‘Exactly,’ said Huang Yiyi. ‘The ciphers they used weren’t particularly difficult, but they were developed for a machine, the world’s first proper encryption machine. Earlier so-called encryption machines were basically more like calculators; fundamentally they brought nothing to the original cipher. You could say that no one up until that time had worked out a way to make an encrypting machine. Enigma was the first, and it’s a landmark in the history of cryptography. If I told you that Sivincy wrote her cipher for a commercially available rotor machine which is basically a carbon copy of Enigma, would you believe me? Of course you wouldn’t, because Enigma is so famous, and so many people have researched it; if you are a thief you don’t go and steal something in plain sight, right? But I am absolutely sure that the machine used is Enigma, and that any differences are superficial – it has wheels where the original had cogs; thirty-four matrices rather than twenty-six, with actuating motors rather than gears, but the underlying principles are fundamentally the same. If you want a comparison, it’s as if someone published a translation claiming it was an original work …’

This discovery really amazed us all. Just as Huang Yiyi said, Sivincy had pulled a very nasty trick on us, the cow. It was very difficult for us to find our footing when dealing with someone so unprincipled.

After supper we went for a walk, and Huang Yiyi and I analysed the motives behind Sivincy’s plagiarism of ULTRA. We decided that the reason Sivincy wrote her cipher for an Enigma machine, rather than anything else, was because it was part of an elaborately crafted scheme. It wasn’t because she was stupid, or because she had no choice, but because she was actually extremely crafty. Ripping off ULTRA is like stealing an advertising hoarding on a busy street, or the portrait of Chairman Mao off the wall outside Tiananmen. If you walk straight up in broad daylight and steal them, even if the police spot you they aren’t going to realize what you are up to. Sivincy was a famous mathematician; most people wouldn’t believe it possible that someone of her calibre would produce a rip-off. Just think about it – if someone you would never imagine stealing anything actually does so, how great are their chances of success? It was clever, but it was a wicked sort of cleverness. If we hadn’t seen this data that day (given that our job was to decrypt her cipher), we might well have been completely misled, digging ourselves further into a rut, not realizing that the answer to the riddle was right beside us in our textbooks.

‘She deserves all the ridicule she gets,’ Huang Yiyi said.