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Comment by jlgreco | Hacker News Reader

That scenario is what "offline" is for. That soldier could call up his mum and ask her to read off the link over the phone. There is no way that anything but an utterly game-changing surveillance and censorship system is going to MiTM that in time. Or he could give some local kid a candy bar to look it up at an internet cafe, or hold onto the data until more alternative communication channels open up for him. If this soldier's communication is blacked out to the point that he cannot ask anyone else to verify the link using an internet connection other than his own, then it probably isn't safe for him to be attempting whatever it is that he is doing in the first place.

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It's not blacked out. It's subtly and near-undetectably changed. Who says the soldier is tech-savvy enough to know to talk on an alternate secure backchannel because s/he can't trust the same Internet that has fantasy football and funny videos on YouTube?

Let's reduce this even further. The New Yorker has put up a webpage saying,"Send your secrets here!" Pretend they put up a phone number instead. 1-800-231-2142. The military phone switching system can either automatically redirect calls to that number to a switchboard of impersonators, or they could change the number to one they already have, so that they can also capture military assets using personal phones, mobiles, etc.

The New Yorker page does not give any information about "offline" validation. They give a pointer to a supposedly secure dropbox. That dropbox may actually be secure, but there are a number of ways to subvert it.

Any information that they gave about offline validation could just be stripped out though! What exactly are you proposing that they do that could not be subverted by the very things you are concerned about?

Offline verification would work, but if we are assuming extensive MiTMing and meatspace impersonation then offline verification is just something the whistleblower needs to figure out themselves.

You're extrapolating things I haven't said. It is well known that signal interception (and communications interception in general) has been a tool used by the military and the government for as long as any of the above have existed.[1]

"offline verification is just something the whistleblower needs to figure out themselves."

You are seeing the point, albeit as if through a glass, darkly. The New Yorker has not advised anyone of this need, nor have they communicated the additional safeguards one much take, proportional to the risk of interception and identification.

[1] http://en.wikipedia.org/wiki/ECHELON, https://www.eff.org/cases/nsa-multi-district-litigation, black ops, http://en.wikipedia.org/wiki/File:Aldrich_Ames_mailbox.jpg, http://web.archive.org/web/20060210092316/http://www.liberty..., http://books.google.com/books?id=mAR0GI5ggf8C&pg=PA62#v=..., http://www.archives.gov/research/holocaust/finding-aid/civil..., http://www.britannica.com/EBchecked/topic/635080/Sir-Francis..., &c.

In cases where offline communication would catch tampering, why would the New Yorker's advisement to use offline communication go through untampered?

You seem to be misunderstanding me. I think that there is value to offline communication with trusted but unanticipated 3rd parties, but I do not think that there is value to the New Yorker pointing this out.

If the whole thing is legit and they made a page about it, they should notice when they lose control over how that page is displayed in various locations. It could be acceptance tested via many proxies. Maybe a counter-interference phishing bot could send emails and fills forms to make sure they go through correctly. Self-safety audits like that could be built into Tor itself so that these "red blood cell"-like bots are themselves distributed processes (maybe only as pre-installed plugins in the full featured Tor browsers).

Unless the Tor site is a honeypot. Hmm a bit odd they don't have any offline validation instructions on there ;)

I guess the downloaded source code could always be diffed with a known legit copy, if it was compiled on a trusted machine.

By the way, how does one determine the right amount of paranoia?

The first response to this thread helped me understand the issues better: http://www.wilderssecurity.com/showthread.php?t=228869

If we assume the adversary controls all network traffic as well as all Tor exit nodes but the would-be whistleblowers and the New Yorker's systems are out of bounds, a valid solution is still possible:

- The plainly accessible page needs to be served through HTTPS, preferably secured with an EV-SSL cert. The adversary would then be unable to read or change any of the site's content; i.e. the whistleblower receives the correct onion link.

- The onion site, too, needs to be served through HTTPS. All traffic passing through Tor is encrypted and thus out of reach of the adversary; traffic leaving Tor for the destination site is encrypted yet again and out of reach as well.

Since few CAs would accept to sign certificates for a .onion domain, that site might have to use a self-signed certificate. This solution remains secure for as long as that certificate's fingerprint is posted on the first page and the whistleblower cross-checks the expected and actual fingerprint values.

This should provide reasonable security for the exchanged message contents. In all likelihood, though, the adversary would be able to prove the whistleblower did communicate with the New Yorker.

One high-risk aspect of this whole deal is a possible breach at any of the whistleblower's trusted CAs. Convergence would be of some help there -- assuming the notaries involved are behaving correctly.

*edit: Sorry, I had a bit of a brain fart right there. Traffic to and from the hidden service (the .onion domain) never leave the Tor network and thus remain secure. Skip the second bullet point.

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