M209 Challenge
M209 homepage

Presentation
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 M209.

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 M209 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 M209 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 M209.
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

Reencodment: Bonus 23 (between two M209 networks), Problem 8
(between two cryptosystems: M209 and M94).
