string NORMAL = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
string ENCRYPT = "YO17KPLVSU50C8WE64GAI3MB2DFNZQ9JXTRH";
string strInput = "NikhilGaur";
string strEncrypted = string.Empty;
string strDecrypted = string.Empty;
string strNewChar;
string strLtr;
int iIdx;
protected EncryptionDecryptionDemo()
{
    Response.Write("Original String : " + strInput);
    Response.Write("
");
    for (int i = 0; i < strInput.Length; i++)
    {
        strLtr = strInput.Substring(i, 1).ToUpper();
        iIdx = NORMAL.IndexOf(strLtr);
        strNewChar = ENCRYPT.Substring(iIdx, 1).ToUpper();
        strEncrypted += strNewChar;
    }
    Response.Write("Encrypted string : " + strEncrypted);
    Response.Write("
");

    for (int i = 0; i < strInput.Length; i++)
    {
        strLtr = strEncrypted.Substring(i, 1).ToUpper();
        iIdx = ENCRYPT.IndexOf(strLtr);
        strNewChar = NORMAL.Substring(iIdx, 1).ToUpper();
        strDecrypted += strNewChar;
    }
    Response.Write("Decrypted string(Original again :" + strDecrypted);
}