--- 1/draft-ietf-dhc-dhcpv6-privacy-01.txt 2015-12-28 22:15:08.732022145 -0800 +++ 2/draft-ietf-dhc-dhcpv6-privacy-02.txt 2015-12-28 22:15:08.772023144 -0800 @@ -1,21 +1,21 @@ dhc S. Krishnan Internet-Draft Ericsson Intended status: Informational T. Mrugalski -Expires: February 27, 2016 ISC +Expires: June 29, 2016 ISC S. Jiang Huawei Technologies Co., Ltd - August 26, 2015 + December 27, 2015 Privacy considerations for DHCPv6 - draft-ietf-dhc-dhcpv6-privacy-01 + draft-ietf-dhc-dhcpv6-privacy-02 Abstract DHCPv6 is a protocol that is used to provide addressing and configuration information to IPv6 hosts. This document described the privacy issues associated with the use of DHCPv6 by the Internet users. It is intended to be an analysis of the present situation and doe not propose any solutions. Status of This Memo @@ -26,78 +26,78 @@ Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working 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 February 27, 2016. + This Internet-Draft will expire on June 29, 2016. Copyright Notice Copyright (c) 2015 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. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 - 3. Identifiers in DHCPv6 . . . . . . . . . . . . . . . . . . . . 4 + 3. DHCPv6 options carrying identifiers . . . . . . . . . . . . . 4 3.1. DUID . . . . . . . . . . . . . . . . . . . . . . . . . . 4 - 3.2. Client ID Option . . . . . . . . . . . . . . . . . . . . 4 + 3.2. Client Identifier Option . . . . . . . . . . . . . . . . 4 3.3. IA_NA, IA_TA, IA_PD, IA Address and IA Prefix Options . . 4 3.4. Client FQDN Option . . . . . . . . . . . . . . . . . . . 5 3.5. Client Link-layer Address Option . . . . . . . . . . . . 5 3.6. Option Request Option . . . . . . . . . . . . . . . . . . 6 3.7. Vendor Class and Vendor-specific Information Options . . 6 3.8. Civic Location Option . . . . . . . . . . . . . . . . . . 6 3.9. Coordinate-Based Location Option . . . . . . . . . . . . 6 3.10. Client System Architecture Type Option . . . . . . . . . 7 3.11. Relay Agent Options . . . . . . . . . . . . . . . . . . . 7 - 3.11.1. Subscriber ID . . . . . . . . . . . . . . . . . . . 7 - 3.11.2. Interface ID . . . . . . . . . . . . . . . . . . . . 7 - 3.11.3. Remote ID . . . . . . . . . . . . . . . . . . . . . 8 + 3.11.1. Subscriber ID Option . . . . . . . . . . . . . . . . 7 + 3.11.2. Interface ID Option . . . . . . . . . . . . . . . . 7 + 3.11.3. Remote ID Option . . . . . . . . . . . . . . . . . . 8 3.11.4. Relay-ID Option . . . . . . . . . . . . . . . . . . 8 4. Existing Mechanisms That Affect Privacy . . . . . . . . . . . 8 4.1. Temporary addresses . . . . . . . . . . . . . . . . . . . 8 4.2. DNS Updates . . . . . . . . . . . . . . . . . . . . . . . 9 4.3. Allocation strategies . . . . . . . . . . . . . . . . . . 9 5. Attacks . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 5.1. Device type discovery (fingerprinting) . . . . . . . . . 10 5.2. Operating system discovery (fingerprinting) . . . . . . . 11 5.3. Finding location information . . . . . . . . . . . . . . 11 5.4. Finding previously visited networks . . . . . . . . . . . 11 5.5. Finding a stable identity . . . . . . . . . . . . . . . . 11 - 5.6. Pervasive monitoring . . . . . . . . . . . . . . . . . . 11 + 5.6. Pervasive monitoring . . . . . . . . . . . . . . . . . . 12 5.7. Finding client's IP address or hostname . . . . . . . . . 12 5.8. Correlation of activities over time . . . . . . . . . . . 12 5.9. Location tracking . . . . . . . . . . . . . . . . . . . . 12 - 5.10. Leasequery & bulk leasequery . . . . . . . . . . . . . . 12 + 5.10. Leasequery & bulk leasequery . . . . . . . . . . . . . . 13 6. Security Considerations . . . . . . . . . . . . . . . . . . . 13 7. Privacy Considerations . . . . . . . . . . . . . . . . . . . 13 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13 - 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 13 - 10.1. Normative References . . . . . . . . . . . . . . . . . . 13 + 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 14 + 10.1. Normative References . . . . . . . . . . . . . . . . . . 14 10.2. Informative References . . . . . . . . . . . . . . . . . 14 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16 1. Introduction DHCPv6 [RFC3315] is a protocol that is used to provide addressing and configuration information to IPv6 hosts. The DHCPv6 protocol uses several identifiers that could become a source for gleaning information about the IPv6 host. This information may include device type, operating system information, location(s) that the device may @@ -105,21 +105,21 @@ identifiers used by DHCPv6 and the potential privacy issues [RFC6973]. In particular, it also takes into consideration the problem of pervasive monitoring [RFC7258]. Future works may propose protocol changes to fix the privacy issues that have been analyzed in this document. Protocol changes are out of scope for this document. The primary focus of this document is around privacy considerations for clients to support client mobility and connection to random - networks. The privacy or DHCP servers and relay agents are + networks. The privacy of DHCP servers and relay agents are considered less important as they are typically open for public services. And, it is generally assumed that relay agent to server communication is protected from casual snooping, as that communication occurs in the provider's backbone. Nevertheless, the topics involving relay agents and servers are explored to some degree. However, future work may want to further explore privacy of DHCP servers and relay agents. 