When Was It First Used?

3,500 years of hiding messages

Cryptography is not a modern invention. The oldest known example dates to around 1900 BC — Egyptian scribes used non-standard hieroglyphs in inscriptions, likely to add a sense of mystery or prestige. It was more stylistic than secret, but the impulse was there.

The first deliberate military use appears around 600–500 BC.

Ancient Sparta: the Scytale

Spartan military commanders used a device called a scytale (SKIT-uh-lee) — a cylindrical rod.

To encrypt a message, the sender would wrap a strip of leather or parchment around the rod in a spiral, then write the message along its length. When unwrapped, the letters appeared scrambled. Only a recipient with an identical rod could re-wrap the strip and read the message.

This is a transposition cipher — the letters aren't changed, just rearranged. The rod is the key.

Ancient Rome: the Caesar Cipher

Julius Caesar famously used a shift cipher to protect military correspondence.

The idea: shift every letter in the message by a fixed number of positions in the alphabet. With a shift of 3, A becomes D, B becomes E, Z becomes C.

`` Plaintext: ATTACK AT DAWN Ciphertext: DWWDFN DW GDZQ ``

Caesar reportedly used a shift of 3. His nephew Augustus used a shift of 1. The shift number is the key.

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The Caesar cipher is trivially breakable — there are only 25 possible shifts. But for an era with low literacy rates and no concept of systematic cryptanalysis, it was sufficient. Security is always relative to the capabilities of your adversary.

Medieval Islam: the birth of cryptanalysis

The Arab polymath Al-Kindi (801–873 AD) wrote the first known text on breaking ciphers: A Manuscript on Deciphering Cryptographic Messages.

His key insight: in any language, letters appear with different frequencies. In Arabic and English, some letters are far more common than others. If you count the frequency of symbols in ciphertext, you can match them to the expected frequencies in the language and deduce the substitution.

This is frequency analysis — and it broke every substitution cipher of the era.

Al-Kindi's work established that the secrecy of a cipher cannot rely on keeping the method secret. Any pattern in the plaintext will leak through a weak cipher. This was the insight that pushed cryptography toward increasingly complex methods.

The Renaissance and polyalphabetic ciphers

To defeat frequency analysis, cryptographers developed polyalphabetic substitutions — using multiple different substitution alphabets, switching between them in a pattern defined by a keyword.

The Vigenère cipher (16th century) was considered unbreakable for 300 years. It was eventually cracked in 1863 by Charles Babbage — though he never published his method.

World War II: the tipping point

Cryptography changed everything in World War II.

Germany's Enigma machine used a series of rotating electromechanical rotors to produce a substitution cipher that changed with every keypress. The same letter typed twice would produce two different cipher letters. With billions of possible configurations, it seemed unbreakable.

Alan Turing and the team at Bletchley Park broke it anyway — using mathematical insight, cribs (known plaintext), and mechanical computation.

Historians estimate the work at Bletchley shortened the war by two to four years.

From mechanical to mathematical

After WWII, cryptography moved from clever mechanical devices to pure mathematics.

Claude Shannon's 1949 paper "Communication Theory of Secrecy Systems" put cryptography on a rigorous mathematical foundation for the first time. Information theory gave cryptographers the tools to prove — not just claim — that a system was secure.

This set the stage for modern cryptography: AES, RSA, elliptic curves, and eventually, zero-knowledge proofs.