Partial Password Authentication

TL;DR

This guide shows you how to allow users to log in even if they only remember part of their password. We’ll use a technique called fuzzy matching, but this significantly reduces security and should be used with extreme caution (e.g., for low-sensitivity accounts or as a temporary recovery option). We will focus on implementing this using Python and the `fuzzywuzzy` library.

Prerequisites

• Python 3 installed
• Basic understanding of Python programming
• A database to store user passwords (e.g., SQLite, PostgreSQL) – we’ll assume you have this set up already.

Step-by-Step Guide

1. Install the FuzzyWuzzy Library

FuzzyWuzzy is a library that helps with fuzzy string matching. Install it using pip:

pip install fuzzywuzzy python-Levenshtein

The python-Levenshtein package provides significant performance improvements to FuzzyWuzzy, so it’s highly recommended.

2. Fetch User Passwords from the Database

You need to retrieve the stored passwords for comparison. The exact method depends on your database setup. Here’s a simplified example assuming you have a function get_passwords() that returns a list of hashed passwords:

def get_passwords():
    # Replace with your actual database query
    return ['hashed_password_1', 'another_hashed_password', 'yet_another_hash']

3. Implement the Fuzzy Matching Function

This function will compare the user’s input against the stored passwords. We’ll use a ratio threshold to determine if there’s a match.

from fuzzywuzzy import fuzz

def authenticate_partial(user_input, known_passwords, threshold=70):
    for password in known_passwords:
        ratio = fuzz.ratio(user_input.lower(), password.lower())
        if ratio >= threshold:
            return True  # Potential match found
    return False # No match found

Important: The threshold value (70 in this example) controls how close the input needs to be to a stored password to be considered a match. Lowering this threshold increases the risk of false positives.

4. Integrate into Your Authentication System

Modify your login process to use the authenticate_partial function *in addition* to (or instead of) standard password verification. Here’s a conceptual example:

passwords = get_passwords()
user_input = request.form['password'] # Get user input

if authenticate_partial(user_input, passwords):
    # Log the user in (with caution!)
    print("Partial match found - logging in...")
else:
    # Standard password verification or error message
    print("Authentication failed.")

Warning: Always log attempts using partial authentication for auditing and security monitoring.

5. Hashing Considerations

The above code compares strings directly. In a real-world application, you should be comparing the hash of the user input with the stored password hashes. This requires hashing the user’s input using the same algorithm used to store passwords (e.g., bcrypt, Argon2). You would then compare the fuzzy matching score between the hashed input and the stored hashes.

import hashlib

def hash_password(password):
    # Example using SHA-256 - use a stronger algorithm like bcrypt in production!
    return hashlib.sha256(password.encode()).hexdigest()

6. Security Implications and Mitigation
• Reduced Security: This method is significantly less secure than standard password verification. Attackers can potentially guess passwords with partial information.
• Rate Limiting: Implement rate limiting to prevent brute-force attacks on the fuzzy matching endpoint.
• Account Lockout: Consider locking accounts after multiple failed attempts, even with partial matches.
• Two-Factor Authentication (2FA): Strongly recommend enabling 2FA for all users who use this feature.
• Auditing: Log all successful and failed partial authentication attempts.
• Limited Use Cases: Only enable this for low-sensitivity accounts or as a temporary recovery option. Avoid using it for primary authentication.