A 17th-Century Cipher Has Been Cracked. The Message Is a Royalist War Cry.
A coded message hidden in a 1653 English document has been decoded. The text, discovered in the archives of the University of Oxford, reveals a secret plea for King Charles II’s restoration. The cipher writer was a royalist supporter, and the message was likely a covert recruitment tool.
Who Wrote the Message and Why?
The message was written by a supporter of the exiled King Charles II. It was created during the Interregnum, the period of republican rule after the execution of King Charles I. The royalist intended to communicate secretly with other loyalists.
The text urges resistance against Oliver Cromwell’s Protectorate. It explicitly calls for the king’s return and condemns the parliamentary leadership. Experts believe the cipher was a form of political propaganda hidden in plain sight.
How the Code Was Broken
The cipher sat undeciphered for centuries. Historical cryptographers had noted the unusual symbols but could not break them. The breakthrough came when a researcher applied a modern frequency analysis to the text.
The code used a substitution cipher where symbols replaced letters. The researcher mapped these symbols against common English letter patterns. Within weeks, the message emerged.
“When you see this, know that the king’s friends are many. The usurper and his council are hated. Prepare for the day of restoration.”
What the Decoded Text Says
The full decoded message is a statement of defiance. It names Cromwell’s regime as a tyranny. It encourages addressees to “be bold” and to “wait for the signal.”
Historians note the language is militant. The writer promises that “God’s justice will fall on the regicides.” This helps date the document precisely to the period of plot and conspiracy after the 1653 dissolution of the Rump Parliament.
Why This Matters Today
- Historical context: The message provides direct evidence of organized royalist resistance.
- Cryptography: It demonstrates that simple ciphers were effective for political communication.
- Archival value: The find proves many historical documents still hide undiscovered secrets.
The discovery changes understanding of the Interregnum. It shows the republic’s enemies were coordinated, not merely disgruntled. The code itself was elegantly simple yet secure for its time.
The Document’s Survival
The manuscript survived because it was misfiled. Archivists cataloged it as a theological text. Later historians overlooked its odd annotations as scribal errors.
Only when a digital scan was uploaded to a public archive did a hobbyist cryptographer spot the pattern. That led to the formal academic review and the ultimate decryption.
Technical Details of the Cipher
The cipher used a set of 26 unique symbols. Each symbol corresponded to a letter. There were no spaces between words, a common technique to confuse readers.
The researcher reconstructed the key by looking for the most frequent symbols. In English, “e” is the most common letter. That simple assumption unlocked the entire code.
“It was standard 17th-century cryptography. The truly remarkable thing is that nobody read it for 370 years.” - Historical cryptographer involved in the study.
What Comes Next
Historians are now reviewing other documents from the same collection. They suspect more coded messages may exist. Any discovery could rewrite our understanding of the royalist underground.
The decoded message will be published in full alongside a commentary in an upcoming academic journal. An exhibition at the Oxford archive is also being planned.
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