STIR (Secure Telephone Identity Revisited)

Secure Telephone Identity Revisited is the IETF framework (RFCs 8224/8225/8226) for cryptographically signing the calling number in a SIP INVITE so that downstream networks can verify that the originating provider attested to the caller's right to use that number. STIR is the cryptographic engine underneath SHAKEN, the operational profile mandated by US and Canadian regulators to combat illegal robocalls and CLI spoofing. It depends on a healthy ecosystem of certificate authorities and policy administrators.

Categories: SignalingIdentity and SubscriberSecurity Controls

STIR in context

Signaling protocols carry the control-plane instructions that set up calls, register subscribers, hand over sessions and route SMS. SS7, Diameter, GTP-C and SIP are the four dominant families, and interconnect exposure of any of them is treated by GSMA FS.11 / FS.19 / FS.20 as a top-tier telecom risk.

Subscriber identifiers (IMSI, SUPI, MSISDN, IMEI) are the anchor for authentication, charging, lawful interception and fraud analytics. Any protocol or interface that leaks a permanent identifier is treated as a serious privacy defect, which is why 5G introduced SUCI concealment on the air interface.

To place STIR in the wider telecom-security picture, review STIR/SHAKEN, AAA, IMSI, Any-Time Interrogation (ATI), CAP and MNP.

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