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Versions: (draft-lendl-enum-validation-token) 00 01 02 03 04 RFC 5105

ENUM -- Telephone Number Mapping                                O. Lendl
Working Group                                                    enum.at
Internet-Draft                                           October 1, 2005
Expires: April 4, 2006

                ENUM Validation Token Format Definition

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
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Copyright Notice

   Copyright (C) The Internet Society (2005).


   An ENUM domain name is tightly coupled with the underlying E.164
   number.  The process of verifying whether 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 an
   signed XML data format -- the Validation Token -- with which
   Validation Entities can convey successful completion of a validation
   procedure in a secure fashion.

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3

   2.  Data Requirements  . . . . . . . . . . . . . . . . . . . . . .  3

   3.  Digital Signature  . . . . . . . . . . . . . . . . . . . . . .  3

   4.  Field Descriptions . . . . . . . . . . . . . . . . . . . . . .  4
     4.1   Mandatory Section  . . . . . . . . . . . . . . . . . . . .  4
     4.2   Optional Section . . . . . . . . . . . . . . . . . . . . .  5

   5.  Examples . . . . . . . . . . . . . . . . . . . . . . . . . . .  5
     5.1   Unsigned Token without Registrant Information  . . . . . .  5
     5.2   Signed token . . . . . . . . . . . . . . . . . . . . . . .  6

   6.  Formal Syntax  . . . . . . . . . . . . . . . . . . . . . . . .  8
     6.1   Token Core Schema  . . . . . . . . . . . . . . . . . . . .  8
     6.2   Token Data Schema  . . . . . . . . . . . . . . . . . . . . 10

   7.  Other applications of the Token concept  . . . . . . . . . . . 12

   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 12

   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 13

   10.   Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13

   11.   References . . . . . . . . . . . . . . . . . . . . . . . . . 14

       Author's Address . . . . . . . . . . . . . . . . . . . . . . . 15

       Intellectual Property and Copyright Statements . . . . . . . . 16

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1.  Introduction

   In the case where an ENUM [2] domain name corresponds to an existing
   E.164 number the delegation of this domain needs to be authorized by
   the Assignee of the corresponding E.164 number.  In the role model
   described in [11] the entity which performs this check is called the
   Validation Entity (VE).

   By conveying an ENUM Validation Token - a signed XML [6] document -
   to the Registry a VE certifies that delegation requirements have been
   met and are current.

2.  Data Requirements

   In this model, the Token is the only data passed from the VE to the
   Registry.  Therefore, the Token needs to contain as least as much
   information as the Registry requires to grant the delegation of the
   requested ENUM domain according to its registration policy.  As such,
   the Registry will need confirmation that
   o  the Token was created by an accredited VE,
   o  the Token's duration of validity conforms to the policy,
   o  the validation procedure employed has met minimum requirements as
      set forth by policy,
   o  and that the Token is protected against tampering and replay

   Beyond such mandatory information, the Token may optionally include
   number holder information, in particular to simplify future re-

   For example, if initial validation requires the steps "Check the
   identity of the Registrant" and "Check the ownership of an E.164
   number" then a later revalidation only needs to re-check the
   ownership as the identity of the Registrant does not change.

   As the Token will be included (see e.g. [12]) in XML-based Registry/
   Registrar protocols like the Extensible Provisioning Protocol (EPP)
   [4] it is a natural choice to use XML to encode Validation Tokens.

3.  Digital Signature

   According to the architecture model the propriety of an ENUM
   delegation depends on the trust relationship between the Registry and
   the VE.  For generality, an untrusted link between Registry and VE
   should be assumed (for instance the Token is passed along with the
   registration request by a Registrar, who might have no role in
   asserting the right-to-use).  Therefore, the Token must be protected
   against forgery, tampering and replay-attacks.

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   A digital signature on the token
   o  asserts that the token was indeed generated by the indicated VE
   o  guarantees that the token was not tampered with in transit
   o  enables auditing the validation process (non-repudiation).

   The cryptographic signature on the token follows XML-DSIG [9].  As
   tokens might be transmitted as part of an already XML based protocol
   the exclusive XML canonicalization [10] is used.  This transform
   guarantees that namespace declarations inherited from the surrounding
   XML do not invalidate the signature.  In order to make the signature
   an integral part of the token the "enveloped"-signature mode is
   employed.  The signature covers all information contained in the

   While XML-DSIG offers a number of cryptographic algorithms, local
   policy should define which algorithms will be accepted by the
   Registry.  It is suggested to use the RSA-SHA1 algorithm with
   embedded X.509 certificates.

