History of Encryption

Unusual Egyptian Hieroglyphs

Unusual signs in Khnumhotep II’s tomb illustrate deliberate variation in writing. Their purpose should not be equated automatically with secret encryption.

Atbash

Atbash — the ancient Hebrew reflection cipher (A<->Z, B<->Y, C<->X), self-inverse and used in the Book of Jeremiah (25:26, 51:41) for SHESHACH.

Scytale

The traditional scytale reconstruction illustrates transposition, but the dates and cryptographic interpretation of ancient evidence are disputed.

Aeneas Tacticus — Water-Clock Signals

Aeneas’s water-clock signaling, preserved in Polybius: synchronized vessels selected preset military messages, not letters of an alphabet.

Polybius Square

Polybius describes coordinate signaling with the Greek alphabet arranged on five tablets. The familiar Latin I/J square is a later adaptation.

Caesar Cipher

Suetonius describes Caesar’s substitution with a shift of three. A short fixed shift can be tested exhaustively; no medieval encounter between Caesar and al-Kindi is implied.

Al-Kindi's Frequency Analysis

Al-Kindi’s surviving treatise gives an early systematic account of frequency analysis. Symbol counts can support substitution analysis, but short samples can remain ambiguous; there is no single six-century contest outcome.

Monoalphabetic Substitution

A fixed substitution preserves letter counts while changing symbols. Al-Kindi’s ninth-century account is a landmark in its analysis, not the invention date of the entire family.

Homophonic Substitution

Mantua’s surviving 1401 key illustrates multiple substitutes for plaintext letters. Such choices can flatten some counts without eliminating higher-order language patterns.

The Voynich Manuscript

The Voynich manuscript remains undeciphered. Radiocarbon dating concerns its parchment; script, language and interpretation remain unresolved.

Alberti Cipher Disk

Alberti’s fifteenth-century cipher disk illustrates changing substitutions using two alphabets. The exhibit distinguishes historical instructions from a regular-step teaching model.

Vigenère Cipher

Bellaso’s 1553 work belongs to the history of polyalphabetic substitution. The familiar repeating-key shift model and its later attribution to Vigenère need to be distinguished from individual historical systems.

Porta's Polyalphabetic

Porta’s work belongs to the history of reciprocal polyalphabetic tables. Repeating-key variants can expose periodic statistical patterns; the museum specifies its own table convention.

The Babington Plot Cipher

The 1586 Babington Plot: intercepted nomenclator letters, a forged postscript, and the difference between compromised keys and an insecure transport channel.

The Argenti Cipher

Matteo succeeded his uncle Giovanni Battista Argenti in papal cryptographic work. Their documented methods include nomenclators, homophones and nulls; Marcello was Matteo’s younger brother.

Bacon's Binary Encoding

Bacon’s biliteral alphabet represents letters with patterns of two forms and can hide them in a carrier. Binary representation is distinct from a direct historical origin for ASCII.

Fermat's Little Theorem

Fermat’s theorem gives aᵖ ≡ a (mod p) for integer a and prime p. It supports some primality tests, but passing a Fermat test does not prove a candidate is prime. Euler’s generalization and a prime-factor argument help explain RSA correctness.

John Wallis and the Civil War Ciphers

John Wallis served successive English governments as a cryptanalyst. The interactive illustrates a nomenclator rather than reproducing an authenticated Royalist key.

The Great Cipher of the Rossignols

The Rossignols’ syllabic nomenclator was deciphered by Bazeries in the 1890s. His proposed Man in the Iron Mask identification remains disputed.

Gronsfeld Cipher

Numeric-key shifts are traditionally associated with Gronsfeld. The attribution and precise invention date are not established by the museum’s modern 0–9 model.

Copiale Cipher

Knight, Megyesi and Schaefer deciphered the Copiale manuscript in 2011 using transcription, statistics and manual analysis. The exhibit separates that result from its invented demonstration alphabet.

