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rfc:rfc7481

Internet Engineering Task Force (IETF) S. Hollenbeck Request for Comments: 7481 Verisign Labs Category: Standards Track N. Kong ISSN: 2070-1721 CNNIC

                                                            March 2015
 Security Services for the Registration Data Access Protocol (RDAP)

Abstract

 The Registration Data Access Protocol (RDAP) provides "RESTful" web
 services to retrieve registration metadata from Domain Name and
 Regional Internet Registries.  This document describes information
 security services, including access control, authentication,
 authorization, availability, data confidentiality, and data integrity
 for RDAP.

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 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc7481.

Copyright Notice

 Copyright (c) 2015 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

Hollenbeck & Kong Standards Track [Page 1] RFC 7481 RDAP Security Services March 2015

Table of Contents

 1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
 2.  Conventions Used in This Document . . . . . . . . . . . . . .   2
   2.1.  Acronyms and Abbreviations  . . . . . . . . . . . . . . .   3
 3.  Information Security Services and RDAP  . . . . . . . . . . .   3
   3.1.  Access Control  . . . . . . . . . . . . . . . . . . . . .   3
   3.2.  Authentication  . . . . . . . . . . . . . . . . . . . . .   3
     3.2.1.  Federated Authentication  . . . . . . . . . . . . . .   4
   3.3.  Authorization . . . . . . . . . . . . . . . . . . . . . .   6
   3.4.  Availability  . . . . . . . . . . . . . . . . . . . . . .   6
   3.5.  Data Confidentiality  . . . . . . . . . . . . . . . . . .   7
   3.6.  Data Integrity  . . . . . . . . . . . . . . . . . . . . .   7
 4.  Privacy Threats Associated with Registration Data . . . . . .   8
 5.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
 6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
   6.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
   6.2.  Informative References  . . . . . . . . . . . . . . . . .  11
 Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  13
 Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

1. Introduction

 The Registration Data Access Protocol (RDAP) is specified in multiple
 documents, including "Registration Data Access Protocol (RDAP) Query
 Format" [RFC7482], "JSON Responses for the Registration Data Access
 Protocol (RDAP)" [RFC7483], and "HTTP Usage in the Registration Data
 Access Protocol (RDAP)" [RFC7480].
 One goal of RDAP is to provide security services that do not exist in
 the WHOIS [RFC3912] protocol, including access control,
 authentication, authorization, availability, data confidentiality,
 and data integrity.  This document describes how each of these
 services is achieved by RDAP using features that are available in
 other protocol layers.  Additional or alternative mechanisms can be
 added in the future.  Where applicable, informative references to
 requirements for a WHOIS replacement service [RFC3707] are noted.

2. 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].

Hollenbeck & Kong Standards Track [Page 2] RFC 7481 RDAP Security Services March 2015

2.1. Acronyms and Abbreviations

    DNR: Domain Name Registry
    HTTP: Hypertext Transfer Protocol
    JSON: JavaScript Object Notation
    RDAP: Registration Data Access Protocol
    RIR: Regional Internet Registry
    TLS: Transport Layer Security

3. Information Security Services and RDAP

 RDAP itself does not include native security services.  Instead, RDAP
 relies on features that are available in other protocol layers to
 provide needed security services, including access control,
 authentication, authorization, availability, data confidentiality,
 and data integrity.  A description of each of these security services
 can be found in "Internet Security Glossary, Version 2" [RFC4949].
 No requirements have been identified for other security services.

3.1. Access Control

 WHOIS does not include specific features to control access to
 registration information.  As described in the following sections,
 RDAP includes features to identify, authenticate, and authorize
 clients, allowing server operators to control access to information
 based on a client's identity and associated authorizations.
 Information returned to a client can be clearly marked with a status
 value (see Section 10.2.2 of [RFC7483]) that identifies the access
 granted to the client.

