ENUM -- Telephone Number Mapping A. Mayrhofer Working Group enum.at Internet-Draft B. Hoeneisen Expires: January 9, 2006 Switch July 8, 2005 ENUM Validation Architecture draft-mayrhofer-enum-validation-arch-00 Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on January 9, 2006. Copyright Notice Copyright (C) The Internet Society (2005). Abstract An ENUM domain name is tightly coupled with the underlying E.164 number. The process of verifying whether or not the Registrant of an ENUM domain name is identical to the Assignee of the corresponding E.164 number is commonly called "validation". This document describes validation requirements and a high level architecture for an ENUM validation infrastructure. Mayrhofer & Hoeneisen Expires January 9, 2006 [Page 1] Internet-Draft ENUM Validation Architecture July 2005 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1 Requirements . . . . . . . . . . . . . . . . . . . . . . . 3 2. ENUM Provisioning Model and Roles . . . . . . . . . . . . . . 4 2.1 Number Assignment Entity (NAE) . . . . . . . . . . . . . . 5 2.2 Assignee . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.3 Registrant . . . . . . . . . . . . . . . . . . . . . . . . 7 2.4 Validation Entity (VE) . . . . . . . . . . . . . . . . . . 7 2.5 Registry . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.6 Registrar . . . . . . . . . . . . . . . . . . . . . . . . 7 2.7 Domain Name System Service Provider (DNS-SP) . . . . . . . 8 2.8 Application Service Provider (ASP) . . . . . . . . . . . . 8 3. Validation Process Assumptions . . . . . . . . . . . . . . . . 8 3.1 Work Flow . . . . . . . . . . . . . . . . . . . . . . . . 8 3.2 Trust Relations . . . . . . . . . . . . . . . . . . . . . 9 3.3 Data Flow and Format . . . . . . . . . . . . . . . . . . . 10 4. Example Scenarios . . . . . . . . . . . . . . . . . . . . . . 10 4.1 E.164 Number Assignment along with ENUM Registration . . . 10 4.2 Fully Disjoint Roles . . . . . . . . . . . . . . . . . . . 12 5. Security Considerations . . . . . . . . . . . . . . . . . . . 14 5.1 Fraud Prevention . . . . . . . . . . . . . . . . . . . . . 14 5.2 Assignee Data . . . . . . . . . . . . . . . . . . . . . . 14 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 15 Intellectual Property and Copyright Statements . . . . . . . . 16 Mayrhofer & Hoeneisen Expires January 9, 2006 [Page 2] Internet-Draft ENUM Validation Architecture July 2005 1. Introduction ENUM [1] uses the Domain Name System (DNS) [2] for mapping E.164 numbers [3] to Uniform Resource Identifiers (URIs). E.164 numbers are converted to ENUM domain names through means described further in RFC 3761 [1]. "Ordinary" domain names are usually allocated on a first-come-first- served basis, where the associated registration data is the complete source of ownership. However, ENUM domain names are linked to E.164 numbers, and thus intrinsically tied to the status and the Assignee of the corresponding E.164 number. 1.1 Requirements Preserving integrity between ENUM and E.164 is one of the main concerns in current ENUM implementations, and often one of the reasons why "trials" precede commercial implementations. To maintain this relationship between E.164 numbers and ENUM domain names, registration processes must ensure that during the entire lifetime of an ENUM delegation the following requirements are fulfilled: o The ENUM domain name either corresponds to an assigned E.164 number, or the respective E.164 number is being assigned during the registration process itself. o The corresponding E.164 number is within a number area approved to be used with ENUM. o The registration of the ENUM domain name is authorized by the Assignee of the corresponding E.164 number; i.e. the entity requesting the registration of an ENUM domain name is either the Assignee of the corresponding E.164 number itself or an entity authorized to request registration on behalf of said Assignee. o The Registrant of the ENUM domain is identical to the Assignee of the corresponding E.164 number. The process of verifying the above requirements during registration is commonly called "initial validation". In addition to this one- time validation process, provisions must be made that ENUM domain name delegations are revoked when the requirements above are no longer met. In other words, it must be ensured that the state of the ENUM domain name tracks any change in state and ownership of the corresponding E.164 number. The regular process of ensuring that the above requirements are still satisfied is commonly called "recurring validation" or "revalidation". The above requirements are usually part of the local registration policy issued by the authorities in charge of ENUM administration. Mayrhofer & Hoeneisen Expires January 9, 2006 [Page 3] Internet-Draft ENUM Validation Architecture July 2005 2. ENUM Provisioning Model and Roles The above requirements lead to the introduction of a new role in the provisioning model, an entity performing validation related tasks. A typical ENUM provisioning model, on which this document is based, is depicted in Figure 1: ENUM Model +----------+ .