Euler's Theorem & the Totient

For a coprime to n, Euler’s theorem states aᵠ⁽ⁿ⁾ ≡ 1 (mod n). It helps explain RSA correctness; treating all message residues also requires the prime-factor or Chinese-remainder argument. The totient theorem alone is not a security proof.

Culper Ring — Washington’s Spy Network

Major Benjamin Tallmadge’s 1779 codebook for George Washington’s Culper Spy Ring. Roughly 760 numbered entries covering people, places, military terms, and common words — used by Abraham Woodhull and Robert Townsend on British-occupied Long Island and Manhattan.

Benedict Arnold & Major André

Arnold and André used successive book references, including Blackstone and dictionary schemes. Kahn distinguishes the changing reference texts and letter-level fallback from a single fixed word-code procedure.

Jefferson Disk

Jefferson proposed an unpublished 36-disk device. The later 25-disk M-94 illustrates a similar mechanism, but direct adoption of Jefferson’s proposal is not established.

Pigpen Cipher

Leeson’s 1794 Masonic inscription is a documented geometric-substitution example discussed by Kahn. It does not establish when every pigpen variant originated.

Wadsworth Cipher Device

Wadsworth’s 1817 device uses geared disks with 33 and 26 positions. A published 2020 ciphertext-only search studied key recovery for this historical design.

Playfair Cipher

Playfair cipher (1854) — Charles Wheatstone's keyed 5x5 digram cipher promoted by Lord Playfair. Used by the British in WWI; broken by digram analysis.

Beaufort Cipher

Beaufort cipher (1857) — Sir Francis Beaufort's reciprocal Vigenère variant where encrypt and decrypt are the same operation. Broken by Kasiski examination.

Civil-War Dictionary Code

Dictionary codes replace words with references in an agreed book. Repeated references and language patterns can still leak information; this widget is a simplified model.

Stager Route Cipher

The Union’s Stager system combined word transposition, code words and operational procedures. Wartime success is a historical claim, not a proof of mathematical security.

Confederate Vigenère

Confederate repeating-key traffic included the Manchester Bluff key documented in an 1863 dispatch. Union success against particular messages does not prove that three keys exposed every Confederate communication.

Kasiski Examination

Kasiski published a repeating-key analysis method in 1863. Repeated-fragment distances suggest candidate periods, which require further checking. Babbage had investigated related attacks earlier.

Chinese Telegraph Code

Viguier’s code and subsequent telegraph books represented Chinese characters numerically. A historical additive example uses digitwise modulo-ten arithmetic; the browser’s modulo-10,000 model is different.

Nihilist Cipher

The additive coordinate construction is associated with Russian revolutionary cryptography. Kahn qualifies its possible inventorship; other systems also bear the Nihilist name.

The Beale Ciphers

Beale ciphers — three numerical ciphers published in an 1885 Lynchburg pamphlet, said to have been written in the 1820s and to point to a Virginia treasure. The pamphlet supplies a reading for #2 using a version of the Declaration of Independence. #1 and #3 remain unresolved; the readable construction does not authenticate a treasure.

Bazeries: Cylinder and Hand Procedures

Bazeries worked with both a cylinder and hand methods. The linked browser exhibit uses a labelled substitution-and-reversal model, not a cylinder simulation.

Four-Square Cipher

Four-Square cipher (1902) — Delastelle's digram cipher using two keyed and two standard 5x5 squares. Disrupts Playfair frequencies but breaks to digrams.

Bifid Cipher

Delastelle’s posthumous 1902 treatise describes fractionation methods. Bifid separates and recombines two-dimensional coordinates over a selected period.

Trifid Cipher

Trifid extends coordinate fractionation to three dimensions. The extra coordinate does not by itself establish greater security than every two-dimensional construction.

German Double Transposition

Two successive columnar transpositions: historical military use, attack conditions, and modern computerized cryptanalysis; not an unbroken cipher until 2013.

One-Time Pad

A one-time pad offers perfect secrecy with a secret, uniform, independent message-length key used once. Try ciphertext tampering to see why secrecy is not authentication.

