Secure UAS Network RID and C2 Transport
draft-moskowitz-drip-secure-nrid-c2-14
| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Authors | Robert Moskowitz , Stuart W. Card , Adam Wiethuechter , Andrei Gurtov | ||
| Last updated | 2024-03-16 | ||
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draft-moskowitz-drip-secure-nrid-c2-14
DRIP R. Moskowitz
Internet-Draft HTT Consulting
Intended status: Standards Track S. Card
Expires: 17 September 2024 A. Wiethuechter
AX Enterprize
A. Gurtov
Linköping University
16 March 2024
Secure UAS Network RID and C2 Transport
draft-moskowitz-drip-secure-nrid-c2-14
Abstract
This document defines a transport mechanism between an Uncrewed
Aircraft System (UAS) and its UAS Service Supplier (USS) for Network
Remote ID (Net-RID) messages. Either the Broadcast Remote ID (B-RID)
messages, or alternatively, appropriate MAVLink Messages can be sent
directly over UDP or via a more functional protocol using CoAP/CBOR
for the Net-RID messaging. This is secured via either HIP/ESP or
DTLS. HIP/ESP or DTLS secure messaging Command-and-Control (C2) for
is also described.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 17 September 2024.
Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
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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
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terms and Definitions . . . . . . . . . . . . . . . . . . . . 4
2.1. Requirements Terminology . . . . . . . . . . . . . . . . 4
2.2. Definitions . . . . . . . . . . . . . . . . . . . . . . . 4
3. Network Remote ID . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Network RID Endpoints . . . . . . . . . . . . . . . . . . 6
3.1.1. Net-RID from the UA . . . . . . . . . . . . . . . . . 6
3.1.2. Net-RID from the GCS . . . . . . . . . . . . . . . . 6
3.1.3. Net-RID from the Operator . . . . . . . . . . . . . . 7
3.2. Network RID Messaging . . . . . . . . . . . . . . . . . . 7
3.2.1. Secure Link Setup . . . . . . . . . . . . . . . . . . 7
3.2.2. Static Messages . . . . . . . . . . . . . . . . . . . 8
3.2.3. Vector/Location Message . . . . . . . . . . . . . . . 9
3.3. The Minimal, UDP, Net-RID Protocol . . . . . . . . . . . 9
3.3.1. Compressing the MNet-RID message headers . . . . . . 10
3.4. The MAVLink Net-RID Protocol . . . . . . . . . . . . . . 11
3.4.1. Compressing the MavNet-RID message headers . . . . . 12
3.5. CoAP Net-RID messages . . . . . . . . . . . . . . . . . . 12
4. Command and Control . . . . . . . . . . . . . . . . . . . . . 13
4.1. Securing MAVLink . . . . . . . . . . . . . . . . . . . . 13
4.1.1. Compressed ESP for MAVLink . . . . . . . . . . . . . 13
4.2. Compressed UDP/DTLS for MAVLink . . . . . . . . . . . . . 14
5. Secure Transports . . . . . . . . . . . . . . . . . . . . . . 14
5.1. HIP for Secure Transport . . . . . . . . . . . . . . . . 14
5.2. DTLS for Secure Transport . . . . . . . . . . . . . . . . 15
5.3. Ciphers for Secure Transport . . . . . . . . . . . . . . 15
5.4. HIP and DTLS contrasted and compared . . . . . . . . . . 16
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
7. Security Considerations . . . . . . . . . . . . . . . . . . . 17
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 17
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 17
9.1. Normative References . . . . . . . . . . . . . . . . . . 17
9.2. Informative References . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20
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1. Introduction
This document defines two sets of messages for Uncrewed Aircraft
System (UAS) Network Remote ID (Net-RID). Minimal Net_RID (MNet-RID)
is derived from the ASTM Remote ID [F3411-22a] broadcast messages and
common data dictionary. MAVLink Net_RID (MVNet-RID) is derived from
the MAVLink protocol [MAVLINK].
These messages are transported from the UAS to its UAS Service
Supplier (USS) Network Service Provider (Net-RID SP) either directly
over UDP or via CoAP/CBOR ([RFC7252]/[RFC8949]).
Direct UDP and CoAP/CBOR were selected for their low communication
"cost". This may not be an issue if Net-RID originates from the
Ground Control Station (GCS, Section 3.1.2), but it may be an
important determinant when originating from the UA (Section 3.1.1).
Particularly, very small messages may open Net-RID transmissions over
a variety of constrained wireless technologies.
This document also defines mechanisms to provide secure transport for
these Net-RID messages and Command and Control (C2) messaging.
