CryptMail

A Chrome Extension for sending and receiving multi-layer encrypted emails through Gmail.

How It Works

1. Key Exchange – You and your contact agree on a shared passphrase (out of band).
2. Encrypt – When composing in Gmail, CryptMail encrypts your message with 100 rounds of AES-256-GCM, each round using a fresh random IV and salt derived from the shared passphrase via PBKDF2.
3. Send – The extension replaces the plaintext in Gmail's compose field with the encrypted envelope and sends it.
4. Decrypt – When you open a received email, the extension automatically detects the encrypted envelope, decrypts it using the stored key for that sender, and displays the plaintext.

Installation

1. Clone or download this repository.
2. Open chrome://extensions/ in Chrome.
3. Enable Developer mode (toggle in the top right).
4. Click Load unpacked and select the repository folder.
5. The CryptMail icon appears in your toolbar.

Usage

Add a Contact Key

1. Click the CryptMail icon in the toolbar.
2. Enter the contact's email address and the shared passphrase.
3. Click Save Key.

Send an Encrypted Email

1. Compose a new email in Gmail.
2. Write your message normally.
3. Click the 🔒 Encrypt & Send button that appears in the compose toolbar.
4. The extension encrypts the message and sends it.

Read an Encrypted Email

When you open an email containing a CryptMail envelope, the extension automatically decrypts and displays the plaintext (if you have the sender's key stored). A toggle button lets you switch between the decrypted and encrypted views.

Encryption Details

• Algorithm: AES-256-GCM
• Key Derivation: PBKDF2 with SHA-256, 600,000 iterations
• Rounds: 100 (configurable) layers of encryption
• Randomness: Each round uses a unique random 16-byte salt and 12-byte IV

Development

Run Tests

npm test

Project Structure

├── manifest.json          # Chrome Extension manifest (MV3)
├── src/
│   ├── crypto.js          # Multi-layer AES-GCM encryption/decryption
│   ├── keystore.js        # Per-contact key storage (chrome.storage)
│   ├── content.js         # Gmail content script (UI integration)
│   ├── content.css        # Content script styles
│   ├── popup.html         # Extension popup UI
│   └── popup.js           # Popup logic
├── icons/                 # Extension icons
└── test/
    └── crypto.test.js     # Crypto module unit tests

License

GNU General Public License v3.0 – see LICENSE for details.