[Docs] [txt|pdf] [Tracker] [WG] [Email] [Nits]

Versions: 00 01 02 03 04 05 06 07 RFC 4016

   PANA Working Group
   Internet Draft                                                Mohan
                                                         Parthasarathy
   Document: draft-ietf-pana-threats-eval-00.txt          Tahoe Networks
   Expires:April 2003                                      October 2002



              PANA Threat Analysis and security requirements



Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026 [i].

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026 except that the right to
   produce derivative works is not granted.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
        http://www.ietf.org/ietf/1id-abstracts.txt
   The list of Internet-Draft Shadow Directories can be accessed at
        http://www.ietf.org/shadow.html.


   This Internet Draft expires April 12, 2003


Abstract

   The PANA (Protocol for carrying authentication for Network Access)
   working group is developing a layer 3 authentication method for
   authenticating clients to the access network. This document discusses
   the various trust models, threats present in these models and
   requirements out of these threats.





<Parthasarathy>          Expires  April 2003                 [Page 1]

Internet-draft           PANA threat analysis             October 2002


Table of Contents

   1.0 Introduction..................................................2
   2.0 Keywords......................................................2
   3.0  Terminology and Definitions.................................2
   4.0  Usage Scenarios.............................................4
   5.0  Assumptions.................................................5
   6.0  Types of Attacks............................................5
   7.0  Threat Scenarios............................................6
      7.1 PAA Discovery..............................................6
      7.2 Authentication.............................................7
      7.3 PaC leaving the network....................................9
      7.4 Attacks on normal communication............................9
      7.5 Miscellaneous attacks.....................................11
   8.0  Summary of Requirements....................................12
   9.0  Security Considerations....................................12
   References.......................................................12
   Acknowledgments..................................................13
   Author's Addresses...............................................13


1.0 Introduction

   The PANA (Public Access and Network Authentication) working group is
   developing a layer 3 authentication method for authenticating to the
   access network. Any client wishing to get access to the network needs
   to discover the IP address of the PANA authentication agent (PAA) and
   then authenticate itself to the network. This document discusses the
   threats involved in PAA discovery and authenticating the client to
   the access network and the resulting security requirements out of the
   threats.

   The requirements specified in this document are yet to be discussed in
   the working group and hence subject to change.

2.0 Keywords

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [KEYWORDS].


3.0  Terminology and Definitions

   Device

   A network element (namely notebook computers, PDAs, etc.) that
   requires access to a provider's network.


<Parthasarathy>           Expires April 2003                  [Page 2]

Internet-draft           PANA threat analysis             October 2002



   Device Identifier (DI)

   The identifier used by the network as a handle to control and police
   the network access of a PANA client. Depending on the access
   technology, identifier might contain any of IP address, link-layer
   address, switch port number, etc. of a device. PANA authentication
   agent keeps a table for binding device identifiers to the PANA
   clients.

   Identity

   The information used to identify the user. It is used for
   authenticating the PaC. Identity could be e.g, NAI [NAI]

   Edge Subnet or link

   The immediate IP subnet that is available to an interface of the
   device for network access.

   Access/Edge Router

   A router that is present in the edge subnet.

   Enforcement Point (EP)

   A node that is capable of filtering packets sent by the PaC to the
   Access/edge router using the DI information authorized by PAA.

   PANA Client (PaC)

   An entity in the edge subnet who is wishing to obtain network access
   from a PANA authentication agent within a network. A PANA client is
   associated with a device and a set of credentials to prove its
   identity within the scope of PANA.

   PANA Authentication Agent (PAA)

   An entity in the edge subnet whose responsibility is to authenticate
   the PANA client (PaC) and grant network access service to the device.

   Authentication Server (AS)



<Parthasarathy>           Expires April 2003                  [Page 3]

Internet-draft           PANA threat analysis             October 2002


   An entity that authenticates the PaC which may be co-located with PAA
   or part of the back-end infrastructure.


   Local Security Association (LSA)

   A temporary security association between a PaC and a PAA, which is
   derived from credentials of the PaC during initial authentication.

   Initial Authentication

   Authentication performed when a device enters into the edge subnet
   and provides the credentials to be authorized for network access
   without having any a priori authorization information. This will
   require a PAA to verify the credentials either locally or by using a
   authentication server.

