Crash Keys Decoder

Decode Crash Keys ARG ciphertext using a nine-step transposition and an optional plaintext-autokey Vigenère layer. All processing happens locally in your browser.

Important: Paste the complete ciphertext, including title and subtitle. Decoding an excerpt will produce gibberish because the permutation depends on the total letter count. For Santa Claus select “Transposition only”. The original spacing, punctuation and line breaks are preserved. The transposition requires the number of A–Z letters to be coprime with 9; otherwise this method cannot decode it. A successful calculation does not guarantee meaningful plaintext or prove a key is correct.

How this decoder works — and why

The Crash Keys messages in the included examples are not encrypted by simply replacing each letter with another letter. Instead, the decoder reverses a rearrangement of all letters and, for some messages, a second Vigenère plaintext-autokey cipher. Both steps are performed locally in your browser.

Always paste the entire encrypted block. Include the heading, subtitle, and every line of the message — not just the sentence you want to read. The algorithm treats all A–Z letters in that block as one continuous sequence. Its rearrangement depends on the total number of letters and their positions. Removing even a title, or changing a single letter, changes the sequence and generally produces nonsense. Decode the whole block first; then read whichever part interests you.

Step 1: Collect the letters

The decoder takes every English letter (A–Z) from the complete block, in order, and temporarily ignores spaces, punctuation, apostrophes, and line breaks. These non-letter characters are saved so they can be put back at the end. Spaces and punctuation do not count toward the permutation, but letters in headings and subtitles absolutely do.

Step 2: Undo the nine-step transposition

Let N be the total number of letters. The decoder reads the collected letters in this order: position (9 × i + 8) mod N, for i = 0, 1, 2, ... N−1. Positions start at zero, so it begins with the ninth letter, then advances by nine, wrapping around the block when necessary. This reverses the scrambling used in the provided examples.

Because the step is nine, N must have no common divisor with nine other than one. Otherwise this particular walk repeats positions instead of visiting them all, and the decoder reports an error.

Step 3: Optionally remove the autokey cipher

For the homepage and Sixth Month examples, the rearranged letters still have another encryption layer. The decoder starts with the key THEMANONTHEMOONRULESTHEINFINITETIME. Each key letter supplies a shift from A = 0 to Z = 25. The decoder subtracts that shift from the corresponding ciphertext letter (wrapping around the alphabet) to recover a plaintext letter.

The unusual part is plaintext-autokey: after the initial key runs out, each newly recovered plaintext letter is appended to the key stream and used to decode later letters. This makes it different from a standard Vigenère cipher with a short, repeating password. The Santa Claus example does not use this extra layer, so choose Transposition only for that block.

Step 4: Put the formatting back

Finally, the decoded letters are placed into the original text's letter positions. Spaces, punctuation, and line breaks are kept as entered. This is why the output looks like the original block but with different letters — and why preserving a block's complete letter sequence is essential.

Which mode should I choose?

  1. Transposition + plaintext-autokey: the known homepage and Sixth Month messages.
  2. Transposition only: the known Santa Claus message (use “Load Santa Claus example” to see it work).
  3. Unknown message: try both modes with the complete block. Readable English is evidence of a match; garbled output can mean the wrong mode, wrong key, missing or mistyped letters, or a different cipher entirely.

Important distinction: this is a working reconstruction based on the known encrypted messages and their recovered plaintext. It does not by itself establish that the ARG creators intended this exact encryption procedure.