[Cryptography] Secret sharing for family members

The Doctor [412/724/301/703/415/510] drwho at virtadpt.net
Fri Oct 16 13:23:42 EDT 2020

‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
On Friday, October 16, 2020 2:45 AM, Jerry Leichter <leichter at lrw.com> wrote:

> I don't know of any stock program to do this kind of secret splitting and recombining,
> but the algorithms are simple enough. You could include a listing of such a program on
> the sheet of paper just in case the program itself isn't readily available years from
> now. I'd suggest FORTRAN as it's likely to survive us all. :-)

Saving out estate information on greenbar paper with a dot matrix printer... classy.
I like it.

I dislike the idea of a contingency plan that uses lots of tricky moving parts like this,
but on the other hand Shamir's secret sharing is also the ideal (if not close to the ideal)
tool to solve this kind of problem.

Shamir seems like the kind of thing that /somebody/ has to have put together in Javascript
and thrown onto a Github page someplace.  A little poking around revealed this one
(https://github.com/iancoleman/shamir).  I think the scenario here would be:

* You throw up a copy of this on your website, probably unlinked from any other page.
* You use it to do an m-of-n split of the core secret (password to the credential database,
  formula for your disappearing/reappearing ink, whatever).
* On another system, you reassemble several combinations of the m-of-n secrets to test that
  they can be used to reconstitute the core secret successfully.
* You get your /n/ friends and family members together, and each one writes down /personally/
  (this helps solve the "I can't read your handwriting" problem) their share of the secret.
  Preferably more than once, so they can be stored in multiple locations (LOCKSS).

There are probably more ways that this procedure can be hardened, but off the cuff it seems
like a good place to start.

The Doctor [412/724/301/703/415/510]
WWW: https://drwho.virtadpt.net/
The old world is dying, and the new world struggles to be born. Now is the time of monsters.

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