Instant Messenger Chat
- 1 General Safety Advice
- 2 Recommendation
- 3 Gajim
- 4 HexChat: IRC Client
- 5 Tox
- 6 Deprecated Chat Clients
- 7 Other Software
- 8 Footnotes / References
- 9 License
General Safety Advice
Tor exit relays can eavesdrop on communications if encryption to the server is disabled. Depending on the protocol, encryption might be disabled by default or not even supported. Tails has noted that without encryption, the exit relay can see the contact list, all messages, file transfers, and audio/video.  While encryption to the server prevents exit relay eavesdropping, it still leaves one problem unresolved: server logging.
High-risk users should also bear in mind that even in the event that strong and secure end-to-end encryption is used -- for example encrypted chat using .onion connections only (staying within the Tor network) -- sophisticated attackers (nation state actors) are capable of compromising the trusted computing base (TCB)  of nearly all platforms: 
All proper end-to-end encrypted (E2EE) messaging systems store private key(s) exclusively on user's device (endpoint). The holy grail of attacks against E2EE systems is called exfiltration where the sensitive data, namely the private keys or plaintext messages, are stolen from the endpoint. The attack is directed against the trusted computing base (TCB) of the target system. The overwhelming majority of TCBs are connected to the network and compromising them with polished malware that exploits a zero-day vulnerability, is trivial and undetectable.
Encrypted server connections do not prevent the server gathering interesting information about users, such as common contacts and the regularity of communications. An example list includes:
- Account names.
- Buddy list (list of contacts).
- The exact date and time of logins.
- Message timestamps.
- Communication patterns like common contacts.
- If the recipient knows the sender and has ever used a non-anonymous account or logged in without Tor, this information can be used to try and determine the sender's identity.
The content of messages will only be protected by using end-to-end encryption, for example Off-the-Record (OTR) encryption.
To completely remove the threat of server logging, prefer decentralized (server-less) instant messengers like Ricochet IM.
Jabber / XMPP
Jabber/XMPP is a free server-federation-based protocol designed with openness in mind: "... All of the existing XMPP servers, clients, and programming libraries support the key features of an IM system, such as one-to-one and multi-party messaging, presence subscriptions and notifications, and contact lists."
The system is decentralized because there is no central authoritative server; anyone can run a server. Some users are confused on this point because there are a number of large and popular public XMPP servers (like jabber.org), to which many have subscribed.  Each network user has a unique XMPP address called a JID (Jabber ID). The JID is similar to an email address insofar as it has a username and domain name like firstname.lastname@example.org 
Safely using the protocol requires proper use of OTR, because it is unwise to trust server connections are properly encrypted between each other. Jabber privacy is also limited, as various adversaries are capable of observing which accounts are communicating. Jabber and Tor combined only guarantee pseudonymous communications, as while the user's current location is hidden, the social graph can still expose their true identity. For tips on operational security when chatting anonymously, see this article by The Intercept. Also see: Why prefer open protocols such as Jabber/XMPP over proprietary ones such as ICQ?
When using IRC inside Whonix-Workstation ™, the Ident Protocol is automatically blocked because Whonix-Workstation ™ is firewalled. Therefore the associated daemon will not identify the username which is linked with a particular TCP connection, as is normally the case.
The Tor Project Internet Relay Chat page contains a number of important recommendations and tips for safe IRC use:
- Use onion services when available.
- Check self-signed certificates have the correct SSL/TLS certificate.
- Cycle Tor circuits to evade censorship bans.
- Chain VPNs and Tor for registration.
- Use OTR for end-to-end encryption.
- Distrust users and servers in general.
- Avoid personally identifiable information in chats.
- Check the user fingerprint before using IRC.
- Harden the IRC client.
- And more.
Applications discussed in this chapter are listed in order of best usability and compatibility with Whonix ™, based on the opinion and experience of Whonix ™ developers.
It should be noted that no single application listed here has a superior feature set. Users must make a choice based on personal preferences and their self-assessed threat model:
- Gajim has better usability, more Jabber users, supports offline messages, and can provide OTR or OMEMO-grade encryption. On the downside, it requires a Jabber server which weakens anonymity.
- HexChat is an open source IRC client based on XChat (therefore not technically an instant messenger). It has better usability and supports encrypted plugins like OTR, but on the downside it relies on centralized IRC servers.
Ricochet IM is a decentralized (server-less) option, but it "only" uses onion encryption and is difficult to set up. OTR or OMEMO-grade encryption is not yet available,  and offline messages are not supported.  Ricochet IM is also not user-friendly.
