The present document aims to address the security aspects of Multi-Access, focusing on DualSteer devices and ATSSS Phase 4 (ATSSS Ph-4) enhancements, as identified in the FS_MASSS study in TR 23.700-54. The scope of this study includes the following key areas:

• Examine the security implications of a simplified architecture over non-3GPP access, where non-3GPP access does not rely on the current TNGF/N3IWF architecture. This involves assessing:
• Whether to keep NAS security context on non-3GPP access.
• Whether to keep IPsec on the user plane and/or control plane of non-3GPP access.
• Whether new security mechanisms are to be considered in UE procedures, particularly regarding registration and connectivity to the 5G system in the context of ATSSS between 3GPP and non-3GPP access without 5G NAS.

The present document leverages insights from the requirements and architectural considerations outlined in the TR 23.700-54.

The following documents contain provisions which, through reference in this text, constitute provisions of the present document.

• References are either specific (identified by date of publication, edition number, version number, etc.) or non-specific.
• For a specific reference, subsequent revisions do not apply.
• For a non-specific reference, the latest version applies. In the case of a reference to a 3GPP document (including a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same Release as the present document.