Pin Strength

A lightweight, flexible TypeScript library for validating the strength of numeric PINs. It checks for common weaknesses like repeated digits, sequential patterns, palindromes, and blacklisted sequences.

Features

• Length Validation: Enforce a minimum length (default: 4).
• Repeated Digits: Detects PINs like 1111.
• Sequential Patterns: Detects sequences like 1234 or 4321.
• Palindromes: Detects PINs like 1221.
• Repeated Patterns: Detects repeating patterns like 1212.
• Blacklist: Rejects commonly used PINs (e.g., 1234, 0000).
• Scoring System: Returns a score (0-100) and strength rating ("weak", "medium", "strong").

Installation

npm install pin-strength
# or
yarn add pin-strength

Usage

Basic Usage

import { checkPinStrength } from 'pin-strength';

const result = checkPinStrength('1234');

console.log(result);
/*
{
  score: 0,
  strength: 'weak',
  reasons: [
    'PIN should not contain sequential digits (e.g. 1234 or 4321)',
    'PIN is in the common blacklist'
  ]
}
*/

With Options

You can customize the validation rules using options:

import { checkPinStrength } from 'pin-strength';

const result = checkPinStrength('9812', {
  minLength: 6,
  blacklist: ['9812'],
  allowSequential: false
});

console.log(result);

API Reference

checkPinStrength(pin: string, options?: PinOptions): PinResult

Calculates the strength of a given PIN.

• pin: string - The numeric string to validate.
• options: PinOptions (optional) - Configuration object.

PinOptions

Property	Type	Default	Description
minLength	number	4	Minimum required length of the PIN/
blacklist	string[]	[]	Array of forbidden PINs.
allowSequential	boolean	false	(Not strictly enforced by interface, but used in logic if applicable)

(Note: The allowSequential option is defined in the types but currently strictly enforced by the sequential.rule. Logic updates may be needed to fully respect this flag if intended to bypass the rule.)

PinResult

Property	Type	Description
score	number	A value between 0 and 100 representing the strength.
strength	'weak' | 'medium' | 'strong'	Textual representation of the score. < 40: weak 40-69: medium >= 70: strong
reasons	string[]	List of reasons why the score was penalized.

Rules

The library applies the following rules, each deducting points from the initial score of 100:

1. Length: Checks if the PIN meets the minimum length.
2. Repeated Digits: Checks if all digits are the same (e.g., "1111").
3. Sequential: Checks for forward or backward sequences (e.g., "1234", "4321").
4. Palindrome: Checks if the PIN reads the same forwards and backwards.
5. Repeated Pattern: Checks for repeating sub-patterns (e.g., "1212").
6. Blacklist: Checks if the PIN is in a list of common weak PINs.

License

MIT