I've been trying to get it as well, however I've saved motes of light hoping for a exotic chest engram from Xur (has he had the chest engram for sale lately? I feel like I haven't seen it for sale). He's been selling exotic helmet engrams though. Just hoping for HOPF or Starfire protocol at least from the exotic chest engram when he sells it. How many engrams have you decrypted without HOPF?