**Molly** 是 Android 的替代 Signal 用戶端，可讓您使用密碼加密本機資料庫、安全地刪除未使用的 RAM 資料、透過 Tor 路由連線；除此之外，還有 [許多](https://blog.privacyguides.org/2022/07/07/signal-configuration-and-hardening#privacy-and-security-features)。 It also has usability improvements including scheduled backups, automatic locking, [UnifiedPush](https://unifiedpush.org) support, and the ability to use your Android phone as a linked device instead of the primary device for a Signal account.
There is a version of Molly called **Molly-FOSS** which removes proprietary code like the Google services used by both Signal and Molly, at the expense of some features like battery-saving push notifications via Google Play Services. You can regain push notifications without Google Play Services in either version of Molly with [UnifiedPush](https://unifiedpush.org), but it requires running a separate program called [Mollysocket](https://github.com/mollyim/mollysocket) on another device to function. Mollysocket can either be self-hosted on a separate computer or server (VPS), or alternatively a public Mollysocket instance can be used ([step-by-step tutorial, in German](https://kuketz-blog.de/messenger-wechsel-von-signal-zu-molly-unifiedpush-mollysocket-ntfy)).
Molly and Molly-FOSS support [reproducible builds](https://github.com/mollyim/mollyim-android/tree/main/reproducible-builds), meaning it's possible to confirm that the compiled APKs match the source code.
SimpleX provides direct messaging, group chats, and E2EE calls secured with the [SimpleX Messaging Protocol](https://github.com/simplex-chat/simplexmq/blob/stable/protocol/simplex-messaging.md), which uses double ratchet encryption with quantum resistance. Additionally, SimpleX Chat provides metadata protection by using unidirectional ["simplex queues"](https://github.com/simplex-chat/simplexmq/blob/stable/protocol/simplex-messaging.md#simplex-queue) to deliver messages.
To participate in conversations on SimpleX Chat, you must scan a QR code or click an invite link. This allows you to verify a contact out-of-band, which protects against man-in-the-middle attacks by network providers. Your data can be exported and imported onto another device, as there are no central servers where this is backed up.
You can find a full list of the privacy and security [features](https://github.com/simplex-chat/simplex-chat#privacy-and-security-technical-details-and-limitations) implemented in SimpleX Chat on the app's repository.
SimpleX Chat was independently audited in [July 2024](https://simplex.chat/blog/20241014-simplex-network-v6-1-security-review-better-calls-user-experience.html#simplex-cryptographic-design-review-by-trail-of-bits) and in [October 2022](https://simplex.chat/blog/20221108-simplex-chat-v4.2-security-audit-new-website).
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.
With the integration of [Element Call](https://element.io/blog/we-have-lift-off-element-x-call-and-server-suite-are-ready) into Element's web app, desktop apps, and its [rewritten mobile apps](https://element.io/blog/element-x-experience-the-future-of-element), group VoIP and video calls are E2EE by default.
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 allows for E2EE in one-on-one chats or closed groups which allow for up to 100 members. It is also possible to [set up](https://docs.oxen.io/oxen-docs/products-built-on-oxen/session/guides/open-group-setup) or join open groups which can host thousands of members, but messages in these open groups are **not** end-to-end encrypted between participants.
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]
