# Question

**Design and implement a privacy-preserving medical records management system with the following requirements:**

1. **System Architecture**: Create a client-server architecture where:
   - Doctors (clients) can register, submit medical reports, and log expenses
   - An auditor can verify reports and perform aggregate analysis without decrypting individual records

2. **Cryptographic Requirements**:
   - Use **RSA** for encrypting sensitive AES keys during report transmission
   - Use **ElGamal** for digitally signing reports with timestamps
   - Use **Paillier homomorphic encryption** for department information to enable privacy-preserving keyword searches
   - Use **RSA-based homomorphic encryption** (exponent trick) to allow summation of encrypted expenses without decryption
   - Use **AES-256** for authenticated encryption of report contents

3. **Functional Features**:
   - Doctor registration with encrypted department information
   - Secure report submission with signature verification
   - Privacy-preserving expense tracking where individual amounts remain encrypted
   - Auditor capabilities to:
     - Search doctors by department keyword without decrypting data
     - Sum all expenses across doctors or per-doctor while maintaining encryption
     - Verify report authenticity and timestamps
     - List and audit all stored records

4. **Implementation Details**:
   - Implement server-side state management with persistent JSON storage
   - Implement client-side key generation and cryptographic operations
   - Use socket-based TCP communication with JSON serialization
   - Handle concurrent connections with thread-safe operations
   - Support multiple independent doctor clients connecting to a single server

**Required**: Provide both server and client implementations with proper key management, error handling, and an interactive menu system for all user roles.

# Answers

- Client - [Code](https://git.aadit.cc/aadit/MIT-Curricular/src/branch/main/IS/Lab/Eval-Endsem/client.py)
- Server - [Code](https://git.aadit.cc/aadit/MIT-Curricular/src/branch/main/IS/Lab/Eval-Endsem/server.py)