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For Students · Shannon Entropy

Shannon Entropy for a Vigenère cipher

Built for students learning it for a class or exam. See the concept move instead of memorizing formulas — and check your homework intuition. Simulate a Vigenère cipher live below — adjust the inputs and watch it respond, right in your browser.

Shannon Entropy & PasswordsLive

measuring information & strength

Entropy

60bits

brute-force time: 1 yr

Controls

Password / string

Shannon entropy measures information in bits — how many yes/no questions it takes to pin down a value. For a password it is length times the log₂ of the character-set size, quantifying how unpredictable it is. Each extra bit doubles the guessing effort, so length beats complexity: a long passphrase can carry more entropy than a short scramble of symbols.

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Data Inspector

Character pool62

Entropy59.5 bits

Strengthreasonable

Crack time1 yr

Governing equation

H = - i \sum p_{i} lo g_{2} p_{i} = lo g_{2} 62 = 5.95 bits/char \Rightarrow 10 \times 5.95 = 59.5 bits

Reading this result: 60 bits is reasonable for low-value logins but short of the ~60-bit bar; each added character here is worth 6.0 more bits.

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More with Shannon Entropy

Shannon Entropy for an RSA key Shannon Entropy for a password hash Shannon Entropy for a digital signature Shannon Entropy for a Diffie-Hellman exchange Shannon Entropy for a block cipher Shannon Entropy for a hash collision Shannon Entropy for a one-time pad Shannon Entropy for a Caesar cipher

Frequently asked questions

Is this good for students?: Yes — this version of "Shannon Entropy for a Vigenère cipher" is framed for students learning it for a class or exam. See the concept move instead of memorizing formulas — and check your homework intuition.
Do I need to install anything?: No. It runs in any modern browser, free, with no account required.