3.2. Authentication

 This section describes security authentication mechanisms and the
 need for authorization policies to include them.  It describes
 requirements for the implementations of clients and servers but does
 not dictate the policies of server operators.  For example, a server
 operator with no policy regarding differentiated or tiered access to
 data will have no authorization mechanisms and will have no need for
 any type of authentication.  A server operator with policies on
 differentiated access will have to construct an authorization scheme
 and will need to follow the specified authentication requirements.

Hollenbeck & Kong Standards Track [Page 3] RFC 7481 RDAP Security Services March 2015

 WHOIS does not provide features to identify and authenticate clients.
 As noted in Section 3.1.4.2 of "Cross Registry Internet Service
 Protocol (CRISP) Requirements" [RFC3707], there is utility in
 allowing server operators to offer "varying degrees of access
 depending on policy and need."  Clients have to be identified and
 authenticated to provide that utility.
 RDAP's authentication framework needs to accommodate anonymous access
 as well as verification of identities using a range of authentication
 methods and credential services.  To that end, RDAP clients and
 servers MUST implement the authentication framework specified in
 "Hypertext Transfer Protocol (HTTP/1.1): Authentication" [RFC7235].
 The "basic" scheme can be used to send a client's user name and
 password to a server in plaintext, base64-encoded form.  The "digest"
 scheme can be used to authenticate a client without exposing the
 client's plaintext password.  If the "basic" scheme is used, HTTP
 over TLS [RFC2818] MUST be used to protect the client's credentials
 from disclosure while in transit (see Section 3.5).
 Servers MUST support either Basic or Digest authentication; they are
 not required to support both.  Clients MUST support both to
 interoperate with servers that support one or the other.  Servers may
 provide a login page that triggers HTTP authentication.  Clients
 should continue sending the HTTP authentication header once they
 receive an initial 401 (Unauthorized) response from the HTTP server
 as long as the scheme portion of the URL doesn't change.
 The Transport Layer Security protocol [RFC5246] includes an optional
 feature to identify and authenticate clients who possess and present
 a valid X.509 digital certificate [RFC5280].  Support for this
 feature is OPTIONAL.
 RDAP does not impose any unique server authentication requirements.
 The server authentication provided by TLS fully addresses the needs
 of RDAP.  In general, transports for RDAP must either provide a
 TLS-protected transport (e.g., HTTPS) or a mechanism that provides an
 equivalent level of server authentication.
 Work on HTTP authentication methods continues.  RDAP is designed to
 be agile enough to support additional methods as they are defined.

3.2.1. Federated Authentication

 The traditional client-server authentication model requires clients
 to maintain distinct credentials for every RDAP server.  This
 situation can become unwieldy as the number of RDAP servers
 increases.  Federated authentication mechanisms allow clients to use
 one credential to access multiple RDAP servers and reduce client

Hollenbeck & Kong Standards Track [Page 4] RFC 7481 RDAP Security Services March 2015

