Internet DRAFT - draft-gont-dhcpv6-stable-privacy-addresses
draft-gont-dhcpv6-stable-privacy-addresses
Dynamic Host Configuration (dhc) F. Gont
Internet-Draft SI6 Networks / UTN-FRH
Intended status: Informational W. Liu
Expires: September 12, 2016 Huawei Technologies
March 11, 2016
A Method for Generating Semantically Opaque Interface Identifiers with
Dynamic Host Configuration Protocol for IPv6 (DHCPv6)
draft-gont-dhcpv6-stable-privacy-addresses-01
Abstract
This document describes a method for selecting IPv6 Interface
Identifiers that can be employed by Dynamic Host Configuration
Protocol for IPv6 (DHCPv6) servers when leasing non-temporary IPv6
addresses to DHCPv6 clients. This method is a DHCPv6 server side
algorithm, that does not require any updates to the existing DHCPv6
specifications. The aforementioned method results in stable
addresses within each subnet, even in the presence of multiple DHCPv6
servers or DHCPv6 server reinstallments. It is a DHCPv6-variant of
the method specified in RFC 7217 for IPv6 Stateless Address
Autoconfiguration.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 12, 2016.
Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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(http://trustee.ietf.org/license-info) in effect on the date of
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Applicability and Design Goals . . . . . . . . . . . . . . . 3
3. Method Specification . . . . . . . . . . . . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
5. Security Considerations . . . . . . . . . . . . . . . . . . . 7
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
7.1. Normative References . . . . . . . . . . . . . . . . . . 8
7.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
The benefits of stable IPv6 addresses are discussed in
[I-D.ietf-6man-ipv6-address-generation-privacy]. Providing address
stability across server re-installations or when a database of
previous DHCPv6 address leases is unavailable is of use not only when
a DHCPv6 server must be re-installed or the address-lease database
becomes corrupted, but is also of use when implementation constraints
(e.g., a DHCPv6 server implementation on an embedded device) make it
impossible for a DHCPv6 server implementation to maintain a database
of previous DHCPv6 address leases. Additionally, [RFC7031] describes
scenarios where multiple DHCPv6 servers are required to run in such a
way as to provide increased availability in case of server failure.
This document describes a method for selecting IPv6 Interface
Identifiers that can be employed by Dynamic Host Configuration
Protocol for IPv6 (DHCPv6) servers when leasing non-temporary IPv6
addresses to DHCPv6 clients (i.e., to be employed with IA_NA
options). This method is a DHCPv6 server side algorithm, that does
not require any updates to the existing DHCPv6 specifications. The
aforementioned method has the following properties:
o The resulting IPv6 addresses remain stable within each subnet for
the same network interface of the same client, even when different
DHCPv6 servers (implementing this specification) are employed.
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o Predicting the IPv6 addresses that will be generated by the method
specified in this document, even with knowledge of the IPv6
addresses generated for other nodes within the same network,
becomes very difficult.
The method specified in this document achieves the aforementioned
properties by means of a calculated technique as opposed to e.g.
state-sharing among DHCPv6 servers. This approach has been already
suggested in [RFC7031]. We note that the method described in this
document is essentially a DHCPv6-version of the "Method for
Generating Semantically Opaque Interface Identifiers with IPv6
Stateless Address Autoconfiguration (SLAAC)" specified in [RFC7217].
2. Applicability and Design Goals
This document simply describes one possible approach for selecting
IPv6 Interface Identifiers to be employed by Dynamic Host
Configuration Protocol for IPv6 (DHCPv6) servers when leasing non-
temporary IPv6 addresses to DHCPv6 clients, with the following
properties:
o The resulting IPv6 addresses remain stable within each subnet for
the same network interface of the same client.
o The resulting IPv6 addresses cannot be predicted by an attacker
without knowledge of a secret key.
o The resulting IPv6 addresses remain stable across DHCPv6 server
re-installations, or even a database of previous DHCPv6 address
leases is not available.
o The resulting IPv6 addresses remain stable when different DHCPv6
servers (implementing this specification) are employed on the same
network.
