“Codes,” Becker said, fascinated. “How do you know where to start? I mean ...how do you break them?”
Susan smiled. “You of all people should know. It's like studying a foreign language. At first the text looks like gibberish, but as you learn the rules defining its structure, you can start to extract meaning.”
Becker nodded, impressed. He wanted to know more.
With Merlutti's napkins and concert programs as her chalkboard, Susan set out to give her charming new pedagogue a minicourse in cryptography. She began with Julius Caesar's “perfect square” cipher box.
Caser, she explained, was the first code-writer in history. When his foot-messengers started getting ambushed and his secret communiqués stolen, he devised a rudimentary way to encrypt his directives. He rearranged the text of his messages such that the correspondence looked senseless. Of course, it was not. Each message always had a letter-count that was a perfect square—sixteen, twenty-five, one hundred—depending on how much Caesar needed to say. He secretly informed his officers that when a random message arrived, they should transcribe the text into a square grid. If they did, and read top-to-bottom, a secret message would magically appear.
Over time Caesar's concept of rearranging text was adopted by others and modified to become more difficult to break. The pinnacle of noncomputer-based encryption came during World War Ⅱ. The Nazis built a baffling encryption machine named Enigma. The device resembled an old-fashioned typewriter with brass interlocking rotors that revolved in intricate ways and shuffled cleartext into confounding arrays of seemingly senseless character groupings. Only by having another Enigma machine, calibrated the exact same way, could the recipient break the code.
Becker listened, spellbound. The teacher had become the student.
One night, at a university performance of The Nutcracher, Susan gave David his first basic code to break. He sat through the entire intermission, pen in had, puzzling over the eleven-letter message:
HL FKZC VD LDS
Finally, just as the lights dimmed for the second half, he got it. To encode, Susan had simply replaced each letter of her message with the letter preceding it in the alphabet. To decrypt the code, all Becker had to do was shift each letter one space forward in the alphabet—“A”became“B”, “B” became “C”, and so on. He quickly shifted the remaining letters. He never imagined four little syllables could make him so happy:
IM GLAD WE MET
He quickly scrawled his response and handed it to her:
Susan read it and beamed.
Becker had to laugh; he was thirty-five years old, and his heart was doing backflips. He'd never been so attracted to a woman in his life. Her delicate European features and soft brown eyes remined him of an ad for Estée Lauder. If Susan's body had been lanky and awkward as a teenager, it sure wasn't now. Somewhere along the way, she had developed a willowy grace—slender and tall with full, firm breasts and a perfectly flat abdomen. David often joked that she was the first swimsuit model he'd ever met with a doctorate in applied mathematics and number theory. As the months passed, they both started to suspect they'd found something that could last a lifetime.