Every case is locked with a cipher. Learn these ten and you can crack any file in the dossier. Web cases always hand you the key — the book makes you earn it.
A Caesar shift replaces every letter with one a fixed number of places further down the alphabet. The shift is the key; slide back by the same number and the message falls out.
In Dossier 01, it locks Files 01–02 — the warm-up cases.
Atbash flips the alphabet end to end — the first letter swaps with the last, the second with the second-to-last, and so on. There's no number to find: the mirror is the key, and it decodes itself.
In Dossier 01, it locks File 03 — the self-undoing warm-up.
The A1Z26 cipher turns each letter into its position in the alphabet — A is 1, B is 2 … Z is 26. Read the numbers back into letters and the words return.
In Dossier 01, it locks File 04 — the last Tier I warm-up.
A substitution cipher replaces every letter with a different fixed letter, using a scrambled alphabet as the key. No shift to count and no pattern to lean on — you break it by frequency and habit.
In Dossier 01, it locks Files 05–07 — where frequency analysis begins.
A keyword substitution cipher builds the cipher alphabet from a keyword written first, then the remaining letters in order. Same one-for-one swap as a plain substitution, but the scramble comes from a word — lose the word, lose the message.
In Dossier 01, it locks Files 08–09 — a substitution you can memorize.
A Polybius square cipher places the alphabet in a 5×5 grid and replaces each letter with its row-and-column number pair. (I and J share a cell.) The whole message turns into number pairs between 1 and 5.
In Dossier 01, it locks File 10 — letters as 5×5 coordinates.
| 1 | 2 | 3 | 4 | 5 | |
|---|---|---|---|---|---|
| 1 | A | B | C | D | E |
| 2 | F | G | H | I/J | K |
| 3 | L | M | N | O | P |
| 4 | Q | R | S | T | U |
| 5 | V | W | X | Y | Z |
A rail fence cipher writes the message in a zig-zag across several rails, then reads it off rail by rail — the letters keep their identity, only their order changes. The number of rails is the key.
In Dossier 01, it locks Files 11–13 — the first transposition tier.
A columnar transposition cipher writes the message in rows under a keyword, then reads the columns out in the alphabetical order of the keyword's letters. Same idea as the rail fence — only the order moves.
In Dossier 01, it locks Files 14–16 — transposition by keyword.
| R | A | V | E |
|---|---|---|---|
| 3 | 1 | 4 | 2 |
| M | E | E | T |
| A | T | T | E |
| N | X | X | X |
A Vigenère cipher is a Caesar shift that changes with every letter: a keyword repeats over the message and each of its letters sets the shift beneath it. Crack the keyword and the whole text unlocks.
In Dossier 01, it locks Files 17–20 — the Vault tier.
The Babington cipher was a nomenclator — invented symbols for letters plus extra symbols for whole words, names, and meaningless nulls — used in the 1586 plot to free Mary, Queen of Scots. Thomas Phelippes broke it, forged a postscript, and the cipher meant to protect her helped send her to the block.
Featured in Dossier 01 as the historical anchor cipher — not a solve case.
Ten ciphers, four tiers. Practise them free on today's case — in the book you get all 20 cases, no keys given.