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Internet Engineering Task Force (IETF)                          J. Gould
Request for Comments: 9154                                    R. Wilhelm
Category: Standards Track                                 Verisign, Inc.
ISSN: 2070-1721                                            December 2021


Extensible Provisioning Protocol (EPP) Secure Authorization Information
                              for Transfer

Abstract

   The Extensible Provisioning Protocol (EPP) (RFC 5730) defines the use
   of authorization information to authorize a transfer of an EPP
   object, such as a domain name, between clients that are referred to
   as "registrars".  Object-specific, password-based authorization
   information (see RFCs 5731 and 5733) is commonly used but raises
   issues related to the security, complexity, storage, and lifetime of
   authentication information.  This document defines an operational
   practice, using the EPP RFCs, that leverages the use of strong random
   authorization information values that are short lived, not stored by
   the client, and stored by the server using a cryptographic hash that
   provides for secure authorization information that can safely be used
   for object transfers.

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/rfc9154.

Copyright Notice

   Copyright (c) 2021 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
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   publication of this document.  Please review these documents
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   to this document.  Code Components extracted from this document must
   include Revised BSD License text as described in Section 4.e of the
   Trust Legal Provisions and are provided without warranty as described
   in the Revised BSD License.

Table of Contents

   1.  Introduction
     1.1.  Conventions Used in This Document
   2.  Registrant, Registrar, Registry
   3.  Signaling Client and Server Support
   4.  Secure Authorization Information
     4.1.  Secure Random Authorization Information
     4.2.  Authorization Information Time To Live (TTL)
     4.3.  Authorization Information Storage and Transport
     4.4.  Authorization Information Matching
   5.  Create, Transfer, and Secure Authorization Information
     5.1.  <Create> Command
     5.2.  <Update> Command
     5.3.  <Info> Command and Response
     5.4.  <Transfer> Request Command
   6.  Transition Considerations
     6.1.  Transition Phase 1 - Features
     6.2.  Transition Phase 2 - Storage
     6.3.  Transition Phase 3 - Enforcement
   7.  IANA Considerations
     7.1.  XML Namespace
     7.2.  EPP Extension Registry
   8.  Security Considerations
   9.  References
     9.1.  Normative References
     9.2.  Informative References
   Acknowledgements
   Authors' Addresses

1.  Introduction

   The Extensible Provisioning Protocol (EPP) [RFC5730] defines the use
   of authorization information to authorize a transfer of an EPP
   object, such as a domain name, between clients that are referred to
   as "registrars".  The authorization information is object specific
   and has been defined in "Extensible Provisioning Protocol (EPP)
   Domain Name Mapping" [RFC5731] and "Extensible Provisioning Protocol
   (EPP) Contact Mapping" [RFC5733] as password-based authorization
   information.  Other authorization mechanisms can be used, but in
   practice the password-based authorization information has been used
   at the time of object creation, managed with the object update, and
   used to authorize an object transfer request.  What has not been
   considered is the security of the authorization information, which
   includes the complexity of the authorization information, the Time To
   Live (TTL) of the authorization information, and where and how the
   authorization information is stored.

   The current/original lifecycle for authorization information involves
   long-term storage of encrypted (not hashed) passwords, which presents
   a significant latent risk of password compromise and is not
   consistent with current best practices.  The mechanisms in this
   document provide a way to avoid long-term password storage entirely
   and to only require the storage of hashed (not retrievable) passwords
   instead of encrypted passwords.

   This document defines an operational practice, using the EPP RFCs,
   that leverages the use of strong, random authorization information
   values that are short lived, not stored by the client, and stored by
   the server using a cryptographic hash to provide secure authorization
   information used for transfers.  This operational practice can be
   used to support transfers of any EPP object, where the domain name
   object as defined in [RFC5731] is used in this document for
   illustration purposes.  Elements of the practice may be used to
   support the secure use of the authorization information for purposes
   other than transfer, but any other purposes and the applicable
   elements are out of scope for this document.

   The overall goal is to have strong, random authorization information
   values that are short lived and are either not stored or stored as
   cryptographic hash values by the non-responsible parties.  In a
   registrant, registrar, and registry model, the registrant registers
   the object through the registrar to the registry.  The registrant is
   the responsible party, and the registrar and the registry are the
   non-responsible parties.  EPP is a protocol between the registrar and
   the registry, where the registrar is referred to as the "client" and
   the registry is referred to as the "server".  The following are the
   elements of the operational practice and how the existing features of
   the EPP RFCs can be leveraged to satisfy them:

   Strong Random Authorization Information:  The EPP RFCs define the
       password-based authorization information value using an XML
       schema "normalizedString" type, so they don't restrict what can
       be used in any substantial way.  This operational practice
       defines the recommended mechanism for creating a strong random
       authorization value that would be generated by the client.

   Short-Lived Authorization Information:  The EPP RFCs don't explicitly
       support short-lived authorization information or a TTL for
       authorization information, but there are EPP RFC features that
       can be leveraged to support short-lived authorization
       information.  All of these features are compatible with the EPP
       RFCs, though not mandatory to implement.  As stated in
       Section 2.6 of [RFC5731], authorization information is assigned
       when a domain object is created, which results in long-lived
       authorization information.  This specification changes the nature
       of the authorization information from long lived to short lived.
       If authorization information is set only when a transfer is in
       process, the server needs to support an empty authorization
       information value on create, support setting and unsetting
       authorization information, and support automatically unsetting
       the authorization information upon a successful transfer.  All of
       these features can be supported by the EPP RFCs.

