It's a sha256. It could definitely be a checksum for a file, although hashes like this is not an uncommon way to generate a large, unique password from a small

It's a sha256. It could definitely be a checksum for a file, although hashes like this is not an uncommon way to generate a large, unique password from a small string or phrase. Most passwords can be easily brute forced. A 64-byte string is a lot harder to brute force. I actually think a sha2 is a little bit weird for a file checksum. I would expect md5 or a regular sha1. Or simply send the file with a gpg signature to validate the integrity (provided he still has some sort of trusted public key). Either way any off-the-shelf Mac can generate and verify these checksums. My guess is that Snowden is starting to feel homesick and wants to start the process of returning to the USA. That's why he said "It's time." The tweet could be a password or a code to something but I don't think it's meant to embarrass or expose anybody.