Signal

Signal is a privacy-focused messaging app with end-to-end encryption and open-source transparency.

Open Source Privacy Friendly Ad-Free No Third-Party Trackers Free of Charge
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Description

Signal is a messaging app that prioritises user privacy above all else. It uses the Signal Protocol, an open-source end-to-end encryption standard, to secure all communications—texts, voice calls, and video calls. The app is developed and maintained by the Signal Foundation, a non-profit organisation funded primarily by donations and a $50 million initial investment from WhatsApp co-founder Brian Acton. This funding model is supposed to ensure that Signal remains independent and ad-free. It was projected that running Signal would cost $50 Million a Year from 2025 on.

Signal’s features include disappearing messages, group chats for up to 1,000 people, and encryption mechanisms that minimise metadata exposure (see infographic by FBI). The app’s code is fully open-source, allowing independent audits and community contributions.

However, Signal’s server infrastructure relies on major cloud providers, which may not align with all sustainability goals, especially because it creates a revenue stream for Big Tech companies and compromises data sovereignty. Its use of Cloudflare CDN also causes location data to be leaked.

Additionally, Signal is vulnerable to timing attacks that let attackers get info about users' device statuses. This vulnerability is affecting all Messaging apps that send delivery receipts.

Signal is exploring the introduction of a paid feature for encrypted backups.

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Sustainability Features of Signal

Open Source - Free and Open-Source Software

Signal is fully open-source, allowing for independent audits and community contributions to its codebase.

Privacy Friendly - It does not track users unnecessarily.

Signal uses end-to-end encryption by default for all communications, ensuring user privacy.

Ad-Free - Services that do not display advertisements to users, ensuring a cleaner and more private experience.

Signal is ad-free and does not engage in data mining or targeted advertising.

No Third-Party Trackers - Services that do not use third-party cookies or trackers, ensuring user privacy.

Signal does not use third-party trackers, ensuring user data is not shared with external parties.

Free of Charge - The services provided can be used for free.

Signal is free to use for all users, with no premium features locked behind paywalls (yet).

Website

Summary

Signal is a privacy-focused, end-to-end encrypted messaging app developed by the non-profit Signal Foundation. It is widely regarded as the gold standard for secure communication, offering features like disappearing messages and automatic face-blurring for sensitive images.

Signal is fully open-source, funded by donations, and does not rely on ads or data mining. However, its reliance on major cloud providers like AWS and Cloudflare for its infrastructure raises some sustainability and resiliency concerns. Despite its image as the most secure messenger out there, it's been shown that Signal is vulnerable to attacks that leak user data.

Sustainability Score
85

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