For those who are still interested in cracking the Floppy disk for Operation Chaos, you need to get the three pieces of evidence.
1st piece of evidence is found on the mission Nowhere Left To Run.
Whilst your interrogating Qasim make sure your don't pick any of the [Throw] options in the dialog. He will then give you the first piece of evidence.
2nd piece of evidence is found on the mission Brick In The Wall
. A little bit into the mission you will meet an informant at the bar and she'll give you a side objective to rescue or silence Lukas Richter. Up to you if you want to free him or not. The evidence will be on a table in the room where you find him.
3rd piece of evidence is found on the mission Redlight, Greenlight
. You need to photograph all six maps that can be all around the mission. I used this to find them all. Credit Eurogamer
Once you've got all three pieces of evidence you are ready to start cracking the floppy disk.
Look at the Newspaper
evidence and write down all the letters that are in red. Then look at the Numbers Station Broadcast
evidence and look at all the cities. You then need to work out what your city is by trying to match the red letters to a city that's on the Number's Station Broadcast.
For example my newspaper had nahele which in turn spells Helena.
Once you've found your city write down the four numbers that are next to it. My four numbers were 7044. I would also advise writing down all the cities in the list for the next section.
You are now ready to start decrypting the floppy disk. Click on Decrypt Floppy Disk. The code will be the four numbers that are next to the city that you had in the newspaper. The passphrase will be a random city that's in the Number's Station Broadcast. If you get Access Denied you didn't pick the right city. Type in the same code and different city to try again. When you type in the right city you will get the message Access Granted.
Hope this helped, recently helped a friend do it on PS4 via share play.
I was struggling to understand the Coded Message evidence.