Cryptography Trivia
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100 free Cryptography trivia questions with answers — history quiz, new questions added Oct 2026.
Secret writing is older than most empires. Spartan generals, Roman commanders, Renaissance diplomats and Tudor spymasters all trusted ciphers with their lives, and the people who broke those ciphers changed wars and decided the fate of monarchs. This quiz follows the story from the ancient world to the Second World War's machine ciphers and the codebreakers of Bletchley Park, then on to code talkers, unsolved manuscripts and sculptures, and the 1970s milestones that gave us public-key cryptography. Every question names its subject and explains the answer, so it works for a family quiz night, a history classroom or a puzzle fan who wants to check how much of the Enigma story they really know.
30 of 100 questions with answers and explanations. Play the quiz
Q 01Which Roman general guarded military messages by shifting each letter three places, so A became D?
Julius Caesar
Julius Caesar's shift is easy to undo, and its 13-place cousin ROT13 was later used on Usenet to hide joke punchlines and spoilers.
Q 02The word cryptography pairs an ancient root for 'writing' with one meaning what?
Hidden
Hidden is the sense of kryptos, the root that opens the word, so cryptography literally means hidden writing; the CIA's Kryptos sculpture borrows the same root.
Q 03Which scholar announced in Paris in 1822 that he could read the Egyptian scripts on the Rosetta Stone?
Jean-François Champollion
Jean-François Champollion showed that hieroglyphs spelled sounds as well as pictures, a trick the stone's Demotic text had already revealed for foreign names in 1802.
Q 04Which German engineer's firm patented the rotor cipher machine in 1918 that went on sale as Enigma?
Arthur Scherbius
Arthur Scherbius co-founded Scherbius & Ritter, which patented the design in 1918 and began selling the finished machine under the Enigma name in 1923.
Q 05When Enigma went on sale in 1923, which buyers was the machine first aimed at?
Commercial firms
Commercial firms were the first target: the machine was pitched to businesses wanting to shield telegrams from rivals, and only later did the German armed forces adopt and modify it.
Q 06Because of its reflector, an Enigma machine could never encrypt a letter as what?
Itself
Itself was the one output Enigma could never give a pressed key, a patented side-effect of the reflector that Allied codebreakers learned to exploit.
Q 07Bletchley Park, bought by MI6's chief with his own money in 1938, lies in which English county?
Buckinghamshire
Buckinghamshire's Bletchley, now inside Milton Keynes, got the codebreakers because Admiral Hugh Sinclair paid £6,000 of his own money when the government said it had no budget.
Q 08Churchill called Bletchley Park's staff 'the geese that laid the golden eggs' and never did what?
Cackled
Cackled is the word: the codebreakers kept quiet for decades, and many families never learned that a parent had done secret war work.
Q 09Eight soldiers of which tribe used their language on Army phones in the 1918 Meuse-Argonne fighting?
Choctaw
Choctaw men of the 36th Infantry Division were among the first code talkers, a generation before the Marines recruited Navajo speakers for the Pacific.
Q 10Which Los Angeles city civil engineer proposed the Navajo language to the Marines in World War II?
Philip Johnston
Philip Johnston pitched the idea at the start of the war, and the first 29 Navajo recruits began boot camp in May 1942.
Q 11In the Zimmermann Telegram of January 1917, Germany proposed a wartime alliance with which country?
Mexico
Mexico was offered German help to recover Texas, Arizona and New Mexico, and the telegram's publication helped push the United States into the war in April 1917.
Q 12Which Admiralty codebreaking section, named for its office, decoded the Zimmermann Telegram?
Room 40
Room 40's Nigel de Grey had partly decoded the message by the next day, in what is called Britain's greatest intelligence triumph of the First World War.
Q 13Deciphered letters from the 1586 Babington Plot led to whose execution in 1587?
Mary, Queen of Scots
Mary, Queen of Scots replied in cipher on 17 July 1586 endorsing the killing of Elizabeth I, and that decoded reply became the evidence that sent her to the block.
Q 21The only solved Beale cipher, describing treasure buried in Virginia, used which document as its key?
Declaration of Independence
Declaration of Independence word numbers unlock the second of three ciphertexts from a pamphlet sold in the 1880s; the two naming the spot and the owners remain unsolved.
Q 22Because it is the most common letter in English, which letter is a single dot in Morse code?
E
E got the shortest code because Alfred Vail sized each symbol to letter frequency, which he estimated by counting the type in a Morristown printer's cases.
Q 23Which 1906 international distress call was picked as a simple Morse rhythm, not as an abbreviation?
SOS
Q 14The Vigenère cipher, once called 'indecipherable', was first described in 1553 by which Italian?
Giovan Battista Bellaso
Giovan Battista Bellaso laid out the key-word system in his 1553 book, but 19th-century writers pinned it on the French diplomat Blaise de Vigenère, and the wrong name stuck.
Q 15Which Prussian infantry officer published the first general attack on the Vigenère cipher in 1863?
Friedrich Kasiski
Friedrich Kasiski's 95-page book of 1863 ended three centuries of the cipher's 'unbreakable' reputation, though Charles Babbage had quietly broken a version around 1854 without publishing.
Q 16Atbash reverses an alphabet end to end; its name comes from four letters of which alphabet?
Hebrew
Hebrew's Aleph, Taw, Bet and Shin spell the name, and the Book of Jeremiah uses the trick to disguise Babylon as 'Sheshach'.
Q 17Spartan commanders read a scytale message by winding its strip of parchment around what?
A rod
A rod of exactly the same diameter as the sender's lines the letters up again; Plutarch gave the earliest surviving description of the device.
Q 18Which 9th-century Baghdad scholar first described breaking ciphers by counting letter frequencies?
Al-Kindi
Al-Kindi's Manuscript on Deciphering Cryptographic Messages introduced frequency analysis, building on the work of al-Khalil, and counts as the birth of cryptanalysis.
Q 19Which Renaissance architect's 1467 cipher disk was one of the first polyalphabetic ciphers?
Leon Battista Alberti
Leon Battista Alberti's device, two concentric disks on a pin that could be turned mid-message, changed the substitution alphabet as it went.
Q 20In 1952 architect Michael Ventris showed that Linear B tablets held an early form of which language?
Greek
Greek in its Mycenaean form is what the tablets hold, centuries older than Homer; Ventris died in a car crash in 1956, weeks before his book on the script appeared.
SOS never stood for 'save our souls'; German maritime rules adopted it in 1905, the 1906 convention made it worldwide, and it stayed the radio distress signal until 1999.
Q 24Which AT&T engineer invented the 1917 teleprinter cipher that became the unbreakable one-time pad?
Gilbert Vernam
Gilbert Vernam's patent was granted in 1919, but Army captain Joseph Mauborgne added the rule that made it unbreakable: a truly random key used only once.
Q 25Diffie and Hellman published public-key cryptography in 1976; which British agency had secretly found the idea first?
GCHQ
GCHQ's James Ellis proposed 'non-secret encryption' in 1970, but the agency kept the work classified until 1997.
Q 26Which MIT mathematician kept finding flaws in Rivest and Shamir's proposals until one held in 1977?
Leonard Adleman
Leonard Adleman could not break the scheme Rivest wrote up after a sleepless Passover night, and it became RSA, named for all three.
Q 27Which Secretary of State shut down the Cipher Bureau in 1929, reputedly calling codebreaking ungentlemanly?
Henry Stimson
Henry Stimson is quoted as saying 'Gentlemen do not read each other's mail', and he was reportedly most offended by Herbert Yardley's boast that he could read the Vatican's traffic.
Q 28In 'The Adventure of the Dancing Men', a stick figure holding what marks the end of a word?
A flag
A flag in a figure's hand ends a word, a rule Sherlock Holmes spots in the 1903 story after Norfolk squire Hilton Cubitt brings him the scrawled messages.
Q 29In whose 1843 story 'The Gold-Bug' does William Legrand decode a cipher to find buried treasure?
Edgar Allan Poe
Edgar Allan Poe won the Philadelphia Dollar Newspaper's $100 prize with the story, probably the largest single sum he ever earned for a piece of writing.
Q 30Which French officer cracked Louis XIV's Great Cipher around 1893 by spotting it encoded syllables?
Étienne Bazeries
Étienne Bazeries took three years over the task, reading messages the Rossignol family had enciphered for the Sun King two centuries earlier.