Challenge M-209 - Bonus

M-209 Challenge

M-209 homepage


If you have enjoyed some of the problems in this challenge you can solve more. This page lists several new problems. Some are very easy, others are difficult even very difficult. But most of them are easier than ones you can find in my Challenge.

If you solve any problems you don't win any medals or rewards. But if you want, you can email me and I'll add your name to the solver list of each bonus.

Good luck!

The longuest Day (Bonus 22)

The 22nd bonus is a bit special. I am very proud to have created it. Indeed, it contains all the messages exchanged in a day within a division (about 80 messages). The messages and procedures are very realistic. The methods you can use to solve it probably require a computer but were known of German cryptanalysts. In fact I have no merit. I copied the Toby's problem "Prelude of War".

The ideal challenge

When I created my challenge, I made some mistakes:

  • It lacked some types of specific problems about deciphering the M-209.
  • Missing several simple exercises to solve.
  • I created messages not realistic because I didn't know the procedures used by the Allies to create and send encrypted messages.

It is the reason why, in the "Bonus" section, I added new problems: simple ones and M-209 specific. Here is the ideal resolution order (from easier to harder), where problems of challenges and bonuses are mixed:

  • Problems and Bonus very easy or easy to solve.
    They only require the use of a pencil and paper. A computer is not required.
    Registration, Bonus 1, Bonus 7, Bonus 10, Bonus 13, Bonus 17,
    Problem 1, Problem 2, Problem 3, Bonus 4, Bonus 2, Problem 5,
    Bonus 19, Problem 4, Problem 6, Bonus 20, Bonus 8, Bonus 24.
  • Problems and Bonus medium or difficult to solve.
    You can use only a pencil and paper but a computer is very useful.
    Problem 8, Bonus 18, Problem 9, Bonus 23, Bonus 16, Bonus 12,
    Bonus 9, Problem 11, Bonus 14, Problem 7, Bonus 21, Bonus 27,
    Bonus 28.
  • Problems and bonus very difficult or very hard to solve.
    The use of a computer is necessary.
    Bonus 22, Bonus 6, Problem 10, Bonus 5, Bonus 3, Bonus 11,
    Bonus 15, Bonus 25, Bonus 26.
  • The last problem (the 12th) may not be solvable ... but it was sovled!

Now I know much better the M-209 and all associated procedures ( handling messages, format of key list, message preparation, drafting, ...). If I create new bonus puzzles, I'll use these new knowledge (Bonus 20, ...).

You can use German methods

During World War II, the German cryptanalysts used several methods to solve Americans messages ciphered by M-209.

Some bonuses and problems illustrate the methods used by the Germans. Can you imitate them?

  • Capture of keys: Registration, Bonus 23
  • Messages in depths: Problem 4, Bonus 8, Problem 6, Problem 9
  • Plain known, very short messages: Bonus 12, Bonus 14
  • Probable word: Bonus 2
  • The same indicator except the double letter (special depth): Bonus 20
  • Stagger (special depth): Bonus 18
  • Absolute setting: Bonus 16
  • The same message ciphered twice with an error in the indicator: Bonus 21
  • Find the position of superpostion: Problem 11, Bonus 22
  • Re-encodment: Bonus 23 (between two M-209 networks), Problem 8 (between two crypto-systems: M-209 and M-94).