Internet Engineering Task Force                                 A. Vives
Internet-Draft                                                  J. Palet
Expires: January 12, 2006                                    Consulintel
                                                               P. Savola
                                                           July 11, 2005

                     Distributed Security Framework

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Copyright Notice

   Copyright (C) The Internet Society (2005).


   Current Internet trends in several fields have brought some security
   concerns with regards to what will happen with the current security
   paradigms and mechanisms.

   This document analyzes two security paradigms, the network-based and
   the host-based.  The former refers to what is being used nowadays out

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   there and the latter is based on the distributed firewall concept

   From the point of view of these security concerns it is stated that
   there is a problem that must be addressed.

   Some insights are given with respect to the host-based security

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Security Models  . . . . . . . . . . . . . . . . . . . . . . .  4
     2.1   Network-based  . . . . . . . . . . . . . . . . . . . . . .  4
     2.2   Host-based . . . . . . . . . . . . . . . . . . . . . . . .  6
   3.  Problem Statement  . . . . . . . . . . . . . . . . . . . . . .  9
   4.  Framework for Distributed Security . . . . . . . . . . . . . . 11
     4.1   Definitions  . . . . . . . . . . . . . . . . . . . . . . . 11
     4.2   Scenarios  . . . . . . . . . . . . . . . . . . . . . . . . 12
       4.2.1   Enterprise . . . . . . . . . . . . . . . . . . . . . . 13
       4.2.2   Home-User  . . . . . . . . . . . . . . . . . . . . . . 14
       4.2.3   Public Hot-Spot  . . . . . . . . . . . . . . . . . . . 14
     4.3   Functions of the Elements  . . . . . . . . . . . . . . . . 14
       4.3.1   Policy Specification Language (PSL)  . . . . . . . . . 14
       4.3.2   Security Policy (SP) . . . . . . . . . . . . . . . . . 15
       4.3.3   Security Status (SS) . . . . . . . . . . . . . . . . . 15
       4.3.4   Security Domain (SD) . . . . . . . . . . . . . . . . . 16
       4.3.5   Policy Enforcement Agent (PEA) . . . . . . . . . . . . 16
     4.4   Issues . . . . . . . . . . . . . . . . . . . . . . . . . . 16
       4.4.1   Node Addition/Deletion . . . . . . . . . . . . . . . . 16
       4.4.2   Authentication . . . . . . . . . . . . . . . . . . . . 17
       4.4.3   Policy Exchange Protocol . . . . . . . . . . . . . . . 17
       4.4.4   Data Integrity and Authenticity  . . . . . . . . . . . 18
       4.4.5   Moving between security domains  . . . . . . . . . . . 18
   5.  Other Issues . . . . . . . . . . . . . . . . . . . . . . . . . 18
   6.  Conclusions  . . . . . . . . . . . . . . . . . . . . . . . . . 18
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 19
   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 19
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 19
     9.1   Normative References . . . . . . . . . . . . . . . . . . . 19
     9.2   Informative References . . . . . . . . . . . . . . . . . . 19
       Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 20
       Intellectual Property and Copyright Statements . . . . . . . . 21

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1.  Introduction

   There are a lot of emerging technologies that lead to scenarios where
   the current security paradigms, mechanisms and practices are not
   capable to protect against current threats, which have increased in
   type and number.  These have raised some security concerns with
   regard to what will happen in a medium/short term.

   Nowadays we are seeing how IP-enabled devices are more common each
   day, so we don�t just see laptops but also PDAs and mobile
   phones walking around and connecting/roaming to/between different
   networks.  This comes together with the use of P2P and GRID
   applications which are based on the end-to-end paradigm.

   In line with the end-to-end paradigm is the new Internet Protocol
   version (IPv6) [3] because of the provision of enough globally
   routable addresses as required.  For example Mobile IP needs several
   addresses for each moving host [4].

   IPv6 also adds the availability of IPsec [5] [7] in the stack, what
   could be used for end-to-end encrypted communications, with all the
   problems that this imply to the security infrastructures currently

   Another kind of IP devices that are appearing are home automation
   devices which have its own IP stack and applications but few
   computing resources.  These devices are susceptible of being
   compromised and used for malicious things but have almost no
   resources to be used for being self-protected.

