private double[] m_cHISTOGRAM = new double[] { .082, .015, .028, .043, .127, .022, .020, .061, .070, .002, .008, .040, .024, .067, .075, .019, .001, .060, .063, .091, .028, .010, .023, .001, .020, .001 };

private int GetKeyLength(string sCipherText)
        {
            int iSize = 30;
            double[] colCoincidence = new double[iSize + 1];
            int iTextLength = sCipherText.Length;

            for (int i = 0; i <= iSize; i++)
            {
                int iDiv = iTextLength - i;

                for (int j = 0; j < sCipherText.Length; j++)
                {
                    if (i + j >= sCipherText.Length)
                        break;

                    char c = sCipherText[j];
                    char k = sCipherText[i + j];

                    if(c == k)
                        colCoincidence[i] = colCoincidence[i] + 1;
                }

                colCoincidence[i] /= iDiv;
            }

            List<int> colIndexes = new List<int>();
            double dMinValue = 0.06;
            //double dEnglishValue = 0.067;
            double dMaxValue = 0.075;

            for (int i = 1; i < colCoincidence.Length; i++)
            {
                double dValue = colCoincidence[i];

                if ((dValue >= dMinValue && dValue <= dMaxValue) || dValue == 1.0)
                    colIndexes.Add(i);
            }

            int iIndex = -1;

            if (colIndexes.Count > 0)
                iIndex = colIndexes[0];

            return iIndex;
        }