Download LTE Security Architecture Fundamentals

3GPP/LTE Security
Session #2: LTE
Security Architecture
Fundamentals
Klaas Wierenga
Consulting Engineer, Corporate Development
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Agenda
 Intro
…
…
…
…
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Intro
…
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The LTE System
 Radio Side (LTE – Long Term
Evolution/Evolved UTRAN EUTRAN)
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 Network Side (SAE – System
Architecture Evolution/Evolved
Packet Core - EPC)
 Improvements in spectral efficiency,
user throughput, latency
 Improvement in latency, capacity,
throughput, idle to active transitions
 Simplification of the radio network
 Simplification of the core network
 Efficient support of packet based
services: Multicast,
VoIP, etc.
 Optimization for IP traffic and
services
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 Simplified support and handover to
non-3GPP access technologies
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Overview of 3GPP LTE/SAE System
eNodeB
UE
S1-MME
MME
HSS
PCRF
X2
eNodeB
S-GW
S1-U
Evolved UTRAN(E-UTRAN)
PDN-GW
S5
Evolved Packet Core (EPC)
• UE = User Equipment
• MME = Mobility Management Entity, termination point in network for
ciphering/integrity protection for NAS signaling, handles the security key
management, authenticating users
• S-GW = Serving Gateway
• PDN-GW = PDN Gateway
• PCRF = Policy Charging Rule Function
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Evolved Packet Core GW Capabilities
 Serving GW functions include:





Local Mobility Anchor point for inter-eNodeB handover (i.e. GTP
termination)
PMIP or GTP support towards PDN Gateway
Per flow QoS Policy Enforcement
Lawful Interception
Traffic Accounting
PDN GW
IP Tunnel
 Both can be combined if there is a full mesh
between base stations and GWs
Serving
GW
IP Tunnel
MAC


Policy Enforcement (QoS, charging, mobility)
Per-user based packet filtering
Mobility anchoring for intra- and inter-3GPP mobility (requires GTP
and MIP HA)
Charging Support
Lawful Interception
Security



Layer 3
 PDN GW functions include:
OFDMA
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Evolving Security Architecture
Radio Controller
Core Network
Handset Authentication
GSM
Ciphering
Handset Authentication + Ciphering
GPRS
Mutual Authentication
3G
Ciphering + Signalling integrity
Mutual Authentication
SAE/LTE
Ciphering + Radio
signalling
integrity
Optional IPSec
Core Signalling integrity
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SAE/LTE Security
 Security implications:
 Flat architecture
 Interworking with legacy and non-3GPP networks
 eNB placement in untrusted locations
 Keep security breaches local
 Result:
 Extended Authentication and Key Agreement
 More complex key hierarchy
 More complex interworking security
 Additional security for (home)eNB
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LTE/SAE architecture
ME
USIM
AN
HE
SN
=
=
=
=
=
Mobile Equipment
Universal Subscriber Identity Module
Access Network
Home Environment
Serving Network
 (I) Network access security: secure access to services, protect against attacks on
(radio) access links
 (II) Network domain security: enable nodes to securely exchange signaling data &
user data (between AN/SN and within AN, protect against attacks wireline network
 (III) User domain security: secure access to mobile stations
 (IV) Application domain security: enable applications in the user and in the
provider domain to securely exchange messages
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Non-3GPP Access
ME
USIM
AN
HE
SN





