Hierarchical HIT RegistriesHTT ConsultingOak ParkMI48237USArgm@labs.htt-consult.comAX Enterprize4947 Commercial DriveYorkvilleNY13495USAstu.card@axenterprize.comAX Enterprize4947 Commercial DriveYorkvilleNY13495USAadam.wiethuechter@axenterprize.com
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HIPRFCRequest for CommentsI-DInternet-DraftHIP
This document describes using the registration protocol and
registries to support hierarchical HITs (HHITs). New and existing
HIP parameters are used to communicate Registry Policies and data
about the HHIT device and the Registries. Further Registries are
expected to provide RVS services for registered HHIT devices.
This document expands on Hierarchical
HITs, defining HIP registration protocol enhancements, the
Registry services to support hierarchical HITs (HHITs), and given a
HHIT, how to get additional information about the device.
Registries will tend to be organized regionally and by nature of
their clients. For example, an RAA may be US centric and only have
HDAs that are US-based.
Registries will need to work in a federation. Devices that are
clients of one HDA/RAA will be needing information and connectivity
to devices that are clients of other HDA/RAA. The policies for
establishing such federations are outside the scope of this
document.
Access to information at a Registry about a device may require
authorization. The nature and process of such an authorization is
outside the scope of this document.
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 when, and only when, they appear in all
capitals, as shown here.
Request to a Certificate Authority to create an X.509
certificate with the provided information.
The 14 bit field identifying the HIT Domain Authority under a RAA.
The 32 bit field providing the HIT Hierarchy ID.
The 18 bit field identifying the Hierarchical HIT Assigning
Authority.
For HHITs to be effectively used, the HHIT Domain Authorities
(HDAs) need to provide information on the HHIT devices. Minimally
this would be the corresponding HI, information on the device owner
(only to authorized requesters), and where in the network the
device has last reported from.
The HHIT space creates a type of a business labeling for the HDAs.
"These are my customers."
An RVS provider may only be willing to provide discovery (RVS)
services to HIP devices it knows and trusts. A flat HIT space does
not provide any intrinsic functionality to support this. A HHIT
space can be mapped to the RVS provider. DNS can effectively be
used to provide the HHIT to IP mapping without Distributed Hash Table (DHT).
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. With HHITs, the HDAs can provide the HI and proof of
registration (e.g. X.509 certificate including HHIT).
This would best be done as either part of the R1 and I2 validation,
or anytime a HHIT is presented.
Hierarchical HIT registration SHOULD be performed using the HIP
Registration Extension . The client
either uses an X.509 certificate ,
or use a PSK, as defined in Appendix A of HIP-DEX , to validate the registration.
The Registration should include additional client information. This
information may be contained within the X.509 certificate (CERT
parameter) and/or is carried in the CLIENT_INFO parameter, see
. The Registrar can include its
requirements in the R1 packet, and the client provide its
information in the I2 packet. This parameter may be encrypted
within the ENCRYPTED parameter. If the CLIENT_INFO contains
Personal Identifying Information (PII), then it MUST be placed into
the ENCRYPTED parameter.
The content and internal format of the CLIENT_INFO parameter is set by
the HDA"s policy and is outside the scope of this document. Examples
of client information can by phone number, IMEI, and ICCID.
This requires the HIP client to possess a client certificate
trusted by the HDA/Registrar. Registration will either succeed or
fail.
Certificate registration can be a "chicken and egg" problem: where
did the device get its certificate? Thus this is more likely used
in a re-registration situation with updated information.
This requires the HIP client and the HDA/Registrar to share a PSK.
The PSK is carried in the ENCRYPTED_KEY parameter . The PSK may already exist prior
to starting the registration and just be used within the
registration. A PSK out-of-band exchange may be triggered by
performing the registration without any authentication.
If no client authentication is included in the I2 packet, the
registration fails with "No Authentication provided". If the I2
packet included the proper HDA required client information, the HDA
can use it to set up a side channel for an out-of-band delivery of
a PSK. And example of this would be to send an SMS message with
the PSK. Once the client possesses the PSK, it can rerun the
registration at which point the HI and HIT duplicate checks are
performed.
The I2 packet may contain a CERT parameter containing a CSR, and
the R2 would return the X.509 certificate for later use.
The HIP parameters carry information that is necessary for
establishing and maintaining a HIP association. For example,
the device's public keys as well as the signaling for negotiating
ciphers and payload handling are encapsulated in HIP
parameters. Additional information, meaningful for end hosts
or middleboxes, may also be included in HIP parameters. The
specification of the HIP parameters and their mapping to HIP
packets and packet types is flexible to allow HIP extensions to
define new parameters and new protocol behavior.
The CERT parameter, , is a container
for certain types of digital certificates.
A new CERT Type, CSR, is defined here. When CERT Type is CSR, CERT
ID is Zero. There is only ONE CSR in a CERT Parameter.
