Registration Protocols Extensions M. Loffredo
Internet-Draft M. Martinelli
Intended status: Standards Track IIT-CNR/
Expires: April 10, 2020 October 8, 2019

Registration Data Access Protocol (RDAP) Reverse search capabilities


The Registration Data Access Protocol (RDAP) does not include query capabilities to find the list of domains related to a set of entities matching a given search pattern. Even if such capabilities, commonly referred as reverse search, respond to some needs not yet readily fulfilled by the current Whois protocol, they have raised concerns from two perspectives: server processing impact and data privacy. Anyway, the impact of the reverse queries on RDAP servers processing is the same as the standard searches and it can be reduced by implementing policies to deal with large result sets, while data privacy risks can be prevented by RDAP access control functionalities. This document describes RDAP query extensions that allow clients to request a reverse search based on the domains-entities relationship.

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Table of Contents

1. Introduction

Reverse Whois is a service provided by many web applications that allow users to find domain names owned by an individual or a company starting from the owner's details, such as name and email. Even if it has been considered useful for some legal purposes (e.g. uncovering trademark infringements, detecting cybercrime cases), its availability as a standardized Whois capability has been objected for two main reasons, which now don't seem to conflict with an RDAP implementation.

The first objection has been caused by the potential risks of privacy violation. However, TLDs community is considering a new generation of Registration Directory Services ([ICANN-RDS1],[ICANN-RDS2]), which provide access to sensitive data under some permissible purposes and according to adequate policies to enforce the requestor accreditation, authentication, authorization, and terms and conditions of data use. It is well known that such security policies are not implemented in Whois ([RFC3912]), while they are in RDAP ([RFC7481]). Therefore, RDAP permits a reverse search implementation complying with privacy protection principles.

Another objection to the implementation of a reverse search capability has been connected with its impact on server processing. Since RDAP supports search queries, the impact of both standard and reverse searches is equivalent and can be mitigated by servers adopting ad hoc strategies. Furthermore, the reverse search is almost always performed by specifying an entity role (e.g. registrant, technical contact) and this can contribute to restricting the result set.

Reverse searches, such as finding the list of domain names associated with contacts, nameservers or DNSSEC keys, may be useful to registrars as well. Usually, registries adopt out-of-band mechanisms to provide results to registrars asking for reverse searches on their domains. Possible reasons for such requests are:

Currently, RDAP does not provide any way for a client to search for the collection of domains associated with an entity ([RFC7482]). A query (lookup or search) on domains can return the array of entities related to a domain with different roles (registrant, registrar, administrative, technical, reseller, etc.), but the reverse operation is not allowed. Only reverse searches to find the collection of domains related to a nameserver (ldhName or ip) can be requested. Since entities can be in relationship with all RDAP objects ([RFC7483]), the availability of a reverse search can be common to all RDAP query paths.

The protocol described in this specification aims to extend the RDAP query capabilities to enable reverse search based on the domains-entities relationship (the classic Reverse Whois scenario). The extension is implemented by adding new path segments (i.e. search paths) and using a RESTful web service ([REST]). The service is implemented using the Hypertext Transfer Protocol (HTTP) ([RFC7230]) and the conventions described in RFC 7480 ([RFC7480]).

1.1. 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 [RFC2119].

2. RDAP Path Segment Specification

The new search paths are OPTIONAL extensions of path segments defined in RFC 7482 ([RFC7482]). The search paths are:

The reverse search pattern is a JSON ([RFC8259]) object including two members:

The search patterns corresponding to the "value" in the first two cases (Figure 1) are the same as specified in paragraph Section 3.2.3 of RFC 7482 ([RFC7482]).



Figure 1: Examples of RDAP queries to find all domains related to any registrant whose handle matches "CID-40*" and whose formatted name matches "Bobby*"

The last two reverse searches are considered by gTLD stakeholders very useful to improve RDS searchability ([ICANN-RDS1], [ICANN-RA]).

Searches for domains by related entity email are specified using this form:


where XXXX is a search pattern representing an email address as defined in RFC 5322 ([RFC5322]).

Searches for domains by related entity postal address are specified using this form:


where YYYY is a JSON object containing the information described in Section 2.4 of RFC 5733 ([RFC5733]), respectively: "street", "city", "sp", "pc" and "cc" (Figure 2). All the members of the postal address object are OPTIONAL but at least one is REQUIRED. The constraints on the members are implicitly joined by AND.


Figure 2: Example of an RDAP query to find all domains related to any registrant whose postal address contains the country code equals to "CA" and the city equals to "Sydney"

3. Implementation Considerations

The implementation of the proposed extension is technically feasible. The search paths "handle" and "fn" are used as standard paths to search for entities. With regards to the last two reverse searches, both email and postal address information are usually required by the registries but, while the former is usually mapped onto a DBMS indexed field, the latter is mapped onto a combination of non-indexed fields. As a consequence, while the former should not significantly decrease the performance, the latter might have an impact on server processing. Anyway, this impact is evaluated to be the same as other query capabilities already presented in RDAP (e.g. wildcard prefixed search pattern) so the risks to generate huge result sets are the same as those related to other standard searches and can be mitigated by adopting the same policies (e.g. restricting the search functionalities, limiting the rate of search requests according to the user profile, truncating and paging the results, returning partial responses).