=
=
=
=
=
Mobile Equipment
Universal Subscriber Identity Module
Access Network
Home Environment
Serving Network
(I) Network access security
(II) Network domain security
(III) Non-3GPP domain security
(IV) Application domain security
(V) User domain security
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Network access security
 User identity (and location) confidentiality
 Entity authentication
 Confidentiality
 Data integrity
 Mobile equipment identification
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The use of a SIM
 Subscription Identification Module
 SIM holds secret key Ki, Home network holds another
 Used as Identity & Security key
 IMSI is used as user identity
 Benefits
 Easy to get authentication from home network while in visited network without
having to handle Ki
Source: ETRI
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Network Access Protection
 Authentication and key agreement
 UMTS AKA re-used for SAE
 SIM access to LTE explicitly excluded
 Signaling protection
 For core network (NAS) signaling, integrity and confidentiality protection
terminates in MME (Mobile Management Entity)
 For radio network (RRC) signaling, integrity and confidentiality protection
terminates in eNodeB
 User plane protection
 Encryption terminates in eNodeB
 Network domain security for network internal interfaces
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Authentication and Key Agreement
 HSS generates authN data and provides it to MME
 Challenge-response authN and key agreement between MME
and UE
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Confidentiality and Integrity of Signaling
 RRC signaling between UE and E-UTRAN
 NAS signaling between UE and MME
 S1 interface signaling (optional) protection not UE-specific
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User Plane Confidentiality
 S1-U (optional) protection not UE-specific, based on
IPsec
 Integrity not protected
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Key Hierarchy in LTE/SAE
 Cryptographic network separation
 Authentication vectors specific to serving network
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Handovers without MME
 Handovers possible between eNB’s (performance)
 If keys are passed unmodified, compromised eNB
compromises other eNB
 One-way function before passing over
 MME is involved after HO for further key passing
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Home eNodeB security threats
 Compromise HeNB credentials
 Physical attack HeNB
 Configuration attack
 MitM attacks etc.
 DoS attacks etc.
 User data and privacy attacks
 Radio Resources and management attacks
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Home ENodeB security measures
 Mutual AuthN HeNB and home network
 Secure tunnel for backhaul
 Trusted environment inside HeNB
 Access Control
 OAM security mechanisms
 Hosting Party authentication (Hosting party Module)
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Network Domain Security
 Enable nodes to securely exchange signaling data & user data
 between Access Network and Serving Network and within Access
Network
 Protect against attacks on wireline network
 No security in 2G core network
 Now security is needed:
 IP used for signaling and user traffic
 Open and easily accessible protocols
 New service providers (content, data service, HLR)
 Network elements can be remote (eNB)
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Security Domains
 Managed by single administrative authority
 Border between security domains protected by
Security Gateway (SEG)
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Security Gateway
 Handle communication over Za interface (SEG-SEG)
 AuthN/integrity mandatory, encryption recommended using IKEv1 or IKEv2
for negotiating, establishing and maintaining secure ESP tunnel
 Handle communication over (optional) Zb interface (SEG- NE or NE-NE)
 Implement ESP tunnel and IKEv1 or IKEv2
 ESP with AuthN, integrity, optional encryption
 All traffic flows through SEG before leaving or entering security domain
 Secure storage of long-term keys used for IKEv1 and IKEv2
 Hop-by-hop security (chained tunnels or hub-and-spoke)
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Security for Network Elements
 Services
 Data integrity
 Data origin authentication
 Anti-replay
 Confidentiality (optional)
 Using IPsec ESP (Encapsulation Security Payload)
 Between SEGs: tunnel mode
 Key management: IKEv1 or IKEv2
 Security associations from NE only to SEG or NE’s in own
domain
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Trust validation with IPsec
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Trust validation for TLS
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User domain security
 Secure access to mobile stations
 Few slides
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Application domain security
 The set of security features that enable applications in
the user and in the provider domain to securely
exchange messages.
 Secure messaging between the USIM and the network
(TS 22.048)
 Slides about IMS, SIP
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IMS Security
 Security/AuthN mechnism
 Mutual AuthN using UMTS AKA
 Typically implemented on UICC (ISIM application)
 UMTS AKA integrated into HTTP digest (RFC3310)
 NASS-IMS bundled AuthN
 SIP Digest based AuthN
 Access security with TLS
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Interworking with legacy network
 Few slides about CDMA-3GPP interworking
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References
 Principles, objectives and requirements
 TS 33.120 Security principles and objectives
 TS 21.133 Security threats and requirements
 Architecture, mechanisms and algorithms
 TS 33.102 Security architecture
 TS 33.103 Integration guidelines
 TS 33.105 Cryptographic algorithm requirements
 TS 35.20x Access network algorithm specifications
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References

TS 33.210 v8.3.0: Network Domain Security: IP-layer
(http://www.3gpp.org/ftp/Specs/archive/33_series/33.210/)

TS 33.310 V9.0.0: Network Domain Security: Authentication Framework
http://www.3gpp.org/ftp/Specs/archive/33_series/33.310/

TS 33.401 V9.0.0: SAE security architecture
http://www.3gpp.org/ftp/Specs/archive/33_series/33.401/

TS 33.402 V9.0.0: SAE security aspects of non 3GPP access
http://www.3gpp.org/ftp/Specs/archive/33_series/33.402/

TR 33.820 V8.1.0: Security of H(e)NB
http://www.3gpp.org/ftp/Specs/archive/33_series/33.820/33820-810.zip

3GPP TS 33.102 V8.3.0: Security architecture
http://www.3gpp.org/ftp/Specs/archive/33_series/33.102/33102-830.zip
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Credits
 Valterri Niemi (3GPP SA3 chair)
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Backup
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UMTS Authentication and Key
Agreement (AKA)
 Procedure to authenticate the user and establish pair
of cipher and integrity between VLR/SGSN and USIM
Source: ETRI
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X2 Routing and Handover
Source
ENB
SGW
Target
ENB
30 ms
Interruption
Time
Out of Order
Packets
Expect out of order packets around handover
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Summary
 In this session, we reviewed …
See you in 2 weeks for the Final Session!
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How does all we discussed relate to LTE/SAE
architecture?
eNodeB
UE
S1-MME
MME
PCRF
X2
eNodeB
S-GW
S1-U
User Plane: Integrity Protection Not Used
Encryption Recommended
HSS
PDN-GW
S5/S8
S1-MME: Integrity Protection Required
Security Mechanisms highly
recommended for inter-network
connections such as for roaming
(under study?)
Signalling: Integrity Protection Required
Encryption Recommended
S1-U: ?
Authentication Required
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