What was the first European manual on cryptography?
As a curious student of financial history and cryptography, I'm fascinated by the early works that laid the foundations for modern encryption techniques. Could you elaborate on what the first European manual on cryptography was? I'm particularly interested in knowing who its author was, what era it emerged from, and perhaps a brief overview of its significance in the development of cryptographic methods. Understanding the historical context of these early works is crucial for appreciating the advancements we've made in the field today.