Registration Data Access Protocol (RDAP) Reverse Search

Status of This Memo

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Table of Contents

2. Reverse Search Path Segment Specification

A generic reverse search path is described by the syntax:¶

{searchable-resource-type}/reverse_search/{related-resource-type}?<search-condition>¶

The path segments are defined as in the following:¶

• searchable-resource-type: it MUST be one of the resource types for search defined in Section 3.2 of [RFC9082] (i.e. "domains", "nameservers" and "entities") or a resource type extension;¶

• 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") or a resource type extension;¶

• search-condition: a sequence of "property=search pattern" predicates separated by the ampersand character ('&', US-ASCII value 0x0026).¶

While related-resource-type is defined as having one of a number of different values, the only reverse searches defined in this document are for a related-resource-type of "entity". Reverse searches for the other resource types specified in [RFC9082] and resource type extensions may be defined by future documents.¶

3. Reverse Search Definition

Based on the content of Section 2, defining a reverse search means to define the triple <searchable resource type, related resource type, property> and the mapping with the corresponding RDAP object member. The mapping is done through the use of a JSONPath expression [I-D.ietf-jsonpath-base]. Reverse searches are registered in the Reverse Search registry (see Section 12.2.3), while reverse search mappings are registered in the Reverse Search Mapping registry (see Section 12.2.4). The reason for having two registries is that it may be possible for a single type of reverse search to rely on different members, depending on the server's configuration (see Section 5).¶

All of the reverse searches defined by this document (see Section 8) have property names that are the same as the name of the RDAP object member that is the subject of the search: for example, the reverse search with the property name "fn" relies on the value of the "fn" member inside the jCard of an entity object. However, it is not necessary that these two names be the same. In particular, remapping of searches as part of the deprecation of an existing member (see Section 5) will typically lead to a member with a different name being used for the search.¶

Servers MUST NOT provide or implement reverse searches or reverse search mappings that are not registered with IANA.¶

4. Reverse Search Properties Discovery

Servers complying with this specification MUST extend the help response [RFC9083] with the "reverse_search_properties" member which contains an array of objects with the following mandatory child members:¶

"searchableResourceType":

the searchable resource type of the reverse search query as defined in Section 2;¶

"relatedResourceType":

the related resource type of the reverse search query as defined in Section 2;¶

"property":

the reverse search property used in the predicate of the reverse search query as defined in Section 2;¶

An example of the help response including the "reverse_search_properties" member is shown in Figure 2.¶

5. Reverse Search Properties Mapping

To permit clients to determine the member used by the server for a reverse search, servers MUST detail the mapping that is occurring by adding the "reverse_search_properties_mapping" member to the topmost object of a reverse search response. This data is included in the search response, rather than in the help response, because it may differ depending on the query that is sent to the server.¶

Documents that deprecate or restructure RDAP responses such that a registered reverse search is no longer able to be used MUST either note that the relevant reverse search is no longer available (in the case of deprecation) or describe how to continue supporting the relevant search by adding another mapping for the reverse search property (in the case of restructuring).¶

The "reverse_search_properties_mapping" member contains an array of objects with the following mandatory child members:¶

"property":

the reverse search property used in the predicate of the current query as defined in Section 2;¶

"propertyPath":

the JSONPath expression of the object member (or members) corresponding to the reverse search property.¶

The searchable and the related resource types are derived from the query, so there is no need to include them in addition to the property in this member.¶

This member MUST be included for all properties used in the search, regardless of whether that property has multiple registered mappings as at the time of the search, because new mappings may be registered at any time.¶

When applied to an object, the JSONPath expression MUST produce a list of values, each of which is a JSON number or string.¶

An example of a reverse search response including the "reverse_search_properties_mapping" member is shown in Figure 3.¶

6. Reverse Search Response Specification

Reverse search responses use the formats defined in section 8 of [RFC9083], which correspond to the searchable resource types defined in Section 2.¶

7. Reverse Search Query Processing

To process a reverse search, the server returns the objects from its data store that are of type searchable-resource-type and that match each of the predicates from the search conditions. To determine whether an object matches a predicate, the server:¶

• applies the mapping it uses for the reverse search property to the object in order to generate a list of values, each of which MUST be a JSON number or string; and¶
• checks whether the search pattern matches one or more of those values.¶

A search pattern matches a value where it equals the string representation of the value, or where it is a match for the value in accordance with the partial string matching behaviour defined in section 4.1 of [RFC9082].¶

Objects are only included in the search results if they satisfy all included predicates. This includes predicates that are for the same property: it is necessary in such a case for the related object to match against each of those predicates.¶

Based on their policy, servers MAY restrict how predicates are used to make a valid search condition, by returning a 400 (Bad Request) response when a problematic request is received.¶