We note that the algorithm specified in this document employs a
(lightweight) calculated technique (as opposed to e.g. state-sharing
among DHCPv6 servers) to achieve address stability in scenarios where
multiple DHCPv6 servers are required to run in such a way as to
provide increased availability, without the need of an additional
protocol to synchronize the lease databases of DHCPv6 servers.
Finally, we note that the algorithm in this document is only meant to
mitigate IPv6 address-based location tracking, device-specific
vulnerability exploitation, and host scanning (please see
[I-D.ietf-6man-ipv6-address-generation-privacy]). The are a number
of ways in which DHCPv6 affects user privacy, which the algorithm
speficied in this document does not mitigate (and does not intend
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to). Please see [I-D.ietf-dhc-anonymity-profile] for a comprehensive
discussion of how DHCPv6 may affect user privacy.
3. Method Specification
Implementations should provide the means for a system administrator
to enable or disable the use of this algorithm for generating IPv6
addresses.
A DHCPv6 server implementing this specification must select the IPv6
addresses to be leased with the following algorithm:
1. Compute a random (but stable) identifier with the expression:
RID = F(Prefix | Client_DUID | IAID | Counter | secret_key)
Where:
RID:
Random (but stable) Identifier
F():
A pseudorandom function (PRF) that must not be computable from
the outside (without knowledge of the secret key). F() must
also be difficult to reverse, such that it resists attempts to
obtain the secret key, even when given samples of the output
of F() and knowledge or control of the other input parameters.
F() should produce an output of at least 64 bits. F() could
be implemented as a cryptographic hash of the concatenation of
each of the function parameters. The default algorithm to be
employed for F() should be SHA-256 [FIPS-SHS]. An
implementation may provide the means for selecting other
algorithms. Note: MD5 [RFC1321] is considered unacceptable
for F() [RFC6151].
Prefix:
The prefix employed for the local subnet, as a 128-bit
unsigned integer in network byte order (with the unused bits
set to 0). If multiple servers operate on the same network to
provide increased availability, all such DHCPv6 servers must
be configured with the same Prefix. It is the administrator's
responsibility that the aforementioned requirement is met.
|:
An operator representing "concatenation".
Client_DUID:
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The DUID value contained in the Client Identifier option
received in the DHCPv6 client message. The DUID can be
treated as an array of 8-bit unsigned integers.
IAID:
The IAID value contained in the IA_NA option received in the
client message. It must be interpreted as a 32-bit unsigned
integer in network byte order.
secret_key:
A secret key configured by the DHCPv6 server administrator,
which must not be known by the attacker. It must be encoded
as an array of 8-bit unsigned integers. An implementation of
this specification must provide an interface for viewing and
changing the secret key. All DHCPv6 servers leasing addresses
from the same address range must employ the same secret key.
Counter:
A 32-bit unsigned integer in network byte order, that is
employed to resolve address conflicts. It must be initialized
to 0.
2. A candidate IPv6 address (IPV6_ADDR) to be leased is obtained by
concatenating as many bits as necessary from the RID value
computed in the previous step (starting from the least
significant bit) to the Prefix employed in the equation above as
follows:
IPV6_ADDR = IPV6_ADDR_LOW +
RID % (IPV6_ADDR_HI - IPV6_ADDR_LOW + 1)
where:
IPV6_ADDR:
The candidate IPv6 address to be leased.
IPV6_ADDR_HI:
An IPv6 address specifying the upper boundary of the IPv6
address pool from which the DHCPv6 server leases IPv6
addresses. If an address range is not explicitly selected,
IPV6_ADDR_HI must be set to the IPv6 address from Prefix (see
the expression above) that has all of the bits of the
Interface Identifier set to 1.