A secure end-to-end transport for Net-RID (UAS to Net-RID SP) should
provide full Confidentiality, Integrity, and Authenticity (CIA). It
may seem that confidentiality is optional, as most of the information
in Net-RID is sent in the clear in Broadcast Remote ID (B-RID), but
this is a potentially flawed analysis. Net-RID has eavesdropping
risks not in B-RID and may contain more sensitive information than
B-RID. The secure transport for Net-RID should also manage IP
address changes (IP mobility) for the UAS.
A secure end-to-end transport for C2 is critical for UAS especially
for Beyond Line of Sight (BLOS) operations. It needs to provide data
CIA. Depending on the underlying network technology, this secure
transport may need to manage IP address changes (IP mobility) for
both the UA and GCS.
Two options for secure transport are provided: HIP [RFC7401] with ESP
[RFC7402] and DTLS 1.3 [RFC9147]. These options are generally
defined and their applicability is compared and contrasted. It is up
to Net-RID and C2 user to select which is preferred for their
situation.
MOBIKE [RFC4555] is an alternative to HIP for ESP key establishment.
It functions enough like HIP that it was left out, but implied, for
document simplicity. There may be some identity pieces needed to map
HHITs and HIs to what MOBIKE uses.
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To further reduce the communication cost, SCHC [RFC8724] is defined
for both the direct UDP and CoAP layer [RFC8824]. For ESP
"compression", ESP Implicit IV, [RFC8750] and Diet ESP [diet-esp] may
be used together. DTLS 1.3 [RFC9147] as defined in Section 5.2 is
fully compressed. DTLS for MNet-RID would only benefit from UDP
compression. CoAP Net-RID and C2 could benefit from specific
application header compression.
UDP SCHC compression is handled separately here from IP header as is
currently defined by IP carrier (e.g. LoRaWAN, [RFC9011]). This is
to allow for the endpoints to not need to know what constrained
carrier is in-path and just design for worst case.
2. Terms and Definitions
2.1. Requirements Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2.2. Definitions
See Section 2.2 of [RFC9153] for common DRIP terms. The following
new terms are used in the document:
B-RID
Broadcast Remote ID. A method of sending RID messages as 1-way
transmissions from the UA to any Observers within radio range.
MNet-RID
A Minimal implementation of Network Remote ID, based on B-RID
messages directly over UDP.
Net-RID
Network Remote ID. A method of sending RID messages via the
Internet connection of the UAS directly to the UTM.
RID
Remote ID. A unique identifier found on all UA to be used in
communication and in regulation of UA operation.
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3. Network Remote ID
In UAS Traffic Management (UTM), the purpose of Net-RID is to provide
situational awareness of UA (in the form of flight tracking) in a
user specified 4D volume. The data needed for this is already
defined in [F3411-22a], but a standard message format, protocol, and
secure communications methodology are missing. F3411, and other UTM
based standards going through ASTM and other SDOs, provide JSON
objects and some of the messages for passing information between
various UTM entities (e.g., Net-RID SP to Net-RID SP and Net-RID SP
to Net-RID DP) but does not specify how the data gets into UTM to
begin with. This document will provide such an open standard.
A full-function CoAP-based Net-RID protocol is defined in
Section 3.5. This provides for either transport of the appropriate
B-RID messages and/or the [F3411-22a] data elements encoded in CBOR.
A minimal messaging approach (MNet-RID, Section 3.3), only using the
Broadcast Remote ID (B-RID) messages in [F3411-22a], is sufficient to
meet the needs of Net-RID. These messages can be sent to the Net-RID
SP when their contents change. Further, a UAS supporting B-RID will
have minimal development to add Net-RID support.
This approach has the added advantage of being very compact,
minimizing the Net-RID communications cost.
Other messages may be needed in some Net-RID situations. Thus a
simple message multiplexer is provided for MNet-RID and CoAP is
defined for a richer messaging environment.
A MAVLink based messaging approach (MavNet-RID, Section 3.4) is also
provided. It differs from MNet-RID in message content, sending the
appropriate MAVLink messages, but uses the same security options. At
this time, this approach is not complete; the minimal set of MAVLink
messages need to be added.
An example where MavNET-RID may be preferred is where the UAS
endpoint is the GCS with the Internet access. Through C2, it has all
the MAVLink messages, and only needs forward appropriate MAVLink
messages on to the Net-RID SP. This is particular value when the UAS
is operating in an area that does not require Broadcast RID but
mandates Network RID.
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3.1. Network RID Endpoints
The US FAA defines the Network Remote ID endpoints as a USS Network
Service Provider (Net-RID SP) and the UAS. Both of these are rather
nebulous items and what they actually are will impact how
communications flow between them.
The Net-RID SP may be provided by the same entity serving as the USS.
This simplifies a number of aspects of the Net-RID communication
flow. The Net-RID SP is likely to be stable in the network, that is
its IP address will not change during a mission. This simplifies
maintaining the Net-RID communications.