- Tox is also a fully-featured, decentralized (server-less) option which employs strong encryption, but the software is in alpha status and is not available as a Debian package.  Tox developers warn in their wiki: "... Keep in mind that these clients are alpha software under heavy development, and are probably not ready for day-to-day use. ..." 
Ubuntu provides a succinct overview of Gajim: 
Gajim is a free software, instant messaging client for the Jabber (XMPP) protocol which uses the GTK+ toolkit. It runs on GNU/Linux, BSD and Windows. The name Gajim is a recursive acronym for Gajim (is) a jabber instant messenger. The goal of Gajim is to provide a full featured and easy to use Jabber client. Gajim works nicely with GNOME, but does not require it to run. It is released under the GNU General Public License.
Gajim has various features, including: 
- Chat client synchronization.
- Group chats.
- Sending of pictures, videos and other files to friends or groups.
- Secure end-to-end encryption via OMEMO or PGP.
- The option to keep and manage all chat history.
- Connection compatibility with other messengers via transports, such as IRC.
- Various other features are available via plugins.
In late-2018, audio/video is reportedly not functional in Gajim. Further, OTR support was dropped in Gajim release 1.0, but the OMEMO plugin is an encryption alternative.  Note that Debian stretch has v0.16 of the Gajim package available, so optionally the OTR plugin can still be used instead of OMEMO (stretch-backports has v1.1 available).
The steps below install Gajim, along with the OMEMO encryption plugin and HTTP Upload plugin (which is required for file transfers).  The latter plugin is fully integrated into the core Gajim software as of v1.0. Upon first launch of the program, users can use an existing XMPP account or create a new one.
Update the package lists.
sudo apt-get update
Install gajim, gajim-omemo and gajim-httpupload.
sudo apt-get install gajim gajim-omemo gajim-httpupload
Start Gajim from the start menu or type in konsole.
On first launch, an Account Creation Wizard Dialog will appear. Use the wizard to either create a new account to connect to the jabber network or use an existing account. For new accounts, there are multiple jabber servers available and only a username and password is required to join. 
The following changes are recommended for better security and privacy.
Gajim cannot be installed by default in Whonix ™ yet, as there is more development work TODO; see Dev/Gajim.
HexChat: IRC Client
Tox   looks like a promising solution for secure, encrypted communications. The official client implementation is based on the Toxcore protocol library, which is very feature-rich and has a variety of functions besides VoIP. By default, Tox does not attempt to cloak your IP address from authorized contacts. However, Tox connections can be tunneled through Tor, allowing communication with others even if they are not anonymous.  Desktop and mobile client versions have been developed for every major OS platform. 
In the Tox design, users are assigned a public and private key, with direct connections being established in a peer-to-peer network. Users can message friends, join chat rooms with friends or strangers, and send each other files. Everything is encrypted using the NaCl crypto library, via libsodium.   Tox helps to protect user privacy by: 
- Removing the need to rely on central authorities to provide messenger services
- Enforcing end-to-end encryption with perfect forward secrecy as the default and only mode of operation for all messages
- Making your identity impossible to forge without the possession of your personal private key, which never leaves your computer
- Voice and video calls.
- Instant messaging.
- Desktop screen sharing / streaming.
- File sharing.
- Typing indicators.
- Message read-receipts.
- Profile encryption.
- Group messaging, voice and video conferencing.
Additional features can be implemented by any client, so long as they are supported by the core protocol. Features that are not related to the core networking system are left up to the client. 
The following instructions will install the "qTox" graphical user client. As qTox is not currently available as a stand-alone Debian package, users have three choices in late-2018:
- Build the package from source (difficult).
- Rely on an unsigned, self-contained AppImage downloaded from the Tox homepage (insecure).
- Install Flatpak from stretch-backports and then install Tox from the Flathub repository (easiest).
It is recommended to create a separate Whonix-Workstation ™ before installing addtional software. Tox is also alpha software which has not been formally audited, therefore it is less trusted.
Add the Flathub Repository and Install qTox
Flathub is a common place to source Flatpak applications. To enable it, run.
flatpak remote-add --if-not-exists flathub https://flathub.org/repo/flathub.flatpakrepo
Next, restart Whonix-Workstation ™ to allow flatpak to finish setting up.
To install qTox from flathub, open a terminal (Konsole) and run. 
flatpak install flathub io.github.qtox.qTox
To launch qTox, run.
flatpak run io.github.qtox.qTox
Deprecated Chat Clients
If you would like to experiment and try to fix it, you can find the archived documentation here.
