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Real-world 'document' encryption

I've been reviewing histories of cryptography recently and here's an interesting thing about pre-computer encryption: it's almost entirely used for communications security. People encrypted messages, but they rarely encrypted documents.

I've finally found a few real-world cases: encrypted diaries. BBC actually did a short segment on them last summer. But I'm still looking - there must be other cases where someone needed to keep some long-term data secret from prying eyes.

It's obvious that one might want to encrypt a message. It's less obvious, but not impossible, for pre-computer writers to want to encrypt a document for long-term storage. I can think of 3 cases for encrypting a document:

  • Treasure maps - the only examples, however, seem to be fictional. Poe talks of a treasure map in The Gold Bug. The Beale Ciphers involve encrypted documents that allegedly describe the location of treasure, but they may well be fakes.
  • Accounting ledgers for secret activities - I could imagine 1920s bootleggers using ciphers to protect accounting data, but I've never heard any reports of such.
  • Diaries - this seems to be the only genuine case.
There's also the Voynich Manuscript, but nobody knows just what that is. Perhaps it's a text in a real language, or perhaps it's a mnemonic device, as opposed to being an actual text in some code.

Below is what I've found out about the principal diary examples, Charles Wesley and Beatrix Potter.

Diary of Charles Wesley

The BBC report was brought about by the recent decryption of some diary entries by Charles Wesley, co-founder of the Methodist Church. Most of Wesley's diary appears to have been in plaintext; a version of the plaintext was published in 1849. You can see Wesley's plaintext diary on-line, with an introduction, at the Charles Wesley Center of the Church of the Nazarene.

Mixed with those readable diary entries were other bits of text in an obscure shorthand that Wesley developed and used himself.  I think it's interesting that neither the originally published diary text, nor its introduction, makes any mention of these indecipherable texts.

Perhaps this explains why the texts remained undeciphered for 250 years: hardly anyone knew about them. Professor Kenneth Newport of Liverpool Hope University spent several years deciphering them. I haven't seen his paper, but here's the citation: Newport, Kenneth G. C. 'Charles Wesley 'Warts and All''. Proceedings of the Wesley Historical Society, 56:4 (2008), 165-188. ISSN 00432873.

Why did Wesley encipher bits of his journal? Let's look at the types of entries described by the news reports: they primarily spoke of sex scandals and of disputes with his brother, John Wesley, the other founder of Methodism. Charles Wesley apparently wanted to record all the important things in his life, but he didn't necessarily want others to read them, too.

Wesley's cipher was a personalized form of shorthand. Some observers on-line have noted the similarity to standard forms of shorthand. Prof. Newport decrypted Wesley's diary entries by using a "crib:" a piece of text whose contents he could find - bits of the King James Bible that Wesley had encrypted with the same method.

Diary of Beatrix Potter

The BBC material also refers to a more prosaic and literary example of an encrypted diary: that of Beatrix Potter, author of childrens books. Nobody seems to address the question of why a fourteen-year-old English girl might feel inclined to hide her writing so thoroughly from family or others. A few literary critics have approached Potter from a psychoanalytic perspective and suggest that she suffered depression, and paranoia isn't an unusual partner to depression.

I think there's an interesting lesson here - though diaries can be incredibly personal, hardly any writers seem to revert to codes to protect their diaries' contents.

I suspect there may be more encrypted diaries out there. However, such things are most likely discarded by the heirs, since they can't make sense out of the text. A careful archivist would save such things, but family members might discard them before the archivist gets the choice.

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