Network Working Group M. Finkel Internet-Draft The Tor Project Intended status: Informational L. Iannone Expires: 27 January 2022 Huawei 26 July 2021 IP Address Privacy Considerations draft-ip-address-privacy-considerations-01 Abstract This document provides an overview of privacy considerations related to user IP addresses. It includes an analysis of some current use cases for tracking of user IP addresses, mainly in the context of anti-abuse. It discusses the privacy issues associated with such tracking and provides input on mechanisms to improve the privacy of this existing model. It then captures requirements for proposed 'replacement signals' for IP addresses from this analysis. In addition, existing and under-development techniques are evaluated for fulfilling these requirements. Discussion Venues This note is to be removed before publishing as an RFC. Discussion of this document takes place on the mailing list (), which is archived at . Source for this draft and an issue tracker can be found at https://github.com/ShivanKaul/draft-ip-address-privacy. 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 documents as Internet-Drafts. The list of current Internet- Drafts is at https://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 27 January 2022. Finkel & Iannone Expires 27 January 2022 [Page 1] Internet-Draft IP Address Privacy Considerations July 2021 Copyright Notice Copyright (c) 2021 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 (https://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 . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. IP address tracking . . . . . . . . . . . . . . . . . . . . . 4 3.1. IP address use cases . . . . . . . . . . . . . . . . . . 4 3.1.1. Anti-abuse . . . . . . . . . . . . . . . . . . . . . 4 3.1.2. DDoS and Botnets . . . . . . . . . . . . . . . . . . 4 3.2. Privacy implications of IP addresses . . . . . . . . . . 4 3.3. IP Privacy Protection and Law . . . . . . . . . . . . . . 5 3.4. Mitigations for IP address tracking . . . . . . . . . . . 6 4. Replacement signals for IP addresses . . . . . . . . . . . . 7 4.1. Requirements . . . . . . . . . . . . . . . . . . . . . . 7 4.1.1. Required properties of replacement reputation signal . . . . . . . . . . . . . . . . . . . . . . . 7 4.1.2. Requirements of a reputation system . . . . . . . . . 8 4.2. Evaluation of existing technologies . . . . . . . . . . . 8 4.3. Potential new technologies . . . . . . . . . . . . . . . 9 5. Security Considerations . . . . . . . . . . . . . . . . . . . 9 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 7.1. Normative References . . . . . . . . . . . . . . . . . . 9 7.2. Informative References . . . . . . . . . . . . . . . . . 9 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 11 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11 1. Introduction The initial intention of this draft is to capture an overview of the problem space and research on proposed solutions concerning privacy considerations related to user IP addresses. The draft is likely to evolve significantly over time and may well split into multiple drafts as content is added. Finkel & Iannone Expires 27 January 2022 [Page 2] Internet-Draft IP Address Privacy Considerations July 2021 Tracking of user IP addresses is common place on the Internet today, and is particularly widely used in the context of anti-abuse, e.g. anti-fraud, DDoS management child protection activities. IP addresses are currently used as a source of "reputation" in conjunction with other signals to protect against malicious traffic, since they are a relatively stable identifier of the origin of a request. Servers use these reputations in determining whether or not a given packet, connection, or flow corresponds to malicious traffic. However, identifying the activity of users based on IP addresses has clear privacy implications ([WEBTRACKING1], [WEBTRACKING2]), e.g. user fingerprinting and cross site identity linking. Many technologies exist today to allow users to hide their IP address to avoid such tracking, e.g. VPNs ([VPNCMP1], [VPNCMP2]) or Tor ([TOR], [VPNTOR]). Several new technologies are also emerging in the landscape e.g. Gnatcatcher [GNATCATCHER], Apple Private Relay [APPLEPRIV] and Oblivious technologies (OHTTP [I-D.thomson-http-oblivious], ODoH [I-D.pauly-dprive-oblivious-doh]). General consideration about privacy for Internet protocols can be found in [RFC6973]. This document is more specific and attempts to capture the following aspects of the tension between valid use cases for user identification and the related privacy concerns including: * An analysis of the current use cases, attempting to categorize/ group such use cases where commonalities exist * Find ways to enhance the privacy of existing uses of IP addresses. * Generating requirements