Network Working Group Sheng Jiang
Internet Draft Sam(Zhongqi) Xia
Intended status: Standards Track Huawei Technologies Co., Ltd
Expires: April 11, 2013 October 10, 2012
Configuring Cryptographically Generated Addresses (CGA) using DHCPv6
draft-ietf-dhc-cga-config-dhcpv6-03
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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
the usage of CGAs. This document defines the process using DHCPv6 to
manage CGAs in detail. A new DHCPv6 option is defined accordingly.
This document also analyses the configuration of the parameters,
which are used to generate CGAs, using DHCPv6. Although the document
does not define new DHCPv6 option to carry these parameters for
various reasons, the configuration procedure is described.
Table of Contents
1. Introduction ................................................ 3
2. Terminology ................................................. 3
3. CGA Configure Process Using DHCPv6 .......................... 4
3.1. Configuration of the parameters required for the generation
of CGA ...................................................... 4
3.2. Host requests CGA Approved to the DHCPv6 server ........ 5
4. CGA Grant Option ............................................ 7
5. Security Considerations ..................................... 8
6. IANA Considerations ......................................... 8
7. Acknowledgments ............................................. 8
8. References .................................................. 8
8.1. Normative References ................................... 8
8.2. Informative References ................................. 9
Author's Addresses ............................................ 10
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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.
CGAs were originally designed for SeND [RFC3971] and SeND is
generally not used in the same environment as a Dynamic Host
Configure Protocol for IPv6 (DHCPv6) [RFC3315] server. However, after
CGA has been defined, as an independent security property, many other
CGA usages have been proposed and defined, such as Site Multihoming
by IPv6 Intermediation (SHIM6) [RFC5533], Enhanced Route Optimization
for Mobile IPv6 [RFC4866], also using the CGA for DHCP security
purpose [I-D.ietf-dhc-secure-dhcpv6], etc. The use of CGAs allows
identity verification in different protocols. In these scenarios,
CGAs may be used in DHCPv6-managed networks.
As [I-D.ietf-csi-dhcpv6-cga-ps] analyses, in the current
specifications, there is a lack of procedures to enable proper
management of the usage of CGAs. Particularly, in a DHCPv6-managed
network, a new DHCPv6 option is missed, therefore, the DHCPv6 server
can NOT grant the use of host-generated CGA addresses on request from
the client, or reject the CGA on the basis of a too-low sec value. In
order to fill this gap, a new DHCPv6 option, CGA Grant Option, is
defined in this document.
This document also analyses the configuration of the parameters,
which are used to generate CGAs, using DHCPv6. Although the document
does not define new DHCPv6 option to carry these parameters for
various reasons, the configuration procedure is described. The
procedure works with existing options or future define options.
The CGA configuration procedure described in this document can work
with a generic address registration mechanism, which discussed in
IETF DHC Working Group, but have not been defined yet. However, even
a generic address registration mechanism was defined, the CGA-
specific option, CGA Grant Option, is still needed so that DHCP
server can indicate hosts the recommended CGA Sec value.
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].
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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, the network
management MAY want to assign/enforcement some parameters to hosts;
the network management MAY also manage the use of CGAs.
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.
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.
In a DHCPv6 managed network, a host may initiate a request for the
relevant CGA configuration information needed to the DHCPv6 server.
The server responds with the configuration information for the host.
The Option Request Option, defined in Section 22.7 in [RFC3315], can
be used for host 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.
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- 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
whether a new Prefix Assignment Option MAY is necessary, this
document does not define it.
- Although the network management MAY want to enforce or configure
a Sec value to the hosts, it is considered as a very dangerous
action. A malicious fake server may send out a high Sec value to
attack clients giving the fact that generation a CGA with a high
Sec value is very computational intensive
[I-D.ietf-csi-dhcpv6-cga-ps]. Another risk is that a malicious
server could propagate a Sec value providing less protection than
intended by the network administrator, facilitating a brute force
attack against the hash, or the selection of the weakest hash
algorithm available for CGA definition. A recommendation Sec value
is considered as confusion information. The receiving host is lack
for information to make choose whether generates a CGA according to
the recommendation or not. Therefore, the document does not define
a DHCPv6 option to propagate the Sec value.
