James Kempf
Research Fellow
DoCoMo USA Labs kempf@docomolabs-usa.com
DIMACS, November 4, 2004

• Existing solutions for auth/authz and their problems
– Pre-IP L2.5
– Universal Access Method (UAM)
• SEND and PANA
• A Different Way - Hyperoperator
• Obstacles to Acceptance
• Summary
Copyright © 2004 DoCoMo Communications Laboratories USA, Inc. All Rights Reserved. James Kempf 4/12/2020 2

• Terminal and network authenticate each other prior to establishing IP service
• Typically thru a Layer 2.5 flow between the terminal and a network access server
– PPP for some cellular protocols
– Proprietary for others
– 802.1x EAPOL for 802.11
• Network access server routes auth request back into the home network via local AAA server
– Radius or Diameter across the Internet
• Home network AAA server authenticates
• Authorization for network access from home network AAA server to local
AAA server
– If a terminal is authenticated, then it is authorized for IP service
– If the network/base station is authenticated, then it is authorized to take the terminal’s traffic
Copyright © 2004 DoCoMo Communications Laboratories USA, Inc. All Rights Reserved. James Kempf 4/12/2020 4

EAP+
Radius +
IP
EAP+
Radius +
IP
AAA-F
PMK pushed to
AP
AP/NAS
Border Router
Access Network
AR
EAP +
EAPoL +
802.11/3
Mobile Terminal
Internet
Copyright © 2004 DoCoMo Communications Laboratories USA, Inc. All Rights Reserved. James Kempf
AAA-H
4/12/2020 5

STA
AP
STA 802.1X blocks port for data traffic
AP 802.1X blocks port for data traffic
AS
802.1X/EAP-Request Identity
802.1X/EAP-Response
Identity (EAP type specific)
Derive Pairwise Master Key
(PMK)
EAP type specific mutual authentication
(e.g. TLS)
RADIUS Access
Request/Identity
Derive Pairwise Master Key
(PMK)
RADIUS Accept + PMK
802.1X/EAP-SUCCESS
Copyright © 2004 DoCoMo Communications Laboratories USA, Inc. All Rights Reserved. James Kempf
4/12/2020 6

• Handover requires lengthy PMK rekeying, delaying handover
• Implicit authorization model for network access is difficult to extend to other services
– Example: multicast
• Authenticated and authorized terminals that are compromised or otherwise decide to behave badly
Copyright © 2004 DoCoMo Communications Laboratories USA, Inc. All Rights Reserved. James Kempf 4/12/2020 7

• Terminal establishes restricted IP access
– Can’t route to the Internet
– Only HTTP
• HTTP GET redirected to Public Access Control (PAC) Gateway
– PAC pushes login page to terminal
• User types in login/password for account access or credit card number for one time access
• PAC routes auth request back into the home network via local AAA server or credit card auth/authz to credit card provider
– Radius or Diameter across the Internet for AAA
– Ecommerce protocol (SET, Mondex, secure channel card payment, GeldKarte, etc.) for credit card.
• Home network AAA server authenticates or credit card provider authorizes
• Authorization for network access from home network AAA server to local
AAA server
– If a terminal is authenticated, then it is authorized for IP service
– If the network/base station is authenticated, then it is authorized to take the terminal’s traffic
Copyright © 2004 DoCoMo Communications Laboratories USA, Inc. All Rights Reserved. James Kempf 4/12/2020 8

Radius +
IP
Radius +
IP
AAA-H
AAA-F
AP
Border Router
Access Network
AR
HTTP + SSL
+
IP
Mobile Terminal
PAC
Secure
Credit Card
Auth/Authz
Internet
Copyright © 2004 DoCoMo Communications Laboratories USA, Inc. All Rights Reserved. James Kempf 4/12/2020 9

STA
PAC
PAC blocks Internet access
HTTP GET + User URL
Redirect Login URL
User types in account login/password or credit card number
HTTP POST credentials
RADIUS Access
Request/Identity + UAM
AVPs*
Redirect User URL
RADIUS Accept + UAM
AVPs*
User URL Displayed
Copyright © 2004 DoCoMo Communications Laboratories USA, Inc. All Rights Reserved. James Kempf
4/12/2020
AS
* Credit card auth/authz protocol if used
10

• If the user isn’t using HTML or the device isn’t capable of Web browsing, the procedure fails
• Piecewise, asymmetric security with many opportunities for compromise
– Network authenticates user through user name/password or credit card number
– Terminal authenticates network through SSL
– RADIUS security depends on VPN or other
• No support for handover at all
• For other services:
– For AAA, implicit authorization model for network access is difficult to extend to other services,
– For credit card, authorization for other services requires user to type in credit card information again
• Authenticated and authorized terminals that are compromised or otherwise decide to behave badly
Copyright © 2004 DoCoMo Communications Laboratories USA, Inc. All Rights Reserved. James Kempf 4/12/2020 11

