Internet Engineering Task Force T. Mizrahi
Internet-Draft MARVELL
Intended status: Informational E. Grossman, Ed.
Expires: April 5, 2018 DOLBY
A. Hacker
MISTIQ
S. Das
Applied Communication Sciences
J. Dowdell
Airbus Defence and Space
H. Austad
Cisco Systems
K. Stanton
INTEL
N. Finn
HUAWEI
October 2, 2017

Deterministic Networking (DetNet) Security Considerations
draft-ietf-detnet-security-00

Abstract

A deterministic network is one that can carry data flows for real-time applications with extremely low data loss rates and bounded latency. Deterministic networks have been successfully deployed in real-time operational technology (OT) applications for some years (for example [ARINC664P7]). However, such networks are typically isolated from external access, and thus the security threat from external attackers is low. IETF Deterministic Networking (DetNet) specifies a set of technologies that enable creation of deterministic networks on IP-based networks of potentially wide area (on the scale of a corporate network) potentially bringing the OT network into contact with Information Technology (IT) traffic and security threats that lie outside of a tightly controlled and bounded area (such as the internals of an aircraft). These DetNet technologies have not previously been deployed together on a wide area IP-based network, and thus can present security considerations that may be new to IP-based wide area network designers. This draft, intended for use by DetNet network designers, provides insight into these security considerations. In addition, this draft collects all security-related statements from the various DetNet drafts (Architecture, Use Cases, etc) into a single location Section 7.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

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This Internet-Draft will expire on April 5, 2018.

Copyright Notice

Copyright (c) 2017 IETF Trust and the persons identified as the document authors. All rights reserved.

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.


Table of Contents

1. Introduction

Security is of particularly high importance in DetNet networks because many of the use cases which are enabled by DetNet [I-D.ietf-detnet-use-cases] include control of physical devices (power grid components, industrial controls, building controls) which can have high operational costs for failure, and present potentially attractive targets for cyber-attackers.

This situation is even more acute given that one of the goals of DetNet is to provide a "converged network", i.e. one that includes both IT traffic and OT traffic, thus exposing potentially sensitive OT devices to attack in ways that were not previously common (usually because they were under a separate control system or otherwise isolated from the IT network). Security considerations for OT networks is not a new area, and there are many OT networks today that are connected to wide area networks or the Internet; this draft focuses on the issues that are specific to the DetNet technologies and use cases.

The DetNet technologies include ways to:

This draft includes sections on threat modeling and analysis, threat impact and mitigation, and the association of various attacks with various use cases both by industry and based on the Use Case Common Themes section of the DetNet Use Cases draft [I-D.ietf-detnet-use-cases].

This draft also provides context for the DetNet security considerations by collecting into one place Section 7 the various remarks about security from the various DetNet drafts (Use Cases, Architecture, etc). This text is duplicated here primarily because the DetNet working group has elected not to produce a Requirements draft and thus collectively these statements are as close as we have to "DetNet Security Requirements".

2. Abbreviations

IT         Information technology (the application of computers to store, study, retrieve, transmit, and manipulate data or information, often in the context of a business or other enterprise - Wikipedia).

OT         Operational Technology (the hardware and software dedicated to detecting or causing changes in physical processes through direct monitoring and/or control of physical devices such as valves, pumps, etc. - Wikipedia)

MITM       Man in the Middle

SN         Sequence Number

STRIDE       Addresses risk and severity associated with threat categories: Spoofing identity, Tampering with data, Repudiation, Information disclosure, Denial of service, Elevation of privilege.

DREAD       Compares and prioritizes risk represented by these threat categories: Damage potential, Reproducibility, Exploitability, how many Affected users, Discoverability.

PTP         Precision Time Protocol [IEEE1588]

3. Security Threats

This section presents a threat model, and analyzes the possible threats in a DetNet-enabled network.

We distinguish control plane threats from data plane threats. The attack surface may be the same, but the types of attacks are different. For example, a delay attack is more relevant to data plane than to control plane. There is also a difference in terms of security solutions: the way you secure the data plane is often different than the way you secure the control plane.

3.1. Threat Model

The threat model used in this memo is based on the threat model of Section 3.1 of [RFC7384]. This model classifies attackers based on two criteria:

DetNet-Service, one of the service scenarios described in [I-D.varga-detnet-service-model], is the case where a service connects DetNet networking islands, i.e. two or more otherwise independent DetNet network domains are connected via a link that is not intrinsically part of either network. This implies that there could be DetNet traffic flowing over a non-DetNet link, which may provide an attacker with an advantageous opportunity to tamper with DetNet traffic. The security properties of non-DetNet links are outside of the scope of DetNet Security, but it should be noted that use of non-DetNet services to interconnect DetNet networks merits security analysis to ensure the integrity of the DetNet networks involved.

3.2. Threat Analysis

3.2.1. Delay

3.2.1.1. Delay Attack

An attacker can maliciously delay DetNet data flow traffic. By delaying the traffic, the attacker can compromise the service of applications that are sensitive to high delays or to high delay variation.

3.2.2. DetNet Flow Identification

3.2.2.1. DetNet Flow Modification or Spoofing

An attacker can modify some header fields of en route packets in a way that causes the DetNet flow identification mechanisms to misclassify the flow. Alternatively, the attacker can inject traffic that is tailored to appear as if it belongs to a legitimate DetNet flow. The potential consequence is that the DetNet flow resource allocation cannot guarantee the performance that is expected when the flow identification works correctly.

Note that in some cases there may be an explicit DetNet header, but in some cases the flow identification may be based on fields from the L3/L4 headers. If L3/L4 headers are involved, for purposes of this draft we assume they are encrypted and/or integrity-protected from external attackers.