   Storing Authorization Information Securely:  The EPP RFCs don't
       specify where and how the authorization information is stored in
       the client or the server, so there are no restrictions on
       defining an operational practice for storing the authorization
       information securely.  The operational practice will require the
       client to not store the authorization information and will
       require the server to store the authorization information using a
       cryptographic hash with at least a 256-bit hash function, such as
       SHA-256 [FIPS-180-4], and with a per-authorization information
       random salt with at least 128 bits.  Returning the authorization
       information set in an EPP info response will not be supported.

1.1.  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.

   XML [W3C.REC-xml-20081126] is case sensitive.  Unless stated
   otherwise, XML specifications and examples provided in this document
   MUST be interpreted in the character case presented in order to
   develop a conforming implementation.

   In examples, "C:" represents lines sent by a protocol client and "S:"
   represents lines returned by a protocol server.  Indentation and
   empty space in examples are provided only to illustrate element
   relationships and are not a required feature of this protocol.

   The examples reference XML namespace prefixes that are used for the
   associated XML namespaces.  Implementations MUST NOT depend on the
   example XML namespaces and instead employ a proper namespace-aware
   XML parser and serializer to interpret and output the XML documents.
   The example namespace prefixes used and their associated XML
   namespaces include the following:

   domain:  urn:ietf:params:xml:ns:domain-1.0

   contact:  urn:ietf:params:xml:ns:contact-1.0

2.  Registrant, Registrar, Registry

   The EPP RFCs refer to "client" and "server", but when it comes to
   transfers, there are three types of actors that are involved.  This
   document will refer to these actors as "registrant", "registrar", and
   "registry".  [RFC8499] defines these terms formally for the Domain
   Name System (DNS).  The terms are further described below to cover
   their roles as actors using the authorization information in the
   transfer process of any object in the registry, such as a domain name
   or a contact:

   Registrant:  [RFC8499] defines the registrant as "an individual or
       organization on whose behalf a name in a zone is registered by
       the registry."  The registrant can be the owner of any object in
       the registry, such as a domain name or a contact.  The registrant
       interfaces with the registrar for provisioning the objects.  A
       transfer is coordinated by the registrant to transfer the
       sponsorship of the object from one registrar to another.  The
       authorization information is meant to authenticate the registrant
       as the owner of the object to the non-sponsoring registrar and to
       authorize the transfer.

   Registrar:  [RFC8499] defines the registrar as "a service provider
       that acts as a go-between for registrants and registries."  The
       registrar interfaces with the registrant for the provisioning of
       objects, such as domain names and contacts, and with the
       registries to satisfy the registrant's provisioning requests.  A
       registrar may (1) directly interface with the registrant or
       (2) indirectly interface with the registrant, typically through
       one or more resellers.  Implementing a transfer using secure
       authorization information extends through the registrar's
       reseller channel up to the direct interface with the registrant.
       The registrar's interface with the registries uses EPP.  The
       registrar's interface with its reseller channel or the registrant
       is registrar specific.  In the EPP RFCs, the registrar is
       referred to as the "client", since EPP is the protocol used
       between the registrar and the registry.  The sponsoring registrar
       is the authorized registrar to manage objects on behalf of the
       registrant.  A non-sponsoring registrar is not authorized to
       manage objects on behalf of the registrant.  A transfer of an
       object's sponsorship is from one registrar, referred to as the
       "losing registrar", to another registrar, referred to as the
       "gaining registrar".

   Registry:  [RFC8499] defines the registry as "the administrative
       operation of a zone that allows registration of names within that
       zone."  The registry typically interfaces with the registrars
       over EPP and generally does not interact directly with the
       registrant.  In the EPP RFCs, the registry is referred to as the
       "server", since EPP is the protocol used between the registrar
       and the registry.  The registry has a record of the sponsoring
       registrar for each object and provides the mechanism (over EPP)
       to coordinate a transfer of an object's sponsorship between
       registrars.

3.  Signaling Client and Server Support

   This document does not define a new protocol; rather, it defines an
   operational practice using existing EPP features, where the client
   and the server can signal support for the operational practice using
   a namespace URI in the login and greeting extension services.  The
   namespace URI "urn:ietf:params:xml:ns:epp:secure-authinfo-transfer-
   1.0" is used to signal support for the operational practice.  The
   client includes the namespace URI in an <svcExtension> <extURI>
   element of the <login> command [RFC5730].  The server includes the
   namespace URI in an <svcExtension> <extURI> element of the greeting
   [RFC5730].

   A client that receives the namespace URI in the server's greeting
   extension services can expect the following supported behavior by the
   server:

   1.  Support for an empty authorization information value with a
       <create> command.

   2.  Support for unsetting authorization information with an <update>
       command.

   3.  Support for validating authorization information with an <info>
       command.

   4.  Support for not returning an indication of whether the
       authorization information is set or unset to the non-sponsoring
       registrar.

   5.  Support for returning an empty authorization information value to
       the sponsoring registrar when the authorization information is
       set in an info response.

   6.  Support for allowing the passing of a matching non-empty
       authorization information value to authorize a transfer.