   Re-authentication

   Authentication that occurs when a device needs to extend the
   authorization lifetime, changes attributes such as IP address and/or
   MAC address, etc., for the same network access after successful
   initial authentication.  This may require a PAA to verify the
   credentials (used for initial authentication) either locally or by
   using a AS.

   Local re-authentication

   A type of re-authentication that occurs locally between a PaC and a
   PAA by using the LSA established between them.  In this type of re-
   authentication, the PaC does not use the same credentials as used for
   initial authentication.


4.0  Usage Scenarios

   PANA is mostly expected to be used in environments where the nodes
   trust the operator of the network to provide the service but do not
   trust the other nodes in the network e.g., Public access networks,
   Hotel, Airport. In these environments, one may observe the following.

       o The link between PaC and PAA may not a shared medium e.g. PPP
          over wireline.




<Parthasarathy>           Expires April 2003                  [Page 4]

Internet-draft           PANA threat analysis             October 2002


       o The link between PaC and PAA may be a shared medium e.g.,
          Ethernet.
       o All the PaCs may be authenticated to the access network at
          layer 2 already e.g., PPP, 802.11.
       o PaCs may already share a security association with “layer 2”
          authentication agent e.g., Access Point in 802.11, that
          provides per-packet authentication and encryption.

   These factors affect the threat model of PANA. This document
   discusses the various threats in the context of the above attributes.

5.0  Assumptions

   The communication paths involved in the discovery and authentication
   are as follows.

     1) The path between PaC and PAA
     2) The path between PAA and EP
     3) The path between PAA and AS

   If PAA and EP are co-located, the path is already secured. Even when
   they are not co-located, the network operators can setup a security
   association between PAA and EP to secure the traffic between PAA and
   EP. Hence it is assumed that path (2) is secure.

   The authentication server could be co-located in the same network as
   PAA or with the back-end system. In either case, this document
   assumes that there exists a security association between PAA and
   back-end system. Without this, it is not possible to authenticate
   users securely. In the current deployment e.g. NAS and RADIUS, path
   (3) is secured.

   Thus, this document considers threats only for path (1).


6.0  Types of Attacks


   The PANA authentication client (PaC) needs to discover the PAA first.
   This involves either sending solicitations or waiting for
   advertisements. Once it has discovered the PAA, it will lead to
   authentication exchange with PAA. Once the access is granted, PaC
   will most likely exchange data with other nodes in the Internet. All
   these packets are vulnerable to attack. Attacker in the path between
   PaC and PAA can launch the following attacks.

          1) Denial of Service (DoS) attacks, in which a malicious node
            (PaC) prevents communication between other PaCs and PAA.
            This includes resource exhaustion attacks etc.


<Parthasarathy>           Expires April 2003                  [Page 5]

Internet-draft           PANA threat analysis             October 2002



          2) Man In The Middle (MITM) attack include interception,
            insertion, deletion, modification, replaying, reflection
            back at the sender and redirecting messages.

          3) Service theft, Stealing the service intended for someone
            else

7.0  Threat Scenarios

7.1 PAA Discovery

   PaC is in the process of discovering the PAA. Agents are normally
   discovered by sending solicitations or receiving advertisements.
   Following are the possible threats.

   T7.1.1: A malicious node can pretend to be a PAA by sending a spoofed
   advertisement.

   T7.1.2: A malicious node can send a spoofed advertisement with
   capabilities that indicate less secure authentication methods than
   what the real PAA supports, thereby fooling the PaC into negotiating
   a less secure authentication method than what would otherwise be
   available. This is a “bidding” down attack.

   T7.1.3: A malicious node can send solicitations to learn more
   information about networks which might help the attacker to launch
   some known attacks e.g., PAA supports weak authentication suite.

   It may not be possible protect the discovery process because the
   security association between PaC and PAA does not exist prior to
   authentication and hence there is no way of protecting the discovery.

   If mutual authentication is performed i.e., client to AS and AS to
   client, via the PAA, the successful authentication response from the
   AS can be used to validate the authenticity of the PAA. This works
   because of the assumption that PAA and the AS share a security
   association. In such cases, a node pretending to be a PAA can be
   detected at the end. Note that this does not prevent DoS attacks
   where the rogue PAA does not send any responses back to the client.