- Although there is an optional Extension Fields in CGA Parameter
data structure, there is NO any defined extension fields. If in the
future, new Extension Fields in CGA Parameter data structure are
defined, future specification may define correspondent DHCPv6
options to carry these 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. Host 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
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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 the CGA Grant Option, defined in Section 4 in this
document, to indicate the DHCPv6 server responses with the address
granting decision.
The client MUST include one or more IA Options, either IA_NA or
IA_TA, in the Request message. Each IA Option MUST includes one or
more IA Address Options. CGAs are carried in the IA Address Options.
Server behavior
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 SHOULD NOT
handle the Request which the CGA_Grant field is not all 1(FFx). The
DHCPv6 server then send an acknowledgement, a Reply message, to the
client to either grant the use of the CGA or decline the requested
CGA. The CGA_Grant field SHOULD be set following the rule, defined in
Section 4 in this document. When the requested CGA is declined, the
DHCPv6 server MAY also recommend a Sec value to the client using the
CGA Grant option in the DHCPv6 Reply message.
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. The client SHOULD silently drop any
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message that has the CGA_Grant field set any other value, but F0x, or
00x~07x. If the server declines the requested CGA, the client MAY
generate a new CGA with the recommended Sec value. If the server
replies with CGA-relevant parameters, the client MAY generate a new
CGA accordingly.
4. CGA Grant Option
DHCPv6 CGA Grant Option is used to indicate the DHCPv6 client whether
the requested address is granted or not. In the decline case, a
recommended Sec value MAY be sent, too.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| CGA Grant |
+-+-+-+-+-+-+-+-+
option-code
OPTION_ADDR_GRANT (TBA1).
option-len
1.
CGA_Grant
The CGA_Grant field sets all 1 (FFx) when a client requests
granting from server in the DHCPv6 Request message.
In the DHCPv6 reply message, the CGA_Grant field sets F0x to
indicate that the requested CGA is granted; it sets 00x to
indicate that the requested Address is declined without any
recommended Sec value. It sets 01x~07x to indicate that
requested Address is declined and the recommended Sec value
(value from 1~7).
Note: On receiving the CGA Grant Option with reject information and a
recommended Sec value, the client MAY generate a new CGA with the
recommended Sec value. . If choosing not use the recommended Sec
value, the client MAY take the risk that it is not able to use full
network capabilities. The network may consider the hosts that use
CGAs with lower Sec values as unsecure users and decline some or all
network services.
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5. Security Considerations
The mechanisms based on DHCPv6 are all vulnerable to attacks to the
DHCP client. 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.
IF a DHCPv6 server rejected a client CGA based on a certain Sec
value, it SHOULD NOT suggest a new Sec value either equal or lower
than the Sec value that has been rejected.
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, or a DHCPv6
configuration token, etc.). However, considering that the values of
these elements could be shared by the hosts in the network segment,
these security elements can be configured more easily in the end
hosts than its addresses.
6. 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 Grant Option, OPTION_ADDR_GRANT (TBA1), described in
Section 4.
7. Acknowledgments
The authors would like to thank Marcelo Bagnulo Braun and Alberto
Garcia-Martinez for been involved in the early requirement
identification. Valuable comments from Bernie Volz, Ted Lemon, John
Jason Brzozowski, Dujuan Gu and other DHC WG members are appreciated.
8. References
8.1. 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.
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[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.
[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.
8.2. 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), February, 2012.
[I-D.ietf-dhc-secure-dhcpv6]
S. Jiang and S. Shen, "Secure DHCPv6 Using CGAs", draft-
ietf-dhc-secure-dhcpv6 (work in progress), Septerber, 2012.
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Author's Addresses
Sheng Jiang
Huawei Technologies Co., Ltd
Q14 Huawei Campus, 156 BeiQi Road,
ZhongGuan Cun, Hai-Dian District, Beijing 100085
P.R. China
Email: jiangsheng@huawei.com
Sam(Zhongqi) Xia
Huawei Technologies Co., Ltd
Q14 Huawei Campus, 156 BeiQi Road,
ZhongGuan Cun, Hai-Dian District, Beijing 100085
P.R. China
Email: xiazhongqi@huawei.com
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