STIR/SHAKEN is a protocol that verifies the authenticity of caller IDs using digital signatures. It consists of two specifications: STIR (Secure Telephone Identity Revisited, IETF RFC 8224/8225) and SHAKEN (Signature-based Handling of Asserted information using toKENs, an ATIS standard). It has attracted attention as an international standard for technically preventing fraud caused by caller ID spoofing.
The mechanism works as follows: the originating carrier attaches a digital signature (public-key cryptography) to the caller ID, and the terminating carrier verifies that signature. Verification results are displayed in three levels. A (Full Attestation) means the carrier has fully confirmed the caller is the legitimate user of the number. B (Partial Attestation) means the origin is confirmed but the number's legitimacy is not verified. C (Gateway Attestation) covers cases where verification is difficult, such as international calls. The receiving device displays indicators like "Verified Call," giving users a clue to distinguish spoofed calls.
In the United States, the FCC (Federal Communications Commission) mandated STIR/SHAKEN adoption for major carriers in 2021. After implementation, robocalls and spoofed nuisance calls reportedly decreased by about 30%. Canada, the UK, France, and other countries are also adopting it, making it an emerging global standard for anti-spoofing measures.
Japan's Ministry of Internal Affairs and Communications is also studying caller ID spoofing countermeasures. Currently, fraud via number spoofing apps and spoofed international calls causing bank transfer fraud is a serious problem, so early adoption is anticipated. However, Japan's telephone network is structured around NTT and differs from the US in inter-carrier interconnection, so implementation adapted to Japan's telecommunications environment is being considered rather than a direct transplant. See Caller ID Spoofing Risks for the latest tactics and countermeasures.