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/venv
/.idea
**/__pycache__
/build
/dist
**/*.egg-info

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<component name="ProjectRunConfigurationManager">
<configuration default="false" name="depaper" type="PythonConfigurationType" factoryName="Python" nameIsGenerated="true">
<module name="paper-secret" />
<option name="INTERPRETER_OPTIONS" value="" />
<option name="PARENT_ENVS" value="true" />
<envs>
<env name="PYTHONUNBUFFERED" value="1" />
</envs>
<option name="SDK_HOME" value="$USER_HOME$/venv-310/bin/python" />
<option name="WORKING_DIRECTORY" value="$PROJECT_DIR$" />
<option name="IS_MODULE_SDK" value="false" />
<option name="ADD_CONTENT_ROOTS" value="true" />
<option name="ADD_SOURCE_ROOTS" value="true" />
<EXTENSION ID="PythonCoverageRunConfigurationExtension" runner="coverage.py" />
<option name="SCRIPT_NAME" value="$PROJECT_DIR$/src/paper_secret/depaper.py" />
<option name="PARAMETERS" value="secret.txt.split-text.txt" />
<option name="SHOW_COMMAND_LINE" value="false" />
<option name="EMULATE_TERMINAL" value="false" />
<option name="MODULE_MODE" value="false" />
<option name="REDIRECT_INPUT" value="false" />
<option name="INPUT_FILE" value="" />
<method v="2" />
</configuration>
</component>

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<component name="ProjectRunConfigurationManager">
<configuration default="false" name="enpaper" type="PythonConfigurationType" factoryName="Python" nameIsGenerated="true">
<module name="paper-secret" />
<option name="INTERPRETER_OPTIONS" value="" />
<option name="PARENT_ENVS" value="true" />
<envs>
<env name="PYTHONUNBUFFERED" value="1" />
</envs>
<option name="SDK_HOME" value="$USER_HOME$/venv-310/bin/python" />
<option name="WORKING_DIRECTORY" value="$PROJECT_DIR$" />
<option name="IS_MODULE_SDK" value="false" />
<option name="ADD_CONTENT_ROOTS" value="true" />
<option name="ADD_SOURCE_ROOTS" value="true" />
<EXTENSION ID="PythonCoverageRunConfigurationExtension" runner="coverage.py" />
<option name="SCRIPT_NAME" value="$PROJECT_DIR$/src/paper_secret/enpaper.py" />
<option name="PARAMETERS" value="secret.txt" />
<option name="SHOW_COMMAND_LINE" value="false" />
<option name="EMULATE_TERMINAL" value="false" />
<option name="MODULE_MODE" value="false" />
<option name="REDIRECT_INPUT" value="false" />
<option name="INPUT_FILE" value="" />
<method v="2" />
</configuration>
</component>

