One document matched: draft-jiang-dhc-cga-config-dhcpv6-01.txt
Differences from draft-jiang-dhc-cga-config-dhcpv6-00.txt
Network Working Group Sheng Jiang
Internet Draft Sam(Zhongqi) Xia
Intended status: Standards Track Huawei Technologies Co., Ltd
Expires: February 24, 2011 August 24, 2010
Configuring Cryptographically Generated Addresses (CGA) using DHCPv6
draft-jiang-dhc-cga-config-dhcpv6-01.txt
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Abstract
A Cryptographically Generated Address is an IPv6 addresses binding
with a public/private key pair. However, the current CGA
specifications are lack of procedures to enable proper management of
CGA generation. Administrators should be able to configure parameters
used to generate CGA. The Dynamic Host Configuration Protocol for
IPv6 (DHCPv6), which enables network management to dynamically
configure hosts, can be used in the CGA configuration. This document
defines the process using DHCPv6 to configure CGA in detail, include
configuration CGA parameters and that a DHCPv6 server grants the CGA
usage. Two new DHCPv6 options are defined accordingly.
Table of Contents
1. Introduction................................................3
2. Terminology.................................................3
3. CGA Configure Process Using DHCPv6...........................3
3.1. Configuration of the parameters required for the generation
of CGA......................................................4
3.2. Node requests CGA Approved to the DHCPv6 server..........5
4. DHCPv6 CGA Sec Option........................................6
5. DHCPv6 Address Grant Option..................................7
6. Security Considerations......................................7
7. IANA Considerations.........................................8
8. Acknowledgments.............................................8
9. References..................................................8
9.1. Normative References....................................8
9.2. Informative References..................................9
Author's Addresses.............................................9
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1. Introduction
Cryptographically Generated Addresses (CGA, [RFC3972]) provide means
to verify the ownership of IPv6 addresses without requiring any
security infrastructure such as a certification authority. The use
of CGAs allows identity verification in different protocols, such as
SEure Neighbor Discovery (SEND, [RFC3971]), Enhanced Route
Optimization for MIPv6 [RFC4866] or Site Multihoming by IPv6
Intermediation (SHIM6 [RFC5533]).
However, as [I-D.ietf-csi-dhcpv6-cga-ps] analyses, in the current
specifications, there is a lack of procedures to enable proper
management of CGA generation, in particular, in the configuration of
the parameters that define the security properties of the addresses.
Administrators should be able to configure parameters used to
generate CGA. The Dynamic Host Configuration Protocol for IPv6
(DHCPv6), which enables network management to dynamically configure
hosts, can be used in the CGA configuration. For example, DHCPv6
server should be able to assign certain level of CGA Sec value or
other relevant parameters to CGA address owner.
This draft provides detailed solutions for CGA configuration. Two
existing DHCPv6 options are re-used. Two new DHCPv6 options, CGA Sec
Option and Address Grant Option, are also defined in this document.
2. Terminology
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 RFC2119 [RFC2119].
3. CGA Configure Process Using DHCPv6
The CGA specifications [RFC3972] define the procedure to generate a
CGA. However, it assumes that hosts decide by itself or have been
preconfigured all CGA relevant parameters. In reality, network
management MAY want to assign/enforcement some parameters to hosts.
Among the mechanisms in which configuration parameters could be
pushed to the end hosts and/or CGA related information sent back to a
central administration, we discuss the stateful configuration
mechanism based on DCHPv6 in this document. Other mechanisms may also
provide similar functions, but out of scope.
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In this section, configuration CGA parameters and that a DHCPv6
server grants the CGA usage are described in details.
3.1. Configuration of the parameters required for the generation of CGA
Each CGA is associated with a CGA Parameters data structure, which is
formed by all input parameters [RFC3972] except for Sec value that is
embedded in the CGA. The CGA associated Parameters used to generate a
CGA includes:
- a Public Key,
- a Subnet Prefix,
- a 3-bit security parameter, Sec. Additionally, it should be noted
that the hash algorithm to be used in the generation of the CGA is
also defined by the Sec value [RFC4982],
- any Extension Fields that could be used.
- Note: the modifier and the Collision Count value in the CGA
Parameter data structure are generated during the CGA generation
process. They do NOT need to be configured.
A node may initiate a request for the relevant CGA configuration
information needed to the DHCPv6 server. The server responds with the
configuration information for the node. The Option Request Option,
defined in Section 22.7 in [RFC3315], can be used for node to
indicate which options the client requests from the server. For
response, the requested Option should be included. The server MAY
also initiatively push these parameters by attaching these option in
the response messages which are initiated for other purposes.
