Pattern- Codebreaking

“Pattern,” he replied. “In the words. Mmm.”

“Of this sheet?” Shallan asked, holding up the page.

“There and others,” Pattern said. “See the first words?”

Shallan frowned, inspecting the sheets. In each one, the first words came from the remote writer. A simple sentence asking after Tyn’s health or status. Tyn replied simply each time.

“I don’t understand,” Shallan said.

“They form groups of five,” Pattern said. “Quintets, the letters. Mmm. Each message follows a pattern—first three words start with one each of three of the quintet of letters. Tyn’s reply, the two that match.”

Shallan looked it over, though she couldn’t see what Pattern meant. He explained it again, and she thought she grasped it, but the pattern was complex.

“A code,” Shallan said. It made sense; you’d want a way to authenticate that the right person was on the other end of the spanreed. She blushed as she realized she had almost ruined this opportunity. If Pattern hadn’t seen this, or if the spanreed had started writing immediately, Shallan would have exposed herself.

Words of Radiance Chapter 42