Crowd Sourced Remote ID

1.1. Draft Status

This draft is still incomplete. New features are being added as capabilities are researched. The actual message formats also still need work.¶

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

B-RID:

Broadcast Remote ID. A method of sending RID messages as 1-way transmissions from the UA to any Observers within radio range.¶

CAA:

Civil Aeronautics Administration. An example is the Federal Aviation Administration (FAA) in the United States of America.¶

DAA:

Detect and Avoid. The process of a UA detecting obstacles, like other UAs and taking the necessary evasive action.¶

ECIES:

Elliptic Curve Integrated Encryption Scheme. A hybrid encryption scheme which provides semantic security against an adversary who is allowed to use chosen-plaintext and chosen-ciphertext attacks.¶

GCS:

Ground Control Station. The part of the UAS that the remote pilot uses to exercise C2 over the UA, whether by remotely exercising UA flight controls to fly the UA, by setting GPS waypoints, or otherwise directing its flight.¶

Finder:

In Internet connected device that can receive B-RID messages and forward them to a UTM.¶

Observer:

Referred to in other UAS documents as a "user", but there are also other classes of RID users, so we prefer "observer" to denote an individual who has observed an UA and wishes to know something about it, starting with its RID.¶

Multilateration:

Multilateration (more completely, pseudo range multilateration) is a navigation and surveillance technique based on measurement of the times of arrival (TOAs) of energy waves (radio, acoustic, seismic, etc.) having a known propagation speed.¶

NETSP:

Network RID Service Provider. USS receiving Network RID messages from UAS (UA or GCS), storing for a short specified time, making available to NETDP.¶

NETDP:

Network RID Display Provider. Entity (might be USS) aggregating data from multiple NETSPs to answer query from observer (or other party) desiring Situational Awareness of UAS operating in a specific airspace volume.¶

N-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.¶

SDSP:

Supplemental Data Service Provider. Entity providing information that is allowed, but not required to be present in the UTM system.¶

UA:

Unmanned Aircraft. In this document UA's are typically though of as drones of commercial or military variety. This is a very strict definition which can be relaxed to include any and all aircraft that are unmanned.¶

UAS:

Unmanned Aircraft System. Composed of Unmanned Aircraft and all required on-board subsystems, payload, control station, other required off-board subsystems, any required launch and recovery equipment, all required crew members, and C2 links between UA and the control station.¶

UTM:

UAS Traffic Management. A "traffic management" ecosystem for uncontrolled operations that is separate from, but complementary to, the FAA's Air Traffic Management (ATM) system.¶

USS:

UAS Service Supplier. Provide UTM services to support the UAS community, to connect Operators and other entities to enable information flow across the USS network, and to promote shared situational awareness among UTM participants. (From FAA UTM ConOps V1, May 2018).¶

3.1. Meeting the needs of Network ID

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.¶

3.2. Advantages of Broadcast Remote ID

B-RID has its advantages over N-RID.¶

• B-RID can more readily be implemented directly in the UA. N-RID will more frequently be provided by the GCS or a pilot's Internet connected device.¶

  • If Command and Control (C2) is bi-directional over a direct radio connection, B-RID could be a straight-forward addition.¶
  • Small IoT devices can be mounted on UA to provide B-RID.¶
• B-RID can also be used by the UA to assist in Detect and Avoid (DAA).¶
• B-RID is available to observers even in situations with no Internet like natural disaster situations.¶

3.3. Trustworthiness of Proxied Data

When a proxy is introduced in any communication protocol, there is a risk of corrupted data and DOS attacks.¶

The Finders, in their role as proxies for B-RID, are authenticated to the SDSP (see Section 4). The SDSP can compare the information from multiple Finders to isolate a Finder sending fraudulent information. SDSPs can additionally verify authenticated messages that follow [tmrid-auth].¶

The SPDP can manage the number of Finders in an area (see Section 4.2) to limit DOS attacks from a group of clustered Finders.¶

3.4. Defense against fraudulent RID Messages

The strongest defense against fraudulent RID messages is to focus on [tmrid-auth] conforming messages. Unless this behavior is mandated, SPDPs will have to use assorted algorithms to isolate messages of questionable content.¶

4.1. The Finder Map

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.¶

4.2. Managing Finders

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.¶

5.1. CS-RID MESSAGE TYPE

The CS-RID MESSAGE TYPE is defined in Figure 1:¶

  Number   CS-RID Message Type
  ------   -----------------
  0        Reserved
  1        B-RID Forwarding
  2        Finder Registration
  3        SDSP Response
  4        Finder Location

CSRID_Object = {
  application-context,
  info                => info_message,
  proxy_message       => broadcast_rid_proxy_message,
  finder_registration => finder_registration_message,
  sdsp_response       => sdsp_response_message,
  location_update     => location_update_message,
}

info_message = {
  common_message_members,
  message_content => tstr,
}

common_message_members = (
  message_type  => message_types,
  mac_address   => #6.37(bstr),
)

message_types = &(
  Reserved            : 0,
  BRD                 : 1,
  Finder-Registration : 2,
  SDSP-Response       : 3,
  Finder-Location     : 4,
)

application-context = (
  application => "DRIP-CSRID",
  ? version => uint .size(1..2),
)

application           = "application"
version               = "version"
info                  = "message_info"
proxy_message         = "proxy_message-type"
finder_registration   = "finder_registration"
sdsp_response         = "sdsp_response"
location_update       = "location_update"
rid                   = "id"
message_type          = "message_type"
mac_address           = "mac_address"
message_content       = "message_content"
timestamp             = "timestamp"
gps                   = "gps"
radio_type            = "radio_type"
broadcast_mac_address = "broadcast_mac_address"
broadcast_message     = "broadcast_message"
sdsp_id               = "sdsp_id"
proxy_status_type     = "proxy_status_type"
update_interval       = "update_interval"

5.2. The CS-RID B-RID Proxy Message

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
  )

broadcast_rid_proxy_message = {
  common_message_members,
  rid                   => tstr,
  timestamp             => tdate,
  gps                   => gps-coordinates,
  radio_type            => radio_types,
  broadcast_mac_address => #6.37(bstr),
  broadcast_message     => #6.37(bstr),
}

radio_types = &(
  EFL : 0,
  VLF : 1,
  LF  : 2,
  MF  : 3,
  HF  : 4,
  HF  : 5,
  VHF : 6,
  UHF : 7,
  SHF : 8,
  EHF : 9,
)

gps-coordinates = [
  latitude : float,
  longitude: float,
]

5.3. CS-RID Finder Registration

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
  )

finder_registration_message = {
  common_message_members,
  rid       => tstr,
  timestamp => tdate,
  gps       => gps-coordinates,
}

gps-coordinates = [
  latitude : float,
  longitude: float,
]

5.4. CS-RID SDSP Response

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.¶

sdsp_response_message = {
  common_message_members,
  sdsp_id           => tstr,
  rid               => tstr,
  proxy_status_type => proxy_status_types,
  update_interval   => uint,
}

gps-coordinates = [
  latitude : float,
  longitude: float,
]

proxy_status_types = &(
  0: "forward",
  1: "reverse",
  2: "bi-directional",
)

5.5. CS-RID Location Update

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
  )

location_update_message = {
  common_message_members,
  rid       => tstr,
  timestamp => tdate,
  gps       => gps-coordinates,
}

gps-coordinates = [
  latitude : float,
  longitude: float,
]

8.1. Privacy Concerns

TBD¶