 credential management complexity.  RDAP MAY include a federated
 authentication mechanism that permits a client to access multiple
 RDAP servers in the same federation with one credential.
 Federated authentication mechanisms used by RDAP MUST be fully
 supported by HTTP.  OAuth, OpenID, Security Assertion Markup Language
 (SAML), and mechanisms based on Certification Authority (CA) are all
 possible approaches to provide federated authentication.  At the time
 of this document's publication, negotiation or advertisement of
 federated authentication services is still an undefined mechanism by
 the noted federated authentication protocols.  Developing this
 mechanism is beyond the scope of this document.
 The OAuth authorization framework [RFC6749] describes a method for
 users to access protected web resources without having to hand out
 their credentials.  Instead, clients are issued access tokens by
 authorization servers with the permission of the resource owners.
 Using OAuth, multiple RDAP servers can form a federation, and the
 clients can access any server in the same federation by providing one
 credential registered in any server in that federation.  The OAuth
 authorization framework is designed for use with HTTP and thus can be
 used with RDAP.
 OpenID [OpenID] is a decentralized single sign-on authentication
 system that allows users to log in at multiple web sites with one ID
 instead of having to create multiple unique accounts.  An end user
 can freely choose which OpenID provider to use and can preserve their
 Identifier if they switch OpenID providers.
 Note that OAuth and OpenID do not consistently require data
 confidentiality services to protect interactions between providers
 and consumers.  HTTP over TLS [RFC2818] can be used as needed to
 provide protection against man-in-the-middle attacks.
 SAML 2.0 [SAML] is an XML-based protocol that can be used to
 implement web-based authentication and authorization services,
 including single sign on.  It uses security tokens containing
 assertions to exchange information about an end user between an
 identity provider and a service provider.
 The Transport Layer Security protocol describes the specification of
 a client certificate in Section 7.4.6 of [RFC5246].  Clients who
 possess and present a valid X.509 digital certificate, issued by a
 CA, could be identified and authenticated by a server who trusts the
 corresponding CA.  A certificate authentication method can be used to
 achieve federated authentication in which multiple RDAP servers all
 trust the same CAs, and then any client with a certificate issued by
 a trusted CA can access any RDAP server in the federation.  This

Hollenbeck & Kong Standards Track [Page 5] RFC 7481 RDAP Security Services March 2015

 certificate-based mechanism is supported by HTTPS and can be used
 with RDAP.

3.3. Authorization

 WHOIS does not provide services to grant different levels of access
 to clients based on a client's authenticated identity.  As noted in
 Section 3.1.4.2 of "Cross Registry Internet Service Protocol (CRISP)
 Requirements" [RFC3707], there is utility in allowing server
 operators to offer "varying degrees of access depending on policy and
 need."  Access control decisions can be made once a client's identity
 has been established and authenticated (see Section 3.2).
 Server operators MAY offer varying degrees of access depending on
 policy and need in conjunction with the authentication methods
 described in Section 3.2.  If such varying degrees of access are
 supported, an RDAP server MUST provide granular access controls (that
 is, per registration data object) in order to implement authorization
 policies.  Some examples:
  1. Clients will be allowed access only to data for which they have a

relationship.

  1. Unauthenticated or anonymous access status may not yield any

contact information.

  1. Full access may be granted to a special group of authenticated

clients.

 The type of access allowed by a server will most likely vary from one
 operator to the next.  A description of the response privacy
 considerations associated with different levels of authorization can
 be found in Section 13 of [RFC7483].

3.4. Availability

 An RDAP service has to be available to be useful.  There are no RDAP-
 unique requirements to provide availability, but as a general
 security consideration, a service operator needs to be aware of the
 issues associated with denial of service.  A thorough reading of
 "Internet Denial-of-Service Considerations" [RFC4732] is advised.
 An RDAP service MAY use an HTTP throttling mechanism to limit the
 number of queries that a single client can send in a given period of
 time.  If used, the server SHOULD return an HTTP 429 (Too Many
 Requests) response code as described in "Additional HTTP Status
 Codes" [RFC6585].  A client that receives a 429 response SHOULD
 decrease its query rate and honor the Retry-After header field if one

Hollenbeck & Kong Standards Track [Page 6] RFC 7481 RDAP Security Services March 2015

 is present.  Note that this is not a defense against
 denial-of-service attacks, since a malicious client could ignore the
 code and continue to send queries at a high rate.  A server might use
 another response code if it did not wish to reveal to a client that
 rate limiting is the reason for the denial of a reply.