CERT format Type number RFC
------------- ----------- ----
PKCS#10 - CSR 9 2986
The Registration Type used in the REG_REQUEST is:
Number Registration Type
------ -----------------
2 HHIT Registration
The Registration may fail. In fact, with PSK, this may be the
response to expect an SMS message with the PSK to use in a second
registration request. Failure Types used in the REG_FAIL are:
Failure Type Reason
------------ -----------------------
[TBD-IANA] Hierarchical HIT Already Registered
[TBD-IANA] HI Already Registered
[TBD-IANA] Previously Registered HI with different
device information
[TBD-IANA] No Authentication provided
[TBD-IANA] Invalid Authentication
[TBD-IANA] Invalid Authentication, new PSK sent via SMS
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ Client Information /
/ /
/ +-------------------------------+
/ | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type [TBD-IANA]
Length length in octets, excluding Type, Length, and
Padding
Client The information required by the HDA in the format
Information required by the HDA.
This parameter contains client information to include in the HIT
registration. The specific content and format is set by the HDA.
If the failure type is "Hierarchical HIT Already
Registered", the client's HI is hashing to an existing HIT and must
generate a new HI and hierarchical HIT and re-register. If the
failure is "HI Already Registered", the client should assume it is
registered. If the failure is "Previously Registered HI with
different device information", either the client managed to
generate a duplicate HI, possibly indicating a weak key generation
algorithm, or the client was previously registered on a different
device. Resolving this conflict will be left to the HDA's policy.
A simple HDA policy would be to require the device to generate a
new HI and thus HHIT and try registration again. The HDA policy
may also provide a URL for "Previous Registration Resolution".
This contact is primarily to assist a device that was registered,
but had some local failure resulting in a new registration attempt.
All HIP clients with hierarchical HITs maintain an RVS connection
with their HDA's RVS server(s). How the HDA scales this service up
to a potential population in the millions is out of scope of this
document. Lifetime management of these connections is also out of
scope.
One approach an HDA can use to address the scaling challenge is to
add an internal level of hierarchy to assign a set number of
devices per RVS server.
Peering agreements between HDAs would allow for geographically
close RVS to a device. This may reduce the latency for use of a
device's current RVS. This is a subject of another document.
A service Initiator uses some service to discover the HIT of the
service Responder. The Initiator uses the hierarchical information
in the HIT to find the Responder's RVS. A trusted RVS discover
method could use the DNS PTR to RVS as shown in Hierarchical
HITs. An I1 is sent to that RVS which forwards it to the
Responder.
The potential Responder uses the HIT in the I1 to query the
Initiator's RVS about the Initiator. The nature of information,
and method of communication are determined by the Initiator's HDA
and the Responder's (and or HDA"s) relationship with it. Based on
the Responder's local policy, this information will be used to
determine if the contact is to be accepted. If accepted, the
Responder may proceed sending an R1 to the Initiator. It may
alternatively initiate some non-HIP process.
It should be noted that this R1 may contain a REG_INFO list for the
Initiator to validate that the Responder does offer the desired
service.
Both the Initiator and Responder MAY validate a peer host as a
defense against a second pre-image attack on the HHIT. This may
occur via a CERT in R1 or I2. It may
be through a back end process associated with the R1 or I2
validation to look up the HHIT and retrieve the registered HI.
IANA will need to make the following changes to the "Host
Identity Protocol (HIP) Parameters" registries:
This document defines the new CERT Type for the
CERT parameter "PKCS#10 - CSR" (see ).
This document defines the new Registration Type for the
REG_REQUEST parameter "HIT Registration" (see ).
This document defines the new Failure Types for the REG_FAIL
parameter (see ).
This document defines the new CLIENT_INFO parameter (see
). The parameter value will be
assigned by IANA.
Introducing the RAA management organization may be the largest
hurdle for hierarchical HITs. Thus it would be best if this were
adopted by an organization already in the business of allocating
numbers within either the Internet or the Mobile, cellular,
infrastructure.
One consideration would be to reserve the first N RAA values to map
to the existing DNS TLDs. For example, these TLDs can be organized
in an ascending order and numbered accordingly. Thus the 2
character TLDs will be a lower number than the 3 character TLDs.
After that, it could be a first come, first numbered assignment
process.
There are potential risks with the hierarchical HIT, the Registry
service, and the discovery of potential peer hosts using its
hierarchical HIT.
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.
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.
By using the HIP Registration Extension, the Registry service is
protected from direct attacks. This service does rely on either
the integrity of a PKI service or an out-of-band PSK delivery
process. Thus the risk to the Registry service is highly related
to the trust in these authentication setup services. Further, the
duplicate HI resolution process may require human interaction with
related social engineering risks.
Finally the peer host discovery process relies on trusting the
finding the proper HDA for the host and its forwarding the I1 to
the proper Responder. A rogue RVS, impersonating the RVS for the
HIT, could redirect the I1 to a client that has forced a collision
with the HIT and the Initiator would be none the wiser. The only
defense against this is if the Initiator has some other source for
the Responder HI and validate the HI in the R1.
Mobile-privacy-attack
details how Eve can follow a communication between two mobile peers
using the session Identifiers and deep knowledge about those
Identifiers gained by hacking servers that log PII related to the
Identifiers.
Hierarchical HITs not only does not mitigate this attack, it can
actually aggravate it by supplying the HDA where the HHIT is
registered.
A HIP Privacy Enhanced Base Exchange, to be defined in a separate
draft, along with a Privacy Enhanced ESP tunnel, can be used to
hide all the HIP and ESP Identifiers from Eve.
Sue Hares of Huawei contributed to the clarity in this document.
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