Sunday, October 17, 2010

C# Random Password Generator

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In an earlier post, I wrote a Random Password Generator class intended for anyone interested to plug into their application.

Following some input I received, I have refactored the code a bit:

using System;
using System.Security.Cryptography;


namespace Security
{

    public class RandomPasswordGenerator
    {
        // Define default password length.
        private static int DEFAULT_PASSWORD_LENGTH = 8;

        //No characters that are confusing: i, I, l, L, o, O, 0, 1, u, v

        public static string PASSWORD_CHARS_ALPHA = 
                                "abcdefghjkmnpqrstwxyzABCDEFGHJKMNPQRSTWXYZ";
        public static string PASSWORD_CHARS_NUMERIC = "23456789";
        public static string PASSWORD_CHARS_SPECIAL = "*$-+?_&=!%{}/";
        public static string PASSWORD_CHARS_ALPHANUMERIC = 
                                PASSWORD_CHARS_ALPHA + PASSWORD_CHARS_NUMERIC;
        public static string PASSWORD_CHARS_ALL = 
                                PASSWORD_CHARS_ALPHANUMERIC + PASSWORD_CHARS_SPECIAL;
        
        //These overloads are only necesary in versions of .NET below 4.0
        #region Overloads

        /// 
        /// Generates a random password with the default length.
        /// 
        /// Randomly generated password.
        public static string Generate()
        {
            return Generate(DEFAULT_PASSWORD_LENGTH,
                            PASSWORD_CHARS_ALL);
        }

        /// 
        /// Generates a random password with the default length.
        /// 
        /// Randomly generated password.
        public static string Generate(string passwordChars)
        {
            return Generate(DEFAULT_PASSWORD_LENGTH, 
                            passwordChars);
        }

        /// 
        /// Generates a random password with the default length.
        /// 
        /// Randomly generated password.
        public static string Generate(int passwordLength)
        {
            return Generate(passwordLength,
                            PASSWORD_CHARS_ALL);
        }

        /// 
        /// Generates a random password.
        /// 
        /// Randomly generated password.
        public static string Generate(int passwordLength,
                                      string passwordChars)
        {
            return GeneratePassword(passwordLength, 
                                    passwordChars);
        }

        #endregion


        /// 
        /// Generates the password.
        /// 
        /// 
        private static string GeneratePassword(int passwordLength,
                                               string passwordCharacters)
        {
            if (passwordLength < 0) 
                throw new ArgumentOutOfRangeException("Password Length");

            if (string.IsNullOrEmpty(passwordCharacters)) 
                throw new ArgumentOutOfRangeException("Password Characters");
            
            var password = new char[passwordLength];

            var random = GetRandom();

            for (int i = 0; i < passwordLength; i++)
                password[i] = passwordCharacters[
                                          random.Next(passwordCharacters.Length)];

            return new string(password);
        }



        

        /// 
        /// Gets a random object with a real random seed
        /// 
        /// 
        private static Random GetRandom()
        {
            // Use a 4-byte array to fill it with random bytes and convert it then
            // to an integer value.
            byte[] randomBytes = new byte[4];

            // Generate 4 random bytes.
            new RNGCryptoServiceProvider().GetBytes(randomBytes);

            // Convert 4 bytes into a 32-bit integer value.
            int seed = (randomBytes[0] & 0x7f) << 24 |
                        randomBytes[1] << 16 |
                        randomBytes[2] << 8 |
                        randomBytes[3];

            // Now, this is real randomization.
            return new Random(seed);
        }


    }
}


6 comments:

rhyous said...

Thanks for this. I had some stricter requirements from my security guy and I used your code and gave it some enhancements, in case you are interested.

http://www.rhyous.com/2011/01/22/c-random-password-generator/

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