Classical ciphers are early methods of encrypting messages to ensure confidentiality. They typically involve simple techniques like substitution, where each letter in the plaintext is replaced by another letter, or transposition, where the positions of letters are rearranged. Famous examples include the Caesar cipher, which shifts letters by a fixed number, and the Vigenère cipher, which uses a keyword to determine the shift for each letter. These ciphers were widely used before the advent of modern cryptography and are often studied for their historical significance. While they can be easily broken with frequency analysis, they laid the groundwork for more complex encryption methods used today.