Computing & NetworkingHTML guide
Security Fundamentals
A concise guide to password entropy as a rough strength estimate, explaining what the number represents, what it does not represent, and why human behaviour still matters.
Key formulas
Entropy estimate
entropy = length x log2(character set size)
What password entropy does and does not mean
Entropy gives a rough mathematical estimate of the size of the search space if characters are chosen unpredictably. It does not automatically describe how humans actually choose passwords.
That makes it useful as a comparison tool, but not as the whole security story.
Common mistakes
- Treating an entropy estimate as a guarantee of real-world resistance.
- Ignoring reuse, dictionary patterns, or predictable substitutions.
- Comparing entropy values without checking the assumed character set.
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