James Kempf
Internet Draft Craig Gentry
Document: draft-kempf-abk-nd-00.txt Alice
Silverberg
Expires: November 2003 May 2003
Securing IPv6 Neighbor Discovery Using Address Based Keys (ABKs)
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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Abstract
When an IPv6 node receives a Router Advertisement, how does it
know that the node which sent the advertisement is authorized to
announce that it routes the prefix? When an IPv6 node receives a
Neighbor Advertisement message, how does it know that the node
sending the message is, in fact, authorized to claim the binding?
The answer is, in the absence of a preconfigured IPsec security
association among the nodes on the link and the routers, they
don't. In this draft, a lightweight protocol is described for
securing the signaling involved in IPv6 Neighbor Discovery. The
protocol allows a node receiving a Router Advertisement or a
Neighbor Advertisement to have the confidence that the message was
authorized by the legitimate owner of the address or prefix being
advertised without requiring a preconfigured IPsec security
association. A certain degree of infrastructural support is
required, but not any more than is currently common for public
access IP networks. The protocol is based on some results in
identity based cryptosystems that allow a publicly known
identifier to function as a public key.
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Contents
1.0 Introduction..................................................2
2.0 Terminology...................................................3
3.0 What are Identity Based Cryptosystems?........................4
4.0 Digital Signature Calculations................................5
5.0 Host and Router Configuration.................................6
5.1 Router Configuration..........................................6
5.2 Host Configuration............................................6
6.0 Securing Router Advertisement.................................7
6.1 Router Advertisement Signature................................7
6.2 Verifying a Router Advertisement..............................8
6.3 Negotiating an Identity based Algorithm.......................8
7.0 Securing Neighbor Discovery...................................9
7.1 Neighbor Advertisement Signature..............................9
7.2 Verifying a Neighbor Advertisement............................9
7.3 Negotiating an Identity Based Algorithm.......................9
8.0 Option Formats...............................................10
8.1 Identity Digital Signature Option............................10
8.2 Identity Algorithm Option....................................11
9.0 Identity Based Key Algorithms................................11
10.0 Previous Work..............................................13
11.0 Infrastructure Requirements................................14
12.0 Security Considerations....................................15
13.0 References.................................................15
14.0 Author's Contact Information...............................16
15.0 Full Copyright Statement...................................17
1.0 Introduction
The IPv6 Neighbor Discovery protocol described in RFC 2461 [1]
plays a critical role in last hop network access for IPv6 nodes.
The protocol allows a IP node joining a link to discover a default
router, and for nodes on the link, including the routers, to
discover the link layer address of an IP node on the link to which
IP traffic must be delivered. Disruption of this protocol can have
a serious impact on the ability of nodes to send and receive IP
traffic.
Yet, security on the protocol is weak. As stated in the Security
Considerations section of RFC 2461:
The protocol contains no mechanism to determine which
neighbors are authorized to send a particular type of
message...; any neighbor, presumably even in the presence of
authentication, can send Router Advertisement messages
thereby being able to cause denial of service. Furthermore,
any neighbor can send proxy Neighbor Advertisements as well
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as unsolicited Neighbor Advertisements as a potential denial
of service attack.
In [2], a list of threats to IPv6 Neighbor Discovery on multi-
access links is outlined. The threats don't occur on point to
point links because the default router and IP address for a host
are determined by PPP negotiation and so Neighbor Discovery is not
required. These threats can occur for both wired and wireless
public multi-access links. They are a particular problem for
wireless links, however, because even private multi-access links
over shared access (as opposed to switched) media with link level
authentication mechanisms such as 802.1x [22] are subject to
disruption if an authenticated node decides to play the trickster.
There are two underlying causes of these threats: a router
advertising a prefix that it is not authorized to route or a node
claiming an IPv6 address that it is not authorized to claim. These
threats occur because the messaging involved in Neighbor Discovery
by default contains no authentication information allowing the
receiver to authenticate the sender. RFC 2461 recommends using
IPsec AH authentication [4] if a security association exists, but
this is a fairly heavyweight solution and is unlikely to be widely
applicable to public access networks. In particular, a roaming
node in a foreign public access network is unlikely to have a
security association with a local access router or with other
nodes on the same link. Indeed, most of the nodes on the same link
may not even have the same home ISP as the roaming node. In
addition, using IKE [28] or any other IPv6 protocol to establish a
dynamic security association won't work if the protocol requires
unsecured Neighbor Discovery. Manual keying can be used, but is
impractical for public access networks.