   In existing dial-up networks, the clients authenticate to the network
   but generally do not verify the authenticity of the messages coming
   from NAS. This mostly works because the link between the device and
   the NAS is not shared with other nodes (assuming that nobody tampers
   with the physical link) and clients trust the NAS to provide the
   service, without which the network operator will not make any profit.
   As the nodes in the network cannot directly communicate with other
   nodes, spoofing is avoided. In this environment, as the PaC may


<Parthasarathy>           Expires April 2003                  [Page 6]

Internet-draft           PANA threat analysis             October 2002


   assume that the other end of the point-to-point link is the PAA,
   spoofing attacks are not present.

   In environments where the link is shared, any node can pretend to be
   a PAA. Even the nodes that are authenticated at layer 2, can pretend
   to be a PAA and hence the threat is still present in such networks.


   Requirement 1:

   PANA MUST not assume that the discovery process is protected.

7.2 Authentication

   PaC is in the process of authenticating to the PAA.

7.2.1 Identity Protection

   Identity protection is a feature where the identities are not sent in
   clear. PaC and the AS exchange identities during the authentication
   process via the PAA. The identity of the AS itself may not be
   interesting to the attacker. But the attacker may be able to learn
   some partial information about the PaC using the identity of the AS
   in some cases e.g., when NAI is used as the identity, the attacker
   can learn the domain to which the PaC belongs to. The identity of the
   PaC, which is most interesting to the attacker, should be protected
   from the following attacks.

   T7.2.1.1: A malicious node can learn identities by eavesdropping.

   T7.2.1.2: A malicious node can send falsified identity requests to
   learn the identity of the PaC. It might typically happen by
   initiating an authentication exchange with the PaC and proceed till
   the identity is revealed. This is known as polling attack [RAT].

   If the link is not shared, other nodes in the network cannot
   eavesdrop on the link. If the PaC ensures that it responds to
   identity requests only from the PAA at the other end (by verifying
   the IP address) of the link, it can avoid the spoofing attacks. This
   assumes that the network does ingress filtering to prevent some other
   node from sending a spoofed identity request.

   If the link is shared and layer 2 does not provide encryption, then
   any node eavesdropping on the link can learn the identity. If the
   layer 2 provides encryption, then the identity can be hidden from the
   attacker.  Polling attack is still possible even if the layer 2 is
   secured. The attacker can pretend to be a PAA and initiate the
   authentication request to learn the identity of the PaC.


<Parthasarathy>           Expires April 2003                  [Page 7]

Internet-draft           PANA threat analysis             October 2002



   Requirement 2:

   PANA SHOULD protect the identity of the PaC from eavesdropping and
   polling attack.

7.2.2 Spoofing success or failure

   An attacker can send falsified authentication success or failure to
   the PaC. By sending false failure, the attacker can prevent the
   client from accessing the network. By sending false success, the
   attacker can let any node gain access to the network.

   If the link is not shared, it may be hard to launch this attack as
   the attacker needs to inject this packet at the right time and the
   PaC can always reject packets coming from any other source address
   other than the PAA.

   If the link is shared and even if per-packet authentication is
   present at layer 2, the attack is still possible. The node which is
   already authenticated at layer 2 can still pretend to be a PAA and
   spoof the success or failure.

   This attack is possible whenever the authentication is one way where
   the client is providing its credentials for accessing the network but
   it never verifies the credentials of the server.

7.2.3 MiTM attack

   A malicious node can claim to be PAA to the real PaC and claim to be
   PaC to the real PAA. This is a MiTM attack where the PaC is fooled to
   think that it is communicating with real PAA and the real PAA is
   fooled to think that it is communicating with real PaC.

   Requirement 3:

   When the PaC and PAA mutually authenticate each other i.e the AS
   verifies the identities of PaC and PaC verify the identity of the AS,
   this attack can be averted.

7.2.4 Replay Attack

   A malicious node can replay the messages that caused authentication
   failure or success at a later time to create false failures or
   success.

