Paper-Secret

Shamir Secret Sharing on paper using gfshare.

Installation

PyPi

• https://pypi.org/project/paper-secret/

Dependencies

gfshare is required to split and merge the secret. See man gfshare for an explanation of Shamir Secret Sharing in gf(2**8).

sudo pacman -S --needed libgfshare

qrencode and imagemagick (convert) are required to create and merge QR-codes during the split process. One can set the according parameters of split_encode to False to skip this step.

sudo pacman -S --needed qrencode imagemagick

enscript and ghostscript (ps2pdf) are required to create a PDF containing the split secret in text form. One can set the according parameters of split_encode to False to skip this step.

sudo pacman -S --needed enscript ghostscript

Usage

Create a secret:

cat > secret.txt

Split the secret into 5 lines:

enpaper secret.txt

Manually delete up to 2 of the 5 lines in secret.txt_txt.txt.

Then recreate the secret:

depaper secret.txt.split-text.txt

Print the secret:

cat secret.txt.split-text.txt.merged.txt

Notes

• https://en.wikipedia.org/Shamir's_Secret_Sharing

Manually reconstructing the secret from k strings:

• For each string of the k strings
  • Create a file which name begins with part and ends with a dot and the first three characters of the string
    • For example part.112
  • Convert the 3rd to last character from base64 to binary and insert it into the file
• Execute gfcombine part.*
• The file part contains the reconstructed secret