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README.md Normal file
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# Paper-Secret
Shamir Secret Sharing on paper using gfshare.
## Installation
`gfshare` is required to split and merge the secret.
See `man gfshare` for an explanation of Shamir Secret Sharing in gf(2**8).
```shell
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.
```shell
sudo pacman -S --needed qrencode imagemagick
```
`enscript` is 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.
```shell
sudo pacman -S --needed enscript
```
## Usage
Create a secret:
```shell
cat > secret.txt
```
Split the secret into 5 lines:
```shell
./enpaper.py secret.txt
```
Manually delete up to 2 of the 5 lines in `secret.txt_txt.txt`.
Then recreate the secret:
```shell
./depaper.py secret.txt.split-text.txt
```
Print the secret:
```shell
cat secret.txt.split-text.txt.merged.txt
```
## Notes
* https://en.wikipedia.org/Shamir's_Secret_Sharing

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# https://packaging.python.org/tutorials/packaging-projects/#creating-pyproject-toml
[build-system]
requires = [
"setuptools>=42",
"wheel"
]
build-backend = "setuptools.build_meta"

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; setup.cfg is the configuration file for setuptools.
; https://packaging.python.org/tutorials/packaging-projects/#configuring-metadata
[metadata]
name = paper-secret
version = 0.1.0
author = Daniel Langbein
author_email = daniel@systemli.org
description = Shamir Secret Sharing on paper using gfshare
long_description = file: README.md
long_description_content_type = text/markdown
url = https://codeberg.org/privacy1st/paper-secret
project_urls =
Bug Tracker = https://codeberg.org/privacy1st/paper-secret/issues
; https://pypi.org/classifiers/
classifiers =
Development Status :: 4 - Beta
Programming Language :: Python :: 3
License :: CC0 1.0 Universal (CC0 1.0) Public Domain Dedication
Operating System :: Unix
[options]
package_dir =
= src
packages = find:
python_requires = >=3.10
[options.packages.find]
where = src
[options.entry_points]
; https://setuptools.readthedocs.io/en/latest/userguide/entry_point.html
console_scripts=
enpaper = paper_secret.enpaper:main
depaper = paper_secret.depaper:main

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src/paper_secret/__init__.py Normal file
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src/paper_secret/depaper.py Executable file
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#!/usr/bin/env python3
# -*- coding: utf-8 -*-
import base64
import tempfile
from pathlib import Path
import sys
import paper_secret.util as util
def main():
assert len(sys.argv) == 2, 'Expected one argument'
merge_decode(Path(sys.argv[1]))
def merge_decode(src: Path) -> Path:
"""
:param src: A file with at least k non-empty lines.
:return: Path to file containing reconstructed secret.
"""
assert src.exists(), str(src)
assert src.is_file(), str(src)
content = src.read_text('UTF-8')
# All non-empty lines
lines = [line.strip() for line in content.splitlines()
if len(line.strip()) > 0]
assert len(lines) >= 2
merged = src.parent.joinpath(src.name + '.merged.txt')
assert not merged.exists()
with tempfile.TemporaryDirectory() as tmpdirname:
tmpdir = Path(tmpdirname)
parts = []
for line in lines:
assert len(line) >= 4
encoded_suffix: str
encoded_part: str
encoded_suffix, encoded_part = line[0:3], line[3:]
binary_part = base64.b64decode(encoded_part.encode('UTF-8'))
part = tmpdir.joinpath('.' + encoded_suffix)
part.write_bytes(binary_part)
parts.append(part)
command = ['gfcombine', '-o', str(merged)] + [str(part) for part in parts]
util.execute_stdin_capture(command)
return merged
if __name__ == '__main__':
main()

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#!/usr/bin/env python3
# -*- coding: utf-8 -*-
import base64
import tempfile
from pathlib import Path
import sys
import paper_secret.util as util
def main():
assert len(sys.argv) == 2, 'Expected one argument'
split_encode(Path(sys.argv[1]))
def split_encode(
secret: Path,
k: int = 3,
n: int = 5,
create_qr_codes: bool = True,
merge_qr_codes: bool = True,
create_text_pdf: bool = True
) -> list[Path]:
"""
Creates a file ending in `_txt.txt`. This file consists of n lines.
k of these n lines are enough to reconstruct the secret.
The same content is also stored in a `.pdf` file.
The lines are split up into n blocks of grouped lines.
k of these n blocks are enough to reconstruct the secret.
Each line is also available as QR-code inside a `.pdf` file.
:param secret: File containing a secret.
:param k: Threshold for recombination.
:param n: Number of shares to generate
:return: List of created files.
"""
assert secret.exists(), str(secret)
assert secret.is_file(), str(secret)
txt_file = secret.parent.joinpath(secret.name + '.split-text.txt')
qr_pdf = secret.parent.joinpath(secret.name + '.split-QR.pdf')
txt_pdf = secret.parent.joinpath(secret.name + '.split-text.pdf')
assert not txt_file.exists() and not qr_pdf.exists() and not txt_pdf.exists()
with tempfile.TemporaryDirectory() as tmpdirname:
tmpdir = Path(tmpdirname)
tmpdirfile = tmpdir.joinpath('_')
# Creates n files _.xxx
# One can reconstruct secret based on k out of n files
util.execute_stdin_capture(['gfsplit', '-n', str(k), '-m', str(n), str(secret), str(tmpdirfile)])
qrcodes = []
lines = ''
for part in tmpdir.iterdir():
binary_part = part.read_bytes()
encoded_part = base64.b64encode(binary_part).decode('UTF-8')
encoded_suffix = part.suffix[1:]
suffix_and_content = encoded_suffix + encoded_part
lines = lines + suffix_and_content + '\n'
encoded = part.parent.joinpath(part.name + '.txt')
encoded.write_text(suffix_and_content)
if create_qr_codes:
qrcode = part.parent.joinpath(part.name + '.png')
qrcodes.append(qrcode)
util.execute_stdin_capture(['qrencode', '-o', str(qrcode), '-s', '10'],
suffix_and_content.encode('UTF-8'))
txt_file.write_text(lines)
if create_text_pdf:
command = ['enscript', '-B', '--margins=24:24:', '-o', str(txt_pdf), '-f', 'Courier@12/12']
util.execute_stdin_capture(command, lines.replace('\n', '\n\n\n').encode('UTF-8'))
if create_qr_codes and merge_qr_codes:
command = ['convert'] + [str(qrcode) for qrcode in qrcodes] + [str(qr_pdf)]
util.execute_stdin_capture(command)
files = [txt_file]
if create_text_pdf:
files.append(txt_pdf)
if create_qr_codes and merge_qr_codes:
files.append(qr_pdf)
return files
if __name__ == '__main__':
main()

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#!/usr/bin/env python3
# -*- coding: utf-8 -*-
import subprocess
import sys
from pathlib import Path
def execute_stdin_capture(command: list[str], stdin: bytes = b'', cwd: Path = Path()):
"""
Executes the given `command`, passes `stdin` into it and returns its stdout.
:raises Exception: In case of non-zero exit code.
This exception includes the exit_code, stdout and stderr in its message.
"""
# If a Linux shell's locale is en_GB.UTF-8, the output will be encoded to UTF-8.
encoding = 'UTF-8'
assert sys.stdout.encoding.upper() == encoding
completed = subprocess.run(
command,
capture_output=True,
cwd=cwd,
input=stdin,
)
if completed.returncode != 0:
raise Exception(
f'command: {command}\n'
f'exit_code: {completed.returncode}\n'
f'stdout: {completed.stdout}\n'
f'stderr: {completed.stderr}'
)