IPV6_ADDR_LOW:
An IPv6 address specifying the lower boundary of the IPv6
address pool from which the DHCPv6 server leases IPv6
addresses. If an address range is not explicitly selected,
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IPV6_ADDR_LOW must be set to the IPv6 address from Prefix (see
the expression above) that has all of the bits of the
Interface Identifier set to 0.
3. The Interface Identifier of the selected IPv6 address must be
compared against the reserved IPv6 Interface Identifiers
[RFC5453] [IANA-RESERVED-IID]. In the event that an unacceptable
identifier has been generated, the Counter variable should be
incremented by 1, and a new IPv6 address should be computed with
the updated Counter value.
4. If the resulting address is not available (e.g., there is a
conflicting binding), the server should increment the Counter
variable, and a new Interface ID and IPv6 address should be
computed with the updated Counter value.
This document requires that SHA-256 be the default function to be
used for F(), such that, all other configuration parameters being the
same, different implementations of this specification result in the
same IPv6 addresses.
Including the Prefix in the PRF computation causes the Interface
Identifier to be different for each address from a different prefix
assigned to the same client. This mitigates the correlation of
activities of multi-homed nodes (since each of the corresponding
addresses will employ a different Interface ID), host-tracking (since
the network prefix will change as the node moves from one network to
another), and any other attacks that benefit from predictable
Interface Identifiers
[I-D.ietf-6man-ipv6-address-generation-privacy].
As required by [RFC3315], an IAID is associated with each of the
client's network interfaces, and is consistent across restarts of the
DHCPv6 client.
The Counter parameter provides the means to intentionally cause this
algorithm to produce different IPv6 addresses (all other parameters
being the same). This can be of use to resolve address conflicts
(e.g. the resulting address having a conflicting binding).
Note that the result of F() in the algorithm above is no more secure
than the secret key. If an attacker is aware of the PRF that is
being used by the DHCPv6 server (which we should expect), and the
attacker can obtain enough material (i.e. addresses generated by the
DHCPv6 server), the attacker may simply search the entire secret-key
space to find matches. To protect against this, the secret key
should be of at least 128 bits. Key lengths of at least 128 bits
should be adequate.
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Providing a mechanism to display and change the secret_key is crucial
for having different DHCPv6 servers produce the same IPv6 addresses,
and for causing a replacement system to generate the same IPv6
addresses as the system being replaced. We note that since the
privacy of the scheme specified in this document relies on the
secrecy of the secret_key parameter, implementations should constrain
access to the secret_key parameter to the extent practicable (e.g.,
require superuser privileges to access it). Furthermore, in order to
prevent leakages of the secret_key parameter, it should not be used
for any other purposes than being a parameter to the scheme specified
in this document.
We note that all of the bits in the resulting Interface IDs are
treated as "opaque" bits [RFC7136]. For example, the universal/local
bit of Modified EUI-64 format identifiers is treated as any other bit
of such identifier.
4. IANA Considerations
There are no IANA registries within this document. The RFC-Editor
can remove this section before publication of this document as an
RFC.
5. Security Considerations
The method specified in this document results in IPv6 Interface
Identifiers (and hence IPv6 addresses) that do not follow any
specific pattern. Thus, attacks that rely on predictable Interface
IDs (such as [I-D.ietf-opsec-ipv6-host-scanning]) are mitigated.
The method specified in this document neither mitigates nor
exacerbates the security considerations for DHCPv6 discussed in
[RFC3315], and does not mitigate a range of other privacy
implications associated with DHCPv6. Please read
[I-D.ietf-dhc-anonymity-profile] for a comprehensive assessment of
the privacy implications of DHCPv6.
Finally, we note that an attacker that is able to attach to each of
the links to which the victim attaches would still be able to
correlate the activities of the victim across networks.
6. Acknowledgements
This document is based on [RFC7217], authored by Fernando Gont.
