Protection of Initial Non-Access Stratum Protocol Message in 5G Systems

Abstract

Systems and methods of protecting an initial NAS message are described. Depending on whether a security contex.1: for a serving PLMN is stored, the UE uses either a public key from the serving PLMN or a key from the security context to encrypt parts of the initial NAS message. An initial NAS message containing the encrypted parts is then sent to an AMF of the serving PLMN. The serving PLMN public key is transmitted via a SIB. Prior to transmission of the initial NAS message or in parallel with it, an RRC message is sent to the base station. The RRC message contains the UE identifier and/or a NSSAI encrypted using the serving PLMN public key.

1 - 20 . (canceled) 
     
     
         21 . An apparatus, comprising:
 a memory configured to store a security context associated with a serving public land mobile network (PLMN) for a user equipment (UE); and   a processor configured to:
 determine whether the security context is stored in the memory; 
 in response to a determination that the security context is not stored in the memory, prepare an information element (IE) to form a cleartext IE; and 
 encode, for transmission to the serving PLMN, an initial non-access stratum (NAS) message, the initial NAS message comprising the cleartext IE and excluding a network slice assistance information (NSSAI) IE, and wherein the NSSAI IE is included at a radio resource control (RRC) level with an RRC setup complete message, wherein the initial NAS message is a first NAS message sent after the UE transitions from an idle state. 
   
     
     
         22 . The apparatus of  claim 21 , wherein the processor is further configured to:
 decode a system information block (SIB) from the serving PLMN; and   extract a public key from the SIB.   
     
     
         23 . The apparatus of  claim 21 , wherein the initial NAS message comprises a plurality of cleartext IEs. 
     
     
         24 . The apparatus of  claim 21 , wherein the cleartext IE comprises a UE identifier. 
     
     
         25 . The apparatus of  claim 21 , wherein:
 the initial NAS message comprises at least one of a Nonce comprising a random number, timestamp or sequence number; and   the processor is further configured to periodically change an outcome of encryption using a public key based on the at least one of the Nonce, timestamp or sequence number.   
     
     
         26 . The apparatus of  claim 21 , wherein the processor is further configured to:
 encrypt at least one of a UE identifier or Network Slice Selection Assistance Information (NSSAI) using a public key; and   encode, for transmission to the serving PLMN, a radio resource control (RRC) message, the RRC message comprising the at least one of the UE identifier or NSSAI.   
     
     
         27 . The apparatus of  claim 21 , wherein the processor is further configured to:
 encrypt at least one of a UE identifier or Network Slice Selection Assistance Information (NSSAI) using another public key that is different from the public key; and   encode, for transmission to the serving PLMN, a radio resource control (RRC) message, the RRC message comprising the at least one of the UE identifier or NSSAI.   
     
     
         28 . The apparatus of  claim 21 , wherein:
 the processor is further configured to, in response to a determination that the security context is stored in the memory, encrypt a second IE using an encryption key of the security context; and   the initial NAS message comprises the second IE.   
     
     
         29 . The apparatus of  claim 21 , wherein the processor is further configured to:
 detect a public key from each of a plurality of neighboring base stations, neighboring base stations of the serving PLMN using the same public key;   compare the public keys from the neighboring base stations; and   detect a rogue base station among the plurality of neighboring base stations based on a different public key received from the rogue base station than others of the plurality of neighboring base stations.   
     
     
         30 . The apparatus of  claim 21 , wherein a public key used to encrypt the IE is independent of which Access and Mobility Function (AMF) of the serving PLMN the UE is to communicate with. 
     
     
         31 . The apparatus of  claim 21 , further comprising a radio communicatively coupled to the processor. 
     
     
         32 . A method comprising:
 at a serving public land mobile network (PLMN):
 receiving, from a user equipment (UE), an initial non-access stratum (NAS) message, the initial NAS message comprising a cleartext information element (IE) and excluding a network slice assistance information (NSSAI) IE, and wherein the NSSAI IE is included at a radio resource control (RRC) level with an RRC setup complete message, wherein the initial NAS message is a first NAS message sent after the UE transitions from an idle state. 
   
     
     
         33 . The method of  claim 32 , wherein the initial NAS message comprises a plurality of cleartext IEs. 
     
     
         34 . The method of  claim 32 , wherein the cleartext IE comprises a UE identifier. 
     
     
         35 . The method of  claim 32 , wherein:
 the initial NAS message comprises at least one of a Nonce comprising a random number, timestamp or sequence number; and   the method further comprises periodically changing an outcome of encryption using a public key based on the at least one of the Nonce, timestamp or sequence number.   
     
     
         36 . A method comprising:
 determining whether a security context associated with a serving public land mobile network (PLMN)is stored in a memory of a user equipment (UE);   in response to a determination that the security context is not stored in the memory, preparing an information element (IE) to form a cleartext IE; and   encoding, for transmission to the serving PLMN, an initial non-access stratum (NAS) message, the initial NAS message comprising the cleartext IE and excluding a network slice assistance information (NSSAI) IE, and wherein the NSSAI IE is included at a radio resource control (RRC) level with an RRC setup complete message, wherein the initial NAS message is a first NAS message sent after transitioning from an idle state.   
     
     
         37 . The method of  claim 36 , wherein the initial NAS message comprises a plurality of cleartext IEs. 
     
     
         38 . The method of  claim 36 , wherein the cleartext IE comprises a UE identifier. 
     
     
         39 . The method of  claim 36 , wherein:
 the initial NAS message comprises at least one of a Nonce comprising a random number, timestamp or sequence number; and   the method further comprises periodically changing an outcome of encryption using a public key based on the at least one of the Nonce, timestamp or sequence number.   
     
     
         40 . The method of  claim 36 , wherein a public key used to encrypt the IE is independent of which Access and Mobility Function (AMF) of the serving PLMN the UE is to communicate with.