Covert Communication: From Invisible Ink to Encryption
· By Archivo Bélico editorial team · Updated
From the scytale and invisible ink to Enigma and public-key cryptography: a non-operational history of hiding messages and meaning.
Covert communication seeks to hide the existence of a message, protect its meaning, or both. Steganography and cryptography solve different problems: the first conceals presence; the second transforms content so it is unintelligible without a key. Their history is a contest among secrecy, interception and analysis.
Antiquity: hiding the medium or changing the text
Herodotus described messages hidden beneath wax or on a messenger’s shaved scalp. The Spartan scytale rearranged letters using a strip wound around a cylinder. Exact accounts should be treated as ancient sources, not manuals or proof of continuous use.
From courts to black chambers
Early modern diplomacy spread cipher alphabets, nomenclators and seals. European states created offices that opened, copied and deciphered correspondence. Security depended on the system and on the discipline of users who might repeat keys or leave patterns.
Invisible ink, radio and world wars
Secret inks and codes accompanied agent networks for centuries. Telegraphy and radio changed the scale: they enabled long-distance communication but created interceptable signals. During the First World War, Britain’s decryption of the Zimmermann Telegram had major diplomatic consequences.
Cipher machines and industrial effort
Enigma was not one device or a simple code, but a family of machines and procedures. Allied success combined mathematics, intelligence, operator error, captured material and industrial capacity. Reducing the story to one machine or person obscures that cooperation.
The public-key revolution
For much of the twentieth century, advanced cryptography was dominated by governments. Published public-key methods in the 1970s made it possible to exchange secrets without first sharing the same key and paved the way for everyday digital security.
What endures
Media change, but three questions persist: who can observe the channel, what communication patterns reveal, and how the other party is authenticated. This article describes historical development; it does not provide current techniques for evading controls or directing clandestine activity.
Frequently asked questions
- Are cryptography and steganography the same?
- No. Cryptography hides a message’s meaning; steganography attempts to hide the message’s existence. They can be combined.
- Was Enigma defeated by Alan Turing alone?
- No. Turing was crucial, but success depended on earlier Polish work, multinational teams, intelligence, German errors and industrial resources.
Sources and references
- David Kahn, The Codebreakers, revised edition, Scribner, 1996.
- John F. Dooley, History of Cryptography and Cryptanalysis, Springer, 2018.
- NSA Center for Cryptologic History, Masked Dispatches.
- The National Archives (UK), The Zimmermann Telegram.
- Gordon Welchman, The Hut Six Story, McGraw-Hill, 1982.
- Whitfield Diffie and Martin Hellman, New Directions in Cryptography, IEEE Transactions on Information Theory, 1976.