📦 Shamir File Splitter

This utility takes an input file (binary or text), base64 encodes it, chunks it based on key strength derived from threshold k, and applies Shamir's Secret Sharing (SSS) to generate n shares per chunk.

✅ How it Works

1. Input: Any file placed inside input/
2. Encoding: The file is base64 encoded and stored in processed/
3. Chunking: The base64 string is split into chunks based on k key size
4. Sharing: Each chunk is run through SSS to generate n shares
5. Output: Shares are written into folders output/1/ to output/n/

📦 Installation

git clone https://github.com/KathiravanMuthaiah/shamir-file-splitter.git
cd shamir-file-splitter
mvn package

🚀 Usage

mvn clean compile
java -cp target/classes com.mikcore.shamir.ShamirEncrypt <filename with path> <k> <n>
java -cp target/classes com.mikcore.shamir.ShamirEncrypt ./input/sampleinput.txt 256 3 5

Example:

java -cp target/classes com.mikcore.shamir.ShamirDecrypt <decrypt folder> <k>
java -cp target/classes com.mikcore.shamir.ShamirDecrypt ./decrypt 3

This will:

• Use a key strength of 256 (from k=3)
• Generate 5 shares per chunk with threshold 3
• Output files in output/1/, output/2/, ..., output/5/

📂 Output Structure

output/
├── 1/
│   ├── secret.jpg_g1_n1.txt
│   ├── secret.jpg_g2_n1.txt
│   └── ...
├── 2/
├── ...

📁 Processed Files

Base64 and chunked segments are saved in processed/ for learning and verification.

Sample Encryption output

Base64 saved: processed/sampleinput.txt_base64.txt Chunk size bytes: 32 Total Chunks : 1 chunkSizeBytes : 32 Choosing simple path with keysize:2048 Sectre:1396797245 processed/sampleinput.txt_g1.txt Chunk 1 uses prime of 2048 bits. All secure shares written to output folders.

Sample Decryption output

Sectre:1396797245 decrypt/sampleinput.txt_g1.txt reconstructedsampleinput.txt_chunk1:SAo= ✅ Reconstructed chunk: sampleinput.txt_chunk1 using 3 shares. Base64 saved: reconstructed/sampleinput.txt_chunk1.b64

=== Reconstruction Complete === Output File: reconstructed/reconstructed_sampleinput.txt Original Hash: d98c786cff70da9d10a2c49cf9d849025d3669b95dd56cc7c27c1ebf4cbabc2c Reconstructed Hash: d98c786cff70da9d10a2c49cf9d849025d3669b95dd56cc7c27c1ebf4cbabc2c ✅ Integrity verified successfully!

📖 Resources

Mathematical Foundation of SSS

Polynomial & Lagrange Interpolation

🏷️ Tags

Java · Cryptography · Shamir's Secret Sharing · File Splitting · College Project

---

📜 License

This project is licensed under the MIT License – free to use for learning and educational purposes.