Encrypted File Transfer Platform with Digital Signatures

Introduction

The Secure File Sharing System is a Python-based application that combines network programming and modern cryptography to enable confidential, authenticated file transfers over untrusted networks.

The system demonstrates how to integrate:

• Low-level socket programming for peer-to-peer and client-server communication
• Hybrid cryptography (RSA for key exchange, AES for data encryption, RSA/DSA for digital signatures)
• Concurrent server design using threading and SQLite for scalable session and metadata management
• Custom security protocols for key distribution, file encryption, and integrity verification

This project goes beyond a simple file transfer utility, it illustrates how secure communication systems are engineered from the ground up. It is intended both as a practical tool and as a learning resource for topics in secure networking, distributed systems, and applied cryptography.

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Features

• Peer-to-peer tamper-proof file transfer over TCP sockets
• Live download progress bar
• Supports files of any size
• Secure hybrid cryptography (RSA + AES)
• Digital signatures for authenticity and integrity
• Concurrent authoritative indexing server with SQLite backend
• Custom socket protocols for encrypted file sharing

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Requirements

Download Python 3

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Dependencies:

Install the following Python dependencies:

pip install -r requirements.txt

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Installation Instructions

Clone the project to your local machine using Git.

git clone https://github.com/NickPrivate/Secure-File-Sharing

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Usage

1. Start the Indexing Server:
   • Navigate to the Server directory and run server.py

   cd src/Server
   python server.py

2. Start User 1 (sender):
   • Navigate to user1 inside the test directory and run client.py

   cd test/user1
   python client.py

3. Start User 2 (receiver):
   • Navigate to user2 inside the test directory and run client.py

   cd test/user2
   python client.py

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Project Overview

Low-Level Sockets Programming

This project involves both the indexing server and Peer-to-Peer (P2P) file transfer using Python sockets. The implementation covers:

• Establishing TCP connections
• Handling multiple connections concurrently using threading
• Custom protocols for file transfer and communication

Cryptographic Principles

The project incorporates several cryptographic techniques to ensure secure file transfer:

• Asymmetric Encryption (RSA): Used for encrypting the AES key and verifying digital signatures.
• Symmetric Encryption (AES): Used for encrypting the file contents.
• Digital Signature (RSA/DSA): Used for verifying the integrity and authenticity of the transferred files.

Concurrent Server and Database

The indexing server is designed to handle multiple peer connections simultaneously. It uses:

• SQLite for managing file metadata and user information.
• Threading for handling concurrent connections and database operations.

Secure Key Distribution and Encrypted File Transfer

The project implements a secure key distribution mechanism and encrypted file transfer protocol:

• Key Distribution: AES key and nonce are encrypted with the receiver's RSA public key.
• File Encryption: The file is encrypted using AES.
• File Transfer: Custom socket protocols are used for transmitting the encrypted file and keys.

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Security Protocols

Key Distribution

1. Initial Key Exchange:
   • Sender and receiver exchange their public RSA/DSA keys.
2. AES Key Generation:
   • The sender generates an AES key and a nonce.
3. Encryption of AES Key:
   • The AES key and nonce are encrypted using the receiver's public RSA key.
4. Transmission:
   • The encrypted AES key and nonce are sent to the receiver.
5. Decryption:
   • The receiver decrypts the AES key and nonce using their private RSA key.

File Encryption and Integrity Verification

1. File Encryption:
   • The file is encrypted using the AES key and nonce.
2. Digital Signature:
   • The sender generates an RSA/DSA signature for the encrypted file.
3. Transmission:
   • The encrypted file and signature are sent to the receiver.
4. Decryption:
   • The receiver decrypts the file using the AES key.
5. Integrity Verification:
   • The receiver verifies the file's integrity using the RSA/DSA signature. If verification fails, the download is canceled; if it succeeds, the file is downloaded.

Secure File Transfer Workflow

sequenceDiagram
    participant Sender as Sender (Server)
    participant Receiver as Receiver (Client)

    Note over Sender,Receiver: Key Exchange Phase
    Receiver->>Sender: Sends public key
    Sender->>Sender: Generate AES key
    Sender->>Receiver: Encrypt AES key with receiver's public key
    Receiver->>Receiver: Decrypt AES key with private key
    Note over Sender,Receiver: AES key securely exchanged

    Note over Sender,Receiver: File Transfer Phase
    Receiver->>Sender: "Ready for file"
    Sender->>Sender: Encrypt file with AES key
    Sender->>Receiver: Send encrypted file
    Receiver->>Receiver: Decrypt file using AES key
    Receiver->>Sender: "Success"
    Sender->>Receiver: End communication

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Contributors

• Nick Goulart - Creator and maintainer

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License

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