[messaging] Two-party consensual file access

Max Skibinsky max at skibinsky.com
Thu Mar 28 20:28:41 PDT 2019

As Ben mentioned, who encrypts the file is crucial differentiator. Either
you can accept one party knows contents of the file beforehand, or you need
to solve quite different challenge first — how file content is created in
the encrypted form without either party ever having full plaintext.

If it is acceptable that one party does encryption as the first step, then
indeed *n/n* Shamir schema is the way to go. We did a lot of thinking how
an application for Shamir split/storage/restore of high-value files should
work, you can take a look at our whitepaper
<https://vault12.com/technology/> , section 4 outlines some practical
storage scenarios.

- Max
blog <http://skibinsky.com> | linkedin <http://bit.ly/max-li>

On Thu, Mar 28, 2019 at 5:26 PM david wong <davidwong.crypto at gmail.com>

> Shamir sharing scheme to split the key in two. Send your half to the other
> one to let them decrypt it.

> On Mar 28, 2019, at 3:36 PM, Ben Laurie <ben at links.org> wrote:
> Who encrypted this file?
> On Thu, 28 Mar 2019 at 13:48, B Da Bahia <bidabahia at gmail.com> wrote:
>> Hello list,
>> I'm looking for a cryptographic algorithm to solve the following problem:
>> Alice and Bob (untrusting partners) want to cooperate to open an
>> encrypted file located at either one's computer. No party should be able to
>> open it without the other party's consent. No trusted third parties are
>> allowed to intervene in the protocol.
>> Could anyone provide useful references to explore?
>> thanks in advance!
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