Philiprehberger.PasswordStrength

Password strength evaluation with entropy calculation, common password detection, and pattern analysis.

Installation

dotnet add package Philiprehberger.PasswordStrength

Usage

using Philiprehberger.PasswordStrength;

var score = Password.Evaluate("MyP@ssw0rd!");
Console.WriteLine(score.Score);     // 3 (0=very weak, 4=very strong)
Console.WriteLine(score.Entropy);   // 52.4 (bits)
Console.WriteLine(score.CrackTime); // "centuries"
foreach (var tip in score.Feedback)
    Console.WriteLine(tip);

Context-Aware Checking

using Philiprehberger.PasswordStrength;

var context = new PasswordContext
{
    UserName = "johndoe",
    Email = "john@example.com",
    FullName = "John Doe",
    DateOfBirth = new DateTime(1990, 5, 15)
};

var result = Password.Evaluate("johndoe1990!", context);
// Penalizes passwords containing username, email, name, or birth date
foreach (var tip in result.Feedback)
    Console.WriteLine(tip);
// "Password contains your username."
// "Password contains part of your email address."
// "Password contains your name ("john")."
// "Password contains your date of birth."

Keyboard Pattern Detection

using Philiprehberger.PasswordStrength;

var patterns = KeyboardPatternDetector.Detect("qwerty123!");
foreach (var pattern in patterns)
    Console.WriteLine(pattern);
// common keyboard pattern "qwerty"
// numeric sequence "1234" (if present)

var result = Password.Evaluate("asdfgh!!");
// Score is lowered due to keyboard pattern detection

Passphrase Evaluation

using Philiprehberger.PasswordStrength;

var result = Password.Evaluate("correct horse battery staple");
Console.WriteLine(result.Score); // 3 (four unique words scores highly)

// Passphrases are detected automatically when input has 3+ words
// separated by spaces, hyphens, or dots
var hyphenated = Password.Evaluate("solar-panel-winter-frost-glow");
Console.WriteLine(hyphenated.Score); // 4

Structured Feedback

using Philiprehberger.PasswordStrength;

var result = Password.Evaluate("qwerty");
foreach (var item in result.StructuredFeedback)
{
    Console.WriteLine($"[{item.Category}] {item.Message}");
}
// [CommonPassword] This is a commonly used password.
// [KeyboardPattern] Password contains a common keyboard pattern "qwerty".
// [TooShort] Use at least 8 characters.
// [LowDiversity] Consider adding uppercase letters.
// [LowDiversity] Consider adding numbers.
// [LowDiversity] Consider adding special characters.

Common Password Detection and Policy Validation

using Philiprehberger.PasswordStrength;

bool common = Password.IsCommon("password123"); // true
bool unique = Password.IsCommon("xK9#mP2!vL");  // false

var policy = new PasswordPolicy(MinLength: 12, MinScore: 3, RejectCommon: true);
bool valid = Password.MeetsPolicy("MyStr0ng!Pass", policy); // true
bool weak  = Password.MeetsPolicy("password", policy);      // false

API

Password

Method	Description
Evaluate(string password)	Evaluate strength and return a PasswordScore
Evaluate(string password, PasswordContext? context)	Evaluate strength with user context awareness
IsCommon(string password)	Check if the password is in the top 1000 common passwords
MeetsPolicy(string password, PasswordPolicy policy)	Check if the password satisfies the given policy

PasswordScore

Member	Type	Description
Score	int	Strength score from 0 (very weak) to 4 (very strong)
Entropy	double	Shannon entropy in bits
CrackTime	string	Human-readable crack time estimate
Feedback	string[]	Array of improvement suggestions
StructuredFeedback	List<FeedbackItem>	Categorized feedback with actionable messages

FeedbackItem

Member	Type	Description
Category	FeedbackCategory	Category of the weakness detected
Message	string	Human-readable, actionable suggestion

FeedbackCategory

Value	Description
CommonPassword	Matches a commonly used password
KeyboardPattern	Contains a keyboard pattern like "qwerty"
TooShort	Password is too short
LowDiversity	Missing uppercase, digits, or symbols
ContextMatch	Contains user context (username, email, name)
SequentialChars	Contains sequential characters
RepeatedChars	Contains repeated characters
CommonSubstitution	Uses common character substitutions
CouldBeLonger	Password could benefit from being longer
FewWords	Passphrase has too few words

PasswordContext

Property	Type	Description
UserName	string?	User's username
Email	string?	User's email address
FullName	string?	User's full name
DateOfBirth	DateTime?	User's date of birth

KeyboardPatternDetector

Method	Description
Detect(string password)	Detect keyboard patterns of 4+ adjacent keys

PassphraseEvaluator

Method	Description
IsPassphrase(string input)	Check if input has 3+ words separated by spaces, hyphens, or dots
Evaluate(string passphrase)	Evaluate passphrase using word count and vocabulary diversity

EntropyCalculator

Method	Description
Calculate(string password)	Calculate Shannon entropy in bits
DetectPatterns(string password)	Detect weakness patterns (sequential, repeated, keyboard walks, substitutions)

PasswordPolicy

Member	Type	Default	Description
MinLength	int	8	Minimum required length
MinScore	int	2	Minimum required score 0-4
RejectCommon	bool	true	Reject passwords in the common list

Development

dotnet build src/Philiprehberger.PasswordStrength.csproj --configuration Release

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License

MIT