In this document, a lightweight protocol that secures IPv6
Neighbor Discovery is described. The protocol allows IP nodes to
verify that a node advertising routing for a local subnet prefix
is authorized to advertise the prefix, and that information
provided in a Neighbor Discovery message is authorized by the
sending node. A certain amount of infrastructure is required, but
no more than is currently needed for public access IP networks. In
particular, no extension of the current NAS-based AAA
infrastructure [24] nor a global PKI are necessary. The protocol
depends on some results in identity based cryptosystems whereby a
publicly known identifier, in this case, parts of a node's IP
address, can serve as a public key. The technique whereby
addresses are used to generate public/private key pairs is called
Address Based Keys (ABKs).
2.0 Terminology
Address Based Keys (ABKs) - A technique whereby an identity
based cryptosystem is used to generate a node's public and
private key from its IPv6 subnet prefix or interface
identifier.
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Identity based cryptosystem - A cryptographic technique that
allows a publicly known identifier, such as the IPv6
address, to be used as a public key for authentication, key
agreement, and encryption.
Identity based Private Key Generator (IPKG) - An agent that
is capable of executing an identity based cryptographic
algorithm to generate a private key when presented with the
public identifier that will act as the public key. The IPKG
is the root of trust in identity based crytosystems.
Public cryptographic parameters - A collection of publicly
known parameters which the IPKG uses to generate the node's
private key and which two nodes involved in securing or
encrypting a message use to perform cryptographic
operations. The public cryptographic parameters are formed
from chosen constants and a secret key known only to the
IPKG, specific to the identity based cryptographic
algorithm.
Network Access Server (NAS) - A server that performs
Authentication, Authorization, and Accounting (AAA) for
nodes in a public access network.
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 [23].
3.0 What are Identity Based Cryptosystems?
Identity based cryptosystems are a collection of cryptographic
techniques that allow a publicly known identifier, such as the
email address or (particularly important in this application) the
IP address of a node, to function as the public key part of a
public/private key pair for purposes of digital signature
calculation, key agreement, and encryption. Section 9.0 provides a
quick overview of the available algorithms, with an extensive
reference list. While identity based cryptosystems have been
investigated for almost 20 years in the cryptographic community,
they have not been widely discussed in the network security
community. The reason is unclear, but it might have to do with the
popularity and algorithmic simplicity of the reigning standard
Diffie-Hellman technique, or possibly to the fact that, until
recently, there have been no known identity based cryptographic
algorithms that can be used to perform encryption. The existing
algorithms have been restricted to digital signature calculation,
and therefore have been fairly limited in scope. Hopefully, should
identity based cryptosystems prove useful to the network security
community, increased communication between the cryptography and
network security communities will lead to a refinement of the
algorithms and applications of identity based algorithms for
application to securing IPv6 signaling.
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Elliptic curve (EC) algorithms are particularly attractive for
identity based keys because they work well with small key sizes,
are computationally efficient on small nodes, such as small
wireless devices, and may generate smaller signatures. In
addition, while non-EC algorithms have been proposed for identity
based digital signature calculation, at the time of this writing,
the most efficient way of performing identity based encryption is
an EC algorithm.
Identity based cryptosystems work in the following way. A publicly
known identifier is submitted to an IPKG. In this application, the
publicly known identifier is either the 64 bit subnet prefix or
the unique 64 bit interface identifier of an IPv6 address. The
IPKG uses a particular algorithm to generate the private key and
returns it. The public and private key can now be used for
authentication and encryption as is typical in cryptosystems.
4.0 Digital Signature Calculations
Digital signatures MUST be calculated using the following
algorithm:
sig = SIGN(hash(contents),IPrK,Params)
where:
sig - The digital signature.
