The desire to keep information private is as old as communication itself. The earliest recorded cipher is the Caesar shift, used by Julius Caesar for military correspondence. It was trivially breakable by frequency analysis, documented by Arab scholar Al-Kindi in the 9th century.
World War II brought the German Enigma machine with 159 quintillion possible configurations. The Allied effort at Bletchley Park, led by Alan Turing, exploited predictable patterns in German messages. Cryptography had become a branch of applied mathematics.
In 1976, Diffie and Hellman introduced the concept of key pairs — one public, one private. The RSA algorithm implemented this using the difficulty of factoring large prime numbers. This solved the key distribution problem that had plagued cryptography for 2,000 years.
From Caesar's letter shift to quantum-resistant algorithms, cryptography has always been a dialogue between mathematics and human ambition. The systems protecting your banking and identity today are the latest chapter in a story that began two millennia ago.