A · Dispatch carbon · Marked 08:10 · Reference CM-17
14 33 18 29 06 41 52 08 27. 19 44 07 25 63.
Filed in the dispatch tray. No signature.
A reader’s mystery from Cipher Museum
The Curator’s
Sealed Letter
A readable message.
A disputed order. Your finding.
A sealed case is about to move. Two instructions disagree about where it should go. Open the file and work out what the records justify. The book’s four optional slips offer another way into the same investigation.
Original modern puzzle · Free · No account required
A second way through the book
The slips appear after chapters 1, 3, 14 and 17 of Secrets of the Cipher Museum. You can also try all four here. They use simplified ideas, not historical ciphertexts. The book’s twenty historical investigations stand on their own.
Work at your own pace. Each slip has a small hint and a separate answer reveal. Nothing depends on page numbers, a purchase or a timer. Your answers are checked in this browser and are not submitted to a server.
The four slips
Follow the marks
Slip 1 · After chapter 1The small key
The first slip has travelled separately from the letter. Its numbers disguise letters, except for two groups that stand for whole words. Someone has helpfully pencilled in an example: 31 24 53 means CAR.
31 08 42 17 24 53 19
08 = O; 17 = P; 19 = E; 24 = A; 31 = C; 42 = M; 53 = R; 65 = TO; 90 = THE.
Use the key to recover the first word. Keep every answer in order; together, the four slips make one instruction.
A nudge
Treat each two-digit group as one entry in the key. The first two groups give CO.
Reveal this slip’s answer
COMPARE. 31, 08, 42, 17, 24, 53 and 19 give C, O, M, P, A, R and E. The unused whole-word groups show how a small code vocabulary can sit beside an alphabet.
A miniature invented nomenclator, prompted by chapter 1. It is not Mary Stuart’s historical cipher.
Slip 2 · After chapter 3The clerk’s route
The second slip contains no disguised letters. The clerk has changed their order. A note on the envelope gives the route: start at the top left, read DOWN to the bottom, then start at the top of the next column to the right.
| T | C | I |
| H | O | E |
| E | P | S |
Read all three columns in that order. Restore the spaces to recover two words.
A nudge
The first column reads T, H, E. Move to the top of the middle column next.
Reveal this slip’s answer
THE COPIES. The columns give THE, COP and IES. Joined and respaced, they read THE COPIES. No letter has changed; its position has.
An invented route puzzle, prompted by chapter 3. It is not a reconstruction of a Union Army message.
Slip 3 · After chapter 14The reused strip
Two slips used the same six secret numbers. Here, letters become numbers (A = 01 through Z = 26). The sender adds one secret number to each letter number. If a sum reaches 100, subtract 100. All the sums in this example stay below 100.
Known letters: L E T T E R
Letter numbers: 12 05 20 20 05 18
First message: 53 22 82 28 40 38
Second message: 43 22 68 23 53 25
The first message is known to say LETTER. Subtract its letter numbers from its sent numbers to recover the secret strip. Subtract that strip from the second message, then turn the results back into letters. For the first position: 53 minus 12 gives the secret number 41; 43 minus 41 gives 02, or B.
A nudge
The recovered strip is 41 17 62 08 35 20. Use it once more on the second message.
Reveal this slip’s answer
BEFORE. Removing the recovered strip gives 02 05 06 15 18 05: BEFORE. Knowing one message helps expose the other because the secret numbers were reused.
A tiny arithmetic illustration prompted by chapter 14, not a VENONA intercept or a secure encryption tool. Actual one-time-pad protection depends on a random secret pad used only once.
Slip 4 · After chapter 17The letters that do nothing
The last slip appears cluttered. Its note is blunt: the lower-case letters are padding. They carry nothing. Keep only the CAPITAL letters, in their existing order. The spaces on the slip were added to mislead.
aYbO cUdT eRfU gShT iTjH kElM
Remove the padding and the false spaces. Restore ordinary word breaks to recover the final three words.
A nudge
The first three capitals are Y, O and U. Keep working from left to right.
Reveal this slip’s answer
YOU TRUST THEM. The capitals spell YOUTRUSTTHEM. The spacing becomes YOU TRUST THEM. The familiar-looking lower-case letters were a distraction.
An invented null-letter puzzle prompted by the change of assumptions in chapter 17. It does not reproduce the Copiale cipher’s symbol system.
At the envelope
What is the instruction?
Show how the four answers fit together
COMPARE / THE COPIES / BEFORE / YOU TRUST THEM.
