| Internet-Draft | CS-RID | March 2020 |
| Moskowitz, et al. | Expires 20 September 2020 | [Page] |
This document describes using the ASTM Broadcast Remote ID (B-RID) specification in a "crowd sourced" smart phone environment to provide much of the FAA mandated Network Remote ID (N-RID) functionality. This crowd sourced B-RID data will use multi-lateration to add a level of reliability in the location data on the Unmanned Aircraft (UA). The crowd sourced environment will also provide a monitoring coverage map to authorized observers.¶
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This document defines a mechanism to capture the ASTM Broadcast Remote ID messages (B-RID) [F3411-19] on any Internet connected device that receives them and can forward them to the SDSP(s) responsible for the geographic area the UA and receivers are in. This will create a ecosystem that will meet most if not all data collection requriments that CAAs are placing on Network Remote ID (N-RID).¶
These Internet connected devices are herein called "Finders", as they find UAs by listening for B-RID messages. The Finders are B-RID forwarding proxies. Their potentially limited spacial view of RID messages could result in bad decisions on what messages to send to the SDSP and which to drop. The SDSP will make any filtering decisions in what it forwards to the UTM(s).¶
Finders can be smartphones, tablets, connected cars, or any computing platform with Internet connectivity that can meet the requirements defined in this document. It is not expected, nor necessary, that Finders have any information about a UAS beyond the content in the B-RID messages.¶
Finders MAY only need a loose association with the SDSP(s). They may only have the SDSP's Public Key and FQDN. It would use these, along with the Finder's Public Key to use ECIES, or other security methods, to send the messages in a secure manner to the SDSP. The SDSP MAY require a stronger relationship to the Finders. This may range from the Finder's Public Key being registered to the SDSP with other information so that the SDSP has some level of trust in the Finders to requiring transmissions be sent over long-lived transport connections like ESP or DTLS.¶
This document has minimal information about the actions of SDSPs. In general the SDSP is out of scope of this document. That said, the SDSPs should not simply proxy B-RID messages to the UTM(s). They should perform some minimal level of filtering and content checking before forwarding those messages that pass these tests in a secure manner to the UTM(s).¶
The SDSPs are also capable of maintaining a monitoring map, based on location of active Finders. UTMs may use this information to notify authorized observers of where this is and there is not monitoring coverage. They may also use there information of where to place pro-active monitoring coverage.¶
An SDSP SHOULD only forward Authenticated B-RID messages like those defined in [tmrid-auth] to the UTM(s). Further, the SDSP SHOULD validate the Remote ID (RID) and the Authentication signature before forwarding anything from the UA.¶
When 3 or more Finders are reporting to an SDSP on a specific UA, the SDSP is in a unique position to perform multilateration on these messages and compute the Finder's view of the UA location to compare with the UA Location/Vector messages. This check against the UA's location claims is both a validation on the UA's reliability as well as the trustworthiness of the Finders. Other than providing data to allow for multilateration, this SDSP feature is out of scope of this document.¶
This draft is still incomplete. New features are being added as capabilities are researched. The actual message formats also still need work.¶
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.¶
The Federal (US) Aviation Authority (FAA), in the December 31, 2019 Remote ID Notice of Proposed Rulemaking [FAA-NPRM], is requiring "Standard" and "Limited" Remote ID. Standard is when the UAS provides both Network and Broadcast RID. Limited is when the UAS provides only Network RID. The FAA has dropped their previous position on allowing for only Broadcast RID. We can guess as to their reasons; they are not spelled out in the NPRM. It may be that just B-RID does not meet the FAA's statutory UA tracking responsibility.¶
The UAS vendors have commented that N-RID places considerable demands on currently used UAS. For some UAS like RC planes, meaningful N-RID (via the Pilot's smartphone) are of limited value. A mechanism that can augment B-RID to provide N-RID would help all members of the UAS environment to provide safe operation and allow for new applications.¶
When a proxy is introduced in any communication protocol, there is a risk of corrupted data and DOS attacks.¶
TBD¶
TBD¶
The SDSP(s) and Finders SHOULD use EDDSA [RFC8032] keys as their trusted Identities. The public keys SHOULD be registered Hierarchical HITS, [hierarchical-hit] and [hhit-registries].¶
The SDSP uses some process (out of scope here) to register the Finders and their EDDSA Public Key. During this registration, the Finder gets the SDSP's EDDSA Public Key. These Public Keys allow for the following options for authenticated messaging from the Finder to the SDSP.¶
