substitution cipher

A substitution cipher is a method of encoding messages by replacing each letter in the original message with a different letter, symbol, or number based on a specific system or key. This way, the original message becomes scrambled and unreadable to anyone without the key. For example, every "A" might be replaced with "M," every "B" with "X," and so on. The security of this cipher depends on how well the substitution system is kept secret. It’s a simple form of encryption used historically and forms the foundation for more complex cryptographic techniques.