Pidgin supports most protocols and OTR end-to-end encrypted chat. However, it is not recommended because it has a very poor security record with many remotely exploitable bugs. Security researcher and developer Micah Lee notes this is the result of reliance on legacy protocols and the libpurple, libotr and libxml libraries which are: "... massive, written in C/C++, and are littered with memory corruption bugs. ..." 
Whonix ™ developers no longer list RetroShare, which is a friend-to-friend (peer-to-peer), decentralized network and not an anonymizing network. Encrypted RetroShare connections support chat, voice and video, mail, file-sharing, forums and Tor.  Although RetroShare is under active development,  there are several serious concerns which disqualify a recommendation:
- The RetroShare package is signed with weak 1024-bit keys (in late-2018).
- A 2016 code review which focused on implementation vulnerabilities discovered multiple security issues: 
- The attack surface is high due to the feature-rich codebase.
- Systemic "insecure coding practice" was identified, particularly "...inconsistent return value checking and error handling, poor usage of explicit and implicit typecasting, and relaxed handling of adverse security edge-cases."
- Within a 24-hour period, auditors had developed proof of concept exploits for web-like vulnerabilities, weak binary protections, and out of bound memory reads and remote memory corruption (promptly rectified by developers).
- A coverity scan of the RetroShare code shows a large number of outstanding defects, along with a relatively high defect density.  
TorChat has not been recommended by Whonix ™ developers since late-2015. The reason is development has been at a standstill since 2013 and the TorChat developer does not respond to other people, suggesting the project has been abandoned. TorChat is also an unofficial project and unaffiliated with The Tor Project. Since communication, support, active development and security fixes are essential for anonymity-related projects, Ricochet IM is strongly recommended as a modern, maintained alternative. 
It was found that although the design of TorChat is sound, its implementation has several flaws, which make TorChat users vulnerable to impersonation, communication confirmation and denial-of-service attacks.
Do not use Tor Messenger! It was deprecated by upstream developers in early-2018. 
For anonymous Voice over IP (VoIP) or encrypted, anonymous phone calls using the Tor anonymity network, see: VoIP.
If a messenger program is not listed in this chapter, it is for now recommended against. If readers feel any privacy-respecting chat clients are missing on this page, first search the Whonix ™ forums to see if that application has been discussed in the recent past. Any additions to this page will be based on an objective analysis of the software's underlying strength and compatibility with Whonix ™. 
Footnotes / References
- See: https://tails.boum.org/todo/Pidgin_Protocol_Review/ for an overview of Pidgin protocols and associated encryption features.
- "... the trusted computing base or TCB comprises the set of all hardware, software, and firmware components that are critical to establishing and maintaining its security. Typically, the TCB consists of an operating system with all its in-built security controls, individual system hardware, network hardware and software, defined security procedures and protocols, and the actual physical location of the system itself." Trusted Computing Base or "TCB"
- Other popular public servers are listed here.
- Tox has not yet been formally audited by security professionals, but this is the case for most software. Further, passing a formal audit does not guarantee that the software is in fact safe.
- Note this feature can be combined with OMEMO for encrypted file transfers.
- anon-apps-config which is installed by default will deactivate gajim plugin installer / updater because it is not secure.
- A new account can always be added with:
- To prevent needlessly leaking your activity to the server.
- For better security, this prevents the automatic start of these applications from the chat client.
- To set use of the Tor network, along with Stream Isolation.
- Depending on the mobile / desktop client in use.
- Users should Prefer Packages from Debian Stable Repository, but using backports is better than manual software installation or using third party package managers since this prefers APT. To contain the risk, Non-Qubes-Whonix ™ users might want to consider using Multiple Whonix-Workstation ™ and Qubes-Whonix ™ users might want to consider using Multiple Qubes-Whonix ™ TemplateVMs or Software Installation in a TemplateBasedVM.
- Most often this step applies before attempting major Whonix upgrades; upgrade instructions are also made available at that time (see Stay Tuned).
- Unlike other private P2P options, the F2F network can grow in size without compromising their users' identities. Also, passwords or digital signatures are required for authentication.
- See also: https://retroshareteam.wordpress.com/2018/03/13/release-notes-for-v0-6-4/
- For example, compare this result with the low number of defects and defect density of the Tor codebase.
- Particularly since Ricochet IM passed a recent (2016) security audit with flying colors.
- Security Analysis of Instant Messenger TorChat
- Also see: https://forums.whonix.org/t/client-server-instant-messengers-im-oct-2016
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