Vernam Tape Cipher

Vernam’s teleprinter system combines text with a key stream. XOR supplies perfect secrecy only when the pad is uniformly random, independent, secret, long enough and never reused.

Zimmermann Telegram

The January 1917 Zimmermann Telegram: code 0075 to Washington, then re-encoded in 13040 for Mexico. Room 40’s reading helped draw the United States into WWI.

ADFGVX Cipher

ADFGVX combined a 6×6 substitution square with columnar transposition. Painvin’s June 1918 solutions exploited particular traffic and keys, not every later message automatically.

ADFGX Cipher

Germany’s ADFGX field cipher appeared in March 1918; Painvin obtained solutions in April. Its square-plus-transposition construction required continuing key recovery.

Chaocipher

Chaocipher (1918) — John F. Byrne's two-disk dynamic cipher. Disclosed in 2010; published known-plaintext and in-depth ciphertext-only attacks recover its keys.

Enigma Machine

Enigma developed from commercial machines into several military systems. Marian Rejewski reconstructed the German military machine in 1932; Polish, British and Allied teams continued the work against changing procedures and keys.

M-94 Cylinder Cipher Device

The M-94, adopted by the US Army in 1922, used 25 alphabet disks. It resembles Jefferson’s earlier unpublished wheel but was independently developed.

KRYHA Machine

Kryha’s clockwork cipher devices used irregularly moving alphabets. Friedman and colleagues attacked a published challenge in 1933; this widget uses generated settings.

Hill Cipher

Hill’s 1929 cipher mixes groups of letters using an invertible matrix modulo 26. Suitable matched plaintext blocks can expose the key by linear algebra.

Siemens Geheimschreiber T52

Beurling’s 1940 analysis of intercepted Siemens traffic preceded the establishment of FRA. T52 variants differ in stepping and circuitry; irregular stepping should not be assigned to every version.

Lorenz Cipher & Colossus

Lorenz SZ40/42: Tiltman recovered messages and key from a 1941 depth; Tutte and the Research Section inferred the structure by early 1942; Colossus accelerated wheel-setting from February 1944.

Purple Broken on September 20

Genevieve Grotjan’s September 1940 insight contributed to the US Army SIS team’s reconstruction of PURPLE. Its six/twenty switching groups were not simply vowels versus consonants.

Hagelin M-209

M-209 US production begins in 1942, following 1940 trials — the US Army's portable Hagelin C-38 with six co-prime pin-wheels and a 27-bar lug cage. Broken in the field in WWII.

Navajo Code Talkers

Navajo code talkers used a specialized military vocabulary and spelling alphabet during World War II. Their language and the constructed code were distinct layers.

VENONA Project

VENONA analysed intercepted Soviet messages, chiefly from the 1940s, by exploiting duplicated pad material. The project ran from 1943 to 1980.

Shannon's Secrecy Theory

Claude Shannon publishes "Communication Theory of Secrecy Systems" (classified 1945, published 1949) — the mathematical foundation of modern cryptography. He formalizes perfect secrecy, including the correctly used one-time pad, and describes confusion and diffusion as cipher-design principles.

KL-7 ADONIS

KL-7: an American eight-rotor cipher machine with irregular stepping and re-entry. Stolen key material compromised traffic during the Walker espionage case.

VIC Cipher

Information from Häyhänen’s defection enabled the Hollow Nickel message recovery in 1957. The linked exhibit separates historical VIC procedures from a simplified browser model.

Fialka M-125

Fialka was a Soviet ten-rotor machine with variant-specific alphabets, stepping and a punched-card permutation. The browser uses a simplified Latin-alphabet model.

Diana Cryptosystem

A public trigraph table can be used with private, one-use pad letters. The table itself is not the secret pad; the exhibit demonstrates the modulo-26 relation without establishing deployment dates.

Tap Code

US prisoners in Vietnam used a 5×5 tap-code convention, communicating row and column counts through knocks. This documented use does not date the origin of every coordinate tapping system.

