Password Strength & Entropy Analyzer

Password security is the cornerstone of digital identity protection. Modern attackers use sophisticated techniques including GPU-accelerated brute force, rainbow tables, and credential stuffing from data breaches. Understanding password entropy helps create genuinely secure credentials.

Understanding Entropy (The Math Behind Security)

Entropy measures password randomness in bits. Each bit doubles the search space an attacker must exhaust. A truly random 8-character lowercase password has ~37 bits of entropy (26^8 possibilities). Adding uppercase, numbers, and symbols increases the character set, while longer passwords multiply guessing difficulty exponentially.

The zxcvbn Approach

Developed by Dropbox, zxcvbn-style analysis goes beyond simple character counting. It identifies patterns attackers actually exploit: dictionary words, keyboard sequences (qwerty, asdfgh), l33t substitutions (p@$$w0rd), dates, and common password structures. A password like 'Tr0ub4dor&3' appears complex but contains a dictionary word with predictable substitutions—far weaker than its character diversity suggests.

Real-World Attack Speeds

Modern GPU clusters achieve 10-100 billion MD5 hash guesses per second. Bcrypt-hashed passwords are slower to crack (~10,000/sec) but offline attacks still succeed against weak passwords. Online attacks are rate-limited (~1000 attempts/sec before lockout), but credential stuffing uses stolen database passwords against other sites—no brute force needed.

Why Length Beats Complexity

Each additional character increases entropy more than adding character types. A 20-character passphrase of lowercase words ('correct horse battery staple') has ~77 bits of entropy—stronger than a complex 10-character password (~66 bits) and far easier to remember.

Passphrase Strategy

Use 4-6 random words totaling 20+ characters. Avoid famous quotes, song lyrics, or predictable combinations. Add a symbol or number in an unexpected position. Example: 'quantum pencil midnight 47 atlas!' provides ~90+ bits of entropy.

Breach Database Reality

Over 10 billion credentials have been exposed in data breaches. Attackers compile these into dictionaries, testing common passwords first. Any password appearing in breaches (check haveibeenpwned.com) is effectively zero-entropy regardless of apparent complexity.

The 2024 NIST Guidelines

NIST SP 800-63B recommends: minimum 8 characters (12+ preferred), no composition rules (they don't improve security), screen against common passwords and breach databases, and allow maximum length (64+ characters). Complexity requirements frustrate users without meaningfully improving security.