2. Terminology @@ -136,81 +136,83 @@ Stable identifier - Any property disclosed by a DHCP client that does not change over time or changes very infrequently and is unique for said client in a given context. Examples may include MAC address, client-id or a hostname. Some identifiers may be considered stable only under certain conditions, for example one client implementation may keep its client-id stored in stable storage while other may generate it on the fly and use a different one after each boot. Stable identifier may or may not be globally unique. -3. Identifiers in DHCPv6 +3. DHCPv6 options carrying identifiers - There are several identifiers used in DHCPv6. This section provides - an introduction to the various options that will be used further in - the document. + In DHCPv6, there are many options which include identification + information or can be used to extract the identification information + about the client. This section enumerates various options and + identifiers conveyed in them, which can be used to disclose client + identification. 3.1. DUID Each DHCPv6 client and server has a DHCPv6 Unique Identifier (DUID) [RFC3315]. The DUID is designed to be unique across all DHCPv6 clients and servers, and to remain stable after it has been initially generated. The DUID can be of different forms. Commonly used forms are based on the link-layer address of one of the device's network interfaces (with or without a timestamp), on the Universally Unique IDentifier (UUID) [RFC6355]. The default type, defined in Section 9.2 of [RFC3315] is DUID-LLT that is based on link-layer address. It is commonly implemented in most popular clients. It is important to understand DUID lifecycle. Clients and servers are expected to generate their DUID once (during first operation) and store it in a non-volatile storage or use the same deterministic algorithm to generate the same DUID value again. This means that most implementations will use the available link-layer address during - its first boot. Even if the administrator enables privacy extensions - (see [RFC4941]) and its equivalent for link-layer address - randomization, it is likely that those privacy mechanisms were - disabled during the first device boot. Hence the original, - unobfuscated link-layer address will likely end up being announced as - client DUID, even if the link-layer address has changed (or even if - being changed on a periodic basis). + its first boot. Even if the administrator enables link-layer address + randomization, it is likely that it was disabled during the first + device boot. Hence the original, unobfuscated link-layer address + will likely end up being announced as client DUID, even if the link- + layer address has changed (or even if being changed on a periodic + basis). The exposure of the original link-layer address in DUID will + also undermine other privacy extensions such as [RFC4941]. -3.2. Client ID Option +3.2. Client Identifier Option The Client Identifier Option (OPTION_CLIENTID) [RFC3315] is used to carry the DUID of a DHCPv6 client between a client and a server. There is an analogous Server Identifier Option but it is not as interesting in the privacy context (unless a host can be convinced to - start acting as a server). Client ID is an example of DUID. See - Section 3.1 for relevant discussion about DUIDs. + start acting as a server). See Section 3.1 for relevant discussion + about DUIDs. 3.3. IA_NA, IA_TA, IA_PD, IA Address and IA Prefix Options The Identity Association for Non-temporary Addresses (IA_NA) option [RFC3315] is used to carry the parameters and any non-temporary addresses associated with the given IA_NA. The Identity Association for Temporary Addresses (IA_TA) option [RFC3315] is analogous to the IA_NA option but for temporary addresses. The IA Address option [RFC3315] is used to specify IPv6 addresses associated with an IA_NA or an IA_TA and is encapsulated within the Options field of such an IA_NA or IA_TA option. The Identity Association for Prefix Delegation (IA_PD) [RFC3633] option is used to carry the prefixes that are assigned to the requesting router. IA Prefix option [RFC3633] is used to specify IPv6 prefixes associated with an IA_PD and is encapsulated within the Options field of such an IA_PD option. - To differentiate between instances of the same type of IA containers, - each IA_NA, IA_TA and IA_PD options have an IAID field that is unique - for each client/option type pair. It is up to the client to pick - unique IAID values. At least one popular implementation uses last - four octets of the link-layer address. In most cases, that means - that merely two bytes are missing for a full link-layer address + To differentiate between instances of the same type of IA containers + for a client, each IA_NA, IA_TA and IA_PD options have an IAID field + with a unique value for a given IA type. It is up to the client to + pick unique IAID values. At least one popular implementation uses + last four octets of the link-layer address. In most cases, that + means that merely two bytes are missing for a full link-layer address reconstruction. However, the first three octets in a typical link- layer address are vendor identifier. That can be determined with high level of certainty using other means, thus allowing full link- layer address discovery. 