STIR WG Response to LS on technical measures and mechanism on countering the spoofed call in the visited network of VoLTE
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LS on technical measures and mechanism on countering the spoofed call in the visited network of VoLTE
Re: Liaison 1353 (ITU SG 17 – COM17_LS149) The IETF STIR WG appreciates the notification from ITU-T SG 17 of the adoption of its new work item X.ticsc, on "Technical measures and mechanism on countering the spoofed call in the visited network of VoLTE." We note that the approach in X.ticsc focuses on the identification of spoofed or impersonated calls, and the IETF STIR WG concurs that impersonation is the primary enabler of robocalling, voicemail hacking, and swatting attacks today, and is thus a proper scope of ongoing work to combat those attacks. The X.ticsc document outlines three measures to address the VoLTE spam problem: IMS-based approaches, RCS-based approaches, and smartphone functions. The IMS-based approach discusses how an application server layer of IMS might detect a spoofed call. The IETF STIR WG believes that intermediaries have a role to play in implementing the functions of an "authentication service," which decides if a caller is authorized to claim a calling number/identity, and a "verification service," which ascertains if a request contains a valid cryptographic assertion of authority. Our "verification service" roughly aligns with the notion that a network-based intermediary in the application server layer of IMS might detect spoofed calls. We note that the IETF STIR WG has a charter item for an "out-of-band" approach to identifying impersonation attacks that relies on smartphone functions or comparable equipment which may be of interest to SG 17. We have deferred this work item until we complete work on the "in-band" SIP-based approach in the IETF STIR WG, but we expect to continue work on "out-of-band" shortly. Broadly, we believe the IETF STIR efforts have applicability beyond the IMS environment, but that does not preclude the IMS and VoLTE visited network environment from making use of the technology designed in STIR. In addition, there is an anti-spoofing Study Item in 3GPP SA3 Security Working Group where STIR work is being examined for applicability in a VoLTE/IMS deployment. We again thank SG 17 for notifying us of this new work item. We would be happy to work with SG 17 on the use of any IETF technology that SG 17 considers for this solution.