   7.  Support for automatically unsetting the authorization information
       upon successful completion of a transfer.

   A server that receives the namespace URI in the client's <login>
   command extension services can expect the following supported
   behavior by the client:

   1.  Support for the generation of authorization information using a
       secure random value.

   2.  Support for only setting the authorization information when a
       transfer is in process.

4.  Secure Authorization Information

   The EPP RFCs ([RFC5731] and [RFC5733]) use password-based
   authorization information to support transfer with the <domain:pw>
   element [RFC5731] and with the <contact:pw> element [RFC5733].  Other
   EPP objects that support password-based authorization information for
   transfer can use secure authorization information as defined in this
   document.  For authorization information to be secure, it must be
   generated using a strong random value and have a short TTL.  The
   security of the authorization information is defined in the following
   sections.

4.1.  Secure Random Authorization Information

   For authorization information to be secure, it MUST be generated
   using a secure random value.  The authorization information is
   treated as a password, and the required length L of a password,
   rounded up to the largest whole number, is based on the size N of the
   set of characters and the desired entropy H, in the equation L =
   ROUNDUP(H / log_2 N).  Given a target entropy, the required length
   can be calculated after deciding on the set of characters that will
   be randomized.  In accordance with current best practices and noting
   that the authorization information is a machine-generated value, the
   implementation SHOULD use at least 128 bits of entropy as the value
   of H.  The lengths below are calculated using that value.

   Calculation of the required length with 128 bits of entropy and with
   the set of all printable ASCII characters except space (0x20), which
   consists of the 94 characters 0x21-0x7E:

   ROUNDUP(128 / log_2 94) =~ ROUNDUP(128 / 6.55) =~ ROUNDUP(19.54) = 20

   Calculation of the required length with 128 bits of entropy and with
   the set of case-insensitive alphanumeric characters, which consists
   of 36 characters (a-z A-Z 0-9):

   ROUNDUP(128 / log_2 36) =~ ROUNDUP(128 / 5.17) =~ ROUNDUP(24.76) = 25

   The strength of the random authorization information is dependent on
   the random number generator.  Suitably strong random number
   generators are available in a wide variety of implementation
   environments, including the interfaces listed in Sections 7.1.2 and
   7.1.3 of [RFC4086].  In environments that do not provide interfaces
   to strong random number generators, the practices defined in
   [RFC4086] and Section 4.7.1 of the NIST Federal Information
   Processing Standards (FIPS) Publication 140-2 [FIPS-140-2] can be
   followed to produce random values that will be resistant to attack.
   (Note: FIPS 140-2 has been superseded by FIPS 140-3, but FIPS 140-3
   does not contain information regarding random number generators.)

4.2.  Authorization Information Time To Live (TTL)

   The authorization information SHOULD only be set when a transfer is
   in process.  This implies that the authorization information has a
   TTL by which the authorization information is cleared when the TTL
   expires.  The EPP RFCs do not provide definitions for TTL, but since
   the server supports the setting and unsetting of the authorization
   information by the sponsoring registrar, the sponsoring registrar can
   apply a TTL based on client policy.  The TTL client policy may be
   based on proprietary registrar-specific criteria, which provides for
   a transfer-specific TTL tuned for the particular circumstances of the
   transaction.  The sponsoring registrar will be aware of the TTL, and
   the sponsoring registrar MUST inform the registrant of the TTL when
   the authorization information is provided to the registrant.

4.3.  Authorization Information Storage and Transport

   To protect the disclosure of the authorization information, the
   following requirements apply:

   1.  The authorization information MUST be stored by the registry
       using a strong one-way cryptographic hash with at least a 256-bit
       hash function, such as SHA-256 [FIPS-180-4], and with a per-
       authorization information random salt with at least 128 bits.

   2.  An empty authorization information value MUST be stored as an
       undefined value that is referred to as a "NULL" value.  The
       representation of a NULL (undefined) value is dependent on the
       type of database used.

   3.  The authorization information MUST NOT be stored by the losing
       registrar.

   4.  The authorization information MUST only be stored by the gaining
       registrar as a "transient" value in support of the transfer
       process.

   5.  The plain-text version of the authorization information MUST NOT
       be written to any logs by a registrar or the registry, nor
       otherwise recorded where it will persist beyond the transfer
       process.

   6.  All communication that includes the authorization information
       MUST be over an encrypted channel (for example, see [RFC5734])
       for EPP.

   7.  The registrar's interface for communicating the authorization
       information with the registrant MUST be over an authenticated and
       encrypted channel.

4.4.  Authorization Information Matching

   To support the authorization information TTL, as described in
   Section 4.2, the authorization information must have either a set or
   unset state.  Authorization information that is unset is stored with
   a NULL (undefined) value.  Based on the requirement to store the
   authorization information using a strong one-way cryptographic hash,
   as described in Section 4.3, authorization information that is set is
   stored with a non-NULL hashed value.  The empty authorization
   information value is used as input in both the <create> command
   (Section 5.1) and the <update> command (Section 5.2) to define the
   unset state.  The matching of the authorization information in the
   <info> command (Section 5.3) and the <transfer> request command
   (Section 5.4) is based on the following rules:

   1.  Any input authorization information value MUST NOT match an unset
       authorization information value.  For example, in [RFC5731] the
       input <domain:pw>2fooBAR</domain:pw> must not match an unset
       authorization information value that used <domain:null/> or
       <domain:pw/>.

   2.  An empty input authorization information value MUST NOT match any
       set authorization information value.

   3.  A non-empty input authorization information value MUST be hashed
       and matched against the set authorization information value,
       which is stored using the same hash algorithm.