   From this perspective, this document analyzes the most (currently)
   used security paradigm, which from now will be referred as network-
   based security scheme.  The objective is to identify its drawbacks
   and advantages against the new foreseen scenarios.

   Based on the distributed firewall concept [2] we introduce the host-
   based security scheme, which extends the security mechanisms used
   from only firewalling to a number of them (IDS, firewalling, anti-
   virus, version control, etc.).  Not only its drawbacks and advantages
   against the new foreseen scenarios are identified but also it is
   presented as a possible direction to follow to solve the above-
   mentioned security concerns.

   Once these two security models are described we state that a security
   problem will arise if no new techniques are used to address the
   coming technologies.

   In order to provide some insights about the distributed security

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   model some definitions and scenarios are given along with some
   concrete issues analysis.

2.  Security Models

2.1  Network-based

   To secure a network one or more Firewalls (FW) are used depending on
   the network topology and size.  The FW can perform security tasks
   over the traffic that goes through/to its interfaces.  The security
   administrator will be in charge of putting the firewalls where it
   considers and to configure them to accomplish the organization&#
   65533;s network security policy.

                  /         \
                 |  Internet |
                  \         /
                      (*) Policy Enforcement Point
                   +---+---+            /---\       +-------+
                   |       |           | \ / |      |       |
       ---+-----(*)+  FW1  +(*)---+----+  X  +---(*)+  FW2  +(*)-----+-----+--
          |        |       |      |    | / \ |      |       |        |     |
        +-+--+     +---+---+   +--+-+   \-+-/       +---+---+     +--+-+ +-+--+
        | S1 |        (*)      | H2 |     |            (*)        | H5 | | H6 |
        +----+         |       +----+     |  +----+     |  +----+ +----+ +----+
                       |                  +--+ H3 |     +--+ H4 |
               +----+  |                  |  +----+     |  +----+
               | H1 +--+
               +----+  |

   Figure 1: Network-based Security

   As an example we can see in Figure 1 a network with one connection to
   Internet and several LANs.  With this configuration the FW1 could
   inspect all the traffic coming in/out from/to Internet.  This means
   that FW1 will be the first node that an outside attack will see.  As
   can be seen the security policy in enforced in all FWs interfaces.
   Note that, for example, traffic between H2 and H3 or between H5 and
   H6 is not noticed by any FW.

   This is the most used scheme, where the security of a host depends on
   the point of the network it is connected to, i.e., depends on the
   topology of the network.

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   The complexity of the security infrastructure will be proportional to
   the size of the network and the decisions taken by the security
   administrator who will decide the number and type of FWs.  There are
   mechanisms to propagate the configuration among different firewalls,
   from the same manufacturer and for big appliances, in order to
   simplify the administration in case of large networks.

   This model is based on the following assumptions to work properly:

   o  The threats come from "outside" the protected network, basically
      the Internet.

   o  Everybody from the same LAN segment is trusted.

   o  The protected nodes won't go "outside" the protected network where
      the security infrastructure won't be able to protect them.

   o  There are no backdoors on the network (modem, WLAN, other

   o  The hosts will not need to be accessed directly from outside (at
      least in a general manner, i.e., potentially all ports on all

   o  The security policy could be applied in one or more of the
      following levels: network, transport and application.

   The advantages of this model are:

   o  It is a mature technology which have been used for a long time.

   o  Its simplicity and easiness as the elements and points of
      configuration are reduced to the minimum.

   The drawbacks of this model are:

   o  This is a firewall-dependant model, i.e., if a FW fails, then all
      the networks connected to it will loose network connectivity
      unless specific fail-over techniques are applied.

   o  A big percentage of the threats come from inside the protected
      network.  To protect all the inter-LAN communications in a large
      network the number and cost of the needed FWs could be too much.
      In any case the hosts are not protected within its own LAN

   o  The most dangerous threats, in the sense that one may not be able
      to protect from them, come from inside the protected network.

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   o  The FW usually acts as NAT and/or proxy box, interfering or even
      disallowing end-to-end communications.  In complex configurations,
      even more than one level of NAT/proxy could appear.

   o  Transport mode secured communications (using IPsec ESP for
      example) need special solutions ([1]).

   o  The same security policy may be enforced for all the nodes of each
      network connected to the FW, but it is also possible to have
      separate policies for all hosts.  In any case, an error in a FW
      will equally expose all hosts on networks connected to that FW.

   o  Virtual organizations, for example those using GRID models, don't
      work with traditional centralized security models.

   o  The lack of secure end-to-end prevents deployment of innovative

2.2  Host-based

   We will call Host-based security model an evolution of the concept of
   distributed firewall already introduced by [2].  It is based on the
   idea of enforcing the security policy in each network host from a
   central control point.

