Internet Engineering Task Force T. Mizrahi
Internet-Draft HUAWEI
Intended status: Informational E. Grossman, Ed.
Expires: September 3, 2019 DOLBY
A. Hacker
S. Das
Applied Communication Sciences
J. Dowdell
Airbus Defence and Space
H. Austad
Cisco Systems
K. Stanton
N. Finn
March 2, 2019

Deterministic Networking (DetNet) Security Considerations


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

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This Internet-Draft will expire on September 3, 2019.

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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 attacks with use cases 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 as well as the motivation behind them, 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:

Care has also been taken to adhere to Section 5 of [RFC3552], both with respect to what attacks are considered out-of-scope for this document, but also what is considered to be the most common threats (explored furhter in Section 3.2. Most of the direct threats to DetNet are Active attacks, but it is highly suggested that DetNet application developers take appropriate measures to protect the content of the streams from passive attacks.

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 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 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.

3.2.3. Resource Segmentation or Slicing 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 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. 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 Path Manipulation

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

A passive eavesdropper can identify DetNet flows and then 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.

Note that in some cases DetNet flows may be identified based on 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.

3.2.8. 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 and rates the impact of the attacks described in Section 3. In this section, the impacts as described assume that the associated mitigation is not present or has failed. Mitigations are discussed 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.

DetNet raises these stakes significantly for OT applications, particularly those which may have been designed to run in an OT-only environment and thus may not have been designed for security in an IT environment with its associated devices, services and protocols.

The severity of various components of the impact of a successful vulnerability exploit to use cases by industry is available in more detail in [I-D.ietf-detnet-use-cases]. Each of the use cases in the DetNet Use Cases draft is represented in the table below, including Pro Audio, Electrical Utilities, Industrial M2M (split into two areas, M2M Data Gathering and M2M Control Loop), and others.

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, only 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.

Table, Part One (of Two) 
|                  | 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 |
|  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  |

Table, Part Two (of Two) 
|                  | Mining | Block | Network |
|                  |        | Chain | Slicing |
| Criticality      | Hi     | Med   | Hi      |
| Effects
|  Financial       | Hi     | Hi    | Hi      |
|  Health/Safety   | Hi     | Low   | Med     |
|  People WB       | Hi     | Low   | Med     |
|  Effect 1 org    | Hi     | Hi    | Hi      |
|  Effect >1 org   | Hi     | Low   | Hi      |
|  Recov Time Obj  | Hi     | Low   | Hi      |
|  Recov Point Obj | Hi     | Low   | Hi      |
|DetNet Dependence
|  Time Dependency | Hi     | Low   | Hi      |
|  Latency/Jitter  | Hi     | Low   | Hi      |
|  Data Integrity  | Hi     | Hi    | Hi      |
|  Src Node Integ  | Hi     | Hi    | Hi      |
|  Availability    | Hi     | Hi    | Hi      |

Figure 2: Impact of Attacks by Use Case Industry

The rest of this section will cover impact of the different groups in more detail.

4.1. Delay-Attacks

4.1.1. Data Plane Delay Attacks

Severely delayed messages in a DetNet link can result in the same behavior as dropped messages in ordinary networks as the services attached to the stream has strict deterministic requirements.

For a single path scenario, disruption is a real possibility, whereas in a multipath scenario, large delays or instabilities in one stream can lead to increased buffer and CPU resources on the elimination bridge.

A data-plane delay attack on a system controlling substantial moving devices, for example in industrial automation, can cause physical damage. For example, if the network promises a bounded latency of 2ms for a flow, yet the machine receives it with 5ms latency, the machine's control loop can become unstable.