for proposed 'replacement signals' from this analysis (these could be different for each category/group of use cases) * Research to evaluate existing technologies or propose new mechanisms for such signals 2. Terminology (Work in progress) * Identity: Any identifying information about an end-user or service, be it a client or server, including IP addresses. * Reputation: A random variable with some distribution. A reputation can either be "bad" or "good" with some probability according to the distribution. Finkel & Iannone Expires 27 January 2022 [Page 3] Internet-Draft IP Address Privacy Considerations July 2021 * Reputation context: The context in which a given reputation applies. * Reputation proof: A non-interactive zero knowledge proof of a reputation signal. * Reputation signal: A representative of a reputation. 3. IP address tracking 3.1. IP address use cases 3.1.1. Anti-abuse Cyber-attackers abuse IP addresses posing a serious risk since legitimate service providers, developers, and end users may be mistakenly blacklisted which lowers the image and hurts the reputation of the service. Account abuse, financial fraud, ad fraud, child abuse... 3.1.2. DDoS and Botnets Cyber-attackers can leverage on the good reputation of an IP address to carry out specific attacks that wouldn't work otherwise. Main examples are Distributed Denial of Service (DDoS) attacks carried out spoofing a trusted (i.e., having good reputation) IP address (which may or may not be the victim of the attack) so that the servers used to generate the DDoS traffic actually respond to the attackers trigger (i.e., spoofed packets). Similarly Botnets may use spoofed addresses in order to gain access and attack services that would not be otherwise reachable. 3.2. Privacy implications of IP addresses IP addresses are sent in clear throughout the packet journey over the Internet. As such, any observer along the path can pick it up and use it for various tracking purposes. Beside basic information about the network or the device, it is possible to associate an IP address to an end user, hence, the relevance of of IP addresses for user privacy. A very short list of information about user, device, and network that can be obtained via the IP address. * Determine who owns and operates the network. Searching the WHOIS database using an IP address can provide a range of information about the organization to which the address is assigned, including a name, phone number, and civic address; Finkel & Iannone Expires 27 January 2022 [Page 4] Internet-Draft IP Address Privacy Considerations July 2021 * Through a reverse DNS lookup and/or traceroute the computer name can be obtained, which often contains clues to logical and physical location; * Geo-localisation of the device (hence the user) through various techniques [GEOIP]. Depending on the lookup tool used, this could include country, region/state, city, latitude/longitude, telephone area code and a location-specific map; * Search the Internet using the IP address or computer names. The results of these searches might reveal peer-to-peer (P2P) activities (e.g., file sharing), records in web server log files, or glimpses of the individual's web activities (e.g., Wikipedia edits). These bits of individuals' online history may reveal their political inclinations, state of health, sexuality, religious sentiments and a range of other personal characteristics, preoccupations and individual interests; * Seek information on any e-mail addresses used from a particular IP address which, in turn, could be the subject of further requests for subscriber information. 3.3. IP Privacy Protection and Law This section aim at providing some basic information about main example of laws adopted worldwide and related to IP address privacy (usually these laws area by product of the broader user privacy protection). Possible content (to focus only on technical IP address related aspects): * GDPR (General Data Protection Regulation) - EUROPE: Europe considers IP addresses as personal identification information that should be treated like any other personal information e.g. social security number. * The United States has opted for a different approach to data protection. Instead of formulating one all-encompassing regulation such as the EU's GDPR, the US chose to implement sector-specific privacy and data protection regulations that work together with state laws to safeguard American citizens' data. * In 2020, China released the first draft of Personal Information Protection Law (PIPL). The PIPL is the equivalent of European GDPR and will have significant influence. Finkel & Iannone Expires 27 January 2022 [Page 5] Internet-Draft IP Address Privacy Considerations July 2021 * Japan Protection of Personal Information (APPI) Act (recent changes put the act close to the GDPR model). 