2026-02-15
STIR/SHAKEN is a call authentication framework mandated by the FCC for US carriers. STIR (Secure Telephone Identity Revisited) defines the standards, and SHAKEN (Signature-based Handling of Asserted information using toKENs) defines how carriers implement it.
The system uses digital certificates to verify that the calling party is authorized to use the caller ID they're presenting.
The carrier knows the customer and confirms they are authorized to use the calling number. This is the highest trust level, typically assigned to numbers directly owned by the customer on that carrier.
The carrier knows the customer but cannot verify their authorization to use the specific number. Common for PBX systems where a business may present various numbers.
The carrier received the call from an international gateway or interconnect and cannot verify the caller or number. This is the lowest trust level and is common for international calls.
No. STIR/SHAKEN does not block calls. It adds attestation information that carriers and phone apps can use to label calls, but the calls still go through. A call with C-level attestation might show without a "Verified" badge, but it won't be blocked.
Most international VoIP calls, including those from services like SpoofGlobal, receive C-level attestation because they enter the US network through international gateways. This is normal for all international calls — not just spoofed ones.
No. STIR/SHAKEN adds verification labels to calls but does not block them. Calls with low attestation still connect normally.
Yes. CLI routes display your chosen number regardless of STIR/SHAKEN attestation. The number shows on the recipient phone as normal.
STIR/SHAKEN was mandated by the FCC for US carriers in 2021. Canada has implemented a similar system. Most other countries have not adopted it yet.
Some phones show a Verified Caller checkmark for calls with A-level attestation. This means the originating carrier verified the caller owns the number. Absence of this label does not mean the call is spam.