3.2.3. Resource Segmentation or Slicing

3.2.3.1. Inter-segment Attack

An attacker can inject traffic, consuming network device resources, thereby affecting DetNet flows. This can be performed using non-DetNet traffic that affects DetNet traffic, or by using DetNet traffic from one DetNet flow that affects traffic from different DetNet flows.

3.2.4. Packet Replication and Elimination

3.2.4.1. Replication: Increased Attack Surface

Redundancy is intended to increase the robustness and survivability of DetNet flows, and replication over multiple paths can potentially mitigate an attack that is limited to a single path. However, the fact that packets are replicated over multiple paths increases the attack surface of the network, i.e., there are more points in the network that may be subject to attacks.

3.2.4.2. Replication-related Header Manipulation

An attacker can manipulate the replication-related header fields (R-TAG). This capability opens the door for various types of attacks. For example:

3.2.5. Path Choice

3.2.5.1. Path Manipulation

An attacker can maliciously change, add, or remove a path, thereby affecting the corresponding DetNet flows that use the path.

3.2.5.2. Path Choice: Increased Attack Surface

One of the possible consequences of a path manipulation attack is an increased attack surface. Thus, when the attack described in the previous subsection is implemented, it may increase the potential of other attacks to be performed.

3.2.6. Control Plane

3.2.6.1. Control or Signaling Packet Modification

An attacker can maliciously modify en route control packets in order to disrupt or manipulate the DetNet path/resource allocation.

3.2.6.2. Control or Signaling Packet Injection

An attacker can maliciously inject control packets in order to disrupt or manipulate the DetNet path/resource allocation.

3.2.7. Scheduling or Shaping

3.2.7.1. Reconnaissance

A passive eavesdropper can gather information about en route DetNet flows, e.g., the number of DetNet flows, their bandwidths, and their schedules. The gathered information can later be used to invoke other attacks on some or all of the flows.

3.2.8. Time Synchronization Mechanisms

An attacker can use any of the attacks described in [RFC7384] to attack the synchronization protocol, thus affecting the DetNet service.

3.3. Threat Summary

A summary of the attacks that were discussed in this section is presented in Figure 1. For each attack, the table specifies the type of attackers that may invoke the attack. In the context of this summary, the distinction between internal and external attacks is under the assumption that a corresponding security mechanism is being used, and that the corresponding network equipment takes part in this mechanism.

         
+-----------------------------------------+----+----+----+----+
| Attack                                  |   Attacker Type   |
|                                         +---------+---------+
|                                         |Internal |External |
|                                         |MITM|Inj.|MITM|Inj.|
+-----------------------------------------+----+----+----+----+
|Delay attack                             | +  |    | +  |    |
+-----------------------------------------+----+----+----+----+
|DetNet Flow Modification or Spoofing     | +  | +  |    |    |
+-----------------------------------------+----+----+----+----+
|Inter-segment Attack                     | +  | +  |    |    |
+-----------------------------------------+----+----+----+----+
|Replication: Increased Attack Surface    | +  | +  | +  | +  |
+-----------------------------------------+----+----+----+----+
|Replication-related Header Manipulation  | +  |    |    |    |
+-----------------------------------------+----+----+----+----+
|Path Manipulation                        | +  | +  |    |    |
+-----------------------------------------+----+----+----+----+
|Path Choice: Increased Attack Surface    | +  | +  | +  | +  |
+-----------------------------------------+----+----+----+----+
|Control or Signaling Packet Modification | +  |    |    |    |
+-----------------------------------------+----+----+----+----+
|Control or Signaling Packet Injection    |    | +  |    |    |
+-----------------------------------------+----+----+----+----+
|Reconnaissance                           | +  |    | +  |    |
+-----------------------------------------+----+----+----+----+
|Attacks on Time Sync Mechanisms          | +  | +  | +  | +  |
+-----------------------------------------+----+----+----+----+
           

Figure 1: Threat Analysis Summary

4. Security Threat Impacts

This section describes the impact of the attacks described in Section 3. Mitigations are discussed further in Section 5.

In computer security, the impact (or consequence) of an incident can be measured in loss of confidentiality, integrity or availability of information. In other words, this section describes the effect of a successful attack. The scope is limited to the effect of a successful attack on DetNet itself, not the applications that _use_ Detnet as this is highly application specific.

4.1. Delay-Attacks

4.1.1. Data Plane Delay Attacks

Dropped messages can result in stream instability. If only a single path is used, the entire stream can be disrupted. In a multipath scenario, large delays on one stream can lead to increased buffer and CPU resources on the elimination bridge.

If the attack is carried out on a sole link (i.e. no multipath), the DetNet stream can be interrupted and result in outages.

4.1.2. Control Plane Delay Attacks

In and of itself, this is not directly a threat, the effects of delaying control messages can have quite adverse effects later.

Delayed messages for tear-down can lead to resource leakage if a stream is not torn down at the correct time. This can in turn result in failure to allocate new streams giving rise to a denial of service attack.

In the case where an End-point should be added to a multicast, failure to deliver said signalling message will prevent the new EP from receiving expected frames.

Likewise, when an EP should be removed from a multicast group, delaying such messages can lead to loss of privacy as the EP will continue to receive messages even after it is removed.

4.2. Flow Identification and Spoofing

4.2.1. Flow identification

Of all the attacks, this is one of the most difficult to detect and counter. Often, an attacker will start out by observing the traffic going through the network and use the knowledge gathered in this phase to mount future attacks.

The attacker can, at their leisure, observe over time all aspects of the messaging and signalling, learning the intent and purpose of all traffic flows. At some later date, possibly at an important time in an operational context, the attacker can launch a multi-faceted attack, possibly in conjunction with some demand for ransom.

The flow-id in the header of the data plane-messages gives an attacker a very reliable identifier for DetNet traffic, and this traffic has a high probability of going to lucrative targets.