5.  Create, Transfer, and Secure Authorization Information

   To secure the transfer process using secure authorization information
   as described in Section 4, the client and server need to implement
   steps where the authorization information is set only when a transfer
   is actively in process and ensure that the authorization information
   is stored securely and transported only over secure channels.  The
   steps for management of the authorization information for transfers
   include the following:

   1.  The registrant requests to register the object with the
       registrar.  The registrar sends the <create> command with an
       empty authorization information value to the registry, as
       described in Section 5.1.

   2.  The registrant requests from the losing registrar the
       authorization information to provide to the gaining registrar.

   3.  The losing registrar generates a secure random authorization
       information value and sends it to the registry, as described in
       Section 5.2, and then provides it to the registrant.

   4.  The registrant provides the authorization information value to
       the gaining registrar.

   5.  The gaining registrar optionally verifies the authorization
       information with the <info> command to the registry, as described
       in Section 5.3.

   6.  The gaining registrar sends the transfer request with the
       authorization information to the registry, as described in
       Section 5.4.

   7.  If the transfer completes successfully, the registry
       automatically unsets the authorization information; otherwise,
       the losing registrar unsets the authorization information when
       the TTL expires; see Section 5.2.

   The following sections outline the practices of the EPP commands and
   responses between the registrar and the registry that supports secure
   authorization information for transfer.

5.1.  <Create> Command

   For a <create> command, the registry MUST allow the passing of an
   empty authorization information value and MAY disallow the passing of
   a non-empty authorization information value.  By having an empty
   authorization information value on create, the object is initially
   not involved in the transfer process.  Any EPP object extension that
   supports setting the authorization information with an
   "eppcom:pwAuthInfoType" element can pass an empty authorization
   information value.  Examples of such extensions are found in
   [RFC5731] and [RFC5733].

   Example of passing an empty authorization information value in a
   domain name <create> command [RFC5731]:

   C:<?xml version="1.0" encoding="UTF-8" standalone="no"?>
   C:<epp xmlns="urn:ietf:params:xml:ns:epp-1.0">
   C:  <command>
   C:    <create>
   C:      <domain:create
   C:        xmlns:domain="urn:ietf:params:xml:ns:domain-1.0">
   C:        <domain:name>example.com</domain:name>
   C:        <domain:authInfo>
   C:          <domain:pw/>
   C:        </domain:authInfo>
   C:      </domain:create>
   C:    </create>
   C:    <clTRID>ABC-12345</clTRID>
   C:  </command>
   C:</epp>

   Example of passing an empty authorization information value in a
   contact <create> command [RFC5733]:

   C:<?xml version="1.0" encoding="UTF-8" standalone="no"?>
   C:<epp xmlns="urn:ietf:params:xml:ns:epp-1.0">
   C:  <command>
   C:    <create>
   C:      <contact:create
   C:       xmlns:contact="urn:ietf:params:xml:ns:contact-1.0">
   C:        <contact:id>sh8013</contact:id>
   C:        <contact:postalInfo type="int">
   C:          <contact:name>John Doe</contact:name>
   C:          <contact:addr>
   C:            <contact:city>Dulles</contact:city>
   C:            <contact:cc>US</contact:cc>
   C:          </contact:addr>
   C:        </contact:postalInfo>
   C:        <contact:email>jdoe@example.com</contact:email>
   C:        <contact:authInfo>
   C:          <contact:pw/>
   C:        </contact:authInfo>
   C:      </contact:create>
   C:    </create>
   C:    <clTRID>ABC-12345</clTRID>
   C:  </command>
   C:</epp>

5.2.  <Update> Command

   For an <update> command, the registry MUST allow the setting and
   unsetting of the authorization information.  The registrar sets the
   authorization information by first generating a strong, random
   authorization information value, based on the information provided in
   Section 4.1, and setting it in the registry in the <update> command.
   The importance of generating strong authorization information values
   cannot be overstated: secure transfers are very important to the
   Internet to mitigate damage in the form of theft, fraud, and other
   abuse.  It is critical that registrars only use strong, randomly
   generated authorization information values.

   Because of this, registries may validate the randomness of the
   authorization information based on the length and character set
   required by the registry -- for example, validating that an
   authorization value contains a combination of uppercase, lowercase,
   and non-alphanumeric characters in an attempt to assess the strength
   of the value and returning an EPP error result of 2202 ("Invalid
   authorization information") [RFC5730] if the check fails.

   Such checks are, by their nature, heuristic and imperfect, and may
   identify well-chosen authorization information values as being not
   sufficiently strong.  Registrars, therefore, must be prepared for an
   error response of 2202 and respond by generating a new value and
   trying again, possibly more than once.

   Often, the registrar has the "clientTransferProhibited" status set,
   so to start the transfer process, the "clientTransferProhibited"
   status needs to be removed, and the strong, random authorization
   information value needs to be set.  The registrar MUST define a TTL,
   as described in Section 4.2, and if the TTL expires, the registrar
   will unset the authorization information.

