History of cryptography

Four thousand years of hiding, scrambling and breaking messages, from a scribe's odd hieroglyphs to the post-quantum algorithms now in every web browser.

The rest of this site describes the algorithms that run today. This section tells how we got them. The story has a clear shape. For most of history cryptography was a craft: clever tricks, kept secret, used by kings, generals and lovers, and broken by patient people with pen and paper. Then came machines, then a war fought partly by codebreakers, then a theory that turned the craft into mathematics. In 1976 two researchers showed that strangers could agree on a secret key in public, and that idea is what made online shopping, messaging and software updates safe. The newest chapter is about quantum computers and the algorithms built to survive them.

Two threads run through every page. Each new cipher was trusted until someone found a way to break it, so the breakers drive the story as much as the makers. And the weak point was rarely the mathematics. It was a reused key, a careless clerk, a predictable message or a leaky chip.

Timeline

The turning points, in date order, with the part of the world each one belongs to and a link to the page that tells the story.

Year	Region	Event	Why it mattered
c. 1900 BC	Africa	A scribe uses unusual hieroglyphs in the tomb of Khnumhotep II in Egypt	The oldest known deliberate change to a script
1600s–1200s BC	Middle East	A Babylonian glaze or glass recipe is written in rare sign values	The oldest writing known to guard a secret, a trade one
600s BC on (disputed)	Europe	Spartans wind messages round a rod, the skytale	Transposition: the letters stay, their order changes
600s–500s BC or later	Middle East	The Book of Jeremiah hides names with Atbash, swapping the alphabet end to end	Substitution: each letter stands for another
c. 499 BC	Middle East	Histiaeus, at the Persian court, sends a message tattooed on a slave's scalp	Steganography: hiding that a message exists at all
400s–200s BC	China	Chinese military texts describe secret tallies and three-part letters	Codes, and a secret split so no single messenger can read it
350s BC	Europe	Aeneas Tacticus writes a chapter on sending secret messages in a siege	The first known writer to collect methods on purpose
100s BC	Europe	Polybius describes a 5 × 5 grid for torch signals	Letters as pairs of numbers, an idea reused for 2,000 years
50s BC	Europe	Julius Caesar shifts each letter three places	The best-known substitution cipher, with only a couple of dozen keys
AD 224–651 (reported later)	Middle East	Sasanian kings are said to write secret letters in a script of their own	Known only from later Arabic writers, and vaguely
c. AD 300 (date uncertain)	India	The Kama Sutra lists secret writing among the 64 arts	Ciphers for private letters, not only for kings and generals
300s–700s	Africa	Coptic and Greek scribes in Egypt use letter swaps and number codes	A cipher alphabet written out on a potsherd at Djeme
700s	Middle East	Al-Khalil, in Basra, writes the first known Arabic book on cryptograms (now lost)	The start of a written tradition of codebreaking
c. 780	Europe	The nun Hygeburg hides her name in a vowel cipher	Monks' and nuns' letter games: most of what survives from early medieval Europe
800s	Middle East	Al-Kindi, in Baghdad, writes the first known account of frequency analysis	The first general method for breaking substitution ciphers
800s	Europe	Sweden's Rök runestone is carved, partly in cipher runes	Ciphers far from any royal office, cut in stone
1040–1044	China	The Song military encyclopedia Wujing Zongyao describes a code built on a poem (details from a weaker source)	Agreed signs for fixed messages, as with the older tallies
1150s	Europe	Hildegard of Bingen invents her unknown letters	A private alphabet: a substitution under new shapes
1200s	Middle East	Ibn 'Adlan asks how long a message must be for letter counts to work	How much ciphertext an attack needs, still a central question
1300s	Middle East	Ibn ad-Durayhim, in Damascus, works through a real solution	Homophones: several substitutes for one letter
1379	Europe	Gabriele de Lavinde puts together cipher keys for the Avignon pope	The oldest surviving European set of cipher keys
c. 1390	Europe	The Book of Ballymote copies the Irish Ogam Tract, with some 100 secret forms of ogham	Secret writing as part of a poet's learning
1412	Africa	Al-Qalqashandi's encyclopedia, written in Cairo, sums up three centuries of Arab cryptology	The most complete treatment of ciphers and codebreaking of its time
1400s–1532	Americas	The Inca state keeps its records on knotted cords, khipu	Not a cipher, but still not fully read
