User plane traffic handling for emergency case

1 . A first terminal device, comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the first terminal device at least to: determine that user plane (UP) traffic is to be communicated between the first terminal device and a second terminal device without confidentiality protection based on at least one of the following: at least one local policy, an emergency relay service code (RSC) received from the second terminal device, at least one UP security policy received from the second terminal device, or capability of the first terminal device; determine that the UP traffic is to be communicated between the first terminal device and the second terminal device without integrity protection or with a partial integrity protection based on an emergency relay service code (RSC) received from the second terminal device; transmit, to the second terminal device, a message indicating that the UP traffic is to be communicated without the confidentiality protection for the integrity protection, or without the confidentiality protection and with the partial integrity protection; and communicate the UP traffic between the first terminal device and the second terminal device without the confidentiality protection or the integrity protection, or without the confidentiality protection and with the partial integrity protection, wherein: the first terminal device is caused to determine that the UP traffic is to be communicated without the confidentiality protection by: determining that no confidentiality protection algorithm is to be applied to the UP traffic; and the first terminal device is caused to communicate the UP traffic by: communicating the UP traffic in plain text,

wherein the determining that the UP traffic is to be communicated without the confidentiality protection or the integrity protection, or without the confidentiality protection and with the partial integrity protection is performed after transmitting a direct security mode command to the second terminal device and before transmitting a direct communication accept message to the second terminal device.

2 . The first terminal device of claim 1 , wherein the first terminal device is caused to determine that the UP traffic is to be communicated without the confidentiality protection further based on a capability of the second terminal device.

3 . The first terminal device of claim 1 , wherein the first terminal device is further caused to determine that the UP traffic is to be communicated without the integrity protection or with the partial integrity protection based on

a capability of the second terminal device.

4 . The first terminal device of claim 1 , wherein:

the first terminal device is caused to determine that the UP traffic is to be communicated without the confidentiality protection by:

determining a null confidentiality protection algorithm is to be applied to the UP traffic; and

the first terminal device is caused to communicate the UP traffic by:

encrypting the UP traffic with a keystream of all zeroes by using the null confidentiality protection algorithm.

5 . The first terminal device of claim 1 , wherein:

the first terminal device is caused to determine that the UP traffic is to be communicated without the integrity protection by:

determining that no integrity protection algorithm is to be applied to the UP traffic; and

the first terminal device is caused to communicate the UP traffic by:

communicating the UP traffic without a message authentication code (MAC).

6 . The first terminal device of claim 1 , wherein:

the first terminal device is caused to determine that the UP traffic is to be communicated without the integrity protection by:

determining a null integrity protection algorithm is to be applied to the UP traffic; and

the first terminal device is caused to communicate the UP traffic by:

generating a first message authentication code (MAC) of all zeroes by using the null integrity protection algorithm; and

communicating the UP traffic with the first MAC.

7 . The first terminal device of claim 1 , wherein:

the first terminal device is caused to determine that the UP traffic is to be communicated with the partial integrity protection by:

determining a non-null integrity protection algorithm for the UP traffic based on capabilities of the first terminal device and the second terminal device; and

the first terminal device is caused to communicate the UP traffic by:

generating, by using the non-null integrity protection algorithm, a second message authentication code (MAC) based on at least one of the following: a COUNT, an identity of a bearer for the UP traffic, an indication of a transmission direction of the UP traffic, an integrity key of all zeroes, or an UP message carrying the UP traffic; and

communicating the UP traffic with the second MAC.

8 . The first terminal device of claim 1 , wherein:

the first terminal device is caused to communicate the UP traffic with the partial integrity protection by:

generating a third message authentication code (MAC) based on at least one of the following: a COUNT, an identity of a bearer for the UP traffic, an indication of a transmission direction of the UP traffic, or an UP message carrying the UP traffic; and

communicating the UP traffic with the third MAC.