Section 2
Polyalphabetic
Many alphabets, and the three centuries of confidence.
4 entries in Polyalphabetic
The whole register →- The table that held for three centuriesA grid of shifted alphabets with a repeating keyword defeated frequency analysis and was called indecipherable for three hundred years — until someone noticed that the keyword repeats, and that the repetition shows.
- The keyword repeatsThe flaw that was there from the beginning and took centuries to be seen.
- Running keyUsing a book instead of a word, and why that is better but still not enough.
- AutokeyLetting the message extend its own key.