| Registry |- -- -- -- -- -- -- . +----------+ | . | . | | Trust DNS Delegation | Relation . | Registration | . | . | | +--------+ +-----------+ +----+ | DNS-SP |-- -- -- -- --| Registrar |----------------| VE | +--------+ Nameservers +-----------+ Validation +----+ : | / | : | E.164 Number : | ENUM Assignment : NAPTR | Management _ Verification : | / | : | _ : | / | +-----+ ENUM enabled +------------+ E.164 Number +-----+ | ASP |- -- -- -- -- --| Assignee = |-- -- -- -- --| NAE | +-----+ Service | Registrant | Assignment +-----+ +------------+ Legend: ASP: Application Service Provider DNS-SP: Domain Name System Service Provider NAE: Number Assignment Entity VE: Validation Entity Figure 1 These different roles are described further below. Note that an entity can act in more than one of these roles simultaneously, e.g. the Registrar, the DNS-SP, and the ASP roles could be performed by a single company. Mayrhofer & Hoeneisen Expires January 9, 2006 [Page 4] Internet-Draft ENUM Validation Architecture July 2005 2.1 Number Assignment Entity (NAE) A Number Assignment Entity (NAE) assigns E.164 numbers to end users. Often, but not always, the Communication Service Provider (CSP) of the end user (Assignee) acts as NAE. There are two main variants for E.164 number assignments: 1. Indirect assignment: The National Number Plan Administrator (NNPA) assigns ranges of E.164 numbers to CSPs. Out of these ranges, the CSPs assign numbers (or number blocks) to their customers (end-users, Assignees). In this variant the CSPs perform the role of the NAE. 2. Direct assignment: In certain cases a NNPA assigns E.164 numbers directly to Assignees (end-users), and therefore the NNPA acts as NAE in this variant. Typically this concerns the assignment of special purpose numbers (e.g. premium rate). These two variants of E.164 number assignment are depicted in Figure 2: Mayrhofer & Hoeneisen Expires January 9, 2006 [Page 5] Internet-Draft ENUM Validation Architecture July 2005 E.164 Number Assignment +--------------------------------------------+ | International Telecommunication Union (ITU)| +--------------------------------------------+ | Country codes (e.g. +41) | v +-------------------------------------------+ | National Number Plan Administrator (NNPA) |------------+ +-------------------------------------------+ | | | Number Ranges | (e.g. +41 44268 xxxx) | | | v | +--------------------------------------+ | | Communication Service Provider (CSP) | | +--------------------------------------+ | | | | Single Numbers Either Single Numbers (e.g. +41 900 123456) or Number Blocks [Variant 2] (e.g. +41 44268 1234, +41 44268 15 xx) | [Variant 1] | | | v | +----------+ | | Assignee |<------------------------------+ +----------+ Figure 2 As the Assignee (subscriber) data associated with the E.164 number is the primary source of number assignment information, the NAE usually holds the authoritative information required to confirm the assignment. A CSP that acts as NAE (indirect assignment) may therefore easily assert the E.164 number assignment for their subscribers. However it is unlikely that all CSPs will participate in ENUM validation. 2.2 Assignee The person or organization to whom a NAE assigns a E.164 number is called Assignee of this number. For the scope of this document, the term Assignee, subscriber, and number-holder are used equivalently. Mayrhofer & Hoeneisen Expires January 9, 2006 [Page 6] Internet-Draft ENUM Validation Architecture July 2005 The Assignee has the "right to use" on the assigned E.164 number. 2.3 Registrant The ENUM Registrant is the end user, the person or organization who is the "holder" of the ENUM domain name. The Registrant usually has control over his ENUM domain name(s) and its DNS zone content. 2.4 Validation Entity (VE) The Validation Entity (VE) verifies, whether or not the Registrant of an ENUM domain name is identical to the Assignee of the corresponding E.164 number. Often it also verifies that the entity requesting the registration of an ENUM domain name is either the Assignee of the corresponding E.164 number itself or an entity authorized to request registration on behalf of said Assignee. This role may be performed by several parties and is not necessarily limited to a single entity. The actual validation methods applied may vary depending on e.g. the particular party, available data-sources, Assignee's choice, and regulatory requirements. 