The Public/Private key pair is generated by hosts themselves and
considered not suitable for network transmission for security
reasons. The configuration of the client key pair or certificate is
out of scope.
Currently, there are convenient mechanisms for allowing an
administrator to configure the subnet prefix for a host, by Router
Advertisement [RFC4861, RFC4862]. However, this does not suitable
for the DHCP-managed network. To propagate the prefix through DHCP
interactions, DHCPv6 Prefix Delegation Option [RFC3633] MAY be used.
However, this option was designed to assign prefix block for
routers. A new Prefix Assignment Option MAY need to be defined.
Since alternative approach is existing and there are debates
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whether a new Prefix Assignment Option MAY is necessary, this
document does not define it.
A new DHCPv6 CGA Sec Option is defined in Section 4.
Although there is an optional Extension Fields in CGA Parameter
data structure, there is NO any defined extension fields. Future
specification may define more options to carry CGA-related
configuration parameters.
Upon reception of the CGA relevant parameters from DHCPv6 server, the
end hosts SHOULD generate addresses compliant with the received
parameters. If the parameters change, the end hosts SHOULD generate
new addresses compliant with the parameters propagated.
3.2. Node requests CGA Approved to the DHCPv6 server
A CGA address is generated by the associated key pair owner, normally
an end host. However, in a DHCPv6-managed network, hosts should use
IPv6 global addresses only from a DHCPv6 server. The process
described below allows a host, also DHCPv6 client, uses self-
generated CGAs in a DHCPv6-managed environment, by requesting the
granting from a DHCPv6 server.
The client sends a CGA, which is generated by itself, to a DHCPv6
server, and requests the DHCP server to determine whether the
generated CGA satisfies the requirements of the network configuration,
wherein the network configuration comprises a CGA security level set
by the DHCP; and generates a new CGA if the generated CGA does not
satisfy the requirements of the network configuration.
Client initiation behavior
In details, a DHCPv6 client SHOULD send a DHCPv6 Request message to
initiate the CGA granting process.
This DHCPv6 Request message MUST include an Option Request option,
which requests Address Grant Option, defined in Section 5 in this
document, to indicate the DHCPv6 server responses with the address
granting decision. The Addr_Grant field in the embedded Address Grant
Option should be set 0.
The client MUST include one or more IA Options, either IA_NA or IA_TA,
in the Request message. Each IA Option MUST include one or more IA
Address Options. CGAs are carried in the IA Address Options.
Server behavior
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Upon reception of the Request message, the DHCPv6 server SHOULD
verify whether the client's CGAs satisfy the CGA-related
configuration parameters of the network. The DHCPv6 server then send
an acknowledgement, a Reply message, to the client to either grant
the use of the CGA or to indicate that the node must generate a new
CGA with the correct CGA-related configuration parameters of the
network. The Addr_Grant field sets 1 indicating that the requested
address is granted; The Addr_Grant field sets 2 indicating that the
requested address is declined, defined in Section 5 in this document.
When the requested CGA is declined, the DHCPv6 server may attach CGA-
relevant parameters in the Reply message to indicate the client
generates a new CGA accordingly.
In the meantime, the DHCPv6 server MAY log the requested CGA
addresses. This information MAY later be used by other network
functions, such as ACL.
Client receiving behavior
Upon reception of the acknowledgement from server, the client can
legally use the granted CGAs. If the server declines the requested
CGA, the client MUST generate a new CGA. If the server replies with
CGA-relevant parameters, the client SHOULD generate a new CGA
accordingly.
4. DHCPv6 CGA Sec Option
DHCPv6 CGA Sec Option is used to carry a Sec value, the parameters
associated with CGA generation on a client. After receiving the CGA
Sec Option, the client SHOULD generate a CGA using a Sec value that
is not lower than the option indicated.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_CGA_SEC | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| CGA SEC |
+-+-+-+-+-+-+-+-+
option-code OPTION_CGA_SEC (TBA1).
option-len 1.
CGA SEC a digit between 0 and 7, the SEC level.
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Note: On receiving the CGA Sec Option, the client MAY choose to
generate a CGA using a lower sec value. It MAY cause that the client
is not able to use full network capabilities.
5. DHCPv6 Address Grant Option
DHCPv6 Address Grant Option is used to indicate the DHCPv6 client
whether the requested address is granted or not.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_ADDR_GRANT | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Addr Grant |
+-+-+-+-+-+-+-+-+
option-code OPTION_ADDR_GRANT (TBA2).
option-len 1.
