True Random and Unique AlphaNumeric Number Generator

public string GetRandomUniqueAlphaNumericCode(int length, bool lowerCase) { int maxSize = 8; char[] chars = new char[62]; string a; a = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890"; chars = a.ToCharArray(); int size = maxSize; byte[] data = new byte[1]; RNGCryptoServiceProvider crypto = new RNGCryptoServiceProvider(); crypto.GetNonZeroBytes(data); size = maxSize; data = new byte[size]; crypto.GetNonZeroBytes(data); StringBuilder result = new StringBuilder(size); foreach (byte b in data) { result.Append(chars[b % (chars.Length - 1)]); } strCode = (result.ToString()).ToUpper(); bool flag = false; for (int i = 0; i < strCode.Length; i++) { if (char.IsDigit(strCode, i)) { flag = true; } } if (flag == false) { GetRandomUniqueAlphaNumericCode(); } return strCode; } here strCode is static class variable. this will generate random and unique alphanumeric string.