在我的情况下，密码必须包含:

至少有一个小写字母。 至少一个大写字母。 至少有一个小数。 至少一个特殊字符。

这是我的代码:

    private string CreatePassword(int len)
    {
        string[] valid = { "abcdefghijklmnopqrstuvwxyz", "ABCDEFGHIJKLMNOPQRSTUVWXYZ", "1234567890", "!@#$%^&*()_+" };
        RNGCryptoServiceProvider rndGen = new RNGCryptoServiceProvider();

        byte[] random = new byte[len];
        int[] selected = new int[len];

        do
        {
            rndGen.GetNonZeroBytes(random);

            for (int i = 0; i < random.Length; i++)
            {
                selected[i] = random[i] % 4;
            }
        } 
        while(selected.Distinct().Count() != 4);

        rndGen.GetNonZeroBytes(random);

        string res = "";

        for(int i = 0; i<len; i++)
        {
            res += valid[selected[i]][random[i] % valid[selected[i]].Length];
        }
        return res;
    }

public static class StringHelpers
{
    public static readonly Random rnd = new Random();

    public static readonly string EnglishAlphabet = "abcdefghijklmnopqrstuvwxyz";
    public static readonly string RussianAlphabet = "абвгдеёжзийклмнопрстуфхцчшщъыьэюя";

    public static unsafe string GenerateRandomUTF8String(int length, string alphabet)
    {
        if (length <= 0)
            return String.Empty;
        if (string.IsNullOrWhiteSpace(alphabet))
            throw new ArgumentNullException("alphabet");

        byte[] randomBytes = rnd.NextBytes(length);

        string s = new string(alphabet[0], length);

        fixed (char* p = s)
        {
            for (int i = 0; i < s.Length; i++)
            {
                *(p + i) = alphabet[randomBytes[i] % alphabet.Length];
            }
        }
        return s;
    }

    public static unsafe string GenerateRandomUTF8String(int length, params UnicodeCategory[] unicodeCategories)
    {
        if (length <= 0)
            return String.Empty;
        if (unicodeCategories == null)
            throw new ArgumentNullException("unicodeCategories");
        if (unicodeCategories.Length == 0)
            return rnd.NextString(length);

        byte[] randomBytes = rnd.NextBytes(length);

        string s = randomBytes.ConvertToString();
        fixed (char* p = s)
        {
            for (int i = 0; i < s.Length; i++)
            {
                while (!unicodeCategories.Contains(char.GetUnicodeCategory(*(p + i))))
                    *(p + i) += (char)*(p + i);
            }
        }
        return s;
    }
}

你还需要这个:

public static class RandomExtensions
{
    public static string NextString(this Random rnd, int length)
    {
        if (length <= 0)
            return String.Empty;

        return rnd.NextBytes(length).ConvertToString();
    }

    public static byte[] NextBytes(this Random rnd, int length)
    {
        if (length <= 0)
            return new byte[0];

        byte[] randomBytes = new byte[length];
        rnd.NextBytes(randomBytes);
        return randomBytes;
    }
}

这:

public static class ByteArrayExtensions
{
    public static string ConvertToString(this byte[] bytes)
    {
        if (bytes.Length <= 0)
            return string.Empty;

        char[] chars = new char[bytes.Length / sizeof(char)];
        Buffer.BlockCopy(bytes, 0, chars, 0, bytes.Length);
        return new string(chars);
    }
}

还有另一个版本:我在测试中使用这种方法生成随机的伪股票代码:

Random rand = new Random();
Func<char> randChar = () => (char)rand.Next(65, 91); // upper case ascii codes
Func<int,string> randStr = null;
    randStr = (x) => (x>0) ? randStr(--x)+randChar() : ""; // recursive

用法:

string str4 = randStr(4);// generates a random 4 char string
string strx = randStr(rand.next(1,5)); // random string between 1-4 chars in length

你可以重新定义randChar函数，使用一个“允许的”字符数组，而不是ascii码:

char[] allowedchars = {'A','B','C','1','2','3'};
Func<char> randChar = () => allowedchars[rand.Next(0, allowedchars.Length-1)];

如果您想为强密码生成一串数字和字符。

private static Random random = new Random();

private static string CreateTempPass(int size)
        {
            var pass = new StringBuilder();
            for (var i=0; i < size; i++)
            {
                var binary = random.Next(0,2);
                switch (binary)
                {
                    case 0:
                    var ch = (Convert.ToChar(Convert.ToInt32(Math.Floor(26*random.NextDouble() + 65))));
                        pass.Append(ch);
                        break;
                    case 1:
                        var num = random.Next(1, 10);
                        pass.Append(num);
                        break;
                }
            }
            return pass.ToString();
        }

只要你使用Asp。Net 2.0或更高版本，也可以使用库调用- System.Web.Security.Membership。生成密码，但它将包括特殊字符。

要获得4个随机字符，其中至少有0个特殊字符-

Membership.GeneratePassword(4, 0)

这个解决方案是Random类的扩展。

使用

class Program
{
    private static Random random = new Random(); 

    static void Main(string[] args)
    {
        random.NextString(10); // "cH*%I\fUWH0"
        random.NextString(10); // "Cw&N%27+EM"
        random.NextString(10); // "0LZ}nEJ}_-"
        random.NextString();   // "kFmeget80LZ}nEJ}_-"
    }
}

实现

public static class RandomEx
{
    /// <summary>
    /// Generates random string of printable ASCII symbols of a given length
    /// </summary>
    /// <param name="r">instance of the Random class</param>
    /// <param name="length">length of a random string</param>
    /// <returns>Random string of a given length</returns>
    public static string NextString(this Random r, int length)
    {
        var data = new byte[length];
        for (int i = 0; i < data.Length; i++)
        {
            // All ASCII symbols: printable and non-printable
            // data[i] = (byte)r.Next(0, 128);
            // Only printable ASCII
            data[i] = (byte)r.Next(32, 127);
        }
        var encoding = new ASCIIEncoding();
        return encoding.GetString(data);
    }

    /// <summary>
    /// Generates random string of printable ASCII symbols
    /// with random length of 10 to 20 chars
    /// </summary>
    /// <param name="r">instance of the Random class</param>
    /// <returns>Random string of a random length between 10 and 20 chars</returns>
    public static string NextString(this Random r)
    {
        int length  = r.Next(10, 21);
        return NextString(r, length);
    }
}