TWAB says "they will drop from playing any of your favorite activities across the solar system" of course after talking to Spider, and completing that quest. Afterwards, wear a mask, and complete activities across the system. How often do they drop? I just completed 4 strikes, with a mask on, and didn't get a single Cipher.
-
I have literally done 3 crucible matches, 7 moon patrols, three strikes, a couple heroic events and three gambit matches and haven't gotten one cipher decoder. I've only gotten the first one in the quest.