What the game is
Encrypted Alibis is a cryptogram mystery. Something valuable vanished from an evening gathering — a chess piece from a manor, a compass from a museum, a tiara from a theatre — and every guest present gave a short written statement. Before filing, the bureau's night clerk enciphered the lot with one key. Your case file holds the encrypted statements, a handful of verified notes from the staff, a map of the rooms and passages, and the promise that matters: exactly one sentence in one statement is false.
The case runs in two acts. First the codebreaking: every statement shares the same key, so a letter cracked on one card fills in on every card at once, and the statements gradually surface like a photograph developing. Then the detection: chart the decoded claims on the evidence timeline, read each alibi against the verified notes and the map's travel rules, and find the sentence that cannot be true. The warrant names the guest and the sentence — both must be right.
Case procedure
- Enter the supplied letters' neighbours first. The brass letters are verified. Read every word they touch and try to finish the common short words — THE, AT, IN, TO, I — before anything clever.
- Work the structure of words. A one-letter word is I or A. A doubled letter is usually LL, SS, EE or OO. A three-letter word ending in a known E is very often THE.
- Chase repeated words between statements. Room names, times of the evening and guests' names recur; crack one and the letters spread to every card.
- Count letters when stuck. The commonest letters in English testimony run E, T, A, O, N. At Chief Cryptanalyst rank the most frequent letter is deliberately not supplied — find it by counting.
- Chart as you decode. Every finished sentence goes on the timeline: a room initial for who was where at which marked moment, and where each object stood.
- Read alibis against the case file. Verified notes are settled truth. Between one marked moment and the next a guest stays put or crosses exactly one passage, and a bolted passage is closed from the time on its notice.
- Accuse with the sentence in hand. When one line conflicts with the trusted evidence, the warrant asks for the guest and that sentence together.
The rulings that matter most
- One key for everything. Every statement in a case uses the same cipher key. A letter cracked anywhere is cracked everywhere.
- The cipher law. One cipher letter always stands for the same true letter, one to one — and never for itself. Key guesses that break the law turn red the moment they appear; that is a reading of your own key against the published rule, never a peek at the answer.
- Exactly one sentence is false. Every other sentence in every statement — including the rest of the culprit's — is entirely true.
- Verified notes are settled truth. The staff's sworn notes were checked by the bureau before the statements were taken. They are never wrong.
- The travel law. Rooms connect only by the listed passages. Between two neighbouring marked moments a guest stays put or crosses exactly one passage — so rooms three passages apart cannot be one moment apart in an honest account.
- Lock notices close passages. A bolted passage cannot be used at or after the time on its notice. An account that walks through one is lying.
- Claims speak to marked moments. “At nine” means the nine o'clock moment exactly; “from nine until ten” includes both ends. Every statement line carries its exact ruling behind a tap.
- Proof never leans on testimony. The false sentence always conflicts with the verified notes, the map, or the statement's own words — never with something another guest merely said.
Choosing a rank
Code Clerk (four suspects, four marked moments, a Caesar shift with six supplied pairs) teaches both acts in about ten minutes — spot the slide, read the evening, make the arrest. Inspector (five suspects, five moments, one scrambled substitution alphabet) brings object sightings, a bolted passage and honest codebreaking. Chief Cryptanalyst (six suspects, six moments, longer statements, two lock notices and as few as two supplied letters) is the full desk: frequency analysis to open the key, and a busier evening to chart before the contradiction shows itself. Higher ranks add more codebreaking and more cross-referencing, never unfair steps.
Fairness, hints and reveal
Every case is generated and then proved before you see it, twice over. The cipher side: the generator confirms that the supplied letters plus the statements admit exactly one consistent reading — an ambiguous corpus is rejected and rebuilt, and if the first supplied letters are not enough, more are supplied before the case ships. The detective side: the bureau's checker confirms that exactly one alibi conflicts with the trusted evidence, that it belongs to the thief, that the conflict points at exactly one sentence, and that removing either the sentence or the evidence it fights would leave a consistent account — so the proof is never mushy and never optional. Check flags wrong key guesses without confirming right ones, and never reads your timeline. Hints escalate politely and follow your work: codebreaking lessons while the key has gaps (a second press settles a letter — the only mark a hint ever makes), then the comparison worth making once the statements read. Reveal unseals the clerk's key, walks the case step by step, and excludes it from your cases-cracked tally. Wrong accusations are stamped on the file; the case stays open — and naming the right guest with the wrong sentence is stamped too, because the bureau acts on proof.