SIGN - The identity based digital signature algorithm
used to calculate the signature.
hash - The HMAC-SHA1 one-way hash algorithm.
IPrK - The Identity based Private Key.
Params - The public cryptographic parameters.
contents - The message contents to be signed.
The digital signature MUST be verified using the following
algorithm:
IPuK = IBC-HASH(ID)
valid = VERIFY(hash(contents),sig,IPuK)
where:
IBC-HASH - A hash function specific to the identity based
algorithm that generates the public key from the
public identifier.
ID - The publicly known identifier used to generate
the key.
IPuK - The Identity based Public Key.
sig - The digital signature.
VERIFY - The identity based public key algorithm used to
verify the signature.
Params - The public cryptographic parameters.
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valid - 1 if the signature is verified, 0 if not.
5.0 Host and Router Configuration
Hosts and last hop routers participating in Neighbor Discovery
require configuration with the identity based private key and with
cryptographic parameters before they can secure messaging.
5.1 Router Configuration
When the ISP or network owner sets up its last hop routers, the
routers are configured with the 64 bit subnet prefix or prefixes
that they should advertise. In addition, the ISP uses its IPKG to
generate a private key per prefix. The router uses this key in
generating digital signatures on Router Advertisements. The
private key and the public cryptographic parameters MUST be
installed on the router through a secure channel. Examples of
possible secure channels include configuration by a network
administrator, installation via an NAS-based AAA network capable
of secure key distribution, installation via a secure message
exchange to a server with which the router has an IPsec security
association, etc.
5.2 Host Configuration
Hosts require an identity based private key associated with their
64 bit interface identifier [3] in the IPv6 address, and the
public cryptographic parameters. There are two possible ways in
which the host can be configured:
- Dynamically, when the host is initially authenticated and
authorized for network access through a secure connection
with the local network's NAS,
- Statically, when its home ISP initially assigns the interface
identifier.
If the dynamic configuration method is used, the local network
must keep track of interface identifiers to avoid duplicates. If
the static configuration method is used, the cryptographic
parameters for the local network's router must be installed on a
roaming host, since the router's parameters may not be the same as
those for the roaming host. Dynamic and static configuration are
discussed in the next two paragraphs.
Most public access networks currently require a host to undergo a
secure authentication and authorization exchange through a NAS
prior to being able to use the network. Since this exchange is
typically performed at Layer 2 before any IP signaling, it can be
done prior to any Neighbor Discovery signaling. The host includes
its interface identifier in a message to the NAS. The NAS sends
the interface identifier to the IPKG, where the private key is
generated. The private key and public cryptographic parameters are
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then securely transferred back to the host where they are
installed. The host uses this private key for securing IPv6
Neighbor Discovery traffic on the foreign network, not for
securing any private data, because the key belongs to the foreign
network. After router discovery, the host uses the interface id
and subnet prefix from the router to construct the router's IP
address using IPv6 Stateless Address Autoconfiguration. The hosts
on the local link and the last hop router then use the public
cryptographic parameters and the private keys given to them by the
network to secure IPv6 Neighbor Discovery signaling.
Some public access networks may not perform secure Layer 2
authentication and authorization prior to allowing the host to
perform Neighbor Discovery. In order to accommodate these kinds of
networks, hosts MUST be configured with public cryptographic
parameters and a private key by their home ISPs or network
operators. The messaging for securing Neighbor Discovery includes
an identifier based on the realm portion of the NAI [25]. The
realm identifies the host's home ISP. This identifier allows the
hosts and routers on the local link to authenticate the signaling
of guest hosts. However, some method is needed to co-ordinate
distribution of public cryptographic parameters between ISPs.
ISPs commonly use roaming consortia to provide remote access in
areas where they do not have POPs. A group of ISPs organize into a
roaming consortium to facilitate billing settlement and
authentication. Roaming consortia can be used to support ABKs as
well. A group of ISPs in a roaming consortium co-ordinate IPKGs so
that the various ISPs in the consortium can accommodate guest
hosts. The IPKGs use the same public cryptographic parameters, or
are organized into an IPKG hierarchy [29]. Any private information
(like a secret key) would need to be distributed between ISPs by
secure means, such as a secure AAA connection or by hand.
