Hierarchical HITs for HIPv2HuaweiOak ParkMI48237USArgm@htt-consult.comHuaweiHuawei Bld, No.156 Beiqing Rd.BeijingHai-Dian District100095Chinaxuxiaohu@huawei.com
Internet
HIPRFCRequest for CommentsI-DInternet-DraftHIP
This document describes using a hierarchical HIT to facilitate large
deployments in mobile networks.
This document expands on HIPv2 to
describe the structure of a hierarchical HIT, the Registry services
to support this hierarchy, and given a hierarchical HIT, how a peer
is found in the network.
A separate document will further expand on the registry service and
how a device can advertise its availability and services provided.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described
in RFC 2119.
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 HIP to be successfully used in mobile networks, it must support
an Identity per person, or upwards to 10 billion Identities.
Perhaps a Distributed Hash Table can scale this large. There is still the operational
challenges in establishing such a world-wide DHT implementation and
how RVS works with
such a large population.
Even though the probability of collisions with 7B HITs in a 96 bit
flat address space is 3.9E-10, it is still real. How are
collisions managed? It is also possible with weak key uniqueness,
as has been shown in deployed TLS certificates, results in a much
greater probability of collisions. Thus resolution of collisions
needs to be a feature in a globally mobile network.
An RVS provider may only what to provide discovery services to HIP
clients it knows and trusts. A flat HIT space does not provide any
intrinsic functionality to support this. A hierarchical HIT space
can be mapped to the RVS provider.
The Hierarchical HIT is a small but important enhancement over the
flat HIT space. It represents 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 ORCHIDs. The change in construction rules
are in .
A Hierarchical HIT is built from the following fields:
28 bit IANA prefix
4 bit HIT Suite ID
32 bit Hierarchy ID (HID)
64 bit ORCHID hash
The Hierarchy ID (HID) provides the structure to organize HITs into
administrative domains. HIDs are further divided into 2 fields:
14 bit Registered Assigning Authority (RAA)
18 bit Hierarchical HIT Domain Authority (HDA)
The RAA is a 14 bit field (16,384 RAAs) assigned sequentially by a
numbers management organization, perhaps ICANN. 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 for discovering HID RVS servers.
This DNS zone may be a reverse PTR for its RAA. Assume that the
RAA is 100. The PTR record is constructed at a 2 bit grouping:
The HDA is an 18 bit field (262,144 HDAs per RAA) assigned
sequentially 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.
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.
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 at
a 2 bit grouping:
ORCHIDv2 has a number of inputs including a context, some header
bits, the hash algorithm, and the public key. The output is a 96
bit value. Hierarchical HIT makes the following changes. The HID
is added as part of the header bits and the output is a 64 bit
value, derived the same way as the 96 bit hash.
Hierarchical HIT uses the same context as all other HIPv2 HIT
Suites as they are clearly separated by the distinct HIT Suite ID.
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
for the collision probability formula.
This risk, however, 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.
The HIP parameters carry information that is necessary for
establishing and maintaining a HIP association. For example,
the peer'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 HIT_SUITE_LIST parameter contains a list of the supported
HIT suite IDs of the Responder. Based on the HIT_SUITE_LIST,
the Initiator can determine which source HIT Suite IDs are
supported by the Responder. The HIT_SUITE_LIST parameter is
defined in Section 5.2.10 of .
The following HIT Suite IDs are defined for Hierarchical HITs,
and the relationship between the four-bit ID value used in the
OGA ID field and the eight-bit encoding within the
HIT_SUITE_LIST ID field is clarified:
Note that the Hierarchical HIP HIT Suite ID allows the peers to
use the hierarchical RVS discovery and authentication services
to validate the peer and discover available services. The
Responder SHOULD respond with a HIP hierarchical HIT suite ID
when the HIT of the Initiator is a HIP hierarchical HIT.
This parameter contains client information to include in the HIT
registration. The specific content and format is set by the HDA.
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 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.
This requires the HIP client and the HDA/Registrar to share a PSK.
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 Registration Type used in the REG_REQUEST is:
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:
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 reregister. 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, probably 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.
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.
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. 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.
The following change to the "Host Identity Protocol (HIP) Parameters"
registries has been made:
This document defines the new HIT Suite "Hierarchy with
ECDSA/SHA256" (see ).
This document defines the new CLIENT_INFO parameter (see
). The parameter value will be
assigned by IANA.
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 ).
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 using its hierarchical
HIT.
The two risks with hierarchical HITs is the use of an invalid HID
and forced HIT collisions. 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 discovery process relies on trusting the finding
the proper HDA for the peer 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.
The accepted formula for calculating the probability of a collision
is: