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This Gist explains how to use Send from Mozilla and Signal Desktop to transmit end-to-end encrypted files.

How to Securely Send Files

Table of Contents

Introduction

From time to time, we need to transmit sensitive information that we want only the sender and the receiver to know the content. It could be your accounting documents, some sensitive client data, etc. We believe that not even the service provider should be able to decrypt the files.

Because people are often reluctant to adopt new procedures and to use new tools, this guide is based on none technical solution, simple enough for adoption, and free. It assumes the all parties have a smart phone, although files are transmitted from the desktop computer. This solution uses two tools from well-known companies that I feel I can trust:

Prerequistes

What you need:

  • A Smart phone (iOS or Android).
  • Chrome Web browser on your desktop.

Installation

  1. Install Google Chrome on your computer.
  2. Install Signal by Open Whisper Systems on your smartphone:
  3. Install Signal Desktop on Chrome.
  4. Register your desktop computer using your smart phone.

Securely Send Files

  1. Open Mozilla Send service.
  2. Drag and drop the file to send.
    • Maximum size is 1GB.
    • It is encrypted on your device. Not even Mozilla can decrypt it.
  3. Copy the link.
    • It expires after either 24h, or the first download.
    • This is the only key to the file. Never send it in clear text, this is why you need Signal Desktop.
  4. Open Signal Desktop from Chrome.
  5. Select your contact.
  6. Write a message and paste the link.
  7. Send your message!

Bravo, you have just sent an end-to-end encrypted message and file. The receiver should also use Signal Desktop to download the file on her own desktop computer.

Register Signal Desktop

  1. Start Signal Desktop App from Chrome:

    Start Signal Desktop

  2. Follow instructions until you have to scan the QR code:

    Scan QR code

  3. Scan the QR code with your smart phone:

    Android

    • Go to Signal
    • Tap on the Menu
    • Choose Settings
    • Choose Linked devices
    • Tap the '+' in the blue circle on the bottom right corner
    • Lift up your phone to your computer screen to fit the QR code displayed on the Desktop in the square field on your Android phone

    iOS

    • Open Signal
    • Tap on the Settings wheel in the top left corner
    • Choose Linked Devices
    • Tap Link New Device
    • Lift up your phone to your computer screen to fit the QR code displayed on the Desktop in the square field on your iPhone
    • Choose Link New Device
  4. Name your device on Signal Desktop:

    Name your device

You ar ready to securly send files.

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