What method does the Enigma machine use for encrypting messages?

The Enigma machine uses a substitution cipher method for encrypting messages. This machine employs a series of rotors that substitute letters based on a complex, changing configuration. As a key is pressed, the electric signal travels through these rotors, which scramble the letters by replacing each letter with another letter according to the specific wiring of the rotors at that moment.

The mechanical arrangement of the rotors means that as you type a letter, it produces a different letter output, thus creating a form of substitution where symbols are replaced with other symbols based on the current state of the rotors. This method offers a high level of security since the same letter can be transformed into different letters depending on the rotor settings, making it significantly more difficult to decode without the proper configuration.

The other options pertain to different encryption methodologies. A transposition cipher rearranges the letters of the plaintext without substituting them, while public key encryption uses a pair of keys (public and private) for security, and block encryption encrypts data in fixed-size blocks. The unique mechanics of the Enigma secure it through a substitution cipher framework, making it distinct from these alternative methods.