There are many people in this world who don’t believe in dreams, but for a cryptographer, dreams are a secret passage that those who fight using only their intellects use to reach the opposite bank victoriously. In the history of cryptography, there is no lack of examples of people who succeeded thanks to some sudden illumination in their dreams. Huang Yiyi told me excitedly that her dream had reminded her that the key to unlocking RECOVERY, that is the key to the cipher, might well be an original and modern cryptographic bombe! To use her imagery, it would be a sieve that created a domino effect. The sieve was separated into nine layers, and each layer would have 365 holes, so that in total the sieve would have 9 × 9 × 365 = 29,565 holes, and each day’s radio messages would correspond to one hole. That would mean the messages could only be decrypted through one hole, but if you found that hole, the entire day’s output could be read. If we compared the numbers in the radio intercepts to grains of rice, and used a sieve to sieve and re-sieve them, in principle once one grain of rice had come through the system and fallen through the final hole at the other end, then we had cracked it, and all the other grains of rice (the remaining radio intercepts picked up on the same day) would all roll through as well. That is the domino effect – the difference being that traditionally with dominoes the first action that sets everything in motion is human, whereas what she had in mind was a sieve-initiated effect. To put it another way, the dominoes weren’t set up to form a line but a circle, a single plane, but once you cut it and lined up the first set of numbers against the first set of holes, once one had found the right path, then the rest would follow suit in order. In very much the same way that if you have a bucket of water and pierce a hole in the bottom, the water will form a stream.