The UAS component in Net-RID may be either the UA, GCS, or the
Operator's Internet connected device (e.g. smartphone or tablet that
is not the GCS). In all cases, mobility MUST be assumed. That is
the IP address of this end of the Net-RID communication may change
during an operation (generally called a flight or mission). The Net-
RID mechanism MUST support this. The UAS Identity for the secure
connection may vary based on the UAS endpoint.
3.1.1. Net-RID from the UA
Some UA will be equipped with direct Internet access. These UA will
also tend to have multiple radios for their Internet access (e.g.,
Cellular and WiFi). Thus multi-homing with "make before break"
behavior is needed. This is on top of any IP address changes on any
of the interfaces while in use.
Multicast (GEN-10 in [RFC9153]) over multiple Internet connection
technologies MAY be used improve QOS (GEN-7 in [RFC9153]) for Net-
RID. (Author's question: Does this really qualify as multicast?)
3.1.2. Net-RID from the GCS
Many UA will lack direct Internet access, but their GCS are
connected. As an Operator is expected to register an operation with
its USS, this may be done via the Internet connected GCS. The GCS
could then be the source of the secure connection for Net-RID (acting
as a gateway).
There are two sources of the RID messages for the GCS, both from the
UA. These are UA B-RID messages, or content from C2 messages that
the GCS converts to RID message format (or sends as MAVLink
messages). In either case, the GCS may be mobile with changing IP
addresses. The GCS may be in a fast moving ground device (e.g.
delivery van), so it can have as mobility demanding connection needs
as the UA.
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In a constrained wireless environment for the UA that is not
functioning autonomously (i.e., at least C2 traffic to the GCS), this
approach may be the most economical. It only uses the wireless to
send the UA status once, to the GCS, that then provides the Net-RID
functionality.
3.1.3. Net-RID from the Operator
Many UAS will have no Internet connectivity, but the UA is sending
B-RID messages and the Operator, when within RF range, can receive
these B-RID messages on an Internet Connected device that can act as
the proxy for these messages, turning them into Net-RID messages.
3.2. Network RID Messaging
Net-RID messaging is tied to a UA operation. This consists of an
initial secure link setup, followed by a set of mostly static
information related to the operation. During the operation,
continuous location information is sent by the UA with any needed
updates to the mostly static operation information.
The Net-RID SP SHOULD send regular "heartbeats" to the UAS. If the
UAS does not receive these heartbeats for some policy set time, the
UA MUST take the policy set response to loss of Net-RID SP
connectivity. For example, this could be a mandated immediate
landing. There may be other messages from the Net-RID SP to the UAS
(e.g., call the USS operator at this number NOW!). The UAS MUST
follow acknowledge policy for these messages.
If the Net-RID SP stops receiving messages from the UAS
(Section 3.2.3), it should notify the UTM of a non-communicating UA
while still in operation.
3.2.1. Secure Link Setup
The secure link setup MUST be done before the operation begins, thus
it can use a high capacity connection like WiFi. It MAY use the ASTM
[F3411-22a] UAS ID for this setup, including other data elements
provided in the B-RID Basic ID (Msg Type 0x0) Message. If the Basic
ID information is NOT included via the secure setup (including the
Net-RID SP querying the USS for this information), it MUST be sent as
part of the Static Messages (Section 3.2.2)
3.2.1.1. UAS Identity
The UAS MAY use its UAS ID if it is a HHIT (DET per [RFC9374]). It
may use some other Identity, based on the Net-RID SP policy.
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The GCS or Operator smart device may have a copy of the UA
credentials and use them in the connection to the Net-RID SP. In
this case, they are indistinguishable from the UA as seen from the
Net-RID SP. Alternatively, they may use their own credentials with
the Net-RID SP which would need some internal mechanism to tie that
to the UA.
3.2.1.2. HIP for ESP Secure Link
HIP [RFC7401] for ESP Secure Link is a natural choice for a DET UAS
ID. For this, the Net-RID SP would also need a HHIT, possibly
following the process in [drip-registries].
3.2.1.3. DTLS Secure Link
There are two approaches for DTLS [RFC9147] secure link.
The DET's HI may be encoded in PKIX SubjectPublicKeyInfo format, and
then follow [RFC7250]. Note that SubjectPublicKeyInfo only contains
a DET's HI. The parties in the DTLS setup will have to have a unique
mapping of HI to DET (i.e. the HID value).
Alternatively, DANCE [dane-clients] may be used with a DET's DNS
lookup to retrieve a TLSA RR [RFC6698] with the DET's HI encoded in
PKIX SubjectPublicKeyInfo format (per [RFC7250]). This has the added
advantage of the full DET is sent in the DTLS exchange as part of the
DET FQDN for DANCE.
