anarsec.guide/content/posts/e2ee/index.md

+++ title="Encrypted Messaging for Anarchists" date=2023-04-02

[taxonomies] categories = ["Defensive"] tags = ["intro", "e2ee", "easy"]

[extra] blogimage="/images/BASE_2.png" toc=true dateedit=2023-05-10 a4="e2ee-a4.pdf" letter = "e2ee-letter.pdf" +++ There are several different options for end-to-end encrypted communication, each with different trade-offs. This article provides an overview and installation instructions for Tails, Qubes OS, and GrapheneOS.

Before proceeding, there are a few concepts that need to be understood, in order to distinguish between the various options.

• End-to-end encryption means that only you and the person you are communicating with can read messages. However, not all encryption is created equal. The quality of the encryption is determined by the encryption protocol used and how it is implemented at the software level.
• Metadata protection means that the metadata (the data about the data) about the communication is obscured. Even if the message itself is encrypted, metadata can reveal who is communicating with whom, when, how often, the sizes of any files that may have been transferred, and so on. Metadata exposure is a major concern.
• Peer-to-peer means that there is no centralized server to trust.
• Tor is an anonymity network, and some applications route your messages through it by default.

For a more in-depth look at these various considerations, we recommend The Guide to Peer-to-Peer, Encryption, and Tor: New Communication Infrastructure for Anarchists. This text criticizes Signal for not being peer-to-peer and not using Tor by default, and goes on to compare Signal, Cwtch, and Briar.

Public-facing projects have additional needs for encrypted communication, because they will be interacting with unknown (and untrusted) contacts:

• Anyone can contact the project without requiring a separate channel
• Resiliency to correlation attacks from untrusted contacts
• Resiliency to exploits from untrusted contacts
• Multiple project members can access the same messages

The following options for encrypted messaging are listed from most metadata protection to least.

TLDR:

• For text communication with other anarchists, prioritize Cwtch.
• For voice or video calls, prioritize SimpleX Chat.
• Don't use Signal to communicate with other anarchists.
• For public projects, PGP email is still the best option.

Cwtch

• Mediums: Text
• Metadata protection: Yes (strong)
• Encryption protocol: Tor Onion Services (v3) + Tapir
• Peer-to-peer: Yes
• Tor: Yes

Cwtch is our preference, by a long shot. For an overview of how Cwtch works, watch the video below. Cwtch is designed with metadata protection in mind; it is peer-to-peer, uses the Tor network, and stores everything locally on the device, encrypted.

How Cwtch works

Like all peer-to-peer communication, Cwtch requires synchronous communication, meaning that both peers must be online at the same time. However, its server feature also allows asynchronous communication by providing offline delivery:

"Cwtch contact to contact chat is fully peer to peer, which means if one peer is offline, you cannot chat, and there is no mechanism for multiple people to chat. To support group chat (and offline delivery) we have created untrusted Cwtch servers which can host messages for a group. [...] the server has no way to know what messages for what groups it might be holding, or who is accessing it."

Once the server exists, contacts can be invited to use it. For asynchronous direct messaging, create a group chat with only two people.

Any Cwtch user can turn the app on their phone or computer into an untrusted server to host a group chat, though this is best for temporary needs like an event or short-term coordination, as the device must remain powered on for it to work. Fortunately, Anarchy Planet runs a public server that is suitable for long-term groups.

Asynchronous conversations on Cwtch need to be started from a synchronous conversation - you need to be online at the same time as your contact to invite them to a group, and then you no longer need to be online at the same time. In the future, Cwtch plans to improve this with hybrid groups. Until hybrid groups are implemented, you will need to establish your asynchronous Cwtch conversations by using a second channel to set a time for when you both need be on Cwtch.

You can learn more about how to use Cwtch with the Cwtch Handbook.

For Public-facing Projects

Anyone can contact the project without requiring a separate channel

Anyone can connect to a public Cwtch account when it is online. In the future, Cwtch bots that are semi-trusted (which are hosted on a Cwtch server) will enable first contact when the public Cwtch account is offline.

