Automated Vigenère cipher decoder

This online calculator provides aid in finding Vigenère cipher key if you can guess part of the encrypted text. It just automates some routine calculations, which you would perform manually otherwise.

Disclaimer: this online calculator does not break Vigenère cipher for you automatically. The one of the definitions of the word automated is "made to operate by machines or computers in order to reduce the work done by humans". Compare it with the definition of automatic, which is "able to operate independently of human control". According to the definition, this online calculator helps you to break the cipher by reducing your manual work. For a fully automatic solution, go to Vigenère cipher breaker. Why this one exists? Read on.

Once seemed unbreakable, Vigenère cipher nowadays is considered to be weak, with several techniques to break it. Now you can meet Vigenère cipher mostly in quests and puzzles. The problem is that fully automatic breakers work the better the more encrypted text you have, but in case of puzzles you have a pretty small amount of text. However, puzzle authors are usually generous enough to leave spaces, not to mention punctuation marks in encrypted text. This allows you to guess some encrypted words.

Take, for example, the encrypted text "gdhh://h.saytb.qgl/mxD7EvC.hmq". We can tell for sure that this is an URL. Hence the "gdhh" is highly likely the "http", and the "qgl" is probably "com". From these, we can recover a part of the key. Next we need to guess the length of the key, and try to apply it to the remaining text. Of course, if our guessed text is in the middle of string, we also need to think about at which position our part of the key starts inside the whole key. However, this work can be automated. And this is how automated decoder works.

  1. Start by copying encrypted text into Encrypted text field
  2. Copy the encrypted text into Guessed text field
  3. Alter parts of the encoded text in Guessed text field, if you think you have guessed encrypted words
  4. The calculator deduce the candidate keys based on your guessed text and applies them to the encrypted text. The most probably keys will be on the top.
  5. You look at the results and make sense of them, guessing other parts of the text if needed

Click below to see how it looks like for the "gdhh://h.saytb.qgl/mxD7EvC.hmq" text when we guessed only "http".

Replace gdhh with http

Click below to see how it looks like for the "gdhh://h.saytb.qgl/mxD7EvC.hmq" text when we guessed only "com".

Replace qgl with com

PLANETCALC, Automated Vigenère cipher decoder

Automated Vigenère cipher decoder

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