3.5. Data Confidentiality

 WHOIS does not provide the ability to protect data from inadvertent
 disclosure while in transit.  RDAP uses HTTP over TLS [RFC2818] to
 provide that protection by encrypting all traffic sent on the
 connection between client and server.  HTTP over TLS MUST be used to
 protect all client-server exchanges unless operational constraints
 make it impossible to meet this requirement.  It is also possible to
 encrypt discrete objects (such as command path segments and JSON-
 encoded response objects) at one endpoint, send them to the other
 endpoint via an unprotected transport protocol, and decrypt the
 object on receipt.  Encryption algorithms as described in "Internet
 Security Glossary, Version 2" [RFC4949] are commonly used to provide
 data confidentiality at the object level.
 There are no current requirements for object-level data
 confidentiality using encryption.  Support for this feature could be
 added to RDAP in the future.
 As noted in Section 3.2, the HTTP "basic" authentication scheme can
 be used to authenticate a client.  When this scheme is used, HTTP
 over TLS MUST be used to protect the client's credentials from
 disclosure while in transit.  If the policy of the server operator
 requires encryption to protect client-server data exchanges (such as
 to protect non-public data that cannot be accessed without client
 identification and authentication), HTTP over TLS MUST be used to
 protect those exchanges.
 A description of privacy threats that can be addressed with
 confidentiality services can be found in Section 4.  Section 10.2.2
 of [RFC7483] describes status values that can be used to describe
 operator actions used to protect response data from disclosure to
 unauthorized clients.

3.6. Data Integrity

 WHOIS does not provide the ability to protect data from modification
 while in transit.  Web services such as RDAP commonly use HTTP over
 TLS [RFC2818] to provide that protection by using a keyed Message
 Authentication Code (MAC) to detect modifications.  It is also
 possible to sign discrete objects (such as command path segments and
 JSON-encoded response objects) at one endpoint, send them to the

Hollenbeck & Kong Standards Track [Page 7] RFC 7481 RDAP Security Services March 2015

 other endpoint via a transport protocol, and validate the signature
 of the object on receipt.  Digital signature algorithms as described
 in "Internet Security Glossary, Version 2" [RFC4949] are commonly
 used to provide data integrity at the object level.
 There are no current requirements for object-level data integrity
 using digital signatures.  Support for this feature could be added to
 RDAP in the future.
 The most specific need for this service is to provide assurance that
 HTTP 30x redirection hints [RFC7231] and response elements returned
 from the server are not modified while in transit.  If the policy of
 the server operator requires message integrity for client-server data
 exchanges, HTTP over TLS MUST be used to protect those exchanges.

4. Privacy Threats Associated with Registration Data

 Registration data has historically included personal data about
 registrants.  WHOIS services have historically made this information
 available to the public, creating a privacy risk by revealing the
 personal details of registrants.  WHOIS services have not had the
 benefit of authentication or access control mechanisms to gate access
 to registration data.  As a result of this, proxy and privacy
 services have arisen to shield the identities of registrants.
 The standardization of RDAP does not change or impact the data that
 operators may require to be collected from registrants, but it
 provides support for a number of mechanisms that may be used to
 mitigate privacy threats to registrants should operators choose to
 use them.
 RDAP includes mechanisms that can be used to authenticate clients,
 allowing servers to support tiered access based on local policy.
 This means that all registration data need no longer be public, and
 personal data or data that may be considered more sensitive can have
 its access restricted to specifically privileged clients.
 RDAP data structures allow servers to indicate via status values when
 data returned to clients has been made private, redacted, obscured,
 or registered by a proxy.  "Private" means that the data is not
 designated for public consumption.  "Redacted" means that some
 registration data fields are not being made available.  "Obscured"
 means that data has been altered for the purposes of not readily
 revealing the actual registration information.  One option that
 operators have available to them to reduce privacy risks to
 registrants is to adopt policies that make use of these status values
 to restrict the registrant data shared with any or all clients

Hollenbeck & Kong Standards Track [Page 8] RFC 7481 RDAP Security Services March 2015

 according to the sensitivity of the data, the privileges of the
 clients, or some other heuristics.
 RDAP uses the jCard [RFC7095] standard format for entity
 representation.  Operators may find that many of the jCard fields are
 irrelevant for registry operation purposes or that they have no
 reason to collect information from registrants that would correspond
 to certain fields.  Operators wishing to reduce privacy risks for
 registrants may restrict which information they collect and/or which
 fields they populate in responses.
 In addition to privacy risks to registrants, there are also potential
 privacy risks for those who query registration data.  For example,
 the fact that a registry employee performs a particular query may
 reveal information about the employee's activities that he or she
 would have preferred to keep private.  RDAP supports the use of HTTP
 over TLS to provide privacy protection for those querying registrant
 data as well as registrants, unless operational constraints make it
 impossible to meet this requirement.