The Net-RID SP DTLS credential may follow DANE [RFC6698] or any other
DTLS server credential method.
3.2.2. Static Messages
For simplicity, a class of UAS information is called here "Static",
though in practice any of it can change during the operation, but
will change infrequently. This information is the contents of the
B-RID Self-ID (Msg Type 0x3), Operator ID (Msg Type 0x5), and System
Messages (Msg Type 0x4). This information can simply be sent in the
same format as the B-RID messages. Alternatively the individual data
elements may be send as separate CBOR objects.
The Basic ID (Msg Type 0x0) Message may be included as a static
message if this information was not used for the secure setup. There
may be more than one Basic ID Message needed if as in the case where
the Japan Civil Aviation Bureau (JCAB) has mandated that the Civil
Aviation Authority (CAA) assigned ID (UA ID type 2) and Serial Number
(UA ID type 1) be broadcasted.
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The information in the System Message is most likely to change during
an operation. Notably the Operator Location data elements are
subject to change if the GCS is physically moving (e.g. hand-held
and the operator is walking or driving in a car). The whole System
Message may be sent, or only the changing data elements as CBOR
objects.
These static message elements may be sent before the operation
begins, thus their transmission can use a high capacity connection
like WiFi. Once the operation is underway, any updates will have to
traverse the operational link which may be very constrained and this
will impact data element formatting.
The Net-RID SP MUST acknowledge these messages. The UAS MUST receive
these ACKs. If no ACK is received, the UAS MUST resend the
message(s). This send/ACK sequence continues either until ACK is
received, or some policy number of tries. If this fails, the UAS
MUST act that the Net-RID SP connection is lost and MUST take the
policy set response to loss of Net-RID SP connectivity. If the
information changes during this cycle, the latest information MUST
always be sent.
3.2.3. Vector/Location Message
Many CAAs mandate that the UA Vector/Location information be updated
at least once per second. Without careful message design, this
messaging volume would overwhelm many wireless technologies. Thus to
enable the widest deployment choices, a highly compressed format is
recommended.
The B-RID Vector/Location Message (Msg Type 0x1) is the simplest
small object (24 bytes) for sending this information as a single CBOR
object or via MNet-RID. It may be possible to send only those data
elements that changed in the last time interval. This may result in
smaller individual transmissions, but should not be used if the
resulting message is larger than the Vector/Location Message.
3.3. The Minimal, UDP, Net-RID Protocol
The Minimal Network Remote ID protocol is a simple UDP messaging
consisting of a 1-byte message type field and a message field of
maximum 25-bytes length.
The Message Type Field is defined as follows:
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Value Type
0 RESERVED
1 B-RID Message [F3411]
2 Net-RID SP ACK
3 Net-RID SP Heartbeat
The B-RID Message is 25 bytes:
Bytes Description
1 B-RID Message Type/version
24 B-RID Message
The Net-RID SP ACK is 5 bytes:
Bytes Description
4 Timestamp
1 B-RID Message Type/version from message ACKed
Should a 12byte hash of message be included as in Manifest?
The Net-RID SP Heartbeat is 4 bytes:
Bytes Description
4 Timestamp
3.3.1. Compressing the MNet-RID message headers
The security envelope (ESP of DTLS) and UDP headers may be compressed
to further minimize the communication cost of MNet-RID.
3.3.1.1. Compressing ESP/UDP headers
A normal ESP/AES-GCM-12/UDP wrapper for the NMet-RID messages is
10+28+8=46 bytes. By applying the SCHC compression via [diet-esp]
and using [RFC8750] Implicit Cipher IVs, this is reduced to 4+12+0=16
bytes.
AES-CCM-12 has a smaller, but valuable, size reduction on
compression, as CCM's IV is only 8 bytes compared to GCM's 16-byte
IV. Thus uncompressed, the wrapper is 10+20+8=38 bytes. Compressed
it is 4+12+0=16 bytes. Or "over the wire", compressed CCM offers no
improvements to GCM and its 2-pass process will tend to result in a
poorer performance compared to GCM, even on these small messages.
Thus GCM is the recommended mode-of-operation for AES.
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Note that [RFC8750] does not provide implicit IV use for AES-GCM-12.
At the time of writing the use case for the smaller ICV was not
apparent. Here, the smaller hash is not a lower risk given the
limited traffic within a single operation. If not provided
elsewhere, this document will request ENCR_AES_GCM_12_IIV for IKE and
both AES_GCM_12 and AES_GCM_12_IIV for HIP.
[diet-esp] may be completely statically configured, or may have HIP
or IKE negotiated values. This will be determined by Net-RID SP
policy.
TBD: diet-esp context and rules.
3.3.1.2. Compressing UDP/DTLS message headers
DTLS 1.3 [RFC9147] is designed for minimal header overhead.
