DRIP Authentication Formats
draft-wiethuechter-drip-auth-03
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft whose latest revision state is "Replaced".
|
|
|---|---|---|---|
| Authors | Adam Wiethuechter , Stuart W. Card , Robert Moskowitz | ||
| Last updated | 2020-07-27 | ||
| Replaces | draft-wiethuechter-tmrid-auth | ||
| Replaced by | draft-ietf-drip-auth, draft-ietf-drip-auth, draft-ietf-drip-auth, draft-ietf-drip-auth, draft-ietf-drip-auth | ||
| RFC stream | (None) | ||
| Formats | |||
| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
| RFC Editor Note | (None) | ||
| IESG | IESG state | I-D Exists | |
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-wiethuechter-drip-auth-03
DRIP A. Wiethuechter
Internet-Draft S. Card
Intended status: Standards Track AX Enterprize
Expires: 28 January 2021 R. Moskowitz
HTT Consulting
27 July 2020
DRIP Authentication Formats
draft-wiethuechter-drip-auth-03
Abstract
This document describes how to include trust into the ASTM Remote ID
specification defined in ASTM 3411-19 under a Broadcast Remote ID
(RID) scenario. It defines a few different message schemes (based on
the Authentication Message) that can be used to assure past messages
sent by a UA and also act as an assurance for UA trustworthiness in
the absence of Internet connectivity at the receiving node.
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
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
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 28 January 2021.
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Simplified BSD License text
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as described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. DRIP Requirements Addressed . . . . . . . . . . . . . . . 3
2. Terms and Definitions . . . . . . . . . . . . . . . . . . . . 3
2.1. Requirements Terminology . . . . . . . . . . . . . . . . 3
2.2. Definitions . . . . . . . . . . . . . . . . . . . . . . . 4
3. Background . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Problem Space And Document Focus . . . . . . . . . . . . 4
3.2. ASTM Authentication Message . . . . . . . . . . . . . . . 4
4. DRIP Authentication Framing Formats . . . . . . . . . . . . . 5
4.1. DRIP Authentication Frame . . . . . . . . . . . . . . . . 6
4.1.1. DRIP Header . . . . . . . . . . . . . . . . . . . . . 7
4.1.2. DRIP Authentication Data . . . . . . . . . . . . . . 8
4.1.3. Forward Error Correction . . . . . . . . . . . . . . 8
4.2. DRIP Wrapper Frame . . . . . . . . . . . . . . . . . . . 8
4.2.1. UA Hierarchical Host Identity Tag . . . . . . . . . . 9
4.2.2. Trust Timestamp . . . . . . . . . . . . . . . . . . . 10
4.2.3. Authentication Data . . . . . . . . . . . . . . . . . 10
4.2.4. Signature . . . . . . . . . . . . . . . . . . . . . . 10
5. Bluetooth 4.X Formats . . . . . . . . . . . . . . . . . . . . 10
5.1. [1-4] Wrapped ASTM Message(s) . . . . . . . . . . . . . . 11
5.2. 5 Wrapped ASTM Message(s) . . . . . . . . . . . . . . . . 11
5.3. Manifest . . . . . . . . . . . . . . . . . . . . . . . . 12
5.3.1. Hash Algorithm And Operation . . . . . . . . . . . . 12
5.3.2. 4 Byte Manifest . . . . . . . . . . . . . . . . . . . 12
5.3.3. 8 Byte Manifest . . . . . . . . . . . . . . . . . . . 13
5.3.4. Pseudo-blockchain Hashes . . . . . . . . . . . . . . 14
5.3.5. Limitations . . . . . . . . . . . . . . . . . . . . . 15
5.4. Certificate . . . . . . . . . . . . . . . . . . . . . . . 15
5.5. Recommendations . . . . . . . . . . . . . . . . . . . . . 16
6. Bluetooth 5 Formats . . . . . . . . . . . . . . . . . . . . . 16
6.1. Certificate . . . . . . . . . . . . . . . . . . . . . . . 17
6.2. Message Pack Signature . . . . . . . . . . . . . . . . . 17
7. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 18
7.1. 2 Wrapped ASTM Messages . . . . . . . . . . . . . . . . . 18
8. Security Considerations . . . . . . . . . . . . . . . . . . . 21
9. ASTM Considerations . . . . . . . . . . . . . . . . . . . . . 21
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 21
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 21
11.1. Normative References . . . . . . . . . . . . . . . . . . 21
11.2. Informative References . . . . . . . . . . . . . . . . . 21
Appendix A. Thoughts on ASTM Authentication Message . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23
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1. Introduction
UA Systems (UAS) are usually in a volatile environment when it comes
to communication. UA are generally small with little computational
(or flying) horsepower to carry standard communication equipment.