   Example of removing the "clientTransferProhibited" status and setting
   the authorization information in a domain name <update> command
   [RFC5731]:

   C:<?xml version="1.0" encoding="UTF-8" standalone="no"?>
   C:<epp xmlns="urn:ietf:params:xml:ns:epp-1.0">
   C:  <command>
   C:    <update>
   C:      <domain:update
   C:        xmlns:domain="urn:ietf:params:xml:ns:domain-1.0">
   C:        <domain:name>example.com</domain:name>
   C:        <domain:rem>
   C:          <domain:status s="clientTransferProhibited"/>
   C:        </domain:rem>
   C:        <domain:chg>
   C:          <domain:authInfo>
   C:            <domain:pw>LuQ7Bu@w9?%+_HK3cayg$55$LSft3MPP
   C:            </domain:pw>
   C:          </domain:authInfo>
   C:        </domain:chg>
   C:      </domain:update>
   C:    </update>
   C:    <clTRID>ABC-12345-XYZ</clTRID>
   C:  </command>
   C:</epp>

   When the registrar-defined TTL expires, the sponsoring registrar MUST
   cancel the transfer process by unsetting the authorization
   information value and MAY add back statuses like the
   "clientTransferProhibited" status.  Any EPP object extension that
   supports setting the authorization information with an
   "eppcom:pwAuthInfoType" element can pass an empty authorization
   information value.  Examples of such extensions are found in
   [RFC5731] and [RFC5733].  Setting an empty authorization information
   value unsets the authorization information.  [RFC5731] supports an
   explicit mechanism of unsetting the authorization information, by
   passing the <domain:null> authorization information value.  The
   registry MUST support unsetting the authorization information by
   accepting an empty authorization information value and accepting an
   explicit unset element if it is supported by the object extension.

   Example of adding the "clientTransferProhibited" status and unsetting
   the authorization information explicitly in a domain name <update>
   command [RFC5731]:

   C:<?xml version="1.0" encoding="UTF-8" standalone="no"?>
   C:<epp xmlns="urn:ietf:params:xml:ns:epp-1.0">
   C:  <command>
   C:    <update>
   C:      <domain:update
   C:        xmlns:domain="urn:ietf:params:xml:ns:domain-1.0">
   C:        <domain:name>example.com</domain:name>
   C:        <domain:add>
   C:          <domain:status s="clientTransferProhibited"/>
   C:        </domain:add>
   C:        <domain:chg>
   C:          <domain:authInfo>
   C:            <domain:null/>
   C:          </domain:authInfo>
   C:        </domain:chg>
   C:      </domain:update>
   C:    </update>
   C:    <clTRID>ABC-12345-XYZ</clTRID>
   C:  </command>
   C:</epp>

   Example of unsetting the authorization information with an empty
   authorization information value in a domain name <update> command
   [RFC5731]:

   C:<?xml version="1.0" encoding="UTF-8" standalone="no"?>
   C:<epp xmlns="urn:ietf:params:xml:ns:epp-1.0">
   C:  <command>
   C:    <update>
   C:      <domain:update
   C:        xmlns:domain="urn:ietf:params:xml:ns:domain-1.0">
   C:        <domain:name>example.com</domain:name>
   C:        <domain:add>
   C:          <domain:status s="clientTransferProhibited"/>
   C:        </domain:add>
   C:        <domain:chg>
   C:          <domain:authInfo>
   C:            <domain:pw/>
   C:          </domain:authInfo>
   C:        </domain:chg>
   C:      </domain:update>
   C:    </update>
   C:    <clTRID>ABC-12345-XYZ</clTRID>
   C:  </command>
   C:</epp>

   Example of unsetting the authorization information with an empty
   authorization information value in a contact <update> command
   [RFC5733]:

   C:<?xml version="1.0" encoding="UTF-8" standalone="no"?>
   C:<epp xmlns="urn:ietf:params:xml:ns:epp-1.0">
   C:  <command>
   C:    <update>
   C:      <contact:update
   C:        xmlns:contact="urn:ietf:params:xml:ns:contact-1.0">
   C:        <contact:id>sh8013</contact:id>
   C:        <contact:chg>
   C:          <contact:authInfo>
   C:            <contact:pw/>
   C:          </contact:authInfo>
   C:        </contact:chg>
   C:      </contact:update>
   C:    </update>
   C:    <clTRID>ABC-12345-XYZ</clTRID>
   C:  </command>
   C:</epp>

5.3.  <Info> Command and Response

   For an <info> command, the registry MUST allow the passing of a non-
   empty authorization information value for verification.  The gaining
   registrar can pre-verify the authorization information provided by
   the registrant prior to submitting the transfer request with the use
   of the <info> command.  The registry compares the hash of the passed
   authorization information with the hashed authorization information
   value stored for the object.  When the authorization information is
   not set or the passed authorization information does not match the
   previously set value, the registry MUST return an EPP error result
   code of 2202 [RFC5730].

   Example of passing a non-empty authorization information value in a
   domain name <info> command [RFC5731] to verify the authorization
   information value:

   C:<?xml version="1.0" encoding="UTF-8" standalone="no"?>
   C:<epp xmlns="urn:ietf:params:xml:ns:epp-1.0">
   C:  <command>
   C:    <info>
   C:      <domain:info
   C:        xmlns:domain="urn:ietf:params:xml:ns:domain-1.0">
   C:        <domain:name>example.com</domain:name>
   C:        <domain:authInfo>
   C:          <domain:pw>LuQ7Bu@w9?%+_HK3cayg$55$LSft3MPP
   C:          </domain:pw>
   C:        </domain:authInfo>
   C:      </domain:info>
   C:    </info>
   C:    <clTRID>ABC-12345</clTRID>
   C:  </command>
   C:</epp>

   The info response in object extensions, such as those defined in
   [RFC5731] and [RFC5733], MUST NOT include the optional authorization
   information element with a non-empty authorization value.  The
   authorization information is stored as a hash in the registry, so
   returning the plain-text authorization information is not possible,
   unless valid plain-text authorization information is passed in the
   <info> command.  The registry MUST NOT return any indication of
   whether the authorization information is set or unset to the non-
   sponsoring registrar by not returning the authorization information
   element in the response.  The registry MAY return an indication to
   the sponsoring registrar that the authorization information is set by
   using an empty authorization information value.  The registry MAY
   return an indication to the sponsoring registrar that the
   authorization information is unset by not returning the authorization
   information element.

