During those three months of professional training, several cryptographers came to lecture us. Their lectures usually focused on the basic principles of the work and their own personal experiences. One day, the comrade in charge of the base told us that the guest instructor today was a high-level cryptographer. Within the intelligence service he was known as the ‘double bull’. What exactly did that mean? Well, it meant that he got angry like a bull, and he was bullish in his work, always attacking things head on. Since his temperament was haughty and bullish, as well as his approach to work, he was the ‘double bull’: overbearing and sure of himself. With this type of disposition, we had to be sure to pay attention during his lecture; we should not anger him in any way. Once he arrived, as expected we all felt he was quite strange. His topic was supposed to be his personal experiences, but once he entered the classroom he didn’t even look at us. For a long time all he did was sit in front of the class, smoking cigarette after cigarette without regard for anyone – he spoke not a word. Silently we looked at him as seconds passed by and the smoke from his cigarettes continued to encircle him. Soon minutes drifted by. We began to grow uncomfortable in our chairs and several students couldn’t help but cough, clearing their throats, perhaps trying to get his attention. It worked. He raised his head and looked at us, stood up, walked around us once, returned to his seat and picked up a piece of chalk. He asked us what it was. He asked student after student and got the same answer each time: it was a piece of chalk. Then he put the chalk in the palm of his hand, he looked ready to recite something. This is what he said:

‘If this is truly a piece of chalk, then it means that you are not cryptographers; conversely, it shouldn’t be a piece of chalk. Many years ago, I sat in the very same chairs you are seated in now, listening attentively to a senior cryptographer, just as you are now. This is what he said to me: “In the world of cryptography, there is nothing that can be seen by the naked eye. Whatever you see with your eyes is not what you think it is” (he gestured with his hand) “you certainly are not you, I certainly am not me, the table certainly is not a table, the blackboard certainly is not a black board, today certainly is not today, the sunshine certainly is not the sunshine.” Everything in the world is like this: it is often the most confusing thing that is the simplest. I think this is all I need tell you today. Class dismissed.’