6.0 Securing Router Advertisement
In this section, a protocol for securing the IPv6 Router
Advertisement messages is discussed.
6.1 Router Advertisement Signature
A Router Advertisement sent by a router configured with a 64 bit
prefix key contains a digital signature. The signature MUST sign
the entire message.
In the signing algorithm described in Section 4.0, the input into
the HMAC-SHA1 algorithm is the following:
contents = (chl,fl,rol,rel,rtt,sllao,mtuo,pro,dso,...)
IPrK in the signing algorithm is the private key having the
router's 64 bit subnet prefix as its public key.
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The digital signature MUST be included in an Identity Digital
Signature option (see Section 8.1) with the signature, algorithm,
and realm identifier. An ICMP option is used instead of IPsec AH
[4] because Neighbor Discovery options that are not recognized by
a host are ignored, so a host that can't verify the signature but
is interested in risking using an unsecured Router Advertisement
can simply ignore the option as a consequence of normal Neighbor
Discovery processing, as opposed to having the Router
Advertisement rejected by IPsec processing.
The Router Advertisement MUST contain a single Prefix option with
the prefix for which the key was assigned. If the router also
announces other prefixes, it MUST advertise them using separate
Router Advertisements. If the router supports multiple identity
based algorithms, it MAY include multiple Identity Digital
Signature options with signatures calculated by the various
algorithms, up to the path MTU.
6.2 Verifying a Router Advertisement
An IPv6 host receiving a Router Advertisement with an Identity
Digital Signature Option verifies that the advertising node is
authorized to send the advertisement in the following way. If the
Router Advertisement does not contain a routing prefix option, or
if it contains more than one routing prefix option, the host
SHOULD discard the Router Advertisement, unless the host wants to
risk using an unsecured Router Advertisement. If the host does not
support one of the algorithms used for signing the message, it
SHOULD discard the Router Advertisement, unless the host wants to
risk using an unsecured Router Advertisement.
The host locates the single routing prefix option and extracts the
subnet prefix which the sending node claims it is allowed to
route. The host then uses the verification algorithm in Section
4.0 to verify the digital signature using the same value for
contents as in Section 6.1. In this calculation, ID is the subnet
prefix in the Prefix option. The identity based algorithm and
router public cryptographic parameters depend on the algorithm and
realm identifier in the Identity Digital Signature option.
6.3 Negotiating an Identity based Algorithm
A lengthy negotiation process for determining which identity based
algorithm to use is obviously not in the interest of supporting a
lightweight protocol. However, algorithms do change over time, and
therefore it is necessary to have some way whereby a host can
indicate in a Router Solicitation which algorithms it supports. If
the router cannot provide an authenticator for any of the
algorithms, it can simply return an unauthenticated Router
Advertisement and the host can take its chances. For this purpose,
the host uses an Identity Algorithm option (see Section 8.2).
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For multicast Router Advertisements, the router can include
Identity Digital Signature options for each algorithm it supports,
up to the path MTU. Alternatively, the host can be required to
solicit the Router Advertisement and tell the router what
algorithms it supports in an Identity Algorithm option.
7.0 Securing Neighbor Discovery
A similar procedure is used for securing IPv6 Neighbor Discovery
messages.
7.1 Neighbor Advertisement Signature
A Neighbor Advertisement sent message contains a digital signature
calculated with the private key generated from the 64 bit
interface identifier and the host public cryptographic parameters.
The signature MUST be calculated over the entire message.
The Target Link Layer Address option MUST be included.
In the signing algorithm described in Section 4.0, the input into
the hash algorithm is the following:
contents = (flg,addr,l2addr)
IPrK is the interface identifier private key.
The digital signature MUST be included in an Identity Digital
Signature option (see Section 8.1) with the signature, algorithm,
and realm identifier. Again, an ICMP option is used instead of
IPsec AH because Neighbor Discovery options that are not
recognized by a node are ignored.
