005 | Catherine of Aragon’s Tudor Cipher

“When Secrecy Was Agency”

Before Henry’s marital emergency became England’s constitutional bonfire, Catherine was already a diplomatic actor, a royal daughter of Ferdinand of Aragon and Isabella of Castile, a widow trapped in English politics, and a woman who understood that information moves power. In 1507, while still stranded in England after Prince Arthur’s death, she was appointed as her father’s ambassador to the English court. She knew the court, knew the people, knew the stakes, and had been educated for rule. It was a radical choice in gender terms, but a practical one in diplomatic terms. She has been described as Europe’s first female ambassador.^[1]

Naturally, history then spent several centuries trying to turn her back into a wronged wife in a bonnet. History can be very committed to missing the point.

For this series, Catherine matters because she used and depended on ciphered communication at a moment when secrecy was not decoration. It was agency.

This is not a story about a cipher being technically brilliant. It is a story about what cipher was for: survival, negotiation, legitimacy, defiance, and the ability to speak across hostile space without every nearby man knowing exactly what you had said.

In an autograph letter written from Greenwich in July 1507, Catherine told Miguel Pérez de Almazán that she wished she could make use of ciphers to write, though her knowledge was not enough for more than working them out. The line matters because it gives us Catherine not as an ornament near a cipher, but as someone conscious of cipher as a political tool. She wanted the capability. She understood the value.^[2]

Two years later, after Henry VII’s death and her marriage to the new Henry VIII, cipher was no longer just an aspiration. A letter of 3 November 1509 from Catherine to her father Ferdinand survives in the Spanish archives, catalogued by PARES as a letter from the Queen of England to the Catholic King. It includes ciphered material, and it sits in exactly the world we should expect: pregnancy, court factions, confession, couriers, father-daughter diplomacy and the machinery of dynastic politics.^[3]

There is no clear evidence that Catherine’s 1509 cipher was broken by English observers at the time. The surviving letter was treated as undeciphered in modern archives until it was solved in the twenty-first century.

There is a wonderfully human operational detail in the accompanying cleartext. Catherine apologises that the ciphered parts are not in her own hand. Illness had taken away the time she needed, and the courier could not be kept waiting, so she had her confessor and chancellor write them.^[4]

There, in one small apology, is half of cybersecurity.

The user is ill. The deadline is real. The message must go. Someone else helps. The courier is waiting. The system depends on trust, delegation, handwriting, timing and people who may or may not be remembered by name.

Cryptography, as usual, is not just cryptography. It is workflow with multiple enemies.

Modern security teams call this threat modelling and operational procedure. Tudor courts called it life, usually with worse dentistry.

Catherine’s ciphered correspondence also pushes against a lazy idea of early cryptography as something men did while women waited to become plot consequences. Catherine was not merely the subject of politics. She practised it. Cipher allowed her to communicate with her father, to negotiate across distance, and to act within a court where her body, marriage, dowry and fertility had all been turned into diplomatic assets.

That is already enough reason to include her here.

But there is another cipher linked to Catherine, and it is stranger, more visual, and somehow more pointed.

In Hans Holbein’s Jewellery Book, a collection of designs by the Tudor court painter, there is an oval pendant design formed from intertwined letters. The British Museum catalogue describes it as a pendant formed with the cipher “AVRNTEKCIS”, one of several jewellery designs with floriated letters, dated to around 1532–1543.^[5]

Vanessa Braganza, a literary scholar, has argued that this tangled design hides the words “Henricvs Rex” and “Katherine”. Her interpretation links the pendant design to Catherine during the period when Henry was trying to end their marriage and elevate Anne Boleyn. Braganza suggests that Catherine may have commissioned it as an assertion of her continuing legitimacy: not discarded wife, not political debris, but queen.^[6]

The caution matters. We should say “linked to Catherine”, “Braganza argues”, and “may have commissioned”, because scholarly claims should not become certainty merely because they make a beautiful story. Beautiful stories are dangerous. They get invited to dinner and then steal the silver.

Even with that caution, the object is powerful.

This is cipher in a different sense from the diplomatic letter. It is not a block of text hidden from an interceptor. It is a public design that invites looking while restricting reading. A person could see the pendant and see ornament. Another person, with the right context, could see names, claim, loyalty, marriage, defiance.

The message is visible. The meaning is rationed.

That is an extraordinarily modern security idea. Access is not just about whether something can be seen. It is about whether it can be understood. The scytale taught us that a strip of writing might need the right staff. Catherine’s jewellery cipher suggests that a public object might need the right political literacy.

A secret can be worn in daylight.

That may be the most Tudor sentence imaginable, outside of Blackadder.

The pendant design also reminds us that “cipher” has never meant only one thing. In early modern contexts it can mean secret writing, a monogram, an interlaced device, a sign of identity, a lover’s knot, a dynastic emblem or a puzzle meant to be solved by some eyes and missed by others. Modern cybersecurity is full of the same ambiguity. Credentials, signatures, tokens, seals, badges, certificates, watermarks and metadata all sit somewhere in the murky swamp between identity and secrecy.

Catherine’s world understood that symbols could authenticate a claim. A name hidden in ornament could say: I am still here. I am still queen. You may pretend otherwise, but the cipher knows.

The attribution story needs care.

First, Catherine herself needs restoring. She was not just a victim of Henry’s story. She was an educated royal woman, a diplomat, a correspondent, a regent and a political actor. Her use of cipher belongs in cybersecurity history because it shows a woman using confidential communication in high-stakes diplomacy.

Third, Catherine’s household and courtly world were not as pale and simple as costume drama often suggests. Historic Royal Palaces records that Catherine’s 1501 entourage included two unnamed enslaved women, and that Catalina of Motril, a Muslim Moorish servant of Catherine’s bedchamber, was probably one of them. John Blanke, a Black royal trumpeter at the courts of Henry VII and Henry VIII, may also have arrived in England with Catherine’s entourage. He is one of the rare Black Tudors with an identifiable surviving image.^[7]

This does not mean Catalina or John handled Catherine’s ciphers. But it does mean that any honest account of Catherine’s world must leave room for the people of colour, enslaved people, servants, musicians and household workers who stood close to power while being pushed to the edges of the record.

Finally, credit also belongs to modern recovery work. Vanessa Braganza’s decoding of the Holbein jewellery-book cipher matters not only because it gives us a possible Catherine-linked object, but because it models the kind of historical attention this series needs: looking again at something long catalogued, long visible, and not fully read.^[6]

That is a cybersecurity lesson too.

Sometimes the artefact has been sitting there all along. The question is whether anyone has the context, patience and suspicion to read it properly.

Catherine’s Tudor cipher is not here because it gives us a new algorithm. It does not. It gives us something more socially interesting and, therefore, more troublesome.

It shows cipher as a tool of agency. It shows secrecy as political survival. It shows identity encoded into objects. It shows workflow, delegation, trust and courier pressure. It shows how women used confidential communication in a world that kept trying to make their choices belong to men.

The previous artefacts taught us about keys, substitution, frequency and repetition.

Catherine teaches us that sometimes the most important question is not how the cipher works.

It is who gets to speak safely.

And who is still queen when other people insist she is not.

References

[1] Emily Zarevich, “Catherine of Aragon: Europe’s First Female Ambassador”, JSTOR Daily, for Catherine’s 1507 diplomatic role and the corrective framing of her as a political actor rather than merely Henry’s discarded wife. (JSTOR Daily)

[2] Luis Jiménez de la Llave, “Carta hológrafa de Catalina de Aragón, Princesa de Gales”, Biblioteca Virtual Miguel de Cervantes, for the 18 July 1507 letter in which Catherine discusses wanting to use ciphers. (Biblioteca Virtual Miguel de Cervantes)

[3] PARES, Archivo General de Simancas, ES.47161.AGS//PTR,LEG,54,51, for the archival record of Catherine’s 3 November 1509 letter to Ferdinand. (pares.mcu.es)

[4] S. Tomokiyo, “Catherine of Aragon’s Letter to King Ferdinand, Her Father (1509)”, MysteryTwister C3, for the cipher challenge, the 1509 context, and the cleartext note about the cipher not being in Catherine’s own hand. (MysteryTwister)

[5] British Museum collection record SL,5308.114, for the Holbein Jewellery Book pendant design formed with the cipher “AVRNTEKCIS”. (British Museum)

[6] Meilan Solly, “The Secrets of a Long-Overlooked Cipher Linked to Catherine of Aragon”, Smithsonian Magazine, for Vanessa Braganza’s decoding of the Holbein jewellery-book cipher and the Catherine legitimacy interpretation. (Smithsonian Magazine)

[7] Historic Royal Palaces, “Catalina of Motril” and “John Blanke”, for the wider overlooked household and court context around Catherine of Aragon. (Historic Royal Palaces) (Historic Royal Palaces)