Internet DRAFT - draft-moskowitz-hip-hierarchical-hit
draft-moskowitz-hip-hierarchical-hit
HIP R. Moskowitz
Internet-Draft HTT Consulting
Updates: 7401 (if approved) S. Card
Intended status: Standards Track A. Wiethuechter
Expires: 13 November 2020 AX Enterprize
12 May 2020
Hierarchical HITs for HIPv2
draft-moskowitz-hip-hierarchical-hit-05
Abstract
This document describes using a hierarchical HIT to facilitate large
deployments of managed devices. Hierarchical HITs differ from HIPv2
flat HITs by only using 64 bits for mapping the Host Identity,
freeing 32 bits to bind in a hierarchy of Registering Entities that
provide services to the consumers of hierarchical HITs.
Status of This Memo
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Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terms and Definitions . . . . . . . . . . . . . . . . . . . . 3
2.1. Requirements Terminology . . . . . . . . . . . . . . . . 3
2.2. Definitions . . . . . . . . . . . . . . . . . . . . . . . 3
3. Problem Space . . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Meeting the future of Mobile Devices in a public space . 4
3.2. Semi-permanency of Identities . . . . . . . . . . . . . . 4
3.3. Managing a large flat address space . . . . . . . . . . . 4
3.4. Defense against fraudulent HITs . . . . . . . . . . . . . 5
4. The Hierarchical Host Identity Tag (HHIT) . . . . . . . . . . 5
4.1. HHIT prefix . . . . . . . . . . . . . . . . . . . . . . . 5
4.2. HHIT Suite IDs . . . . . . . . . . . . . . . . . . . . . 6
4.3. The Hierarchy ID (HID) . . . . . . . . . . . . . . . . . 6
4.3.1. The Registered Assigning Authority (RAA) . . . . . . 6
4.3.2. The Hierarchical HIT Domain Authority (HDA) . . . . . 6
4.3.3. Example of the HID DNS . . . . . . . . . . . . . . . 7
4.3.4. HHIT DNS Retrieval . . . . . . . . . . . . . . . . . 7
4.3.5. Changes to ORCHIDv2 to support Hierarchical HITs . . 7
4.3.6. Collision risks with Hierarchical HITs . . . . . . . 8
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
8.1. Normative References . . . . . . . . . . . . . . . . . . 9
8.2. Informative References . . . . . . . . . . . . . . . . . 9
Appendix A. Calculating Collision Probabilities . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
This document expands on HIPv2 [RFC7401] to describe the structure of
a hierarchical HIT (HHIT). Some of the challenges for large scale
deployment addressed by HHITs are presented. The basics for the
hierarchical HIT registries are defined here.
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Including hierarchy information within the HIT is not a new concept.
This was part of the original HIPv1 Architecture
[draft.moskowitz-hip-arch-02]. It was dropped from the HIPv1 work
for lack of a use case and concerns over the smaller HI mapping
space. It was later brought up in the HIP Research Group (HIP-RG) in
[draft.zhang-hip-hierarchical-parameter-00], but this never gained
concensus.
Hierarchical HITs now have a solid use case with Public, mobile
devices (e.g. Unmanned Aircraft). The math to evaluate the
statistical collision risk is available, Appendix A. And finally,
HHIT Registries [hhit-registries] provide a way to manage the
hierarchy.
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
HDA (Hierarchical HIT Domain Authority):
The 16 bit field identifying the HIT Domain Authority under an
RAA.
HID (Hierarchy ID):
The 32 bit field providing the HIT Hierarchy ID.
RAA (Registered Assigning Authority):
The 16 bit field identifying the Hierarchical HIT Assigning
Authority.
RVS (Rendezvous Server):
The HIP Rendezvous Server for enabling mobility, as defined in
[RFC8004].
3. Problem Space
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3.1. Meeting the future of Mobile Devices in a public space
Public safety may impose a "right to know" what devices are in a
public space. Public space use may only be permitted to devices that
meet an exacting "who are you" query. This implies a device identity
that can be quickly validated by public safety personal and even the
general public in many situations.