7.2 Verifying a Neighbor Advertisement
An IPv6 node receiving a Neighbor Advertisement with an Identity
Digital Signature option verifies that the advertising node is
authorized to send the advertisement in the following way. If the
receiving node does not support one of the algorithms used for
encrypting the signature, it SHOULD discard the Neighbor
Advertisement, unless the node wants to risk using an unsecured
Neighbor Advertisement.
The node uses the verification algorithm in Section 4.0 to verify
the digital signature using the same value for contents as in
Section 7.1. In this calculation, ID is the sending node's 64 bit
interface identifier. The identity based algorithm and node public
cryptographic parameters depend on the algorithm and realm
identifier in the Identity Digital Signature option.
7.3 Negotiating an Identity Based Algorithm
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A node sending a Neighbor Solicitation message can indicate what
algorithms it is capable of accepting by including an Identity
Algorithm option in the message.
8.0 Option Formats
8.1 Identity Digital Signature Option
The Identity Digital Signature Option contains a digital signature
calculated using address based private key. It is always the last
option in the list. The format of this option, after [1], is:
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 | Algorithm Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Realm Identifier |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ +
| Digital Signature (N bits) |
+ +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
Type 8 bit identifier for the option type,
assigned by IANA.
Length 8 bit unsigned integer giving the
option length (including type and
length fields) in units of 8 octets.
Algorithm Identifier 16 bit nonzero algorithm
identifier,assigned by IANA,
indicating the identity based
algorithm used to sign the message.
Realm Identifier Either the 64 bit nonzero HMAC-SHA1
hash of the realm part of the NAI
[25], or zero to indicate that the
current network's IPKG and public
cryptographic parameters should be
used.
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Digital Signature An N bit field containing the digital
signature. The field is zero aligned
to the nearest 8 byte boundary. The
exact number of bits is depends on
the identity based algorithm and use.
8.2 Identity Algorithm Option
The Identity Algorithm Option allows a node to indicate which
identity based keying algorithms it supports for particular realms
when requesting a Router Advertisement or Neighbor Advertisement.
The Identity Algorithm Option has the following format:
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 | Algorithm Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Realm Identifier | ... /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
Type 8 bit identifier for the option type,
assigned by IANA.
Length 8 bit unsigned integer giving the
option length (including type and
length fields) in units of 8 octets.
Algorithm Identifier 16 bit nonzero algorithm
identifier,assigned by IANA,
indicating the identity based
algorithm used to sign the message.
Realm Identifier Either the 64 bit nonzero HMAC-SHA1
hash of the realm part of the NAI
[25], or zero to indicate the current
network's algorithm.
and the option contains as many algorithm identifier-realm
identifier pairs, in order of preference, as the node supports.
The option is zero padded to multiples of 8 bytes. The
9.0 Identity Based Key Algorithms
Shamir [19] introduced the idea of identity based cryptography in
1984. Practical, provably secure identity based signature schemes
[12], [11], [13] and Key Agreement Protocols [16] soon followed.
Practical, provably secure identity based encryption schemes [8],
[10] have only very recently been found.
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In identity based signature protocols, the node signs a message
using its private key supplied by its IPKG and the public
cryptographic parameters. The signature is then verified using the
node's identity together with the public cryptographic parameters.
In identity based key agreement protocols, two parties share a
secret. Each party constructs the secret by using its own private
key and the other party's public identity. In identity based
encryption, the encryptor uses the recipient's public identity to
encrypt a message, and the recipient uses its private key to
decrypt the ciphertext.
As is generally the case with public-key cryptography, the
security of the systems is based on the difficulty of solving a
hard number theory problem, such as factoring or a discrete log
(or Diffie-Hellman) problem.
Elliptic curves and associated pairings have solved the problem of
how to do identity based encryption [8], and are used to construct
identity based signature [18][14][9] and key agreement [18][21]
protocols.
There are a number of advantages to using identity based systems
that are based on elliptic curves and their pairings. One is that
there are compatible elliptic curve-based signature, key
agreement, and encryption schemes. This means firstly that the
same public key/private key pair and public cryptographic
parameters can be used to do signatures, key agreement, and
encryption. Secondly, these protocols overlap, so that results of
computations and pre-computations done for one system can be used
in the others. Further, there are usually efficiency advantages in
using elliptic curves, over using other public-key methods.