Section 5.2 defines the DTLS header fields to use for minimal header
size. The only practical compression gain with SCHC would be the UDP
header, it could be compressed to zero bytes, but would require
[schc-protocol-numbers].
The DTLS header defined in Section 5.2 with a 1-byte Sequence and no
Length is 4 bytes. Only AES-GCM-16 is defined for DTLS, but has an
implicit IV for 16 bytes length. This along with the 8-byte UDP
header is 28 bytes total. Using SCHC for UDP header compression to
zero bytes (and an implicit SCHC rule) would require adding the DTLS
2-byte Length field. This results in a further 6 byte header size
reduction. The resulting 22 bytes is similar to that in ESP
compression above. However the complexity of SCHC for only UDP
compression may not be of value in some implementations.
TBD: udp context and rules.
3.4. The MAVLink Net-RID Protocol
The MAVLink Network Remote ID protocol is also a simple UDP messaging
consisting of a 1-byte message type field as in MNet-RID, the 3-byte
MAVLink Msg ID, 1-byte LEN, and a message field of maximum 255-bytes
length.
The MAVLink Message Type Field is defined as follows:
Value Type
0 RESERVED
1 MAVLink Message
2 Net-RID SP ACK
3 Net-RID SP Heartbeat
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It is initially identical to that in MNet-RID, but may deviate over
time, thus separately defined.
The MAVLink Message format is:
Bytes Description
3 MAVLink ID
1 MAVLink message length
0-255 MAVLink Message
The MAVLink message length is included as this value may be needed to
successfully process some MAVLink messages.
The Net-RID SP ACK and Net-RID SP Heartbeat are the same as defined
in MNet-RID.
3.4.1. Compressing the MavNet-RID message headers
The security envelope (ESP of DTLS) and UDP headers may be compressed
to further minimize the communication cost of MavNet-RID. This is
the same as in MNet-RID with the added potential rule to compress the
MAVLink message length, as it can be computed from the header length.
3.5. CoAP Net-RID messages
The CoAP based Net-RID protocol is intended for a richer conversation
between the UAS and USS. The USS, through the Net-RID SP, may
compare actual UA progress against the filed flight plan and against
other UA actual traffic. The USS may then send to the UAS
recommended changes to the flight plan to de-conflict traffic or
advise the UAS to avoid hazards (1st responder event, avoid space).
The UAS may then negotiate changes to the plan, and act on them, as
appropriate.
This sort of advanced UAS behavior is envisioned as part of total UTM
activities. Discussions now ongoing in UTM will provide the data
models and transactional UAS/USS interactions, that will drive UAS
communications past the MNet-RID defined in Section 3.3 toward this
more functional CoAP Net-RID protocol.
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4. Command and Control
The Command and Control (C2) connection is between the UA and GCS.
This is often over a direct link radio. Some times, particularly for
BLOS, it is via Internet connections. In either case C2 SHOULD be
secure from eavesdropping and tampering. For design and
implementation consistency it is best to treat the direct link as a
local link Internet connection and use constrained networking
compression standards.
Both the UA and GCS need to be treated as fully mobile in the IP
networking sense. Either one can have its IP address change and both
could change at the same time (the double jump problem). It is
preferable to use a peer-to-peer (P2P) secure technology like HIPv2
[RFC7401].
Finally UA may also tend to have multiple radios for their C2
communications. Thus multi-homing with "make before break" behavior
is needed. This is on top of any IP address changes on any of the
interfaces while in use.
4.1. Securing MAVLink
MAVLink [MAVLINK] is a commonly used protocol for C2 that uses UDP
port 14550 for transport over IP. Message authenticity was added in
MAVLink 2 in the form of a SHA-256 (secret | message) left-truncated
to 6 byte. This does not follow HMAC [RFC2104] security
recommendations, nor provides confidentiality.
The MAVLink authentication only provides 24-bit collision resistance
but is not susceptible to a hash length attack. By following the
security approach here, UAS C2 is superior to that currently provided
within MAVLink. It provides 48-bit collision resistance and full
confidentiality.
4.1.1. Compressed ESP for MAVLink
The approach in Section 3.3.1.1 can be used to fully secure MAVLink
and include the UDP header for IP transport. Further, MAVLink itself
can be compressed.
MAVLink messages contain a 1-byte Seq number and 2-byte CRC. Both of
these can be generated from SCHC rules. These 3 bytes along with the
13-byte MAVLink signature provides the 16 bytes so that the over-the-
wire cost is the same.
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This secure MAVLink format may be sent directly over a local wireless
link. The UDP port processing adds little cost. Sending this over
IP provides the needed confidentiality at 8 bytes less than
unencrypted messages.