This limits the mediums of communication to few viable options.
Observer systems (e.g. smartphones and tablets) place further
constraints on the communication options. The Remote ID Broadcast
messages MUST be available to applications on these platforms without
modifying the devices.
The ASTM standard [F3411-19] focuses on two ways of communicating to
a UAS for RID: Broadcast and Network.
This document will focus on adding trust to Broadcast RID in the
Authentication Message format.
1.1. DRIP Requirements Addressed
The following [drip-requirements] will be addressed:
GEN 1: Provable Ownership
This will be addressed using the Certificate Message types
(Section 5.4, Section 6.1).
GEN 2: Provable Binding
This will be addressed using the Wrapped ASTM Message, Manifest
Message and Message Pack Signature types (Section 4.2,
Section 5.3, Section 6.2).
GEN 3: Provable Registration
This will be addressed using the Certificate Message types
(Section 5.4, Section 6.1).
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.
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2.2. Definitions
See [drip-requirements] for common DRIP terms.
Aircraft
In this document whenever the word Aircraft is used it is refering
to an Unmanned Aircraft (UA) not a Manned Aircraft.
HI
Host Identity. The public key portion of an asymmetric keypair
from HIP. In this document it is assumed that the HI is based on
a EdDSA25519 keypair. This is supported by new crypto defined in
[new-hip-crypto].
HIT
Host Identity Tag. A 128 bit handle on the HI. Defined in HIPv2
[RFC7401].
HHIT
Hierarchical Host Identity Tag. A 128 bit handle on the HI contain
extra information not found in a standard HIT. Defined in
[hierarchical-hit].
3. Background
3.1. Problem Space And Document Focus
The current standard for Remote ID (RID) does not, in any meaningful
capacity, address the concerns of trust in the UA space with
communication in the Broadcast RID environment. This is a
requirement that will need to be addressed eventually for various
different parties that have a stake in the UA industry.
The following subsections will provide a high level reference to the
ASTM standard for Authentication Messages and how their current
limitations effect trust in the Broadcast RID environment.
3.2. ASTM Authentication Message
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Page 0:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+-----------------------------------------------+
| Auth Header | |
+---------------+ ASTM Authentication Headers +---------------+
| | |
+-----------------------------------------------+ |
| |
| Authentication Data / Signature |
| |
| |
+---------------------------------------------------------------+
Page 1 - 4:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+-----------------------------------------------+
| Auth Header | |
+---------------+ |
| |
| Authentication Data / Signature |
| |
| |
| |
+---------------------------------------------------------------+
Auth Header (1 byte):
Contains Authentication Type and Page Number. For
DRIP Authentication this is a value of 0xD.
ASTM Authentication Headers: (6 bytes)
Contains other header information for the Authentication
Message from ASTM UAS RID Standard.
Authentication Data / Signature: (109 bytes: 17+23*4)
Opaque authentication data.
The above diagram is the format defined by ASTM that is the frame
which everything this document fits into. The specific details of
the ASTM headers are abstracted away as they are not necessarily
required for this document.
4. DRIP Authentication Framing Formats
Currently the ASTM AuthType of 0xD should be used to denote DRIP
based Authentication. The max page count of the Authentication
Message is also 10, instead of 5.
