← Secret Writing · Lesson 3 of 3
Longer keys
A shift cipher fails because every letter is moved the same way. In the 1500s, codes used a keyword instead: each letter of the message is shifted by a different amount, given by the next letter of the keyword.
Now E is not always coded as the same letter, so simple counting stops working. Modern codes take this idea much further, which is why a longer key is generally harder to break.
Why is a keyword cipher harder to crack than a shift cipher?
A lesson is kept once you've answered the question and written at least 8 words. Nobody grades it; it stays on this device.