3.4. Client FQDN Option The Client Fully Qualified Domain Name (FQDN) option [RFC4704] is used by DHCPv6 clients and servers to exchange information about the client's fully qualified domain name and about who has the @@ -262,84 +264,81 @@ and server to client communications. The information contained in the data area of this option is contained in one or more opaque fields that identify details of the hardware configuration, for example, the version of the operating system the client is running or the amount of memory installed on the client. 3.8. Civic Location Option - DHCPv6 servers use the Civic Location option [RFC4776] to delivery of + DHCPv6 servers use the Civic Location option [RFC4776] to deliver the location information (the civic and postal addresses) from the DHCPv6 server to the DHCPv6 clients. It may refer to three locations: the location of the DHCPv6 server, the location of the network element believed to be closest to the client, or the location of the client, identified by the "what" element within the option. 3.9. Coordinate-Based Location Option The GeoLoc options [RFC6225] is used by DHCPv6 server to provide the coordinate- based geographic location information to the DHCPv6 clients. It enable a DHCPv6 client to obtain its location. - After the relevant DHCPv6 exchanges have taken place, the location - information is stored on the end device rather than somewhere else, - where retrieving it might be difficult in practice. - 3.10. Client System Architecture Type Option The Client System Architecture Type option [RFC5970] is used by DHCPv6 client to send a list of supported architecture types to the - DHCPv6 server. It is used to provide configuration information for a - node that must be booted using the network rather than from local - storage. + DHCPv6 server. It is used by clients that must be booted using the + network rather than from local storage, so the server can decide + which boot file should be provided to the client. 3.11. Relay Agent Options A DHCPv6 relay agent may include a number of options. Those option contain information that can be used to identify the client. Those options are almost exclusively exchanged between the relay agent and the server, thus never leaving the operators network. In particular, they're almost never present in the last wireless hop in case of WiFi networks. The only exception to that rule is somewhat infrequently used Relay Supplied Options option [RFC6422]. This fact implies that the threat model related relay options is slightly different. Traffic sniffing at the last hop and related class of attacks typically do not apply. On the other hand, all attacks that involve operator's intfrastructure (either willing or coerced cooperation or infrastructure being compromised) usually apply. The following subsections describe various options inserted by the relay agents. -3.11.1. Subscriber ID +3.11.1. Subscriber ID Option A DHCPv6 relay may include a Subscriber ID option [RFC4580] to associate some provider-specific information with clients' DHCPv6 messages that is independent of the physical network configuration. In many deployments, the relay agent that inserts this option is configured to use client's link-layer address as Subscriber ID. -3.11.2. Interface ID +3.11.2. Interface ID Option A DHCPv6 relay includes the Interface ID [RFC3315] option to identify the interface on which it received the client message that is being relayed. Although in principle Interface ID can be arbitrarily long with - completely random values, it is often a text string that includes the - relay agent name followed by interface name. This can be used for - fingerprinting the relay or determining client's point of attachment. + completely random values, it is sometimes a text string that includes + the relay agent name followed by interface name. This can be used + for fingerprinting the relay or determining client's point of + attachment. -3.11.3. Remote ID +3.11.3. Remote ID Option A DHCPv6 relay includes a Remote ID option [RFC4649] to identify the remote host end of the circuit. The remote-id is vendor specific, for which the vendor is indicated in the enterprise-number field. The remote-id field may encode the information that identified the DHCPv6 clients: o a "caller ID" telephone number for dial-up connection @@ -354,48 +353,53 @@ 3.11.4. Relay-ID Option Relay agent may include Relay-ID [RFC5460], which contains a unique relay agent identifier. While its intended use is to provide additional information for the server, so it would be able to respond to leasequeries later, this information can be also used to identify client's location within the network. 