Addr Grant The Addr_Grant field sets 0 when a client
requests granting from server. It sets 1
indicating that the requested Address is granted;
it sets 2 indicating that the requested Address
is declined.
6. Security Considerations
The mechanisms based on DHCPv6 are all vulnerable to attacks to the
DHCP client, such as request for CGA generation with a high Sec value.
Proper use of DHCPv6 autoconfiguration facilities [RFC3315], such as
AUTH option or Secure DHCP [I-D.ietf-dhc-secure-dhcpv6] can prevent
these threats, provided that a configuration token is known to both
the client and the server.
Note that, as expected, it is not possible to provide secure
configuration of CGA without a previous configuration of security
information at the client (either a trust anchor, a DHCPv6
configuration token...). However, considering that the values of
these elements could be shared by the nodes in the network segment,
these security elements can be configured more easily in the end
nodes than its addresses.
Regarding to the configuration of the Sec parameter, one risk is that
a malicious node could propagate a Sec value providing less
protection than intended by the network administrator, facilitating a
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brute force attack against the hash, or the selection of the weakest
hash algorithm available for CGA definition. However, even in the
worst case, if the hash algorithm cannot be inverted, the expected
number of iterations required for a brute force attack is O(2^59) in
order to find a CGA Parameters data structure that matches a given
CGA. Another risk is the use of a Sec, higher than intended by the
administrator, which would require a large number of resources of the
client to compute the modifier, requiring a long time before the
device can communicate. This can be considered a kind of DOS attack.
A variation of this attack is the propagation of different Sec values.
This kind of attack may be prevented by protected DHCPv6 interactions.
7. IANA Considerations
This document defines two new DHCPv6 [RFC3315] options, which must be
assigned Option Type values within the option numbering space for
DHCPv6 messages:
The DHCPv6 CGA Sec Option (TBA1), described in Section 4.
The DHCPv6 Address Grant Option (TBA2), described in Section 5.
8. Acknowledgments
The authors would like to thank Marcelo Bagnulo Braun and Alberto
Garcia-Martinez from Universidad Carlos III de Madrid for been
involved in the early requirement identification. Valuable comments
from Bernie Volz, Cisco and Dujuan Gu, Huawei are appreciated.
9. References
9.1. Normative References
[RFC2119] S. Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", RFC2119, March 1997.
[RFC3315] R. Droms, Ed., "Dynamic Host Configure Protocol for IPv6",
RFC3315, July 2003.
[RFC3633] O. Troan and R. Droms, "IPv6 Prefix Options for Dynamic
Host Configuration Protocol (DHCP) version 6", RFC 3633,
December 2003.
[RFC3971] J. Arkko, J. Kempf, B. Zill and P. Nikander, "SEcure
Neighbor Discovery (SEND) ", RFC 3971, March 2005.
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[RFC3972] T. Aura, "Cryptographically Generated Address", RFC3972,
March 2005.
[RFC4861] T. Narten, et al., "Neighbor Discovery for IP version 6
(IPv6)", RFC 4861, September 2007.
[RFC4862] S. Thomson, T. Narten and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC4862, September 2007.
[RFC4866] J. Arkko, C. Vogt and W. Haddad, "Enhanced Route
Optimization for Mobile IPv6", RFC4866, May 2007.
[RFC4982] M. Bagnulo, "Support for Multiple Hash Algorithms in
Cryptographically Generated Addresses (CGAs) ", RFC4982,
July 2007.
[RFC5533] E. Nordmark and M. Bagnulo, "Shim6: Level 3 Multihoming
Shim Protocol for IPv6" FRC 5533, June 2009.
9.2. Informative References
[I-D.ietf-csi-dhcpv6-cga-ps]
S. Jiang, S. Shen and T. Chown, "DHCPv6 and CGA Interaction:
Problem Statement", draft-ietf-csi-dhcpv6-cga-ps (work in
progress), June, 2010.
[I-D.ietf-dhc-secure-dhcpv6]
S. Jiang and S. Shen, "Secure DHCPv6 Using CGAs", draft-
ietf-dhc-secure-dhcpv6 (work in progress), June 2010.
Author's Addresses
Sheng Jiang
Huawei Technologies Co., Ltd
Huawei Building, No.3 Xinxi Rd.,
Shang-Di Information Industry Base, Hai-Dian District, Beijing 100085
P.R. China
Email: shengjiang@huawei.com
Sam(Zhongqi) Xia
Huawei Technologies Co., Ltd
Huawei Building, No.3 Xinxi Rd.,
Shang-Di Information Industry Base, Hai-Dian District, Beijing 100085
P.R. China
Email: xiazhongqi@huawei.com
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