TBD: MAVLink SCHC context and rules. These will be part of the
MAVLink ESP setup.
4.2. Compressed UDP/DTLS for MAVLink
At this time, DTLS is NOT recommended for C2 security, as it is
challenged with server mobility. It may be added at a later time.
DTLS may be viable when there is no possibility for an IP address
change for the GCS during an operation. An example of this is where
the GCS is an Operations Center like might be used in a package
delivery business.
5. Secure Transports
Secure UDP-based protocols are preferred for both Network Remote ID
(Net-RID) and C2. Both HIPv2 and DTLS can be used. It will be shown
below that HIPv2 is better suited in most cases.
For IPv6 and CoAP over both WiFi and Bluetooth (or any other radio
link), SCHC [RFC8724] is defined to significantly reduce the per
packet transmission cost. SCHC is used both within the secure
envelope and before the secure envelope as shown in Section 5.2.10 of
[schc-architecture]. For Bluetooth, there is also IPv6 over
Bluetooth LE [RFC7668] for more guidance.
Local link (direct radio) C2 security is possible with the link's MAC
layer security. SCHC SHOULD still be used as above. Both WiFi and
Bluetooth link security can provide appropriate security, but this
would not provide trustworthy multi-homed security.
5.1. HIP for Secure Transport
HIP has already been used for C2 mobility, managing the ongoing
connectivity over WiFi at start of an operation, switching to LTE
once out of WiFi range, and returning to WiFi connectivity at the end
of the operation. This functionality is especially important for
BLOS. HHITs are already defined for RID, and need only be added to
the GCS via a GCS Registration as part of the UAS to USS registration
to be usedfor C2 HIP.
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When the UA is the UAS endpoint for Net-RID (Section 3.1.1), and
particularly when HIP is used for C2, HIP for Net-RID simplifies
protocol use on the UA. The Net-RID SP endpoint may already support
HIP if it is also the HHIT Registrar. If the UA lacks any IP ability
and the RID HHIT registration was done via the GCS or Operator
device, then they may also be set for using HIP for Net-RID.
Further, double jump and multi-homing support is mandatory for C2
mobility. This is inherent in the HIP design. The HIP address
update can be improved with [hip-fast-mobility].
5.2. DTLS for Secure Transport
DTLS is a good fit for Net-RID for any of the possible UAS endpoints.
There are challenges in using it for C2. To use DTLS for C2, the GCS
will need to be the DTLS server. How does it 'push' commands to the
UA? How does it reestablish DTLS security if state is lost? And
finally, how is the double jump scenario handled?
All the above DTLS for C2 probably have solutions. None of them are
inherent in the DTLS design.
DTLS implementations SHOULD use a CID of 2 bytes. This is to support
mobility and simplify SCHC rule handling. The Sequence Number size
is a deployment choice. For MNet-RID rate of one Vector/Location
update per second, a 1-byte value would result in a rollover in 4
minutes. This should not poise an operational challenge. The length
field is recommended when SCHC is used as it can provided an
authenticated length to use to regenerate the UDP header length field
and any application length field like that in MAVLink.
5.3. Ciphers for Secure Transport
The cipher choice for either HIP or DTLS depends, in large measure,
on the UAS endpoint. If the endpoint is computationally constrained,
the cipher computations become important. If any of the links are
constrained or expensive, then the over-the-wire cost needs to be
minimized. AES-CCM and AES-GCM are the preferred, modern, AEAD
ciphers. Section 3.3.1.1 shows that proper compression can provide
the more efficient GCM at no over-the-wire cost. Thus AES-GCM is the
recommended AES mode-of-operation.
NIST has selected a new lightweight cipher, ASCON, that may be the
best choice for use on a UA. Work will be needed to develop full
support for Ascon in both ESP and DTLS.
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5.4. HIP and DTLS contrasted and compared
This document specifies the use of DTLS 1.3 for its 0-RTT mobility
feature and improved (over 1.2) handshake. DTLS 1.3 is still an IETF
draft, so there is little data available to properly contrast it with
HIPv2. This section will be based on the current DTLS 1.2. The
basic client-server model is unchanged.
The use of DTLS vs HIPv2 (both over UDP, HIP in IPsec ESP BEET mode)
has pros and cons. DTLS is currently at version 1.2 and based on TLS
1.2. It is a more common protocol than HIP, with many different
implementations available for various platforms and languages.
DTLS implements a client-server model, where the client initiates the
communication. In HIP, two parties are equal and either can be an
Initiator or Responder of the Base Exchange. HIP provides separation
between key management (base exchange) and secure transport (for
example IPsec ESP BEET) while both parts are tightly coupled in DTLS.