5. Security Considerations

 One of the goals of RDAP is to provide security services that do not
 exist in the WHOIS protocol.  This document describes the security
 services provided by RDAP and associated protocol layers, including
 authentication, authorization, availability, data confidentiality,
 and data integrity.  Non-repudiation services were also considered
 and ultimately rejected due to a lack of requirements.  There are,
 however, currently deployed WHOIS servers that can return signed
 responses that provide non-repudiation with proof of origin.  RDAP
 might need to be extended to provide this service in the future.
 As an HTTP-based protocol, RDAP is susceptible to code injection
 attacks.  Code injection refers to adding code into a computer system
 or program to alter the course of execution.  There are many types of
 code injection, including SQL injection, dynamic variable or function
 injection, include-file injection, shell injection, and HTML-script
 injection, among others.  Data confidentiality and integrity services
 provide a measure of defense against man-in-the-middle injection
 attacks, but vulnerabilities in both client- and server-side software
 make it possible for injection attacks to succeed.  Consistently
 checking and validating server credentials can help detect
 man-in-the-middle attacks.
 As noted in Section 3.2.1, digital certificates can be used to
 implement federated authentication.  There is a risk of too
 promiscuous, or even rogue, CAs being included in the list of
 acceptable CAs that the TLS server sends the client as part of the

Hollenbeck & Kong Standards Track [Page 9] RFC 7481 RDAP Security Services March 2015

 TLS client-authentication handshake and lending the appearance of
 trust to certificates signed by those CAs.  Periodic monitoring of
 the list of CAs that RDAP servers trust for client authentication can
 help reduce this risk.
 The Transport Layer Security protocol [RFC5246] includes a null
 cipher suite that does not encrypt data and thus does not provide
 data confidentiality.  This option MUST NOT be used when data
 confidentiality services are needed.  Additional considerations for
 secure use of TLS are described in [SECURE-TLS-DTLS].
 Data integrity services are sometimes mistakenly associated with
 directory service operational policy requirements focused on data
 accuracy.  "Accuracy" refers to the truthful association of data
 elements (such as names, addresses, and telephone numbers) in the
 context of a particular directory object (such as a domain name).
 Accuracy requirements are out of scope for this protocol.
 Additional security considerations are described in the
 specifications for HTTP [RFC7231], HTTP Basic and Digest access
 authentication [RFC7235], HTTP over TLS [RFC2818], and additional
 HTTP status codes [RFC6585].  Security considerations for federated
 authentication systems can be found in the OAuth [RFC6749] and OpenID
 [OpenID] specifications.

6. References

6.1. Normative References

 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997,
            <http://www.rfc-editor.org/info/rfc2119>.
 [RFC2818]  Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000,
            <http://www.rfc-editor.org/info/rfc2818>.
 [RFC6585]  Nottingham, M. and R. Fielding, "Additional HTTP Status
            Codes", RFC 6585, April 2012,
            <http://www.rfc-editor.org/info/rfc6585>.
 [RFC7231]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
            Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
            June 2014, <http://www.rfc-editor.org/info/rfc7231>.
 [RFC7235]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
            Protocol (HTTP/1.1): Authentication", RFC 7235, June 2014,
            <http://www.rfc-editor.org/info/rfc7235>.

