# US 10,455,417 B2 · Method and arrangement in a telecommunication system

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- Number: US 10,455,417 B2
- Document ID: US10455417B2
- Status: Granted
- Kind: B2
- Application number: 16/043,596
- Filed: 2018-07-24
- Published: 2018-11-15
- Granted: 2019-10-22
- Earliest claimed: 2007-09-17
- Assignees: Telefonaktiebolaget LM Ericsson (publ)
- Applicants: Telefonaktiebolaget Lm Ericsson (Publ)
- Inventors: Rolf Blom; Gunnar Mildh; Karl Norrman
- Web page: https://patentgrep.com/patent/US10455417B2

## CPC

- H04L 9/083: {involving central third party, e.g. key distribution center [KDC] or trusted third party [TTP]}
- H04L 9/0816: {Key establishment, i.e. cryptographic processes or cryptographic protocols whereby a shared secret becomes available to two or more parties, for subsequent use}
- H04L 9/0869: {involving random numbers or seeds}
- 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)}
- H04W 8/20: Transfer of user or subscriber data
- H04W 12/041: Key generation or derivation
- H04W 12/0471: Key exchange
- H04L 2209/24: Key scheduling, i.e. generating round keys or sub-keys for block encryption
- H04L 2209/80: Wireless
- H04L 2463/061: applying further key derivation, e.g. deriving traffic keys from a pair-wise master key
- H04W 92/10: between terminal device and access point, i.e. wireless air interface
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)
- H04W: WIRELESS COMMUNICATION NETWORKS (broadcast communication H04H; communication systems using wireless links for non-selective communication, e.g. wireless extensions H04M1/72)

## Abstract

A method in a User Equipment (UE) of an Evolved Packet System (EPS) establishes a security key (K_eNB) for protecting Radio Resource Control/User Plane (RRC/UP) traffic exchanged with a serving eNodeB. The method comprises sending a Non-Access Stratum (NAS) Service Request to a Mobility Management Entity (MME), the request indicating a NAS uplink sequence number (NAS_U_SEQ). The method further comprises receiving an indication of the NAS_U_SEQ of the NAS Service Request sent to the MME, back from the MME via the eNodeB. The method further comprises deriving the K_eNB from at least the received indication of the NAS_U_SEQ and from a stored Access Security Management Entity-key (K_ASME) shared with said MME.

## Claims

### Claim 1

A method comprising:
establishing, in a Mobility Management Entity of a Packet System, a security key for protecting Radio Resource Control/User Plane traffic between a User Equipment (UE) and a radio base station serving the UE, wherein establishing comprises:
receiving an integrity-protected Non-Access Stratum (NAS) Service Request from the UE, the NAS Service Request indicating an NAS uplink sequence number;
deriving the security key from at least said received NAS uplink sequence number and from a stored Access Security Management Entity-key shared with said UE, using a pseudo-random function, taking the NAS uplink sequence number and the Access Security Management Entity-key as inputs; and
forwarding said derived security key to the radio base station serving said UE.

### Claim 2 (depends on 1)

The method according to claim 1, comprising the further step of reconstructing the full NAS uplink sequence number from received low order bits.

### Claim 3 (depends on 1)

The method according to claim 1, comprising the further step of integrity checking the NAS Service Request received from the UE.

### Claim 4 (depends on 1)

The method according to claim 1, comprising the further step of returning an indication of the received NAS uplink sequence number to the UE.

### Claim 5 (depends on 4)

The method according to claim 4, wherein the NAS uplink sequence number is included in the set-up message forwarding the security key to the radio base station.

### Claim 6

A method comprising:
establishing, in a User Equipment (UE) of a Packet System, a security key for protecting Radio Resource Control/User Plane traffic exchanged with a serving radio base station, wherein establishing comprises:
sending an integrity-protected Non-Access Stratum (NAS) Service Request to a Mobility Management Entity, the request indicating a NAS uplink sequence number; and
deriving the security key from at least said NAS uplink sequence number and from a stored Access Security Management Entity-key shared with said Mobility Management Entity, using a pseudo-random function, taking the NAS uplink sequence number and the Access Security Management Entity-key as inputs.

### Claim 7 (depends on 6)

The method according to claim 6, comprising the step of storing the NAS uplink sequence number of the NAS Service Request sent to the Mobility Management Entity.

### Claim 8 (depends on 6)

The method according to claim 6, comprising the step of receiving an indication of the NAS uplink sequence number of the NAS Service Request sent to the Mobility Management Entity, back from the Mobility Management Entity via the radio base station.

### Claim 9 (depends on 8)

The method according to claim 8, wherein the security key is derived from the NAS uplink sequence number and the Access Security Management Entity-key after the reception of a security configuration message from the radio base station.

### Claim 10

A system comprising:
a Mobility Management Entity adapted for a Packet System, the Mobility Management Entity arranged to establish a security key for protection of Radio Resource Control/User Plane traffic between a User Equipment and a radio base station serving the UE, the Mobility Management Entity comprising:
a receiver configured to receive an integrity-protected Non-Access Stratum (NAS) Service Request from the UE, the NAS Service Request indicating a NAS uplink sequence number;
processing circuitry configured to derive a security key from at least said received NAS uplink sequence number and from a stored Access Security Management Entity-key shared with said UE, using a pseudo-random function, taking the NAS uplink sequence number and the Access Security Management Entity-key as inputs; and
a transmitter configured to send said derived security key to the radio base station serving said UE.

### Claim 11 (depends on 10)

The system according to claim 10, arranged to reconstruct the full NAS uplink sequence number from received low order bits.

### Claim 12 (depends on 10)

The system according to claim 10, arranged to integrity check the NAS Service Request received from the UE.

### Claim 13 (depends on 10)

The system according to claim 10, arranged to forward an indication of the NAS uplink sequence number to the radio base station, to be returned to the UE from the radio base station.

### Claim 14

A system comprising:
a user equipment (UE) adapted for a Packet System, the UE arranged to establish a security key for protecting Radio Resource Control/User Plane (RRC/UP) traffic exchanged with a serving radio base station, wherein the UE comprises:
a transmitter configured to send an integrity-protected NAS Service Request to a Mobility Management Entity, the request indicating a NAS uplink sequence number; and
processing circuitry configured to derive a security key from at least said NAS uplink sequence number, and from a stored Access Security Management Entity-key shared with said Mobility Management Entity, using a pseudo-random function, taking the NAS uplink sequence number and the Access Security Management Entity-key as inputs.

### Claim 15 (depends on 14)

The system according to claim 14, arranged to store the NAS uplink sequence number of the NAS Service Request sent to the Mobility Management Entity.

### Claim 16 (depends on 14)

The system according to claim 14, arranged to receive an indication of the NAS uplink sequence number of the NAS Service Request sent to the Mobility Management Entity, back from the Mobility Management via the radio base station.

### Claim 17 (depends on 15)

The system according to claim 15, arranged to derive the security after the reception of a security configuration message from the radio base station.