🔒 Aegis — Hybrid RSA/AES Secure Messages (macOS)

Aegis is a modern macOS desktop application that provides secure end-to-end message encryption using a hybrid RSA-AES design. It combines the speed of symmetric AES encryption with the robust key exchange and digital signature capabilities of RSA.

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✨ Features

• 🧠 Automatic key generation and storage using the macOS Keychain
• 🔐 Hybrid encryption (AES-GCM + RSA-OAEP)
• 🖋️ Digital signatures with RSA-PSS for message integrity
• 📎 Base64-encoded JSON envelope for easy sharing
• 💬 Clean SwiftUI interface only two buttons: Encrypt and Decrypt
• 💾 Local key management no servers, no data collection

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🧩 Requirements

• 🖥️ macOS 14.0 (Sonoma) or later
• 🧰 Optional: Homebrew for command-line installation

⚠️ Aegis is not compatible with macOS versions earlier than 14.0.

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📦 Installation

🍺 Option 1: Install via Homebrew (recommended)

You can install Aegis directly from your terminal using Homebrew:

brew tap khalidt/aegis
brew install --cask aegis

Homebrew will automatically download, verify, and place Aegis.app in your /Applications folder.

🛡️ First launch and macOS Security Note: Since Aegis is distributed outside the Mac App Store, macOS Gatekeeper may display a warning the first time you open it. Just go to System Settings → Privacy & Security → Allow Anyway, or right-click → Open to trust the app.

To update later:

brew upgrade --cask aegis

To uninstall completely:

brew uninstall --cask aegis

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💾 Option 2: Download manually

Download the latest version of Aegis from the Releases page:

1. Download the latest Aegis-vX.X.X-app.zip or Aegis-vX.X.X.dmg file.
2. Unzip it, you’ll see Aegis.app.
3. Drag it into your Applications folder.

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🧑‍💻 Option 3: Build from source in Xcode

If you’d like to build Aegis yourself:

git clone https://github.com/khalidt/Aegis.git
cd Aegis
open Aegis.xcodeproj

In Xcode:

1. Open Aegis.xcodeproj in Xcode (macOS >= 14.6).
2. Select the Device scheme.
3. Choose target “Any Mac (Apple Silicon, Intel)”.
4. Build and run (⌘R). (Go to Product → Build or Product → Run.)

Or build via Terminal:

xcodebuild -project Aegis.xcodeproj \
           -scheme Device \
           -configuration Release \
           -destination 'platform=macOS' \
           build

Your compiled app will appear under:

~/Library/Developer/Xcode/DerivedData/.../Build/Products/Release/Aegis.app

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🧩 How It Works

Encryption

1. A random 256-bit AES key is generated.
2. The plaintext is encrypted using AES-GCM.
3. The AES key is encrypted using RSA-OAEP with the recipient’s public key.
4. The ciphertext is signed using RSA-PSS with the sender’s private key.
5. The resulting Base64 JSON envelope is ready to share.

Decryption

1. The recipient decrypts the AES key with their RSA private key.
2. The AES-GCM ciphertext is decrypted to recover the plaintext.
3. The sender’s signature is verified for authenticity.

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🧮 Algorithm Summary

Purpose	Algorithm
Key generation	RSA-4096
Symmetric encryption	AES-256-GCM
Asymmetric wrapping	RSA-OAEP-SHA256
Digital signature	RSA-PSS-SHA256
Key fingerprint	SHA-256

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🧱 Architecture

• Swift 5 + SwiftUI
• CryptoKit : for AES-GCM encryption
• Security framework : for RSA keypair management and signing
• AppKit : for Keychain access and About panel
• macOS 15+ : native UI

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🗝️ Security Model

• Private keys are generated and stored inside the macOS Keychain.
• AES keys are ephemeral, generated per message and never reused.
• Signatures verify both message integrity and sender authenticity.
• The app does not connect to any external server or API.

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🧾 Example of Decrypted Envelope (message)

{
  "alg": "RSA-OAEP-256 + AES-GCM + RSA-PSS-256",
  "nonce": "a1b2c3d4e5f6g7h8",
  "enc_key": "Base64(...)",
  "ciphertext": "Base64(...)",
  "signature": "Base64(...)"
}

📜 License

GPLv3 License © 2025 — Khalid Alkhaldi See LICENSE for details.

Aegis is a modern macOS desktop application that provides secure end-to-end message encryption 
using a hybrid RSA-AES design.
Copyright (C) 2025 Khalid Alkhaldi (k.t.alkhaldi@gmail.com)

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program.  If not, see <https://www.gnu.org/licenses/>.

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❤️ Enjoy!

If you encounter issues, please open a GitHub Issue with details or screenshots.