3.4. Mitigations for IP address tracking The ability to track individual people by IP address has been well understood for decades. Commercial VPNs and Tor are the most common methods of mitigating IP address-based tracking. * Commerical VPNs offer a layer of indirection between the user and the destination, however if the VPN endpoint's IP address is static then this simply substitutes one address for another. In addition, commerial VPNs replace tracking across sites with a single company that may track their users' activities. * Tor is another mitigation option due to its dynamic path selection and distributed network of relays, however its current design suffers from degraded performance. In addition, correct application integration is difficult and not common. * Address anonymization (e.g. [GNATCATCHER] and similar): { - {GNATCATCHER}} is a single-hop proxy system providing more protection against third-party tracking than a traditional commercial VPN. However, its design maintains the industry- standard reliance on IP addresses for anti-abuse purposes and it provides near backwards compatibility for select services that submit to periodic audits. - [APPLEPRIV] iCloud Private Relay is described as using two proxies between the client and server, and it would provide a level of protection somewhere between a commercial VPN and Tor. * Recent interest has resulted in new protocols such as Oblivious DNS (ODoH (https://www.ietf.org/staging/draft-pauly-oblivious-doh- 02.html)) and Oblivious HTTP (OHTTP (https://www.ietf.org/archive/id/draft-thomson-http-oblivious- 00.html)). While they both prevent tracking by individual parties, they are not intended for the general-purpose web browsing use case. * Finally, iCloud Private Relay is described as using two proxies between the client and server, and it would provide a level of protection somewhere between a commercial VPN and Tor. * Temporary addresses Finkel & Iannone Expires 27 January 2022 [Page 6] Internet-Draft IP Address Privacy Considerations July 2021 4. Replacement signals for IP addresses Fundamentally, the current ecosystem operates by making the paths of a connection accountable for bad traffic, rather than the sources of the traffic itself. This is problematic because paths are shared by multiple clients and are impermanent. Ideally, clients could present proof of reputation that is separate from the IP address, and uniquely bound to a given connection. Reputation services ([RFC7070]) are critical components present at multiple layers across the Internet and they are responsible for predicting whether a client will be abusive. However, these services are constrainted by available identifiers when making a decision. As a result of this constraint, IP addresses tend to be an influential signal in the reputation assigned to an identity. Identifying alternatives for this dependency on IP addresses is a goal of this document. 4.1. Requirements In the following the requirements of reputation signals are listed. Note that by "client(s)" it is intended an end user device (e.g., a PC or a mobile phone), while by "server(s)" it is intended a device offering an Internet service, which belong to an organisation/company but is not a personal device. Some considerations about reputation services are documented already in [I-D.kucherawy-repute-consid] from the perspective of organizations being operationally reliant on a third-party service. However, these considerations are relevant for and extend to a service's impact on clients, as well. With the goal of replacing IP addresses as a fundemental signal in calculating a reputation, we describe two classes of requirements: properties of a replacement reputation signal, and properties of a reputation system. Each class is further divided into requirements of the client and requirements of the service. 4.1.1. Required properties of replacement reputation signal 4.1.1.1. General Requirements The following requirements apply to reputation signals in general, independently from whether is the reputation of a client or a server. * Reputation signals MUST NOT remain valid indefinitely. New reputation signals periodically must be obtained periodically. Finkel & Iannone Expires 27 January 2022 [Page 7] Internet-Draft IP Address Privacy Considerations July 2021 * Reputation MUST NOT be transferable. * Reputation signals MUST be bound to a context, and MUST NOT be transferrable across contexts. 4.1.1.2. Client requirements The following requirement are specific to clients. * Clients MUST be able to request and present new reputation proofs on demand. * A reputation signal MUST NOT be linkable to any identifying information for which the signal corresponds. * Clients MUST be able to demonstrate good faith and improve reputation if needed. * Clients MUST be able to dispute their reputation. * Clients MUST be able to determine and verify the context in which a given reputation applies. 