Hi,
Just looked at your savefile (I had the same doubt some days ago, and asked in discord channel), and you still miss some crucial clues to unlock the alien decryption key.
Hint: continue exploring the hybrid arc...
Detailed (spoiler):
looks like you miss a live human clone to capture (hybrid mission), and to discover something interesting in the secret hybrid clinic missions. Once you get both you can unlock the other alien infiltration methods in research.