The Finders are regularly providing their SDSP with their location. This is through the B-RID Proxy Messages and Finder Location Update Messages. With this information, the SDSP can maintain a monitoring map. That is a map of where there Finder coverage.¶
Finder density will vary over time and space. For example, sidewalks outside an urban train station can be packed with pedestrians at rush hour, either coming or going to their commute trains. An SDSP may want to proactively limit the number of active Finders in such situations.¶
Using the Finder mapping feature, the SDSP can instruct Finders to NOT proxy B-RID messages. These Finders will continue to report their location and through that reporting, the SDSP can instruct them to again take on the proxying role. For example a Finder moving slowly along with dozens of other slow-moving Finders may be instructed to suspend proxying. Whereas a fast-moving Finder at the same location (perhaps a connected car or a pedestrian on a bus) would not be asked to suspend proxying as it will soon be out of the congested area.¶
The CS-RID messages between the Finders and the SDSPs primarily support the proxy role of the Finders in forwarding the B-RID messages. There are also Finder registration and status messages.¶
CS-RID information is represented in CBOR [RFC7049]. COSE [RFC8152] may be used for CS-RID MAC and COAP [RFC7252] for the CS-RID protocol.¶
The following is a general representation of the content in the CS-RID messages.¶
( CS-RID MESSAGE TYPE,
CS-RID MESSAGE CONTENT,
CS-RID MAC)
¶
The CS-RID MESSAGE CONTENT varies by MESSAGE TYPE.¶
The CS-RID MESSAGE TYPE is:¶
Number CS-RID Message Type ------ ----------------- 0 Reserved 1 B-RID Forwarding 2 Finder Registration 3 SDSP Response 4 Finder Location¶
The Finders add their own information to the B-RID messages, permitting the SDSP(s) to gain additional knowledge about the UA(s). The RID information is the B-RID message content plus the MAC address. The MAC address is critical, as it is the only field that links a UA's B-RID messages together. Only the ASTM Basic ID Message and possibly the Authentication Message contain the UAS ID field.¶
The Finders add an SDSP assigned ID, a 64 bit timestamp, GPS information, and type of B-RID media to the B-RID message. Both the timestamp and GPS information are for when the B-RID message(s) were received, not forwarded to the SDSP. All this content is MACed using a key shared between the Finder and SDSP.¶
The following is a representation of the content in the CS-RID messages.¶
( CS-RID MESSAGE TYPE,
CS-RID ID,
RECEIVE TIMESTAMP,
RECEIVE GPS,
RECEIVE RADIO TYPE,
B-RID MAC ADDRESS,
B-RID MESSAGE,
CS-RID MAC)
¶
The CS-RID ID is the ID recognized by the SDSP. This may be an HHIT Hierarchical HITs [hierarchical-hit], or any ID used by the SDSP.¶
The CS-RID Finder MAY use HIPv2 [RFC7401] with the SDSP to establish a Security Association and a shared secret to use for the CS-RID MAC generation. In this approach, the HIPv2 mobility functionality and ESP [RFC4303] support are not used.¶
When HIPv2 is used as above, the Finder Registration is a SDSP "wake up". It is sent prior to the Finder sending any proxied B-RID messages to ensure that the SDSP is able to receive and process the messages.¶
In this usage, the CS-RID is the Finder HIT. If the SDSP has lost state with the Finder, it initiates the HIP exchange with the Finder to reestablish HIP state and a new shared secret for the CS-RID B-RID Proxy Messages. In this case the Finder Registration Message is:¶
( CS-RID MESSAGE TYPE,
CS-RID ID,
CS-RID TIMESTAMP,
CS-RID GPS,
CS-RID MAC)
¶
The SDSP MAY respond to any Finder messages to instruct the Finder on its behavior.¶
( CS-RID MESSAGE TYPE,
SDSP ID,
CS-RID ID,
CS-RID PROXY STATUS,
CS-RID UPDATE INTERVAL,
CS-RID MAC)
¶
The Proxy Status instructs the Finder if it should actively proxy B-RID messages, or suspend proxying and only report its location.¶
The Update Interval is the frequency that the Finder SHOULD notify the SDSP of its current location using the Location Update message.¶
The Finder SHOULD provide regular location updates to the SDSP. The interval is based on the Update Interval from Section 5.4 plus a random slew less than 1 second. The Location Update message is only sent when no other CS-RID messages, containing the Finder's GPS location, have been sent since the Update Interval.¶
If the Finder has not recieved a SDSP Registration Response, a default of 5 minutes is used for the Update Interval.¶
( CS-RID MESSAGE TYPE,
CS-RID ID,
CS-RID TIMESTAMP,
CS-RID GPS,
CS-RID MAC)
¶
TBD¶
TBD¶
The Crowd Sourcing idea in this document came from the Apple "Find My Device" presentation at the International Association for Cryptographic Research's Real World Crypto 2020 conference.¶
If the Finder has LIDAR or similar detection equipment (e.g. on a connected car) that has full sky coverage, the Finder can use this equipment to locate UAs in its airspace. The Finder would then be able to detect non-participating UAs.¶
This would provide valuable information to SDSPs to forward to UTMs on potential at-risk situations.¶
At this time, research on LIDAR and other detection technology is needed. Would more than UA location information be available? What information can be sent in a CS-RID message for such "unmarked" UAs?¶