c. 1467	Europe	Leon Battista Alberti describes his cipher disk	The first polyalphabetic cipher in Europe
1474	Europe	Cicco Simonetta, in Milan, writes rules for solving ciphers without the key	Europe's first written codebreaking
1500s (attributed)	Japan	Uesugi Kenshin is said to use an iroha cipher square	Polybius's idea with kana, if it was used at all
1518	Europe	Trithemius's Polygraphia is printed, with the tabula recta	The first printed book on cryptography
1553	Europe	Giovan Battista Bellaso publishes the keyword cipher later called "Vigenère"	Called unbreakable for three centuries
1586	Europe	Blaise de Vigenère describes a true autokey cipher	Stronger than the cipher that carries his name
1587	Europe	Mary, Queen of Scots, is executed after her ciphered letters are read	Codebreaking decides the fate of a queen
1590	Europe	François Viète reads Philip II's cipher for Henri IV	A mathematician as codebreaker; Philip blames black magic
1600s	Europe	The Rossignols build Louis XIV's Great Cipher	A code that stayed unread for 200 years
1640s	Europe	John Wallis deciphers royalist letters for Parliament	His job passed to the Willes family, and England kept a Decipherer until 1844
1700s	Europe	Vienna's black chamber opens, copies and reseals the embassies' mail every morning	Reading other states' letters as a daily routine
1744	Russia	A French envoy's intercepted letters are deciphered, and he is expelled	Russia's chancellor reads the mail like the rest of Europe
1778–1783	Americas	Washington's Culper Ring uses a numbered code book and invisible ink	Spying with codes in the American Revolution
1779–1780	Americas	Benedict Arnold plots treason in a book code	Page, line and word: strong only while the book is secret
1790s (date uncertain)	Americas	Thomas Jefferson describes a wheel cypher of 36 disks	Reinvented by Bazeries in 1891; the US Army's M-94 from 1922
1796–1800	Korea	King Jeongjo runs politics through secret letters, sometimes in code	Almost the only Korean record found for this page before modern times
1797	Middle East	Selim III's new embassies begin Ottoman diplomatic ciphers	A late start, through diplomacy
1800s–1900s (described)	Africa	Drums and slit-gongs carry spoken messages for miles	Long stock phrases make tonal messages clear
1854	Europe	Charles Wheatstone invents the Playfair cipher	Encrypting letters in pairs, by hand
1854–1863	Europe	Charles Babbage, then Friedrich Kasiski, break the Vigenère cipher	The "indecipherable cipher" falls
1861–1865	Americas	The US Civil War is fought partly over the telegraph	Union route ciphers hold; Confederate keyword ciphers are read
1869–1879	Japan	The telegraph arrives, then government code charts and a cipher wheel	Japan's first official ciphers
1871–1872	China	The Chinese telegraph code gives each character four digits	Chinese on the wire, and an easy way to add a secret key
1881–1917	Russia	The Okhrana's black chambers read the empire's mail	Mass mail reading by the political police
1883	Europe	Auguste Kerckhoffs publishes La cryptographie militaire	The rule that only the key, not the method, may be secret
1914–1918	Europe	Room 40 in London reads German naval and diplomatic codes	Radio lets the enemy hear every message
1917	Europe	British codebreakers read the Zimmermann telegram	Helps bring the United States into the First World War
1917–1919	Americas	Gilbert Vernam's teleprinter cipher leads to the one-time pad	The only cipher that can be proven unbreakable
1917–1919	Europe	Hebern, Scherbius, Koch and Damm invent rotor machines; Scherbius's becomes Enigma	Cipher machines go commercial
1918	Europe	Georges Painvin breaks Germany's ADFGVX field cipher	A decoded order points to where the next German attack will fall
1918	Americas	Choctaw soldiers become the first code talkers	A language the enemy doesn't know, on the field telephone
1920	Americas	William Friedman's index of coincidence	Statistics find a keyword's length with no guessing
1924	Japan	A Polish officer teaches Japan's army and navy codebreaking	The start of Japan's codebreaking services
1932	Europe	Marian Rejewski reconstructs the wiring of the military Enigma	Mathematics enters codebreaking
1938–1939	Europe	The Poles build the bomba, then share everything with Britain and France	Five weeks before the war, the Allies learn how Enigma can be broken
1938–1940	China	Herbert Yardley works on Japanese army codes in Chongqing	China builds its own codebreaking bureau
1940	Americas	The US Army breaks Japan's Purple machine	"Magic" intelligence through the Pacific war
1940–1944	Europe	Bletchley Park's bombes break Enigma; Colossus attacks the Lorenz cipher	Codebreaking at industrial scale, and the first electronic computers
1942	Americas	US Navy codebreakers read JN-25 before Midway	A code read in time turns a battle
