RFC9536: Registration Data Access Protocol (RDAP) Reverse Search
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(RDAP)
(Reverse search)
Internet Engineering Task Force (IETF) M. Loffredo
Request for Comments: 9536 M. Martinelli
Category: Standards Track IIT-CNR/Registro.it
ISSN: 2070-1721 April 2024
Registration Data Access Protocol (RDAP) Reverse Search
Abstract
The Registration Data Access Protocol (RDAP) does not include query
capabilities for finding the list of domains related to a set of
entities matching a given search pattern. Considering that an RDAP
entity can be associated with any defined object class and other
relationships between RDAP object classes exist, a reverse search can
be applied to other use cases besides the classic domain-entity
scenario. This document describes an RDAP extension that allows
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.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9536.
Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction
1.1. Background
1.2. Conventions Used in This Document
2. Reverse Search Path Segment Specification
3. Reverse Search Definition
4. Reverse Search Properties Discovery
5. Reverse Search Properties Mapping
6. Reverse Search Response Specification
7. Reverse Search Query Processing
8. Reverse Searches Based on Entity Details
9. RDAP Conformance
10. Implementation Considerations
11. IANA Considerations
11.1. RDAP Extensions Registry
11.2. RDAP Reverse Search Registries
11.2.1. Creation of the RDAP Reverse Search Registries
11.2.2. Submit Requests to IANA
11.2.3. RDAP Reverse Search Registry
11.2.3.1. Template
11.2.3.2. Initial Content
11.2.4. RDAP Reverse Search Mapping Registry
11.2.4.1. Template
11.2.4.2. Initial Content
12. Privacy Considerations
13. Security Considerations
14. References
14.1. Normative References
14.2. Informative References
Appendix A. Paradigms to Enforce Access Control on Reverse Search
in RDAP
Acknowledgements
Authors' Addresses
1. Introduction
The protocol described in this specification aims to extend the RDAP
query capabilities and response to enable reverse search based on the
relationships defined in RDAP between an object class for search and
a related object class. The reverse search based on the domain-
entity relationship is treated as a particular case of such a generic
model.
RDAP providers willing to implement this specification should
carefully consider its implications on the efficiency (see
Section 10), the security (see Section 13), and the compliance with
privacy regulations (see Section 12) of their RDAP service.
1.1. Background
Reverse WHOIS is a service provided by many web applications that
allows 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 and detecting cybercrimes), its
availability as a standardized WHOIS [RFC3912] capability has been
objected to for two main reasons, which now don't seem to conflict
with an RDAP implementation.
The first objection concerns the potential risks of privacy
violation. However, the domain name community is considering a new
generation of Registration Directory Services [ICANN-RDS] [ICANN-RA]
that provide access to sensitive data under some permissible purposes
and in accordance with appropriate policies for requestor
accreditation, authentication, and authorization. RDAP's reliance on
HTTP means that it can make use of common HTTP-based approaches to
authentication and authorization, making it more useful than WHOIS in
the context of such directory services. Since RDAP consequently
permits a reverse search implementation complying with privacy
protection principles, this first objection is not well-founded.
The second objection to the implementation of a reverse search
capability has been connected with its impact on server processing.
However, the core RDAP specifications already define search queries,
with similar processing requirements, so the basis of this objection
is not clear.
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 and
* the need for such data to perform bulk Extensible Provisioning
Protocol (EPP) [RFC5730] updates (e.g., changing the contacts of a
set of domains, etc.).
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 that relates to another query matching a given search
pattern.
1.2. Conventions Used in This Document
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.
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 follows:
"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
[RFC9535]. Reverse searches are registered in the "RDAP Reverse
Search" registry (see Section 11.2.3), whereas reverse search
mappings are registered in the "RDAP Reverse Search Mapping" registry
(see Section 11.2.4). 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 that
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 structure 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 behavior 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; in such a case, it is necessary for the related object to
match against each of those predicates.
Servers MUST return an HTTP 501 (Not Implemented) [RFC9110] response
to inform clients of unsupported reverse searches.
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 behavior past that set out in this
section.
8. Reverse Searches Based on Entity Details
Since an entity can be associated with any other object class in
RDAP, 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, entity-searchable resource types,
and 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: $.entities[*].vcardArray[1][?(@[0]=='email')][3]
Reference: Section 6.4.2 of [RFC6350]
The presence of a predicate on the reverse search property "role"
means that the RDAP response property "roles" MUST contain at least
the specified role.
The last two properties are related to jCard elements [RFC7095], but
the field references are to vCard [RFC6350], since jCard is the JSON
format for vCard.
Examples of reverse search paths based on the domain-entity
relationship are presented in Figure 1.
/domains/reverse_search/entity?handle=CID-40*&role=technical
/domains/reverse_search/entity?fn=Bobby*&role=registrant
/domains/reverse_search/entity?handle=RegistrarX&role=registrar
Figure 1: Examples of Reverse Search Queries
An example of the help response including the supported reverse
search properties is shown in Figure 2.
{
"rdapConformance": [
"rdap_level_0",
"reverse_search"
],
...
"reverse_search_properties": [
{
"searchableResourceType": "domains",
"relatedResourceType": "entity",
"property": "fn"
},
{
"searchableResourceType": "domains",
"relatedResourceType": "entity",
"property": "handle"
},
{
"searchableResourceType": "domains",
"relatedResourceType": "entity",
"property": "email"
},
{
"searchableResourceType": "domains",
"relatedResourceType": "entity",
"property": "role"
}
],
...
}
Figure 2: An Example of the Help Response including the
"reverse_search_properties" Member
An example of a response including the mapping that is occurring for
the first reverse search in Figure 1 is shown below.
{
"rdapConformance": [
"rdap_level_0",
"reverse_search"
],
...
"reverse_search_properties_mapping": [
{
"property": "handle",
"propertyPath": "$.entities[*].handle"
},
{
"property": "role",
"propertyPath": "$.entities[*].roles"
}
],
...
}
Figure 3: An Example of an RDAP Response including the
"reverse_search_properties_mapping" Member
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 11.1.
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. IANA Considerations
11.1. RDAP Extensions Registry
IANA has registered the following value in the "RDAP Extensions"
registry:
Extension Identifier: reverse_search
Registry Operator: Any
Specification: RFC 9536
Contact: IETF <iesg@ietf.org>
Intended Usage: This extension identifier is used for both URI path
segments and response extensions related to the reverse search in
RDAP.
11.2. RDAP Reverse Search Registries
11.2.1. Creation of the RDAP Reverse Search Registries
IANA has created the "RDAP Reverse Search" and "RDAP Reverse Search
Mapping" registries within the "Registration Data Access Protocol
(RDAP)" category in the protocol registries.
These registries follow the Specification Required registration
policy, as defined in Section 4.6 of [RFC8126].
The designated expert should prevent collisions and confirm that
suitable documentation, as described in Section 4.5 of [RFC8126], is
available to ensure interoperability.
Creators of either new RDAP reverse searches or new mappings for
registered reverse searches SHOULD NOT replicate functionality
already available by way of other documents referenced in these
registries. Creators MAY register additional reverse search mappings
for existing properties, but they SHOULD NOT map a registered reverse
search property to a response field with a meaning other than that of
the response fields referenced by the mappings already registered for
that property. In other words, all the mappings for a reverse search
property MUST point to response fields with the same meaning.
11.2.2. Submit Requests to IANA
Registration requests can be sent to <iana@iana.org>.
11.2.3. RDAP Reverse Search Registry
11.2.3.1. Template
Property: The name of the reverse search property.
Description: A brief human-readable text describing the reverse
search property.
Searchable Resource Type: The searchable resource type of the
reverse search query (Section 2) including the reverse search
property. Multiple reverse search properties differing only by
this field can be grouped together by listing all the searchable
resource types separated by comma (see Section 11.2.3.2).
Related Resource Type: The related resource type of the reverse
search query (Section 2) including the reverse search property.
Registrant: The name of the person registering the reverse search
property.
Contact Information: An email address, postal address, or some other
information to be used to contact the registrant.
Reference: Document (e.g., the RFC number) and section reference
where the reverse search property is specified.
The combination of Searchable Resource Type, Related Resource Type,
and Property MUST be unique across the registry entries.
11.2.3.2. Initial Content
IANA has registered the following entries in the "RDAP Reverse
Search" registry. For all entries, the common values are shown in
Table 1, whereas the specific values are shown in Table 2.