4.1.2. Control Plane Delay Attacks

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

4.2. Flow Modification and Spoofing

4.2.1. Flow Modification


4.2.2. Spoofing 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. Control Plane Spoofing

A successful control plane spoofing-attack will potentionally have adverse effects. It can do virtually anything from:

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 increased CPU utilization in elimination bridges. If enough paths are subject to malicious injection, the legitimate messages can be dropped. Likewise it can cause an increase in buffer usage. In total, it will consume more resources in the bridges than normal, giving rise to a 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 control messages to be interpreted by nodes in the network, unbeknownst to the central controller or the network engineer. This has the potential to create

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. Control or Signaling Packet Modification


4.6. Control or Signaling Packet Injection


4.7. Reconnaissance

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.

4.8. Attacks on Time Sync Mechanisms


4.9. Attacks on 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.

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


Related attacks

5.2. Integrity Protection


Related attacks

5.3. DetNet Node Authentication


Related attacks

5.4. Encryption


Related attacks

5.4.1. Encryption Considerations for DetNet

Any compute time which is required for encryption and decryption processing ('crypto') must be included in the flow latency calculations. Thus, crypto algorithms used in a DetNet must have bounded worst-case execution times, and these values must be used in the latency calculations.

Some crypto algorithms are symmetric in encode/decode time (such as AES) and others are asymmetric (such as public key algorithms). There are advantages and disadvantages to the use of either type in a given DetNet context.

Asymmetrical crypto is typically not used in networks on a packet-by-packet basis due to its computational cost. For example, if only endpoint checks or checks at a small number of intermediate points are required, asymmetric crypto can be used to authenticate distribution or exchange of a secret symmetric crypto key; a successful check based on that key will provide traffic origin verification, as long as the key is kept secret by the participants. TLS and IKE (for IPsec) are examples of this for endpoint checks.

However, if secret symmetrical keys are used for this purpose the key must be given to all relays, which increases the probability of a secret key being leaked. Also, if any relay is compromised or misbehaving it may inject traffic into the flow.

Alternatively, asymmetric crypto can provide traffic origin verification at every intermediate node. For example, a DetNet flow can be associated with an (asymmetric) keypair, such that the private key is available to the source of the flow and the public key is distributed with the flow information, allowing verification at every node for every packet. However, this is more computationally expensive.

In either case, origin verification also requires replay detection as part of the security protocol to prevent an attacker from recording and resending traffic, e.g., as a denial of service attack on flow forwarding resources.

If crypto keys are to be regenerated over the duration of the flow then the time required to accomplish this must be accounted for in the latency calculations.

5.5. Control and Signaling Message Protection


Related attacks

5.6. Dynamic Performance Analytics


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         |                     |
|Reconnaissance        |-Enabler for other   |-Encryption          |
|                      | attacks             |                     |
|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     |                     |
|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

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].

See also Figure 2 for a mapping of the impact of attacks per use case by industry.

6.1. Use Cases by Common Themes

In this section we review each theme and discuss the attacks that are applicable to that theme, as well as anything specific about the impact and mitigations for that attack with respect to that theme. The table Figure 5 then provides a summary of the attacks that are applicable to each theme.

6.1.1. Network Layer - AVB/TSN Ethernet

DetNet is expected to run over various transmission mediums, with Ethernet being explicitly supported. Attacks such as Delay or Reconnaissance might be implemented differently on a different transmission medium, however the impact on the DetNet as a whole would be essentially the same. We thus conclude that all attacks and impacts that would be applicable to DetNet over Ethernet (i.e. all those named in this draft) would also be applicable to DetNet over other transmission mediums.

With respect to mitigations, some methods are specific to the Ethernet medium, for example time-aware scheduling using 802.1Qbv can protect against excessive use of bandwidth at the ingress - for other mediums, other mitigations would have to be implemented to provide analogous protection.

6.1.2. Central Administration

A DetNet network is expected to be controlled by a centralized network configuration and control system (CNC). 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.