A given reverse search or reverse search mapping MAY define additional or alternative search behaviour past that set out in this section.¶

8. Reverse Searches Based on Entity Details

Since in RDAP, an entity can be associated with any other object class, the most common kind of reverse search is one based on an entity's details. Such reverse searches arise from the 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 conditions.¶

This section defines the reverse search properties servers SHOULD support for the domain, nameserver, and entity searchable resource types and the entity related resource type:¶

Reverse search property:

role¶

RDAP member path:

$..entities[*].roles¶

Reference:

Section 10.2.4 of [RFC9083]¶

Reverse search property:

handle¶

RDAP member path:

$..entities[*].handle¶

Reference:

Section 5.1 of [RFC9083]¶

Reverse search property:

fn¶

RDAP member path:

$..entities[*].vcardArray[1][?(@[0]=='fn')][3]¶

Reference:

Section 6.2.1 of [RFC6350]¶

Reverse search property:

email¶

RDAP member path:

$..entities[*].vcardArray[1][?(@[0]=='email')][3]¶

Reference:

Section 6.4.2 of [RFC6350]¶

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.¶

The last two properties are related to jCard elements [RFC7095], but the field references are to vCard [RFC6350], since jCard is the JSON format for vCard.¶

Examples of reverse search paths based on the domain-entity relationship are presented in Figure 1.¶

 /domains/reverse_search/entity?handle=CID-40*&role=technical

 /domains/reverse_search/entity?fn=Bobby*&role=registrant

 /domains/reverse_search/entity?handle=RegistrarX&role=registrar

An example of the help response including the reverse search properties supported is shown below.¶

   {
     "rdapConformance": [
       "rdap_level_0",
       "reverse_search"
     ],
     ...
     "reverse_search_properties": [
       {
         "searchableResourceType": "domains",
         "relatedResourceType": "entity",
         "property": "fn"
       },
       {
         "searchableResourceType": "domains",
         "relatedResourceType": "entity",
         "property": "handle"
       },
       {
         "searchableResourceType": "domains",
         "relatedResourceType": "entity",
         "property": "email"
       },
       {
         "searchableResourceType": "domains",
         "relatedResourceType": "entity",
         "property": "role"
       }
     ],
     ...
   }

An example of a response including the mapping that is occurring for the first reverse search in Figure 1 is shown below.¶

   {
     "rdapConformance": [
       "rdap_level_0",
       "reverse_search"
     ],
     ...
     "reverse_search_properties_mapping": [
       {
         "property": "handle",
         "propertyPath": "$..entities[*].handle"
       },
       {
         "property": "role",
         "propertyPath": "$..entities[*].roles"
       }
     ],
     ...
   }

9. RDAP Conformance

Servers complying with this specification MUST include the value "reverse_search" in the rdapConformance property of the help response [RFC9083] and any other response including the "reverse_search_properties_mapping" member. The information needed to register this value in the "RDAP Extensions" registry is described in Section 12.1.¶

10. Implementation Considerations

To limit the impact of processing the search predicates, servers are RECOMMENDED to make use of techniques to speed up the data retrieval in their underlying data store such as indexes or similar. In addition, risks with respect to performance degradation or result set generation can be mitigated by adopting practices used for standard searches, e.g. restricting the search functionality, limiting the rate of search requests according to the user's authorization, truncating and paging the results [RFC8977], and returning partial responses [RFC8982].¶

11. 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 [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".¶

13. Privacy Considerations

The search functionality defined in this document may affect the privacy of entities in the registry (and elsewhere) in various ways: see [RFC6973] for a general treatment of privacy in protocol specifications. Registry operators should be aware of the tradeoffs that result from implementation of this functionality.¶

Many jurisdictions have laws or regulations that restrict the use of "Personal Data", per the definition in [RFC6973]. Given that, registry operators should ascertain whether the regulatory environment in which they operate permits implementation of the functionality defined in this document.¶

In general, given the sensitivity of this functionality, it SHOULD be accessible to authorized users only, and for specific use cases only.¶

Since reverse search requests and responses could contain Personally Identifiable Information (PII), reverse search functionality MUST be available over HTTPS only.¶

Providing reverse search in RDAP carries the following threats as described in [RFC6973]:¶

• Correlation¶
• Disclosure¶
• Misuse of information¶

Therefore, RDAP providers are REQUIRED to mitigate the risk of those threats by implementing appropriate measures supported by security services (see Section 14).¶

14. Security Considerations

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.¶

Appendix A. Paradigms to Enforce Access Control on Reverse Search in RDAP

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 static grants to each category. 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, being the intended use 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 the data to be returned;¶

• 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 the data to be returned;¶

• Time-Based Access Control: data access is allowed for a limited time only. It can be implemented by assigning the users with temporary credentials linked to access grants whose scope is limited.¶

Authors' Addresses