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Signal introduces automatic key verification for encrypted chats
Signal has introduced automatic key verification, a key-transparency feature designed to make encrypted-chat security checks easier without requiring an in-person comparison or a second communication channel.
Signal has introduced automatic key verification, a new feature designed to make an important encrypted-messaging check easier to perform. The system complements Signal’s existing Safety Number process by helping users confirm that a contact’s public encryption key remains consistent across the service.
The change addresses a difficult but important question in secure messaging: how can someone know that the key used to encrypt a conversation really belongs to the intended contact? Signal’s messaging remains end-to-end encrypted, but encrypted communication also depends on correctly associating an account identifier with the right public key.
What automatic key verification changes
When a person registers with Signal, the app creates a public and private key pair. The private key stays on the user’s device, while the public key is used by Signal to help other people encrypt messages for that account. Signal’s existing Safety Number system allows two contacts to compare or scan information manually, often through an in-person meeting or a separate trusted channel.
Automatic key verification is intended to reduce that friction. Signal says users can open a contact’s profile, select View Safety Number, and then choose Verify automatically under the relevant section. When the check is available and succeeds, the interface displays a green checkmark and the message Encryption verified.
The process does not depend on both people arranging a meeting or exchanging a long verification number elsewhere. Instead, it combines checks performed by the user, the Signal connection and independent third-party auditors. Together, those checks are designed to provide assurance comparable to manually verifying Safety Numbers.
Why key transparency matters
The feature is built on a security approach known as key transparency. Signal’s explanation compares the system with a public, append-only ledger. When an account changes its phone number, username or encryption key, the event is recorded as a new entry rather than silently replacing an older record.
This structure is designed to make inconsistencies detectable. A malicious or compromised directory could theoretically try to show one public key to one person and a different key to another. A globally consistent transparency log makes that kind of split view harder to hide because clients and auditors can compare the same history of changes.
Signal has also published an open-source key transparency server for the system. The project describes a cryptographically protected log that records mappings between public identifiers and public keys, while using search structures that make large histories practical to query.
Independent auditors and privacy protections
Signal identifies Cloudflare and Trail of Bits as independent auditors for its implementation. Their role is not to read message content or identify users. Instead, they check that successive versions of the transparency data are consistent and that the service is not presenting different histories to different participants.
The system is designed to avoid exposing plaintext user identifiers to auditors. Signal says public identifiers are processed through cryptographic techniques before they enter the transparency log, while the associated values are protected with keyed hashing. That approach is intended to let the system verify consistency without turning the log into a public directory of phone numbers or usernames.
What the feature does not prove
Automatic key verification confirms an important part of the encryption setup, but it is not a complete identity check. Signal explicitly notes that key transparency does not prove who controls a particular phone number or username. If an attacker has taken over an account, the key can still be consistent with the compromised account.
A changed key also does not automatically mean an attack has occurred. People may reinstall Signal, change devices or recreate an account. Signal recommends following up through a separate trusted channel when a change is unexpected. Its support guidance on Safety Number changes remains relevant in those situations.
There are also cases where automatic verification is unavailable. For example, Signal says a user may not be able to verify a connection discovered only through a username if the corresponding phone number is not available. People who prefer not to rely on any third party can disable automatic key verification in Signal’s privacy settings and continue using manual Safety Number checks.
A lower-friction security check
Signal’s announcement is less about changing the encryption users already rely on than about making key integrity easier to inspect. The feature turns a specialist security task into a guided check inside the mobile app, while keeping manual verification available for situations that require stronger human confirmation.
That distinction matters. Automatic verification can reduce the chance that users ignore an important security warning simply because the existing process feels inconvenient, but it cannot replace careful judgment after an unexpected account or key change. Signal’s approach combines automated consistency checks, independent auditing and user follow-up rather than presenting any single step as a complete guarantee.