Generally, one obtains shorter signatures, shorter ciphertexts,
and shorter key lengths for the same security as other systems.
Efficiency can be further enhanced by using abelian varieties in
place of elliptic curves [20].
There are identity based signature schemes [9] using elliptic
curves and pairings that base their security on the difficulty of
solving the elliptic curve Diffie-Hellman problem. This is the
same classical hard problem on which standard Elliptic Curve
Cryptography (ECC) [17][15] is based. Identity based encryption
and key agreement schemes using elliptic curves (or abelian
varieties) and pairings rely on the difficulty of solving the
bilinear Diffie-Hellman problem.
Identity based cryptosystems can be constructed with or without
key escrow. Protocols with key escrow can be performed in fewer
passes than corresponding systems that do not provide for key
escrow.
Techniques from threshold cryptography allow the master key
information to be distributed or shared among a number of IPKGs so
that all of them would have to collude for a node's private key to
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be known to them. Such a scenario would allow for key escrow if
necessary, by agreement among all the IPKGs, but guards against
knowledge of the private keys by the IPKGs without their mutual
agreement.
10.0 Previous Work
RFC 3401 [27] describes a protocol for generating randomized
interface identifiers for the bottom 64 bits of the IPv6 address.
RFC 3401 is not designed to address any of the security concerns
raised in RFC 2461; however, it is just designed to provide a
measure of privacy to users by frustrating attempts to correlate
particular addresses with particular network activity. Randomized
interface identifiers can be used if the host is re-keyed every
time it changes its interface identifier. In practice, this may be
somewhat impractical in public access networks, unless the ABK is
being provided by the local network and not the home ISP.
Cryptographically Generated Addresses (CGAs) [6], also called SUCV
identifiers [7], are another way to construct a cryptographic
binding for addresses. In CGAs, the interface identifier is
generated from the public key, rather than the other way around as
in ABKS. The primary difference between CGAs and ABKs are the
following:
- CGAs use the hash of the public key as the interface id
in the address suffix, whereas ABKs hash the interface id
or subnet prefix to form the public key.
- CGAs allow the node to generate the public key/private
key pair on its own, whereas ABKs require that the node
be provided with a private key by the entity that assigns
its address.
- ABKs require configuration with the public cryptographic
parameters because the IPKG uses a master secret to
perform the private key generation, and the master secret
might expire or be compromised.
The consequences of the first point are that CGAs are not
cryptographically active and therefore a separate mechanism is
required to distribute the public key. This may be as simple as
including it as a separate field in the message. In addition,
CGAs are not "topologically active" and therefore cannot be
used to sign the subnet prefix in routing.
The consequences of the second point are that there is less
computational load on the node for ABKs, since it only has to
perform signature verification, not public key/private key pair
generation. However, CGAs can be used in the absence of any
infrastructure whereas ABKs require the node to be assigned an
address-based private key.
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The consequences of the third point are nodes must be
preconfigured with the private key and public cryptographic
parameters for the operation. In principle, this is no
different than key distribution in Diffie-Hellman. In this
case, either dynamic or static configuration of the private key
and public cryptographic parameters is performed, but in a way
that doesn't require Neighbor Discovery.
11.0 Infrastructure Requirements
As mentioned previously, ABKs require a certain amount of
infrastructure to generate the private keys from the subnet
prefix and interface ids. This requirement, in and of itself,
is a hindrance for ad hoc networking designs that call for
nodes to simply autoconfigure their addresses without requiring
an ISP or network operator to be involved. For networks that
are run by ISPs or enterprises, this requirement is not likely
to be a problem, however.
ABKs place certain constraints on address provisioning. In
particular, an address used for ABK cannot be assigned using
DHCP [30]. To the extent DHCP requires Neighbor Discovery,
there is a bootstrapping problem in using a DHCP address for
ABK. An address used for ABK can be constructed using IPv6
Stateless Address Autoconfiguration [26] as long as the node
performing the Stateless Address Autoconfiguration has an ABK
interface id and private key for the suffix 64 bits of the
address and no duplicate is detected. Indeed, the same
mechanism described here to secure Neighbor Discovery could
also be used to secure Stateless Address Autoconfiguration.
