One document matched: draft-rafiee-6man-ra-privacy-03.txt
Differences from draft-rafiee-6man-ra-privacy-02.txt
IPv6 maintenance Working Group (6man) H. Rafiee
INTERNET-DRAFT C. Meinel
Updates RFC 4941 , RFC 4862 (if approved) Hasso Plattner Institute
Intended status: Proposed Standard
Expires: November 23, 2013 May 23, 2013
Router Advertisement based privacy extension in IPv6 autoconfiguration
<draft-rafiee-6man-ra-privacy-03.txt>
Abstract
Privacy is an important issue which concerns many governments and
users, with its importance becoming more evident every day. Nodes
change their IP addresses frequently in order to avoid being tracked
by attackers. The act of frequently changing IP addresses also helps
to prevent the leakage of information by nodes. In IPv6 networks
there is currently one solution for maintaining the privacy of nodes
when IPv6 StateLess Address AutoConfiguration (SLAAC) (RFC 4862) is
used. Unfortunately there are some problems associated with this
solution which entails the use of the Privacy Extension (RFC 4941).
One of the issues with this RFC concerns the wording that is used
which allows the implementation to make the choice as to what
approach to use and in so doing, in some cases, the choice made is
not the most prudent or best approach and this is not ideal and can
cause some problems. Some of these problems are concerned with not
generating a new Interface ID (IID) after changing the router prefix.
Another concern would be the fact that nodes may use an IID that was
generated based on a MAC address as a public address, and then use
this in their response. The act of cutting the current connections to
other nodes, if the max lifetime of the old IID has elapsed, is also
not clearly explained nor is whether or not the already used IID
should be kept in stable storage, There is also a concern about the
need to have stable storage available for the generation of a
randomized IID. The RFC gives no explanation as to how to make use of
CGA in its randomizing solution when stable storage is not available
or how to use the same approach for random value generation in all
implementations where there is a lack of stable storage. The purpose
of this document is to address these issues and to update the current
RFC.
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 working
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documents as Internet-Drafts. The list of current Internet-Drafts is
at http://datatracker.ietf.org/drafts/current.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on Expires: November 23, 2013.
Copyright Notice
Copyright (c) 2013 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 (http://trustee.ietf.org/license-info) in effect on the
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions used in this document . . . . . . . . . . . . . . 4
3. Algorithm Overview . . . . . . . . . . . . . . . . . . . . . 4
3.1. Duplicate Address Detection (DAD) Process . . . . . . . . 5
4. Modification to the use of stable storage . . . . . . . . . . 5
5. Interface ID (IID) generation based on the MAC address . . . 5
6. Lifetime of Interface ID (IID) . . . . . . . . . . . . . . . 6
6.1. Automate the process for setting the lifetime . . . . . . 7
7. Threat Analysis . . . . . . . . . . . . . . . . . . . . . . . 7
7.1. Location based tracking . . . . . . . . . . . . . . . . . 7
7.2. Obtaining confidential data . . . . . . . . . . . . . . . 7
8. Security Considerations . . . . . . . . . . . . . . . . . . . 8
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
10. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 8
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
12.1. Normative . . . . . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
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1. Introduction
Privacy and security have a close relationship. Privacy, simply
stated, is the act of allowing a user to choose which data he wants
to make available to others or which data he wants to keep from
prying eyes. Security, on the other hand, is the ability to protect
your data or to keep your data confidential. There are times,
however, where one will have to be sacrificed for the sake of the
other. The gathering of location information, for security reasons,
might prove detrimental to privacy. But in many cases, when
cryptography or other approaches are used to protect the content of
the data, you are not only securing it but also providing privacy.
This document defines the meaning of privacy as it relates to methods
for maintaining our confidential data so that it does not become
available to or exposed to unscrupulous people who would use it to
harm us or would use it for their ill gotten gains. There is
currently only one solution available in IPv6 autoconfiguration (RFC
4682):, Privacy Extension [RFC4941]. In the Privacy Extension
document two different approaches are used for IID generation. In the
first approach, the use of stable storage enables a node to find
which IIDs are currently in use and which are in reserve. In the
second approach, where stable storage is not available, it suggests
the use of some randomizing approaches and also comments about other
available randomizing mechanisms such as Cryptographically Generated
Addresses (CGA) [RFC3972] or Dynamic Host Configuration Protocol
(DHCPv6). The Privacy Extension document also refers to the use of
named approaches as a mechanism for greater randomization. Here we
offer an update to section 3.2.3 of RFC 4941 in order to explain how
to use CGA when security is not the issue. An additional update to
this RFC will explain how to maintain the lifetime of the IP address
when the router prefix changes or the lifetime of the IID in general.
This is needed because, in this RFC, the key role is the lifetime of
the IID, which might not expire when the router prefix is changed.
