Truco C# en .NET 2008:Como generar passwords aleatorios

creamos una clase RandomPassword.cs y agregamos este codigo:

using System.Security.Cryptography;

namespace WindowsFormsApplication1
{
    public class RandomPassword
    {
        // Define default min and max password lengths.
        private static int DEFAULT_MIN_PASSWORD_LENGTH = 8;
        private static int DEFAULT_MAX_PASSWORD_LENGTH = 10;

        // Define supported password characters divided into groups.
        // You can add (or remove) characters to (from) these groups.
        private static string PASSWORD_CHARS_LCASE = "abcdefgijkmnopqrstwxyz";
        private static string PASSWORD_CHARS_UCASE = "ABCDEFGHJKLMNPQRSTWXYZ";
        private static string PASSWORD_CHARS_NUMERIC = "23456789";
        private static string PASSWORD_CHARS_SPECIAL = "*$-+?_&=!%{}/";


        public static string Generate()
        {
            return Generate(DEFAULT_MIN_PASSWORD_LENGTH,
                            DEFAULT_MAX_PASSWORD_LENGTH);
        }


        public static string Generate(int length)
        {
            return Generate(length, length);
        }


        public static string Generate(int minLength,
                                      int maxLength)
        {
            // Make sure that input parameters are valid.
            if (minLength <= 0 || maxLength <= 0 || minLength > maxLength)
                return null;


            char[][] charGroups = new char[][] 
        {
            PASSWORD_CHARS_LCASE.ToCharArray(),
            PASSWORD_CHARS_UCASE.ToCharArray(),
            PASSWORD_CHARS_NUMERIC.ToCharArray(),
            PASSWORD_CHARS_SPECIAL.ToCharArray()
        };

            // Use this array to track the number of unused characters in each
            // character group.
            int[] charsLeftInGroup = new int[charGroups.Length];

            // Initially, all characters in each group are not used.
            for (int i = 0; i < charsLeftInGroup.Length; i++)
                charsLeftInGroup[i] = charGroups[i].Length;

            // Use this array to track (iterate through) unused character groups.
            int[] leftGroupsOrder = new int[charGroups.Length];

            // Initially, all character groups are not used.
            for (int i = 0; i < leftGroupsOrder.Length; i++)
                leftGroupsOrder[i] = i;




            byte[] randomBytes = new byte[4];

            // Generate 4 random bytes.
            RNGCryptoServiceProvider rng = new RNGCryptoServiceProvider();
            rng.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.
            Random random = new Random(seed);

            // This array will hold password characters.
            char[] password = null;

            // Allocate appropriate memory for the password.
            if (minLength < maxLength)
                password = new char[random.Next(minLength, maxLength + 1)];
            else
                password = new char[minLength];

            // Index of the next character to be added to password.
            int nextCharIdx;

            // Index of the next character group to be processed.
            int nextGroupIdx;

            // Index which will be used to track not processed character groups.
            int nextLeftGroupsOrderIdx;

            // Index of the last non-processed character in a group.
            int lastCharIdx;

            // Index of the last non-processed group.
            int lastLeftGroupsOrderIdx = leftGroupsOrder.Length - 1;

            // Generate password characters one at a time.
            for (int i = 0; i < password.Length; i++)
            {

                if (lastLeftGroupsOrderIdx == 0)
                    nextLeftGroupsOrderIdx = 0;
                else
                    nextLeftGroupsOrderIdx = random.Next(0,
                                                         lastLeftGroupsOrderIdx);

                // Get the actual index of the character group, from which we will
                // pick the next character.
                nextGroupIdx = leftGroupsOrder[nextLeftGroupsOrderIdx];

                // Get the index of the last unprocessed characters in this group.
                lastCharIdx = charsLeftInGroup[nextGroupIdx] - 1;

                // If only one unprocessed character is left, pick it; otherwise,
                // get a random character from the unused character list.
                if (lastCharIdx == 0)
                    nextCharIdx = 0;
                else
                    nextCharIdx = random.Next(0, lastCharIdx + 1);

                // Add this character to the password.
                password[i] = charGroups[nextGroupIdx][nextCharIdx];

                // If we processed the last character in this group, start over.
                if (lastCharIdx == 0)
                    charsLeftInGroup[nextGroupIdx] =
                                              charGroups[nextGroupIdx].Length;
                // There are more unprocessed characters left.
                else
                {
                    // Swap processed character with the last unprocessed character
                    // so that we don't pick it until we process all characters in
                    // this group.
                    if (lastCharIdx != nextCharIdx)
                    {
                        char temp = charGroups[nextGroupIdx][lastCharIdx];
                        charGroups[nextGroupIdx][lastCharIdx] =
                                    charGroups[nextGroupIdx][nextCharIdx];
                        charGroups[nextGroupIdx][nextCharIdx] = temp;
                    }
                    // Decrement the number of unprocessed characters in
                    // this group.
                    charsLeftInGroup[nextGroupIdx]--;
                }

                // If we processed the last group, start all over.
                if (lastLeftGroupsOrderIdx == 0)
                    lastLeftGroupsOrderIdx = leftGroupsOrder.Length - 1;
                // There are more unprocessed groups left.
                else
                {
                    // Swap processed group with the last unprocessed group
                    // so that we don't pick it until we process all groups.
                    if (lastLeftGroupsOrderIdx != nextLeftGroupsOrderIdx)
                    {
                        int temp = leftGroupsOrder[lastLeftGroupsOrderIdx];
                        leftGroupsOrder[lastLeftGroupsOrderIdx] =
                                    leftGroupsOrder[nextLeftGroupsOrderIdx];
                        leftGroupsOrder[nextLeftGroupsOrderIdx] = temp;
                    }
                    // Decrement the number of unprocessed groups.
                    lastLeftGroupsOrderIdx--;
                }
            }

            // Convert password characters into a string and return the result.
            return new string(password);
        }
    }
}

ahora en el boton ponemos este codigo:

textBox1.Text = RandomPassword.Generate(8,10);

y listo =) espero les haya servido el ejemplo