Password vs. Passphrase: The Entropy Battle
For decades, we've been told that secure passwords need uppercase letters, numbers, and symbols. But this advice has led to passwords like "P@ssw0rd123!" that are both hard to remember AND easy to crack. Let's explore why a simple-looking passphrase like "correct-horse-battery-staple" is actually more secure.
Traditional "Complex" Password
P@ssw0rd123!
~28 bits
of effective entropy
VS
Random Word Passphrase
correct-horse-battery-staple
~44 bits
of entropy
The passphrase is over 65,000 times harder to crack than the "complex" password, yet it's far easier to remember and type.
Understanding Entropy
Entropy measures the randomness or unpredictability of a password. It's expressed in bits—each additional bit doubles the number of possibilities an attacker must try.
The Entropy Formula
For Random Character Passwords:
Entropy = Length × log₂(Character Pool Size)
Example: 12 random characters from 95 possible = 12 × 6.57 = 78.8 bits
For Random Word Passphrases:
Entropy = Number of Words × log₂(Dictionary Size)
Example: 4 words from 7,776-word list = 4 × 12.9 = 51.7 bits
Why "P@ssw0rd123!" Has Low Entropy
While this password technically uses uppercase, lowercase, numbers, and symbols, it wasn't generated randomly. Attackers know common patterns:
- Base word "password" (in every dictionary attack)
- @ substituted for 'a' (first thing attackers try)
- 0 substituted for 'o' (second thing they try)
- Numbers appended at the end (extremely common)
- ! added to satisfy symbol requirements (most common choice)
The reality: Password crackers have rule sets that try "password" → "p@ssword" → "p@ssw0rd" → "P@ssw0rd" → "P@ssw0rd1" → "P@ssw0rd12" → "P@ssw0rd123" → "P@ssw0rd123!" within the first few million guesses. This takes under a second.
The XKCD Revelation
In 2011, webcomic XKCD published a famous illustration showing why random word passphrases beat traditional complex passwords. The core insight: length and true randomness matter more than character complexity.
How Attackers Actually Crack Passwords
- Dictionary attacks: Try common passwords and words
- Rule-based attacks: Apply transformations (capitalize first letter, add numbers, substitute letters with symbols)
- Hybrid attacks: Combine dictionary words with rules
- Brute force: Try every possible combination (last resort)
Human-created "complex" passwords follow predictable patterns that rules can exploit. Truly random passphrases force attackers into slower dictionary combination attacks.
Entropy Comparison Table
| Password Type |
Example |
Theoretical Entropy |
Effective Entropy |
| Common password |
password123 |
72 bits |
~0 bits (in dictionaries) |
| Predictable substitution |
P@ssw0rd123! |
79 bits |
~28 bits (rule-based) |
| Random 8-char password |
Kx9#mP2$ |
52 bits |
52 bits |
| Random 12-char password |
vL4@nQ8&jR2! |
79 bits |
79 bits |
| 4-word passphrase (Diceware) |
correct-horse-battery-staple |
51 bits |
51 bits |
| 5-word passphrase |
piano-zebra-mountain-clock-river |
64 bits |
64 bits |
| 6-word passphrase |
ocean-laptop-forest-puzzle-train-maple |
77 bits |
77 bits |
| Random 16-char password |
Kx9#mP2$vL4@nQ8& |
105 bits |
105 bits |
Key insight: "Theoretical entropy" assumes random generation. "Effective entropy" accounts for how attackers actually crack passwords. Human-created passwords almost always have lower effective entropy than theoretical.
When to Use Each Approach
Use Random Character Passwords When:
- You use a password manager that auto-fills credentials
- The site has strict length limits (under 20 characters)
- You need maximum entropy per character
- You're generating API keys, tokens, or database credentials
Use Passphrases When:
- You need to memorize the credential (master passwords)
- You'll type it frequently across different devices
- The system allows long passwords (30+ characters)
- You want something secure that humans can actually use
Best practice for 2026: Use a password manager with a 6+ word passphrase as your master password. Let the manager generate random 16-20 character passwords for individual sites.
How to Generate Strong Passphrases
The Diceware Method
Diceware is a proven method for generating truly random passphrases:
- Roll five dice (or use a secure random generator)
- Look up the resulting number in the Diceware word list
- Repeat for each word you need (minimum 5 words for modern security)
- Optionally add separators (hyphens, spaces, or numbers)
Critical Rules for Secure Passphrases
- Words must be truly random: Don't pick words yourself—use dice or a CSPRNG
- Don't use phrases from books, songs, or movies: These are in cracking dictionaries
- Don't use related words: "blue-sky-cloud-rain" is weaker than random words
- Use at least 5 words: 4 words is now borderline for high-security needs
- Consider adding a random symbol or number: Increases entropy further
Passphrase Strength by Word Count
| Words |
Entropy (7,776-word list) |
Crack Time (10B guesses/sec) |
Recommendation |
| 3 words |
~39 bits |
~1 minute |
Not recommended |
| 4 words |
~52 bits |
~52 days |
Minimum acceptable |
| 5 words |
~65 bits |
~1,100 years |
Good for most uses |
| 6 words |
~78 bits |
~9 million years |
Strong |
| 7 words |
~90 bits |
~70 billion years |
Very strong |
The Bottom Line
Both strong random passwords and properly generated passphrases can be highly secure. The key differences are:
- Passwords: Maximum entropy per character, requires password manager
- Passphrases: Memorable, typeable, requires more characters for same security
What matters most is that your credentials are truly random—whether that's random characters or random words. Human-chosen "complex" passwords remain the weakest option regardless of how many symbols they contain.
Action item: Generate a secure password now using our password generator, or create a 6-word Diceware passphrase for credentials you need to memorize.