   Example of returning an empty authorization information value in a
   domain name info response [RFC5731] to indicate to the sponsoring
   registrar that the authorization information is set:

   S:<?xml version="1.0" encoding="UTF-8" standalone="no"?>
   S:<epp xmlns="urn:ietf:params:xml:ns:epp-1.0">
   S:  <response>
   S:    <result code="1000">
   S:      <msg>Command completed successfully</msg>
   S:    </result>
   S:    <resData>
   S:      <domain:infData
   S:       xmlns:domain="urn:ietf:params:xml:ns:domain-1.0">
   S:        <domain:name>example.com</domain:name>
   S:        <domain:roid>EXAMPLE1-REP</domain:roid>
   S:        <domain:status s="ok"/>
   S:        <domain:clID>ClientX</domain:clID>
   S:        <domain:authInfo>
   S:          <domain:pw/>
   S:        </domain:authInfo>
   S:      </domain:infData>
   S:    </resData>
   S:    <trID>
   S:      <clTRID>ABC-12345</clTRID>
   S:      <svTRID>54322-XYZ</svTRID>
   S:    </trID>
   S:  </response>
   S:</epp>

5.4.  <Transfer> Request Command

   For a <transfer> request command, the registry MUST allow the passing
   of a non-empty authorization information value to authorize a
   transfer.  The registry compares the hash of the passed authorization
   information with the hashed authorization information value stored
   for the object.  When the authorization information is not set or the
   passed authorization information does not match the previously set
   value, the registry MUST return an EPP error result code of 2202
   [RFC5730].  Whether the transfer occurs immediately or is pending is
   up to server policy.  When the transfer occurs immediately, the
   registry MUST return the EPP success result code of 1000 ("Command
   completed successfully") [RFC5730], and when the transfer is pending,
   the registry MUST return the EPP success result code of 1001
   ("Command completed successfully; action pending").  The losing
   registrar MUST be informed of a successful transfer request using an
   EPP <poll> message.

   Example of passing a non-empty authorization information value in a
   domain name <transfer> request command [RFC5731] to authorize the
   transfer:

   C:<?xml version="1.0" encoding="UTF-8" standalone="no"?>
   C:<epp xmlns="urn:ietf:params:xml:ns:epp-1.0">
   C:  <command>
   C:    <transfer op="request">
   C:      <domain:transfer
   C:        xmlns:domain="urn:ietf:params:xml:ns:domain-1.0">
   C:        <domain:name>example1.com</domain:name>
   C:        <domain:authInfo>
   C:          <domain:pw>LuQ7Bu@w9?%+_HK3cayg$55$LSft3MPP
   C:          </domain:pw>
   C:        </domain:authInfo>
   C:      </domain:transfer>
   C:    </transfer>
   C:    <clTRID>ABC-12345</clTRID>
   C:  </command>
   C:</epp>

   Upon successful completion of the transfer, the registry MUST
   automatically unset the authorization information.  If the transfer
   request is not submitted within the TTL (Section 4.2) or the transfer
   is canceled or rejected, the registrar MUST unset the authorization
   information, as described in Section 5.2.

6.  Transition Considerations

   The goal of the transition considerations is to minimize the impact
   to the registrars in supporting the Secure Authorization Information
   Model defined in this document by supporting incremental transition
   steps.  The transition steps are dependent on the starting point of
   the registry.  Registries may have different starting points, since
   some of the elements of the Secure Authorization Information Model
   may have already been implemented.  The considerations assume a
   starting point, referred to as the "Classic Authorization Information
   Model", which incorporates the following steps for management of the
   authorization information for transfers:

   1.  The registrant requests to register the object with the
       registrar.  The registrar sends the <create> command, with a non-
       empty authorization information value, to the registry.  The
       registry stores the authorization information as an encrypted
       value and requires a non-empty authorization information value
       for the life of the object.  The registrar may store the long-
       lived authorization information.

   2.  At the time of transfer, the registrant requests from the losing
       registrar the authorization information to provide to the gaining
       registrar.

   3.  The losing registrar retrieves the locally stored authorization
       information or queries the registry for authorization information
       using the <info> command, and provides it to the registrant.  If
       the registry is queried, the authorization information is
       decrypted and the plain-text authorization information is
       returned in the info response to the registrar.

   4.  The registrant provides the authorization information value to
       the gaining registrar.

   5.  The gaining registrar optionally verifies the authorization
       information with the <info> command to the registry, by passing
       the authorization information in the <info> command to the
       registry.

   6.  The gaining registrar sends the transfer request with the
       authorization information to the registry.  The registry will
       decrypt the stored authorization information to compare to the
       passed authorization information.

