Internet Engineering Task Force (IETF) J. Gould

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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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>[email protected]</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 ([email protected])
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: [email protected]
URI: https://www.verisign.com

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

Email: [email protected]
URI: https://www.verisign.com