Classical Cryptography refers to the techniques used to secure communication before the digital age. It primarily involves methods like substitution ciphers, where letters in a message are replaced with other letters, and transposition ciphers, which rearrange the letters in a specific order. These techniques were often used in military and diplomatic communications to protect sensitive information. Historically, famous examples include Julius Caesar's cipher, which shifted letters by a fixed number, and the Vigenère cipher, which used a keyword to determine the letter substitutions. While these methods are relatively simple by today's standards, they laid the groundwork for modern cryptography and the development of more complex encryption systems.