Secret Splitter

• Turn your digital secrets into digital puzzles (literally).
• Distribute the pieces among a group of people.
• Anyone can decode the secret by collecting all the pieces back.
• But if even one piece is missing, all they have is random data.
• You then trust that group of people to only share their pieces for a good reason.
• You can add resilience by allowing for some pieces to be missing / corrupt.

Overview (wikipedia)

This module implements:

• block-wise SSS: a block-wise version of Shamir's secret sharing. Full implementation details on https://secret-splitter.com.

  Working on blocks makes the algorithm linear in the number of bytes of the secret rather than exponential.

Splitting

1. Apply a random mask to the secret
2. For each block of the mask, generate a polynomial of degree D-1
3. A piece consists of the masked secret and one point of each polynomial

Recovery

1. Collect D pieces: D polynomials for each block of the mask
2. Interpolate the points to retrieve the blocks of the mask
3. Recover the secret by re-applying the mask to the masked version

Standard piece format

A puzzle piece is a yaml serialisation of the following mapping:

# string, tells if the secret encoded is a string encoded as UTF-8 ("utf-8") or a raw stream of bytes ("none")
encoding: utf-8

# one  puzzle piece, exact format depending on the implementation
# this implementation stores a sequence of [point, value] items, one per block of the secret
# Flow-sequence format preferred to keep it on one line
puzzle piece: [[1,258],[1,3]]

# base64 representation of the result of the mask XOR the byte representation of the secret
encoded secret: YXo=

# name of the algorithm used for splitting
algorithm: block-wise SSS

# different algorithms might add additional information required for recovering the secret.

Installation

• Using PyPi

  python3 -m pip install secret-splitter

• From source

  git clone https://git.sr.ht/~retzoh/secret-splitter-py && cd secret-splitter-py && python3 -m pip install .

Usage

• Command line

  echo "secret" | python3 -m secret_splitter split 3 2 --stdin | python3 -m secret_splitter solve

  See python3 -m secret_splitter --help for all options.

• Python script

  >>> from secret_splitter import split, solve
  >>> pieces = split('secret', 3, 2)
  >>> secret = solve(pieces)
  

Contibute

Contributions of new algorithms are welcome as long as they pass the test & lint suite.

To add a new algorithm, create src/secret_splitter/algorithm.py and add it to ALGORITHMS in src/secret_splitter/secret_splitter.py.

Install redo and run redo from the root folder to run the tests.