4.1.1.3. Server requirements * A reputation signal MUST NOT remain valid indefinitely meaning a client must obtain a new reputation signals periodically. * A reputation signal MUST be bound to a reputation context, and MUST NOT be transferable across contexts. 4.1.2. Requirements of a reputation system 4.1.2.1. Client requirements TODO 4.1.2.2. Server requirements TODO 4.2. Evaluation of existing technologies Technologies exist that solve problems in similar problem spaces, however none fulfill the above criteria. Finkel & Iannone Expires 27 January 2022 [Page 8] Internet-Draft IP Address Privacy Considerations July 2021 PrivacyPass [I-D.ietf-privacypass-protocol] is not directly applicable for this use case, but it has been shown to be a useful building block for solving numerous problems. Its design simply allows substituting a CAPTCHA challenge with a token. The token can't carry additional information about the client's reputation, the token is not guaranteed to expire, and the tokens are not bound to an identity. Furthermore, PrivacyPass does not itself specify a reputation system, therefore it cannot be used to derive an unlinkable reputation signal. Trust Tokens [TRUSTTOKEN] are an extension of PrivacyPass where the tokens are allowed to carry private metadata. This additional metadata would allow for encoding information about a client's reputation, but Trust Tokens are not bound to an identity and they do not necessarily expire. 4.3. Potential new technologies 5. Security Considerations TODO 6. IANA Considerations This document has no IANA actions. 7. References 7.1. Normative References [RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., Morris, J., Hansen, M., and R. Smith, "Privacy Considerations for Internet Protocols", RFC 6973, DOI 10.17487/RFC6973, July 2013, . 7.2. Informative References [APPLEPRIV] "Apple iCloud Private Relay", n.d., . [GEOIP] Dan, O., Parikh, V., and B. Davison, "IP Geolocation Using Traceroute Location Propagation and IP Range Location Interpolation", Companion Proceedings of the Web Conference 2021, DOI 10.1145/3442442.3451888, April 2021, . Finkel & Iannone Expires 27 January 2022 [Page 9] Internet-Draft IP Address Privacy Considerations July 2021 [GNATCATCHER] "Global Network Address Translation Combined with Audited and Trusted CDN or HTTP-Proxy Eliminating Reidentification", n.d., . [I-D.ietf-privacypass-protocol] Celi, S., Davidson, A., and A. Faz-Hernandez, "Privacy Pass Protocol Specification", Work in Progress, Internet- Draft, draft-ietf-privacypass-protocol-01, 22 February 2021, . [I-D.kucherawy-repute-consid] Kucherawy, M. S., "Considerations Regarding Third-Party Reputation Services", Work in Progress, Internet-Draft, draft-kucherawy-repute-consid-00, 27 November 2013, . [I-D.pauly-dprive-oblivious-doh] Kinnear, E., McManus, P., Pauly, T., Verma, T., and C. A. Wood, "Oblivious DNS Over HTTPS", Work in Progress, Internet-Draft, draft-pauly-dprive-oblivious-doh-06, 8 March 2021, . [I-D.thomson-http-oblivious] Thomson, M. and C. A. Wood, "Oblivious HTTP", Work in Progress, Internet-Draft, draft-thomson-http-oblivious-01, 21 February 2021, . [RFC7070] Borenstein, N. and M. Kucherawy, "An Architecture for Reputation Reporting", RFC 7070, DOI 10.17487/RFC7070, November 2013, . [TOR] "The Tor Project", n.d., . [TRUSTTOKEN] "Trust Token API Explainer", n.d., . [VPNCMP1] Osswald, L., Haeberle, M., and M. Menth, "Performance Comparison of VPN Solutions", Universität Tübingen article, DOI 10.15496/PUBLIKATION-41810, May 2020, . Finkel & Iannone Expires 27 January 2022 [Page 10] Internet-Draft IP Address Privacy Considerations July 2021 [VPNCMP2] Khanvilkar, S. and A. Khokhar, "Virtual private networks: an overview with performance evaluation", IEEE Communications Magazine Vol. 42, pp. 146-154, DOI 10.1109/mcom.2004.1341273, October 2004, . [VPNTOR] Ramadhani, E., "Anonymity communication VPN and Tor: A comparative study", n.d., . [WEBTRACKING1] Bujlow, T., Carela-Espanol, V., Lee, B., and P. Barlet- Ros, "A Survey on Web Tracking: Mechanisms, Implications, and Defenses", Proceedings of the IEEE Vol. 105, pp. 1476-1510, DOI 10.1109/jproc.2016.2637878, August 2017, . [WEBTRACKING2] Mishra, V., Laperdrix, P., Vastel, A., Rudametkin, W., Rouvoy, R., and M. Lopatka, "Don’t Count Me Out: On the Relevance of IP Address in the Tracking Ecosystem", Proceedings of The Web Conference 2020, DOI 10.1145/3366423.3380161, April 2020, . Acknowledgments TODO Authors' Addresses Matthew Finkel The Tor Project Email: sysrqb@torproject.org Luigi Iannone Huawei Technologies France S.A.S.U Email: luigi.iannone@huawei.com Finkel & Iannone Expires 27 January 2022 [Page 11]