4. Existing Mechanisms That Affect Privacy - This section describes available DHCPv6 mechanisms that one can use - to protect or enhance one's privacy. + This section describes deployed DHCPv6 mechanisms that can affect + privacy. 4.1. Temporary addresses [RFC3315] defines a mechanism for a client to request temporary addresses. The idea behind temporary addresses is that a client can request a temporary address for a specific purpose, use it, and then never renew it. i.e. let it expire. - There are number of serious issues, both protocolar and - implementational, that make them nearly useless for their original - goal. First, [RFC3315] does not include T1 and T2 renewal timers in - IA_TA (a container for temporary addresses). However, it mentions - that temporary addresses can be renewed. Many client implementations - renew those addresses during a renewal procedure initiated by other - resources (non-temporary addresses or prefixes), thus forfeiting - shortliveness. Second, [RFC4704] allows servers to update DNS for - assigned temporary addresses. Publishing client's IPv6 address in - DNS that is publicly available is a major privacy breach. + There are a number of serious issues, both related to protocol and + its implementations, that make temporary addresses nearly useless for + their original goal. First, [RFC3315] does not include T1 and T2 + renewal timers in IA_TA (a container for temporary addresses). + However, in section 18.1.3 it explicitly mentions that temporary + addresses can be renewed. Client implementations may mistakenly + renew temporary addresses if they are not careful (i.e., by including + the IA_TA with the same IAID in Renew or Rebind requests, rather than + a new IAID - see [RFC3315] Section 22.5), thus forfeiting short + liveness. [RFC4704] does not explicitly prohibit servers to update + DNS for assigned temporary addresses and there are implementations + that can be configured to do that. However, this is not advised as + publishing a client's IPv6 address in DNS that is publicly available + is a major privacy breach. 4.2. DNS Updates - DNS Updates [RFC4704] defines a mechanism that allows both clients - and server to insert into DNS domain information about clients. Both - forward (AAAA) and reverse (PTR) resource records can be updated. - This allows other nodes to conveniently refer to a host, despite the - fact that its IPv6 address may be changing. + The Client FQDN Option[RFC4704] used along with DNS Update [RFC2136] + defines a mechanism that allows both clients and server to insert + into the DNS domain information about clients. Both forward (AAAA) + and reverse (PTR) resource records can be updated. This allows other + nodes to conveniently refer to a host, despite the fact that its IPv6 + address may be changing. This mechanism exposes two important pieces of information: current address (which can be mapped to current location) and client's hostname. The stable hostname can then by used to correlate the client across different network attachments even when its IPv6 address keeps changing. 4.3. Allocation strategies A DHCPv6 server running in typical, stateful mode is given a task of @@ -407,30 +411,31 @@ strategies are possible. Choices in this regard may have privacy implications. Iterative allocation - a server may choose to allocate addresses one by one. That strategy has the benefit of being very fast, thus can be favored in deployments that prefer performance. However, it makes the resources very predictable. Also, since the resources allocated tend to be clustered at the beginning of available pool, it makes scanning attacks much easier. - Identifier-based allocation - a server may choose to allocate an - address that is based on one of available identifiers, e.g. IID or - MAC address. This has a property of being convenient for converting - IP address to/from other identifiers, especially if the identifier is - or contains MAC address. It is also convenient, as returning client - is very likely to get the same address, even if the server does not - store previous client's address. Those properties are convenient for - system administrators, so DHCPv6 server implementors are sometimes - requested to implement it. There is at least one implementation that - supports it. On the other hand, the downside of such allocation is + Identifier-based allocation - some server implementations use a fixed + identifier for a specific client, seemingly taken from the client's + MAC address when available or some lower bits of client's source IPv6 + address. This has a property of being convenient for converting IP + address to/from other identifiers, especially if the identifier is or + contains MAC address. It is also convenient, as returning client is + very likely to get the same address, even if the server does not + retain previous client's address. Those properties are convenient + for system administrators, so DHCPv6 server implementors are + sometimes requested to implement it. There is at least one + implementation that supports it. The downside of such allocation is that the client now discloses its identifier in its IPv6 address to all services it connects to. That means that correlation of activities over time, location tracking, address scanning and OS/ vendor discovery apply. Hash allocation - it's an extension of identifier based allocation. Instead of using the identifier directly, it is being hashed first. If the hash is implemented correctly, it removes the flaw of disclosing the identifier, a property that eliminates susceptibility to address scanning and OS/vendor discovery. If the hash is poorly @@ -491,21 +497,23 @@ using the Remote ID Option, the Interface ID option (e.g. if an access circuit on an Access Node corresponds to a civic location), or the Subscriber ID Option (if the attacker has access to subscriber info). 