Resiliency to correlation attacks from untrusted contacts

Real-time messaging applications are particularly susceptible to end-to-end correlation attacks because of the ability of an adversary, once they know their target's ID on the messaging platform, to trigger incoming network traffic on the target's side by sending them messages on the platform (when the target is online). "Appear Offline Mode" in Cwtch allows a user to selectively connect to trusted contacts and groups, while appearing offline to everyone else. An issue is open to further address this.

Content padding exists to frustrate correlation attacks via message size.

Resiliency to exploits from untrusted contacts

A vulnerability in any application can be targeted with exploits - a severe vulnerability can allow an adversary to hack your system, such as by permitting Remote Code Execution. Cwtch does fuzz testing to find bugs. For public-facing project accounts, we recommend that you do not enable the "file sharing experiment" or the "image previews and profile pictures experiment" in the settings.

Multiple project members can access the same messages

If a project has multiple members, all of them should be able to access the same messages independently. Currently, this is not possible with Cwtch.

Note

Briar is another application that works in a similar way (with peer-to-peer and Tor), using the Bramble Transport Protocol (BTP). Briar's main distinguishing feature is that it continues to work even when the underlying network infrastructure is down. It was audited in 2017. Unfortunately, Briar Desktop does not yet work with Tails or Qubes-Whonix because it cannot use the system Tor. Unlike Cwtch, to connect to a contact on Briar, you both have to add each other first. You can either exchange briar:// links or scan a contact’s QR code if they are nearby. Briar Mailbox allows asynchronous communication.

OnionShare has a chat feature that creates an ephemeral peer-to-peer chat room that is routed over the Tor network. The metadata protection works in the same way as Cwtch; it uses the Tor network as a shield and stores everything (ephemerally) locally on the device running OnionShare. OnionShare doesn’t implement any chat encryption on its own - it relies on the Tor onion service’s encryption. Cwtch and Briar both have more features (including the additional Tapir and BTP encryption protocols). The only advantage of OnionShare is that it is installed on Tails by default.

Cwtch Installation on GrapheneOS

If you have decided to use a smartphone despite our recommendation not to use phones, Cwtch is available for Android. Install Cwtch as you would any app that doesn't require Google Services (we don't recommend F-Droid).

Cwtch Installation on Tails

Cwtch support for Tails is very new and not thoroughly tested.

• Start Tails with an Adminstration Password.
• Download Cwtch for Linux with Tor Browser
• Verify your download
  • Open the folder using the Tor Browser's download icon
  • Right-click in the file manager and select "Open a Terminal Here"
  • Run sha512sum cwtch-VERSION-NUMBER.tar.gz (replace the version number as appropriate)
  • Compare the hash of the file to what is listed on the download page
• According to our Tails Best Practices, personal data should be stored on a second LUKS USB and Persistent Storage should not be enabled. Extract the file with the file manager (right click, select "Extract Here"), then copy the cwtch folder to such a personal data LUKS USB.
  • OPTIONAL - If you enable Persistent Storage: with Persistent Storage unlocked, in Terminal run sudo sed -i '$ a /home/amnesia/.cwtch source=cwtch' /live/persistence/TailsData_unlocked/persistence.conf && sudo sed -i '$ a /home/amnesia/.local source=cwtch_install' /live/persistence/TailsData_unlocked/persistence.conf then restart Tails for the changes to take effect, again with an Adminstration Password.
• Run the install script
  • In the File Manager, browse to the directory you just created, cwtch. Right click in the File Manager and select "Open a Terminal Here"
  • Run install-tails.sh and enter the Administration Password when prompted.
• As the documentation states, "When launching, Cwtch on Tails should be passed the CWTCH_TAILS=true environment variable". In the Terminal, run:
  • exec env CWTCH_TAILS=true LD_LIBRARY_PATH=~/.local/lib/cwtch/:~/.local/lib/cwtch/Tor ~/.local/lib/cwtch/cwtch
• With Persistent Storage disabled, configuration and profile data must be restored from backup every session you need to install Cwtch. Backup /home/amnesia/.cwtch/ to the personal data LUKS USB, and copy it back to /home/amnesia/ the next time you install Cwtch.
• Updates to new versions must be done manually - back up your profile first.

