Substitution Cipher Puzzle

The encouraging phrase you've decoded, "Just Keep Swimming," originates from the beloved 2003 animated film Finding Nemo (Review). It is famously uttered by Dory, a blue tang fish with short-term memory loss, who offers it as a simple yet powerful mantra to her anxious companion, Marlin. The quote embodies perseverance and optimism, reminding us to continue moving forward even when faced with daunting challenges and the urge to give up. Dory's character, voiced by the well-known comedian Ellen DeGeneres, became a fan favorite for her cheerful and ditzy personality, making the message of resilience particularly impactful as she helps Marlin in his search for his lost son, Nemo.

This puzzle employed a substitution cipher, one of the oldest and most fundamental forms of encryption. In a substitution cipher, each letter in the original message is systematically replaced with a different letter or symbol. The practice of cryptography, which means "hidden writing" from Greek words, dates back thousands of years to ancient civilizations. Early examples of cryptography can be found in ancient Egypt, Greece, and Rome, where various methods were used to protect military secrets and diplomatic communications. A well-known historical example of a substitution cipher is the Caesar cipher, used by Julius Caesar himself.