+==========================+================================+
| Registry Property | Value |
+==========================+================================+
| Searchable Resource Type | domains, nameservers, entities |
+--------------------------+--------------------------------+
| Related Resource Type | entity |
+--------------------------+--------------------------------+
| Registrant | IETF |
+--------------------------+--------------------------------+
| Contact Information | iesg@ietf.org |
+--------------------------+--------------------------------+
| Reference | RFC 9536 |
+--------------------------+--------------------------------+
Table 1: Common Values for All Entries in the RDAP
Reverse Search Registry
+==========+==============================================+
| Property | Description |
+==========+==============================================+
| fn | The server supports the domain/nameserver/ |
| | entity search based on the full name (a.k.a. |
| | formatted name) of an associated entity |
+----------+----------------------------------------------+
| handle | The server supports the domain/nameserver/ |
| | entity search based on the handle of an |
| | associated entity |
+----------+----------------------------------------------+
| email | The server supports the domain/nameserver/ |
| | entity search based on the email address of |
| | an associated entity |
+----------+----------------------------------------------+
| role | The server supports the domain/nameserver/ |
| | entity search based on the role of an |
| | associated entity |
+----------+----------------------------------------------+
Table 2: Specific Values for Entries in the RDAP
Reverse Search Registry
11.2.4. RDAP Reverse Search Mapping Registry
11.2.4.1. Template
Property: The same as defined in the "RDAP Reverse Search" registry.
Property Path: The JSONPath of the RDAP property this reverse search
property maps to.
Searchable Resource Type: The same as defined in the "RDAP Reverse
Search" registry.
Related Resource Type: The same as defined in the "RDAP Reverse
Search" registry.
Registrant: The name of the person registering this reverse search
property mapping.
Contact Information: The same as defined in the "RDAP Reverse
Search" registry.
Reference: Document (e.g., the RFC number) and section reference
where this reverse search property mapping is specified.
The combination of Searchable Resource Type, Related Resource Type,
Property, and Property Path MUST be unique across the registry
entries.
11.2.4.2. Initial Content
IANA has registered the following entries in the "RDAP Reverse Search
Mapping" registry. For all entries, the common values are the same
as defined in the "RDAP Reverse Search" registry (see Table 1),
whereas the specific values are shown below (see Table 3).
+==========+==================================================+
| Property | Property Path |
+==========+==================================================+
| fn | $.entities[*].vcardArray[1][?(@[0]=='fn')][3] |
+----------+--------------------------------------------------+
| handle | $.entities[*].handle |
+----------+--------------------------------------------------+
| email | $.entities[*].vcardArray[1][?(@[0]=='email')][3] |
+----------+--------------------------------------------------+
| role | $.entities[*].roles |
+----------+--------------------------------------------------+
Table 3: Specific Values for Entries in the RDAP Reverse
Search Mapping Registry
12. 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 trade-offs
that result from implementing 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 those cases where this functionality makes use of sensitive
information, the information MUST only be accessible to authorized
users under a lawful basis.
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 data
Therefore, RDAP providers need to mitigate the risk of those threats
by implementing appropriate measures supported by security services
(see Section 13).
13. Security Considerations
Security services that are 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.
As an additional measure to enforce security by preventing reverse
searches to be accessed from unauthorized users, the RDAP providers
may consider physically separating the reverse search endpoints from
the other ones by configuring a proxy routing the reverse searches to
a dedicated backend server and leveraging further security services
offered by other protocol layers, such as digital certificates and IP
allow-listing.
Finally, the specification of the relationship within the reverse
search path allows the RDAP servers to implement different
authorization policies on a per-relationship basis.
14. References
14.1. 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,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC6350] Perreault, S., "vCard Format Specification", RFC 6350,
DOI 10.17487/RFC6350, August 2011,
<https://www.rfc-editor.org/info/rfc6350>.
[RFC7095] Kewisch, P., "jCard: The JSON Format for vCard", RFC 7095,
DOI 10.17487/RFC7095, January 2014,
<https://www.rfc-editor.org/info/rfc7095>.
[RFC7481] Hollenbeck, S. and N. Kong, "Security Services for the
Registration Data Access Protocol (RDAP)", STD 95,
RFC 7481, DOI 10.17487/RFC7481, March 2015,
<https://www.rfc-editor.org/info/rfc7481>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC9082] Hollenbeck, S. and A. Newton, "Registration Data Access
Protocol (RDAP) Query Format", STD 95, RFC 9082,
DOI 10.17487/RFC9082, June 2021,
<https://www.rfc-editor.org/info/rfc9082>.
[RFC9083] Hollenbeck, S. and A. Newton, "JSON Responses for the
Registration Data Access Protocol (RDAP)", STD 95,
RFC 9083, DOI 10.17487/RFC9083, June 2021,
<https://www.rfc-editor.org/info/rfc9083>.
[RFC9110] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP Semantics", STD 97, RFC 9110,
DOI 10.17487/RFC9110, June 2022,
<https://www.rfc-editor.org/info/rfc9110>.
[RFC9535] Gössner, S., Ed., Normington, G., Ed., and C. Bormann,
Ed., "JSONPath: Query Expressions for JSON", RFC 9535,
DOI 10.17487/RFC9535, February 2024,
<https://www.rfc-editor.org/info/rfc9535>.
