End-to-end encryption explained
Understand the difference between encryption in transit, encryption at rest and end-to-end encryption.
Start with the type of encryption
An app can encrypt data in several ways. Encryption in transit protects the connection between systems. Encryption at rest protects stored data. End-to-end encryption protects message content so the communicating devices hold the keys needed to read it.
These terms are not interchangeable. A claim that a chat is encrypted does not, by itself, explain who can decrypt it.
Check the conversation, not just the app
Different conversation types and platforms can have different protections. Check the published information for group chats, individual chats, calls, files and backups separately.
Look for whether end-to-end encryption applies to the conversation you are using, whether it requires a setting, and what happens when you add a device or create a backup.
What this means in SYNC
Mobile messages, including group messages, and calls use end-to-end encryption. Photos, videos and other files are encrypted in transit and at rest. Optional Encrypted Backup is a separate recovery feature.
Your end-to-end encrypted message content is different from your account information and operational metadata. Privacy does not mean the service keeps no records.
Keep the device in mind
Encryption does not prevent someone from reading an unlocked screen or saving a screenshot. A strong device lock, careful notification settings and a separate PIN for selected chats add practical controls.
Choose what you share with a group as carefully as you choose the app. Every recipient can potentially save or forward content.
What happens when you send a message?
Imagine sending a friend a meeting address. You can read the message on your screen before sending it. In an end-to-end encrypted conversation, your device turns that readable content into ciphertext before it travels through the service. The recipient’s device uses the appropriate key material to turn it back into readable text.
The service can deliver the message without needing its readable contents. That is the central distinction: the systems carrying the message do not also hold the keys needed to read it. This describes the encryption model, not a promise that every part of an account or every attachment receives the same protection.
Who holds the keys?
Encryption keys are data used by cryptographic algorithms, not the PIN you type to unlock your screen. A device lock protects access to your device. A message-encryption key protects the message itself. Both matter, but they solve different problems.
Private keys need to remain protected. Some systems also offer identity or key verification, which helps people check they are communicating with the intended recipient. If your app offers this feature, follow its instructions and compare the information through a channel you already trust. Do not assume that recognising a profile picture is the same as verifying an identity.
What changes in a group conversation?
A group has more endpoints because several people are authorised to read its messages. Each member’s device becomes part of the practical security picture. Encryption can protect delivery, but it cannot control what a member does after reading a message.
Adding or removing members also raises questions about history and future access. Whether a new member can read earlier messages depends on the application’s design. Before sharing sensitive information, check the participant list, review the group’s settings and ask how history is handled when membership changes.
Are backups and linked devices included?
A backup creates another copy of your information. Its protection depends on how that copy is encrypted, who can recover its keys and which recovery method is enabled. End-to-end encryption for live messages does not automatically describe the backup system.
Linked devices create additional places where conversations may be readable. Review devices you no longer use and remove access through the available account controls. In SYNC, the published end-to-end encryption statements on this site concern mobile messages and calls. See the Encrypted Backup section for the separate recovery feature.
What should you check before choosing an app?
Start with concrete questions. Does protection apply to the conversation type you use? Are messages, calls and files covered by the same model? How are backups recovered? What happens when you change phones? Clear answers are more useful than a general claim that everything is secure.
Read the privacy policy alongside the product description. It explains information the service may process beyond message content. Then review the controls you can actually configure, including screen locks, notification previews, linked devices and SYNC’s security suite.
A useful next step
Choose one conversation you care about and review its settings today. Confirm the participants, check the protection that applies and decide whether you want notification previews or an encrypted backup. Small, deliberate choices help turn an encryption feature into useful everyday privacy.
For a general introduction independent of SYNC, read the Electronic Frontier Foundation’s guide to encryption.
