Original sentence: During World War I, inventors in several countries realized that a purely random key sequence, containing no repetitive pattern, would make a polyalphabetic substitution, in principle, unbreakable.For some three centuries, the Vigenère cipher was considered to be completely secure (le chiffre indéchiffrable—"the indecipherable cipher").In the 15th and 16th centuries, in Europe, the idea of a polyalphabetic substitution cipher was developed, among others by the French diplomat Blaise de Vigenère (1523-96).It was this repetition that allowed Babbage and Kasiski to achieve their breaks.The cryptographic key for the Vigenère cipher consists of a word or phrase that is repeated many times to cover the length of the message.The key's letters indicate which line of the Vigenère square is used to encipher each letter of the plaintext to produce the ciphertext.This led to the development, in several countries, of rotor cipher machines such as Arthur Scherbius' Enigma
Edited sentence: During World War I, inventors in several countries developed rotor cipher machines such as Arthur Scherbius' Enigma, in an attempt to suppress the repetition which had been exploited to break the Vigenère system.For some three centuries, the Vigenère cipher, which uses a repeating key to select different encryption alphabets in rotation, was considered to be completely secure (le chiffre indéchiffrable—"the indecipherable cipher").In Europe during the 15th and 16th centuries, the idea of a polyalphabetic substitution cipher was developed, among others by the French diplomat Blaise de Vigenère (1523-96)