• Recently standardized addition to IPv6 Neighbor Discovery (RFC 2461) for securing:
– Local link address resolution
– Router discovery
– No RFC number yet
• Prevents a fully authenticated and authorized terminal from behaving badly for a limited set of actions
– DoSing nodes on the same link
– MiM attacks by spoofing access router
• Local link address resolution secured by using cryptographically generated addresses
– Ties the IP address to the node’s public key
– Together with a signature, establishes the node’s authorization to claim the address
• Router discovery secured by certified public keys on the router, together with certificates
– Node checks router certificate against a certification path for which the node has a certificate for trust anchor
– Router’s certified public key used to check signature on Router
Advertisements
Copyright © 2004 DoCoMo Communications Laboratories USA, Inc. All Rights Reserved. James Kempf 4/12/2020 13

Certification
Path
Solicitation +
Names of
Trust
Anchors
AR
Certification
Path
Advertisement +
Certification
Paths to Trust
Anchor
AP
Mobile Terminal
Router’s Certified Pubic Key
Copyright © 2004 DoCoMo Communications Laboratories USA, Inc. All Rights Reserved. James Kempf 4/12/2020 14

AR
Router
Solicitation
AP
Router
Advertisement +
Signature
Validate Signature
Mobile Terminal
Copyright © 2004 DoCoMo Communications Laboratories USA, Inc. All Rights Reserved. James Kempf 4/12/2020 15

Internet Traffic
AR
AP
Neighbor Solicitation for CGA
+ Signature
Mobile Terminal
Hash!
Subnet Prefix
Copyright © 2004 DoCoMo Communications Laboratories USA, Inc. All Rights Reserved. James Kempf
Terminal’s RSA Key
Cryptographically
Generated IPv6
Address
4/12/2020 16

• SEND solves half the problem
– Allows the terminal to authenticate the network
• Adding a certificate on the terminal would allow the network to authenticate the terminal
– But no way to check terminal’s authorization nor provide accounting so network service can be billed
• SEND WG discussed using a terminal certificate for address resolution security but issue was dropped
– Want to see whether any market acceptance for SEND first
• Authentication of terminal using certificate provided by home network would provide a lighter weight alternative to AAA flows
– No need to do AAA on handover, just check certificate
• Or an authorization token issued by the access network after authentication and authorization are complete
Copyright © 2004 DoCoMo Communications Laboratories USA, Inc. All Rights Reserved. James Kempf 4/12/2020 17

• PANA is an IP level encapsulation for Extensible Authentication
Protocol (EAP)
• Provides authentication transport if no Layer 2.5 transport is available.
• PANA framework contains a network access enforcement point to limit types of traffic until terminal is authenticated.
– Router solicitation/advertisement
– Address autoconfiguration
– DHCP
– PANA
• Enforcement point may also provide cryptographic protection for traffic if unavailable from link layer
– IKE/IPsec
• Replaces use of HTML in UAM
Copyright © 2004 DoCoMo Communications Laboratories USA, Inc. All Rights Reserved. James Kempf 4/12/2020 18

Radius/Diameter
+EAP
+
IP
Radius/Diameter +
IP
AAA-H
AAA-F
PAC
Border Router
Access Network
AR
EC
Internet
AP
PANA +
EAP +
IP
Mobile Terminal
Copyright © 2004 DoCoMo Communications Laboratories USA, Inc. All Rights Reserved. James Kempf 4/12/2020 19

Radius/Diameter
+EAP
+
IP
Radius/Diameter +
IP
AAA-H
AAA-F
PAC
Border Router
Access Network
AR
EC
Internet
AP
PANA +
EAP +
IP
Mobile Terminal
Copyright © 2004 DoCoMo Communications Laboratories USA, Inc. All Rights Reserved. James Kempf
SNMP
4/12/2020 20

• Arguments against PANA
– Layer 2 protocols all have their own ways of doing authentication
– Terminal should authenticate before obtaining an IP address
– PANA is architecturally wrong
– ...
•
PANA is really a replacement for UAM
– UAM is really architecturally wrong
• Forces the terminal to support HTTP
• HTTP is really the wrong stack layer for network access authentication signaling
– Widespread deployment of UAM indicates market interest in using IP as network access authentication transport
• Primary issue: PANA only solves a very small part of the problem
– If the link layer is not secure, then IKE/IPsec must be used for confidentiality on the link
• Too heavy weight
– Many of the problems surrounding other authentication methods remain
Copyright © 2004 DoCoMo Communications Laboratories USA, Inc. All Rights Reserved. James Kempf 4/12/2020 21