4.2.2. Spoofing

4.2.2.1. Dataplane Spoofing

Spoofing dataplane messages can result in increased resource consumptions on the bridges throughout the network as it will increase buffer usage and CPU utilization. This can lead to resource exhaustion and/or increased delay.

If the attacker manages to create valid headers, the false messages can be forwarded through the network, using part of the allocated bandwidth. This in turn can cause legitimate messages to be dropped when the budget has been exhausted.

Finally, the endpoint will have to deal with invalid messages being delivered to the endpoint instead of (or in addition to) a valid message.

4.2.2.2. Control Plane Spoofing

A successful control plane spoofing-attack has a very large potential. It can do anything from modifying existing streams by changing the available bandwidth, add or remove endpoints or drop the stream altogether. It would also be possible to falsely create new streams, which could give an attacker the ability to exhaust the systems resources, or just enable a high quality DetNet stream outside the Network engineer's control.

4.3. Segmentation attacks (injection)

4.3.1. Data Plane Segmentation

Injection of false messages in a DetNet stream could lead to exhaustion of the available bandwidth for a stream if the bridges accounts false messages to the stream's budget.

In a multipath scenario, injected messages will cause an increased CPU utilization on elimination bridges and if enough paths are subject to malicious injection, the legitimate messages could be dropped. Likewise it can cause an increase in buffer usage. In total, this will consume more resources on the bridges than normal, giving rise to a potential resource exhaustion attack on the bridges.

If a stream is interrupted, the end application will be affected by what is now a non-deterministic stream.

4.3.2. Control Plane segmentation

A successful Control Plane segmentation attack will cause control messages to be interpreted by nodes in the network. This has the potential to create new streams (exhausting resources), drop existing (denial of service), add/remove end-stations to a multicast group (loss of privacy) or modify the stream attributes (reducing available bandwidth, or increasing it so that new streams cannot reserve a path).

In short, this means that you cannot trust the stream reservation properties or the network itself.

As with spoofing, if an attacker is able to inject control-plane messages and the receiving end does not detect it, the receiving station must be able to.

4.4. Replication and Elimination

The Replication and Elimination is relevant only to Data Plane messages as Signalling is not subject to multipath routing.

4.4.1. Increased Attack Surface

Covered briefly in Section 4.3

4.4.2. Header Manipulation at Elimination Bridges

Covered briefly in Section 4.3

4.5. Impact of Attacks to Path Choice

This is covered in part in Section 4.3, and as with Replication and Elimination (Section 4.4, this is relevant for DataPlane messages.

4.6. Impact of Attacks by Use Case Industry

This section rates the severity of various components of the impact of a successful vulnerability exploit to use cases by industry as described in [I-D.ietf-detnet-use-cases], including Pro Audio, Electrical Utilities, Building Automation, Wireless for Industrial, Cellular Radio, and Industrial M2M (split into two areas, M2M Data Gathering and M2M Control Loop).

Components of Impact (left column) include Criticality of Failure, Effects of Failure, Recovery, and DetNet Functional Dependence. Criticality of failure summarizes the seriousness of the impact. The impact of a resulting failure can affect many different metrics that vary greatly in scope and severity. In order to reduce the number of variables, the following were included: Financial, Health and Safety, People well being, Affect on a single organization, and affect on multiple organizations. Recovery outlines how long it would take for an affected use case to get back to its pre-failure state (Recovery time objective, RTO), and how much of the original service would be lost in between the time of service failure and recovery to original state (Recovery Point Objective, RPO). DetNET dependence maps how much the following DetNet service objectives contribute to impact of failure: Time dependency, data integrity, source node integrity, availability, latency/jitter.

The scale of the Impact mappings is low, medium, and high. In some use cases there may be a multitude of specific applications in which DetNET is used. For simplicity this section attempts to average the varied impacts of different applications. This section does not address the overall risk of a certain impact which would require the likelihood of a failure happening.

In practice any such ratings will vary from case to case; the ratings shown here are given as examples.

            
+------------------+-----------------------------------------+-----+
|                  | Pro A | Util | Bldg |Wire- | Cell |M2M  |M2M  |
|                  |       |      |      | less |      |Data |Ctrl |    
+------------------+-----------------------------------------+-----+
| Criticality      | Med   | Hi   | Low  | Med  | Med  | Med | Med |
+------------------+-----------------------------------------+-----+
| Effects          
+------------------+-----------------------------------------+-----+
|  Financial       | Med   | Hi   | Med  | Med  | Low  | Med | Med | 
+------------------+-----------------------------------------+-----+
|  Health/Safety   | Med   | Hi   | Hi   | Med  | Med  | Med | Med |
+------------------+-----------------------------------------+-----+
|  People WB       | Med   | Hi   | Hi   | Low  | Hi   | Low | Low |
+------------------+-----------------------------------------+-----+
|  Effect 1 org    | Hi    | Hi   | Med  | Hi   | Med  | Med | Med |
+------------------+-----------------------------------------+-----+
|  Effect >1 org   | Med   | Hi   | Low  | Med  | Med  | Med | Med |
+------------------+-----------------------------------------+-----+
|Recovery                                                                              
+------------------+-----------------------------------------+-----+
|  Recov Time Obj  | Med   | Hi   | Med  | Hi   | Hi   | Hi  | Hi  |
+------------------+-----------------------------------------+-----+
|  Recov Point Obj | Med   | Hi   | Low  | Med  | Low  | Hi  | Hi  |
+------------------+-----------------------------------------+-----+
|DetNet Dependence                                                    
+------------------+-----------------------------------------+-----+
|  Time Dependency | Hi    | Hi   | Low  | Hi   | Med  | Low | Hi  |  
+------------------+-----------------------------------------+-----+
|  Latency/Jitter  | Hi    | Hi   | Med  | Med  | Low  | Low | Hi  |
+------------------+-----------------------------------------+-----+
|  Data Integrity  | Hi    | Hi   | Med  | Hi   | Low  | Hi  | Low |
+------------------+-----------------------------------------+-----+
|  Src Node Integ  | Hi    | Hi   | Med  | Hi   | Med  | Hi  | Hi  |
+------------------+-----------------------------------------+-----+
|  Availability    | Hi    | Hi   | Med  | Hi   | Low  | Hi  | Hi  |
+------------------+-----------------------------------------+-----+

Figure 2: Impact of Attacks by Use Case Industry

5. Security Threat Mitigation

This section describes a set of measures that can be taken to mitigate the attacks described in Section 3. These mitigations should be viewed as a toolset that includes several different and diverse tools. Each application or system will typically use a subset of these tools, based on a system-specific threat analysis.

