Share:
Glossary Security

Entropy

In security, entropy measures how unpredictable something is, such as a password or key, usually expressed in bits.

Last reviewed:

AdSense Placeholder
Slot: header_reference_page

In more detail

Each bit doubles the number of guesses an attacker needs. A truly random password of n characters from an alphabet of k symbols has n × log2(k) bits; for example 12 random characters from 94 printable symbols is about 79 bits. Human-chosen passwords have far less entropy than their length suggests, which is why random generators and long passphrases are recommended.

Try these tools

Password Strength & Entropy Auditor

Audit password strength entirely in your browser with live entropy-bit calculation, crack-time estimates across hardware scales.

Password Generator

Generate high-entropy, secure passwords instantly with our free online tool.

Diceware Passphrase Generator

Generate a random, memorable multi-word passphrase from a curated word list using cryptographically secure randomness.

See also

  • Glossary Brute-force attack
    A brute-force attack tries every possible password or key, or a huge list of likely ones, until one works.
  • Glossary Multi-factor authentication (MFA)
    Multi-factor authentication (MFA) requires two or more kinds of proof to sign in.
Back to Glossary
AdSense Placeholder
Slot: footer_leaderboard