2.5 Registry The ENUM Registry operates the master database of ENUM domain delegations and runs the authoritative nameservers for the relevant zone under e164.arpa. The Registry is a natural monopoly. While the Registry could try to check the legitimacy of incoming delegation requests, it is often undesirable for the Registry to deal with the validation problem, as it may have no direct link to the Registrant. 2.6 Registrar An ENUM Registrar performs ENUM domain delegations on behalf of a Registrant by interacting with the Registry, typically through a protocol like Extensible Provisioning Protocol (EPP). This role is similar to the one that Registrars fulfill in the "ordinary" domain name registration world. The Registrar may well not be the same entity as the CSP of the Mayrhofer & Hoeneisen Expires January 9, 2006 [Page 7] Internet-Draft ENUM Validation Architecture July 2005 Registrant. Therefore a Registrar may lack authoritative number- assignment information. If the Registrar and the CSP are the same entity (or has a source of authoritative data), the Registrar could perform the role of the VE itself. However, prior to the registration of an ENUM domain name, the Registrar has to ensure a proper validation through a VE. 2.7 Domain Name System Service Provider (DNS-SP) The Domain Name System Service Provider (DNS-SP) operates the nameservers for the ENUM DNS zones, which contain the ENUM Naming Authority Pointer (NAPTR) Resource Record (RR) entries [1]. In most cases the Registry delegates the ENUM DNS zones to the nameservers at the DNS-SP. Usually the DNS-SP is not involved in the validation process. 2.8 Application Service Provider (ASP) The Application Service Provider (ASP) operates a service for the Registrant. This service could be an IP telephony service, whereby the service provider populates the ENUM zone for their customers so that others can discover that customer's URI. Usually the ASP is not involved in the validation process. 3. Validation Process Assumptions 3.1 Work Flow The prototypical initial validation workflow using the above roles and definitions consists of the following steps: 1. A potential Registrant approaches a Registrar, and orders an ENUM domain name. 2. The Registrar chooses a cooperating Validation Entity, and requests an initial validation for the ENUM domain name ordered. 3. The Validation Entity performs the actual validation, which could require interaction with the Assignee/Registrant. 4. The Validation Entity indicates the result of the initial validation to the Registrar. 5. If the validation process was successful, the Registrar provisions the ENUM domain name with the Registry. Depending on the local Registry policy, validation related information may be provided to the Registry along with this registration. In most cases, local policy mandates expiration dates to be imposed on successful validations. If the ENUM delegation is to be kept Mayrhofer & Hoeneisen Expires January 9, 2006 [Page 8] Internet-Draft ENUM Validation Architecture July 2005 beyond this expiration date, recurring validation has to be performed. A typical revalidation workflow involves the following steps: 1. In good time before the current validation expires, the Registrar requests the Validation Entity to revalidate the domain name in question. 2. The Validation Entity verifies if the delegation requirements are still met. It may use information acquired during the initial validation or associated to the registration data. 3. The Validation Entity indicates the result of the recurring validation to the Registrar. 4. In case the revalidation has been successful, the domain delegation may persist. Local Registry policy may require updating domain name registration data, especially in case the Registry keeps validation related expiry information. 