IPv6 maintenance Working Group (6man) H. Rafiee INTERNET-DRAFT C. Meinel Updates RFC 4941 (if approved) Hasso Plattner Institute Intended status: Proposed Standard Expires: February 8, 2014 August 8, 2013 Router Advertisement based privacy extension in IPv6 autoconfiguration 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, to update the current RFC and to introduce a new algorithm for the lifetime of IID. 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 Rafiee, et al. Expires February 8, 2014 [Page 1] INTERNET DRAFT RA-base Privacy Extension August 8, 2013 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: February 8, 2014. 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 date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of 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 . . . 6 6. Lifetime of Interface ID (IID) . . . . . . . . . . . . . . . 6 6.1. Automate the process for setting the lifetime . . . . . . 6 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. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 11.1. Normative . . . . . . . . . . . . . . . . . . . . . . . . 8 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10 Rafiee, et al. Expires February 8, 2014 [Page 2] INTERNET DRAFT RA-base Privacy Extension August 8, 2013 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 data or to keep it 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, it is not only being secured but is also being provided privacy. This document defines the meaning of privacy as it relates to methods for maintaining data confidentiality so that it does not become available to or exposed to unscrupulous people who would use it to the detriment of the user or would use it for their ill gotten gains. There is currently one solution available in IPv6 autoconfiguration (RFC 4682):, Privacy Extension [RFC4941]. The Privacy Extension document explains two different approaches for use in 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 names approaches as a mechanism for greater randomization. This document addresses the following problems: - RFC 4941 promotes the use of IIDs generated by a MAC address as a public address for the node - The node might not generate a new IID when it receives a new RA message if the option in the router advertisement tells the node to extend the lifetime of its address, and if the maximum lifetime of that address has not been reached, then the node will keep its current IID without generating a new one. - A node may determine a need for the use of a large stable storage area in which to store each newly generated IID. This needs to be done to prevent the generation of another currently "in use" value.When there is no stable storage available the node may not be able to make use of a greatly randomized IID because, according to section 3.2.2 of RFC 4941, there is nothing to force the use RFC 4086. The Updates pertain to the following sections and concepts in RFC 4941: Rafiee, et al. Expires February 8, 2014 [Page 3] INTERNET DRAFT RA-base Privacy Extension August 8, 2013 - Section 3.2.3 in order to explain the use of 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 changes. This is needed because, in this RFC, the key role is the lifetime of the IID. 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 in doing so, to obtain enough confidential information about this node, to assist in further attacks. - There should be an update made to step 4, Section 3.2.1, clarifying which IIDs should be kept in stable storage. If there is no stable storage available, and if none of the methods explained in RFC 4086 [RFC4086] for randomization are used, then the node may make a bad choice as to the approach to use for the randomization process, and, thus, may not be able to make use of a highly randomized IID. This is due to the fact that, in section 3.2.2 of RFC 4941, the word "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 Rafiee, et al. Expires February 8, 2014 [Page 4] INTERNET DRAFT RA-base Privacy Extension August 8, 2013 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 is 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. 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 Rafiee, et al. Expires February 8, 2014 [Page 5] INTERNET DRAFT RA-base Privacy Extension August 8, 2013 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 4086, then it MUST also include a timestamp in order to preclude the generation of an already used IID. 5. Interface ID (IID) generation based on the MAC address Step 3 in Section 3.3 of RFC 4941 MUST be ignored. When a node uses the mechanism explained in this document to generate an IID, it MUST not use any other IID generation approaches that are based on MAC addresses ( RFC 4862) for either temporary or non temporary IID generation. The node MIGHT use the algorithm explained in this document or another algorithm [StableAddresses] that does not make use of EUI-64 or the MAC address for public (global) addresses. The choice of whether or not to list a node's address in the DNS undisguised depends on many factors, including the set of applications to be run on the host. Not listing a node's address in the public DNS may increase the node's privacy, but may also impair its ability to support certain applications. For debugging and troubleshooting purposes, the implementation MUST provide a way 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 new IIDs and SHOULD change the IID's lifetime to a large number. As soon as the trouble shooting process 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) The node MIGHT make use of the same algorithm and the same lifetime as is explained in RFC 4941, or the node MIGHT choose a lifetime based on some other algorithms or policies. If it uses the lifetime explained in RFC 4941, then it should generate a new IID whenever it receives a new router prefix, regardless of the option in the Router Advertisement message to extend this lifetime. 6.1. Automate the process for setting the lifetime The implementations MIGHT consider an option where, when RA messages Rafiee, et al. Expires February 8, 2014 [Page 6] INTERNET DRAFT RA-base Privacy Extension August 8, 2013 are being processed , the RA message can be used to update the lifetime for all addresses generated by the 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 are 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 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 user. With this new information he would then be able to start attacks against him. But Rafiee, et al. Expires February 8, 2014 [Page 7] INTERNET DRAFT RA-base Privacy Extension August 8, 2013 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 This document is updating RFC 4941 in order to prevent nodes from using addresses that were generated based on a MAC address and also some other deficiencies that exist in RFC 4941 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. References 11.1. 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 (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. [RFC4086] Eastlake, D., Schiller, J., and S. Crocker, Rafiee, et al. Expires February 8, 2014 [Page 8] INTERNET DRAFT RA-base Privacy Extension August 8, 2013 "Randomness Requirements for Security", BCP 106, RFC 4086, June 2005. [StableAddresses] Gont, F., "A method for Generating Stable Privacy-Enhanced Addresses with IPv6 Stateless Address Autoconfiguration (SLAAC)", Work In Progress, http://tools.ietf.org/html/draft-ietf-6man-stable-privacy-addresses-10, June 2013 Rafiee, et al. Expires February 8, 2014 [Page 9] INTERNET DRAFT RA-base Privacy Extension August 8, 2013 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 Rafiee, et al. Expires February 8, 2014 [Page 10]