| Internet-Draft | RDAP Reverse search | April 2022 |
| Loffredo & Martinelli | Expires 10 October 2022 | [Page] |
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. In the RDAP context, an entity can be associated with any defined object class. Moreover, other relationships between object classes exist and might be used for providing a reverse search capability. Therefore, a reverse search can be applied to other use cases than the classic domain-entity scenario. This document describes RDAP query extensions that allow servers to provide a reverse search feature based on the relationship defined in RDAP between an object class for search and any related object class. The reverse search based on the domain-entity relationship is treated as a particular case but with a special focus on its privacy implications.¶
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Copyright (c) 2022 IETF Trust and the persons identified as the document authors. All rights reserved.¶
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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 cybercrimes), its availability as a standardized Whois capability has been objected to 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] [ICANN-RA], 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.¶
The other 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 or nameservers may be useful to registrars as well. Usually, registries adopt out-of-band solutions to provide results to registrars asking for reverse searches on their domains. Possible reasons for such requests are:¶
the loss of synchronization between the registrar database and the registry database;¶
Currently, RDAP does not provide any means for a client to search for the collection of domains associated with an entity [RFC9082]. 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 an entity can be in relationship with any RDAP object [RFC9083], the availability of a reverse search as largely intended can be common to all the object classes allowed for search. Through a further step of generalization, the meaning of reverse search in the RDAP context can be extended to include any query for retrieving all the objects in relationship with another matching a given search pattern.¶
The protocol described in this specification aims to extend the RDAP query capabilities to enable the reverse search based on the relationships defined in RDAP between an object class for search and any related object class. The reverse search based on the domain-entity relationship is treated as a particular case of such a generic query model but with a special focus on its privacy implications. 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 [RFC7480].¶
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.¶
The new search paths are OPTIONAL extensions of those defined in [RFC9082]. A generic reverse search path is described by the syntax:¶
{searchable-resource-type}/reverse/{related-resource-type}?<search-condition>¶
The path segments are defined as in the following:¶
searchable-resource-type: it MUST be one of resource types for search defined in Section 3.2 of [RFC9082], i.e. "domains", "nameservers" and "entities";¶
related-resource-type: it MUST be one of the resource types for lookup defined in Section 3.1 of [RFC9082], i.e. "domain", "nameserver", "entity", "ip" and "autnum";¶
Partial string matching in search patterns is allowed as defined in section 4.1 of [RFC9082].¶
Since in RDAP, an entity can be associated with any other object class, the most common kind of reverse searches are based on the entity details. Such reverse searches arise from the above query model by setting the related resource type to "entity".¶
By selecting a specific searchable resource type, the resulting reverse search aims at retrieving all the objects (e.g. all the domains) that are related to any entity object matching the search condition.¶
This section defines the following reverse search properties to be used regardless of the searchable resource type being selected:¶
Regarding the above definitions, it must be noted that:¶
the mapping between the reverse search property and the corresponding RDAP response property is done through the use of a JSONPath expression [I-D.ietf-jsonpath-base];¶
the presence of a predicate on the reverse search property "role" means that the RDAP response property "roles" must contain at least the specified role;¶
Servers MAY implement other properties than those defined in this section.¶
Examples of reverse search paths based on the domain-entity relationship are presented below:¶
/domains/reverse/entity?handle=CID-40*&role=technical
/domains/reverse/entity?fn=Bobby*&role=registrant
/domains/reverse/entity?handle=RegistrarX&role=registrar
Servers complying with this specification MUST include the value "reverse_search_0" in the rdapConformance property of the help response [RFC9083]. The information needed to register this value in the "RDAP Extensions" registry is described in Section 6.¶
The implementation of the proposed extension is technically feasible. To limit the impact of processing the search predicates, servers are RECOMMENDED to mandate the use of at least one property among those mapped to indexed fields of the registry database. Other properties, such as "role", MAY be allowed to further restrict the set of possible results. In addition, the risks to degrade the performance or to generate huge result sets can be mitigated by adopting the same policies valid for handling searches (e.g. restricting the search functionality, limiting the rate of search requests according to the user profile, truncating and paging the results, returning partial responses).¶
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 [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".¶
IANA is requested to register the following value in the RDAP Extensions Registry:¶
The use of the capability described in this document whenever a contact detail is taken 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. This feature SHOULD be only accessible to authorized users and only for a specified use case.¶
Since the request for this feature could contain Personal Identifiable Information, it SHOULD only be accessible to authorized users and available over HTTPS.¶
Providing reverse search in RDAP carries the following threats as described in [RFC6973]:¶
Therefore, RDAP providers are REQUIRED to mitigate the risk of those threats by implementing appropriate measures supported by security services (see Section 8).¶
Security services required to provide controlled access to the operations specified in this document are described in [RFC7481]. A non-exhaustive list of access control paradigms an RDAP provider can implement is presented in Appendix A.¶
The specification of the relationship within the reverse search path allows the RDAP servers to implement different authorization policies on a per-relationship basis.¶
The authors would like to acknowledge the following individuals for their contributions to this document: Francesco Donini, Scott Hollenbeck, Francisco Arias, Gustavo Lozano, Eduardo Alvarez and Ulrich Wisser.¶
Tom Harrison and Jasdip Singh provided relevant feedback and constant support to the implementation of this proposal. Their contributions are greatly appreciated.¶
Access control can be implemented according to different paradigms introducing increasingly stringent rules. The paradigms reported here in the following leverage the capabilities either supported natively or provided as extensions by the OpenID Connect [OIDCC]:¶
Role-Based Access Control: access rights are granted depending on roles. Generally, this is done by grouping users into fixed categories and assigning each category with static grants. A more dynamic approach can be implemented by using the OpenID Connect "scope" claim;¶
Purpose-Based Access Control: access rules are based on the notion of purpose which means the intended usage of some data by a user. It can be implemented by tagging a request with the usage purpose and making the RDAP server check the compliance between the given purpose and the control rules applied to data to be returned. The purpose can be stated within an out-of-band process by setting the OpenID Connect RDAP specific "purpose" claim as defined in [I-D.ietf-regext-rdap-openid];¶
Attribute-Based Access Control: rules to manage access rights are evaluated and applied according to specific attributes describing the context within which data are requested. It can be implemented by setting within an out-of-band process additional OpenID Connect claims describing the request context and making the RDAP server check the compliance between the given context and the control rules applied to data to be returned;¶