Hollenbeck & Kong Standards Track [Page 10] RFC 7481 RDAP Security Services March 2015

 [RFC7480]  Newton, A., Ellacott, B., and N. Kong, "HTTP Usage in the
            Registration Data Access Protocol (RDAP)", RFC 7480, March
            2015, <http://www.rfc-editor.org/info/rfc7480>.
 [RFC7482]  Newton, A. and S. Hollenbeck, "Registration Data Access
            Protocol (RDAP) Query Format", RFC 7482, March 2015,
            <http://www.rfc-editor.org/info/rfc7482>.
 [RFC7483]  Newton, A. and S. Hollenbeck, "JSON Responses for the
            Registration Data Access Protocol (RDAP)", RFC 7483, March
            2015, <http://www.rfc-editor.org/info/rfc7483>.

6.2. Informative References

 [OpenID]   OpenID Foundation, "OpenID Authentication 2.0 - Final",
            December 2007, <http://specs.openid.net/auth/2.0>.
 [RFC3707]  Newton, A., "Cross Registry Internet Service Protocol
            (CRISP) Requirements", RFC 3707, February 2004,
            <http://www.rfc-editor.org/info/rfc3707>.
 [RFC3912]  Daigle, L., "WHOIS Protocol Specification", RFC 3912,
            September 2004, <http://www.rfc-editor.org/info/rfc3912>.
 [RFC4732]  Handley, M., Ed., Rescorla, E., Ed., and IAB, "Internet
            Denial-of-Service Considerations", RFC 4732, December
            2006, <http://www.rfc-editor.org/info/rfc4732>.
 [RFC4949]  Shirey, R., "Internet Security Glossary, Version 2", FYI
            36, RFC 4949, August 2007,
            <http://www.rfc-editor.org/info/rfc4949>.
 [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
            (TLS) Protocol Version 1.2", RFC 5246, August 2008,
            <http://www.rfc-editor.org/info/rfc5246>.
 [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
            Housley, R., and W. Polk, "Internet X.509 Public Key
            Infrastructure Certificate and Certificate Revocation List
            (CRL) Profile", RFC 5280, May 2008,
            <http://www.rfc-editor.org/info/rfc5280>.
 [RFC6749]  Hardt, D., Ed., "The OAuth 2.0 Authorization Framework",
            RFC 6749, October 2012,
            <http://www.rfc-editor.org/info/rfc6749>.
 [RFC7095]  Kewisch, P., "jCard: The JSON Format for vCard", RFC 7095,
            January 2014, <http://www.rfc-editor.org/info/rfc7095>.

Hollenbeck & Kong Standards Track [Page 11] RFC 7481 RDAP Security Services March 2015

 [SAML]     OASIS, "Security Assertion Markup Language (SAML) v2.0",
            March 2005, <https://www.oasis-open.org/
            standards#samlv2.0>.
 [SECURE-TLS-DTLS]
            Sheffer, Y., Holz, R., and P. Saint-Andre,
            "Recommendations for Secure Use of TLS and DTLS", Work in
            Progress, draft-ietf-uta-tls-bcp-09, February 2015.

Hollenbeck & Kong Standards Track [Page 12] RFC 7481 RDAP Security Services March 2015

Acknowledgements

 The authors would like to acknowledge the following individuals for
 their contributions to this document: Richard Barnes, Marc Blanchet,
 Alissa Cooper, Ernie Dainow, Spencer Dawkins, Jean-Philippe Dionne,
 Byron Ellacott, Stephen Farrell, Tony Hansen, Peter Koch, Murray
 Kucherawy, Barry Leiba, Andrew Newton, and Linlin Zhou.

Authors' Addresses

 Scott Hollenbeck
 Verisign Labs
 12061 Bluemont Way
 Reston, VA  20190
 United States
 EMail: shollenbeck@verisign.com
 URI:   http://www.verisignlabs.com/
 Ning Kong
 China Internet Network Information Center
 4 South 4th Street, Zhongguancun, Haidian District
 Beijing  100190
 China
 Phone: +86 10 5881 3147
 EMail: nkong@cnnic.cn

Hollenbeck & Kong Standards Track [Page 13]

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