Many proposals for mobile device identities are nothing more than a
string of bits. These may provide information about the device but
provide no assurance that the identity associated with a device
really belongs to a particular device; they are highly susceptible to
fraudulent use. Further they may impose a slow, complex method to
discover the device owner to those with appropriate authorization.
The Host Identity Tag (HIT) from the Host Identity Protocol (HIP)
provides a self-asserting Identity through a public key signing
operation using the Host Identity's (HI) private key.
Although the HIT provides a "trust me, I am me" claim, it does not
provide an assertion as to why the claim should be trusted and any
additional side information about the device. The later could be
distributed directly from the device in a secure manner, but again
there is no 3rd-party assertion of such a claim.
3.2. Semi-permanency of Identities
A device Identity has some degree of permanency. A device creates
its identity and registers it to some 3rd-party that will assert a
level of trust for that identity. A device may have multiple
identities to use in different contexts, and it may deprecate an
identity for any number of reasons. The asserting 3rd-party may
withdraw its assertion of an identity for any number of reasons. An
identity system needs to facilitate all of this.
3.3. Managing a large flat address space
For HITs to be successfully used by a large population of mobile
devices, they must support an Identity per device; potentially 10
billion Identities. Perhaps a Distributed Hash Table [RFC6537] can
scale this large. There is still the operational challenges in
establishing such a world-wide DHT implementation and how RVS
[RFC8004] works with such a large population. There is also the
challenge of how to turn this into a viable business. How can
different controlling jurisdictions operate in such an environment?
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Even though the probability of collisions with 7B HITs (one HIT per
person) in a 96 bit flat address space is 3.9E-10, it is still real.
How are collisions managed? It is also possible that weak key
uniqueness, as has been shown in deployed TLS certificates
[WeakKeys], results in a much greater probability of collisions.
Thus resolution of collisions needs to be a feature in a global
namespace.
3.4. Defense against fraudulent HITs
How can a host protect against a fraudulent HIT? That is, a second
pre-image attack on the HI hash that produces the HIT. A strong
defense would require every HIT/HI registered and openly verifiable.
This would best be done as part of the R1 and I2 validation. Or any
other message that is signed by the HI private key.
4. The Hierarchical Host Identity Tag (HHIT)
The Hierarchical HIT (HHIT) is a small but important enhancement over
the flat HIT space. By adding two levels of hierarchical
administration control, the HHIT provides for device registration/
ownership, thereby enhancing the trust framework for HITs.
HHITs represent the HI in only a 64 bit hash and uses the other 32
bits to create a hierarchical administration organization for HIT
domains. Hierarchical HITs are "Using cSHAKE in ORCHIDs"
[new-orchid]. The input values for the Encoding rules are in
Section 4.3.5.
A HHIT is built from the following fields:
* 28 bit IANA prefix
* 4 bit HIT Suite ID
* 32 bit Hierarchy ID (HID)
* 64 bit ORCHID hash
4.1. HHIT prefix
A unique 28 bit prefix for HHITs is recommended. It clearly
separates the flat-space HIT processing from HHIT processing per
Section 4 of "Using cSHAKE in ORCHIDs" [new-orchid].
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4.2. HHIT Suite IDs
The HIT Suite IDs specifies the HI and hash algorithms. Any HIT
Suite ID can be used for HHITs, provided that the prefix for HHITs is
different from flat space HITs. Without a unique prefix,
Section 4.1, additional HIT Suite IDs would be needed for HHITs.
This would risk exhausting the limited Suite ID space of only 15 IDs.
4.3. The Hierarchy ID (HID)
The Hierarchy ID (HID) provides the structure to organize HITs into
administrative domains. HIDs are further divided into 2 fields:
* 16 bit Registered Assigning Authority (RAA)
* 16 bit Hierarchical HIT Domain Authority (HDA)
4.3.1. The Registered Assigning Authority (RAA)
An RAA is a business or organization that manages a registry of HDAs.
For example, the Federal Aviation Authority (FAA) could be an RAA.
