Sung-Min Park, 47, amateur cryptographer who has been decoding messages in public noise sources—radio static, CCTV footage, ambient city audio—since 2011. He has found no messages. He considers the absence of messages informative. He maintains detailed logs and submits occasional papers to cryptography conferences that are reviewed politely and not accepted. He distrusts GPS on the grounds that he cannot verify the signal source. He uses paper maps.