Signal supports [private groups](https://signal.org/blog/signal-private-group-system/). 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. Signal requires your phone number as a personal identifier.
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/).
We have some additional tips on configuring and hardening your Signal installation:
[Signal Configuration and Hardening :material-arrow-right-drop-circle:](https://blog.privacyguides.org/2022/07/07/signal-configuration-and-hardening/)
**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 [was audited](https://simplex.chat/blog/20221108-simplex-chat-v4.2-security-audit-new-website.html) by Trail of Bits in October 2022.
Currently SimpleX Chat only provides a client for Android and iOS. Basic group chatting functionality, direct messaging, editing of messages and markdown are supported. 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 has a fully [published specification](https://code.briarproject.org/briar/briar-spec).
Briar supports perfect forward secrecy 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 Perfect [Forward Secrecy](https://en.wikipedia.org/wiki/Forward_secrecy) (PFS), 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 for the [Matrix](https://matrix.org/docs/guides/introduction) protocol, an [open standard](https://matrix.org/docs/spec) for secure decentralized real-time communication.
Messages and files shared in private rooms (those which require an invite) are by default E2EE as are one to one voice and video calls.
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 PFS](https://gitlab.matrix.org/matrix-org/olm/blob/master/docs/megolm.md#partial-forward-secrecy), 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](https://matrix.org/docs/projects/other/olm) cryptographic ratchet 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 does [not](https://getsession.org/blog/session-protocol-technical-information) support PFS, which is when an encryption system automatically and frequently changes the keys it uses to encrypt and decrypt information, such that if the latest key is compromised it exposes a smaller portion of sensitive information.
Oxen requested an independent audit for Session in March of 2020. The audit [concluded](https://getsession.org/session-code-audit) in April of 2021, “The overall security level of this application is good and makes it usable for privacy-concerned people.”
Session has a [whitepaper](https://arxiv.org/pdf/2002.04609.pdf) describing the technicals of the app and protocol.
**Privacy Guides는 권장 목록의 어떠한 프로젝트와도 제휴를 맺지 않았습니다.** 객관적인 권장 목록을 제공하기 위해, [일반적인 평가 기준](about/criteria.md)에 더해 명확한 요구 사항을 정립하였습니다. 어떠한 프로젝트를 선택해 사용하기 전에, 이러한 요구 사항들을 숙지하고 여러분 스스로 조사하는 과정을 거쳐 적절한 선택을 하시기 바랍니다.
Privacy Guides 팀은 사이트의 모든 항목마다 명확한 평가 기준을 정립하는 중이며, 따라서 세부 내용은 변경될 수 있습니다. 평가 기준에 대해서 질문이 있다면 [포럼에서 문의](https://discuss.privacyguides.net/latest)하시기 바랍니다. (무언가가 목록에 존재하지 않다고 해서 권장 목록을 작성할 때 고려한 적이 없을 것으로 단정 짓지 마세요.) 권장 목록에 어떤 프로젝트를 추가할 때 고려하고 논의해야 할 요소는 매우 많으며, 모든 요소를 문서화하는 것은 현재 진행 중인 작업입니다.