Printing a case
Any case can be downloaded as a PDF pack built entirely in your browser from the same case number as the on-screen case: the briefing, verified notes, map and guest list on the case sheet; every encrypted statement set in typewriter capitals with a ruled write-over line beneath each line of cipher; a key worksheet with the supplied letters already entered; a blank evidence timeline for pencil work; and an optional answer key holding the full key, every statement in clear with the false sentence marked, the case walkthrough and the warrant. Cryptograms are a natural fit for paper — nothing is uploaded anywhere, and the dialog shows the sheet count before you download.
Questions from the cipher desk
What is Encrypted Alibis?
Encrypted Alibis is a cryptogram mystery. Something valuable vanished during an evening gathering, every guest gave a short written statement, and the bureau’s night clerk enciphered the lot before filing. All the statements share one cipher key, so every letter you crack spreads across every card at once. Decoded, the statements chart the whole evening — and exactly one sentence in one statement cannot possibly be true. Finding that sentence, and proving it against the case file, closes the case.
How does the cipher work?
Every statement is enciphered with the same substitution key: one cipher letter always stands for the same true letter, one to one, and no letter ever stands for itself. At Code Clerk rank the key is a Caesar shift — the whole alphabet slides by one secret number, and six letter pairs come supplied, so lining one pair up against the alphabet reveals the slide and the entire key. At Inspector and Chief Cryptanalyst ranks the key is a scrambled substitution alphabet, with fewer letters supplied the higher you climb.
Is every case guaranteed decodable?
Yes. Before a case ships, the generator proves that the supplied letters plus the statements themselves admit exactly one consistent reading — if a corpus could be decoded two different ways, it is thrown away and rebuilt. If the letters supplied at first are not enough to pin the reading down, the bureau supplies more before you ever see the case. Check is always safe as a recovery lane, and a second press of Hint will settle a letter outright.
What makes an alibi false?
The false sentence always conflicts with evidence you can point to: it claims a journey the map’s passages cannot allow in the time between two marked moments, it contradicts a verified sighting from the case file, it places an object in one room while a verified note places it in another at the same moment, or it walks through a passage the lock notices say was bolted. The proof never depends on trusting another guest’s statement — verified notes, the map and the statement’s own words are enough.
Do I have to trust the other statements?
You never need to. Every innocent guest’s statement is entirely true, and testimony is useful for charting the evening — but the accusation is proved against trusted evidence only: the bureau’s verified notes, the map’s passages and lock notices, and the suspect’s own words. If two statements seem to disagree, that can point you somewhere interesting, but the warrant always rests on the case file.
What do Check, Hint and Reveal do?
Check flags any key guess that cannot be right, without filling in a single letter — and it never reads your timeline, which is your private worksheet. Hints come in two strengths and follow your work: while the key has gaps, the first press teaches a codebreaking move (a one-letter word, a doubled letter, a word repeated across statements, a frequency count) and a second press settles that letter; once the key is complete, the first press names the comparison worth making and the second states exactly what it proves. Reveal unseals the clerk’s own key and walks the whole case, and a revealed case never joins your cases-cracked tally.
What are the case ranks?
Code Clerk is four suspects, four marked moments and a Caesar shift with six supplied pairs — a whole case in about ten minutes, and the place to learn the desk. Inspector is five suspects and five moments under one scrambled substitution alphabet, with object sightings and a bolted passage joining the case file. Chief Cryptanalyst is six suspects, six moments, longer statements, two lock notices and as few as two supplied letters — the most frequent letter is deliberately left for you to find by frequency analysis.
What is the evidence timeline for?
The timeline is a worksheet: one row per guest (and per traceable object), one column per marked moment of the evening. As statements decode, stamp a room initial wherever a sentence or a verified note places someone. It is deliberately manual — the interface never extracts a claim for you, because reading testimony closely is the detective work. A square holding two different room stamps is a disagreement between papers, and one of those papers is lying.
Can I play on a phone?
Yes. Tap any letter — on the key board or inside a statement — and choose the true letter from the strip beneath; the guess fills everywhere that cipher letter appears, across every statement at once. The statements and timeline scroll inside their own panels at phone widths, every control is a proper button, and your key, timeline and dossier marks save automatically between visits. Each case has a case number, so the same evening can be reopened anywhere.
Can I print a case?
Yes. Any case can be downloaded as a PDF pack built entirely in your browser from the same case number as the on-screen case: the briefing, verified notes, map and dossiers on the case sheet, every encrypted statement set in typewriter capitals with a ruled write-over line beneath each line of cipher, a key worksheet with the supplied letters entered, a blank evidence timeline, and an optional answer key with the full key, the statements in clear and the warrant. Nothing is uploaded anywhere.
Is Encrypted Alibis free?
Yes. All ranks are free to play in your browser with no account or sign-up. Every case is generated fresh — a new evening, new statements, a new key — and proved fair before it reaches the desk, so no two cases read the same.