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copied!<p>I can't take the credit, as I stole this from <a href="http://social.msdn.microsoft.com/Forums/is/csharpgeneral/thread/5e3f27d2-49af-410a-85a2-3c47e3f77fb1">here</a></p> <pre><code>using System.Text; using System.Text.RegularExpressions; public enum PasswordScore { Blank = 0, VeryWeak = 1, Weak = 2, Medium = 3, Strong = 4, VeryStrong = 5 } public class PasswordAdvisor { public static PasswordScore CheckStrength(string password) { int score = 0; if (password.Length < 1) return PasswordScore.Blank; if (password.Length < 4) return PasswordScore.VeryWeak; if (password.Length >= 8) score++; if (password.Length >= 12) score++; if (Regex.Match(password, @"/\d+/", RegexOptions.ECMAScript).Success) score++; if (Regex.Match(password, @"/[a-z]/", RegexOptions.ECMAScript).Success && Regex.Match(password, @"/[A-Z]/", RegexOptions.ECMAScript).Success) score++; if (Regex.Match(password, @"/.[!,@,#,$,%,^,&,*,?,_,~,-,£,(,)]/", RegexOptions.ECMAScript).Success) score++; return (PasswordScore)score; } } </code></pre> <p>Note the use of regex for checking for upper case characters. This appears to be a decent approach, as it checks length, use of upper and lower case characters, numeric digits and special characters.</p> <p>** Update **</p> <p>I know the question is now closed, but I can add more explanation for VoidKing to understand some of the concepts.</p> <p>A PasswordScore is returned from the CheckStrength method, which can be used as the condition for what to do next in your code.</p> <p>Here's an untested demo of how the above code could be used:</p> <pre><code>String password = "MyDummy_Password"; // Substitute with the user input string PasswordScore passwordStrengthScore = PasswordAdvisor.CheckStrength(password); switch (passwordStrengthScore) { case PasswordScore.Blank: case PasswordScore.VeryWeak: case PasswordScore.Weak: // Show an error message to the user break; case PasswordScore.Medium: case PasswordScore.Strong: case PasswordScore.VeryStrong: // Password deemed strong enough, allow user to be added to database etc break; } </code></pre> <p>Enums are used in this case as a means of classifying the strength of the password into human-readable groups. Keeps the code clean, and makes it obvious what is going on in the code.</p> <p>Regarding the use of Regex's, if you're unfamiliar with the concept of them and how and when to use them, I suggest doing some research as these can be useful in many different scenarios for checking for patterns in strings. Perhaps start <a href="http://www.regular-expressions.info/">here</a>.</p>

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