In this draft we distinguish between attacks on the DetNet Control plane vs. Data plane. But is an attack affecting control plane packets synonymous with an attack on the CNC itself? For purposes of this draft let us consider an attack on the CNC itself to be out of scope, and consider all attacks named in this draft which are relevant to control plane packets to be relevant to this theme, including Path Manipulation, Path Choice, Control Packet Modification or Injection, Reconaissance and Attacks on Time Sync Mechanisms.

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.

An attack surface related to Hot Swap is that the DetNet network must at least consider input at runtime from devices that were not part of the initial configuration of the network. Even a "perfect" (or "hitless") replacement of a device at runtime would not necessarily be ideal, since presumably one would want to distinguish it from the original for OAM purposes (e.g. to report hot swap of a failed device).

This implies that an attack such as Flow Modification, Spoofing or Inter-segment (which could introduce packets from a "new" device (i.e. one heretofore unknown on the network) could be used to exploit the need to consider such packets (as opposed to rejecting them out of hand as one would do if one did not have to consider introduction of a new device).

Similarly if the network was designed to support runtime replacement of a clock device, then presence (or apparent presence) and thus consideration of packets from a new such device could affect the network, or the time sync of the network, for example by initiating a new Best Master Clock selection process. Thus attacks on time sync should be considered when designing hot swap type functionality.

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?

This is TBD, thus there are no specific entries in our table, however that does not imply that there could be no relevant attacks.

6.1.5. L2 and L3 Integration

A DetNet network integrates Layer 2 (bridged) networks (e.g. AVB/TSN LAN) and Layer 3 (routed) networks via the use of well-known protocols such as IPv6, MPLS-PW, and Ethernet. Presumably security considerations applicable directly to those individual protocols is not specific to DetNet, and thus out of scope for this draft. However enabling DetNet to coordinate Layer 2 and Layer 3 behavior will require some additions to existing protocols (see draft-dt-detnet-dp-alt) and any such new work can introduce new attack surfaces.

This is TBD, thus there are no specific entries in our table, however that does not imply that there could be no relevant attacks.

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).

A Data plane attack may force packets to be dropped, for example a "long" Delay or Replication/Elimination or Flow Modification attack.

The same result might be obtained by a Control plane attack, e.g. Path Manipulation or Signaling Packet Modification.

It may be that such attacks are limited to Internal MITM attackers, but other possibilities should be considered.

An attack may also cause packets that should not be delivered to be delivered, such as by forcing packets from one (e.g. replicated) path to be preferred over another path when they should not be (Replication attack), or by Flow Modification, or by Path Choice or Packet Injection. A Time Sync attack could cause a system that was expecting certain packets at certain times to accept unintended packets based on compromised system time or time windowing in the scheduler.

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. In cases where a DetNet intersects with remnants of such networks or their protocols, such as by protocol emulation or access to such a network via a gateway, new attack surfaces can be opened.

For example an Inter-Segment or Control plane attack such as Path Manipulation, Path Choice or Control Packet Modification/Injection could be used to exploit commands specific to such a protocol, or that are interpreted differently by the different protocols or gateway.

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. In cases where a DetNet intersects with such fieldbuses or their protocols, such as by protocol emulation or access via a gateway, new attack surfaces can be opened.

For example an Inter-Segment or Control plane attack such as Path Manipulation, Path Choice or Control Packet Modification/Injection could be used to exploit commands specific to such a protocol, or that are interpreted differently by the different protocols or gateway.

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.

The presence of IT traffic on a network carrying OT traffic has long been considered insecure design [reference needed here]. With DetNet, this coexistance will become more common, and mitigations will need to be established. The fact that the IT traffic on a DetNet is limited to a corporate controlled network makes this a less difficult problem compared to being exposed to the open Internet, however this aspect of DetNet security should not be underestimated.

Most of the themes described in this draft address OT (reserved) streams - this item is intended to address issues related to IT traffic on a DetNet.

