Going down the procedure I see down at "The Bigram Table" it gets interesting. For a start it states that we need to use trigram and some dummy letters where added in the beginning of the first and end of the second one. With that info the interesting part is that the first two groups need to be stacked on top of each other YSNS LPNO
With that we get 4 Bigrams to decode YL SP NN & SO Looking at the bigram table we then get YL=RM SP=XF NN=IA SO=DW Now flatten out that and we get RMXF IADW
Now over to the Doppelbuchstabentauschtafel B and look at
Drop the first letter of the first group but keep the last letter of the second group since we have a M4 and we have Schlüsselkenngruppe ( key indicator group): MXF Verfahrenkenngruppe (encryption indicator group) IADW
Setup the enigma sim at www.enigmaworldcodegroup.com/#!encypting-kriegsmarine/c1xi2 the way Arduino Enigma extracted Model:M4 UKW:B Rotors:Beta VII I II Ringstellung: A D J N or 01 04 10 14 Plugboard: NQ DP YT SU CV JG EI BR OH FA
set wheels to starting position ("grundstellung"), type second trigram, get new starting position, set all 4 rotors to that setting. Grundstellung: XAJO IADW => jgob New grundstellung -> JGOB
and it is still bad decrypt Did try using just 3 letters but no luck
Took another stab at this After reading the procedure and what Arduino Enigma wrote a few more times (and less late) I see that I did resolve the bigram wrong, the splitup and restacking is done in reverse order when doing decrypting.
So I did same as Arduino Enigma but using 4 letters instead of 3 so XGTB decrypts to WASW
That's the solution, thanks a lot Lpaseen and Arduino! I read about Enigma and Kriegsmarine for a while and I understood the mechanics, but I couldn't figure out when to start using the plugboard for example. Do I use the plugboard when decoding the first bigrams already, or only when decoding the final message? Same thing went for ring settings and the wheels: I didn't understand whether to start out in the day setting for day 15, or only start using those settings after solving the first bigrams. So thanks again for also showing the steps to get there
When doing enigma encryption/decryption you need to have most things done before starting. Plugboard is part of the key and setup first thing in the morning, would be way to painful to have to redo that for every message (remember, we talking 10 physical wires). As for rings and wheels - same thing plus that if you don't set them before a real enigma wouldn't have anything at all there (and again painful to switch around any kind of default in the middle of the message). For me the the biggest challenge here was to get the bigram properly lined up and decrypted, knew about it but this was the first time I done that.