| CPC H04W 12/033 (2021.01) [H04W 12/037 (2021.01)] | 5 Claims |

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1. A method for determining a user plane security algorithm, comprising:
receiving, by a second terminal (UE 2), a direct communication request message from a first terminal (UE 1), wherein the direct communication request message comprises a security capability of the UE 1 and a control plane security policy of the UE 1;
determining, by the UE 2, a control plane security protection mode between the UE 2 and the UE 1 based on the control plane security policy of the UE 1 and a control plane security policy of the UE 2; and
when the control plane security protection mode is that control plane integrity protection is enabled and control plane confidentiality protection is not enabled:
sending, by the UE 2, a direct security mode command message to the UE 1, and when receiving a direct security mode complete message carrying a user plane security policy of the UE 1 from the UE 1, regardless of the user plane security policy of the UE 1 and a user plane security policy of the UE 2, determining, by the UE 2, that user plane confidentiality protection between the UE 2 and the UE 1 is not enabled, wherein
the direct security mode command message comprises a non-null integrity protection algorithm and a null confidentiality protection algorithm.
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