5.1. Path Redundancy

Description

Related attacks

5.2. Integrity Protection

Description

Related attacks

5.3. DetNet Node Authentication

Description

Related attacks

5.4. Encryption

Description

Related attacks

5.5. Control and Signaling Message Protection

Description

Related attacks

5.6. Dynamic Performance Analytics

Description

Related attacks

5.7. Mitigation Summary

The following table maps the attacks of Section 3 to the impacts of Section 4, and to the mitigations of the current section. Each row specifies an attack, the impact of this attack if it is successfully implemented, and possible mitigation methods.

         
+----------------------+---------------------+---------------------+
| Attack               |      Impact         |     Mitigations     |
+----------------------+---------------------+---------------------+
|Delay Attack          |-Non-deterministic   |-Path redundancy     |
|                      | delay               |-Performance         |
|                      |-Data disruption     | analytics           |
|                      |-Increased resource  |                     |
|                      | consumption         |                     |
+----------------------+---------------------+---------------------+
|DetNet Flow Modificat-|-Increased resource  |-Path redundancy     |
|ion or Spoofing       | consumption         |-Integrity protection|
|                      |-Data disruption     |-DetNet Node         |
|                      |                     | authentication      |
+----------------------+---------------------+---------------------+
|Inter-Segment Attack  |-Increased resource  |-Path redundancy     |
|                      | consumption         |-Performance         |
|                      |-Data disruption     | analytics           |
+----------------------+---------------------+---------------------+
|Replication: Increased|-All impacts of other|-Integrity protection|
|attack surface        | attacks             |-DetNet Node         |
|                      |                     | authentication      |
+----------------------+---------------------+---------------------+
|Replication-related   |-Non-deterministic   |-Integrity protection|
|Header Manipulation   | delay               |-DetNet Node         |
|                      |-Data disruption     | authentication      |
+----------------------+---------------------+---------------------+
|Path Manipulation     |-Enabler for other   |-Control message     |
|                      | attacks             | protection          |
+----------------------+---------------------+---------------------+
|Path Choice: Increased|-All impacts of other|-Control message     |
|Attack Surface        | attacks             | protection          |
+----------------------+---------------------+---------------------+
|Control or Signaling  |-Increased resource  |-Control message     |
|Packet Modification   | consumption         | protection          |
|                      |-Non-deterministic   |                     |
|                      | delay               |                     |
|                      |-Data disruption     |                     |
+----------------------+---------------------+---------------------+
|Control or Signaling  |-Increased resource  |-Control message     |
|Packet Injection      | consumption         | protection          |
|                      |-Non-deterministic   |                     |
|                      | delay               |                     |
|                      |-Data disruption     |                     |
+----------------------+---------------------+---------------------+
|Reconnaissance        |-Enabler for other   |-Encryption          |
|                      | attacks             |                     |
+----------------------+---------------------+---------------------+
|Attacks on Time Sync  |-Non-deterministic   |-Path redundancy     |
|Mechanisms            | delay               |-Control message     |
|                      |-Increased resource  | protection          |
|                      | consumption         |-Performance         |
|                      |-Data disruption     | analytics           |
+----------------------+---------------------+---------------------+
           

Figure 3: Mapping Attacks to Impact and Mitigations

6. Association of Attacks to Use Cases

6.1. Use Cases by Common Themes

Different attacks can have different impact and/or mitigation depending on the use case, so we would like to make this association in our analysis. However since there is a potentially unbounded list of use cases, we categorize the attacks with respect to the common themes of the use cases as identified in the Use Case Common Themes section of the DetNet Use Cases draft [I-D.ietf-detnet-use-cases]. We describe each theme and its associated attacks, impacts and mitigations.

6.1.1. Network Layer - AVB/TSN Ethernet

Presumably it will be possible to run DetNet over other underlying network layers besides Ethernet, but Ethernet is explicitly supported. Is the attack specific to the Ethernet AVB/TSN protocols? Does the threat affect only Ethernet, or any underlying network layer?

6.1.2. Central Administration

A DetNet network is expected to be controlled by a centralized network configuration and control system. Such a system may be in a single central location, or it may be distributed across multiple control entities that function together as a unified control system for the network. Is the attack directed at threat the central control system of the network? Does it interfere with OAM?

6.1.3. Hot Swap

A DetNet network is not expected to be "plug and play" - it is expected that there is some centralized network configuration and control system. However, the ability to "hot swap" components (e.g. due to malfunction) is similar enough to "plug and play" that this kind of behavior may be expected in DetNet networks, depending on the implementation. Does the attack target "hot swap" ("plug and play") operation in the network?

6.1.4. Data Flow Information Models

Data Flow Information Models specific to DetNet networks are to be specified by DetNet. Thus they are "new" and thus potentially present a new attack surface. Does the threat take advantage of any aspect of our new Data Flow Info Models?

6.1.5. L2 and L3 Integration

A DetNet network is intended to integrate between Layer 2 (bridged) network(s) (e.g. AVB/TSN LAN) and Layer 3 (routed) network(s) (e.g. using IP-based protocols). Does the attack target L2? L3? Both? The interaction between the two?