14.2. Informative References
[ICANN-RA] ICANN, "Base Registry Agreement", January 2024,
<https://www.icann.org/en/registry-agreements/base-
agreement>.
[ICANN-RDS]
ICANN, "Final Report from the Expert Working Group on gTLD
Directory Services: A Next-Generation Registration
Directory Service (RDS)", June 2014,
<https://www.icann.org/en/system/files/files/final-report-
06jun14-en.pdf>.
[OIDCC] Sakimura, N., Bradley, J., Jones, M., de Medeiros, B., and
C. Mortimore, "OpenID Connect Core 1.0 incorporating
errata set 2", December 2023,
<http://openid.net/specs/openid-connect-core-1_0.html>.
[RFC3912] Daigle, L., "WHOIS Protocol Specification", RFC 3912,
DOI 10.17487/RFC3912, September 2004,
<https://www.rfc-editor.org/info/rfc3912>.
[RFC5730] Hollenbeck, S., "Extensible Provisioning Protocol (EPP)",
STD 69, RFC 5730, DOI 10.17487/RFC5730, August 2009,
<https://www.rfc-editor.org/info/rfc5730>.
[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,
<https://www.rfc-editor.org/info/rfc6973>.
[RFC8977] Loffredo, M., Martinelli, M., and S. Hollenbeck,
"Registration Data Access Protocol (RDAP) Query Parameters
for Result Sorting and Paging", RFC 8977,
DOI 10.17487/RFC8977, January 2021,
<https://www.rfc-editor.org/info/rfc8977>.
[RFC8982] Loffredo, M. and M. Martinelli, "Registration Data Access
Protocol (RDAP) Partial Response", RFC 8982,
DOI 10.17487/RFC8982, February 2021,
<https://www.rfc-editor.org/info/rfc8982>.
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 listed below
leverage the capabilities that are either built in or provided as
extensions by the OpenID Connect [OIDCC]:
Role-Based Access Control (RBAC): 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 (PBAC): 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 (ABAC): 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 within an out-of-band process by setting additional
OpenID Connect claims that describe the request context and make
the RDAP server check for compliance between the given context and
the control rules that are applied to the data to be returned.
Time-Based Access Control (TBAC): Data access is allowed for a
limited time only. It can be implemented by assigning users
temporary credentials linked to access grants with limited scopes.
With regard to the privacy threats reported in Section 12,
correlation and disclosure can be mitigated by minimizing both the
request features and the response data based on user roles (i.e.,
RBAC). Misuse can be mitigated by checking for the purpose of the
request (i.e., PBAC). It can be accomplished according to the
following approaches:
Full Trust: The registry trusts the fairness of an accredited user.
The requestor is always legitimized to submit their requests under
a lawful basis. Additionally, they can be required to specify the
purpose as either a claim of their account or a query parameter.
In the former case, the purpose is assumed to be the same for
every request. In the latter case, the purpose must be one of
those associated to the user.
Zero Trust: The registry requires documents that assess whether the
requestor is legitimized to submit a given request. It can be
implemented by assigning the requestor a temporary OpenID account
linked to the given request (i.e., TBAC) and describing the
request through a set of claims (i.e., ABAC). The association
between the temporary account and the claims about the request is
made by an out-of-band application. In so doing, the RDAP server
is able to check that the incoming request is consistent with the
request claims linked to the temporary account.
The two approaches can be used together:
* The former is suitable for users carrying out a task in the public
interest or exercising their official authority (e.g., an officer
of a cybercrime agency). Similarly, registrars can submit reverse
searches on their domains and contacts based on their contractual
relationship with the domain holders. In this case, the query
results can be restricted to those pertaining to a registrar by
adding an implicit predicate to the search condition.
* The latter can be taken to allow domain name dispute resolution
service providers to request information in defense of the
legitimate interests of complainants.
Acknowledgements
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, Ulrich
Wisser, James Gould, and Pawel Kowalik.
Tom Harrison and Jasdip Singh provided relevant feedback and constant
support to the implementation of this proposal. Their contributions
have been greatly appreciated.
Authors' Addresses
Mario Loffredo
IIT-CNR/Registro.it
Via Moruzzi,1
56124 Pisa
Italy
Email: mario.loffredo@iit.cnr.it
URI: http://www.iit.cnr.it
Maurizio Martinelli
IIT-CNR/Registro.it
Via Moruzzi,1
56124 Pisa
Italy
Email: maurizio.martinelli@iit.cnr.it
URI: http://www.iit.cnr.it