1942	Russia	The Soviet pad office prints key pages twice	The flaw that Venona later found
1942–1945	India	The Wireless Experimental Centre near Delhi works on Japanese army codes	One of Bletchley Park's two overseas outposts
1940s	Americas	SIGABA, and Navajo, Comanche and Meskwaki code talkers	Systems the enemy never read
1943–1980	Americas	The Venona project reads reused Soviet one-time pads	The one-time pad is only as safe as its key handling
1949	Americas	Claude Shannon publishes "Communication Theory of Secrecy Systems"	Cryptography becomes a mathematical science
1952	Americas	The National Security Agency is created	Codebreaking becomes a permanent peacetime industry
c. 1956	Russia	The Soviet Fialka rotor machine enters service across the Warsaw Pact	Rotor machines last into the 1990s
late 1960s–1971	Americas	Horst Feistel at IBM designs the Feistel network and Lucifer	The structure inside DES and many later ciphers
1970	Europe	The CIA and West Germany's BND secretly buy Crypto AG, supplier to more than 120 countries	Rigged machines read the world's diplomatic traffic for decades
1974	Americas	Ralph Merkle's puzzles, in a rejected student project	The first public-key idea in the open
1976–1977	Americas	Diffie–Hellman key exchange, then RSA	Public-key cryptography: strangers agree on secrets in the open
1977	Americas	DES becomes the first public standard cipher	Strong encryption for business, and a fight over key length
1985	Americas	Neal Koblitz and Victor Miller propose elliptic-curve cryptography	The same security as RSA with much shorter keys
late 1980s	Africa	The ANC's Operation Vula sends encrypted messages by laptop, tape and phone	Strong encryption for a liberation movement, and for Mandela in prison
1991–2000	Americas	PGP, the Clipper chip and the US export fights	The crypto wars over who may use strong encryption
1994	Americas	Peter Shor's quantum algorithm for factoring	A future quantum computer would break RSA and elliptic curves
1995	Worldwide	SSL ships in Netscape Navigator; in Finland, Tatu Ylönen writes SSH	Encryption for everyone's network traffic
1996–1999	Americas	Timing and power-analysis attacks	Hardware leaks keys even when the math is sound
1997	Europe	GCHQ reveals that its staff found public-key methods in 1970–1974	The same ideas, discovered first in secret
1998	Americas	The EFF's Deep Crack finds a DES key in 56 hours	Proof that 56-bit keys were too short
2000	Japan	NTT and Mitsubishi Electric publish the Camellia cipher	A national cipher with the same shape as AES
2001	Worldwide	AES, designed in Belgium, is published as a US standard, FIPS 197	A cipher chosen in an open, worldwide competition
2003–2004	Korea	The ARIA cipher becomes a Korean standard	Korea's own block cipher, used in government services
2004–2017	Worldwide	MD5, then SHA-1, collisions, starting with Wang Xiaoyun's team in China	Hash functions break in practice
2006–2012	China	SMS4 is published, later renamed SM4; with SM2 and SM3 it forms China's national suite	China's own standard algorithms
2008–2009	Worldwide	The Bitcoin paper, then the network: cryptography as money	Hashes and signatures keep a public ledger honest with no bank
2012	Worldwide	Keccak is chosen as SHA-3	A second standard hash that works in a completely different way
2013	Americas	The Snowden documents	Mass surveillance, and a random number generator that was almost certainly backdoored
2014	Worldwide	Heartbleed	One bug in OpenSSL exposes much of the web
2015	Russia	GOST R 34.12-2015 adds the Kuznyechik cipher	Russia's own block cipher standard
2015–2016	Worldwide	Let's Encrypt starts issuing free certificates	Encrypted web traffic becomes the default
2016	Worldwide	WhatsApp switches a billion users to the Signal protocol	End-to-end encryption for ordinary messaging
2016–2024	Worldwide	NIST's post-quantum competition, with entries from around the world	ML-KEM, ML-DSA and SLH-DSA become standards in August 2024
2018	Worldwide	TLS 1.3 is published	A faster, cleaner protocol with forward secrecy built in
2020	China	China's Cryptography Law comes into force	Core, common and commercial cryptography in law
2022–2026	Worldwide	Hybrid post-quantum key exchange becomes the default in SSH, browsers and Signal	Recorded traffic stays safe if a quantum computer arrives
2025	Korea	Korea's own competition, KpqC, picks four post-quantum algorithms	Post-quantum standards beyond NIST
2025	China	China opens a worldwide call for new national algorithms, post-quantum ones among them	Post-quantum standards beyond NIST
2026	Americas	NIST IR 8547 sets 2030 and 2035 as the end dates for RSA and elliptic curves	The old public-key algorithms get a retirement date