6.1.6. End-to-End Delivery

Packets sent over DetNet are guaranteed not to be dropped by the network due to congestion. (Packets may however be dropped for intended reasons, e.g. per security measures). Does the attack result in packets (which should be delivered) not being delivered? Does it result in packets that should not be delivered being delivered?

6.1.7. Proprietary Deterministic Ethernet Networks

There are many proprietary non-interoperable deterministic Ethernet-based networks currently available; DetNet is intended to provide an open-standards-based alternative to such networks. Does the threat relate to a specific such network that is being "emulated" or "replaced" by DetNet, for example by exploiting specific commands specific to that network protocol?

6.1.8. Replacement for Proprietary Fieldbuses

There are many proprietary "field buses" used in today's industrial and other industries; DetNet is intended to provide an open-standards-based alternative to such buses. Does the threat relate to a specific fieldbus that is being "emulated" or "replaced" by DetNet, for example by exploiting specific commands specific to that network protocol?

6.1.9. Deterministic vs Best-Effort Traffic

DetNet is intended to support coexistence of time-sensitive operational (OT, deterministic) traffic and information (IT, "best effort") traffic on the same ("unified") network. Does the attack affect only IT or only OT or both types of traffic? Does the threat affect any interaction between IT and OT traffic, e.g. by changing relative priority or handling of IT vs. OT packets?

6.1.10. Deterministic Flows

Reserved bandwidth data flows (deterministic flows) must be isolated from each other and from best-effort traffic, so that even if the network is saturated with best-effort and/or reserved bandwidth traffic the configured flows are not adversely affected. Does the attack affect the isolation of one (reserved) flow from another?

6.1.11. Unused Reserved Bandwidth

If bandwidth reservations are made for a stream but the associated bandwidth is not used at any point in time, that bandwidth is made available on the network for best-effort traffic. If the owner of the reserved stream then starts transmitting again, the bandwidth is no longer available for best-effort traffic, on a moment-to-moment basis. (Such "temporarily available" bandwidth is not available for time-sensitive traffic, which must have its own reservation). Does the attack affect the system's ability to allocate unused reserved BW to best-effort traffic?

6.1.12. Interoperability

The DetNet network specifications are intended to enable an ecosystem in which multiple vendors can create interoperable products, thus promoting device diversity and potentially higher numbers of each device manufactured. Does the threat take advantage of differences in implementation of "interoperable" products made by different vendors?

6.1.13. Cost Reductions

The DetNet network specifications are intended to enable an ecosystem in which multiple vendors can create interoperable products, thus promoting higher numbers of each device manufactured, promoting cost reduction and cost competition among vendors. Does the threat take advantage of "low cost" HW or SW components or other "cost-related shortcuts" that might be present in devices?

6.1.14. Insufficiently Secure Devices

The DetNet network specifications are intended to enable an ecosystem in which multiple vendors can create interoperable products, thus promoting device diversity and potentially higher numbers of each device manufactured. Does the threat attack "naivete" of SW, for example SW that was not designed to be sufficiently secure (or secure at all) but is deployed on a DetNet network that is intended to be highly secure? (For example IoT exploits like the Mirai video-camera botnet ([MIRAI]).

6.1.15. DetNet Network Size

DetNet networks range in size from very small, e.g. inside a single industrial machine, to very large, for example a Utility Grid network spanning a whole country, and involving many "hops" over various kinds of links for example radio repeaters, microwave links, fiber optic links, etc.. Does the attack affect DetNet networks of only certain sizes, e.g. very large networks, or very small? This might be related to how the attack is introduced into the network, for example if the entire network is local, there is a threat that power can be cut to the entire network. If the network is large, perhaps only a part of the network is attacked. Does the threat take advantage of attack vectors that are specific to network size?

6.1.16. Multiple Hops

DetNet networks range in size from very small, e.g. inside a single industrial machine, to very large, for example a Utility Grid network spanning a whole country, and involving many "hops" over various kinds of links for example radio repeaters, microwave links, fiber optic links, etc.. Does the attack exploit the presence of more than one "hop"? Does the threat exploit the presence of more than one type of "hop", e.g. between radio and microwave links? Does the threat exploit a specific type of "hop", e.g. something specific to a fiber optic link, or other type of link?

6.1.17. Level of Service

A DetNet is expected to provide means to configure the network that include querying network path latency, requesting bounded latency for a given stream, requesting worst case maximum and/or minimum latency for a given path or stream, and so on. It is an expected case that the network cannot provide a given requested service level. In such cases the network control system should reply that the requested service level is not available (as opposed to accepting the parameter but then not delivering the desired behavior). Does the attack affect any querying or replying to such service-level-related traffic? Can the attack cause incorrect responses from the system regarding timing-related configuration? For example replying that a requested level of service is available when it isn't, or that the requested level of service is not available when it actually is available?

6.1.18. Bounded Latency

Does the threat affect the network's ability to deliver packets within the agreed-upon latency boundaries?

6.1.19. Low Latency

Applications may require "extremely low latency" however depending on the application these may mean very different latency values; for example "low latency" across a Utility grid network is on a different time scale than "low latency" in a motor control loop in a small machine. The intent is that the mechanisms for specifying desired latency include wide ranges, and that architecturally there is nothing to prevent arbitrarily low latencies from being implemented in a given network. Does the threat affect the network's ability to deliver packets within the agreed-upon low latency?

6.1.20. Symmetrical Path Delays

Some applications would like to specify that the transit delay time values be equal for both the transmit and return paths. Does the attack affect the network's ability to provide matched transmit and return path delays (latencies)?

6.1.21. Reliability and Availability

DetNet based systems are expected to be implemented with essentially arbitrarily high availability (for example 99.9999% up time, or even 12 nines). The intent is that the DetNet designs should not make any assumptions about the level of reliability and availability that may be required of a given system, and should define parameters for communicating these kinds of metrics within the network. Does the attack affect the reliability of the DetNet network? Is it a large or small change, e.g. the difference between completely taking down the network for some period of time, vs reducing its reliability by just one "nine"? Does the threat affect the availability of the DetNet network?

6.1.22. Redundant Paths

DetNet based systems are expected to be implemented with essentially arbitrarily high reliability/availability. A strategy used by DetNet for providing such extraordinarily high levels of reliability is to provide redundant paths that can be seamlessly switched between, all the while maintaining the required performance of that system. Does the attack affect the configuration or operation of redundant paths?

6.1.23. Security Measures

A DetNet network must be made secure against devices failures, attackers, misbehaving devices, and so on. Does the threat affect such security measures themselves, e.g. by attacking SW designed to protect against device failure?

6.2. Attack Types by Use Case Common Theme

The following table lists the attacks of Section 3, assigning a number to each type of attack. That number is then used as a short form identifier for the attack in Figure 5.

            
+--+----------------------------------------+----------------------+
|  | Attack                                 |       Section        |
+--+----------------------------------------+----------------------+
| 1|Delay Attack                            |  Section 3.2.1       |
+--+----------------------------------------+----------------------+
| 2|DetNet Flow Modification or Spoofing    |  Section 3.2.2       |
+--+----------------------------------------+----------------------+
| 3|Inter-Segment Attack                    |  Section 3.2.3       |
+--+----------------------------------------+----------------------+
| 4|Replication: Increased attack surface   |  Section 3.2.4.1     |
+--+----------------------------------------+----------------------+
| 5|Replication-related Header Manipulation |  Section 3.2.4.2     |
+--+----------------------------------------+----------------------+
| 6|Path Manipulation                       |  Section 3.2.5.1     |
+--+----------------------------------------+----------------------+
| 7|Path Choice: Increased Attack Surface   |  Section 3.2.5.2     |
+--+----------------------------------------+----------------------+
| 8|Control or Signaling Packet Modification|  Section 3.2.6.1     |
+--+----------------------------------------+----------------------+
| 9|Control or Signaling Packet Injection   |  Section 3.2.6.2     |
+--+----------------------------------------+----------------------+
|10|Reconnaissance                          |  Section 3.2.7       |
+--+----------------------------------------+----------------------+
|11|Attacks on Time Sync Mechanisms         |  Section 3.2.8       |
+--+----------------------------------------+----------------------+
           

Figure 4: List of Attacks

The following table maps the use case themes presented in this memo to the attacks of Figure 4. Each row specifies a theme, and the attacks relevant to this theme are marked with a '+'.

         
+----------------------------+--------------------------------+
| Theme                      |             Attack             |
|                            +--+--+--+--+--+--+--+--+--+--+--+
|                            | 1| 2| 3| 4| 5| 6| 7| 8| 9|10|11|
+----------------------------+--+--+--+--+--+--+--+--+--+--+--+
|Network Layer - AVB/TSN Eth.| +| +| +| +| +| +| +| +| +| +| +|
+----------------------------+--+--+--+--+--+--+--+--+--+--+--+
|Central Administration      |  |  |  |  |  | +| +| +| +| +| +|
+----------------------------+--+--+--+--+--+--+--+--+--+--+--+
|Hot Swap                    |  | +| +|  |  |  |  |  |  |  | +|
+----------------------------+--+--+--+--+--+--+--+--+--+--+--+
|Data Flow Information Models|  |  |  |  |  |  |  |  |  |  |  |
+----------------------------+--+--+--+--+--+--+--+--+--+--+--+
|L2 and L3 Integration       |  |  |  |  | +| +|  |  |  |  |  |
+----------------------------+--+--+--+--+--+--+--+--+--+--+--+
|End-to-end Delivery         |  |  |  | +| +|  |  |  |  |  |  |
+----------------------------+--+--+--+--+--+--+--+--+--+--+--+
|Proprietary Deterministic   |  |  | +|  |  | +| +| +| +|  |  |
|Ethernet Networks           |  |  |  |  |  |  |  |  |  |  |  |
+----------------------------+--+--+--+--+--+--+--+--+--+--+--+
|Replacement for Proprietary |  |  | +|  |  | +| +| +| +|  |  |
|Fieldbuses                  |  |  |  |  |  |  |  |  |  |  |  |
+----------------------------+--+--+--+--+--+--+--+--+--+--+--+
|Deterministic vs. Best-     |  |  | +|  |  |  |  |  |  |  |  |
|Effort Traffic              |  |  |  |  |  |  |  |  |  |  |  |
+----------------------------+--+--+--+--+--+--+--+--+--+--+--+
|Deterministic Flows         |  |  | +|  |  |  |  |  |  |  |  |
+----------------------------+--+--+--+--+--+--+--+--+--+--+--+
|Unused Reserved Bandwidth   |  |  | +|  |  |  |  |  |  |  |  |
+----------------------------+--+--+--+--+--+--+--+--+--+--+--+
|Interoperability            |  |  |  |  |  |  |  |  |  |  |  |
+----------------------------+--+--+--+--+--+--+--+--+--+--+--+
|Cost Reductions             |  |  |  |  |  |  |  |  |  |  |  |
+----------------------------+--+--+--+--+--+--+--+--+--+--+--+
|Insufficiently Secure       |  |  |  |  |  |  |  |  |  |  |  |
|Devices                     |  |  |  |  |  |  |  |  |  |  |  |
+----------------------------+--+--+--+--+--+--+--+--+--+--+--+
|DetNet Network Size         | +|  |  |  |  | +| +|  |  |  | +|
+----------------------------+--+--+--+--+--+--+--+--+--+--+--+
|Multiple Hops               | +| +|  |  |  | +| +|  |  |  | +|
+----------------------------+--+--+--+--+--+--+--+--+--+--+--+
|Level of Service            |  |  |  |  |  |  |  | +| +| +|  |
+----------------------------+--+--+--+--+--+--+--+--+--+--+--+
|Bounded Latency             | +|  |  |  |  |  |  |  |  |  | +|
+----------------------------+--+--+--+--+--+--+--+--+--+--+--+
|Low Latency                 | +|  |  |  |  |  |  |  |  |  | +|
+----------------------------+--+--+--+--+--+--+--+--+--+--+--+
|Symmetric Path Delays       | +|  |  |  |  |  |  |  |  |  | +|
+----------------------------+--+--+--+--+--+--+--+--+--+--+--+
|Reliability and Availability| +| +| +| +| +| +| +| +| +| +| +|
+----------------------------+--+--+--+--+--+--+--+--+--+--+--+
|Redundant Paths             |  |  |  | +| +|  |  | +| +|  |  |
+----------------------------+--+--+--+--+--+--+--+--+--+--+--+
|Security Measures           |  |  |  |  |  |  |  |  |  |  |  |
+----------------------------+--+--+--+--+--+--+--+--+--+--+--+
           

Figure 5: Mapping Between Themes and Attacks

7. Appendix A: DetNet Draft Security-Related Statements

This section collects the various statements in the currently existing DetNet Working Group drafts. For each draft, the section name and number of the quoted section is shown. The text shown here is the work of the original draft authors, quoted verbatim from the drafts. The intention is to explicitly quote all relevant text, not to summarize it.

7.1. Architecture (draft 8)

7.1.1. Fault Mitigation (sec 4.5)

One key to building robust real-time systems is to reduce the infinite variety of possible failures to a number that can be analyzed with reasonable confidence. DetNet aids in the process by providing filters and policers to detect DetNet packets received on the wrong interface, or at the wrong time, or in too great a volume, and to then take actions such as discarding the offending packet, shutting down the offending DetNet flow, or shutting down the offending interface.

It is also essential that filters and service remarking be employed at the network edge to prevent non-DetNet packets from being mistaken for DetNet packets, and thus impinging on the resources allocated to DetNet packets.

There exist techniques, at present and/or in various stages of standardization, that can perform these fault mitigation tasks that deliver a high probability that misbehaving systems will have zero impact on well-behaved DetNet flows, except of course, for the receiving interface(s) immediately downstream of the misbehaving device. Examples of such techniques include traffic policing functions (e.g. [RFC2475]) and separating flows into per-flow rate- limited queues.

7.1.2. Security Considerations (sec 7)

Security in the context of Deterministic Networking has an added dimension; the time of delivery of a packet can be just as important as the contents of the packet, itself. A man-in-the-middle attack, for example, can impose, and then systematically adjust, additional delays into a link, and thus disrupt or subvert a real-time application without having to crack any encryption methods employed. See [RFC7384] for an exploration of this issue in a related context.

Furthermore, in a control system where millions of dollars of equipment, or even human lives, can be lost if the DetNet QoS is not delivered, one must consider not only simple equipment failures, where the box or wire instantly becomes perfectly silent, but bizarre errors such as can be caused by software failures. Because there is essential no limit to the kinds of failures that can occur, protecting against realistic equipment failures is indistinguishable, in most cases, from protecting against malicious behavior, whether accidental or intentional.

Security must cover:

7.2. Data Plane Alternatives (draft 4)

7.2.1. Security Considerations (sec 7)

This document does not add any new security considerations beyond what the referenced technologies already have.

7.3. Problem Statement (draft 5)

7.3.1. Security Considerations (sec 5)

Security in the context of Deterministic Networking has an added dimension; the time of delivery of a packet can be just as important as the contents of the packet, itself. A man-in-the-middle attack, for example, can impose, and then systematically adjust, additional delays into a link, and thus disrupt or subvert a real-time application without having to crack any encryption methods employed. See [RFC7384] for an exploration of this issue in a related context.

Typical control networks today rely on complete physical isolation to prevent rogue access to network resources. DetNet enables the virtualization of those networks over a converged IT/OT infrastructure. Doing so, DetNet introduces an additional risk that flows interact and interfere with one another as they share physical resources such as Ethernet trunks and radio spectrum. The requirement is that there is no possible data leak from and into a deterministic flow, and in a more general fashion there is no possible influence whatsoever from the outside on a deterministic flow. The expectation is that physical resources are effectively associated with a given flow at a given point of time. In that model, Time Sharing of physical resources becomes transparent to the individual flows which have no clue whether the resources are used by other flows at other times.

Security must cover:

7.4. Use Cases (draft 11)

7.4.1. (Utility Networks) Security Current Practices and Limitations (sec 3.2.1)

Grid monitoring and control devices are already targets for cyber attacks, and legacy telecommunications protocols have many intrinsic network-related vulnerabilities. For example, DNP3, Modbus, PROFIBUS/PROFINET, and other protocols are designed around a common paradigm of request and respond. Each protocol is designed for a master device such as an HMI (Human Machine Interface) system to send commands to subordinate slave devices to retrieve data (reading inputs) or control (writing to outputs). Because many of these protocols lack authentication, encryption, or other basic security measures, they are prone to network-based attacks, allowing a malicious actor or attacker to utilize the request-and-respond system as a mechanism for command-and-control like functionality. Specific security concerns common to most industrial control, including utility telecommunication protocols include the following:

7.4.2. (Utility Networks) Security Trends in Utility Networks (sec 3.3.3)

Although advanced telecommunications networks can assist in transforming the energy industry by playing a critical role in maintaining high levels of reliability, performance, and manageability, they also introduce the need for an integrated security infrastructure. Many of the technologies being deployed to support smart grid projects such as smart meters and sensors can increase the vulnerability of the grid to attack. Top security concerns for utilities migrating to an intelligent smart grid telecommunications platform center on the following trends:

This development of a diverse set of networks to support the integration of microgrids, open-access energy competition, and the use of network-controlled devices is driving the need for a converged security infrastructure for all participants in the smart grid, including utilities, energy service providers, large commercial and industrial, as well as residential customers. Securing the assets of electric power delivery systems (from the control center to the substation, to the feeders and down to customer meters) requires an end-to-end security infrastructure that protects the myriad of telecommunications assets used to operate, monitor, and control power flow and measurement.

"Cyber security" refers to all the security issues in automation and telecommunications that affect any functions related to the operation of the electric power systems. Specifically, it involves the concepts of:

When designing and deploying new smart grid devices and telecommunications systems, it is imperative to understand the various impacts of these new components under a variety of attack situations on the power grid. Consequences of a cyber attack on the grid telecommunications network can be catastrophic. This is why security for smart grid is not just an ad hoc feature or product, it's a complete framework integrating both physical and Cyber security requirements and covering the entire smart grid networks from generation to distribution. Security has therefore become one of the main foundations of the utility telecom network architecture and must be considered at every layer with a defense-in-depth approach. Migrating to IP based protocols is key to address these challenges for two reasons:

Securing OT (Operation technology) telecommunications over packet-switched IP networks follow the same principles that are foundational for securing the IT infrastructure, i.e., consideration must be given to enforcing electronic access control for both person-to-machine and machine-to-machine communications, and providing the appropriate levels of data privacy, device and platform integrity, and threat detection and mitigation.

7.4.3. (BAS) Security Considerations (sec 4.2.4)

When BAS field networks were developed it was assumed that the field networks would always be physically isolated from external networks and therefore security was not a concern. In today's world many BASs are managed remotely and are thus connected to shared IP networks and so security is definitely a concern, yet security features are not available in the majority of BAS field network deployments .

The management network, being an IP-based network, has the protocols available to enable network security, but in practice many BAS systems do not implement even the available security features such as device authentication or encryption for data in transit.

7.4.4. (6TiSCH) Security Considerations (sec 5.3.3)

On top of the classical requirements for protection of control signaling, it must be noted that 6TiSCH networks operate on limited resources that can be depleted rapidly in a DoS attack on the system, for instance by placing a rogue device in the network, or by obtaining management control and setting up unexpected additional paths.

7.4.5. (Cellular radio) Security Considerations (sec 6.1.5)

Establishing time-sensitive streams in the network entails reserving networking resources for long periods of time. It is important that these reservation requests be authenticated to prevent malicious reservation attempts from hostile nodes (or accidental misconfiguration). This is particularly important in the case where the reservation requests span administrative domains. Furthermore, the reservation information itself should be digitally signed to reduce the risk of a legitimate node pushing a stale or hostile configuration into another networking node.

Note: This is considered important for the security policy of the network, but does not affect the core DetNet architecture and design.

7.4.6. (Industrial M2M) Communication Today (sec 7.2)

Industrial network scenarios require advanced security solutions. Many of the current industrial production networks are physically separated. Preventing critical flows from be leaked outside a domain is handled today by filtering policies that are typically enforced in firewalls.

8. IANA Considerations

This memo includes no requests from IANA.

9. Security Considerations

The security considerations of DetNet networks are presented throughout this document.

10. Informative References

[ARINC664P7] ARINC, "ARINC 664 Aircraft Data Network, Part 7, Avionics Full-Duplex Switched Ethernet Network", 2009.
[I-D.ietf-detnet-architecture] Finn, N., Thubert, P., Varga, B. and J. Farkas, "Deterministic Networking Architecture", Internet-Draft draft-ietf-detnet-architecture-03, August 2017.
[I-D.ietf-detnet-use-cases] Grossman, E., Gunther, C., Thubert, P., Wetterwald, P., Raymond, J., Korhonen, J., Kaneko, Y., Das, S., Zha, Y., Varga, B., Farkas, J., Goetz, F., Schmitt, J., Vilajosana, X., Mahmoodi, T., Spirou, S., Vizarreta, P., Huang, D., Geng, X., Dujovne, D. and M. Seewald, "Deterministic Networking Use Cases", Internet-Draft draft-ietf-detnet-use-cases-13, September 2017.
[I-D.varga-detnet-service-model] Varga, B. and J. Farkas, "DetNet Service Model", Internet-Draft draft-varga-detnet-service-model-02, May 2017.
[IEEE1588] IEEE, "IEEE 1588 Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control Systems Version 2", 2008.
[MIRAI] krebsonsecurity.com, "https://krebsonsecurity.com/2016/10/hacked-cameras-dvrs-powered-todays-massive-internet-outage/", 2016.
[RFC7384] Mizrahi, T., "Security Requirements of Time Protocols in Packet Switched Networks", RFC 7384, DOI 10.17487/RFC7384, October 2014.

Authors' Addresses

Tal Mizrahi Marvell EMail: talmi@marvell.com
Ethan Grossman (editor) Dolby Laboratories, Inc. 1275 Market Street San Francisco, CA 94103 USA Phone: +1 415 645 4726 EMail: ethan.grossman@dolby.com URI: http://www.dolby.com
Andrew J. Hacker MistIQ Technologies, Inc Harrisburg, PA USA EMail: ajhacker@mistiqtech.com URI: http://www.mistiqtech.com
Subir Das Applied Communication Sciences 150 Mount Airy Road, Basking Ridge New Jersey, 07920, USA EMail: sdas@appcomsci.com
John Dowdell Airbus Defence and Space Celtic Springs Newport, NP10 8FZ United Kingdom EMail: john.dowdell.ietf@gmail.com
Henrik Austad Cisco Systems Philip Pedersens vei 1 Lysaker, 1366 Norway EMail: henrik@austad.us
Kevin Stanton Intel EMail: kevin.b.stanton@intel.com
Norman Finn Huawei EMail: norman.finn@mail01.huawei.com