   The biggest challenge is trusting that the hosts comply to the rules
   they've received, for example that the user can't just disable the
   firewall if (s)he dislike the policy.  Of course, this only can
   happen in the case (s)he has administrative rights for that (often
   not the case in non-personal systems, those not owned by the end-
   user, such as corporate PCs or laptops).  It seems that one or more
   network entities would have to keep watch over the hosts in order to
   detect if they are not following the received policy.

   From a security point of view this model somehow eases the work to
   the "enemies", putting the Policy Enforcement Point in their hands.
   So, not only mechanisms to prevent direct attacks to the security
   solution must be developed but mechanisms to minimize the
   consequences as well.

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                          /         \
                         |  Internet |
              +------+    \         /
              |Secur.|     \---+---/
              |Policy|         |
              +--+---+         |
                (*)          /-+-\
                 |          | \ / | LAN-3
                -+---+------+  x  +-------+--
               LAN-1(*)     | / \ |      (*)  Policy Enforcement Point
                  +--+-+     \-+-/      +-+--+
                  | H1 |       | LAN-2  | H3 |
                  +----+       |        +----+
                            | H2 |

   Figure 2: Host-based Security

   This model is based on the following assumptions:

   o  Each host can be uniquely and securely identified.

   o  The security policy could be applied in one or more of the
      following levels: network, transport and application.

   o  Threats come from anywhere in the network.

   o  "Outside" hosts may be able to access all hosts "Inside",
      depending on the policies.

   o  No assumptions are made about where the host can be connected.

   The advantages of this model are:

   o  The flexibility in the definition of security policies, as it is
      based on the assumption of an available Policy Specification
      Language which can be used for high-level definitions of all the
      needed policies.

   o  A host can take better decisions as it knows what it is doing or
      trying to do, that means it can better detect strange packets.
      For example, it could allow mail traffic to only one application
      on the system.

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   o  Enables the usage of end-to-end applications level security (e.g.,
      web services security standards).

   o  Enables better protection from attacks by the "internal" users,
      and possibly even to a degree from those in the local segment.
      For example address spoofing can be detected and avoided coming
      from the same LAN segment, without router participation, because a
      host in a LAN can detect packets from other host with source
      addresses that are not used in that LAN.

   o  Can protect a host independent of the topology, i.e., wherever the
      host is connected.

   o  Does not need specific devices to secure a host.  Consider the
      case of a single host with a CPE (Customer Premises Equipment), if
      the CPE has no (user-controllable) firewall functions.

   o  Can control the outgoing attempts from each host, avoiding local
      network misbehavior or malicious practices.

   o  The collection of audit information could be more complete in a
      distributed model, despite the processing of that information is
      done in a distributed or centralized fashion.

   o  It maintains the centralized control of the security policies,
      from where they are distributed to each host (central decisions,
      local enforcement), despite the size of the network to protect.
      In general it scales well.

   o  It enables new distributed and cooperative solutions to improve
      the network security.

   The drawbacks of this model are:

   o  It is more complex than the Network-based one as more elements are
      needed, some of them need to be defined or even designed.

   o  The uniqueness and secured identification of hosts is not trivial
      (for example, [2] proposes the use of certificates).

   o  The hosts must be trusted (or designed appropriately) so that they
      will operate according to the policy.  For example, it must be
      impossible to disable the firewall functions or if the policy is
      not followed network communication is not allowed.

   o  A host that becomes compromised or infected with a worm or virus
      in any case can't be trusted to operate according to the policies,
      as the worms/viruses probably first create holes or disable the

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      protections if they can.

   o  It may be challenging to design the system so that policy updates
      are made available to the nodes which may not be network-reachable
      all the time.

   o  It may be difficult to distinguish a misbehaving application from
      a legitimate application (for example, many email worms may be
      channeled through the MUA which must be authorized to send the
      mails to operate correctly).

   o  Because of having a centralized Policy Decision Point (PDP) from
      where the Security Policies are distributed a weakness is
      introduced in form of a central point of failure unless more
      complexity is added, for example with a distributed/replicated

   o  The host security is in some sense 'server-dependant'.  It must be
      able to detect the lost of connectivity with the PDP and act in
      consequence.  It also seems that being disconnected from the PDP
      for a long period could be dangerous because updated security
      information raise the security level.

