OpenTestudox Client

Frontend client for a privacy-first, end-to-end encrypted messaging system powered by the OpenTestudox Protocol.

OpenTestudox Client is responsible for secure user interaction, local cryptographic operations, and device-level identity management. All encryption and decryption occur strictly on the client, ensuring that no plaintext data is ever exposed to the backend or network intermediaries.

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🚀 Getting Started

npm install
npm run dev

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🔐 Security Model

OpenTestudox follows a strict client-side trust model:

• End-to-end encryption enforced at the client layer
• No plaintext messages leave the device
• Cryptographic keys never leave the client environment
• Backend acts only as a relay, not a trusted entity

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🧠 Architecture Overview

The system is built around a cryptography-first design:

• libsodium (WebAssembly) for secure primitives
• Device-based identity system (per-device key pairs)
• Stateless backend communication
• Secure local key storage
• QR-based identity verification

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🔒 E2E Core Logic (Important)

All core encryption logic is implemented inside the E2E/ directory.

This includes:

• Identity creation and secure storage
• Identity loading and decryption
• Signed PreKey generation and rotation
• One-Time PreKey generation and consumption
• X3DH key agreement protocol
• Double Ratchet initialization and message key derivation
• HKDF-based key derivation

All of this logic is written in JavaScript using WebAssembly-backed libsodium, ensuring high-performance and secure cryptographic operations.

👉 You can study the full protocol implementation directly inside the E2E/ folder.

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🔑 Protocol Breakdown

Identity System

• Ed25519 identity keypair
• Private key encrypted locally using a user-derived storage key
• Prevents identity reset to avoid breaking trust

Reference:

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Identity Loading

• Decrypts identity using storageKey
• Validates integrity and prevents tampering
• Throws error if corrupted or wrong passphrase

Reference:

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Signed PreKeys

• X25519 keypair signed by identity key
• Rotates periodically (~30 days)
• Prevents server-side key substitution attacks

Reference:

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One-Time PreKeys (Forward Secrecy)

• Multiple X25519 keypairs generated
• Each used exactly once
• Deleted immediately after use

Reference: and

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X3DH Key Exchange

• Performs 3–4 Diffie-Hellman operations
• Verifies signed prekey authenticity
• Derives shared secret using HKDF

Reference: and

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HKDF Key Derivation

• Uses HKDF-SHA256
• Separates root keys, chain keys, and message keys
• Prevents key reuse and ensures cryptographic separation

Reference:

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Double Ratchet Initialization

• Derives sending and receiving chain keys
• Tracks message counters
• Supports replay protection and out-of-order messages

Reference:

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🔁 High-Level Flow

Generate Identity → Store Securely → Share Public Keys
        ↓
X3DH Handshake → Derive Root Key
        ↓
Initialize Double Ratchet
        ↓
Encrypt Messages → Send via Server → Decrypt Locally

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⚠️ Important Notes

• Clearing browser storage will permanently remove identity keys
• Multi-tab usage must be handled carefully to avoid identity mismatch
• Corrupted identity or wrong storageKey will break decryption

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🤝 Contributing

Pull requests are welcome. For major changes, open an issue first.

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🔐 Security Disclosure

Report vulnerabilities privately:

📧 varadmodhekar101@gmail.com

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📜 License

GNU Affero General Public License v3.0 (AGPLv3) https://www.gnu.org/licenses/agpl-3.0.html

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⚠️ Cryptography Notice

This software includes cryptographic functionality. Users are responsible for complying with local laws regarding encryption usage.