An Inter-segment attack can flood the network with IT-type traffic with the intent of disrupting handling of IT traffic, and/or the goal of interfering with OT traffic. Presumably if the stream reservation and isolation of the DetNet is well-designed (better-designed than the attack) then interference with OT traffic should not result from an attack that floods the network with IT traffic.

However the DetNet's handling of IT traffic may not (by design) be as resilient to DOS attack, and thus designers must be otherwise prepared to mitigate DOS attacks on IT traffic in a DetNet.

6.1.10. Deterministic Flows

Reserved bandwidth data flows (deterministic flows) must provide the allocated bandwidth, and must be isolated from each other.

A Spoofing or Inter-segment attack which adds packet traffic to a bandwidth-reserved stream could cause that stream to occupy more bandwidth than it is allocated, resulting in interference with other deterministic flows.

A Flow Modification or Spoofing or Header Manipulation or Control Packet Modification attack could cause packets from one flow to be directed to another flow, thus breaching isolation between the flows.

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).

An Inter-segment attack could flood the network with IT traffic, interfering with the intended IT traffic.

A Flow Modification or Spoofing or Control Packet Modification or Injection attack could cause extra bandwidth to be reserved by a new or existing stream, thus making it unavailable for use by 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?

This is TBD, thus there are no specific entries in our table, however that does not imply that there could be no relevant attacks.

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?

This is TBD, thus there are no specific entries in our table, however that does not imply that there could be no relevant attacks.

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]).

This is TBD, thus there are no specific entries in our table, however that does not imply that there could be no relevant attacks.

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.

The size of the network 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.

A Delay attack might be as relevant to a small network as to a large network, although the amount of delay might be different.

Attacks sourced from IT traffic might be more likely in large networks, since more people might have access to the network. Similarly Path Manipulation, Path Choice and Time Sync attacks seem more likely relevant to large networks.

6.1.16. Multiple Hops

Large DetNet networks (e.g. a Utility Grid network) may involve many "hops" over various kinds of links for example radio repeaters, microwave links, fiber optic links, etc..

An attack that takes advantage of flaws (or even normal operation) in the device drivers for the various links (through internal knowledge of how the individual driver or firmware operates, perhaps like the Stuxnet attack) could take proportionately greater advantage of this topology. We don't currently have an attack like this defined; we have only "protocol" (time or packet) based attacks. Perhaps we need to define an attack like this? Or is that out of scope for DetNet?

It is also possible that this DetNet topology will not be in as common use as other more homogeneous topologies so there may be more opportunity for attackers to exploit software and/or protocol flaws in the implementations which have not been wrung out by extensive use, particularly in the case of early adopters.

Of the attacks we have defined, the ones identified above as relevant to "large" networks seem to be most relevant.

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).

Control plane attacks such as Signaling Packet Modification and Injection could be used to modify or create control traffic that could interfere with the process of a user requesting a level of service and/or the network's reply.

Reconnaissance could be used to characterize flows and perhaps target specific flows for attack via the Control plane as noted above.

6.1.18. Bounded Latency

DetNet provides the expectation of guaranteed bounded latency.

Delay attacks can cause packets to miss their agreed-upon latency boundaries.

Time Sync attacks can corrupt the system's time reference, resulting in missed latency deadlines (with respect to the "correct" time reference).

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.

Attacks on the Control plane (as described in the Level of Service theme) and Delay and Time attacks (as described in the Bounded Latency theme) both apply here.

6.1.20. Bounded Jitter (Latency Variation)

DetNet is expected to provide bounded jitter (packet to packet latency variation).

Delay attacks can cause packets to vary in their arrival times, resulting in packet to packet latency variation, thereby violating the jitter specification.

6.1.21. Symmetrical Path Delays

Some applications would like to specify that the transit delay time values be equal for both the transmit and return paths.

Delay attacks can cause path delays to differ.

Time Sync attacks can corrupt the system's time reference, resulting in differing path delays (with respect to the "correct" time reference).

6.1.22. 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.