   The choice of RSA-SHA1 does not require a public key infrastructure.
   Whether the Registry acts as a certificate authority, accepts certs
   from a public CA, or only accepts pre-registered keys is a local
   policy choice.

4.  Field Descriptions

4.1  Mandatory Section

   A token must contain a <validation> tag which contains the following:
   o  A single validation "serial" string identifying a validation token
      for a certain VE.  It must be unique per VE.
   o  A single "E164Number" tag containing the underlying E.164 number
      in fully qualified (international) format.
   o  An optional "lastE164Number" tag.  If present it indicates that
      the whole number block starting with "E164Number" up to and
      including "lastE164Number" has been validated.  To avoid
      ambiguity, both numbers must be of the same length.
   o  A single "validationEntityID" tag identifying the VE.
   o  A single "registrarID" tag identifying the Registrar on whose
      behalf the validation was performed.
   o  A single "methodID" tag identifying the method used by the VE for
   o  A single "executionDate" attribute containing the date of
      validation formatted as "full-date" according to RFC 3339 [3].

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   o  An optional "expirationDate" attribute marking the expiration date
      of the validation token formatted as "full-date" according to RFC
      3339.  The Registry will automatically revoke the delegation at
      this date unless a new Token has been submitted that extends the
      lifetime of the validation.  A missing expirationDate indicates
      infinite validity of the Token.

   The format and the uniqueness-constraints of these IDs is left to the
   local policy of the Registry.

4.2  Optional Section

   A token may contain a "tokendata" section containing information
   about the number holder.
   o  A single "organization" tag containing the full name of the
   o  A single "commercialregisternumber" tag.  If the Registrant is a
      company, then this field can be used to uniquely identify that
      company by its official registration number.  The interpretation
      of this field is country-specific.
   o  A single "title" tag
   o  A single "firstname" tag
   o  A single "lastname" tag
   o  A single "address" section containing the following tags:
      *  A single mandatory "streetname"
      *  A single optional "streetnumber"
      *  A single optional "apartment"
      *  A single mandatory "postalcode"
      *  A single mandatory "city"
      *  A single optional "state"
      *  A single mandatory "country"
   o  up to 10 "phone" tags containing full E.164 numbers
   o  up to 10 "fax" tags containing full E.164 numbers
   o  up to 10 "email" tags

   All attributes are optional.  In case an address section is used,
   several components are mandatory for conformance with the E.115 [1]
   recommendation.  The reason for this is that "computerized directory
   assistance" accessible through the E.115 interface may be a source of
   validation information.

5.  Examples

5.1  Unsigned Token without Registrant Information

   This basic Token without any information about the Registrant and
   without the cryptographic signature shows the basic layout of the
   required elements.

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   <?xml version="1.0" encoding="utf-8" standalone="no" ?>
   <token xmlns="urn:ietf:params:xml:ns:enum-token-1.0" Id="TOKEN"
     "urn:ietf:params:xml:ns:enum-token-1.0 enum-token-1.0.xsd">
     <validation serial="acmeve-000002">

5.2  Signed token

   This example uses an X.509 based signature which includes the
   certificate of the signing validation entity.  Thus the validity of
   the signature can be verified without the need for a key-server.

   <?xml version="1.0" encoding="utf-8" standalone="no" ?>
   <token xmlns="urn:ietf:params:xml:ns:enum-token-1.0" Id="TOKEN"
     "urn:ietf:params:xml:ns:enum-token-1.0 enum-token-1.0.xsd">
     <validation serial="acmeve-000001">
     <tokendata xmlns="urn:ietf:params:xml:ns:enum-tokendata-1.0"
   "urn:ietf:params:xml:ns:enum-tokendata-1.0 enum-tokendata-1.0.xsd">
         <organisation>Example GmbH</organisation>

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     <Signature xmlns="http://www.w3.org/2000/09/xmldsig#">
         <Reference URI="#TOKEN">
             <Transform Algorithm=
             <Transform Algorithm=
                PrefixList="enum-token enum-tokendata"/>

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6.  Formal Syntax

   The formal syntax of the validation token is specified using XML
   schema notation [7] [8].  Two schemas are defined: The "token core
   schema" contains mandatory attribute definitions, the "token data
   schema" defines the format of the optional "tokendata" section.

6.1  Token Core Schema

   <?xml version="1.0" encoding="UTF-8"?>

   <schema targetNamespace="urn:ietf:params:xml:ns:enum-token-1.0"

   <!--  Import common element types.  -->

     <import namespace="http://www.w3.org/2000/09/xmldsig#"
     <import namespace="urn:ietf:params:xml:ns:enum-tokendata-1.0"


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         enum.at Validation Token core schema

     <element name="token" type="enum-token:tokenBaseType"/>

     <simpleType name="shortTokenType">
       <restriction base="token">
         <minLength value="1"/>
         <maxLength value="20"/>

     <simpleType name="e164numberType">
       <restriction base="token">
         <maxLength value="20"/>
         <pattern value="\+\d\d*"/>

     <complexType name="validationDataType">
         <element name="E164Number"
         <element name="lastE164Number" minOccurs="0"
         <element name="validationEntityID"
         <element name="registrarID"
         <element name="methodID"
         <element name="executionDate" type="date"/>
         <element name="expirationDate"
                         type="date" minOccurs="0"/>
       <attribute name="serial" type="enum-token:shortTokenType"

     <complexType name="tokenBaseType">
         <element name="validation"
         <any namespace="urn:ietf:params:xml:ns:enum-tokendata-1.0"
         <any namespace="http://www.w3.org/2000/09/xmldsig#"/>

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       <attribute name="Id" type="ID" use="required"/>

6.2  Token Data Schema

   <?xml version="1.0" encoding="UTF-8"?>

   <schema targetNamespace="urn:ietf:params:xml:ns:enum-tokendata-1.0"

         enum.at Validation Token tokendata schema.

     <element name="tokendata" type="enum-tokendata:tokenDataType"/>

     <simpleType name="streetNameType">
       <restriction base="token">
         <minLength value="1"/>
         <maxLength value="128"/>

     <simpleType name="shortTokenType">
       <restriction base="token">
         <minLength value="1"/>
         <maxLength value="20"/>

     <simpleType name="longTokenType">
       <restriction base="token">
         <minLength value="1"/>
         <maxLength value="64"/>

     <complexType name="addressType">
         <element name="streetname"

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         <element name="streetnumber"
          type="enum-tokendata:shortTokenType" minOccurs="0"/>
         <element name="apartment"
          type="enum-tokendata:shortTokenType" minOccurs="0"/>
         <element name="postalcode"
         <element name="city"
         <element name="state"
          type="enum-tokendata:longTokenType" minOccurs="0"/>
         <element name="country"

     <group name="tokenContactBaseGroup">
         <element name="organisation"
          type="enum-tokendata:shortTokenType" minOccurs="0"/>
         <element name="commercialregisternumber"
          type="enum-tokendata:shortTokenType" minOccurs="0"/>
         <element name="title"
          type="enum-tokendata:shortTokenType" minOccurs="0"/>
         <element name="firstname"
          type="enum-tokendata:longTokenType" minOccurs="0"/>
         <element name="lastname"
          type="enum-tokendata:longTokenType" minOccurs="0"/>
         <element name="address"
          type="enum-tokendata:addressType" minOccurs="0"/>
         <element name="phone" type="enum-tokendata:shortTokenType"
          minOccurs="0" maxOccurs="10" />
         <element name="fax"   type="enum-tokendata:shortTokenType"
          minOccurs="0" maxOccurs="10" />
         <element name="email" type="enum-tokendata:shortTokenType"
          minOccurs="0" maxOccurs="10" />

     <complexType name="contactType">
         <group ref="enum-tokendata:tokenContactBaseGroup"/>

     <complexType name="tokenDataType">
         <element name="contact" type="enum-tokendata:contactType"/>

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7.  Other applications of the Token concept

   The concept of the validation token may be useful in other registry-
   type applications where the proof of an underlying right is a
   condition for a valid registration.

   An example is a TLD (Top Level Domain) where registration is subject
   to proof of some precondition, like a trade mark or the right in a
   name.  Such situations often arise during the introduction of a new
   TLD, e.g. during a "sunrise" phase.

   A Number Portability (NP) database faces very similar verification
   issues.  An NP system based on the Token concept could potentially be
   superior to current methods, and aid in the convergence of NP and

8.  IANA Considerations

   This document uses URNs to describe XML namespaces and XML schemas
   conforming to a registry mechanism described in RFC 3688 [5].  Four
   URI assignments are requested.
   1.  Registration request for the Token namespace:
       *  URI: urn:ietf:params:xml:ns:enum-token-1.0
       *  Registrant Contact: See the "Author's Address" section of this
       *  XML: None.  Namespace URIs do not represent an XML
   2.  Registration request for the Token XML schema:
       *  URI: urn:ietf:params:xml:schema:enum-token-1.0
       *  Registrant Contact: See the "Author's Address" section of this
       *  XML: See Section 6.1 of this document.
   3.  Registration request for the Token Data namespace:
       *  URI: urn:ietf:params:xml:ns:enum-tokendata-1.0
       *  Registrant Contact: See the "Author's Address" section of this
       *  XML: None.  Namespace URIs do not represent an XML
   4.  Registration request for the Token Data XML schema:
       *  URI: urn:ietf:params:xml:schema:enum-tokendata-1.0

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       *  Registrant Contact: See the "Author's Address" section of this
       *  XML: See Section 6.2 of this document.

