + num6), num5 + num6);
                num3++;
                index = (index + 1) % this.Crt;
                num2 = (num2 + 1) % this.Crc;
            }
        }

        public uint rotRight(uint x, uint y)
        {
             uint num = x;
             uint num2 = x;
             for (uint i = 0; i < (y & (this.Crw - 1)); i++)
             {
                 num = num >> 1;
             }
             for (uint j = 0; j < (this.Crw - (y & (this.Crw - 1))); j++)
             {
                     num2 = num2 << 1;
             }
             return (num | num2);
        }

        public uint rotLeft(uint x, uint y)
        {
            uint num = x;
            uint num2 = x;
            for (uint i = 0; i < (y & (this.Crw - 1)); i++)
            {
                num = num << 1;
            }
            for (uint j = 0; j < (this.Crw - (y & (this.Crw - 1))); j++)
            {
                num2 = num2 >> 1;
            }
            return (num | num2);
        }

        public void decrypt(uint[] ct, uint[] pt)
        {
            uint y = ct[1];
            uint num2 = ct[0];
            for (uint i = this.Crr; i > 0; i--)
            {
                y = rotRight(y - this._S[(int)((IntPtr)((2 * i) + 1))], num2) ^ num2;
                num2 = rotRight(num2 - this._S[(int)((IntPtr)(2 * i))], y) ^ y;
            }

            pt[1] = y - this._S[1];
            pt[0] = num2 - this._S[0];
        }

        public void encrypt(uint[] ct, uint[] pt)
        {
            //  HELP NEEDED
        }


}

}

I am having a hard time trying to reverse the XOR in the decrypt method. If anyone can help I would highly appreciate it.

Thank you.

[tabstop]

Is your question how to reverse XOR? How to get y? What?

[mmmmmm]

I have the "decrypt" moethod.
I am trying to implement the method "encrypt" method that will work as below.

uint[] test = new uint[2]{1, 1};
decrypt(test, test); //<-this stores in the test array some values {238972, 238972}
// the values are not the actual ones; just for exemplification

I suppose that if the "encrypt" method gets "238972" it should output "1".
So the sequence when using both methods should be;

uint[] test = new uint[2]{1, 1};
encrypt(test, test); //<- now the array is {238972, 238972}
decrypt(test, test); //<- now the array is {1, 1}

Thank you

[C_ntua]

Are we sure that encrypt-->decrypt-->encrypt-->decrypt will give the initial value for all encryption methods?