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4.1. DRIP Authentication Frame
Page 0:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+-----------------------------------------------+
| Auth Header | |
+---------------+ ASTM Authentication Headers +---------------+
| | DRIP Header |
+-----------------------------------------------+---------------+
| |
| DRIP Authentication Data |
| |
| |
+---------------------------------------------------------------+
Page 1 - Page N-1:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+-----------------------------------------------+
| Auth Header | |
+---------------+ |
| |
| DRIP Authentication Data |
| |
| |
| |
+---------------------------------------------------------------+
Page N:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+-----------------------------------------------+
| Auth Header | |
+---------------+ |
| |
| Forward Error Correction |
| |
| |
| |
+---------------------------------------------------------------+
DRIP Header (1 byte):
7 6 5 4 3 2 1 0
+-----+-----+-----+-----+-----+-----+-----+-----+
| FEC | DRIP AuthType |
+-----+-----+-----+-----+-----+-----+-----+-----+
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FEC (1 bit):
Enabled [1] or Disabled [0]. Signals if Page N is
filled with Reed Solomon FEC.
DRIP AuthType (7 bits):
DRIP AuthType Values
------------- ------
0 Wrapped ASTM Message(s) 0
1 Wrapped ASTM Message(s) 1
2 Wrapped ASTM Message(s) 2
3 Wrapped ASTM Message(s) 3
4 Wrapped ASTM Message(s) 4
5 Wrapped ASTM Message(s) 5
8 Byte Manifest 6
4 Byte Manifest 7
Reserved (Wrapped Messages) 8-15
Certificate: Registry on Aircraft 16
Reserved (Certificates) 17-31
Private Use 32-63
Reserved 64-111
Experimental Use 112-127
DRIP Authentication Data (223 bytes):
DRIP Authentication data. 0 to 223 bytes.
Forward Error Correction (23 bytes):
Optional and signaled using DRIP Header. Always last
Authentication page. Reed Solomon across preceding pages.
4.1.1. DRIP Header
The DRIP Header is used to signal what kind of Authentication under
DRIP that the message is using and consists of two fields.
The Most Significant Bit is used to signal if FEC is present in the
final page of the Authentication Message. It MUST be set to 1 if FEC
is being used.
The lower 7 bits are used as the DRIP AuthType field denoting what
Authentication type is being used. There are 5 major areas carved
out of the DRIP AuthType defined by the following bitmaps:
000 xxxx (0x00-0x0F): Wrapped Messages (16)
001 xxxx (0x10-0x1F): Certificates (16)
01x xxxx (0x20-0x3F): Private Use (32)
1xx xxxx (0x40-0x6F): Reserved (48)
111 xxxx (0x70-0x7F): Experimental Use (16)
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4.1.2. DRIP Authentication Data
This field has a maximum size of 223 bytes. If the data is less than
223 bytes and a page is only partially filled then the rest of the
partially filled page must be null padded.
4.1.3. Forward Error Correction
To help Bluetooth (specifically Bluetooth 4) achieve the goal of
reliable receipt of paged messages a Forward Error Correction (FEC)
scheme is introduced and SHOULD be used for Bluetooth 4 and SHOULD
NOT be used for Bluetooth 5 under DRIP.
Due to the nature of Bluetooth 4 and the existing ASTM paging
structure an optimization can be used. If a Bluetooth frame fails
its CRC check, then the frame is dropped without notification to the
upper protocol layers. From the Remote ID perspective this means the
loss of a complete frame/message/page. In Authentication Messages,
each page is already numbered so the loss of a page allows the
receiving application to build a "dummy" page filled with nulls
(other than the ASTM Header and Auth Header which is known).
A compliant implementation of this standard MUST use Reed Solomon for
the FEC. With this the entire authentication message (all pages,
including headers) are used to generate 23 bytes of parity. This
parity is appended in one full page (always the last) allowing for
recovery when any single page is lost in transmission.
If more than one page is lost (>1/5 for 5 page messages, >1/10 for 10
page messages) than the error rate of the link is already beyond
saving and the application has more issues to deal with.
