[C#] Password Generator

在用戶管理時, 總有須要重設密碼, 若密碼設定太簡單(e.g. 123456), 用戶不去改便容易有保安漏洞, 所以寫了個PasswordGenerator class, 以singleton 形式去產生password. 為了更方便設定, 亦加入了password complexity 相關設定(最少10個字, 英文字母大小楷, 包括符號), 提供更大的彈性.

PasswordGeneratorCondition.cs

public class PasswordGeneratorCondition
    {
        public int UppercaseCount { get; set; }
        public int LowercaseCount { get; set; }
        public int AlphanCharacterCount { get; set; }
        public int DigitCount { get; set; }

        public PasswordGeneratorCondition()
        {
            this.UppercaseCount = 2;
            this.LowercaseCount = 3;
            this.AlphanCharacterCount = 3;
            this.DigitCount = 2;
        }
    }

PasswordGenerator.cs

public static class PasswordGenerator
    {
        private const string LOWERCASE_CHARACTERS = "abcdefghijklmnopqrstuvwxyz";
        private const string UPPERCASE_CHARACTERS = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
        private const string DIGIT_CHARACTERS = "1234567890";
        private const string ALPHAN_CHARACTERS = @"~!@#$%^&*_-+=`|\(){}[]:;""'<>,.?/";

        public static string Generate(PasswordGeneratorCondition condition = null)
        {
            if (condition == null)
                condition = new PasswordGeneratorCondition();

            string value = "";
           
            value += condition.LowercaseCount>0 ? GetRandomString(condition.LowercaseCount, LOWERCASE_CHARACTERS) : "";
            value += condition.UppercaseCount > 0 ? GetRandomString(condition.UppercaseCount, UPPERCASE_CHARACTERS) : "";
            value += condition.AlphanCharacterCount > 0 ? GetRandomString(condition.AlphanCharacterCount, ALPHAN_CHARACTERS) : "";
            value += condition.DigitCount > 0 ? GetRandomString(condition.DigitCount, DIGIT_CHARACTERS) : "";

            return value.Shuffle();
        }

        private static string GetRandomString(int length, string charactors)
        {
            StringBuilder res = new StringBuilder();
            Random rnd = new Random(Guid.NewGuid().GetHashCode());
            while (0 < length--)
            {
                res.Append(charactors[rnd.Next(charactors.Length)]);
            }
            return res.ToString();
        }

        private static string Shuffle(this string input)
        {
            char[] source = input.ToArray();
            int cnt = source.Length;
            Random rnd = new Random(Guid.NewGuid().GetHashCode());
            while (cnt > 1) {
                cnt--;
                int k = rnd.Next(cnt+1);
                char temp = source[k];
                source[k] = source[cnt];
                source[cnt] = temp;
            }
            return new string(source);
        }
    }

用一個console app 做示範, 如何叫用:

class Program
    {
        static void Main(string[] args)
        {
            string password = PasswordGenerator.Generate();
            System.Console.WriteLine("Generated Password: "+password);
            System.Console.WriteLine("Length: " + password.Length);
            ConsoleKeyInfo Key=System.Console.ReadKey();
        }
    }

當然, 若果沒啥特別的話, 直接利用.net 都可以直接產生.

return System.Web.Security.Membership.GeneratePassword(<<length>>, <<No. of alpher characters required>>);

Reference

• Passwords must meet complexity requirements, Microsoft TechNet
• Fisher–Yates shuffle, Wikipedia