Zodiac Z-340 Cipher

Z408 was solved by the Hardens in 1969. Z340 combines homophonic substitution with transposition and exceptions; Oranchak, Blake and Van Eycke announced its solution in 2020.

Diffie-Hellman Key Exchange

Diffie and Hellman published New Directions in Cryptography in 1976. Their key-agreement construction and public-key vision transformed public research. GCHQ’s earlier classified work had distinct contributions by Ellis, Cocks and Williamson; authentication remains a separate protocol requirement.

RSA & DES

RSA was publicly introduced in 1977, and NBS standardised DES that year. Public-key encryption, signatures and symmetric block encryption serve different purposes. Cocks’s related classified proposal at GCHQ preceded public RSA research.

ROT13 on Usenet

ROT13 became popular on Usenet as a spoiler obscurer in the 1980s. It is the self-inverse Caesar shift of 13. One operation toggles text in and out.

Kryptos at CIA Headquarters

Kryptos: K1–K3 publicly solved; K4 plaintext recovered from an archive in 2025, without a publicly demonstrated cryptanalytic solution.

Shor's Algorithm

Peter Shor gives polynomial-time quantum algorithms for factoring and discrete logarithms. A sufficiently large, fault-tolerant quantum computer could defeat RSA and conventional Diffie–Hellman and elliptic-curve systems. Post-quantum alternatives include lattice-based ML-KEM and ML-DSA and hash-based SLH-DSA, standardized in 2024.

Solitaire / Pontifex

Solitaire / Pontifex (1999) — Bruce Schneier's hand cipher driven by a 54-card deck (written for Cryptonomicon). Crowley reported adjacent repeated output letters at about 1/22.5 rather than the 1/26 uniform expectation.

AES Standardized

NIST began the AES selection process in 1997, selected Rijndael in October 2000 and published FIPS 197 in November 2001. The standard and the selection announcement are distinct milestones.

SHA-1 Collision Attack

Xiaoyun Wang and team demonstrate theoretical collision attacks against SHA-1, beginning the transition to SHA-256 and SHA-3. A practical collision was demonstrated by the CWI and Google SHAttered team in 2017.

Learning With Errors

Oded Regev introduces Learning With Errors: noisy modular equations hide a secret vector. His result connects suitable LWE parameters to worst-case lattice problems through a quantum reduction. Hardness depends on parameters; noise is not sufficient by itself. The later ML-KEM and ML-DSA standards use structured module problems, with additional assumptions for signatures.

Snowden Revelations

The 2013 disclosures intensified public debate about surveillance and communications security. HTTPS protects a connection to its TLS endpoint; it is not the same as end-to-end encryption between messaging users.

Post-Quantum Cryptography

NIST launches the Post-Quantum Cryptography project in 2016. In 2024, ML-KEM (FIPS 203), ML-DSA (FIPS 204), and SLH-DSA (FIPS 205) are standardized — intended to resist known classical and quantum attacks, under their respective assumptions.

Rail Fence Cipher

Rail Fence transposes a message along a zigzag route. Rail count, offset conventions and message length define the search; there is no universal ten-rail maximum.

Geʿez Context and a Teaching Model

The interactive uses a modern Latin-letter substitution. No identified manuscript authenticates it as a particular Geʿez monastic cipher.

Running-Key Cipher

A running-key construction uses a passage of text as key material. Natural-language keys have statistical structure and are not uniformly random one-time pads.

Columnar Transposition

Explore columnar transposition and multiple anagramming: rearrange column strips across three synthetic same-key intercepts and compare a different-key control.

Straddling Checkerboard

A keyed variable-length digit substitution gives selected letters one digit and others two. It is a component of historical hand systems, including VIC, rather than a complete secure cipher by itself.

Fractionated Morse

Fractionated Morse — converts text to Morse, regroups dots, dashes, and separators in trigrams, then substitutes via a keyed alphabet. Broken by trigram stats.

Two-Square Cipher

Two-square uses two keyed 5×5 squares to encipher letter pairs. This demo follows the ACA horizontal rectangle rule and discloses its extra filler-escape convention.