4.2. DRIP Wrapper Frame
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| |
| UA Hierarchical |
| Host Identity Tag |
| |
+---------------+---------------+---------------+---------------+
| Trust Timestamp |
+---------------+---------------+---------------+---------------+
| |
. .
. Authentication Data .
. .
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| |
+---------------+---------------+---------------+---------------+
| |
| |
| |
| |
| |
| |
| |
| Signature |
| |
| |
| |
| |
| |
| |
| |
| |
+---------------+---------------+---------------+---------------+
UA Hierarchial Host Identity Tag (16 bytes):
The UAs HHIT in byte form. Hashed from the EdDSA25519
public key.
Trust Timestamp (4 bytes):
Timestamp denoting current time plus an offset to trust
message to.
Authentication Data (116/139 bytes):
Opaque authentication data using DRIP format specified in
the DRIP Header. 0 to 116 bytes when FEC bit is 1, 0 to
139 bytes when FEC bit is 0.
Signature (64 bytes):
Signature over preceding fields using the EdDSA25519
keypair.
This framing resides within the General Frame's DRIP Authentication
Data (Section 4.1.2).
4.2.1. UA Hierarchical Host Identity Tag
To avoid needing the UAs HHIT via the ASTM Basic ID in a detached
fashion the 16 byte HHIT of the UA is included in the wrapper frame.
The HHIT for the UA (and other entities in the RID and greater UTM
system under DRIP) is an enhancement of the Host Identity Tag (HIT)
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of HIPv2 [RFC7401] introducing hierarchy as defined in HHIT
[hierarchical-hit].
Using Hierarchical HITs for UAS RID is outlined in HHIT based UAS RID
[drip-uas-rid].
4.2.2. Trust Timestamp
Trust Timestamp MUST be current UNIX time plus an offset into the
future. To avoid replay attacks the Trust Timestamp field must be
well founded.
When wrapping a Vector (Position) Message the payload WILL contain
(by ASTM rules) constantly changing data, this includes its own
timestamp. This timestamp is only 2 bytes, which is easily attacked
and only expresses the 1/10th of seconds since the last hour.
Other ASTM message types, such as Basic ID and Self-ID are static
messages with no changing data. To protect a replay of these signed
messages the Trust Timestamp is the field during signing to be
guaranteed to change.
The offset used against the UNIX timestamp is not defined in this
document. Best practices to identify a acceptable offset should be
used taking into consideration the UA environment, and propagation
characteristics of the messages being sent.
4.2.3. Authentication Data
This field has a maximum of 116 bytes in length when the FEC bit of
the DRIP Header is turned on and 139 bytes of maximum length when
turned off.
4.2.4. Signature
The wrapper signature is generated using the private key half of the
the UAs Host Identity (HI) and is done over all preceding data.
ASTM/DRIP Headers are exclude from this operation only information
within the DRIP Wrapper Frame is signed.
5. Bluetooth 4.X Formats
With Bluetooth 4.X formatting the goal is to attempt to bring
reliable receipt of paged messages.
Unless otherwise specified the FEC Bit of the DRIP Header MUST be set
to 1 when using Bluetooth 4 to take advantage of FEC for lost frames.
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5.1. [1-4] Wrapped ASTM Message(s)
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| |
. .
. ASTM Message: Type 0-1, 3-5 (1 to 4) .
. .
| |
+---------------+---------------+---------------+---------------+
DRIP Header:
With FEC: 0x81-0x84 [129-132] (RECOMMENDED)
Without FEC: 0x01-0x04 [1-4]
ASTM Message: Type 0-1, 3-5 (25 bytes):
Valid ASTM Messages of Type 0, 1, 3, 4, or 5.
If more than 1 then ASTM Messages in Message Type order.
This DRIP Authentication type uses the Wrapper Frame format
(Section 4.2), filling the Authentication Data (Section 4.2.3) field
with an ASTM Message (all types except Message Pack [0xF] and
Authentication [0x2]).