With some identity based algorithms, the IPKG maintains a copy
of the private key, the so-called "key escrow" property.
Consequently, the address assignor's IPKG knows the private
keys for every address, and can potentially snoop authenticated
or encrypted traffic. However, the ABK is only being used to
secure IPv6 signaling traffic and not sensitive private data.
Both the network operator and the legitimate client/user have
an interest in seeing efficient operation of the network. Most
users today are happy to trust their ISPs with their credit
card number, trusting their ISP to guard their ABK is probably
of equal or lesser extent.
If a group of ISPs in a roaming consortium choose to support
ABKs, they have to co-ordinate in order to share a master key.
There are techniques that allow secure generation of ABKs in
such circumstances, but in principle ISPs in a roaming
consortium must trust each other for billing and settlement, so
business procedures and computational mechanisms for guarding
privileged information are likely to be in place. A collection
of ISPs that share a contract for IPKGs will allow their
customers to securely use their networks, others will either
get insecure or no service, just as is the case currently with
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roaming. The practical considerations involving co-ordinating
the IPKGs between ISPs can be considerably reduced by using a
hierarchical key generation system, such as is described in
[29].
12.0 Security Considerations
The computation involved in verifying Neighbor Discovery messages
could be utilized by an attacker to mount a "computational DoS
attack." The attacker bombards the victim with bogus Neighbor
Discovery messages, which the victim is forced to verify. This
ties the victim up in performing cryptography on the messages.
13.0 References
[1] Narten, T., Nordmark, E., and Simpson, W., "Neighbor
Discovery for IP Version 6 (IPv6)", RFC 2461, December,
1998.
[2] Kempf, J., and Nordmark, E., "Threat Analysis for IPv6
Public Multi-Access Links," draft-kempf-netaccess-threats-
00.txt, a work in progress.
[3] Hinden, R., and Deering,S., " IP Version 6 Addressing
Architecture", RFC 2373, July 1998.
[4] Kent, S., and Atkinson, R., " IP Authentication Header," RFC
2402, November 1998.
[5] Droms, R. (ed), " Dynamic Host Configuration Protocol for
IPv6 (DHCPv6)", draft-ietf-dhc-dhcpv6-23.txt, a work in
progress.
[6] O'Shea, G., and Roe, M., "Child-proof Authentication for
MIPv6 (CAM)", ACM Computer Communications Review, April,
2001.
[7] Montenegro, G., and Castellucia, C., "SUCV Identifiers and
Addresses," draft-montenegro-sucv-02.txt, a work in
progress.
[8] D. Boneh and M. Franklin, "Identity based encryption from
the Weil pairing", Advances in Cryptology --- Crypto 2001,
Lecture Notes in Computer Science 2139, (2001), Springer,
213-229, http://www.cs.stanford.edu/~dabo/papers/ibe.pdf
[9] J. C. Cha and J. H. Cheon, "An Identity-Based Signature from
Gap Diffie-Hellman Problem", Cryptology ePrint Archive:
Report 2002/018, http://eprint.iacr.org/2002/018/
[10] C. Cocks, "An identity based encryption scheme based on
quadratic residues", http://www.cesg.gov.uk/technology/id-
pkc/media/ciren.
[11] U. Feige, A. Fiat, and A. Shamir, "Zero-knowledge Proofs of
Identity", Journal of Cryptology 1, (1988), 77-94.
[12] A. Fiat and A. Shamir, "How to prove yourself: Practical
solutions to identification and signature problems",
Advances in Cryptology --- Crypto '86, Lecture Notes in
Computer Science 263, 1986), Springer, 186-194.
[13] L. C. Guillou and J.-J. Quisquater, "A practical zero-
knowledge protocol fitted to security microprocessors
minimizing both transmission and memory", Advances in
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Cryptology --- EUROCRYPT '88, Lecture Notes in Computer
Science 330, (1988), Springer, 123-128.