3.  Problem Statement

   The starting points are the new technologies we mentioned above and
   the network-based security model.  We will demonstrate that things
   like IPv6 deployment or P2P applications impose a problem to the most
   common security models.

   Finally we will outline how the host-based security model is able to
   address a number of those problems.

   Not only new technologies but also new threats have appeared that use
   security holes in the software.  Viruses, spyware, adware, spam,
   worms and (D)DoS attacks have made necessary to use several security
   tools to fight these threats.  This is the reason of the appearance
   of different software pieces that are installed on both the servers
   (anti-spam and anti-virus) and the user hosts (software version
   control, anti-virus and anti-spyware).  The trend seems to be to
   direct the attacks against user hosts, the attacks directed to
   servers are decreasing.

   We can summarize the consequences of the appearance of new
   technologies (IPv6, P2P, GRID, mobile IP, etc.), new behaviors and
   new threats as:

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   1.  The need/use of end-to-end communications.

   2.  The availability/use of IPsec on all IP devices.  For example,
       all IPv6 stacks have IPsec capability that can be used if

   3.  Nomadic IP devices that will move between different networks
       under different security administration.

   4.  A number of different security mechanisms are needed in order to
       protect a network/host.

   The network-based security model has problems addressing the above
   points.  This can be summarized in:

   1.  It difficults/avoids end-to-end communications because of the FWs
       acting as NAT and/or proxy.

   2.  Transport mode secured communications (using IPsec ESP for
       example) need special solutions ([1]).  The basic idea is that
       the encrypted payload can�'t be inspected.

   3.  It is not able to protect nomadic nodes that move out of the
       protected network.  In foreign network the nodes are exposed to
       threats and can be infected when they come back to their "home"

   In the other hand the host-based security model could address the
   following points from the above-mentioned:

   1.  It assumes end-to-end connectivity of all nodes, so the end-to-
       end communications are the natural way of doing things.

   2.  As the security rules could be applied before encrypting the
       payload, the encrypting does not affect the security mechanism
       which could work in a straightforward way.

   3.  Nodes will be protected wherever they are as always will have
       security mechanisms on the hosts.  It should be taken into
       account that the security policy update must be done as
       frequently as possible.

   In any case it should be clearly stated that the network-based
   security model is a mature technology which have been used for a long
   time.  The host-based security model is basically just this, a model,
   and several issues must be solved before it takes place.

   Security improvements in both the network-based and the host-based

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   security models are required, for example to be able to cope with all
   the actual security threats.  The idea is to try to integrate in a
   unique solution as much mechanisms as possible, and tune them to
   follow the security policy within a protected network and its hosts,
   in case they move to a foreign network.

   Following this idea a hybrid model could be used where both the
   network-based and host-based models are used.  The tasks could be
   distributed among both or be activated depending of where the host is
   connected to, if there is a security alert situation, etc.

   Insights over the problems that host-based security model must
   resolve before being deployed in real life are outlined in following

4.  Framework for Distributed Security

4.1  Definitions

   To describe the distributed security model several terms will be
   used.  They are defined here as follows:

   o  SD (Security Domain): Network portion under the administration of
      the same Security Administrator/Organization.

   o  SP (Security Policy): We refer to the information that is
      distributed to each policy enforcement point within a SD in order
      to achieve the desired level of security.  This information will
      follow the whole protected network security policy defined by the
      Security Administrator of that network.  This information will be
      converted to specific rules for each platform by the Policy
      Enforcement Agent.

   o  SS (Security Status): Information about host different aspects
      that could be used to measure how secure it is.

   o  PSL (Policy Specification Language): Language used to define SP
      and SS.

   o  PDP (Policy Decision Point): The node where the SPs for a SD are
      defined.  From the PDP the SPs are distributed to PEPs.

   o  PEP (Policy Enforcement Point): The place where a SP is applied.

   o  PEA (Policy Enforcement Agent): The entity in charge of applying
      the SP at the PEP.

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   o  PXP (Policy Exchange Protocol): The protocol used for distribution
      of the SP to the PEA.

                           /         \
                          (  Internet )
                           \         /
              +-----+       \---+---/
              | PDP |           |
              +--+--+          (*)
                (*)          /--+--\
                 |          | \   / |         LAN-3
                -+---+---(*)+ PEA4  +(*)----+--
           LAN-1    (*)     | /   \ |      (*)
                  +--+-+     \--+--/      +-+--+
                  |PEA1|       (*)        |PEA3|
                  +----+        |         +----+
                               (*)  LAN-2
                             |PEA2|           (*) Policy Enforcement Point

   Figure 3: Definitions: Basic Scheme

   The basic idea is simple: the Security Policy is centrally defined
   using the Policy Specification Language and distributed to each
   Policy Enforcement Agent by means of the Policy Exchange Protocol.
   The PEA will apply the SP to each Policy Enforcement Point it is
   responsible for.  The network entities need to be authenticated in
   order to be trusted, for example to allow an incoming connection or
   to trust on the received Security Policy.

4.2  Scenarios

   In order to gain some insights in the distributed security analysis
   some scenarios are depicted to be considered when drawbacks and
   advantages are outlined.

   The idea is to address some general scenarios which already exist and
   where new technologies, devices, users and behaviors take place.  For
   example the deployment of the new Internet Protocol, IPv6, the use of
   P2P and GRID applications and new nomadic IP devices could be seen as
   some of the issues that bring new security scenarios that should be

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   One important issue that must be taken into account is the movement
   of a host between different scenarios/networks.  This point will be
   addressed in section 4.4.5 of this document.

   Basically three possible scenarios have to be addressed, all of them
   interconnected through Internet:

   o  Enterprise.

   o  ISP-Client.

   o  Public.

        /\         /-------------------------\     \  /
      /    \      /   INTERNET                \     \/
    /       \    /                        /-\  \   +--+     +---+
   *---------*  /                        | X +-|---|AP| ))) |PEA|
   |         | |   /--------\             \-/  |   +--+     +---+
   |    +---+| |  |  /-\  ISP|                 |  Public
   |    |PEA++-|--+-+ X |    |                 | Hot-Spot
   |+-+ +---+| |  |  \+/     |                 |
   || |      | |  |   |      |                 |
   ++-+------+ |  | +-+-+    |    /--------\   |
    Home-User  |  | |PDP|    |   |   /-\ ISP|  |
               |   \+---+---/    |  | X |   |  |
               |                 |   \+/    |  /
                \                |    |     | /
                 \                \---+----/ /
                                     /-\  Enterprise
                             -+-----+ X +-----+-
                              |      \+/      |
                            +-+-+     |     +-+-+
                            |PEA|   +-+-+   |PEA|
                            +---+   |PDP|   +---+

   Figure 4: Scenarios

4.2.1  Enterprise

   This scenario considers the case of an organization with its own
   infrastructure containing both PDP(s) and PEP(s).  This means that

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   all the security infrastructure elements will be within the
   organization premises under the same administration.

   All the hosts connected to the protected network will also be
   administered by the above-mentioned administration.  So, it is highly
   probable that they use some kind of distributed security software
   that would collaborate to increase the security.

4.2.2  Home-User

   This scenario considers the case of an Residential Customer which has
   its PEP as part of the security solution.  The user has several
   choices as PDP.  The user could even not have a PDP and define by
   himself the Security Policy.  Also could use one provided as a paid
   service from a company located somewhere in Internet.  The ISP could
   also offer a PDP service for its customers.

   In case of a user connecting to his/her enterprise VPN the PDP used
   should be the one from that network.  Even in the case of not using a
   VPN the PDP could be the one from the user company.

   Other hosts in the same network will be in charge of the Home-User,
   so they could use some kind of distributed security software that
   would collaborate to increase the security.

4.2.3  Public Hot-Spot

   This scenario considers the case of the host being connected to a
   pubic Internet connection (not neccesarily only the case of a Wi-Fi
   Hot-Spot).  In this case the PEP will be located at the host but
   could not be sure to trust/have connectivity to a foreign PDP.

   Other hosts in the same network can not be trusted at all to be using
   some kind of distributed security software that would collaborate to
   increase the security.

