STIR/SHAKEN (Secure Telephone Identity Revisited / Signature-based Handling of Asserted information using toKENs) is a US framework for authenticating the caller ID of telephone calls over IP networks. Implemented under FCC mandate, STIR/SHAKEN requires carriers to digitally sign and verify caller identity information. Calls receive an attestation level: A-level (full attestation โ carrier has verified the customerโs right to use the number), B-level (partial), or C-level (gateway). A-level attestation improves call answer rates and reduces the risk of calls being flagged as spam or spoofed.
STIR/SHAKEN is a US framework that adds a cryptographic digital signature to VoIP calls to verify that the caller ID displayed is accurate and has not been spoofed. Carriers sign outbound calls using a certificate issued by the STIR/SHAKEN governance authority, and receiving carriers verify the signature before delivering the call. For businesses, this matters because calls that pass STIR/SHAKEN verification are less likely to be labelled as โSpam Likelyโ or โScam Likelyโ by mobile carriers, improving answer rates on outbound calls.
STIR/SHAKEN uses three attestation levels. A-level (Full Attestation) means the originating carrier has verified the customerโs identity and their authorisation to use the specific calling number โ this is the strongest signal and the most beneficial for call delivery. B-level (Partial Attestation) means the carrier has verified the customer but cannot confirm they are authorised to use that specific number. C-level (Gateway Attestation) means the carrier cannot verify the origin of the call โ typically applied to calls entering the IP network from a foreign or legacy network. A-level calls are treated most favourably by receiving carriers.
Yes. The FCC mandated STIR/SHAKEN implementation for all US voice carriers under the TRACED Act (Telephone Robocall Abuse Criminal Enforcement and Deterrence Act). Large carriers (those with more than 100,000 voice subscriber lines) were required to implement it by June 2021; smaller carriers and non-IP networks had extended deadlines. Today, virtually all US voice traffic carried over IP networks is expected to bear a STIR/SHAKEN signature, and carriers that cannot sign calls must apply for an extension or use a third-party signing service.
IDT Express provides a free STIR/SHAKEN lookup tool at idtexpress.com/tools/stir-shaken/ that lets you check the attestation level associated with your outbound calls. You can also check by reviewing the PASSporT (Personal ASsertion Token) embedded in your SIP INVITE headers โ the โattestโ field will show A, B, or C. If your calls are receiving B or C attestation when you expect A-level, contact your carrier to confirm your number registration and account verification status.
