Millionero
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March 02, 2019, 06:06:09 AM
Merited by vapourminer (1), Hueristic (1), Saint-loup (1), d_eddie (1)

No need to pay ripoff prices.
Using simple combinatorics you can set up (for example) a three-of-five secret sharing scheme.
Divide a long random number (your entropy*) into ten concatenated segments Seg(1), Seg(2)... Seg(10).  Assign each segment to a row in this table.  Each row has three red blocks.  Give Seg(i) of the rand to each person who has a red square in row(i).
Any three persons out of the five can put their shares together and recreate the entire rand.

Note that for a two-of-five secret sharing scheme, you would need four red blocks in each row, the combinatoric "5 choose 4" which has five rows.
A four-of-five secret sharing scheme would require two red squares in each row.  5 choose 2 has ten rows.
*Since a bitcoin address privkey is based on a 256 bit random number, you could simply use a 256 bit rand and create a bitcoin privkey directly from that.  In that case, each segment of the key would have 25 or 26 bits, which might not be enough security for you.  To increase security, you could use a 1000 bit rand so that each segment has 100 bits.  Then derive the privkey from the 1000 bit number, perhaps by simply hashing it down to 256 bits using sha256sum (the way bitaddress.org does it).