Cwtch Installation on Qubes-Whonix

Cwtch on Whonix currently has an issue - support is forthcoming.

SimpleX Chat

• Mediums: Video call, voice call, text
• Metadata protection: Yes (strong)
• Encryption protocol: SimpleX Messaging Protocol, audited (2022), and SimpleX File Transfer Protocol
• Peer-to-peer: No
• Tor: Not default

SimpleX Chat functions without persistent user IDs, which creates strong metadata protection. This means that an adversary can't easily observe how users are connected to each other in a network. This is possible because connection requests work by sharing an invitation link that is communicated through a separate channel, or in person. When connecting to another user you have the choice to use "Incognito mode", which creates a new random profile for each contact. This avoids sharing any data between contacts.

As a design choice to facilitate asynchronous communication, SimpleX Chat is not peer-to-peer - it uses decentralized servers that anyone can host and does not rely on any centralized component. Servers do not store any user information (no user profiles or contacts, or messages once they are delivered), and primarily use in-memory persistence. To understand what a server can and cannot see, read the threat model. Your data can be exported, and imported onto another device, as there are no central servers where this is backed up.

Due to needing to place some trust in the SimpleX servers, we recommend prioritizing Cwtch over SimpleX Chat for text communication with other anarchists, and using SimpleX Chat for voice and video calls. For people who are unlikely to start using Cwtch because it has an unfamiliar user experience, SimpleX Chat is still an acceptable solution for text communication. The experience of using SimpleX Chat is very similar to Signal, but unlike Signal, it won't expose the identities of your network to an adversary if they get access to your device.

SimpleX Chat will work with Tor if used on an operating system that forces it to, such as Whonix or Tails. However, voice and video calls are generally not very functional over Tor with any application due to the latency Tor will introduce.

You can learn more about how to use SimpleX Chat with their guide.

For Public-facing Projects

Anyone can contact the project without requiring a separate channel

Unlike the one-time invitation links that are normally used by SimpleX Chat and shared through a separate channel, you also have a long term address that can be published online so that anyone can connect to you. We recommend not enabling "Auto-accept".

Resiliency to correlation attacks from untrusted contacts

Real-time messaging applications are particularly susceptible to end-to-end correlation attacks because of the ability of an adversary, once they know their target's ID on the messaging platform, to trigger incoming network traffic on the target's side by sending them messages on the platform (when the target is online). An issue is open to address this. Message "mixing" is also planned.

Content padding exists to frustrate correlation attacks via message size.

Resiliency to exploits from untrusted contacts

A vulnerability in any application can be targeted with exploits - a severe vulnerability can allow an adversary to hack your system, such as by permitting Remote Code Execution. For public-facing project accounts, we recommend that you set SimpleX Chat preferences to only allow text (prohibiting voice messages and attachments).

Multiple project members can access the same messages

If a project has multiple members, all of them should be able to access the same messages independently. Currently, this is not possible with SimpleX Chat.

Signal

• Mediums: Video call, voice call, text
• Metadata protection: Yes (Moderate)
• Encryption protocol: Signal Protocol, audited (2017)
• Peer-to-peer: No
• Tor: Not default

The Signal Protocol has a moderate amount of metadata protection; sealed sender, private contact discovery, and the private group system. Message recipient identifiers are only stored on Signal's servers for as long as it takes to deliver each message. As a result, if Signal is served with a warrant, they will only be able to provide the time of account creation and the date of the account's last connection to the Signal servers. Still, Signal relies on the Google Services Framework (though it's possible to use it without it), and the sealed sender metadata protection applies only to contacts (by default).

Signal is not peer-to-peer; it uses centralized servers that we must trust. Signal will work with Tor if used on an operating system that forces it to, such as Whonix or Tails.

Signing up for a Signal account is difficult to do anonymously. The account is tied to a phone number that the user must still control - due to changes in "registration lock", it is no longer sufficient to register with a disposable phone number. An anonymous phone number can be obtained on a burner phone or online and must be maintained - most people will not do this. There have been unfounded rumors that Signal plans to remove the need for a phone number after the release of a username feature - however, registration will still require a phone number.