   7.  If the transfer completes successfully, the authorization
       information is not touched by the registry and may be updated by
       the gaining registrar using the <update> command.  If the
       transfer is canceled or rejected, the losing registrar may reset
       the authorization information using the <update> command.

   The gaps between the Classic Authorization Information Model and the
   Secure Authorization Information Model include the following:

   1.  Registry requirement for a non-empty authorization information
       value on create and for the life of the object versus the
       authorization information not being set on create and only being
       set when a transfer is in process.

   2.  Registry not allowing the authorization information to be unset
       versus providing support for unsetting the authorization
       information in the <update> command.

   3.  Registry storing the authorization information as an encrypted
       value versus a hashed value.

   4.  Registry support for returning the authorization information
       versus not returning the authorization information in the info
       response.

   5.  Registry not touching the authorization information versus the
       registry automatically unsetting the authorization information
       upon a successful transfer.

   6.  Registry possibly validating a shorter authorization information
       value using password complexity rules versus validating the
       randomness of a longer authorization information value that meets
       the required bits of entropy.

   The transition can be handled in the three phases defined in
   Sections 6.1, 6.2, and 6.3.

6.1.  Transition Phase 1 - Features

   The goal of "Transition Phase 1 - Features" is to implement the
   needed features in EPP so that the registrar can optionally implement
   the Secure Authorization Information Model.  The features to
   implement are broken out by the commands and responses below:

   <Create> Command:  Change the <create> command to make the
      authorization information optional, by allowing both a non-empty
      value and an empty value.  This enables a registrar to optionally
      create objects without an authorization information value, as
      described in Section 5.1.

   <Update> Command:  Change the <update> command to allow unsetting the
      authorization information, as described in Section 5.2.  This
      enables the registrar to optionally unset the authorization
      information when the TTL expires or when the transfer is canceled
      or rejected.

   Transfer Approve Command and Transfer Auto-Approve:  Change the
      transfer approve command and the transfer auto-approve to
      automatically unset the authorization information.  This sets the
      default state of the object to not have the authorization
      information set.  The registrar implementing the Secure
      Authorization Information Model will not set the authorization
      information for an inbound transfer, and the registrar
      implementing the Classic Authorization Information Model will set
      the new authorization information upon a successful transfer.

   Info Response:  Change the <info> command to not return the
      authorization information in the info response, as described in
      Section 5.3.  This sets up the implementation of "Transition Phase
      2 - Storage" (Section 6.2), since the dependency on returning the
      authorization information in the info response will be removed.
      This feature is the only one that is not an optional change to the
      registrar, and this change could potentially break the client, so
      it's recommended that the registry provide notice of the change.

   <Info> Command and Transfer Request:  Change the <info> command and
      the transfer request to ensure that a registrar cannot get an
      indication that the authorization information is set or not set by
      returning the EPP error result code of 2202 when comparing a
      passed authorization to a non-matching set authorization
      information value or an unset value.

6.2.  Transition Phase 2 - Storage

   The goal of "Transition Phase 2 - Storage" is to transition the
   registry to use hashed authorization information instead of encrypted
   authorization information.  There is no direct impact on the
   registrars, since the only visible indication that the authorization
   information has been hashed is that the set authorization information
   is not returned in the info response, as addressed in "Transition
   Phase 1 - Features" (Section 6.1).  Transitioning the authorization
   information storage includes the following three steps:

   Hash New Authorization Information Values:  Change the <create>
      command and the <update> command to hash rather than encrypt the
      authorization information.

   Support Comparison against Encrypted or Hashed Authorization
   Information:  Change the <info> command and the <transfer> request
      command to be able to compare a passed authorization information
      value with either a hashed or encrypted authorization information
      value.  This requires that the stored values be self-identifying
      as being in hashed or encrypted form.

   Hash Existing Encrypted Authorization Information Values:  Convert
      the encrypted authorization information values stored in the
      registry database to hashed values.  This update will not be
      visible to the registrar.  The conversion can be done over a
      period of time, depending on registry policy.

6.3.  Transition Phase 3 - Enforcement

   The goal of "Transition Phase 3 - Enforcement" is to complete the
   implementation of the Secure Authorization Information Model, by
   enforcing the following:

   Disallow Authorization Information on <Create> Command:  Change the
      <create> command to not allow the passing of a non-empty
      authorization information value.  This behavior could potentially
      break the client, so it's recommended that the registry provide
      notice of this change.

   Validate the Strong Random Authorization Information:  Change the
      validation of the authorization information in the <update>
      command to ensure at least 128 bits of entropy.

7.  IANA Considerations

7.1.  XML Namespace

   This document uses URNs to describe XML namespaces conforming to the
   registry mechanism described in [RFC3688].  IANA has assigned the
   following URI in the "ns" subregistry within the "IETF XML Registry"
   for secure authorization information for the transfer namespace:

   URI:  urn:ietf:params:xml:ns:epp:secure-authinfo-transfer-1.0
   Registrant Contact:  IESG
   XML:  None.  Namespace URIs do not represent an XML specification.

7.2.  EPP Extension Registry

   IANA has registered the EPP operational practice described in this
   document in the "Extensions for the Extensible Provisioning Protocol
   (EPP)" registry as defined in [RFC7451].  The details of the
   registration are as follows:

   Name of Extension:  "Extensible Provisioning Protocol (EPP) Secure
      Authorization Information for Transfer"
   Document status:  Standards Track
   Reference:  RFC 9154
   Registrant Name and Email Address:  IESG (iesg@ietf.org)
   TLDs:  Any
   IPR Disclosure:  None
   Status:  Active
   Notes:  None

8.  Security Considerations

   Section 4.1 defines the use of a secure random value for the
   generation of authorization information.  The client SHOULD choose a
   length and set of characters that result in at least 128 bits of
   entropy.