This means that the node might not change its IID when it moves to
another network unless the node is rebooted. This can afford an
attacker the ability to track this node, and obtain enough
confidential information about this node, to allow for further
attacks. The third problem occurs if the node responds to the request
from other nodes using the IID generated based on the MAC address.
This could happen if the RFC does not force the node to use only an
IID that was generated by use of this approach or other approaches
that are not based on a MAC address. The forth problem can occur when
the node cuts current connections to other nodes because the maximum
lifetime for this IID has expired. Finally, there should be an update
made to step 4, section 3.2.1 RFC 4941 clarifying which IIDs should
be kept in stable storage. If there is no stable storage available,
and if the timestamp is not used as a method of randomization, then
the node may not choose a good approach fo ther randomization process
and thus may not be able to make use of a greatly randomized IID.
This is due to the fact that, in section 3.2.2 RFC 4941, the word
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"might" is used in explaining the proper randomization approach to be
used. The approach should be specified.
2. Conventions used in this document
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 [RFC2119].
In this document, these words will appear with that interpretation
only when in ALL CAPS. Lower case uses of these words are not to be
interpreted as carrying RFC 2119 significance.
In this document the use of || indicates the concatenation of the
values on either side of the sign.
3. Algorithm Overview
This section explains how to use the modified version of the CGA
algorithm for higher randomization of the IID without a need for
stable storage. This approach is RECOMMENDED and preferable over the
first approach, where stable storage is needed.
1. Generate a 16 byte random number called modifier. To generate this
modifier implementations SHOULD use a random seed to aid in the
randomization of this number.
2. Obtain the router prefix from the Router Advertisement
3. Obtain the nodes' current time and convert it to a timestamp. The
timestamp field consists of a 64-bit, unsigned integer field
containing a timestamp whose value iis computed from the number of
seconds since January 1, 1970, 00:00 UTC, by using a fixed point
format.
4. Concatenate the modifier with the timestamp and the router prefix.
R1=(modifier(16 bytes)||timestamp(8 bytes)|| router prefix)
5. Execute SHA2 (256) against the result from step 4.
digest=SHA256(R1)
The use of SHA2 (256) is RECOMMENDED because the chances of finding a
collision are less than when using SHA1 and the time for the
generation is acceptable (in microseconds using a standard CPU). In
the future, if a faster and collision free algorithm becomes
available, then it SHOULD be used. It is RECOMMENDED that the
implementation be able to support any new algorithms.
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6. Take the 64 leftmost bits from the resulting output of step 5
(SHA2 digest) and set bits u and g (bits 7 and 8) to one and call
this the IID.
7. Concatenate the IID with the local subnet prefix in order to set
the local IP address. If the lifetime of the old local address has
not expired, then the node MIGHT skip this step. Otherwise it will
receive a new router prefix.
8. Concatenate the IID with the router subnet prefix (Global subnet
prefix), obtained from the RA message, and set it as a tentative
privacy IP address. This IP address will become permanent after
Duplicate Address Detection (DAD) processing. This constitutes
another update to RFC 4941. The status of IP addresses defined in RFC
4941 are temporary while they SHOULD be permanent with a lifetime as
explained in section 4.
3.1. Duplicate Address Detection (DAD) Process
After the DAD process has completed, if the node finds collisions in
the network, then the modifier will be incremented and the DAD
process will be repeated. If, after 3 times, it receives the same
result, it will consider this an attack and will start using that IP
address.
4. Modification to the use of stable storage
The stable storage (section 3.2.1 RFC 4941) MUST only contain the
last generated value of the node. The node MUST not keep older,
already used, IIDs. This modification is made to eliminate the need
for large stable storage. For the randomization approach, if the node
cannot pick the best algorithm from among the ones already explained
in RFC 4088, then it MUST also include a timestamp in order preclude
the generation of an already used IID.
5. Interface ID (IID) generation based on the MAC address
When a node uses the mechanism explained in this document for IID
generation, it MUST not use any other IID generation approaches which
are based on MAC addresses ( RFC 4862). It is not RECOMMENDED for the
nodes that privacy is so important for them to use public addresses,
but in case they need to use public addresses, for generating public
addresses, the node SHOULD use the approach explained in this
document and set it as a public address. The public addresses are
permanent addresses and MIGHT not expire. These addresses are added
to DNS records and are RECOMMENDED for use with nodes that are
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servers or routers. For debugging and trouble shooting purposes, the
implementation MUST provide a means of partially disabling the
mechanism explained in this document. Allowing for manually setting
and unsettling a flag, which would indicate the debugging mode, is
one way to accomplish this. This means that when this flag is set,
the node SHOULD not generate any new IIDs and SHOULD change the IID's
lifetime to a large number. As soon as trouble shooting ends, and the
flag is set back to zero, then the node MUST generate a new IID and
start using it. The lifetime of the old IID must also be set to an
appropriate value at this time.