4.3  Functions of the Elements

4.3.1  Policy Specification Language (PSL)

   The host-based model is based on the assumption of the use of a
   number of security mechanisms, for example firewall, IDS, anti-virus
   and software version control.

   This requirement means that the PSL must be flexible enough to
   specify the information about different objects and rules to behave
   depending on the value of that information.

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   Also the PSL must be able to specify security policies for new
   mechanism that could be added or appear in the future.

   The flexibility in the PSL will allow the coordinated use of the
   different security mechanisms by the PEA.  For example it could be
   defined that if the version of the mail user agent is not a safe one
   (version control security mechanism) the mail traffic is not allowed
   (firewall security mechanism).

   The syntax and semantics of the PSL must be clearly defined in a
   standard way.

4.3.2  Security Policy (SP)

   Thanks to the flexibility of the PSL the SP will include all the
   needed rules to follow the Security Administrator needs.

   The security policy should have rules to define configuration for all
   the security mechanisms used, based on the Security Status of the

   The SP could be specified with different granularity and using
   conditional statements.

   Granularity refers to the ability of referencing, at each layer, to
   all the possible elements.  For example, TCP/UDP ports or any IP
   header element�s value.  It is a matter of the implementation
   to reach a compromise between granularity and complexity.

   Conditional statements refers to the ability of taking decisions
   based on the values of different elements, as detailed as the
   granularity allows.  Even different complete sets of rules could be
   defined for different situations, like changing to a different SD
   (see Scenarios section above).  For example, in case of the change of
   a value the PEA could already have a rule on the received SP for the
   new value, avoiding the need of communicating it to the PDP, which
   would have to define a new SP and send it to the PEA.

   The SP also will be used to manage the update of elements in the host
   in order to increase the security, for example, a new anti-virus
   signature file or a new patched version of a piece of software with a
   known security breach.

4.3.3  Security Status (SS)

   Security Status is the list of the defined properties of the system,
   to be used for checking the conformance to the Security Policy.  For
   example: "firefox", "1.0.2"; where the security policy might mandate

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   that version 1.0.3 would be required.

4.3.4  Security Domain (SD)

   The concept of Security Domain is of capital importance in order to
   clarify where a SP must be applied.  Also the concept of changing
   from one SD to another one is important and will be addressed leter
   in this document in detail.

   A host that connects to a SD must accept the SP it receives and apply
   it.  In case of not following this rule the host could not be sure to
   have network connectivity.  It is matter of the security solution how
   to manage the hosts that don't apply the received policy.

4.3.5  Policy Enforcement Agent (PEA)

   The PEA will have a key role in the whole system as it will be the
   one in charge of assuring that the received SP is applied.  To
   accomplish this task several issues must be addressed:

   o  Verification of Authenticity and integrity of the received SP.

   o  Verification of the Security Status (SS) of the PEP.

   o  Comparison between the SS and the received SP and application of
      the specified rules depending on the comparison results.

   o  Running the different security mechanisms.

   o  Being able to communicate with other PEAs in order to allow
      distributed security mechanisms.

   o  Being proactive in order to detect and respond to any security

4.4  Issues

4.4.1  Node Addition/Deletion

   We refer to addition to both:

   o  The process of configuring a totally new node, installing the PEA
      and its first message exchange with the PDP or other PEAs.

   o  The addition of a node to the process launched when a node that
      has been off-line get reconnected again and tries to communicate
      with one PDP to get the last available SP.

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   This dual approach applies also for the deletion process.

   During the process of a node addition the host must be able to find
   the correct PDP which should authenticate itself as must do the host
   as well.

   The solution must support the addition and deletion of hosts from the
   SD dynamically with no degradation of the functionality and

   When a new node is connected to the SD network it should follow the
   required steps in order to be authenticated and configured following
   the appropriated SP.

   It will be a matter of the solution to assure that the hosts are
   following the received SP during the time they are connected to the
   SD network.

4.4.2  Authentication

   It is required that new hosts connected to the network demonstrate
   their identity for both receiving a useful SP and to communicate with
   other hosts within the same SD.

   This way, a host needs to authenticate itself first.  After that, the
   host may or may not be authorized to have connectivity with other
   networks through a switch/router or to be able to communicate with
   other hosts.