The RAA is a 16 bit field (65,536 RAAs) assigned by a numbers
management organization, perhaps ICANN's IANA service. An RAA must
provide a set of services to allocate HDAs to organizations. It must
have a public policy on what is necessary to obtain an HDA. The RAA
need not maintain any HIP related services. It must maintain a DNS
zone minimally for discovering HID RVS servers.
This DNS zone may be a PTR for its RAA. It may be a zone in a HHIT
specific DNS zone. Assume that the RAA is 100. The PTR record could
be constructed:
100.hhit.arpa IN PTR raa.bar.com.
4.3.2. The Hierarchical HIT Domain Authority (HDA)
An HDA may be an ISP or any third party that takes on the business to
provide RVS and other needed services for HIP enabled devices.
The HDA is an 16 bit field (65,536 HDAs per RAA) assigned by an RAA.
An HDA should maintain a set of RVS servers that its client HIP-
enabled customers use. How this is done and scales to the
potentially millions of customers is outside the scope of this
document. This service should be discoverable through the DNS zone
maintained by the HDA's RAA.
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An RAA may assign a block of values to an individual organization.
This is completely up to the individual RAA's published policy for
delegation.
4.3.3. Example of the HID DNS
HID related services should be discoverable via DNS. For example the
RVS for a HID could be found via the following. Assume that the RAA
is 100 and the HDA is 50. The PTR record is constructed as:
50.100.hhit.arpa IN PTR rvs.foo.com.
The RAA is running its zone, 100.hhit.arpa under the hhit.arpa zone.
4.3.4. HHIT DNS Retrieval
The HDA SHOULD provide DNS retrieval per [RFC8005]. Assume that the
Host_ID suite of EdDSA25519 (5), RAA of 10 and the HDA of 20 and the
HHIT example is:
2001:5:a:14:a3ad:1952:ad0:a69e
The HHIT FQDN is:
2001:0005:a:14:a3ad:1952:0ad0:a69e.20.10.hhit.arpa.
The NS record for the HDA zone is constructed as:
20.10.hhit.arpa IN NS registry.foo.com.
registry.foo.com returns a HIP RR with the HHIT and matching HI. The
HDA sets its policy on TTL for caching the HIP RR. Optionally, the
HDA may include RVS information. Including RVS in the HIP RR may
impact the TTL for the response.
4.3.5. Changes to ORCHIDv2 to support Hierarchical HITs
A new format for ORCHIDs to support Hierarchical HITs is defined in
"Using cSHAKE in ORCHIDs" [new-orchid]. For this use the following
values apply:
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Prefix := HHIT Prefix
Note: per section 4.1, this should be different
than the Prefix for RFC 7401
OGA ID := 4-bit Orchid Generation Algorithm identifier
The HHIT Suite ID
Context ID := 0x00B5 A69C 795D F5D5 F008 7F56 843F 2C40
Info (n) := 32 bit HID (Hierarchy ID)
Hash := Hash_function specified in OGA ID
If hash is not a variable length output hash,
then en Encode_m, similar to ORCHID Encode_96
is used
m := 64
4.3.6. Collision risks with Hierarchical HITs
The 64 bit hash size does have an increased risk of collisions over
the 96 bit hash size used for the other HIT Suites. There is a 0.01%
probability of a collision in a population of 66 million. The
probability goes up to 1% for a population of 663 million. See
Appendix A for the collision probability formula.
However, this risk of collision is within a single HDA. Further, all
HDAs are expected to provide a registration process for reverse
lookup validation. This registration process would reject a
collision, forcing the client to generate a new HI and thus
hierarchical HIT and reapplying to the registration process.
5. IANA Considerations
Because HHIT use of ORCHIDv2 format is not compatible with [RFC7343],
IANA is requested to allocated a new 28-bit prefix out of the IANA
IPv6 Special Purpose Address Block, namely 2001:0000::/23, as per
[RFC6890].
6. Security Considerations
A 64 bit hash space presents a real risk of second pre-image attacks.
