From Atlas Obscura:
On March 15, 1898, the eminent botanist Joseph Dalton Hooker sat down at his desk, picked up a pen, and started writing a letter to his friend and confidant, the Reverend James Digues La Touche. “My dear La Touche,” he began, before continuing what had been many years of correspondence, updating his pen pal on his family life, his intellectual preoccupations, and his professional exploits.
Over a century later, an archivist at Kew Gardens in London—the largest botanical garden in the world, where Dalton served a long stint as director—reached into a folder of the pair’s correspondence, drew out a page, and stopped cold.
The archivists were already deep into the process of digitizing and transcribing Hooker’s letters for posterity. But a few lines into this particular letter, the words suddenly disappeared, censored by row after row of black squiggles. The same went for a number of Hooker’s missives to La Touche. “We were quite mystified by it,” says Virginia Mills, an archivist at Kew. “They stood out to us, because we hadn’t come across anything else like it in his papers. So we just started kind of speculating about what it might be.”
. . . .
Kew Gardens has thousands of pages of correspondence from Hooker. Of these, only a small percentage of lines are blacked out. But these pages play an outsized role in the imaginative life of those who work with them. “The letters are full of unpublished material, private thoughts, scientific exchange and criticism, and intimate details shared with friends and family,” writes Mills in a blog post about the letters. “But perhaps most intriuging of all, to those of us who have got to know the collection, are the stories that remain obscured.”
. . . .
In some cases, obscurity is professionally (or personally) required. Codes, for example, seem to be favored by two very different types of people: businessmen seeking to protect their economic interests, and teenagers and young adults guarding their feelings.
. . . .
Beatrix Potter, later famous for her children’s books, kept a diary written in a self-invented cipher that took a dedicated fan years to crack.
Link to the rest at Atlas Obscura
PG says Potter’s secrets might be forever secure had she online encryption and decryption for her diary.
For example (make sure you copy the entire encrypted text – There are no spaces, so it doesn’t wrap and extends beyond the right side of the post):
PG says you might want to try:
Modes: CBC (cipher block chaining)