Signal is adding automatic key verification to confirm that participants see the same mapping between a phone number, username and public key. The feature complements manually compared safety numbers and relies on a cryptographic log audited by Cloudflare and Trail of Bits.
The short answer
| Question | Answer |
|---|---|
| Where is the check? | Open a contact profile, choose View Safety Number, then Verify automatically. |
| What does the green check mean? | The observed public key is consistent in the transparency system. |
| Does it prove the contact’s physical identity? | No. It verifies a key mapping, not the person controlling the account. |
| Does it replace manual QR verification? | No. Manual comparison remains available and more independent. |
The risk: silent key substitution
End-to-end encryption uses the recipient’s public key. If a compromised server supplied a different key to selected users, it could attempt to insert an intermediary without showing the same view to everyone.
Key transparency records mappings and changes in a verifiable structure. The app, contacts and third-party auditors can detect inconsistent views. Identifiers are cryptographically obscured before auditors process them.
A more accessible check
Comparing a long number or scanning a QR code in person gives strong assurance, but few users do it. The new option provides a useful check without a meeting or second channel.
It has prerequisites. Signal says verification currently requires access to the contact’s phone number. A relationship started only through a username may therefore be ineligible.
What it cannot detect
If an attacker fully controls an account while retaining its legitimate key, transparency cannot prove the usual owner remains in control. A legitimate phone-number change may also trigger a warning.
For a sensitive conversation, confirm an unexpected change through a known call, meeting or another channel. The green check is not a universal substitute for human identity verification.
Auditors without plaintext contacts
Cloudflare and Trail of Bits verify cryptographic-tree consistency. Signal says phone numbers and usernames are transformed and lookups are unauthenticated so they are not tied to a specific account.
Users who do not want any third-party dependency can disable the feature under advanced privacy settings and continue comparing safety numbers.
Signal is automating a check that too few people performed manually. The green check strengthens confidence in key distribution, but it proves neither a correspondent’s identity nor the integrity of their device.
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