**Signal** is a mobile app developed by Signal Messenger LLC. The app provides instant messaging and calls secured with the Signal Protocol, an extremely secure encryption protocol which supports forward secrecy[^1] and post-compromise security.[^2]
Signal requires your phone number for registration, however you should create a username to hide your phone number from your contacts:
1. In Signal, open the app's settings and tap your account profile at the top.
2. Tap **Username** and choose **Continue** on the "Set up your Signal username" screen.
3. Enter a username. Your username will always be paired with a unique set of digits to keep your username unique and prevent people from guessing it, for example if you enter "John" your username might end up being `@john.35`.
4. Go back to the main app settings page and select **Privacy**.
5. Select **Phone Number**
6. Change the **Who Can See My Number** setting to: **Nobody**
You can optionally change the **Who Can Find Me By Number** setting to **Nobody** as well, if you want to prevent people who already have your phone number from discovering your Signal account/username.
Contact lists on Signal are encrypted using your Signal PIN and the server does not have access to them. Personal profiles are also encrypted and only shared with contacts you chat with. Signal supports [private groups](https://signal.org/blog/signal-private-group-system), where the server has no record of your group memberships, group titles, group avatars, or group attributes. Signal has minimal metadata when [Sealed Sender](https://signal.org/blog/sealed-sender) is enabled. The sender address is encrypted along with the message body, and only the recipient address is visible to the server. Sealed Sender is only enabled for people in your contacts list, but can be enabled for all recipients with the increased risk of receiving spam.
The protocol was independently [audited](https://eprint.iacr.org/2016/1013.pdf) in 2016. The specification for the Signal protocol can be found in their [documentation](https://signal.org/docs).
**SimpleX** Chat is an instant messenger that is decentralized and doesn't depend on any unique identifiers such as phone numbers or usernames. Users of SimpleX Chat can scan a QR code or click an invite link to participate in group conversations.
SimpleX Chat supports basic group chatting functionality, direct messaging, and editing of messages and markdown. E2EE Audio and Video calls are also supported. Your data can be exported, and imported onto another device, as there are no central servers where this is backed up.
**Briar** is an encrypted instant messenger that [connects](https://briarproject.org/how-it-works) to other clients using the Tor Network. Briar can also connect via Wi-Fi or Bluetooth when in local proximity. Briar’s local mesh mode can be useful when internet availability is a problem.
To add a contact on Briar, you must both add each other first. You can either exchange `briar://` links or scan a contact’s QR code if they are nearby.
The client software was independently [audited](https://briarproject.org/news/2017-beta-released-security-audit), and the anonymous routing protocol uses the Tor network which has also been audited.
Briar supports forward secrecy[^1] by using the Bramble [Handshake](https://code.briarproject.org/briar/briar-spec/blob/master/protocols/BHP.md) and [Transport](https://code.briarproject.org/briar/briar-spec/blob/master/protocols/BTP.md) protocol.
These messengers do not have forward secrecy[^1], and while they fulfill certain needs that our previous recommendations may not, we do not recommend them for long-term or sensitive communications. Any key compromise among message recipients would affect the confidentiality of **all** past communications.
**Element** is the reference [client](https://matrix.org/ecosystem/clients) for the [Matrix](https://matrix.org/docs/chat_basics/matrix-for-im) protocol, an [open standard](https://spec.matrix.org/latest) for secure decentralized real-time communication.
Group voice and video calls are [not](https://github.com/vector-im/element-web/issues/12878) E2EE, and use Jitsi, but this is expected to change with [Native Group VoIP Signalling](https://github.com/matrix-org/matrix-doc/pull/3401). Group calls have [no authentication](https://github.com/vector-im/element-web/issues/13074) currently, meaning that non-room participants can also join the calls. We recommend that you do not use this feature for private meetings.
The Matrix protocol itself [theoretically supports forward secrecy](https://gitlab.matrix.org/matrix-org/olm/blob/master/docs/megolm.md#partial-forward-secrecy)[^1], however this is [not currently supported in Element](https://github.com/vector-im/element-web/issues/7101) due to it breaking some aspects of the user experience such as key backups and shared message history.
The protocol was independently [audited](https://matrix.org/blog/2016/11/21/matrixs-olm-end-to-end-encryption-security-assessment-released-and-implemented-cross-platform-on-riot-at-last) in 2016. The specification for the Matrix protocol can be found in their [documentation](https://spec.matrix.org/latest). The [Olm cryptographic ratchet](https://matrix.org/docs/matrix-concepts/end-to-end-encryption) used by Matrix is an implementation of Signal’s [Double Ratchet algorithm](https://signal.org/docs/specifications/doubleratchet).
**Session** is a decentralized messenger with a focus on private, secure, and anonymous communications. Session offers support for direct messages, group chats, and voice calls.
Session uses the decentralized [Oxen Service Node Network](https://oxen.io) to store and route messages. Every encrypted message is routed through three nodes in the Oxen Service Node Network, making it virtually impossible for the nodes to compile meaningful information on those using the network.
Session allows for E2EE in one-on-one chats or closed groups which allow for up to 100 members. Open groups have no restriction on the number of members, but are open by design.
Session was previously based on Signal Protocol before replacing it with their own in December 2020. Session Protocol does [not](https://getsession.org/blog/session-protocol-technical-information) support forward secrecy.[^1]
Oxen requested an independent audit for Session in March 2020. The audit [concluded](https://getsession.org/session-code-audit) in April 2021, “The overall security level of this application is good and makes it usable for privacy-concerned people.”
**Please note we are not affiliated with any of the projects we recommend.** In addition to [our standard criteria](about/criteria.md), we have developed a clear set of requirements to allow us to provide objective recommendations. We suggest you familiarize yourself with this list before choosing to use a project, and conduct your own research to ensure it's the right choice for you.
Our best-case criteria represents what we would like to see from the perfect project in this category. Our recommendations may not include any or all of this functionality, but those which do may rank higher than others on this page.
- Decentralized, i.e. [federated or P2P](advanced/communication-network-types.md).
- Uses E2EE for all messages by default.
- Supports Linux, macOS, Windows, Android, and iOS.
[^1]: [Forward Secrecy](https://en.wikipedia.org/wiki/Forward_secrecy) is where keys are rotated very frequently, so that if the current encryption key is compromised, it does not expose **past** messages as well.
[^2]: Future Secrecy (or Post-Compromise Security) is a feature where an attacker is prevented from decrypting **future** messages after compromising a private key, unless they compromise more session keys in the future as well. This effectively forces the attacker to intercept all communication between parties, since they lose access as soon as a key exchange occurs that is not intercepted.
