OnionShare is a anonymous, peer-to-peer file sharing application. It lets people share files of any size private and securely.
OnionShare is built on top of Tor hidden services. There are a number of security and privacy advantages to sharing files over Tor hidden services using OnionShare.
- Tor hidden service connections are end-to-end encrypted, meaning that the file transfer is encrypted at every point between the client and server.
- Tor hidden service connections are anonymous. File transfers can occur without the either the client or the server knowing the IP address of each other. The server is hidden behind an .onion address on the Tor network. The client is hidden because it connects to the hidden service through different rendezvous points.
- OnionShare file shares are designed to be short-lived. They can shut down after the file transfer occurs, meaning the server stops listening and the .onion address disappears from the Tor network.
Subgraph OS enhances the security of OnionShare by sandboxing it with Oz. File shares exist in their own sandbox, without access to other sensitive files on the computer. If OnionShare is affected by a security vulnerability, running it Oz limits the consequences of the vulnerability.
When a user shares files, OnionShare starts a hidden service with its own .onion address. The user then sends the .onion address to the people they wish to share files with. The .onion address should be sent over a secure communication channel. This is important to prevent unwanted parties from accessing your shared files. Once files are shared, people with the .onion address can download the files using the Tor Browser.
What is a secure communication channel?
A communication channel is secure if people can communicate with some expectation that their conversation cannot be intercepted or tampered with. Ideally, all communications should be encrypted along with their metadata. Metadata includes things such as the time, date, and frequency of the conversations. It can also include the identities and location of the people who are communicating. Even without the content of a conversation, metadata can reveal a lot about the nature of the communication.
Establishing truly secure communications channels is difficult. Many communications tools rely on third-parties, making them privy to communications metadata. This may include the third-party servers themselves or intermediary servers that pass on the communications. Communications, even encrypted ones, often leak metadata as they travel to their final destination.
Subgraph OS includes applications to help our users communicate over secure channels. These examples are ranked according to the amount of metadata they reveal:
- Ricochet instant messager (uses Tor hidden services for anonymity and end-to-end encryption, no metadata, no third-party servers required)
- CoyIM instant messager (uses the XMPP protocol, some metadata, requires third-party servers)
- Encrypted email using Icedove/Torbirdy (uses the SMTP protocol, lots of metadata, requires third-party servers)
More information about OnionShare is on the following website:
https://github.com/micahflee/onionshare
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OnionShare is integrated into the file explorer of Subgraph OS. To share a file, right-click on the file and select Share via OnionShare.
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Selecting Share via OnionShare will start OnionShare and open the onionshare-gui. It may take a few seconds for OnionShare to create the hidden service. The status indicator will turn green when it is ready.
onionshare-gui includes the following options to manage shared files:
- Add Files
- Add Folder
- Delete (Files and Folders)
- Stop Sharing (all files and folders, this closes OnionShare)
OnionShare runs inside of the Oz sandbox. To add files and folders after OnionShare has started, they must be added through the Oz menu at the top right corner of the desktop. See the section on Viewing PDFs for further information on adding files and folders to an application in the Oz sandbox.
The URL for the hidden service (the .onion address) is provided along with a button to Copy URL to the clipboard. This URL should be sent over a secure communication channel to the people you want to share files with.
The Stop sharing automatically checkbox determines whether OnionShare will close automatically after the file is downloaded by a user. Un-check this option if you are sharing files with multiple users.
OnionShare runs as a Tor hidden service. To download files over OnionShare, you can use the Tor Browser. Paste the .onion address for the file share into the address bar of Tor Browser. This will open the web interface for OnionShare.
NOTE: In this screenshot, OnionShare (the server) and Tor Browser (the client) are both running on the same computer. Because the OnionShare server is only accessible over a Tor hidden service, Tor Browser connects to the file share over Tor. This is the case even if they are running on the same computer. Of course, normally the server and the client would run on different computers
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