   Section 4.2 defines the use of an authorization information TTL.  The
   registrar SHOULD only set the authorization information during the
   transfer process by setting the authorization information at the
   start of the transfer process and unsetting the authorization
   information at the end of the transfer process.  The TTL value is
   left up to registrar policy, and the sponsoring registrar MUST inform
   the registrant of the TTL when providing the authorization
   information to the registrant.

   Section 4.3 defines the storage and transport of authorization
   information.  The losing registrar MUST NOT store the authorization
   information and the gaining registrar MUST only store the
   authorization information as a "transient" value during the transfer
   process, where the authorization information MUST NOT be stored after
   the end of the transfer process.  The registry MUST store the
   authorization information using a one-way cryptographic hash of at
   least 256 bits and with a per-authorization information random salt
   with at least 128 bits.  All communication that includes the
   authorization information MUST be over an encrypted channel.  The
   plain-text authorization information MUST NOT be written to any logs
   by the registrar or the registry.

   Section 4.4 defines the matching of the authorization information
   values.  The registry stores an unset authorization information value
   as a NULL (undefined) value to ensure that an empty input
   authorization information value never matches it.  The method used to
   define a NULL (undefined) value is database specific.

9.  References

9.1.  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>.

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              DOI 10.17487/RFC3688, January 2004,
              <https://www.rfc-editor.org/info/rfc3688>.

   [RFC4086]  Eastlake 3rd, D., Schiller, J., and S. Crocker,
              "Randomness Requirements for Security", BCP 106, RFC 4086,
              DOI 10.17487/RFC4086, June 2005,
              <https://www.rfc-editor.org/info/rfc4086>.

   [RFC5730]  Hollenbeck, S., "Extensible Provisioning Protocol (EPP)",
              STD 69, RFC 5730, DOI 10.17487/RFC5730, August 2009,
              <https://www.rfc-editor.org/info/rfc5730>.

   [RFC5731]  Hollenbeck, S., "Extensible Provisioning Protocol (EPP)
              Domain Name Mapping", STD 69, RFC 5731,
              DOI 10.17487/RFC5731, August 2009,
              <https://www.rfc-editor.org/info/rfc5731>.

   [RFC5733]  Hollenbeck, S., "Extensible Provisioning Protocol (EPP)
              Contact Mapping", STD 69, RFC 5733, DOI 10.17487/RFC5733,
              August 2009, <https://www.rfc-editor.org/info/rfc5733>.

   [RFC5734]  Hollenbeck, S., "Extensible Provisioning Protocol (EPP)
              Transport over TCP", STD 69, RFC 5734,
              DOI 10.17487/RFC5734, August 2009,
              <https://www.rfc-editor.org/info/rfc5734>.

   [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>.

   [RFC8499]  Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
              Terminology", BCP 219, RFC 8499, DOI 10.17487/RFC8499,
              January 2019, <https://www.rfc-editor.org/info/rfc8499>.

   [W3C.REC-xml-20081126]
              Bray, T., Paoli, J., Sperberg-McQueen, M., Maler, E., and
              F. Yergeau, "Extensible Markup Language (XML) 1.0 (Fifth
              Edition)", World Wide Web Consortium Recommendation REC-
              xml-20081126, November 2008,
              <https://www.w3.org/TR/2008/REC-xml-20081126>.

9.2.  Informative References

   [FIPS-140-2]
              National Institute of Standards and Technology, U.S.
              Department of Commerce, "NIST Federal Information
              Processing Standards (FIPS) Publication 140-2",
              DOI 10.6028/NIST.FIPS.140-2, May 2001,
              <https://csrc.nist.gov/publications/detail/fips/140/2/
              final>.

   [FIPS-180-4]
              National Institute of Standards and Technology, U.S.
              Department of Commerce, "Secure Hash Standard, NIST
              Federal Information Processing Standards (FIPS)
              Publication 180-4", DOI 10.6028/NIST.FIPS.180-4, August
              2015,
              <https://csrc.nist.gov/publications/detail/fips/180/4/
              final>.

   [RFC7451]  Hollenbeck, S., "Extension Registry for the Extensible
              Provisioning Protocol", RFC 7451, DOI 10.17487/RFC7451,
              February 2015, <https://www.rfc-editor.org/info/rfc7451>.

Acknowledgements

   The authors wish to thank the following persons for their feedback
   and suggestions: Michael Bauland, Martin Casanova, Scott Hollenbeck,
   Benjamin Kaduk, Jody Kolker, Barry Leiba, Patrick Mevzek, Matthew
   Pozun, Srikanth Veeramachaneni, and Ulrich Wisser.

Authors' Addresses

   James Gould
   Verisign, Inc.
   12061 Bluemont Way
   Reston, VA 20190
   United States of America

   Email: jgould@verisign.com
   URI:   https://www.verisign.com


   Richard Wilhelm
   Verisign, Inc.
   12061 Bluemont Way
   Reston, VA 20190
   United States of America

   Email: 4rickwilhelm@gmail.com
   URI:   https://www.verisign.com