5. In case the revalidation has failed, the ENUM domain delegation must be suspended, either by explicit interaction with the Registry or -- if the Registry keeps validation related information -- automatically when the current validation expires. Local policy may grant a grace period on the expiration date. This work flow ensures the integrity between the E.164 and ENUM namespaces. ENUM domain delegations which fail to meet the validation requirements are suspended from DNS. 3.2 Trust Relations The above validation workflow implies the following trust relations: o The Registry trusts the Validation Entities to enforce the local validation policy. o The Registrars trust the Validation Entities properly to perform validation based on the Registrar's request. o Depending on the amount of validation data provided to the Registry additional trust relations may be necessary. Three cases can be differentiated: * The Registry receives no validation related data: The Registry needs to trust the Registrar that validation has been performed, and the result was positive. In addition, the Registry needs to trust the Registrar that it will properly remove delegations for which revalidation fails. * The Registry receives validation related data including expiry date, but there are no means of checking its authenticity: The Registry needs to trust the Registrar that the validation data provided is authentic. * The Registry receives validation related data including expiry date and means to verify its authenticity (e.g. a cryptographic signature issued by the VE): No additional trust relations are necessary. Mayrhofer & Hoeneisen Expires January 9, 2006 [Page 9] Internet-Draft ENUM Validation Architecture July 2005 3.3 Data Flow and Format The validation process requires the following regular data flows (Note: data flows not directly related to validation are out of scope of this document): o Registrars communicate with Validation Entities to initiate, modify or cancel validation requests. Validation Entities act upon validation requests, and provide validation results to Registrars. Since Registrars could potentially communicate with several Validation Entities, and Validation Entities could provide services to several Registrars (worst case: full mesh), a standardized protocol and data format should be used in this data flow. o If the local Registry policy mandates that validation related information is to be stored along with delegation records, a validation related data flow between Registry and Registrar is required. Since the registration itself already requires communication between those entities, validation related information in a standardized data format should be embedded into the existing Registry-Registrar protocol data flow. o Validation Entities may need to communicate with Assignees to perform validation. A Validation Entity may choose to perform all communication with the Assignee via the requesting Registrar rather than contacting the Assignee by itself. Since the actual communication form and process is expected to greatly vary, it does not make sense to specify any data formats or processes for this purpose. 4. Example Scenarios 4.1 E.164 Number Assignment along with ENUM Registration In this simple scenario we assume that the roles of the Registrar, the VE, and the NAE are performed by the same entity, e.g. a Internet Telephony Service Provider (ITSP). This ITSP is a CSP, that was assigned number ranges by the NNPA. Out of these ranges he assigns numbers to his customers (Assignees) to provide those with communication services. The ITSP chooses to assign an E.164 number together with the corresponding ENUM domain name. Therefore it can perform the validation simply by reference to its subscriber database. Figure 3 shows the external interactions needed for the ENUM domain name provisioning process: Mayrhofer & Hoeneisen Expires January 9, 2006 [Page 10] Internet-Draft ENUM Validation Architecture July 2005 E.164 Number Assignment along with ENUM Registration +----------+ | Registry | +----------+ ^ | |(3) | +--------------------------------------+ | | | ITSP | | +-----------+ +----+ | | | Registrar | | VE | | | +-----------+ (2) +----+ | | | +--------------------------+ | ^ | | | | | |(1) | | | | | | | | +------------+ (4) | +-----+ | | Assignee = |<----------| | NAE | | | Registrant | | +-----+ | ------------- | | +-----------+ Legend: ITSP: Internet Telephony Service Provider NAE: Number Assignment Entity VE: Validation Entity Figure 3 1. The ITSP receives an order for ENUM Services. 2. The ITSP assigns a free E.164 number and performs the validation at the same time. 3. The ITSP sends an ENUM registration request to the Registry, which might contain additional information about the validation applied. 