   The IDs used in the validationEntityID, RegistrarID, and methodID
   tags are subject to local policy and thus do not require IANA

9.  Security Considerations

   The security of the Validation Token depends on the security of the
   underlying XML DSIG algorithms.  As such, all the security
   considerations from [9] apply here as well.  Two points from there
   merit repetition:

   Transforms are used to select the relevant data for signing and to
   discard irrelevant information (e.g. pretty-printing and name-space
   local names).

   The <Reference URI="#TOKEN"> element and attribute combined with the
   Id="TOKEN" attribute in <token> specifies that the signature should
   cover the complete token.  Moving the Id="TOKEN" attribute to e.g.
   the <tokendata> tag would make the signature worthless.

   It is thus critical that the Registry does not only check whether the
   Token passes a generic XML-DSIG signature check, but also that the
   signature uses approved transforms and references the <token> tag as
   well as that the certificate belongs to an accredited VE.

   The Token content is not encrypted.  If local policy dictates that
   the information contained within the token should be protected then
   this has to be handled through a different mechanism.

   When processing a delegation request the Registry must verify that
   the information contained in the Token matches the delegation
   request.  To avert replay attacks, local policy has to specify for
   how long after "executionDate" the Token can be used to authorize a
   delegation.  The "registrarID" tag in the Token prevents a malicious
   second Registrar from using an eavesdropped Token to register a
   domain in his name.

10.  Acknowledgements

   The author would like to thank the following persons for their
   valuable suggestions and contributions: Michael Haberler, Alexander
   Mayrhofer, Bernie Hoeneisen, Michael Braunoeder, Staffan Hagnell,
   Lawrence Conroy.

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11.  References

   [1]   ITU-T, "Computerized Directory Assistance",
         Recommendation E.115, February 1995.

   [2]   Faltstrom, P. and M. Mealling, "The E.164 to Uniform Resource
         Identifiers (URI) Dynamic Delegation Discovery System (DDDS)
         Application (ENUM)", RFC 3761, April 2004.

   [3]   Klyne, G. and C. Newman, "Date and Time on the Internet:
         Timestamps", RFC 3339, July 2002.

   [4]   Hollenbeck, S., "Extensible Provisioning Protocol (EPP)",
         RFC 3730, March 2004.

   [5]   Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
         January 2004.

   [6]   Paoli, J., Sperberg-McQueen, C., Bray, T., and E. Maler,
         "Extensible Markup Language (XML) 1.0 (Second Edition)", W3C
         FirstEdition REC-xml-20001006, October 2000.

   [7]   Maloney, M., Beech, D., Mendelsohn, N., and H. Thompson, "XML
         Schema Part 1: Structures", W3C REC REC-xmlschema-1-20010502,
         May 2001.

   [8]   Malhotra, A. and P. Biron, "XML Schema Part 2: Datatypes", W3C
         REC REC-xmlschema-2-20010502, May 2001.

   [9]   Solo, D., Reagle, J., and D. Eastlake, "XML-Signature Syntax
         and Processing", W3C REC REC-xmldsig-core-20020212,
         February 2002.

   [10]  3rd, D., Boyer, J., and J. Reagle, "Exclusive XML
         Canonicalization Version 1.0", W3C REC REC-xml-exc-c14n-
         20020718, July 2002.

   [11]  Mayrhofer, A. and B. Hoeneisen, "ENUM Validation Architecture",
         draft-ietf-enum-validation-arch-00 (work in progress),
         July 2005.

   [12]  Hoeneisen, B., "ENUM Validation Information Mapping for the
         Extensible Provisioning  Protocol",
         draft-ietf-enum-validation-epp-00 (work in progress),
         September 2005.

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Author's Address

   Otmar Lendl
   enum.at GmbH
   Karlsplatz 1/2/9
   Wien  A-1010

   Phone: +43 1 5056416 33
   Email: otmar.lendl@enum.at
   URI:   http://www.enum.at/

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Intellectual Property Statement

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Disclaimer of Validity

   This document and the information contained herein are provided on an

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.


   Funding for the RFC Editor function is currently provided by the
   Internet Society.

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