IPv6 maintenance Working Group (6man) H. Rafiee INTERNET-DRAFT C. Meinel Updates RFC 4941 (if approved) Hasso Plattner Institute Intended status: Proposed Standard Expires: December 18, 2013 June 18, 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 December 18, 2013 [Page 1] INTERNET DRAFT RA-base Privacy Extension June 18, 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: December 18, 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 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 . . . . . . . . . . 6 5. Interface ID (IID) generation based on the MAC address . . . 6 6. Application Layer based Lifetime for the Interface ID (IID) . 6 6.1. Automate the process for setting the lifetime . . . . . . 8 7. Threat Analysis . . . . . . . . . . . . . . . . . . . . . . . 8 7.1. Location based tracking . . . . . . . . . . . . . . . . . 9 7.2. Obtaining confidential data . . . . . . . . . . . . . . . 9 8. Security Considerations . . . . . . . . . . . . . . . . . . . 9 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 10. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 10 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 10 11.1. Normative . . . . . . . . . . . . . . . . . . . . . . . . 10 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11 Rafiee, et al. Expires December 18, 2013 [Page 2] INTERNET DRAFT RA-base Privacy Extension June 18, 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 only 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 cuts his connections with other nodes if the lifetime of the temporary IIDs is expired. - 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. Rafiee, et al. Expires December 18, 2013 [Page 3] INTERNET DRAFT RA-base Privacy Extension June 18, 2013 The Updates pertain to the following sections and concepts in RFC 4941: - 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 the timestamp is not used as a method for randomization, then the node may not choose a good approach 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 Rafiee, et al. Expires December 18, 2013 [Page 4] INTERNET DRAFT RA-base Privacy Extension June 18, 2013 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 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. Rafiee, et al. Expires December 18, 2013 [Page 5] INTERNET DRAFT RA-base Privacy Extension June 18, 2013 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 to preclude the generation of an already used IID. 5. Interface ID (IID) generation based on the MAC address Step 3 of Section 3.3 of RFC 4941 MUST be ignored. When a node uses the mechanism explained in this document for IID generation, it MUST not use any other IID generation approaches that are based on MAC addresses ( RFC 4862). For nodes where privacy is an important issue the use of public addresses is not RECOMMENDED unless security approaches are employed in the higher layers such as using SSL, TLS, etc where all data is encrypted. In cases where a public address must be used,then the method for generating the public address SHOULD use the approach explained in this document, or any other document, where the MAC address is not used as a part of the public address.. Public addresses are permanent addresses and MIGHT not expire. These addresses are added to DNS records and are RECOMMENDED for use by nodes that are servers or routers. For debugging and troubleshooting purposes, the implementation MUST provide a way of partially disabling the mechanism as 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. Application Layer based Lifetime for the Interface ID (IID) Figure 1 depicts the algorithm used to determine the lifetime of an IID. The use of this algorithm minimizes the chance of an attacker obtaining a user's private information. It is RECOMMENDED that the node uses encryption mechanisms if the IID is in use for more than a week. This is because attackers might be able to watch this node and thereby obtain a user's private information. This might negatively impact a user's privacy. start Rafiee, et al. Expires December 18, 2013 [Page 6] INTERNET DRAFT RA-base Privacy Extension June 18, 2013 + v +-------------------+ +--------+ |new Router prefix |Yes |c_IID=0 |+------------+ | received? +--->|L_i=0 | | +---------+---------+ +--------+ | |No | v +--------------------+ | +---------------+ | Find_largest(L_i) | | |max_IID > c_IID+-->| t_app_i ++ | | +-------+-------+ No| Assign(IID_i,app_i)| | | Yes +--------------------+ | +-------v----------+------------+ | | n_i < t_app_i + No | | +-------+----------+ +---------v----------+ | Yes | | Generate_New(IID) | | +-----------v--------+ | c_IID ++ <--+ | Find_largest(L_i) | | Assign(IID_i,app_i)| | Assign(IID_i,app_i)| +--------------------+ | n_i ++ | +--------------------+ One possible way of maintaining the lifetime of an IID is connection based, although this way may prove problematic for ftp and other applications. Another possible way of maintaining the lifetime of an IID is application layer based. The application will open a connection using an IID and this connection will remain active for as long as the application uses it. - app_i is new application started by the node - t_app is the maximum number of applications per IID - L is the maximum lifetime of an IID - max_IID is the maximum number of valid IIDs - c_IID is the current number of IIDs - IID_i is a specific IID - t_app_i is the total number of applications per specific IID - n_i is the current number of applications for specific IID - L_i is the current lifetime of a specific IID When a node wants to use a new application, it first checks to see whether or not it has also received a new router advertisement. In the case where a new router advertisement is received, the node sets the total lifetime of the current valid IID to zero and resets the c_IID to zero. In this case all of the current IIDs associated with Rafiee, et al. Expires December 18, 2013 [Page 7] INTERNET DRAFT RA-base Privacy Extension June 18, 2013 this node MUST be expired and the node MUST generate, and use,new IIDs for any upcoming applications. But the node can still use an expired IID as long as the current applications using them are active. If the node does not receive a new router advertisement, then it checks whether or not the current number of IIDs is less than the maximum number of IIDs. If the condition is met, the node then checks whether or not there are any IIDs where the current number of applications, n_i , is less than the total number of applications, t_app_i. If the condition is met the node SHOULD sort these IIDs based on their current lifetime, L_i, in descending order, and then assign app_i to the IID with higher L_i. The current number of applications, n_i, for this specific IID is then incremented. If n_i is equal to t_app_i, then the node generates a new IID and assigns this application to this new IID. In cases where the current number of IIDs is equal to max_IID, and n_i is equal to t_app, the node is unable to generate a new IID for the application nor is it able to assign a current IID to the application. In this case the node SHOULD find the IID with the longest lifetime and then increase the total number of applications, t_app_i, that can be assigned to it. The node then assigns this IID to the new application. The advantage to using this algorithm, with regard to the IID lifetime, is that it allows for the control of the number of valid IIDs, while at the same time allowing users to keep their current application layer connections. This results in user satisfaction. 6.1. Automate the process for setting the lifetime The implementations MIGHT consider an option where, when RA messages 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 Rafiee, et al. Expires December 18, 2013 [Page 8] INTERNET DRAFT RA-base Privacy Extension June 18, 2013 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 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 Rafiee, et al. Expires December 18, 2013 [Page 9] INTERNET DRAFT RA-base Privacy Extension June 18, 2013 - 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. Rafiee, et al. Expires December 18, 2013 [Page 10] INTERNET DRAFT RA-base Privacy Extension June 18, 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 December 18, 2013 [Page 11]