What is STIR/SHAKEN?

STIR/SHAKEN is the system that lets a carrier sign a call, cryptographically, to prove the number is real. Here is what the signature actually promises, and what it does not.

Signing a call the way you would sign a document

STIR/SHAKEN is a system that lets your carrier cryptographically sign an outgoing call, attaching proof that the call genuinely originated from a number the carrier can vouch for. STIR defines the technical signing method, SHAKEN defines how carriers actually deploy and check it across the phone network. In practice people just say the two names together.

Three levels of attestation, not a single yes or no

A signed call carries one of three grades, and the difference between them matters more than most people realise:

• A, full attestation: the carrier authenticated the caller and confirmed they are actually authorised to use this exact number.
• B, partial attestation: the carrier knows who the customer is, but could not confirm they own this specific number.
• C, gateway attestation: the carrier only authenticated the network the call entered from, nothing about the original caller at all.

What A actually proves, and what it does not

Full attestation confirms the number is authorised. It does not confirm the person calling is honest. A scammer who legitimately rents a real number can still earn a genuine A signature, because the system verifies authorisation, not intention. This is the single most misunderstood part of how call spoofing is actually being fought.

Why it only covers part of the world

STIR/SHAKEN is mandated in the United States and Canada. Calls that stay entirely within that ecosystem can carry a verified signature end to end. The moment a call crosses an international boundary, into a country without an equivalent mandate, that signature is typically stripped away entirely, leaving no attestation at all rather than a weaker one.