Key safety vs Backup : History of a bad day (key-restoration problem)

Robert J. Hansen rjh at
Sun Oct 28 12:21:22 CET 2007

Atom Smasher wrote:
> i wouldn't generally advocate a vernam cipher for encrypting messages, but 
> i think it is the best real-world-practical way to do secret sharing (at 
> least until someone builds an application that ~uses~ a real secret 
> sharing algorithm).

See _The Art of Computer Programming_, Volume 2, section 4.6.4,
"Evaluation of Polynomials".  In my copy it's on page 505; YMMV if you
have a different edition.  Knuth characterizes it as "an important and
somewhat surprising application of polynomial interpolation", as well as
"amazingly simple".

I can vouch for the "amazingly simple" part.  I volunteer at a local
elementary school and help teach their talented-and-gifted fourth
graders.  One of the first things we do each year is go over the Shamir

PGP Corporation also uses it to divide up key shares, if I recall correctly.

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