The table picks out turning points; each page opens with a fuller table of its own. Some parts of the world have far fewer rows than others, and mostly that is about what survives and what has been studied, not about what people did. The thinnest stretches are early medieval Europe, Byzantium, Persia before Islam, Mughal India, Korea before modern times, Southeast Asia and Ethiopia, where the research for these pages found little or nothing in reliable sources that describes actual ciphers. Where a page says a record is thin, that is the reason.

How to read this section

The pages run in time order, and each one stands on its own:

1. The ancient world: Egyptian and Babylonian scribes, the Spartan skytale, Polybius, Caesar, Atbash, hidden messages, China's tallies, India's Kama Sutra, the Sasanian kings' script, Coptic ciphers
2. Arab cryptanalysis: al-Kindi and frequency analysis, the scholars of Basra, Baghdad, Damascus and Cairo who built on it, and the gap where Byzantium should be
3. The Renaissance: medieval monks' ciphers, cipher runes and secret ogham, cipher disks, the "Vigenère" cipher, nomenclators, Mary Queen of Scots, Inca khipu, Japan and Korea, the black chambers from Paris to Saint Petersburg, the Ottomans, the American Revolution
4. The telegraph age: Vigenère broken, Playfair, Africa's talking drums, the Chinese and Japanese telegraph codes, the Okhrana, Kerckhoffs, Room 40 and the Zimmermann telegram, the Choctaw code talkers, the one-time pad
5. Machines and World War II: rotor machines, Enigma, Poland and Bletchley Park, Colossus, China's black chamber, Purple, Japan's codebreakers, Delhi, the code talkers, Venona
6. From Shannon to DES: Shannon's theory, NSA and GCHQ, Crypto AG, Fialka, Feistel and Lucifer, DES and its key
7. Public-key cryptography: Merkle, Diffie–Hellman, RSA, GCHQ's secret, elliptic curves, PGP, Clipper and the crypto wars, the ANC's Operation Vula
8. The internet era: SSL to TLS 1.3, SSH, the AES competition, broken hashes, famous bugs, Snowden and Dual_EC, Let's Encrypt, Signal and end-to-end messaging
9. Hardware and engineering: HSMs, smart cards, TPMs and secure enclaves, AES instructions, side channels, cracking machines, security keys, quantum key distribution
10. Quantum and post-quantum: Shor and Grover, the machines, the NIST competition, ML-KEM, ML-DSA, SLH-DSA, FN-DSA and HQC, Korea's and China's own processes, hybrid rollouts, deadlines, and what is still open

Each page opens with a short summary and an at-a-glance table, then tells the story in sections you can skip between. Where an idea from history lives on in a modern algorithm, the text links to that algorithm's page.

The Python examples use only the standard library and print their results, so you can paste them into python3 and see the same output shown under each one. They are toys for understanding the idea, never for protecting anything.

Sources. History of secret work is full of myths, and some famous stories are told with more confidence than the evidence allows. The pages lean on primary sources (the ancient texts, the original papers, NIST documents, declassified agency histories) and serious historians, above all David Kahn's The Codebreakers. Where a story is disputed, the text says so. Each page's references end with a line marked Weaker sources, listing anything that rests on news reports, blogs, encyclopedia articles or search summaries, so you can judge it for yourself.