# US 11,122,427 B2 · Managing security contexts and performing key derivation at handover in a wireless communication system

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- Number: US 11,122,427 B2
- Document ID: US11122427B2
- Status: Granted
- Kind: B2
- Application number: 16/067,256
- Filed: 2018-04-18
- Published: 2020-03-19
- Granted: 2021-09-14
- Earliest claimed: 2017-09-26
- Assignees: Telefonaktiebolaget LM Ericsson (publ)
- Applicants: Telefonaktiebolaget LM Ericsson (publ)
- Inventors: Oscar Ohlsson; Gunnar Mildh; Prajwol Kumar Nakarmi
- Web page: https://patentgrep.com/patent/US11122427B2

## CPC

- H04W 12/04: Key management, e.g. using generic bootstrapping architecture [GBA]
- H04W 12/041: Key generation or derivation
- H04L 9/0866: {involving user or device identifiers, e.g. serial number, physical or biometrical information, DNA, hand-signature or measurable physical characteristics}
- H04L 63/061: {for key exchange, e.g. in peer-to-peer networks (cryptographic mechanisms or cryptographic arrangements for key agreement H04L9/0838)}
- H04W 8/02: Processing of mobility data, e.g. registration information at HLR [Home Location Register] or VLR [Visitor Location Register]; Transfer of mobility data, e.g. between HLR, VLR or external networks
- H04W 36/0038: {of security context information}
- H04L 63/062: {for key distribution, e.g. centrally by trusted party (cryptographic mechanisms or cryptographic arrangements for key distribution involving a central third party H04L9/0819)}
- H04L 2209/80: Wireless
- H04W 36/14: Reselecting a network or an air interface
- H04W: WIRELESS COMMUNICATION NETWORKS (broadcast communication H04H; communication systems using wireless links for non-selective communication, e.g. wireless extensions H04M1/72)
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)

## Abstract

There is provided a method for determining a security context for communication between a wireless device and a target network node at handover. The method comprises obtaining (S1) information representative of the type of Radio Access Technology, also referred to as RAT type, of the target network node, and deriving and/or determining (S2) the security context at least partly based on the information representative of the RAT type.

## Claims

### Claim 1

A method for determining a security context for communication between a wireless device and a target network node at handover of the wireless device in a wireless network, wherein the method is performed by a network node or device other than the target network node, wherein the method comprises:
obtaining first information representative of the type of Radio Access Technology (RAT) of the target network node and second information representing properties, other than the type of RAT, of a target cell for the handover, wherein the first information does not represent the properties represented by the second information; and
deriving and/or determining the security context at least partly based on the first information representative of the type of RAT.

### Claim 2 (depends on 1)

The method of claim 1, wherein the security context comprises at least an Access Stratum (AS) base security key.

### Claim 3 (depends on 2)

The method of claim 2, wherein the AS base security key is KgNB* or Kng-eNB*.

### Claim 4 (depends on 1)

The method of claim 1, wherein the first information representative of the type of RAT is obtained by at least one of receiving the first information and determining the first information.

### Claim 5 (depends on 1)

The method of claim 1, further comprising deriving a new security key based on the first information representative of the type of RAT and information representative of a security key valid before handover.

### Claim 6 (depends on 5)

The method of claim 5, wherein the information representative of a security key valid before handover includes information about one of the following: a base security key used before handover, or an intermediary key valid before handover.

### Claim 7 (depends on 1)

The method of claim 1, wherein deriving and/or determining the security context is further based on the second information representing the properties of the target cell other than the type of RAT.

### Claim 8 (depends on 1)

The method of claim 1, wherein deriving and/or determining the security context is based on using a parameter representative of the type of RAT as an input to a new or existing key derivation function.

### Claim 9 (depends on 8)

The method of claim 8, wherein the input to the key derivation is different for Long Term Evolution (LTE) and New radio (NR) RATs.

### Claim 10 (depends on 1)

The method of claim 1, wherein deriving and/or determining the security context is based on using different key derivation functions (KDFs) for different types of RATs.

### Claim 11 (depends on 10)

The method of claim 10, wherein the different KDFs comprise a first KDF for LTE and a second KDF for NR.

### Claim 12 (depends on 1)

The method of claim 1, wherein the method is applied at intra-RAT and/or inter-RAT handovers within the same core network.

### Claim 13 (depends on 1)

The method of claim 1, wherein the method is performed by the wireless device.

### Claim 14 (depends on 1)

The method of claim 1, wherein the method is performed by a network node.

### Claim 15 (depends on 14)

The method of claim 14, wherein the handover is from a source network node to the target network node, and the method is performed by the source network node.

### Claim 16 (depends on 15)

The method of claim 15, wherein the handover is an Xn handover and the first information representative of the type of RAT is obtained based on Xn signaling or pre-configuration.

### Claim 17 (depends on 1)

The method of claim 1, wherein the method is performed by an Access and Mobility management Function (AMF) network device in the core network.

### Claim 18 (depends on 17)

The method of claim 17, wherein the first information representative of the type of RAT is obtained based on N2 signaling or pre-configuration.

### Claim 19 (depends on 1)

The method of claim 1, wherein communication between the wireless device and the target network node is protected, based on the security context, for at least one of integrity and confidentiality.

### Claim 20

A device configurable to determine a security context for communication between a wireless device and a target network node at handover of the wireless device in a wireless network, the device being a network node or device other than the target network node, the device comprising:
at least one processor; and
at least one memory storing computer-executable instructions that, when executed by the at least one processor, configure the device to:
obtain first information representative of the type of Radio Access Technology (RAT) of the target network node and second information representing properties, other than the type of RAT, of a target cell for the handover, wherein the first information does not represent the properties represented by the second information; and
derive and/or determine the security context based on the first information representative of the type of RAT.

### Claim 21 (depends on 20)

The device of claim 20, wherein execution of the instructions configures the device to derive and/or determine at least an Access Stratum (AS) base security key as part of the security context.

### Claim 22 (depends on 21)

The device of claim 21, wherein the AS base security key is KgNB* or Kng-eNB*.

### Claim 23 (depends on 20)

The device of claim 20, wherein execution of the instructions configures the device to receive and/or determine the first information representative of the type of RAT.

### Claim 24 (depends on 20)

The device of claim 20, wherein execution of the instructions configures the device to derive a new security key to be used after handover based on the first information representative of the type of RAT and information representative of a security key valid before handover.

### Claim 25 (depends on 20)

The device of claim 20, wherein execution of the instructions configures the device to derive the security context based on the first information representative of the type of RAT by using a parameter representative of the type of RAT as an input to a new or existing key derivation function.

### Claim 26 (depends on 20)

The device of claim 20, wherein execution of the instructions configures the device to derive the security context based on the first information representative of the type of RAT by using different key derivation functions for different types of RATs.