When multiple ASTM Messages are being wrapped they MUST be in Message
Type order.
5.2. 5 Wrapped ASTM Message(s)
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| |
. .
. ASTM Message: Type 0-1, 3-5 (5) .
. .
| |
+---------------+---------------+---------------+---------------+
DRIP Header:
With FEC: 0x85 [133] (RECOMMENDED)
Without FEC: 0x05 [5]
ASTM Message: Type 0-1, 3-5 (25 bytes):
5 valid ASTM Message of Types 0, 1, 3, 4, or 5.
ASTM Messages in Message Type order.
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This DRIP Authentication type uses the Wrapper Frame format
(Section 4.2), filling the Authentication Data (Section 4.2.3) field
with an ASTM Message (all types except Message Pack [0xF] and
Authentication [0x2]).
ASTM Messages being wrapped MUST be in Message Type order.
5.3. Manifest
This DRIP Authentication type uses the Wrapper Frame format
(Section 4.2), filling the Authentication Data (Section 4.2.3) field
with hashes of previously sent messages.
By hashing previously sent messages and signing them we gain trust in
UAs previous reports. An observer who has been listening for any
length of time can hash received messages and cross check against
listed hashes. The signature is signed across the list of hashes.
5.3.1. Hash Algorithm And Operation
The hash algorithm used for the Manifest Message is the same hash
algorithm used in creation of the HHIT that is signing the Manifest.
A standard HHIT would be using cSHAKE128 from [NIST.SP.800-185].
With cSHAKE128, the hash is computed as follows:
cSHAKE128(MAC|Message, 8*H-Len, "", "RemoteID Auth Hash")
The message MAC is prepended to the message, as the MAC is the only
information that links UA messages from a specific UA.
5.3.2. 4 Byte Manifest
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| Hash of Previous Manifest |
+---------------+---------------+---------------+---------------+
| Hash of Current Manifest |
+---------------+---------------+---------------+---------------+
| Message Hash 1 |
+---------------+---------------+---------------+---------------+
| Message Hash 2 |
+---------------+---------------+---------------+---------------+
. .
. .
. .
+---------------+---------------+---------------+---------------+
| Message Hash 27 |
+---------------+---------------+---------------+---------------+
DRIP Header:
With FEC: 0x86 [132] (RECOMMENDED)
Without FEC: 0x06 [6]
Hash of Previous Manifest: (4 bytes)
A hash of the previously sent Authentication message.
Hash of Current Manifest: (4 bytes)
A hash of the current Authentication message.
Message Hash: (4 bytes)
A hash of a previously sent message. 27 max.
5.3.3. 8 Byte Manifest
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| Hash of Previous Manifest |
| |
+---------------+---------------+---------------+---------------+
| Hash of Current Manifest |
| |
+---------------+---------------+---------------+---------------+
| Message Hash 1 |
| |
+---------------+---------------+---------------+---------------+
| Message Hash 2 |
| |
+---------------+---------------+---------------+---------------+
. .
. .
. .
+---------------+---------------+---------------+---------------+
| Message Hash 12 |
| |
+---------------+---------------+---------------+---------------+
DRIP Header:
With FEC: 0x87 [135] (RECOMMENDED)
Without FEC: 0x07 [7]
Hash of Previous Manifest: (8 bytes)
A hash of the previously sent Authentication message.
Hash of Current Manifest: (8 bytes)
A hash of the current Authentication message.
Message Hash: (8 bytes)
A hash of a previously sent message. 12 max.
5.3.4. Pseudo-blockchain Hashes
Two special hashes are included; a previous manifest hash, which
links to the previous manifest message, as well as a current manifest
hash. This gives a pseudo-blockchain provenance to the manifest
message that could be traced back if the observer was present for
extended periods of time.
In regards to the creation and use of the current manifest hash
field:
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During creation and signing of this message format this field MUST
be set to 0. So the signature will be based on this field being
0, as well as its own hash. It is an open question of if we
compute the hash, then sign or sign then compute.