6. Lifetime of Interface ID (IID)
One problem with the Privacy Extension document, as explained
earlier, is that the IID might not change when the node joins a new
network or receives a new router prefix. This is due to the wording
used in the RFC. Here we update this document. The router prefix has
a higher priority than the IID's current lifetime. This means that,
if the node receives a new router prefix, while its current IID is
still valid, then it MUST generate a new randomized IID and start
using it. The IIDs MUST be valid for only a short period of time
which will depend on the network policy in vogue. Any implementations
SHOULD provide a means of allowing for users to change the lifetime's
default value.
Another problem that occurs with the use of this Privacy Extension
document is that the node will cut its current connections to the
other nodes using this IID when the maximum lifetime for the IID
expires. The update to that document will make use of an application
layer based lifetime. This means that a node will be allowed to start
an x number of new application layer connections using its current
IID. It MIGHT not be allowed to start any new connection with this
IID if:
- none of the x connections are closed and those connections are
still valid
- the IID has already been used for x number of connections
In these cases, the node will need to generate a new IID for another
x number of connections. The node can still use any of the current
IIDs if:
- one of the x connections opened by this IID is closed
- the lifetime of this IID has not yet expired
In cases where the router prefix changes, the node MUST cut the
connection. If for any reason there is a need to maintain the old
connections, this document RECOMMENDS the use of Mobile IPv6 (RFC
6275).
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6.1. Automate the process for setting the lifetime
The implementations MIGHT consider an option where, when RA messages
are being process , the RA message can be used to update the lifetime
for all addresses generated by use of this approach. This will
eliminate the need for the manual step, used during installation, to
set the default value for the lifetime (based on network policy) for
any future IIDs generated using this approach. The format for this
lifetime value will be the same as that explained in section 5.3.1
RFC 3971. The "type" SHOULD be set to the next sequential number
available in the SeND options, i.e., 15. when use is made of the
lifetime option, This field SHOULD be added to the ICMPv6 option for
RA messages.
7. Threat Analysis
Privacy consists of personal data that contains any information
relating to an individual, whether it relates to his or her private,
professional or public life. It can be anything from a name, a photo,
an email address, bank details, his posts on social networking
websites, his medical information, or his computer's IP address. Any
unauthorized efforts to obtain this information is considered an
attack against a user's privacy. The following sections will explain
how the mechanism detailed in this document can protect a user's
privacy.
7.1. Location based tracking
As the node MUST only keep its IID for a short period of time, and
MUST also change it when the prefix changes, it is not very easy for
an attacker to track this node based on its IP address. This is also
the case when the node changes the IID within the same network. The
reason for this is because it is very difficult for the attacker to
realize that this node is the same node, only with a newly generated
IID. This is especially true when there is an unlimited number of
nodes on the same network.
7.2. Obtaining confidential data
When a node changes its IID frequently within the network and among
networks, the attacker probably won't have enough time to obtain the
user's confidential data. It will also be difficult for the attacker
to correlate the information that he does obtain to a specific user's
IP address. This means that it will be difficult for the attacker to
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obtain more information about this user based on any correlation of
data. An example would be when an attacker obtains a confidential
document from a user, but he is unsure about the location of this
user. If the attacker had the location the user, he would be able to
obtain much more information about this use, and then he would be
abler to start attacks against him. But changing the IID prevents the
attacker from finding the location of this user and thus prevents
further attacks.
8. Security Considerations
As is explained in the Privacy Extension document. the same
approaches are used to maintain security, such as using Secure
Neighbor Discovery (SeND)(RFC 3971) or using a monitoring system
which would inform the administrator of the status of the network and
of any suspended activities in the network.
9. IANA Considerations
-
10. Conclusions
Privacy has become a very important issue in recent years. There is
one solution to the privacy issues, but the current solution has some
deficiencies. The purpose of the current document is to address and
solve the problem which exists with the Privacy Extension document
[RFC4941].
11. Acknowledgements
The authors would like to thank Dave Thaler for his useful and
greatly appreciated comments.
12. References
12.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to
Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4291] Hinden, R., Deering, S., "IP Version 6 Addressing
Architecture," RFC 4291, February 2006.
[RFC3972] Aura, T., "Cryptographically Generated Addresses
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(CGA)," RFC 3972, March 2005.
[RFC4941] Narten, T., Draves, R., Krishnan, S., "Privacy
Extensions for Stateless Address Autoconfiguration in
IPv6", RFC 4941, September 2007.
[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T.,
Perkins, C., Carney, M. , " Dynamic Host Configuration
Protocol for IPv6 (DHCPv6)", RFC 3315, July 2003.
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Authors' Addresses
Hosnieh Rafiee
Hasso-Plattner-Institute
Prof.-Dr.-Helmert-Str. 2-3
Potsdam, Germany
Phone: +49 (0)331-5509-546
Email: ietf@rozanak.com
Dr. Christoph Meinel
(Professor)
Hasso-Plattner-Institute
Prof.-Dr.-Helmert-Str. 2-3
Potsdam, Germany
Email: meinel@hpi.uni-potsdam.de
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