   This threat is absent if the link is not a shared medium. If the link
   is shared, then the attacker can replay old messages to revoke the
   access to the client. Even if per-packet authentication is present at


<Parthasarathy>           Expires April 2003                  [Page 8]

Internet-draft           PANA threat analysis             October 2002


   layer 2, the attacker can pretend to be a PAA and replay the old
   messages.

   Requirement 4:

   PANA MUST be resistant to replay attacks.


7.3 PaC leaving the network

   When the PaC leaves the network, it needs to inform the PAA before
   disconnecting from the network so that the resources used by PaC can
   be accounted properly. PAA may also choose to revoke the access any
   time if it deems necessary. Disconnect and revocation messages needs
   to be protected to avoid the following attacks.

   T7.3.1: A malicious node can pretend to be a PAA and revoke the
   access to PaC.

   T7.3.2: A malicious node can pretend to be a real PaC and disconnect
   from the network.

   T7.3.2: A malicious node can use the above 2 schemes to disconnect
   the PaC from the network and steal it’s IP address and MAC address to
   gain unauthorized access into the network.

   This threat is absent if the link between PaC and PAA is not a shared
   medium.

   If the link is shared, any node on the link can spoof the disconnect
   message. Even if the layer 2 has per-packet authentication, the
   attacker can pretend to be a PaC e.g. by spoofing the IP address, and
   disconnect from the network. Similarly, any node can pretend to be a
   PAA and revoke the access to the PaC.

   Requirement 5:

   Disconnect and revocation messages MUST be authenticated.


7.4 Attacks on normal communication


   PaC is exchanging data with some other node. Following threats are
   possible.

   T7.4.1: Attacker can modify data packets.




<Parthasarathy>           Expires April 2003                  [Page 9]

Internet-draft           PANA threat analysis             October 2002


   T7.4.2: Attacker can use the IP address and MAC address of a
   different PaC to gain unauthorized access to the network.

   Once the PaC is successfully authenticated, EP will have filters in
   place to prevent unauthorized access into the network. The filters
   will be based on something that will be carried on every packet. For
   example, the filter could be based on IP and MAC address where the
   packets will be dropped unless the packets coming with certain IP
   address match the MAC address also. Attacker can spoof both the IP
   and MAC address and inject packets into the communication of some
   other node.

   This threat is absent in links that are not shared as simple ingress
   filtering can prevent one node from impersonating as another node.

   If the link between PaC and PAA is shared, it is easy to launch this
   attack. Layer 2 authentication cannot prevent the node from using the
   IP address of some other node.

   If the PaC is using a secure VPN service e.g. using IPsec, IPsec
   already provides per-packet data origin authentication and integrity.
   In this case, this threat is not present.

   Requirement 6

   PANA MUST be able to derive keys in order to enable per-packet
   authentication and integrity. PaC SHOULD be able to negotiate this
   feature if needed.

   T7.4.3: Attacker can eavesdrop on the communication to learn useful
   information.

   If the link between PaC and PAA is not a shared medium, attackers
   cannot eavesdrop and hence this threat is absent in such links.

   If the layer 2 is shared, anyone can eavesdrop on the communication.
   If the layer 2 already provides encryption, then other nodes cannot
   learn any information by eavesdropping.

   If the PaC is using a secure VPN service e.g. using IPsec, IPsec
   already provides per-packet confidentiality by encrypting the
   packets. In this case, this threat is not present.

   Requirement 7

   PANA MUST be able to derive keys in order to enable confidentiality.
   PaC SHOULD be able to negotiate this feature if needed.




<Parthasarathy>           Expires April 2003                 [Page 10]

Internet-draft           PANA threat analysis             October 2002


   T7.4.4: Attacker can replay packets at a later point in time causing
   old packets to be re-injected.

   If the link between PaC and PAA is not a shared medium, attacker
   cannot inject packets into the communication and hence this threat is
   absent in such links.

   If the layer 2 is shared and even if it is secure, an attacker can
   easily replay old packets.

   If the PaC is using a secure VPN service e.g. using IPsec, IPsec
   already provides replay protection. In this case, this threat is not
   present.

   Requirement 8

   PANA per-packet authentication MUST provide anti-replay service.


