Schneier on Security

Clive Robinson • July 19, 2013 10:28 AM

With regards,

Any real-world situation involves multiple adversaries, and it’s important to keep all of them in mind when designing a security system

To do that requires you to know both the drivers and motivations of all potential attackers, which is probably not practical to do.

Thus you need to consider how to make yourself safer than a $10,000 Rolex at a pick pockets convention.

The easiest way to do that is to make your major adversary want to keep you safe and sound.

The question is how?

The answer is along the lines of ask J. Edger Hoover.

History has shown that in the UK for instance –and most other first world nations– having sufficient “blackmail material” on key members of society including members of the Lords and Royal Family has worked like a charm in the past.

I’m sure there are sufficient “great and the good” in the two US houses and amongst the 400 or so US citizens that control well over half the US –and a significant proportion of the world– net worth.

The information would probably not be of ordinary crimes because they are of short lived value. Probably more to do with sex/drugs –or worse– that the politicos keep going on about (ie has high hypocracy as well as immoral value). Such information is usually considered to have a life time of a minimum of 100years past the persons death depending on how promenent the persons are in society.

Now we can assume that either Mr Snowdens employers or those he worked for know fairly accuratly what he has accessed or could have accessed during his employment. So we can be fairly certain they know what is behind his “deadman’s switch”.

As for how to implement the “still alive” system, some blog readers will know that I’ve described a way to do this as a way to control a botnet without having an identifiable control head using search engines and blogs that allow anonymous comments or those that only require what looks like a valid email address –of which there are tens of thousands– and some kind of One Time Code identifier system.

As others have noted shared secret systems can provide a high degree of autonomy as can more old fashioned systems such as Tontiens that only require solicitors at any point in the world to make work.

Clive Robinson • July 20, 2013 8:51 AM

@ mt,

The quick answer is the files are simply encrypted files placed at various points and with various people around the world.

But having identical files around of the same size is not wise as it makes them easier to find. So at the very least I would expect the files within the encrypted file to be in different orders with some kind of unique file to each encrypted file inserted in the first position and one or more files of random data making the total size bigger by +10% to +50% put prior to compression and then encryption. Also I would double chain encrypt using two different effectivly orthagonal encryption systems say a good stream cipher first and a good block cipher second using appropriate modes for each.

Now this can all be done without ever seeing the keys used so they can not be beaten or druged out of Mr Snowden. The keys should then be split into a number of shared secrets (N) that require a minimum of (M) secrets be brought together to recover the keys. Idealy M should be two thirds or more of N with N being 20 or more to limit the possibility of “others” –not the NSA/FBI who already know the file contents– “rubber hosing” the secret holders.

That’s the easy bit done.

The first hard bit is actually distributing the encrypted files and shared secrets without anyone (including Mr Snowden) being able to find out where they are or get access to them.

The second hard bit is working out a method of sending out an unforgable and unspoofable “Still Alive” message without previous ones being used to track down the secret holders. It is this part that is the most dangerous part of the whole scheam, and thus the part that needs carefull consideration and planning.

The third hard part is working out how to arange for the secrets to be brrought together safely but unstoppably to ensure that the hidden encrypted files get found and decrypted and diseminated as widely as possible.

Get any one of these three hard bits done and potentialy it’s “game over” in a very short period.

I must admit I’m still in two minds over the release of the WikiLeaks file key. That is was the journalist who wrote the book that disclosed it being very stupid or very clever…