There a few different ways to cycle this message. We can "roll
up" the hash of 'current' to 'previous' when needed or to
completely recompute the hash. This mostly depends on the
previous note.
5.3.5. Limitations
A potential limitation to this format is dwell time of the UA. If
the UA is not sticking to a general area then most likely the
Observer will not obtain many (if not all) of the messages in the
manifest. Without the original messages received no verification can
be done. Examples of such scenarios include delivery or survey UA.
5.4. Certificate
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| |
. .
. Certificate: Registry on Aircraft .
. .
| |
+---------------+---------------+---------------+---------------+
DRIP Header:
With FEC: 0x90 [144] (RECOMMENDED)
Without FEC: 0x10 [16]
Certificate: Registry on Aircraft (200 bytes):
A certificate granted by the Registry that asserts the
binding of UA to the given Registry.
This DRIP Authentication type uses the General Frame format
(Section 4.1), filling the DRIP Authentication Data (Section 4.1.2)
field with a 200 byte Certificate: Registry on Aircraft.
What this grants is the ability to authenticate UA Remote ID when the
receiving device of the observer (e.g. a smartphone with a dedicated
RID application) has no Internet service (e.g. LTE signal).
The Certificate: Registry on Aircraft (Cra) is in practice a binding
claim between the Registry and the Aircraft, asserting the
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relationship between the two entities. Cra signs another
certificate, Caa (Certificate: Aircraft on Aircraft), that is created
during UA provisioning.
Importantly this certificate allows offline signature verification
from the UA. This is as the UA HI is included in the certificate.
Also included is the HHIT of the Registry to check the local
shortlist of Registries that the Observer device trusts (mapping
HHITs to HIs).
More details about Caa, Cra, other certificates and the provisioning
process can be found in [drip-identity-claims].
5.5. Recommendations
Under ASTM Bluetooth 4.X rules, transmission of dynamic messages are
at least every 1 second while static messages (which is what
Authentication is classified under) are sent at least every 3
seconds.
Under DRIP the Certificate Message MUST be transmitted to properly
meet the GEN 1 and GEN 3 requirement.
The ASTM Message Wrapper and Manifest both satisfy the GEN 2
requirement. At least one MUST be implemented to comply with the GEN
2 requirement.
A single Manifest can carry at most (using the full 10 page limit and
8 byte hashes) 12 unique hashes of previously sent messages (of any
type). This results in a total of 22 (12 + 10) frames of Bluetooth
data being transmitted over Bluetooth.
In comparison the Message Wrapper sends 6 pages (each a single frame)
for each wrapped message. For backwards compatibility the
implementation should also send the standard ASTM message that was
wrapped for non-DRIP compliant receivers to obtain. This method
results in 84 total Bluetooth frames (12 + (12 * 6)) sent.
The question of which is better suited is up to the implementation.
6. Bluetooth 5 Formats
Under ASTM specification, Bluetooth 5 transport of Remote ID is to
use the Message Pack (Type 0xF) format for all transmissions. Under
Message Pack all messages are sent together (in Message Type order)
in a single Bluetooth frame (up to 250 bytes). Message Packs are
required by ASTM to be sent at a rate of 1 per second (like dynamic
messages).
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This gives the benefit of no longer is there any message or page
fragmentation in transmission. For this reason the recommended use
of FEC such as Reed Solomon using in Bluetooth 4.X is not needed here
and is impractical.
Any of the Bluetooth 4.X formats can theoretically be used during
Bluetooth 5 operation under ASTM, however the following subsections
define a number of formats optimized for Message Pack and Bluetooth
5.
6.1. Certificate
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| |
. .
. Certificate: Registry on Aircraft .
. .
| |
+---------------+---------------+---------------+---------------+
DRIP Header:
With FEC: 0x90 [144]
Without FEC: 0x10 [16] (RECOMMENDED)
Certificate: Registry on Aircraft (200 bytes):
A certificate granted by the Registry that asserts the
binding of UA to the given Registry.