DTLS 1.2 still has quite chatty connection establishment taking 3-5
RTTs and 15 packets. HIP connection establishment requires 4 packets
(I1,R1,I2,R2) over 2 RTTs. This is beneficial for constrained
environments of UAs. HIPv2 supports cryptoagility with possibility
to negotiate cryptography mechanisms during the Base Exchange.
Both DTLS and HIP support mobility with a change of IP address.
However, in DTLS only client mobility is well supported, while in HIP
either party can be mobile. The double-jump problem (simultaneous
mobility) is supported in HIP with a help of Rendezvous Server (RVS)
[RFC8004]. HIP can implement secure mobility with IP source address
validation in 2 RTTs, and in 1 RTT with fast mobility extension.
One study comparing DTLS and IPsec-ESP performance concluded that
DTLS is recommended for memory-constrained applications while IPSec-
ESP for battery power-constrained [Vignesh].
6. IANA Considerations
TBD: May need ESP ciphers defined.
TBD: Add MNet-RID Message Type Field to DRIP registry.
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7. Security Considerations
Designing secure transports is challenging. Where possible, existing
technologies SHOULD be used. Both ESP and DTLS have stood "the test
of time" against many attack scenarios. Their use here for Net-RID
and C2 do not represent new uses, but rather variants on existing
deployments.
The same can be said for both key establishment, using HIPv2 and
DTLS, and the actual cipher choice for per packet encryption and
authentication. Net-RID and C2 do not present new challenges, rather
new opportunities to provide communications security using well
researched technologies.
8. Acknowledgments
Stuart Card and Adam Wiethuechter provided information on their use
of HIP for C2 at the Syracuse NY UAS test corridor. This, in large
measure, was the impetus to develop this document.
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014,
<https://www.rfc-editor.org/info/rfc7252>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8949] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", STD 94, RFC 8949,
DOI 10.17487/RFC8949, December 2020,
<https://www.rfc-editor.org/info/rfc8949>.
9.2. Informative References
[dane-clients]
Huque, S. and V. Dukhovni, "TLS Client Authentication via
DANE TLSA records", Work in Progress, Internet-Draft,
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draft-ietf-dance-client-auth-05, 13 January 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-dance-
client-auth-05>.
[diet-esp] Migault, D., Guggemos, T., Bormann, C., and D. Schinazi,
"ESP Header Compression Profile", Work in Progress,
Internet-Draft, draft-mglt-ipsecme-diet-esp-10, 29 June
2023, <https://datatracker.ietf.org/doc/html/draft-mglt-
ipsecme-diet-esp-10>.
[drip-registries]
Wiethuechter, A. and J. Reid, "DRIP Entity Tag (DET)
Identity Management Architecture", Work in Progress,
Internet-Draft, draft-ietf-drip-registries-14, 4 December
2023, <https://datatracker.ietf.org/doc/html/draft-ietf-
drip-registries-14>.
[F3411-22a]
ASTM International, "Standard Specification for Remote ID
and Tracking - F3411−22a", July 2022,
<http://www.astm.org/f3411-22a.html>.
[hip-fast-mobility]
Moskowitz, R., Card, S. W., and A. Wiethuechter, "Fast HIP
Host Mobility", Work in Progress, Internet-Draft, draft-
moskowitz-hip-fast-mobility-07, 7 December 2023,
<https://datatracker.ietf.org/doc/html/draft-moskowitz-
hip-fast-mobility-07>.
[MAVLINK] "Micro Air Vehicle Communication Protocol", 2021,
<http://mavlink.io/>.
[RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
Hashing for Message Authentication", RFC 2104,
DOI 10.17487/RFC2104, February 1997,
<https://www.rfc-editor.org/info/rfc2104>.
[RFC4555] Eronen, P., "IKEv2 Mobility and Multihoming Protocol
(MOBIKE)", RFC 4555, DOI 10.17487/RFC4555, June 2006,
<https://www.rfc-editor.org/info/rfc4555>.
[RFC6698] Hoffman, P. and J. Schlyter, "The DNS-Based Authentication
of Named Entities (DANE) Transport Layer Security (TLS)
Protocol: TLSA", RFC 6698, DOI 10.17487/RFC6698, August
2012, <https://www.rfc-editor.org/info/rfc6698>.
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[RFC7250] Wouters, P., Ed., Tschofenig, H., Ed., Gilmore, J.,
Weiler, S., and T. Kivinen, "Using Raw Public Keys in
Transport Layer Security (TLS) and Datagram Transport
Layer Security (DTLS)", RFC 7250, DOI 10.17487/RFC7250,
June 2014, <https://www.rfc-editor.org/info/rfc7250>.
[RFC7401] Moskowitz, R., Ed., Heer, T., Jokela, P., and T.
Henderson, "Host Identity Protocol Version 2 (HIPv2)",
RFC 7401, DOI 10.17487/RFC7401, April 2015,
<https://www.rfc-editor.org/info/rfc7401>.
