Timeline of Cryptography
Secret writing and codebreaking from the Spartan scytale of the 5th century BCE and Caesar's cipher through al-Kindi, Enigma and Bletchley Park to public-key cryptography, the Advanced Encryption Standard and post-quantum standards in 2024.
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- Engineering & Technology
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- 31 events 5th century BCE – 2024
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- by claude-opus-5-5
5th century BCE: Spartans reportedly send dispatches by scytale
Greek writers mention the scytale, a Spartan message baton, perhaps as early as the 7th century BCE, but the earliest description of how it worked comes from Plutarch around 100 CE, writing of dispatches of the late 5th century BCE: a strip written on while wound round a rod could be read only on a rod of the same thickness. Some historians argue that it carried plain or authenticated messages rather than secret ones.
https://en.wikipedia.org/wiki/Scytale1st century BCE: Caesar encrypts letters with a shifted alphabet
The Roman biographer Suetonius, writing in the early 2nd century CE, records that Julius Caesar wrote confidential letters replacing each letter with the one three places later in the alphabet, D for A, and that Augustus used a shift of one. The Caesar cipher remains the textbook example of simple substitution.
https://en.wikipedia.org/wiki/Caesar_cipher9th century: Al-Kindi describes frequency analysis
In Abbasid Baghdad, the philosopher Abu Yusuf al-Kindi wrote a treatise on deciphering encrypted messages with the earliest known description of frequency analysis: counting how often each symbol occurs in a ciphertext and matching the counts to letter frequencies in the same language. Later Arab scholars, including the 14th-century Ibn al-Durayhim, extended the methods.
https://en.wikipedia.org/wiki/Frequency_analysis~1467: Alberti describes a polyalphabetic cipher disk
In "De componendis cifris", the Italian humanist and architect Leon Battista Alberti described a cipher disk with a fixed outer ring and a movable inner ring that was turned during a message, so that its letters were enciphered with several different alphabets. It is one of the earliest known polyalphabetic ciphers, a type that resists simple frequency analysis.
https://en.wikipedia.org/wiki/Alberti_cipher1553: Bellaso publishes the cipher later named for Vigenère
In a booklet printed in Venice, Giovan Battista Bellaso described a polyalphabetic cipher in which a memorable key phrase chose the alphabet for each letter, building on the table of shifted alphabets in Johannes Trithemius's "Polygraphia" (1518). Nineteenth-century writers credited it to the French diplomat Blaise de Vigenère, who published a different, stronger autokey cipher in 1586.
https://en.wikipedia.org/wiki/Vigen%C3%A8re_cipher1586: Decrypted letters expose the Babington Plot
Agents of Sir Francis Walsingham, Elizabeth I's secretary of state, intercepted the letters smuggled in a beer barrel to and from the imprisoned Mary, Queen of Scots, and his decipherer Thomas Phelippes read her nomenclator, a cipher alphabet with code symbols for common words. Her July reply approving a plot to kill Elizabeth was used at her trial, and she was executed in February 1587.
https://en.wikipedia.org/wiki/Babington_Plot17th century: Rossignols devise Louis XIV's Great Cipher
Antoine Rossignol, a codebreaker for Cardinal Richelieu, and his son Bonaventure built the Great Cipher for Louis XIV, who reigned from 1643: a nomenclator of numbers standing for French syllables, with nulls and traps to mislead codebreakers. After it fell out of use, archives written in it went unread until Étienne Bazeries, a French army cryptanalyst, solved it in the 1890s.
https://en.wikipedia.org/wiki/Great_Cipher1863: Kasiski publishes a general attack on Vigenère ciphers
Friedrich Kasiski, a retired Prussian army major, published "Die Geheimschriften und die Dechiffrir-Kunst", the first published general method against repeating-key polyalphabetic ciphers: distances between repeated fragments of ciphertext reveal the key length, reducing the message to simple substitutions. Charles Babbage had broken such ciphers by the 1850s but never published his method.
https://en.wikipedia.org/wiki/Kasiski_examination1883: Kerckhoffs says a cipher must survive capture
In "La cryptographie militaire", the Dutch-born linguist Auguste Kerckhoffs, a professor in Paris, set out six requirements for military ciphers in the telegraph age. The second, that a system must not depend on secrecy and can fall into enemy hands without harm, became known as Kerckhoffs's principle: security should rest on the key alone.
https://en.wikipedia.org/wiki/Kerckhoffs%27s_principle1917: Room 40 decrypts the Zimmermann telegram
Codebreakers in Room 40 of the British Admiralty decrypted a January telegram from the German foreign secretary Arthur Zimmermann offering Mexico an alliance, and the return of Texas, New Mexico and Arizona, if the United States entered World War I. Published in the American press on March 1 and admitted by Zimmermann two days later, it helped build support for the US declaration of war in April.
https://en.wikipedia.org/wiki/Zimmermann_telegram1917: Vernam devises an automatic teleprinter cipher
Gilbert Vernam, an AT&T engineer, designed a teleprinter cipher that combined each character's five-unit Baudot code with a character from a punched key tape, the operation now called exclusive or (XOR); his patent was granted in 1919. With a random key tape never reused, an idea credited at least partly to US Army officer Joseph Mauborgne, it became a one-time pad, a system the banker Frank Miller had described for telegraph codes in 1882.
https://en.wikipedia.org/wiki/One-time_pad1918: Scherbius files a patent for a rotor cipher machine
The German engineer Arthur Scherbius filed a patent for a cipher machine whose wired rotors changed the substitution alphabet with every key press; others, including two Dutch naval officers in 1915 and Edward Hebern in the United States, conceived rotor machines independently. Sold to businesses as the Enigma from 1923, it was adopted in modified form by the German navy in 1926 and the army around 1928.
https://en.wikipedia.org/wiki/Enigma_machine1932: Rejewski reconstructs the military Enigma
Using permutation theory, Marian Rejewski of the Polish Cipher Bureau worked out the rotor wiring of the German army's Enigma in December, helped by settings that French intelligence had obtained from Hans-Thilo Schmidt, a German cipher-office employee. With Jerzy Różycki and Henryk Zygalski he developed ways to find daily keys, and in July 1939, near Warsaw, the Poles shared their results with British and French codebreakers.
https://en.wikipedia.org/wiki/Marian_Rejewski1940: First Turing bombe installed at Bletchley Park
At the Government Code and Cypher School at Bletchley Park, Alan Turing designed an electromechanical machine that tested a guessed piece of plaintext, a crib, against Enigma ciphertext to rule out impossible settings, building on the Polish bomba but working on a different principle. The first was installed on March 18; with Gordon Welchman's diagonal board, bombes became the main tool for reading Enigma, the source of much of the intelligence codenamed Ultra.
https://en.wikipedia.org/wiki/Bombe1942: US codebreakers read Japanese naval plans for Midway
After US Army cryptanalysts built a working copy of Japan's Purple diplomatic cipher machine in 1940 without ever seeing one, US Navy codebreakers at Station HYPO in Hawaii under Joseph Rochefort, with other Allied units, partly broke JN-25, the Japanese navy's main code. They learned the target, timing and order of battle of the planned attack on Midway, where in June Japan lost four fleet carriers.
https://en.wikipedia.org/wiki/Japanese_naval_codes#JN-251944: Colossus breaks Lorenz messages at Bletchley Park
Designed by the Post Office engineer Tommy Flowers, Colossus used vacuum tubes to find the wheel settings of the Lorenz teleprinter cipher of the German high command, whose logic Bill Tutte had deduced without seeing the machine; it broke its first message on February 5. Ten were working by May 1945. Often called the first programmable electronic digital computer, though not general-purpose, it stayed secret until the 1970s.
https://en.wikipedia.org/wiki/Colossus_computer1949: Shannon publishes a mathematical theory of secrecy
In "Communication Theory of Secrecy Systems", based on a classified 1945 Bell Labs report, Claude Shannon analyzed ciphers with information theory, introduced the principles of confusion and diffusion, and proved that a one-time pad, whose truly random key is as long as the message and used only once, provides perfect secrecy when the key remains secret. Soviet reuse of pad pages during World War II let US codebreakers in the Venona project read some Soviet intelligence traffic.
https://en.wikipedia.org/wiki/Communication_Theory_of_Secrecy_Systems1973: Cocks devises public-key encryption in secret at GCHQ
At Government Communications Headquarters (GCHQ), the British signals intelligence agency, Clifford Cocks turned James Ellis's 1970 idea of "non-secret encryption" into a scheme based on the difficulty of factoring a product of two large primes, essentially the later Rivest–Shamir–Adleman (RSA) system; Malcolm Williamson soon found an equivalent of Diffie–Hellman key exchange. The work stayed classified until 1997 and did not influence the public inventions.
https://en.wikipedia.org/wiki/Clifford_Cocks1976: Diffie and Hellman propose public-key cryptography
In "New Directions in Cryptography", published in November, Whitfield Diffie and Martin Hellman of Stanford University proposed public-key cryptosystems, in which an encryption key can be published while the decryption key stays private, and digital signatures. Their key exchange, drawing on Ralph Merkle's work, gave two parties a way to agree on a secret key over an open channel using exponentiation modulo a prime.
https://en.wikipedia.org/wiki/Diffie%E2%80%93Hellman_key_exchange1977: DES becomes the US federal encryption standard
The US National Bureau of Standards published the Data Encryption Standard (DES), a block cipher developed at IBM from Horst Feistel's Lucifer design and modified after consultation with the National Security Agency. Critics including Whitfield Diffie and Martin Hellman objected to its 56-bit key and unexplained substitution boxes, but as an openly published, government-endorsed cipher it was adopted internationally and drew intense academic study.
https://en.wikipedia.org/wiki/Data_Encryption_Standard1977: Rivest, Shamir and Adleman devise RSA
At the Massachusetts Institute of Technology (MIT), Ron Rivest, Adi Shamir and Leonard Adleman devised the Rivest–Shamir–Adleman (RSA) public-key system for encryption and digital signatures; factoring its modulus, the product of two large primes, would reveal the private key. Martin Gardner described it in Scientific American in August with a challenge message that went unsolved until 1994; MIT's patent expired in 2000.
https://en.wikipedia.org/wiki/RSA_cryptosystem1985: Koblitz and Miller propose elliptic-curve cryptography
Neal Koblitz and Victor Miller independently proposed building public-key cryptography on the points of an elliptic curve over a finite field, where discrete logarithms appear much harder to compute than in ordinary modular arithmetic. Because comparable security needs far shorter keys, about 256 bits against 3,072 for the Rivest–Shamir–Adleman (RSA) system, elliptic-curve algorithms entered wide use from the mid-2000s.
https://en.wikipedia.org/wiki/Elliptic-curve_cryptography1990: Biham and Shamir publish differential cryptanalysis
Eli Biham and Adi Shamir described differential cryptanalysis, which traces how chosen differences between plaintexts propagate through a cipher, and applied it to the Data Encryption Standard (DES), which proved unusually resistant. In 1994 Don Coppersmith of IBM revealed that its DES team had known the technique by 1974 and kept it secret after discussions with the National Security Agency.
https://en.wikipedia.org/wiki/Differential_cryptanalysis1991: Zimmermann releases PGP for encrypting email
Phil Zimmermann released Pretty Good Privacy (PGP), which combined public-key and conventional encryption so that individuals could encrypt and sign email and files; it was free for noncommercial use and came with its source code. After it spread abroad, the US government investigated him from 1993 for exporting munitions without a license, as strong cryptography was then classed, and dropped the case in 1996.
https://en.wikipedia.org/wiki/Pretty_Good_Privacy1993: US government proposes the Clipper chip
The Clinton administration proposed the Clipper chip, a National Security Agency design for encrypting phone calls with the classified Skipjack cipher, each chip's key held in escrow so that law enforcement could decrypt intercepted calls. Civil liberties groups such as the Electronic Frontier Foundation opposed it, Matt Blaze of AT&T showed in 1994 that the escrow could be bypassed, and it was defunct by 1996.
https://en.wikipedia.org/wiki/Clipper_chip1994: Shor shows quantum computers could break RSA
Peter Shor of AT&T Bell Laboratories presented quantum algorithms for factoring integers and computing discrete logarithms in polynomial time. On a sufficiently large, reliable quantum computer, they would defeat the mathematical foundations of the Rivest–Shamir–Adleman (RSA), Diffie–Hellman and elliptic-curve systems. The result drove research into cryptography resistant to quantum attacks.
https://en.wikipedia.org/wiki/Shor%27s_algorithm1995: Netscape releases SSL to encrypt web traffic
Netscape Communications released version 2.0 of its Secure Sockets Layer (SSL) protocol, which used public-key cryptography to authenticate web servers by certificate and set up session keys for encrypted browsing. Flaws led to a redesigned SSL 3.0 in 1996, which the Internet Engineering Task Force developed into Transport Layer Security (TLS) 1.0 in 1999; TLS 1.3 followed in 2018.
https://en.wikipedia.org/wiki/Transport_Layer_Security2001: NIST adopts Rijndael as the Advanced Encryption Standard
After an open competition begun in 1997 in which 15 candidate ciphers were analyzed publicly, the US National Institute of Standards and Technology (NIST) published the Advanced Encryption Standard (AES), based on Rijndael by the Belgian cryptographers Joan Daemen and Vincent Rijmen. It replaced the Data Encryption Standard, whose 56-bit key the Electronic Frontier Foundation's Deep Crack machine had found in 56 hours in 1998.
https://en.wikipedia.org/wiki/Advanced_Encryption_Standard2004: Wang Xiaoyun's team finds collisions in MD5
At the Crypto 2004 conference in August, Wang Xiaoyun of Shandong University and colleagues presented collisions, different inputs with the same hash, for the widely used Message Digest 5 (MD5) and related hash functions. Her team announced a shortcut attack on Secure Hash Algorithm 1 (SHA-1) in 2005, and Google and the Dutch institute Centrum Wiskunde & Informatica published the first SHA-1 collision in 2017.
https://en.wikipedia.org/wiki/MD52013: Leaked documents reveal NSA efforts against encryption
The Guardian, The New York Times and ProPublica published documents leaked by the former National Security Agency (NSA) contractor Edward Snowden describing Bullrun, an NSA program to defeat encryption, partly by influencing standards. Reports that the NSA had shaped the Dual Elliptic Curve Deterministic Random Bit Generator, suspected since 2007 of hiding a backdoor, led the National Institute of Standards and Technology to drop it from its guidance in 2014.
https://en.wikipedia.org/wiki/Bullrun_(decryption_program)2024: NIST publishes its first post-quantum standards
The US National Institute of Standards and Technology (NIST) published its first three standards designed to resist quantum computers: the Module-Lattice-Based Key-Encapsulation Mechanism (ML-KEM), derived from the Kyber submission, and lattice-based and hash-based digital signature schemes. They came from a public process opened in 2016 that received 82 submissions from 25 countries; in 2025 NIST chose a backup to ML-KEM based on different mathematics.
https://en.wikipedia.org/wiki/NIST_Post-Quantum_Cryptography_Standardization