shamir-lbodlev 0.1.2

Simple implementation of Shamir's Secret Sharing scheme

🔐 Shamir Secret Sharing — Python Implementation

A clean and minimal Python implementation of Shamir’s Secret Sharing Scheme (SSS) —
a cryptographic method to divide a secret into multiple parts (shares),
so that only a threshold number of them are required to reconstruct the original secret.

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🚀 Features

• Pure Python, minimal dependencies (pycryptodome)
• Generate any number of secure shares
• Reconstruct the secret using only the threshold shares
• Human-readable export/import formats (JSON + Base64)
• Easy-to-use API for both sharing and recovery

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📦 Installation

Install the package from PyPI:

pip install shamir-lbodlev

Importing the Package

from Shamir import Shamir

Quick Start Example

1. Split a Secret into Shares

from Shamir import Shamir

# Create shares for a secret message
shamir = Shamir(secret=b"My top secret message", n=5, k=3)
# total of 5 shares with 3 threshold(minimal amount of shares to reconstruct the message)

# Export parameters and shares
shamir.export_public("public.json")
shamir.export_shares("share{}.dat")  # Creates share1.dat, share2.dat, ...

This produces:

• public.json → contains public data (prime number p, total shares n, threshold k)
• share1.dat, share2.dat, ... → Base64-encoded shares

2. Reconstruct the Secret

from Shamir import Shamir

# Initialize recovery instance
recoverer = Shamir()
recoverer.load_public("public.json")

# Load any 3 of the generated shares
recoverer.load_shares("share{}.dat", indexes=[1, 3, 5])

# Recover the secret
secret = recoverer.recover()
print(secret.decode())

API Reference

class Shamir(secret: bytes | None = None, n: int | None = None, k: int | None = None) Initializes a new instance of the Shamir scheme.

Parameter	Type	Description
secret	bytes, optional	The secret to share (as bytes).
n	int, optional	Total number of shares to generate.
k	int, optional	Minimum number of shares needed to reconstruct the secret.

Raises ValueError if k > n.

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recover() -> bytes

Reconstructs and returns the shared secret (in bytes). Must be called after loading public parameters and shares.

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export_public(filename: str) -> None

Exports public data (p, n, k) in JSON format. Required for secret reconstruction.

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shamir.export_public("public.json")

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export_shares(template: str) -> None

Exports all generated shares using a filename template. The share index is automatically inserted into the template.

shamir.export_shares("share{}.dat")
# Produces: share1.dat, share2.dat, share3.dat, ...

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load_public(filename: str) -> None Loads the public parameters from a previously exported JSON file.

shamir.load_public("public.json")

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load_shares(template: str, indexes: list[int]) -> None

Loads share files according to a template and list of indexes. If more than k shares are given, only the first k are used.

shamir.load_shares("share{}.dat", indexes=[1, 2, 5])

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Internal Methods

The following methods are used internally and should not be called directly:

• __generate_coefs()
• __generate_shares()
• __generate_random_point()

How It Works

1. The secret (bytes) is converted into a large integer.
2. A random polynomial of degree k-1 is generated in a finite field defined by a large prime.
3. Each share corresponds to a point (x, y) on that polynomial.
4. Reconstruction uses Lagrange interpolation modulo the same prime to recover the constant term — the original secret.

Author

Laurentiu Bodlev 📍 Cahul, Republic of Moldova 💡 Passionate about cryptography, networking, and distributed systems. 🌐 GitHub: https://github.com/lbodlev888

License

This project is licensed under the MIT License — see the LICENSE file for details.