Another barrier to anonymous registration is that Signal Desktop will only work if Signal is first registered from a smartphone. For users familiar with the command line, it is possible to register an account from a computer using Signal-cli. The VoIP account used for registration would have to be obtained anonymously.

These barriers to anonymous registration mean that Signal is rarely used anonymously. This has significant implications if the State gains physical or remote access to the device. One of the primary goals of State surveillance of anarchists is network mapping, and it's common for them to gain physical access to devices through house raids or even simple arrests. For example, if your device's authentication is bypassed, it is easy for the police to identify all of your Signal contacts (as well as the members of any groups you are in) simply by their phone number. This is a serious security breach, especially in the context of Signal groups. Compare this to the same attack on a Cwtch or SimpleX Chat user - all contacts are anonymous so device compromise does not contribute to network mapping.

In a recent repressive operation in France against a riotous demonstration, the police did exactly that. The phones of suspects were accessed through physically seizing them during arrests and house raids, as well as through spyware, and then Signal contacts and group members were identified. These identities were added to the list of suspects who were subsequently investigated. We need to understand this as a wake-up call that it is time for anarchist networks to stop using Signal.

A company that sells spyware to governments has a product called JASMINE that is marketed to deanonymize Signal users, based on the analysis of metadata.

In its targeted interception mode – which starts from a single target – JASMINE has claimed it is able to identify communicating parties in encrypted but peer-to-peer applications [...] the JASMINE documentation explicitly claims support for identifying the IP addresses of participants in encrypted apps such as WhatsApp and Signal during voice and video calls where peer-to-peer connections are also used for calling by default.

The JASMINE documentation also explains that by analysing encrypted traffic “events” for a whole country – in mass interception mode – JASMINE has the ability to correlate and identify the participants in encrypted group chats on messaging apps.

A similar product would not work against Cwtch, because it uses Tor by default.

Simply put, Signal is not a good fit for an anarchist threat model - it was designed to bring encrypted communication to the masses. Because it's very difficult to use Signal anonymously, and because we recommend against using phones whenever possible, we recommend prioritizing Cwtch over Signal for text communication with other anarchists, and prioritizing SimpleX Chat over Signal for voice and video calls. We only provide installation instructions because it has become the norm in the anarchist space in many countries, and it may be difficult to contact someone without it.

Signal Installation on GrapheneOS

If you have decided to use a smartphone despite our recommendation not to use phones, we recommend the Signal Configuration and Hardening Guide. As noted above, unless you are familiar with the Command Line Interface, Signal needs to be registered on a smartphone before it can be connected to a computer. Install Signal as you would any app that doesn't require Google Services (we don't recommend F-Droid).

Molly-FOSS is a fork of Signal with hardening and anti-forensic features available on Android - we recommend it over Signal for anarchists, and extending trust to the Molly team is made easier by its reproducible builds. Follow the instructions for installing software that isn't available in the Play Store. You can migrate from an existing Signal account. Turn on database encryption.

Signal Installation on Tails

About.Privacy maintains a guide for installing Signal Desktop on Tails. There is a guide for registering an account from Tails without a smartphone (using Signal-cli), and another guide for if you already have a Signal account.

Some of the Signal Configuration and Hardening Guide also applies to Signal Desktop.

Signal Installation on Qubes-Whonix

Signal Desktop on Whonix is not guaranteed to have Tor Stream Isolation from other applications in the same qube, so we will install it in a dedicated qube. Signal Desktop is installed in a Template, not an App qube (because it is available as a .deb from a third party repository).

Some of the Signal Configuration and Hardening Guide also applies to Signal Desktop.