7.5 Miscellaneous attacks

   T7.5.1: Attacker can bombard the PAA with lots of authentication
   requests. This can lead to DoS attack, if the resources needed for
   discarding the request are more than what is needed for
   authenticating a real PaC. At least, PAA should not try to allocate
   resources till it completes authentication. EP may need to add
   filters at the beginning (as soon as the address is assigned) to
   prevent unauthorized access. Adding filters might consume resources
   if it has to allocate one for each PaC it is authenticating. PAA
   should not allocate resources till the authentication is completed.

   T7.5.2: PaC acquires IP address before PANA authentication begins
   using methods like e.g., DHCP in IPv4 and auto-configuration in IPv6
   [PANAREQ]. If IP addresses are assigned before authentication, it
   opens up the possibility of DoS attack where malicious nodes can
   deplete the IP addresses by assigning multiple IP addresses. This
   threat does not apply to IPv6 if stateless auto-configuration
   [ADDRCONF] is used. If stateful mechanism is used in IPv6 e.g.,
   DHCPv6, then this attack is still possible. Address depletion attack
   is not specific to PANA, but a known attack in DHCP [DHCP-AUTH]. If
   PANA assumes that the client has an IP address already, it opens up
   the network to the DoS attack where addresses could be depleted.

   Requirement 9

   PANA should not assume that the client has a valid IP address.





<Parthasarathy>           Expires April 2003                 [Page 11]

Internet-draft           PANA threat analysis             October 2002


8.0  Summary of Requirements


       o PANA MUST not assume that the discovery process is protected.

       o The authentication exchange SHOULD protect the identity of the
          PaC from eavesdropping and polling attack.

       o PaC and PAA MUST mutually authenticate each other to prevent
          MiTM attacks.

       o Disconnect and revocation messages MUST be authenticated.

       o PANA MUST be able to derive keys in order to enable per-packet
          authentication, integrity, confidentiality and protection
          against replay attacks. PaC SHOULD be able to negotiate this
          feature if needed.

       o PANA SHOULD not assume that the PaC has a valid IP address.


9.0  Security Considerations

   This draft discusses various threats when using PAA for
   authenticating network access and does not give rise to any threats.


References

   i  Bradner, S., "The Internet Standards Process -- Revision 3", BCP
      9, RFC 2026, October 1996.


   2. Bernard Aboba, “Pros and Cons of Upper Layer Network  Access”

   3. Arunesh Mishra, William A. Arbaugh, “An Initial Security Analysis
      of the IEEE 802.1x Standard”

   4. IEEE. Standard for port based network access control. IEEE Draft
      P802.1X

   5. [PANAUS] Yoshihiro Ohba et. al, “Problem Space and Usage Scenarios
      for PANA”, draft-ietf-pana-usage-scenarios-02.txt

   6.[RAT] Dan Harkins et. al, “Design Rationale for IKEv2”, draft-ietf-
      ipsec-ikev2-rationale-00.txt

   7.[NAI] B. Aboba, M. Beadles, “The Network Access Identifier”



<Parthasarathy>           Expires April 2003                 [Page 12]

Internet-draft           PANA threat analysis             October 2002




   8. [PANAREQ] A. Yegin et al., “Protocol for Carrying Authentication
      for Network Access (PANA) Requirements and Terminology”, Internet-
      Draft, Work in progress

   9. [ADDRCONF] Susan Thomson et.al “IPv6 Stateless Address
      Configuration”, RFC2462.

   10. [DHCP-AUTH] R. Droms, et. al “Authentication for DHCP messages”,
      RFC3118.
   11. [KEYWORDS] S. Bradner, “Key words for use in RFCS to indicate
      requirement levels”, RFC 2119, March 1997


Acknowledgments

   Thanks to Alper Yegin and Basavaraj Patil for the initial feedback on
   this document. Pekka Nikkander provided comments that helped clarify
   this document and also helped identify some threats. Michael Thomas
   pointed out the missing replay attack and helped clarify the
   document.


Author's Addresses

   Mohan Parthasarathy
   Tahoe Networks
   San Jose
   Email: mohanp@tahoenetworks.com





















<Parthasarathy>           Expires April 2003                 [Page 13]


Html markup produced by rfcmarkup 1.108, available from http://tools.ietf.org/tools/rfcmarkup/