A transposition cipher is a method of encryption where the positions of the characters in the plaintext are shifted according to a specific system. Unlike substitution ciphers, which replace characters with others, transposition ciphers rearrange the existing characters to create the ciphertext. This means that the same letters are used, but their order is changed, making it difficult to decipher without knowing the key. One common example of a transposition cipher is the rail fence cipher, where the plaintext is written in a zigzag pattern across multiple lines. The characters are then read off line by line to create the encrypted message. Transposition ciphers can vary in complexity, but they all rely on the principle of rearranging characters rather than altering them.