ICE Edition

string getRndPW(Random r){
    string strAllPW = "";
    for(int i=0;i<8;i++){
        string value = Convert.ToString(Convert.ToChar(r.Next(65,91)));
        if(r.Next(0,2)==0){
            strAllPW += value.ToUpper();
        }else{
            strAllPW += value.ToLower();
        }
    }
    return strAllPW;
}

Simple Edition

public string CreateRandomPassword(int passwordLength){
    string _allowedChars = "abcdefghjkmnpqrstuvwxyzABCDEFGHJKLMNPQRSTUVWXYZ23456789!@$?_-";
    Byte[] randomBytes = new Byte[passwordLength];
    char[] chars = new char[passwordLength];
    int allowedCharCount = _allowedChars.Length;
    Random randomizer = new Random();
    for(int i = 0;i<passwordLength;i++){
        randomizer.NextBytes(randomBytes);
        chars[i] = _allowedChars[(int)randomBytes[i] % allowedCharCount];
    }
    return new string(chars);
}

Advance Edition - 不含模糊字元(such as [1,l,I] or [O,0]).

///////////////////////////////////////////////////////////////////////////////
// SAMPLE: Generates random password, which complies with the strong password
// rules and does not contain ambiguous characters.
//
// To run this sample, create a new Visual C# project using the Console
// Application template and replace the contents of the Class1.cs file with
// the code below.
//
// THIS CODE AND INFORMATION IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND,
// EITHER EXPRESSED OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE IMPLIED
// WARRANTIES OF MERCHANTABILITY AND/OR FITNESS FOR A PARTICULAR PURPOSE.
//
// Copyright (C) 2004. Obviex(TM). All rights reserved.
//
using System;
using System.Security.Cryptography;

///

/// This class can generate random passwords, which do not include ambiguous
/// characters, such as I, l, and 1. The generated password will be made of
/// 7-bit ASCII symbols. Every four characters will include one lower case
/// character, one upper case character, one number, and one special symbol
/// (such as '%') in a random order. The password will always start with an
/// alpha-numeric character; it will not start with a special symbol (we do
/// this because some back-end systems do not like certain special
/// characters in the first position).
///

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= "*$-+?_&=!%{}/";

///

/// Generates a random password.
///

///
/// Randomly generated password.
///
///
/// The length of the generated password will be determined at
/// random. It will be no shorter than the minimum default and
/// no longer than maximum default.
///
public static string Generate()
{
return Generate(DEFAULT_MIN_PASSWORD_LENGTH,
DEFAULT_MAX_PASSWORD_LENGTH);
}

///

/// Generates a random password of the exact length.
///

///
/// Exact password length.
///
///
/// Randomly generated password.
///
public static string Generate(int length)
{
return Generate(length, length);
}

///

/// Generates a random password.
///

///
/// Minimum password length.
///
///
/// Maximum password length.
///
///
/// Randomly generated password.
///
///
/// The length of the generated password will be determined at
/// random and it will fall with the range determined by the
/// function parameters.
///
public static string Generate(int minLength,
int maxLength)
{
// Make sure that input parameters are valid.
if (minLength <= 0 || maxLength <= 0 || minLength > maxLength)
return null;

// Create a local array containing supported password characters
// grouped by types. You can remove character groups from this
// array, but doing so will weaken the password strength.
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[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[i] = i;

// Because we cannot use the default randomizer, which is based on the
// current time (it will produce the same "random" number within a
// second), we will use a random number generator to seed the
// randomizer.

// 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.
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 {
// If only one character group remained unprocessed, process it;
// otherwise, pick a random character group from the unprocessed
// group list. To allow a special character to appear in the
// first position, increment the second parameter of the Next
// function call by one, i.e. lastLeftGroupsOrderIdx + 1.
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.
lastLeft