Password Policy/Strength ASP .NET Validator Web Control

Shantanu
14y
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Article

Toolkit.Web.UI.WebControls.zip

Purpose

Many a time, entities want to implement a password policy and/or determine password strength for their security purposes.

The ASP .NET Password Policy Validator web control allows the entity to set a password policy for users of their web systems.

Implementation Details

The control inherits from BaseValidator web control.

[ToolboxData("<{0}:PasswordPolicyValidator1 runat=server></{0}:PasswordPolicyValidator1>")]
public class PasswordPolicyValidator : BaseValidator

The control exposes properties which can be used to configure/set the password policy/strength requirements.

The Policy properties are

Property	Explanation	Accepted values
UnicodeCharSetRanges	Ranges of Unicode character sets. Validator defaults to English if property not specified.	Comma separated Upper/Uni case followed by Lower case (if applicable) of Unicode Character Set Ranges
MinPasswordLength	Minimum number of characters in password	0 or greater
MinNoOfUniCaseChars	Minimum number of Unicase characters in password. This property is to be used by Unicase languages.	0 or greater
MinNoOfLowerCaseChars	Minimum number of lower case characters in password	0 or greater
MinNoOfUpperCaseChars	Minimum number of upper case characters in password	0 or greater
MinNoOfNumbers	Minimum number of numbers in password	0 or greater
MinNoOfSymbols	Minimum number of symbols in password	0 or greater
MaxNoOfAllowedRepetitions	Max number of allowed repetitions of any character in password	0 or greater
DisallowedChars	Characters not allowed in password	Empty or list of characters
UserNameControlID	Specified to confirm that user name (case – insensitive) is not part of password	ID of the user name text box control

The Strength properties are

Property	Explanation	Accepted values
StrengthCategories	The strength categories of the password. This property is mandatory for strength determination.	Comma separated list of strength categories
StrengthColours	The colours (supported in javascript) for the corresponding strength categories	Comma separated list of strength category colours
MinNoOfUniCaseCharsStrength	List of no. of occurrences of Uni case characters to match for strength categories	Empty or comma separated list of positive integer values
MinNoOfUpperCaseCharsStrength	List of no. of occurrences of Upper Case characters to match for strength categories	Empty or comma separated list of positive integer values
MinNoOfLowerCaseCharsStrength	List of no. of occurrences of Lower Case characters to match for strength categories	Empty or comma separated list of positive integer values
MinNoOfNumbersStrength	List of no. of occurrences of Number characters to match for strength categories	Empty or comma separated list of positive integer values
MinNoOfSymbolsStrength	List of no. of occurrences of Symbols characters to match for strength categories	Empty or comma separated list of positive integer values
MaxNoOfAllowedRepetitionsStrength	List of allowed repetitions to match for strength categories	Empty or comma separated list of positive integer values
MinPasswordLengthStrength	List of password lengths to match for strength categories	Empty or comma separated list of positive integer values

Policy

Policy properties are those that the password MUST confirm to.

Strength

Strength properties are used for determining the password strength.

StrengthCategories property is where the strength categories can be specified as below. This is mandatory for Strength determination.

StrengthCategories="weak,medium,strong"

Then, other relevant properties need to be specified for determining the strength. For eg.

MinNoOfLowerCaseCharsStrength="3,5,7"

means that 4 or less lower case chars is weak, 6 - 5 is medium and 7 or more is strong.

The Strength and Policy can be used independent of each other. Properties need not be specified if not required.

Note : It is good if the strength value of the lowest category is the same as the Min policy property if both Policy and Strength are being used.

Multi-lingual support

The Validator can be used with passwords entered in different languages. The language should be supported in Unicode.

The property UnicodeCharSetRanges is used to specify the Unicode character set ranges of the desired language. If the language is case-sensitive then it is a comma separated list of the upper-case character set range/s followed by the lower-case char set range/s. The Unicode ranges shown below will work for French, German character sets.

UnicodeCharSetRanges="A-Z\u00C0-\u00DE,a-z\u00DF-\u00F6\u00F8-\u00FF"

If the language is Uni-case then there is only one range. The Unicode range shown below is for Japanese Hiragana range.

UnicodeCharSetRanges="\u3040-\u309F"

More information on Unicode character set ranges can be found in below Unicode Chart:

http://www.ssec.wisc.edu/~tomw/java/unicode.html

The properties MinNoOfLowerCaseChars and MinNoOfUpperCaseChars are only valid for case-sensitive languages while for Uni-case languages there is a property called MinNoOfUniCaseChars.