   As a guideline, cryptographic certificates could be used for this
   purpose, in order to guarantee the identity of the sender of a
   message.  As the identity will be used within the SD a SD-wide PKI
   could be used.

4.4.3  Policy Exchange Protocol

   The PXP is in charge of the distribution of the corresponding SP(s)
   to the PEAs.  This protocol should assure the delivery and update of
   the SP even in the case of possible problems, like the chance of a
   PDP failure or some kind of unreachability, for example in case of
   network segmentation.

   Also either the PEA or the PDP could launch an event that results in
   a SP update or change.  The PDP will update the SP in case of new
   security information is received for one or more of the used security
   mechanisms.  The PEA could also inform the PDP of a new Security
   Status because of some change in the PEP configuration.  Based in
   this new status the PDP could update the SP.

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   There could be some active mechanisms, like IDS, that could lead to
   some SP change.

4.4.4  Data Integrity and Authenticity

   There are several pieces of information that will be passed among
   entities within the security solution that would be a good target for
   an attack.  This information should be protected both while stored in
   a host and while transmitted from one host to another.

   As a guideline, cryptographic certificates could be used for this
   purpose, in order to guarantee the integrity and origin of the
   information.  As the identity will be used within the SD a SD-wide
   PKI could be used.

4.4.5  Moving between security domains

   As have been seen above a host, with its PEA, could move between
   different SD or between different scenarios, some of them with no
   security guarantees at all and no PDP available.

   If all network devices are globally reachable there will be no
   problem on reaching other hosts belonging to the same security
   solution cluster, including the PDP, which could be inside the
   corporate network.

   The solution must be able to manage this situation both being able to
   detect a network/SD change and responding in consequence, for example
   establishing a default SP in foreign networks (presumably a
   restrictive SP).

5.  Other Issues

   Further elaboration is required (TBD) on:

   o  Malicious users: We can't protect the network from malicious users
      that have physical access to network hosts in the protected
      network.  The objective is to minimize the danger they can cause.

   o  In the host-based security, the host that stores and distributes
      the security policies seems to be the best option to be the one
      that acts as IDS information collector.

6.  Conclusions

   New technologies (IPv6, P2P, GRID, Mobile IP, etc.), behaviors (use
   of small devices like PDAs and moving to different networks) and

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   threats (Virus, spam, spyware, adware, etc.) require improving the
   security mechanisms actually being used.  By one side the integration
   of different mechanisms and by other side the movement of the
   security policy enforcement point towards the hosts interfaces are
   recommended in order to improve the security of the hosts and in
   consequence of the network.

   Also a centralized control over the policy definition and enforcement
   is of importance in order to have a scalable solution.

   The network-based security model has problems addressing the new
   technologies and threats.  The host-based model has been described as
   a reference for a possible solution.  The latter model is presented
   as complementary to the former one.

7.  Security Considerations

   This document is concerned entirely with security.

8.  Acknowledgements

   The authors would like to acknowledge the inputs of Brian Carpenter,
   Satoshi Kondo, Shinsuke Suzuki, Peter Bieringer and the European
   Commission support in the co-funding of the Euro6IX project, where
   this work is being developed.

9.  References

9.1  Normative References

9.2  Informative References

   [1]  "IETF midcom WG",

   [2]  Bellovin, S., "Distributed Firewalls", November 1999,

   [3]  Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6)
        Specification", RFC 2460, December 1998.

   [4]  Johnson, D., Perkins, C., and J. Arkko, "Mobility Support in
        IPv6", RFC 3775, June 2004.

   [5]  Kent, S. and R. Atkinson, "Security Architecture for the
        Internet Protocol", RFC 2401, November 1998.

   [6]  Kent, S. and R. Atkinson, "IP Authentication Header", RFC 2402,

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        November 1998.

   [7]  Kent, S. and R. Atkinson, "IP Encapsulating Security Payload
        (ESP)", RFC 2406, November 1998.

Authors' Addresses

   Alvaro Vives Martinez
   San Jose Artesano, 1
   Alcobendas - Madrid
   E-28108 - Spain

   Phone: +34 91 151 81 99
   Fax:   +34 91 151 81 98

   Jordi Palet Martinez
   San Jose Artesano, 1
   Alcobendas - Madrid
   E-28108 - Spain

   Phone: +34 91 151 81 99
   Fax:   +34 91 151 81 98

   Pekka Savola


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