[14] F. Hess, "Exponent Group Signature Schemes and Efficient
Identity Based Signature Schemes Based on Pairings",
Cryptology ePrint Archive: Report 2002/012,
http://eprint.iacr.org/2002/012/
[15] N. Koblitz, "Elliptic curve cryptosystems", Mathematics of
Computation 48 (1987), 203-209.
[16] U. Maurer and Y. Yacobi, "Non-interactive public-key
cryptography," Advances in Cryptology --- Eurocrypt '92,
Lecture Notes in Computer Science 658,(1993), Springer, 458-
460.
[17] V. S. Miller, "Uses of elliptic curves in cryptography",
Advances in Cryptology --- Crypto'85, Lecture Notes in
Computer Science 218, (1986), Springer, 417-426.
[18] R. Sakai, K. Ohgishi, and M. Kasahara, "Cryptosystems based
on pairing", SCIC 2000-C20, Okinawa, Japan, January 2000
[19] A. Shamir, "Identity-Based Cryptosystems and Signature
Schemes", Advances in Cryptology --- Crypto '84, Lecture
Notes in Computer Science 196, (1984), Springer, 47-53.
[20] A. Silverberg and K. Rubin, "The best and worst of
supersingular abelian varieties in cryptology", Cryptology
e-Print Archive: Report 2002/006,
http://eprint.iacr.org/2002/006/
[21] N. P. Smart, "An identity Based authenticated key agreement
protocol based on the Weil pairing", Cryptology ePrint
Archive: Report 2001/111, http://eprint.iacr.org/2001/111/
[22] "802.1x - Port Based Access Control", IEEE Standard for
Local and Metropolitan Area Networks, 2001.
[23] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, March 1997.
[24] Mitton, D., and Beadles, M., "Network Access Server
Requirements Next Generation (NASREQNG) NAS Model", RFC
2881, July 2000.
[25] Aboba, B., and Beadles, M., "The Network Access Identifier",
RFC 2486, January, 1999.
[26] Thomas, S., and Narten, T., "IPv6 Address Stateless
Autoconfiguration", RFC 2462, December, 1998.
[27] Narten, T., and Draves, R., "Privacy Extensions for
Stateless Address Autoconfiguration in IPv6", RFC 3041,
January, 2001.
[28] Harkins, D., and Carrel, D., "The Internet Key Exchange
(IKE)", RFC 2409, November, 1998.
[29] Gentry, C., and Silverberg. A., "Hierarchical ID-based
Cryptography," http://eprint.iacr.org/2002/056/.
[30] Droms, R., et. al., "Dynamic Host Configuration Protocol for
IPv6," draft-ietf-dhc-dhcpv6-26.txt, a work in progress.
14.0 Author's Contact Information
James Kempf Phone: +1 408 451 4711
DoCoMo Labs USA Email: kempf@docomolabs-
usa.com
Kempf, J. Informational [Page 16]
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180 Metro Drive, Suite 300
San Jose, CA 95430
USA
Craig Gentry Phone: +1 408 451 4723
DoCoMo Labs USA Email: cgentry@docomolabs-usa.com
180 Metro Drive, Suite 300
San Jose, CA 95430
USA
Alice Silverberg Phone: +1 614 292 4975
Department of Mathematics Email: silver@math.ohio-state.edu
Ohio State University
Columbus, OH 43210
USA
15.0 Full Copyright Statement
Copyright (C) The Internet Society (2002). All Rights Reserved.
This document and translations of it may be copied and furnished
to others, and derivative works that comment on or otherwise
explain it or assist in its implementation may be prepared,
copied, published and distributed, in whole or in part, without
restriction of any kind, provided that the above copyright notice
and this paragraph are included on all such copies and derivative
works. However, this document itself may not be modified in any
way, such as by removing the copyright notice or references to the
Internet Society or other Internet organizations, except as needed
for the purpose of developing Internet standards in which case the
procedures for copyrights defined in the Internet Standards
process must be followed, or as required to translate it into
languages other than English. The limited permissions granted
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THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE
DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT
LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN
WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
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Kempf, J. Informational [Page 17]