Who: Bill Weasley
What: Bill has a brilliant idea.
Where: The Burrow, where else?
When: July 18th,
very early morning.
Rating: PG
Closed, Complete
If Bill had studied from home rather than at Hogwarts, he reckoned that he might've looked something like he did now, sitting at his desk, spread across with papers, an abycus, several number charts, many of them not made with a Greco-Roman number system, and a number of woebegone quills. There was ink under his fingernails from the constant writing. Occasionally, he would pick up a paper from his desk and pace the room with it, brow furrowed, concentrating until the beads of sweat formed on his brow and temples in the heat. His wand was in his trouser pocket, as good as abandoned. Any magic performed here occurred somewhere between his mind and the press of quill to paper.
Transpositional and substitutional ciphers were far too outdated, and Bill was convinced that the solution was to use number theory to write the cipher Charlie was looking for, but the inherent problem was the same for anyone in arithmancy and ancient runes, or in any type of code-writing: the cipher must be designed so that a layperson could use it. Bill did have magic on his side, this was true, and the cipher might become encrypted into the journal in such a way that it would respond and translate messages only at his command.
Then an idea occurred to Bill. If the message automatically encrypted itself once written, and would decode for any individual Charlie selected, then there was a possibility that a changing-cipher system based on quantum mechanics might be used to mathematically construct personalized keys with each message, ones that Charlie need never learn because the translation would be two way between Charlie and the receiver of the message. Anyone interfering with the code would ultimately change the cipher just by observing it. Not only would the message be strictly two way, but the system would also detect attempts at eavesdropping.
Bill's heart was pounding, and not from revelation. The grocery and apothecary list were ashes on his desk and Bill felt an acute urgency in his task. In order to create the cipher, Bill would need to construct a multi-variable equation that would self-determine the cipher key for each message based on the alphabetic content of what Charlie wrote. Since Charlie wrote in English, a language based on the Greco-Roman alphabet, the best way to construct the cipher would be from another language with another symbol system.
Walking over to his desk, Bill pulled out a fresh piece of paper and scrubbed his tired face with his fingers and began writing, his quill drawing shapes that were foreign to his fingers but familiar and friendly to his brain.