With Message Pack the following SHOULD be included in it when sending
a DRIP Certificate Message: 1x Location Message 1x Authentication
Message, DRIP AuthType 16 The Certificate Message (without FEC) only
needs 9 pages for transmission, allowing the final 25 bytes to be
used for another ASTM Message.
6.2. Message Pack Signature
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| Trust Timestamp |
+---------------+---------------+---------------+---------------+
| |
| |
| |
| |
| |
| |
| |
| Signature |
| |
| |
| |
| |
| |
| |
| |
| |
+---------------+---------------+---------------+---------------+
Trust Timestamp: (4 bytes)
Timestamp denoting current time plus an offset to trust
message to.
Signature: (64 bytes)
Signature over all messages in Message Pack using the
EdDSA25519 keypair.
The DRIP Message Pack Signature is a DRIP AuthType 0. All messages
in the message pack (excluding the Authentication Message itself) is
signed.
7. Examples
7.1. 2 Wrapped ASTM Messages
Page 0:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+-----------------------------------------------+
|1 1 0 1 0 0 0 0| |
+---------------+ ASTM Authentication Headers +---------------+
| |1 0 0 0 0 0 1 0|
+-----------------------------------------------+---------------+
| |
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| UA Hierarchical |
| Host Identity Tag |
| |
+---------------------------------------------------------------+
Page 1:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+-----------------------------------------------+
|1 1 0 1 0 0 0 1| Trust Timestamp /
+---------------+-----------------------------------------------+
/ | |
+---------------+ |
| |
| ASTM Message #1 (Bytes 1 - 19) |
| |
| |
+---------------------------------------------------------------+
Page 2:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+-----------------------------------------------+
|1 1 0 1 0 0 1 0| ASTM Message #1 (Bytes 20 - 25) |
+---------------+ +---------------+
| | |
+-----------------------------------------------+ |
| |
| ASTM Message #2 (Bytes 1 - 17) |
| |
| |
+---------------------------------------------------------------+
Page 3:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+-----------------------------------------------+
|1 1 0 1 0 0 1 1| |
+---------------+ |
| ASTM Message #2 (Bytes 18 - 25) |
| +-----------------------------------------------+
| | |
+---------------+ |
| Signature (Bytes 1 - 15) |
| |
| |
+---------------------------------------------------------------+
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Page 4:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+-----------------------------------------------+
|1 1 0 1 0 1 0 0| |
+---------------+ |
| |
| Signature (Bytes 16 - 38) |
| |
| |
| |
+---------------------------------------------------------------+
Page 5:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+-----------------------------------------------+
|1 1 0 1 0 1 0 1| |
+---------------+ |
| |
| Signature (Bytes 38 - 61) |
| |
| |
| |
+---------------------------------------------------------------+
Page 6:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+-----------------------------------------------+
|1 1 0 1 0 1 1 0| Signature (Bytes 62 - 64) |
+---------------+-----------------------------------------------+
| |
| |
| Null Padding |
| |
| |
+---------------------------------------------------------------+
Page 7:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+-----------------------------------------------+
|1 1 0 1 0 1 1 1| |
+---------------+ |
| |
| Forward Error Correction |
| |
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| |
| |
+---------------------------------------------------------------+
8. Security Considerations
TBD
9. ASTM Considerations
1. Increase Authentication Page Count maximum from 5 to 10.
2. Add Authentication Type for DRIP.
10. Acknowledgments
Ryan Quigley and James Mussi at AX Enterprize for early prototyping
to find holes in the draft specifications.
11. References
11.1. Normative References
[NIST.SP.800-185]
Kelsey, J., Change, S., and R. Perlner, "SHA-3 derived
functions: cSHAKE, KMAC, TupleHash and ParallelHash",
National Institute of Standards and Technology report,
DOI 10.6028/nist.sp.800-185, December 2016,
<https://doi.org/10.6028/nist.sp.800-185>.
[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>.
[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>.
