Retroshare

Retroshare [9], which has been in development for more than 15 years, is primarily used for decentralized file sharing and encrypted communication. Besides file sharing, the program focuses on services such as email, instant messaging, and feed readers.

All of these services do without central servers and use OpenSSL and asymmetric encryption based on OpenPGP. This end-to-end encryption keeps the contents of the transferred data completely hidden from third parties. You can also use Retroshare over the Tor or I2P network, so even neighboring nodes will not see your IP address.

Retroshare relies on friend lists. The local node with a user's account can connect to another node only if the remote node is entered in the friend list.

Arch Linux, Slackware, Solus, and Void Linux come with Retroshare in their package sources. On Retroshare's website, you will find additional instructions for installation on many other Linux derivatives, as well as a cross-distribution AppImage package. You can also pick up a Flatpak from Flathub. In addition, Retroshare runs on the Raspberry Pi. Provided you install with a binary package customized for your choice of distribution, the routine will create a starter in the menu of the desktop environment.

Retroshare comes with a sophisticated graphical interface and an initial setup wizard. For the setup wizard, you first need to specify whether the machine will act as a default node or as a hidden node within the Retroshare network on the Tor network. You also create a user account in the start-up screen. The bar in the lower part of the window shows the progress (Figure 7).

Figure 7: When Retroshare launches for the first time, a profile is generated.

Press the Go! button to start Retroshare. Two separate windows then open. In addition to the application window, Retroshare displays an information window telling you how to get started. At the same time, an icon with a white envelope on a blue background appears in the system tray, which gives you quick access to the Retroshare window at the push of a button.

At first glance, Retroshare's interface resembles a conventional email program: A small pane contains various folders and below that is a quick view with different attributes for labeling the inputs. Messages received appear in two large window segments on the right, and a buttonbar below contains controls and a view field for the messages. A status bar at the very bottom provides information about the received and uploaded data.

The buttonbar located horizontally at the top of the screen opens up the full functionality of the application. You can use it to access the various communication modules such as chat, email, data transfer, forums, and contacts.

To use Retroshare, you need to invite friends who are also part of the Retroshare network by exchanging Retroshare IDs.

Pressing Home in the user interface reveals your own identifier; below that you can add a friend to your installation by clicking on Add friend. The friend must have sent you their Retroshare ID (by email, for example).

Please note that participating nodes must use the latest version 0.6.6 Retroshare, which is the first release in which the Retroshare ID replaces the conventional certificates used up to now. Mixing old certificates and new retroshare IDs will not work and will result in an error message.

After adding your friends to your Retroshare instance, there are unlimited possibilities for communicating through the system. Retroshare automatically transfers any registered friends to the respective contact lists. One specific advantage of Retroshare is that, unlike centralized, web-based forums, the forum function lets you compose your posts offline. They are automatically displayed in the forum after logging in again.

The file-sharing feature works in a similar way to the BitTorrent service, with Retroshare transferring files across multiple nodes in blocks. This makes it easy to share even very large files, and the individual nodes do not have to be directly connected to each other. But when a transfer relies on multiple nodes, all of the nodes need to be running or the file transfer will fail.

However, you can also use the chat or the email function for file transfer – as long as the files are not too large. In both chat and email, you will find a paper clip icon, which opens a file manager from which you can select the files you want to attach. Retroshare then attaches the files to the content for dispatch.

Tor Network

The Tor network is the best known network for anonymized communication [10], dating back to the 1990s. At the end of 2002, the Tor network was released for general use for the first time. Its now very high profile due in no small part to the Tor Browser, which is based on Mozilla Firefox and uses the Tor network for Internet access. In addition, the Tor network provides access to the Deep Web and also to the Dark Web.

The Tor network operates with thousands of servers through which it routes all traffic. Data packets pass through three servers, known as relays. The relays work in a similar way to proxies, with the data path constantly changing. Instead of fixed cascades, variable paths are used. In addition, the data is fully encrypted.

Due to the encryption mechanism, which cryptographically processes the data multiple times, this type of data transfer is also called onion routing. Step-by-step encryption prevents tracking of data packets, because each node only performs one encryption step. Unless additional end-to-end encryption of the data is enabled, only the last node sees the transported data packets in the clear [11].

The Tor Browser further increases the user's anonymity by providing different levels of security. By default, the HTTPS Everywhere and NoScript add-ons are also enabled. Moreover, the Tor Browser isolates every web page visited and also blocks the Flash video format, which is a security risk. Besides this, the Tor Browser lets you switch data transfer routes at the push of a button to provide additional security. Although the Tor Browser is based on and compatible with Firefox ESR, the developers advise against integrating other plugins into the browser, as they may contain security vulnerabilities.

The Tor Browser comes with the client infrastructure required to connect to the Tor network. You will find countless language variants of it on the project's website. For all the individual variants, 32- and 64-bit versions are available.

Unpack the downloaded tarball in any folder. You will then find the Tor Browser launcher in the newly created folder tor-browser_en/ (for the English language variant). Double-clicking on it opens the browser and displays a connection dialog. In the dialog, press the Connect button to connect to the Tor network. Checking the Always connect automatically option lets you automate the process of opening the connection for future use of the browser.

The browser opens the DuckDuckGo search engine as the home page. You can now work with the Tor Browser as you would with any regular web browser. You can see the specific route taken by the web pages opened in the browser by clicking the icon with the padlock on the left in the URL bar. In an overlapping small window, you will then see the three nodes through which the data is routed (Figure 8), with the entry server highlighted as the guard. This server remains the same for a few months, while the other two relays change for each new web page you access. However, if necessary, you can switch the last two relays for each open web page on the fly by clicking the New Circuit for this Site button.

Figure 8: You can view and modify the routes your data takes in the Tor Browser.

The Tor Browser also gives you access to content hosted on the Tor network. This content available on the Deep Web [12] is not accessible for conventional Firefox variants or other web browsers. The Deep Web contains only non-indexed web pages that conventional search engines do not list.

The often-cited Dark Web forms just a small part of the Deep Web, which is distinguished from it by special additional cryptographic mechanisms. In this case, the transmission of hosted data is encrypted, and the channels involved for communication are established through various servers on the Tor network using hashes. This means that the computers involved in the communication remain completely anonymous.

There are various search engines such as Torch [13] or Candle [14] to help you find Deep Web pages on the Tor network. By default, however, the Tor Browser uses DuckDuckGo, which is also Deep Web-enabled.

Conclusions

Overlay networks on the Internet contribute significantly to anonymous communication. They target different audiences here. While some P2P networks are simply about transferring individual files with the greatest possible anonymity, others focus on anonymous browsing on the conventional Internet. Others have embraced truly anonymous communication using conventional technologies such as email, chat, or IRC.

What all overlay networks have in common is that they actually make it more difficult to inject malicious or spy code into the individual applications thanks to free licenses and the resulting free availability of the source code. As a user, however, you need to investigate in detail each overlay network in advance, especially if you are using the Dark Web, in order to be sure of obtaining a communications solution that is truly hardened against a wide variety of attack scenarios through a combination of different security mechanisms.