3.1. JSON in URLs

Many web services, including RDAP, rely on the HTTP GET method to take advantage of some of its features:

Sometimes, it happens that such advantages should be combined with the requirement to pass objects and arrays in the query string. JSON is the best candidate as data interchange format, but it contains some characters that are forbidden from appearing in a URL. Anyway, escaping the invalid characters is not an issue because, on the client side, modern browsers automatically encode URLs and, on the server side, several URL encoding/decoding libraries for all web development programming languages are available. The downside of URL encoding is that it can make a pretty long URL, which, depending on the initial length and the number of invalid characters, might exceed the practical limit of web browsers (i.e. 2,000 characters).

Other solutions to pass a JSON expression in a URL could be:

The extensions proposed in this document rely on URL encoding because it is widely supported and the risk to exceed the maximum URL length is considered to be very unlikely in RDAP.

4. Implementation Status

NOTE: Please remove this section and the reference to RFC 7942 prior to publication as an RFC.

This section records the status of known implementations of the protocol defined by this specification at the time of posting of this Internet-Draft, and is based on a proposal described in RFC 7942 ([RFC7942]). The description of implementations in this section is intended to assist the IETF in its decision processes in progressing drafts to RFCs. Please note that the listing of any individual implementation here does not imply endorsement by the IETF. Furthermore, no effort has been spent to verify the information presented here that was supplied by IETF contributors. This is not intended as, and must not be construed to be, a catalog of available implementations or their features. Readers are advised to note that other implementations may exist.

According to RFC 7942, "this will allow reviewers and working groups to assign due consideration to documents that have the benefit of running code, which may serve as evidence of valuable experimentation and feedback that have made the implemented protocols more mature. It is up to the individual working groups to use this information as they see fit".

4.1. IIT-CNR/

5. Privacy Considerations

The use of the capability described in this document MUST be compliant with the rules about privacy protection each RDAP provider is subject to. Sensitive registration data MUST be protected and accessible for permissible purposes only. Therefore, RDAP servers MUST provide reverse search only to those requestors who are authorized according to a lawful basis. Some potential users of this capability include registrars searching for their own domains and operators in the exercise of an official authority or performing a specific task in the public interest that is set out in a law. Another scenario consists of permitting reverse searches, which take into account only those entities that have previously given the explicit consent for publishing and processing their personal data.

6. Security Considerations

Security services required to provide controlled access to the operations specified in this document are described in RFC 7481 ([RFC7481]).

7. IANA Considerations

This document has no actions for IANA.

8. Acknowledgements

The authors would like to acknowledge Scott Hollenbeck, Francisco Arias, Gustavo Lozano and Eduardo Alvarez for their contribution to this document.

9. References

9.1. 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.
[RFC3912] Daigle, L., "WHOIS Protocol Specification", RFC 3912, DOI 10.17487/RFC3912, September 2004.
[RFC5322] Resnick, P., "Internet Message Format", RFC 5322, DOI 10.17487/RFC5322, October 2008.
[RFC5730] Hollenbeck, S., "Extensible Provisioning Protocol (EPP)", STD 69, RFC 5730, DOI 10.17487/RFC5730, August 2009.
[RFC5733] Hollenbeck, S., "Extensible Provisioning Protocol (EPP) Contact Mapping", STD 69, RFC 5733, DOI 10.17487/RFC5733, August 2009.
[RFC7230] Fielding, R. and J. Reschke, "Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing", RFC 7230, DOI 10.17487/RFC7230, June 2014.
[RFC7480] Newton, A., Ellacott, B. and N. Kong, "HTTP Usage in the Registration Data Access Protocol (RDAP)", RFC 7480, DOI 10.17487/RFC7480, March 2015.
[RFC7481] Hollenbeck, S. and N. Kong, "Security Services for the Registration Data Access Protocol (RDAP)", RFC 7481, DOI 10.17487/RFC7481, March 2015.
[RFC7482] Newton, A. and S. Hollenbeck, "Registration Data Access Protocol (RDAP) Query Format", RFC 7482, DOI 10.17487/RFC7482, March 2015.
[RFC7483] Newton, A. and S. Hollenbeck, "JSON Responses for the Registration Data Access Protocol (RDAP)", RFC 7483, DOI 10.17487/RFC7483, March 2015.
[RFC8259] Bray, T., "The JavaScript Object Notation (JSON) Data Interchange Format", STD 90, RFC 8259, DOI 10.17487/RFC8259, December 2017.

9.2. Informative References

[ICANN-RA] Internet Corporation For Assigned Names and Numbers, "Registry Agreement", July 2017.
[ICANN-RDS1] Internet Corporation For Assigned Names and Numbers, "Final Report from the Expert Working Group on gTLD Directory Services: A Next-Generation Registration Directory Service (RDS)", June 2014.
[ICANN-RDS2] Internet Corporation For Assigned Names and Numbers, "Final Issue Report on a Next-Generation gTLD RDS to Replace WHOIS", October 2015.
[JSURL], "JSURL", 2016.
[REST] Fielding, R., "Architectural Styles and the Design of Network-based Software Architectures", 2000.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006.
[RFC7942] Sheffer, Y. and A. Farrel, "Improving Awareness of Running Code: The Implementation Status Section", BCP 205, RFC 7942, DOI 10.17487/RFC7942, July 2016.
[RISON], "Rison - Compact Data in URIs", 2017.
[URLON], "URL Object Notation", 2017.

Appendix A. Change Log

Initial working group version ported from draft-loffredo-regext-rdap-reverse-search-04
Updated "Privacy Considerations" section.
Revised the text.

Authors' Addresses

Mario Loffredo IIT-CNR/ Via Moruzzi,1 Pisa, 56124 IT EMail: URI:
Maurizio Martinelli IIT-CNR/ Via Moruzzi,1 Pisa, 56124 IT EMail: URI: