private string StringXor( string Str , string Key )
{
int vKeyLen = Key . Length;
char [] StrChars = Str . ToCharArray();
char [] KeyChars = Key . ToCharArray();
int j = 0 ;
for ( int i = 0 ; i < Str . Length; i ++ )
StrChars[i] ^= KeyChars[j ++ % Key . Length];
return new string(StrChars);
}