• Infrastructure deployment costs for a managed microcellular network like
802.11 are really high
• Nobody has managed to make a viable business out of subscription based hot-spots
• Well, maybe T-Mobile, but...
• Best business model seems to be a managed network model
– 802.11 provider sells network management service to hotels, convention centers, etc.
• For B3G or 4G, deployment, infrastructure, and network management costs of standard cellular business model might be steep to unaffordable
– Low end distruptors based on cheap, unmanaged spectrum devices with macrocellular characteristics are a threat
• Private individuals and small businesses with 802.11 really don’t want the hassles of managing security in a wireless network
– And some people who might want 802.11 always on might not want to pay for it until they really use it
Copyright © 2004 DoCoMo Communications Laboratories USA, Inc. All Rights Reserved. James Kempf 4/12/2020 23

• Multiple federated, independent, small access networks
– Maybe your neighbor, maybe you
• They contract with an operator to provide wireless service in exchange for discount on their network access or payment
– Like solar power in California – PG&E doesn’t pay you but you sell them power during the day/summer and buy back at night/winter
– Or maybe like solar power in Germany where the power company pays you for power you generate
• Operator provides them with:
– Security and management software and expertise to make their network more secure than if they had to manage it themselves
– Software for user service provisioning, charging and accounting so the operator’s users are properly charged
– Software to regulate usage of the federated network so that the owner is guaranteed some percentage of the bandwidth
→ We call this model Hyperoperator
Copyright © 2004 DoCoMo Communications Laboratories USA, Inc. All Rights Reserved. James Kempf 4/12/2020 24

Foxborough Drive
Mountain View kempf-and-associates
AR
AP
AR wakerley-house
Hyperoperator
AP
Copyright © 2004 DoCoMo Communications Laboratories USA, Inc. All Rights Reserved. James Kempf 4/12/2020 25

• Mobile Firewall
• Authorization Certificates
Copyright © 2004 DoCoMo Communications Laboratories USA, Inc. All Rights Reserved. James Kempf 4/12/2020 26

• Previous work
– SEND handles some threats on the last hop
– IETF 56 DefCon BOF
• Discussed protocol for distributed firewall but no agreement on forming a
WG
• Firewall on the access router protects network from virus and worm traffic originating on a fully authenticated and authorized host
• Firewall detects mal-traffic, cuts off host’s network service
• Other uses
– Bandwidth control
– Differential service provisioning
Copyright © 2004 DoCoMo Communications Laboratories USA, Inc. All Rights Reserved. James Kempf 4/12/2020 27

AR
Mobile Firewall
X
Real time traffic analysis identifies threat
Compromised host starts spewing maltraffic
Virus traffic is blocked
Mobile Terminal
G. Fu, D. Funato, J. Wood, and T. Kawahara, "Mobile
Firewall", The Fifth International Conference on Mobile and Wireless Communications Networks (MWCN 2003) ,
Singapore, October 2003.
Copyright © 2004 DoCoMo Communications Laboratories USA, Inc. All Rights Reserved. James Kempf 4/12/2020 28

• Home network provides terminal with proof of authorization for a service
• Terminal presents proof of authorization to foreign network for initial access
• Access network grants terminal a token for handover
• Terminal presents token on each handover (including between federated operators)
Copyright © 2004 DoCoMo Communications Laboratories USA, Inc. All Rights Reserved. James Kempf 4/12/2020 29

Send Access Token
Foreign
Accounting
Server
Radius Flow
(ugh! Do we really need this?)
10
Border Router
Access Network
Hyperopertor
AP
10
Send Authorization
Certificate
Send Access Token
Mobile Terminal
Copyright © 2004 DoCoMo Communications Laboratories USA, Inc. All Rights Reserved. James Kempf
Home Accounting
Server
4/12/2020 30

*Or why this idea might not get traction

• Risk analysis of how much the operator stands to lose if the federated system cheats
Copyright © 2004 DoCoMo Communications Laboratories USA, Inc. All Rights Reserved. James Kempf 4/12/2020 32

• THE issue!
• This is a disruptive business model
– Either low end if the customers are overserved by 3G network
– Or nonconsumption if the customers are people who are not using existing 3G networks or are not using them for particular jobs
• The cellular providers can’t disrupt themselves
– Unless they establish a separate business unit
Copyright © 2004 DoCoMo Communications Laboratories USA, Inc. All Rights Reserved. James Kempf 4/12/2020 33

• Reviewed existing methods of doing wireless auth/authz
– Pre-IP Layer 2.5
– UAM
• Discussed problems with existing technologies
• Reviewed two new IETF protocols that may provide some benefit
– SEND mitigates some threats on the local link, could be expanded to include network access authentication
– PANA removes HTTP hack in UAM
• Described a more radical proposal – hyperoperator
– Federated model of many small operators, with privately owned access points
– Mobile firewall between host and the network to control traffic from compromised hosts
– Authentication certificates and access tokens for authorization and accounting
• Discussed problems in
– Existing infrastructural and intellectual investment in traditional AAA
Copyright © 2004 DoCoMo Communications Laboratories USA, Inc. All Rights Reserved. James Kempf 4/12/2020 35