Using these properties, passwords in languages supported in Unicode can be validated. The Error/Strength message can be set in different languages too.

If the UnicodeCharSetRanges property is not specified, the Validator defaults to English.

Code snippets

In the Page Load of the control, the Validation Expression is generated using the properties of the control.

 
void PasswordPolicyValidator_Load(object sender, EventArgs e)
{
   try
   {
      this.ValidationExpression = new Toolkit.Security.PasswordPolicy
      {
         UnicodeCharSetRanges = UnicodeCharSetRanges,
         MaxNoOfAllowedRepetitions = MaxNoOfAllowedRepetitions,
         MinNoOfLowerCaseChars = MinNoOfLowerCaseChars,
         MinNoOfUniCaseChars = MinNoOfUniCaseChars,
         MinNoOfNumbers = MinNoOfNumbers,
         MinNoOfUpperCaseChars = MinNoOfUpperCaseChars,
         MinNoOfSymbols = MinNoOfSymbols,
         MinPasswordLength = MinPasswordLength,
         DisallowedChars = DisallowedChars
       }.GetExpression();
   }
   catch (Exception ex) { }
}

The property values are passed to a helper class (PasswordPolicy) which generates the Validation Expression using the GetExpression() API. The GetExpression() API generates a Regular Expression based on the supplied properties.

 
public string GetExpression()
{
   if (DisallowedChars.Length > 0)
   {
      DisallowedChars = DisallowedChars.Replace(@"\", @"\\");
   }
    
   string Unicase = String.IsNullOrEmpty(UnicodeCharSetRanges) ? "A-Z" : UnicodeCharSetRanges.Split(',')[0].Trim();
   string Lowercase = String.IsNullOrEmpty(UnicodeCharSetRanges) ? "a-z" : (UnicodeCharSetRanges.Split(',').Length >= 2 ? UnicodeCharSetRanges.Split(',')[1] : "a-z");
   
   return @"^" 
         + (MaxNoOfAllowedRepetitions > -1 ? @"(?=^((.)(?!(.*?\2){" + (MaxNoOfAllowedRepetitions + 1).ToString() + @",}))+$)" : "")
         + (MinPasswordLength > -1 ? "(?=.{" + MinPasswordLength.ToString() + @",})" : "") 
         + (MinNoOfNumbers > -1 ? @"(?=([^0-9]*?\d){" + MinNoOfNumbers.ToString() + ",})" : "")
         + (MinNoOfUniCaseChars > -1 ? "(?=([^" + Unicase + @"]*?[" + Unicase + @"]){" + MinNoOfUniCaseChars.ToString() + @",})" : "")
         + (MinNoOfLowerCaseChars > -1 ? "(?=([^" + Lowercase + @"]*?[" + Lowercase + @"]){" + MinNoOfLowerCaseChars.ToString() + ",})" : "")
         + (MinNoOfUpperCaseChars > -1 ? "(?=([^" + Unicase + @"]*?[" + Unicase + @"]){" + MinNoOfUpperCaseChars.ToString() + @",})" : "") 
         + (MinNoOfSymbols > -1 ? "(?=([" + Unicase + Lowercase + @"0-9]*?[^" + Unicase + Lowercase + @"]){" + MinNoOfSymbols.ToString() + ",})" : "")
         + (DisallowedChars.Length > 0 ? @"(?=[^" + DisallowedChars + @"]+$)" : "")
         + @".*$";
}

This Expression does the validation of the password entered by the user.

Concepts of

Character sets (Unicode too)
Look ahead (positive/negative)
Grouping
Back references
Lazy/Greedy match

are used in the Regular Expression.

Usage

Add a reference to Toolkit.Web.UI.WebControls.dll

In the ASPX page:

<%@ Register Assembly="Toolkit.Web.UI.WebControls" Namespace="Toolkit.Web.UI.WebControls" TagPrefix="cc1" %>

And then add the validator

<asp:TextBox ID="tbUserName" runat="server"></asp:TextBox>
<asp:TextBox ID="tbPassword" TextMode="Password" runat="server"></asp:TextBox>

<cc1:PasswordPolicyValidator ID="ppv1" runat="server" ControlToValidate="tbPassword" ErrorMessage=" Password policy did not match! Try again."