11.2. Informative References
[drip-identity-claims]
Wiethuechter, A., Card, S., and R. Moskowitz, "DRIP
Identity Claims", Work in Progress, Internet-Draft, draft-
wiethuechter-drip-identity-claims-00, 23 March 2020,
<https://tools.ietf.org/html/draft-wiethuechter-drip-
identity-claims-00>.
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[drip-requirements]
Card, S., Wiethuechter, A., Moskowitz, R., and A. Gurtov,
"Drone Remote Identification Protocol (DRIP)
Requirements", Work in Progress, Internet-Draft, draft-
ietf-drip-reqs-03, 13 July 2020,
<https://tools.ietf.org/html/draft-ietf-drip-reqs-03>.
[drip-uas-rid]
Moskowitz, R., Card, S., Wiethuechter, A., and A. Gurtov,
"UAS Remote ID", Work in Progress, Internet-Draft, draft-
moskowitz-drip-uas-rid-03, 13 July 2020,
<https://tools.ietf.org/html/draft-moskowitz-drip-uas-rid-
03>.
[F3411-19] ASTM International, "Standard Specification for Remote ID
and Tracking", February 2020,
<http://www.astm.org/cgi-bin/resolver.cgi?F3411>.
[hierarchical-hit]
Moskowitz, R., Card, S., and A. Wiethuechter,
"Hierarchical HITs for HIPv2", Work in Progress, Internet-
Draft, draft-moskowitz-hip-hierarchical-hit-05, 13 May
2020, <https://tools.ietf.org/html/draft-moskowitz-hip-
hierarchical-hit-05>.
[new-hip-crypto]
Moskowitz, R., Card, S., and A. Wiethuechter, "New
Cryptographic Algorithms for HIP", Work in Progress,
Internet-Draft, draft-moskowitz-hip-new-crypto-04, 23
January 2020, <https://tools.ietf.org/html/draft-
moskowitz-hip-new-crypto-04>.
[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>.
Appendix A. Thoughts on ASTM Authentication Message
The format standardized by the ASTM is designed with a few major
considerations in mind, which the authors of this document feel put
significant limitations on the expansion of the standard.
The primary consideration (in this context) is the use of the
Bluetooth 5.X Extended Frame format. This method allows for a 255
byte payload to be sent in what the ASTM refers to as a "Message
Pack".
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The idea is to include up to five standard ASTM Broadcast RID
messages (each of which are 25 bytes) plus a single authentication
message (5 pages of 25 bytes each) in the Message Pack. The
reasoning is then the Authentication Message is for the entire
Message Pack.
The authors have no issues with this proposed approach; this is a
valid format to use for the Authentication Message provided by the
ASTM. However, by limiting the Authentication Message to ONLY five
pages in the standard it ignores the possibility of other formatting
options to be created and used.
Another issue with this format, not fully addressed in this document
is fragmentation. Under Bluetooth 4.X, each page is sent separately
which can result in lose of pages on the receiver. This is
disastrous as the loss of even a single page means any signature is
incomplete.
With the current limitation of 5 pages, Forward Error Correction
(FEC) is nearly impossible without sacrificing the amount of data
sent. More pages would allow FEC to be performed on the
Authentication Message pages so loss of pages can be mitigated.
All these problems are further amplified by the speed at which UA fly
and the Observer's position to receive transmissions. There is no
guarantee that the Observer will receive all the pages of even a 5
page Authentication Message in the time it takes a UA to traverse
across their line of sight. Worse still is that is not including
other UA in the area, which congests the spectrum and could cause
further confusion attempting to collate messages from various UA.
This specific problem is out of scope for this document and our
solutions in general, but should be noted as a design consideration.
Authors' Addresses
Adam Wiethuechter
AX Enterprize
4947 Commercial Drive
Yorkville, NY 13495
United States of America
Email: adam.wiethuechter@axenterprize.com
Stuart W. Card
AX Enterprize
4947 Commercial Drive
Yorkville, NY 13495
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United States of America
Email: stu.card@axenterprize.com
Robert Moskowitz
HTT Consulting
Oak Park, MI 48237
United States of America
Email: rgm@labs.htt-consult.com
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