4. The ITSP sends a confirmation about the E.164 number assignment and the ENUM registration to its customer, who is now Assignee and Registrant. This scenario is quite close to "ordinary" domain name registrations. Mayrhofer & Hoeneisen Expires January 9, 2006 [Page 11] Internet-Draft ENUM Validation Architecture July 2005 4.2 Fully Disjoint Roles In this more complex scenario we assume that all roles of the ENUM provisioning model are performed by different entities. In contrast with the previous example (in Section 4.1), here we assume that the ENUM domain name to be registered is based on an already assigned E.164 number and the NAE in question provides the VE with access to the subscriber database. We further assume that there is a requirement for the VE to verify the intention of the Assignee. The validation process therefore involves also contacting the Assignee. Figure 4 shows the interactions needed for the ENUM domain name provisioning process: Mayrhofer & Hoeneisen Expires January 9, 2006 [Page 12] Internet-Draft ENUM Validation Architecture July 2005 Fully Disjoint Roles +----------+ | Registry | +----------+ ^ | |(9) | | | (3) +-----------+ ---------->+----+ | Registrar |<---------- | VE | +-----------+ (8) > +----+ ^ / / ^ | | / / | | | (7)/ / | | |(2) / / | | | / / (5)| | | / / | | | / / | | | / /(6) | | | / / | |(4) | / / | | | / / | | +------------+< | v | Assignee = | +-----+ | Registrant |<---------- | NAE | +------------+ (1) +-----+ Legend: NAE: Number Assignment Entity VE: Validation Entity Figure 4 1. The NAE assigns an E.164 number. This assignment could have been done long before the ENUM domain name registration, e.g. at the time when the Assignee subscribed to a common telephony service. 2. The Assignee orders the corresponding ENUM domain name at a Registrar of his choice. 3. The Registrar requests validation at an independent VE. 4. The VE contacts the subscriber database of the NAE, to verify that the Assignee of the E.164 number corresponds to the Registrant of the ENUM domain name. Mayrhofer & Hoeneisen Expires January 9, 2006 [Page 13] Internet-Draft ENUM Validation Architecture July 2005 5. The result of the NAE subscriber database is positive. 6. The VE performs a call-back to the E.164 number to be registered as ENUM domain name, makes provisions for authentication and asks the Assignee to confirm his intention. 7. The Assignee confirms and the VE documents this confirmation. 8. The VE returns a positive answer to the Registrar. The answer might contain some additional information about the validation process, such as expiration date, validation method applied, and so on. 9. Finally the Registrar can send an ENUM registration request to the Registry. Additional information about the validation process might be sent along with the registration request. 5. Security Considerations 5.1 Fraud Prevention Situations where an entity has control over the ENUM domain of a third party's E.164 number impose high fraud potential. Unauthorized control over an ENUM domain of a bank could eg. be used for "man in the middle" attacks on telephone banking applications. Cases of such attacks could discredit ENUM as a whole. Implementing high quality validation processes is therefore crucial to any ENUM deployment, and should receive high attention. 5.2 Assignee Data When handling Assignee data, privacy and discretion issues must be considered. Implementations transporting assignee data over the internet must use authenticated and encrypted transport protocols. Local registration/validation policy and agreements should clearly limit usage of Assignee data. 6. Acknowledgements The authors would like to thank the following persons for their valuable suggestions and contributions: Lawrence Conroy, Michael Haberler, Otmar Lendl, Marcel Parodi, Patrik Schaefer, Richard Stastny 7. References [1] Faltstrom, P. and M. Mealling, "The E.164 to Uniform Resource Identifiers (URI) Dynamic Delegation Discovery System (DDDS) Application (ENUM)", RFC 3761, April 2004. [2] Mockapetris, P., "Domain names - Implementation and Mayrhofer & Hoeneisen Expires January 9, 2006 [Page 14] Internet-Draft ENUM Validation Architecture July 2005 Specification", STD 13, RFC 1035, November 1987. [3] ITU-T, "The international public telecommunication numbering plan", Recommendation E.164, May 1997. Authors' Addresses Alexander Mayrhofer enum.at GmbH Karlsplatz 1/9 Wien A-1010 Austria Phone: +43 1 5056416 34 Email: alexander.mayrhofer@enum.at URI: http://www.enum.at/ Bernie Hoeneisen Switch Neumuehlequai 6 CH-8001 Zuerich Switzerland Phone: +41 44 268 1515 Email: hoeneisen@switch.ch, b.hoeneisen@ieee.org URI: http://www.switch.ch/ Mayrhofer & Hoeneisen Expires January 9, 2006 [Page 15] Internet-Draft ENUM Validation Architecture July 2005 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Disclaimer of Validity This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Copyright Statement Copyright (C) The Internet Society (2005). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Mayrhofer & Hoeneisen Expires January 9, 2006 [Page 16]