New WhatsApp multi-device support

WhatsApp is rolling out a limited public beta of its app that includes improved multi-device capability.

This will allow the app to be used on other devices without an actively connected smartphone.

As it stands, WhatsApp offers web, macOS, Windows, and Portal apps, but these have to be connected to a smartphone with the app that is connected to the Internet.

The phone acts as the primary device or  “source of truth” for all user data and is the only device in the system capable of encrypting messages end-to-end, initiating calls, and more.

“Companion devices maintain a persistent secure connection with the phone and simply mirror its contents on their own UI,” WhatsApp explains.

WhatsApp acknowledged that while this architecture made it easy to deliver a synchronised experience between a phone and companion device without compromising security, it comes with significant reliability trade-offs.

“By requiring the phone to perform all operations, companion devices are slower and frequently get disconnected — especially when the phone has a poor connection, its battery is running low, or the application process gets killed by the phone’s OS,” the company stated.

“It also allows for only a single companion device to be operative at a time, meaning people can’t be on a call in Portal while checking their messages on their PC, for example.”

The image below illustrates what the current multi-device architecture looks like in the latest official version of the app.

The new WhatsApp multi-device architecture removes the need for the smartphone app to act as the central hub to use the service.

“With this new capability, you can now use WhatsApp on your phone and up to four other non-phone devices simultaneously — even if your phone battery is dead,” WhatsApp said.

“Each companion device will connect to your WhatsApp independently while maintaining the same level of privacy and security through end-to-end encryption.”

Any easy way to achieve multi-device support while syncing data like contact names, chat archives and starred messages across devices would have been to store people’s private messages on its servers.

However, WhatsApp said it wanted to enable multi-device capability while ensuring that privacy and end-to-end encryption remains.

“To achieve this, we had to rethink WhatsApp’s architecture and design new systems to enable a standalone multi-device experience while preserving privacy and end-to-end encryption,” WhatsApp said.

Before the multi-device support, everyone on WhatsApp was identified by a single identity key from which all encrypted communication keys were derived. With multi-device, each device now has its own identity key.

“The WhatsApp server maintains a mapping between each person’s account and all their device identities. When someone wants to send a message, they get their device list keys from the server,” the company said.

“Each message is individually encrypted using the established pairwise encryption session with each device. Messages are not stored on the server after they are delivered,” the company said.

The image below shows how the new architecture functions.

WhatsApp said it is also using a combination of technologies to prevent malicious or compromised servers from eavesdropping on someone’s communication by adding devices to someone’s account.

This includes:

  • Extended security codes — These unique identifiers now represent the combination of all of someone’s device identities so that contacts can verify all the devices they are sending messages to.
  • Automatic Device Verification — Devices can automatically establish trust between each other in a way that someone needs to compare another user’s security code only if that user reregisters their entire account, rather than each time they link a new device to their account.
  • Biometric authentication for linking devices — Compatible devices will now require you to scan your fingerprint or face to link them to the WhatsApp account.
  • Device list — Users can see all companion devices linked to their account and when they were last used and can log out of them remotely if needed.

WhatsApp said it plans to initially test the experience with a small group of users from its existing beta program, so it will be a while before it reaches general release.

“We will continue optimising performance and adding a few additional features before slowly rolling it out more broadly,” WhatsApp stated. Users of the official app will be able to opt out of the feature once it is available on their device.

For more information about the beta and to sign up, you can visit the WhatsApp Help Centre.

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New WhatsApp multi-device support