CIPHERNAUT
csen
Cipher catalogue
SubstitutionDifficulty: Medium

Vigenère cipher

A Caesar cipher with a password: each letter shifts by a different amount set by the keyword. Much tougher than plain shifting.

Try it

27 characters

Result · Vigenère cipher

Cpktoe ugcdiio qwt dsm evfj

How it works

  1. 1Pick a keyword, say KLIC. Write it under your message and repeat it until every letter is covered (skip spaces).
  2. 2Each letter of the keyword says how far to shift the letter above it: A = 0 places, B = 1, C = 2 ... K = 10.
  3. 3Example: above K sits the letter P. K means a shift of 10, so P becomes Z.
  4. 4To decode, shift backward using the same keyword. Without it, the message is far harder to crack than a Caesar cipher.

Example

Hello world

Rptny hwtvo

Did you know

The cipher was described as early as 1553 by Giovan Battista Bellaso, yet it carries the name of the French diplomat Blaise de Vigenère, who described a different, stronger cipher in 1586. For about three centuries it was regarded as unbreakable and nicknamed le chiffre indéchiffrable (the indecipherable cipher). The Prussian officer Friedrich Kasiski published a way to break it in 1863; Charles Babbage had found one earlier but never published it.

Try to decode

This message is encrypted with Vigenère cipher using the default settings:

BIWI EL ILW DPV BMDA

Hint

The key has three letters: it is the Czech word for a dog. The first letter P means a shift of 15.

Show solution

MEET AT THE OLD MILL

More ciphers in this category