The HHIT Registry services effectively block attempts to "take over"
a HHIT. It does not stop a rogue attempting to impersonate a known
HHIT. This attack can be mitigated by the Responder using DNS to
find the HI for the HHIT or the RVS for the HHIT that then provides
the registered HI.
Another mitigation of HHIT hijacking is if the HI owner supplies an
object containing the HHIT and signed by the HI private key of the
HDA.
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The two risks with hierarchical HITs are the use of an invalid HID
and forced HIT collisions. The use of the "hhit.arpa." DNS zone is
a strong protection against invalid HIDs. Querying an HDA's RVS for
a HIT under the HDA protects against talking to unregistered clients.
The Registry service has direct protection against forced or
accidental HIT hash collisions.
7. Acknowledgments
The RDA/HDA 16/16 bit split, replacing the original 14/18 split was
the result of discussions on lookup and implementation challenges of
byte boundaries over nibble boundaries.
The initial versions of this document were developed with the
assistance of Xiaohu Xu and Bingyang Liu of Huawei.
Sue Hares contributed to the clarity in this document.
8. References
8.1. Normative References
[new-orchid]
Moskowitz, R., Card, S., and A. Wiethuechter, "Using
cSHAKE in ORCHIDs", Work in Progress, Internet-Draft,
draft-moskowitz-orchid-cshake-00, 11 December 2019,
<https://tools.ietf.org/html/draft-moskowitz-orchid-
cshake-00>.
[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>.
[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>.
[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>.
8.2. Informative References
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[draft.moskowitz-hip-arch-02]
Moskowitz, R., "Host Identity Payload", Superseded
Internet-Draft, draft-moskowitz-hip-arch-02, 22 February
2001.
[draft.zhang-hip-hierarchical-parameter-00]
Dacheng, Z. and X. Xiaohu, "Extensions of Host Identity
Protocol (HIP) with Hierarchical Information", Abandoned
Internet-Draft, draft-zhang-hip-hierarchical-parameter-00,
27 May 2009.
[hhit-registries]
Moskowitz, R., Card, S., and A. Wiethuechter,
"Hierarchical HIT Registries", Work in Progress, Internet-
Draft, draft-moskowitz-hip-hhit-registries-02, 9 March
2020, <https://tools.ietf.org/html/draft-moskowitz-hip-
hhit-registries-02>.
[RFC6537] Ahrenholz, J., "Host Identity Protocol Distributed Hash
Table Interface", RFC 6537, DOI 10.17487/RFC6537, February
2012, <https://www.rfc-editor.org/info/rfc6537>.
[RFC6890] Cotton, M., Vegoda, L., Bonica, R., Ed., and B. Haberman,
"Special-Purpose IP Address Registries", BCP 153,
RFC 6890, DOI 10.17487/RFC6890, April 2013,
<https://www.rfc-editor.org/info/rfc6890>.
[RFC7343] Laganier, J. and F. Dupont, "An IPv6 Prefix for Overlay
Routable Cryptographic Hash Identifiers Version 2
(ORCHIDv2)", RFC 7343, DOI 10.17487/RFC7343, September
2014, <https://www.rfc-editor.org/info/rfc7343>.
[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>.
[RFC8005] Laganier, J., "Host Identity Protocol (HIP) Domain Name
System (DNS) Extension", RFC 8005, DOI 10.17487/RFC8005,
October 2016, <https://www.rfc-editor.org/info/rfc8005>.
[WeakKeys] Heninger, N.H., Durumeric, Z.D., Wustrow, E.W., and J.A.H.
Halderman, "Detection of Widespread Weak Keys in Network
Devices", August 2012,
<https://factorable.net/weakkeys12.extended.pdf>.
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Appendix A. Calculating Collision Probabilities
The accepted formula for calculating the probability of a collision
is:
p = 1 - e^{-k^2/(2n)}
P Collision Probability
n Total possible population
k Actual population
Authors' Addresses
Robert Moskowitz
HTT Consulting
Oak Park, MI 48237
United States of America
Email: rgm@labs.htt-consult.com
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
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