Book Cipher Decoder & Encoder

1. Paste the key text exactly as the sender used it. Line breaks only matter for line-based references.
2. Paste the numbers. The tool reads whether each group has one, two or three numbers and offers to switch to that style.
3. Pick what each reference gives: one letter (most ciphers) or the whole word (messages built from words). Then read the lookup table: any number that runs past the end of the text, or lands on an unexpected word, shows up there.

Words are counted as printed by default. If the result is garbled after a certain point, switch to split hyphens: one word counted differently shifts every number after it.

For page.line.word references, paste the one page the message uses and drop the page number. Benedict Arnold's book cipher used Blackstone's Commentaries on the Laws of England as its key text (Wikipedia: Book cipher).

The second of the three Beale ciphers, printed in The Beale Papers (1885), is 762 numbers keyed to the Declaration of Independence (763 once one misprinted 108 is read as 10, 8). Each number is a word position; the word's first letter is the plaintext. The first seven:

That spells “I have de…”, the start of “I have deposited in the county of Bedford…”. Decode all 762 numbers in the tool. The other two Beale ciphers have never been solved (background; the pamphlet is on Wikisource).

We ran the tool's decoder over Beale No. 2 (with the pamphlet's six misprinted numbers corrected) against four versions of the same key, and counted letters that match the known plaintext (763 letters):

Counting “self-evident” as one word instead of two drops the score from 630 to 371 correct letters, because every later word number lands one word too far along. Using the standard text instead of Beale's printing, which differs in five places, costs another 120. The last 13 errors all come from two word numbers Beale always read as “y” and “x”. Right book, wrong edition or counting rule: parts of the message turn to nonsense. Try the standard text yourself.

Method: key from Project Gutenberg eBook #1, which already reads “unalienable” and “mean time” (two words) as Beale did; Beale's word differences and misprints as documented in the Wikipedia article above; numbers transcribed from page 20 of the pamphlet. The test suite re-runs this table on every build.

Switch to Encode, paste the key text, and type the message. For each letter the tool finds a matching position and rotates through different matches, so repeated letters do not repeat the same number. A space becomes /; anything missing from the key is kept as a quoted literal.

Example with the key “the old lighthouse / kept every sailor home” in line.word.letter style: HELLO → 1.1.2 1.1.3 1.2.2 1.3.1 1.2.1. The two L's get different references. Change one word of the key and decoding breaks, so both sides must keep identical copies.