As long as there has been civilization and written language, there has been a need for encryption. Encryption is basically the act of disguising your message so that (hopefully) only the intended recipient can read it.
While you likely associate encryption with internet protocols and WiFi passwords today, there’s a very long and interesting history of encryption dating back to ancient times. I recently read a fascinating history of cryptography called The Code Book by Simon Singh.
While the book is a bit dated in terms of modern cryptography (it was published in 2000, so don’t expect anything about blockchain), it’s still a fantastic read that I would recommend to any programmer.
The most basic and ancient example of cryptography is the “Caesar Cipher“, or “Caesar Shift”. You’ve probably created your own Caesar Cipher as a kid without even knowing the name or history of it. The basics of it are this