[Cryptography] The Trust Problem

[Tom Ritter]

We've reached the point where most people are trying to build apps
that directly tackle a 'hard problem'.  Hard problem is subjective of
course, but we can probably roughly agree on them.

Mustbin syncs data between devices - the 'hard problem' there is how
do you get a key on device 1 & 2 without giving it to Mustbin.  Based
on their blog post, they would have to encrypt a key using your
password and using your answers to security questions, and on device
two you login and can decrypt that key.  That solves the 'hard
problem' of sharing keys and moves the onus on the user to have a
secure password and answers to secret questions.

But they _also_ say that you can share photos with other people.  Now
we have another hard problem! Assuming the photo is even encrypted,
how do I get the key for the other person, and how do I know that key
is really their key and it's not the central service impersonating
them? This is the same problem iMessage, Silent Circle, Wickr, and a
host of others have.   And although I've never used the latter two - I
bet none of them attempt to address or solve it.

So to answer the question - I determine, in a large part, whether or
not to trust someone by identifying the 'hard problem' they're working
against, and if they address is plainly and simply, explaining how
they traded against usability and simplicity and security.  Mustbin
does not seem to meet these criteria.

-tom

On 20 May 2014 10:50, Jerry Leichter <leichter at lrw.com> wrote:
> So I ran across the Mustbin iOS app (http://mustbin.com).  Cool, simple idea:  Take pictures of important documents, the contents of your wallet, etc.; organize them in "bins"; upload and sync to all your devices.  The data is encrypted with "military grade security" (they actually specify RSA - no key length mentioned - and AES-256); they don't have access to your decryption keys.    "Our technology has been reviewed and verified by one of the best firms in the security analysis business."  (This is mainly from a blog entry:  http://mustbin.com/blog/read/mustbin-security-military-grade-certified.)
>
> So ... should I believe their stuff is secure?  Let's suppose they really are good guys doing their best to provide a secure service:  What could they do to help me trust them with such sensitive information?
>
> With security, we're now at a level well beyond technical questions about algorithms and key lengths.  What should you demand to be convinced that you can use some software safely?  What should someone offering secure software put out there that would help you reach a decision?
>
> The facile answer is "only use OSS" - like OpenSSL, home of Heartbleed.  :-( (Actually, Mustbin uses OpenSSL - they have another blog entry about what affect Heartbleed had on them.)
>
> Openness is certainly *part of* the answer.  I'd find Mustbin's comments much more convincing it they named that "best firm" *and published their report* so I could judge what was actually examined.  But it's not the whole story.
>
> Apple's recent white paper on iOS security http://images.apple.com/ipad/business/docs/iOS_Security_Feb14.pdf may not be perfect - what is? - but it's certainly way beyond what you get with most products, which basically say "We're experts, trust us."
>
>                                                         -- Jerry
>
>
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