Password Strength Analysis: How Strong Is Your Password Really?
Learn the science behind password strength meters and entropy calculations. Understand what makes a password truly secure, how attackers crack weak passwords, and practical strategies for creating memorable yet unbreakable credentials.
Key Takeaways
- Password strength is measured in bits of entropy — the mathematical randomness that determines how long a brute-force attack would take.
- Attackers rarely rely on pure brute force.
- The most effective approach combines length with randomness.
- Most online strength meters check only basic criteria — length, character variety, and common patterns.
- A four-word passphrase like `correct-horse-battery-staple` provides roughly 44 bits of entropy from a standard dictionary — adequate for low-value accounts but insufficient for critical ones.
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Understanding Password Entropy
Password strength is measured in bits of entropy — the mathematical randomness that determines how long a brute-force attack would take. A password with 40 bits of entropy can be cracked in hours, while 80+ bits would take centuries with current hardware. Entropy depends on both the character set and the password length.
| Character Set | Pool Size | Entropy/Char |
|---|---|---|
| Lowercase only | 26 | 4.7 bits |
| Mixed case | 52 | 5.7 bits |
| Mixed + digits | 62 | 5.9 bits |
| All printable ASCII | 95 | 6.6 bits |
Common Attack Methods
Attackers rarely rely on pure brute force. Dictionary attacks test common words and phrases first. Rule-based attacks apply transformations like appending numbers or substituting letters (e.g., p@ssw0rd). Rainbow table attacks use precomputed hashes for known passwords. Modern GPUs can test billions of hashes per second against weak algorithms like MD5.
Building Strong Passwords
The most effective approach combines length with randomness. A four-word passphrase like correct-horse-battery-staple provides roughly 44 bits of entropy from a standard dictionary — adequate for low-value accounts but insufficient for critical ones. Adding mixed case, symbols, and a fifth word pushes entropy above 80 bits. Password managers eliminate the need to memorize complex strings entirely.
What Password Meters Miss
Most online strength meters check only basic criteria — length, character variety, and common patterns. They cannot detect whether your password appears in leaked databases or matches personal information an attacker might know. Use the Peasy password strength analyzer for entropy-based scoring that goes beyond simple rule checks, and always verify your password against known breach databases.