Enter that instruction above to open the document investigation.
Case file 01 · An original fictional investigation
The room that changed
A sealed loan case is waiting to move. Two copies of its order name different rooms. Can you protect the case without making a bad accusation?
You are the museum’s duty reader. A transfer scheduled for nine is on hold while the paperwork is checked. Ellis, who holds the case keys, has been accused of arranging a theft. The curator needs a finding before the transfer can proceed. Recover the dispatch, compare the records, and decide what the museum should do.
All people, documents and events in this case are invented. The simplified word code is a teaching puzzle. The times and signatures below are information in the records, not independent verification.
1 · Read the message
A dispatch in numbers
The retained dispatch uses a tiny codebook. Each two-digit group stands for a whole word. Use the entries below to read the message. Which room does it name?
The working codebook
- 06 TO
- 07 KEYS
- 08 AT
- 14 MOVE
- 18 SEALED
- 19 KEEP
- 25 WITH
- 27 NINE
- 29 CASE
- 33 THE
- 41 ROOM
- 44 BOTH
- 52 FOUR
- 63 ELLIS
A nudge
Find the code for ROOM. The group immediately after it gives the destination.
More help
41 means ROOM. Look up the next group, 52.
Show the answer and continue
The dispatch names ROOM FOUR. You can still investigate the records if decoding is not your favourite part.
2 · Compare the documents
A readable message is not the end
Here is your reading beside the delivered copy. Keep the supporting records in view. You can establish a difference before you know how it happened.
A · Dispatch carbon · Marked 08:10 · Reference CM-17
The retained copy, decoded
MOVE THE SEALED CASE TO ROOM FOUR AT NINE. KEEP BOTH KEYS WITH ELLIS.
Filed in the dispatch tray. No signature.
B · Delivery copy · Marked 08:25 · Reference CM-17
The delivered copy
MOVE THE SEALED CASE TO ROOM FIVE AT NINE. KEEP BOTH KEYS WITH ELLIS.
Found beside the receiving desk. No signature.
C · Handling log
An opened envelope
08:17 — Envelope received, outer seal intact.
08:20 — Envelope opened for routine inspection. Initial: R.
08:25 — Copy placed at receiving desk.
The log does not identify who wrote either copy.
D · Inventory note · Marked 09:12
A later observation
Sealed case present in room four. Seal appears intact. Contents not checked.
This note was made after the scheduled transfer time. It does not record what happened at nine. There is no accompanying record for room five.
Help me compare
Ignore the document labels for a moment. Read the two instructions word for word. The time and the name at the end agree.
3 · Ask for another source
Which record would help most?
You can request one record from the archive. You want evidence about the authorised destination, not another reason to suspect someone.
A nudge about sources
Which record is connected to this particular instruction and the person who authorised it?
E · Dispatch register · Marked 08:09 · Reference CM-17
The record you requested
Authorised destination: ROOM FOUR.
Scheduled move: 09:00.
Key custodian: Ellis.
Signed: M. Vale, curator.
The register supports the retained copy’s destination. Its signature has not been independently authenticated. It does not identify who prepared the delivered copy.
Case file completed
Your finding reaches the curator.
The curator’s response: “Keep both copies. Keep the transfer on hold until we have checked the register and the chain of custody. Do not treat possession of a key as a verdict against its keeper.”
Your reading established FOUR in the encoded dispatch. Comparison established FIVE in the delivered copy. The register supplied another source supporting FOUR. That is enough to question the disputed order and preserve the evidence. It is not enough to identify an author or a motive.
The later inventory note adds an observation, with a limit: someone recorded an apparently intact seal, but nobody recorded checking the contents. A copying error, an authorised change not reflected in the register, and a deliberate alteration still require investigation.
Your next checks: authenticate the register, locate the dispatch original, identify the writers and handlers of both copies, and inspect the case’s contents. You have resolved what the documents disagree about while keeping the unresolved questions visible.
The curator’s response is the fictional ending to this exercise. It is not a new document you were expected to infer or evidence proving a culprit.
Take the question into the museum
In the Babington exhibit, follow who controls the correspondence channel. At the one-time pad exhibit, distinguish a sound method from the consequences of reusing its secret material. Then ask the same question of each recovery: what does readable text actually establish?
For the physical side of interception, visit Cabinet Noir to explore how postal offices opened, copied and resealed letters.
Read the history behind the investigation →Help shape the next case
Would you open another envelope?
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