[RFC7402] Jokela, P., Moskowitz, R., and J. Melen, "Using the
Encapsulating Security Payload (ESP) Transport Format with
the Host Identity Protocol (HIP)", RFC 7402,
DOI 10.17487/RFC7402, April 2015,
<https://www.rfc-editor.org/info/rfc7402>.
[RFC7668] Nieminen, J., Savolainen, T., Isomaki, M., Patil, B.,
Shelby, Z., and C. Gomez, "IPv6 over BLUETOOTH(R) Low
Energy", RFC 7668, DOI 10.17487/RFC7668, October 2015,
<https://www.rfc-editor.org/info/rfc7668>.
[RFC8004] Laganier, J. and L. Eggert, "Host Identity Protocol (HIP)
Rendezvous Extension", RFC 8004, DOI 10.17487/RFC8004,
October 2016, <https://www.rfc-editor.org/info/rfc8004>.
[RFC8724] Minaburo, A., Toutain, L., Gomez, C., Barthel, D., and JC.
Zuniga, "SCHC: Generic Framework for Static Context Header
Compression and Fragmentation", RFC 8724,
DOI 10.17487/RFC8724, April 2020,
<https://www.rfc-editor.org/info/rfc8724>.
[RFC8750] Migault, D., Guggemos, T., and Y. Nir, "Implicit
Initialization Vector (IV) for Counter-Based Ciphers in
Encapsulating Security Payload (ESP)", RFC 8750,
DOI 10.17487/RFC8750, March 2020,
<https://www.rfc-editor.org/info/rfc8750>.
[RFC8824] Minaburo, A., Toutain, L., and R. Andreasen, "Static
Context Header Compression (SCHC) for the Constrained
Application Protocol (CoAP)", RFC 8824,
DOI 10.17487/RFC8824, June 2021,
<https://www.rfc-editor.org/info/rfc8824>.
[RFC9011] Gimenez, O., Ed. and I. Petrov, Ed., "Static Context
Header Compression and Fragmentation (SCHC) over LoRaWAN",
RFC 9011, DOI 10.17487/RFC9011, April 2021,
<https://www.rfc-editor.org/info/rfc9011>.
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[RFC9147] Rescorla, E., Tschofenig, H., and N. Modadugu, "The
Datagram Transport Layer Security (DTLS) Protocol Version
1.3", RFC 9147, DOI 10.17487/RFC9147, April 2022,
<https://www.rfc-editor.org/info/rfc9147>.
[RFC9153] Card, S., Ed., Wiethuechter, A., Moskowitz, R., and A.
Gurtov, "Drone Remote Identification Protocol (DRIP)
Requirements and Terminology", RFC 9153,
DOI 10.17487/RFC9153, February 2022,
<https://www.rfc-editor.org/info/rfc9153>.
[RFC9374] Moskowitz, R., Card, S., Wiethuechter, A., and A. Gurtov,
"DRIP Entity Tag (DET) for Unmanned Aircraft System Remote
ID (UAS RID)", RFC 9374, DOI 10.17487/RFC9374, March 2023,
<https://www.rfc-editor.org/info/rfc9374>.
[schc-architecture]
Pelov, A., Thubert, P., and A. Minaburo, "Static Context
Header Compression (SCHC) Architecture", Work in Progress,
Internet-Draft, draft-ietf-schc-architecture-01, 6 October
2023, <https://datatracker.ietf.org/doc/html/draft-ietf-
schc-architecture-01>.
[schc-protocol-numbers]
Moskowitz, R., Card, S. W., Wiethuechter, A., and P.
Thubert, "Protocol Numbers for SCHC", Work in Progress,
Internet-Draft, draft-ietf-intarea-schc-protocol-numbers-
01, 12 October 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-intarea-
schc-protocol-numbers-01>.
[Vignesh] Vignesh, K., "Performance analysis of end-to-end DTLS and
IPsec-based communication in IoT environments", Thesis
no. MSEE-2017: 42, 2017, <http://www.diva-
portal.org/smash/get/diva2:1157047/FULLTEXT02>.
Authors' Addresses
Robert Moskowitz
HTT Consulting
Oak Park, MI 48237
United States of America
Email: rgm@labs.htt-consult.com
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Stuart W. Card
AX Enterprize
4947 Commercial Drive
Yorkville, NY 13495
United States of America
Email: stu.card@axenterprize.com
Adam Wiethuechter
AX Enterprize
4947 Commercial Drive
Yorkville, NY 13495
United States of America
Email: adam.wiethuechter@axenterprize.com
Andrei Gurtov
Linköping University
IDA
SE-58183 Linköping
Sweden
Email: gurtov@acm.org
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