Any attack on the system, of any type, can affect its overall reliability and availability, thus in our table we have marked every attack. Since every DetNet depends to a greater or lesser degree on reliability and availability, this essentially means that all networks have to mitigate all attacks, which to a greater or lesser degree defeats the purpose of associating attacks with use cases. It also underscores the difficulty of designing "extremely high reliability" networks. I hope that in future drafts we can say something more useful here.

6.1.23. 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.

Replication-related attacks are by definition applicable here. Control plane attacks can also interfere with the configuration of redundant paths.

6.1.24. 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?

This is TBD, thus there are no specific entries in our table, however that does not imply that there could be no relevant attacks.

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     |
| 5|Replication-related Header Manipulation |  Section     |
| 6|Path Manipulation                       |  Section     |
| 7|Path Choice: Increased Attack Surface   |  Section     |
| 8|Control or Signaling Packet Modification|  Section     |
| 9|Control or Signaling Packet Injection   |  Section     |
|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                 | +|  |  |  |  |  |  | +| +| +| +|
|Bounded Jitter              | +|  |  |  |  |  |  |  |  |  |  |
|Symmetric Path Delays       | +|  |  |  |  |  |  |  |  |  | +|
|Reliability and Availability| +| +| +| +| +| +| +| +| +| +| +|
|Redundant Paths             |  |  |  | +| +|  |  | +| +|  |  |
|Security Measures           |  |  |  |  |  |  |  |  |  |  |  |

Figure 5: Mapping Between Themes and Attacks

6.3. Security Considerations for OAM Traffic

This section considers DetNet-specific security considerations for packet traffic that is generated and transmitted over a DetNet as part of OAM (Operations, Administration and Maintenance). For purposes of this discussion, OAM traffic falls into one of two basic types:

Thus OAM traffic presents no additional (i.e. OAM-specific) DetNet security considerations.

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.

Existing power automation security standards can inform network security. For example the NERC CIP (North American Electric Reliability Corporation Critical Infrastructure Protection) plan is a set of requirements designed to secure the assets required for operating North America's bulk electric system. Another standardized security control technique is Segmentation (zones and conduits including access control).

The requirements in Industrial Automation and Control Systems (IACS) are quite similar, especially in new scenarios such as Industry 4.0/Digital Factory where workflows and protocols cross zones, segments, and entities. IEC 62443 (ISA99) defines security for IACS, typically for installations in other critical infrastructure such as oil and gas.

Availability and integrity are the most important security objectives for the lower layers of such networks; confidentiality and privacy are relevant if customer or market data is involved, typically handled by higher layers.

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-11, February 2019.
[I-D.ietf-detnet-use-cases] Grossman, E., "Deterministic Networking Use Cases", Internet-Draft draft-ietf-detnet-use-cases-20, December 2018.
[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], "", 2016.
[RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC Text on Security Considerations", BCP 72, RFC 3552, DOI 10.17487/RFC3552, July 2003.
[RFC7384] Mizrahi, T., "Security Requirements of Time Protocols in Packet Switched Networks", RFC 7384, DOI 10.17487/RFC7384, October 2014.

Authors' Addresses

Tal Mizrahi Huawei Network.IO Innovation Lab EMail:
Ethan Grossman (editor) Dolby Laboratories, Inc. 1275 Market Street San Francisco, CA 94103 USA Phone: +1 415 645 4726 EMail: URI:
Andrew J. Hacker MistIQ Technologies, Inc Harrisburg, PA USA EMail: URI:
Subir Das Applied Communication Sciences 150 Mount Airy Road, Basking Ridge New Jersey, 07920, USA EMail:
John Dowdell Airbus Defence and Space Celtic Springs Newport, NP10 8FZ United Kingdom EMail:
Henrik Austad Cisco Systems Philip Pedersens vei 1 Lysaker, 1366 Norway EMail:
Kevin Stanton Intel EMail:
Norman Finn Huawei EMail: