Signal Adds Automatic Key Verification for Encrypted Chats

Signal announced Automatic Key Verification on 11 August. The feature uses key transparency to check that the public encryption key associated with a contact's phone number or username is presented consistently across Signal's ecosystem.

Signal messages were already end-to-end encrypted. This addition is designed to make a rare but serious key-substitution attack easier to detect, supplementing the existing option to compare a conversation's safety number in person or through another trusted channel. It is not a response to a disclosed break of Signal's encryption.

A sender needs the intended recipient's public key before encrypting a message. If a compromised directory secretly returned an attacker's key instead, the sender could encrypt for the wrong person while believing the conversation was secure.

Signal's design records public-key associations in a verifiable history and uses checks by users, their contacts and independent auditors. Signal named Cloudflare and Trail of Bits as external auditors. Trail of Bits says clients require recent endorsements from all three auditors, limiting how long a fully malicious server could sustain an inconsistent view before warnings appear.

First enable the feature under Settings, Privacy, Advanced, Automatic Key Verification. Signal's instructions are then to open the contact's profile, select View Safety Number, and choose Verify automatically. When the check is available for that connection and succeeds, the app displays Encryption verified with a green checkmark. The app also periodically verifies its own public identifier records.

Automatic verification does not prove that the human holding a device is who they claim to be, and an unavailable check is not automatically evidence of an attack. People handling especially sensitive conversations can still compare safety numbers through a trusted second channel and should investigate unexpected key changes before continuing.

A VPN encrypts traffic between a device and the VPN server and can hide the user's usual public IP address from many destinations. That can reduce exposure to local network operators, particularly on public Wi-Fi.

It does not verify which public key belongs to a Signal contact, control Signal's directory or authenticate the person at the other end of a conversation. Conversely, end-to-end encrypted messaging does not hide all connection metadata or protect unrelated browser traffic. These tools address different layers and should not be treated as substitutes.

Security features are most useful when they reduce the work required from ordinary users without concealing what is being checked. Automatic Key Verification improves the default path while keeping the manual safety-number option available for situations that demand direct identity confirmation.

The larger lesson is that 'encrypted' is not one control. Transport privacy, message encryption, key authenticity, device security and human identity are separate questions, each needing the right safeguard.