The authors would like to thank Marc Blanchet, Stephane Bortzmeyer,
Tatuya Jinmei, Andre Kostur, Tomek Mrugalski, Hosnieh Rafiee, Jim
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Schaad, Jean-Francois Tremblay, Tina Tsou, and Bernie Volz, for
providing valuable comments on earlier versions of this documents.
The authors would like to thank Ted Lemon, who kindly answered some
DHCPv6-related questions.
Finally, the authors would like to thank Nevil Brownlee for his
guidance while pursuing this document.
7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
December 1998, <http://www.rfc-editor.org/info/rfc2460>.
[RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins,
C., and M. Carney, "Dynamic Host Configuration Protocol
for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July
2003, <http://www.rfc-editor.org/info/rfc3315>.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, DOI 10.17487/RFC4291, February
2006, <http://www.rfc-editor.org/info/rfc4291>.
[RFC5453] Krishnan, S., "Reserved IPv6 Interface Identifiers",
RFC 5453, DOI 10.17487/RFC5453, February 2009,
<http://www.rfc-editor.org/info/rfc5453>.
[RFC7136] Carpenter, B. and S. Jiang, "Significance of IPv6
Interface Identifiers", RFC 7136, DOI 10.17487/RFC7136,
February 2014, <http://www.rfc-editor.org/info/rfc7136>.
7.2. Informative References
[FIPS-SHS]
FIPS, , "Secure Hash Standard (SHS)", Federal Information
Processing Standards Publication 180-4, March 2012,
<http://csrc.nist.gov/publications/fips/fips180-4/
fips-180-4.pdf>.
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[I-D.ietf-6man-ipv6-address-generation-privacy]
Cooper, A., Gont, F., and D. Thaler, "Privacy
Considerations for IPv6 Address Generation Mechanisms",
draft-ietf-6man-ipv6-address-generation-privacy-08 (work
in progress), September 2015.
[I-D.ietf-dhc-anonymity-profile]
Huitema, C., Mrugalski, T., and S. Krishnan, "Anonymity
profile for DHCP clients", draft-ietf-dhc-anonymity-
profile-08 (work in progress), February 2016.
[I-D.ietf-opsec-ipv6-host-scanning]
Gont, F. and T. Chown, "Network Reconnaissance in IPv6
Networks", draft-ietf-opsec-ipv6-host-scanning-08 (work in
progress), August 2015.
[IANA-RESERVED-IID]
Reserved IPv6 Interface Identifiers, ,
"http://www.iana.org/assignments/ipv6-interface-ids/
ipv6-interface-ids.xml".
[RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
DOI 10.17487/RFC1321, April 1992,
<http://www.rfc-editor.org/info/rfc1321>.
[RFC6151] Turner, S. and L. Chen, "Updated Security Considerations
for the MD5 Message-Digest and the HMAC-MD5 Algorithms",
RFC 6151, DOI 10.17487/RFC6151, March 2011,
<http://www.rfc-editor.org/info/rfc6151>.
[RFC7031] Mrugalski, T. and K. Kinnear, "DHCPv6 Failover
Requirements", RFC 7031, DOI 10.17487/RFC7031, September
2013, <http://www.rfc-editor.org/info/rfc7031>.
[RFC7217] Gont, F., "A Method for Generating Semantically Opaque
Interface Identifiers with IPv6 Stateless Address
Autoconfiguration (SLAAC)", RFC 7217,
DOI 10.17487/RFC7217, April 2014,
<http://www.rfc-editor.org/info/rfc7217>.
Authors' Addresses
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Fernando Gont
SI6 Networks / UTN-FRH
Evaristo Carriego 2644
Haedo, Provincia de Buenos Aires 1706
Argentina
Phone: +54 11 4650 8472
Email: fgont@si6networks.com
URI: http://www.si6networks.com
Will(Shucheng) Liu
Huawei Technologies
Bantian, Longgang District
Shenzhen 518129
P.R. China
Email: liushucheng@huawei.com
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