• Go to Applications menu → Qubes Tools → Qube Manager
• Clone whonix-ws-16 and name it something like whonix-ws-16-signal.
  • We do this so as not to add attack surface to the base Whonix Workstation template. If you also install other messaging applications like Element Desktop, they could share a cloned template with a name like whonix-ws-16-e2ee
• Open a Terminal in the new Template: Applications menu → Template: whonix-ws-16-signal: Xfce Terminal
• Run the commands in the Signal installation guide to install Signal Desktop in the Template.
  • Note that the layout of the Signal installation guide is a bit confusing for users unfamiliar with the command line; wget and cat are separate commands, but echo in #2 is a command so long that it takes two lines (which is why the second line is indented).
  • Template qubes require a proxy for wget. Before running the command, create a configuration file at ~/.wgetrc in the Template, with the following contents:

use_proxy = on
http_proxy = 127.0.0.1:8082
https_proxy = 127.0.0.1:8082

• Create an App qube with the Template whonix-ws-16-signal and networking sys-whonix.
• In the Settings → Applications tab of the new App qube, move Signal to the Selected column and press OK.
• Updates will be handled by Qubes Update as you would expect.

Alternative method

You can install Signal Desktop in a Whonix Workstation App qube using Qube Apps and not need to bother with Templates. Signal Desktop on Flathub is community maintained, not official, which is a security consideration.

PGP Email

• Mediums: Text
• Metadata protection: No
• Encryption protocol: RSA or ed25519, no forward secrecy
• Peer-to-peer: No
• Tor: Not default

PGP (Pretty Good Privacy) is not so much a messaging platform as it is a way to encrypt messages on top of existing messaging platforms (in this case, email). PGP email does not have the encryption property of forward secrecy. The goal of forward secrecy is to protect past sessions from future key or password compromises. It maintains the secrecy of past communications even if the current communication is compromised. This means that an adversary could decrypt all future PGP messages in one fell swoop. When you also consider the metadata exposure inherent in email, PGP simply doesn't meet the standards of modern cryptography. For a more technical critique, see The PGP Problem and Stop Using Encrypted Email. Privacy Guides agrees that "email is best used for receiving transactional emails [...], not for communicating with others." We recommend that anarchists don't use PGP email for communication with other anarchists.

There is an exception: for public-facing projects, we still recommend using PGP email because it is the best option that meets the additional needs required by a public account. Use a radical server that doesn't require an invite code and read the Riseup Guide to Encrypted Email.

For Public-facing Projects

Anyone can contact the project without requiring a separate channel

Anyone can send a message to a public email account regardless of whether the recipient is online or offline.

Resiliency to correlation attacks from untrusted contacts

Email is not a real-time messaging application - this means that it is not particularly susceptible to end-to-end correlation attacks via time.

No content padding exists to frustrate correlation attacks via message size in email protocols, but if you access the mail servers through Tor then the traffic is padded.

Resiliency to exploits from untrusted contacts

A vulnerability in any application can be targeted with exploits - a severe vulnerability can allow an adversary to hack your system, such as by permitting Remote Code Execution. Email can be accessed through webmail (via Tor Browser) or through a client like Thunderbird - these have different attack surfaces. For example, a Cwtch developer found an exploit to turn Thunderbird into a decryption oracle when it displays messages with HTML.

We recommend using Thunderbird, using the setting to display email as "Plain Text" rather than as HTML: View → Message Body As → Plain Text. Most webmail will not function with Tor Browser in "Safest" mode.

Multiple project members can access the same messages

If a project has multiple members, all of them should be able to access the same messages independently. This is straight forward with email, if all project members have the email password and the private PGP key.

Note

PGP is used for another purpose outside of communication: verifying the integrity and authenticity of files. For this use case, see our explanation.

Warnings

We recommend to not use:

• Telegram: Telegram has no end-to-end encryption for group chats, and it is opt-in for one-on-one chats. The encryption doesn't use established protocols, and has had cryptographers describe it as "The Most Backdoor-Looking Bug I’ve Ever Seen".
• Matrix/Element: Matrix has a problem that is inherent in federated networks - terrible metadata leakage and data ownership. It has no forward secrecy, the Element client has a large attack surface, and there is a long list of other issues. What's more, the developers are very friendly with various national police agencies.
• XMPP Clients: Regardless of the client, an XMPP server will always be able to see your contact list. Additionally, server-side parties (e.g., administrators, attackers, law enforcement) can inject arbitrary messages, modify address books, and log passwords in cleartext.