Instant Messenger Chat
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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 OMEMO [archive]. The threat of server logging can be completely removed with decentralized (server-less) instant messengers like Ricochet IM, but unfortunately it is non-functional in Whonix ™ at present.
Jabber / XMPP
Jabber/XMPP [archive] is a libre server-federation 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 encryption (such as OMEMO), 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 [archive] by The Intercept [archive]. Also see: Why prefer open protocols such as Jabber/XMPP over proprietary ones such as ICQ? [archive]
When using IRC inside Whonix-Workstation ™, the Ident Protocol [archive] 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.
- 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 (or OMEMO if available) 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:
- Dino IM is the best option currently. It provides the best UX, a modern and clean look and OMEMO support.
- Gajim has more Jabber users, is written in memory-safe python, supports offline messages, and can provide 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.
- Tox is also a fully-featured, decentralized (server-less) option which employs strong encryption, but the software is in alpha status.  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. ..." 
- Quaternion is a libre Matrix desktop client that can be used for Telegram and IRC channels.
Dino IM [archive] is a modern XMPP ("Jabber") Chat Client written in GTK+/Vala for GNU/Linux and available in Debian. OMEMO is supported, but needs to be toggled in the chat window. Additonaly OpenPGP Is supported too.
A Tor compatible version is currently available from Buster Backports repo.
It's planned for inclusion by default in Whonix 16. Other issues currently is broken OMEMO compatibility with Gajim users.
In addition to the fingerprint displayed in clients, OMEMO uses session/ephemeral keys: as soon as you chat with someone, these keys are created and they are replaced with new ones after every message exchange.
Without the latest session keys, you can't decrypt incoming messages. Thus when importing session keys from an older backup, you are likely going to have issues if the keys were used in between.
Both types of keys are stored in the
~/.local/share/dino/omemo.db (a SQLite DB). As long as you only backup them while Dino is not running and do not start Dino from the same database twice, there is no issue.
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.
Figure: Gajim Client in Whonix ™
The steps below install Gajim, along with the OMEMO encryption plugin and HTTP Upload plugin [archive] (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
To connect to other Matrix users and/or our Telegram channel without dealing with Telegram Desktop, you can create an account on the tchncs.de [archive] or privacytools.io [archive] home server for a more private experience (it doesn't collect as much data about users as the matrix.org home server). The privacy issues are inherent in the synapse server side software itself, check this list [archive] for a full write-up. Besides federating with other Matrix instances, it supports bridging to IRC and Telegram and many other protocols .
Web clients can provide weaker or stronger security depending on the user's threat model.
Furthermore, installed applications can utilize TLS certificate pinning to better mitigate man-in-the-middle attacks by eliminating the dependence on potentially compromised certificate authorities. Certificate pinning is already being extensively used by applications such as Signal , ProtonMail  and others.
In addition, the stateless design of Tor Browser will erase any keys created and approved by communicating parties causing confusion about trusting their contacts in subsequent sessions - a workaround is to use a dedicated install of Firefox for that purpose.
However, there are advantages to web clients too. Websites are much less privileged than installed applications and have no direct access to system resources. Common browsers also often employ browser sandboxing technologies to contain malicious websites even in the event of a browser exploit (unless chained with an additional sandbox escape exploit).
Deprecated Chat Clients
List of chat clients which where previously documented here. Not a list of all deprecated chat clients that ever existed.
No longer maintained. Last time being touched on 2018 
No longer included in Whonix due to technical issues. Namely, currently not available from Debian stable or backports package sources packages.debian.org.  Chances are it gets reintroduced when Whonix 16 (based on Debian
bullseye) gets released. Manual software installation might be possible, see Install Software but it is undocumented by Whonix developers.
Pidgin supports most protocols and OTR end-to-end encrypted chat. However, it is not recommended because it has a very poor security record [archive] 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 [archive] (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 [archive],  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.  
Interested readers are most welcome to experiment with Ricochet IM to try and fix the problem -- refer to the archived documentation here.
TorChat has not been recommended by Whonix ™ developers since late-2015. The reason is development has been at a standstill [archive] 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, modern software alternatives are recommended. 
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 [archive] 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/ [archive] 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" [archive]
- https://github.com/maqp/tfc/wiki/Security-design#the-issue-of-endpoint-security [archive]
- Other popular public servers are listed here [archive].
- https://en.wikipedia.org/wiki/Xmpp [archive]
- Ricochet 'only' uses onion encryption and is difficult to set up and use. OTR or OMEMO-grade encryption is not yet available and offline messages are not supported.
- https://github.com/ricochet-im/ricochet/issues/72 [archive]
- https://github.com/ricochet-im/ricochet/issues/405 [archive]
- 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.
- https://wiki.tox.chat/binaries [archive]
- 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).
- https://forums.whonix.org/t/dino-im-messenger/7773/22 [archive]
- https://help.ubuntu.com/community/Gajim [archive]
- https://gajim.org/ [archive]
- https://dev.gajim.org/gajim/gajim/wikis/help/gajimfaq [archive]
- Note this feature can be combined with OMEMO for encrypted file transfers.
- anon-apps-config [archive] which is installed by default will deactivate gajim plugin installer / updater [archive] 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.
- https://matrix.org/bridges/ [archive]
- https://protonmail.com/blog/cryptographic-architecture-response/ [archive]
- https://www.signal.org/blog/certifiably-fine/ [archive]
- https://protonmail.com/blog/tls-ssl-certificate/#Extra-security-precautions-taken-by-ProtonMail [archive]
This repository has been archived by the owner. It is now read-only.
- https://forums.whonix.org/t/coyim-in-whonix-development-discussion/5901/16 [archive]
- https://micahflee.com/2013/02/using-gajim-instead-of-pidgin-for-more-secure-otr-chat/ [archive]
- 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/ [archive]
- https://www.elttam.com.au/blog/a-review-of-the-eff-secure-messaging-scorecard-pt1/ [archive]
- https://scan.coverity.com/projects/retroshare-retroshare [archive]
- For example, compare this result with the low number of defects and defect density of the Tor [archive] codebase.
- Ricochet IM was previously recommended in this section, since it passed a recent (2016) security audit with flying colors.
- Security Analysis of Instant Messenger TorChat [archive]
- https://en.wikipedia.org/wiki/TorChat#Security [archive]
- Also see: https://forums.whonix.org/t/client-server-instant-messengers-im-oct-2016 [archive]
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