5.4. Finding previously visited networks When DHCPv6 clients connect to a network, they attempt to obtain the same address they had used before they attached to the network. They do this by putting the previously assigned address(es) in the IA - Address Option(s) inside the IA_NA, IA_TA. By observing these + Address Option(s). [RFC3315] does not exclude IA_TA in such a case, + so it is possible that a client implementation includes an address + contained in an IA_TA for the Confirm message. By observing these addresses, an attacker can identify the network the client had previously visited. 5.5. Finding a stable identity An attacker might use a stable identity gleaned from DHCPv6 messages to correlate activities of a given client on unrelated networks. The Client FQDN option, the Subscriber ID Option and the Client ID options can serve as long lived identifiers of DHCPv6 clients. The Client FQDN option can also provide an identity that can easily be @@ -568,50 +576,50 @@ Location information is information needed by the access concentrator to forward traffic to a broadband-accessible host. This information includes knowledge of the host hardware address, the port or virtual circuit that leads to the host, and/or the hardware address of the intervening subscriber modem. Furthermore, the attackers may use DHCPv6 bulk leasequery [RFC5460] mechanism to obtain bulk information about DHCPv6 bindings, even without knowing the target bindings. - Additionally, active leasequery - [I-D.ietf-dhc-dhcpv6-active-leasequery] is a mechanism for + Additionally, active leasequery [RFC7653] is a mechanism for subscribing to DHCPv6 lease update changes in near real-time. The intent of this mechanism is to update operator's database, but if misused, an attacker could defeat server's authentication mechanisms and subscribe to all updates. He then could continue receiving updates, without any need for local presence. 6. Security Considerations In current practice, the client privacy and the client authentication are mutually exclusive. The client authentication procedure reveals additional client information in their certificates/identifiers. Full privacy for the clients may mean the clients are also anonymous for the server and the network. 7. Privacy Considerations This document at its entirety discusses privacy considerations in - DHCPv6. As such, no dedicated section about this is needed. + DHCPv6. As such, no dedicated discussion is needed. 8. IANA Considerations This draft does not request any IANA action. 9. Acknowledgements - The authors would like to thanks the valuable comments made by - Stephen Farrell, Ted Lemon, Ines Robles, Russ White, Christian - Schaefer and other members of DHC WG. + The authors would like to thank Stephen Farrell, Ted Lemon, Ines + Robles, Russ White, Christian Schaefer, Jinmei Tatuya, Bernie Volz, + Marcin Siodelski, Christian Huitema and other members of DHC WG for + their valuable comments. This document was produced using the xml2rfc tool [RFC2629]. 10. References 10.1. 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, @@ -630,27 +638,27 @@ [RFC7258] Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May 2014, . 10.2. Informative References [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-07 (work - in progress), June 2015. + draft-ietf-6man-ipv6-address-generation-privacy-08 (work + in progress), September 2015. - [I-D.ietf-dhc-dhcpv6-active-leasequery] - Dushyant, D., Kinnear, K., and D. Kukrety, "DHCPv6 Active - Leasequery", draft-ietf-dhc-dhcpv6-active-leasequery-04 - (work in progress), July 2015. + [RFC2136] Vixie, P., Ed., Thomson, S., Rekhter, Y., and J. Bound, + "Dynamic Updates in the Domain Name System (DNS UPDATE)", + RFC 2136, DOI 10.17487/RFC2136, April 1997, + . [RFC2629] Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629, DOI 10.17487/RFC2629, June 1999, . [RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic Host Configuration Protocol (DHCP) version 6", RFC 3633, DOI 10.17487/RFC3633, December 2003, . @@ -704,20 +712,24 @@ . [RFC6422] Lemon, T. and Q. Wu, "Relay-Supplied DHCP Options", RFC 6422, DOI 10.17487/RFC6422, December 2011, . [RFC6939] Halwasia, G., Bhandari, S., and W. Dec, "Client Link-Layer Address Option in DHCPv6", RFC 6939, DOI 10.17487/RFC6939, May 2013, . + [RFC7653] Raghuvanshi, D., Kinnear, K., and D. Kukrety, "DHCPv6 + Active Leasequery", RFC 7653, DOI 10.17487/RFC7653, + October 2015, . + Authors' Addresses Suresh Krishnan Ericsson 8400 Decarie Blvd. Town of Mount Royal, QC Canada Phone: +1 514 345 7900 x42871 Email: suresh.krishnan@ericsson.com