[Cryptography] Secret sharing for family members

Jerry Leichter leichter at lrw.com
Fri Oct 16 05:45:40 EDT 2020

>>> Store an offline copy (such as a CD) of the password manager file
>>> holding all those digital estates in a safe....
> Now it is easier with a USB "disk" or SD card and an essential printed HOWTO, 
> all held in a safe deposit box along with the HOWTO in custody elsewhere, such 
> as wherever a copy of your will is retained.  Refresh appropriately from 
> time-to-time.
Neither writable CD's nor SSD media are good for long-term storage.  Both will deteriorate and become unreadable in a fairly small number of years.  Given the underlying nature of the task here - making data available to heirs - the limits on the lifetime of the media is significant.

Others have suggested, for other reasons, going with paper.  Paper, if reasonably carefully stored, should remain readable for many decades.  Go with acid-free paper and store it in a safety deposit box and it should be good for many centuries.

I wouldn't go fancy with QR codes - a technology that might fade.  Just use a couple of randomly chosen worss - easy for anyone to type, easy to get enough entropy for a portion of a key.

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. :-)

                                                        -- Jerry

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