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Internet Engineering Task Force (IETF) C. Huitema
Request for Comments: 8882 Private Octopus Inc.
Category: Informational D. Kaiser
ISSN: 2070-1721 University of Luxembourg
September 2020
DNS-Based Service Discovery (DNS-SD) Privacy and Security Requirements
Abstract
DNS-SD (DNS-based Service Discovery) normally discloses information
about devices offering and requesting services. This information
includes hostnames, network parameters, and possibly a further
description of the corresponding service instance. Especially when
mobile devices engage in DNS-based Service Discovery at a public
hotspot, serious privacy problems arise. We analyze the requirements
of a privacy-respecting discovery service.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
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). Not all documents
approved by the IESG are candidates for any level of Internet
Standard; see 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/rfc8882.
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction
2. Threat Model
3. Threat Analysis
3.1. Service Discovery Scenarios
3.1.1. Private Client and Public Server
3.1.2. Private Client and Private Server
3.1.3. Wearable Client and Server
3.2. DNS-SD Privacy Considerations
3.2.1. Information Made Available Via DNS-SD Resource Records
3.2.2. Privacy Implication of Publishing Service Instance
Names
3.2.3. Privacy Implication of Publishing Node Names
3.2.4. Privacy Implication of Publishing Service Attributes
3.2.5. Device Fingerprinting
3.2.6. Privacy Implication of Discovering Services
3.3. Security Considerations
3.3.1. Authenticity, Integrity, and Freshness
3.3.2. Confidentiality
3.3.3. Resistance to Dictionary Attacks
3.3.4. Resistance to Denial-of-Service Attacks
3.3.5. Resistance to Sender Impersonation
3.3.6. Sender Deniability
3.4. Operational Considerations
3.4.1. Power Management
3.4.2. Protocol Efficiency
3.4.3. Secure Initialization and Trust Models
3.4.4. External Dependencies
4. Requirements for a DNS-SD Privacy Extension
4.1. Private Client Requirements
4.2. Private Server Requirements
4.3. Security and Operation
5. IANA Considerations
6. References
6.1. Normative References
6.2. Informative References
Acknowledgments
Authors' Addresses
1. Introduction
DNS-Based Service Discovery (DNS-SD) [RFC6763] over Multicast DNS
(mDNS) [RFC6762] enables zero-configuration service discovery in
local networks. It is very convenient for users, but it requires the
public exposure of the offering and requesting identities along with
information about the offered and requested services. Parts of the
published information can seriously breach the user's privacy. These
privacy issues and potential solutions are discussed in [KW14a],
[KW14b], and [K17]. While the multicast nature of mDNS makes these
risks obvious, most risks derive from the observability of
transactions. These risks also need to be mitigated when using
server-based variants of DNS-SD.
There are cases when nodes connected to a network want to provide or
consume services without exposing their identities to the other
parties connected to the same network. Consider, for example, a
traveler wanting to upload pictures from a phone to a laptop when
both are connected to the Wi-Fi network of an Internet cafe, or two
travelers who want to share files between their laptops when waiting
for their plane in an airport lounge.
We expect that these exchanges will start with a discovery procedure
using DNS-SD over mDNS. One of the devices will publish the
availability of a service, such as a picture library or a file store
in our examples. The user of the other device will discover this
service and then connect to it.
When analyzing these scenarios in Section 3.1, we find that the DNS-
SD messages leak identifying information, such as the Service
Instance Name, the hostname, or service properties. We use the
following definitions:
Identity
In this document, the term "identity" refers to the identity of
the entity (legal person) operating a device.
Disclosing an Identity
In this document, "disclosing an identity" means showing the
identity of operating entities to devices external to the
discovery process, e.g., devices on the same network link that are
listening to the network traffic but are not actually involved in
the discovery process. This document focuses on identity
disclosure by data conveyed via messages on the service discovery
protocol layer. Still, identity leaks on deeper layers, e.g., the
IP layer, are mentioned.
Disclosing Information
In this document, "disclosing information" is also focused on
disclosure of data conveyed via messages on the service discovery
protocol layer, including both identity-revealing information and
other still potentially sensitive data.
2. Threat Model
This document considers the following attacker types sorted by
increasing power. All these attackers can either be passive (they
just listen to network traffic they have access to) or active (they
additionally can craft and send malicious packets).
external
An external attacker is not on the same network link as victim
devices engaging in service discovery; thus, the external attacker
is in a different multicast domain.
on-link
An on-link attacker is on the same network link as victim devices
engaging in service discovery; thus, the on-link attacker is in
the same multicast domain. This attacker can also mount all
attacks an external attacker can mount.
MITM
A Man-in-the-Middle (MITM) attacker either controls (parts of) a
network link or can trick two parties to send traffic via the
attacker; thus, the MITM attacker has access to unicast traffic
between devices engaging in service discovery. This attacker can
also mount all attacks an on-link attacker can mount.
3. Threat Analysis
In this section, we analyze how the attackers described in the
previous section might threaten the privacy of entities operating
devices engaging in service discovery. We focus on attacks
leveraging data transmitted in service discovery protocol messages.
3.1. Service Discovery Scenarios
In this section, we review common service discovery scenarios and
discuss privacy threats and their privacy requirements. In all three
of these common scenarios, the attacker is of the type passive on-
link.
3.1.1. Private Client and Public Server
Perhaps the simplest private discovery scenario involves a single
client connecting to a public server through a public network. A
common example would be a traveler using a publicly available printer
in a business center, in a hotel, or at an airport.
( Taking notes:
( David is printing
( a document.
~~~~~~~~~~~
o
___ o ___
/ \ _|___|_
| | client server |* *|
\_/ __ \_/
| / / Discovery +----------+ |
/|\ /_/ <-----------> | +----+ | /|\
/ | \__/ +--| |--+ / | \
/ | |____/ / | \
/ | / | \
/ \ / \
/ \ / \
/ \ / \
/ \ / \
/ \ / \
David Adversary
In that scenario, the server is public and wants to be discovered,
but the client is private. The adversary will be listening to the
network traffic, trying to identify the visitors' devices and their
activity. Identifying devices leads to identifying people, either
for surveillance of these individuals in the physical world or as a
preliminary step for a targeted cyber attack.
The requirement in that scenario is that the discovery activity
should not disclose the identity of the client.
3.1.2. Private Client and Private Server
The second private discovery scenario involves a private client
connecting to a private server. A common example would be two people
engaging in a collaborative application in a public place, such as an
airport's lounge.
( Taking notes:
( David is meeting
( with Stuart.
~~~~~~~~~~~
o
___ ___ o ___
/ \ / \ _|___|_
| | server client | | |* *|
\_/ __ __ \_/ \_/
| / / Discovery \ \ | |
/|\ /_/ <-----------> \_\ /|\ /|\
/ | \__/ \__/ | \ / | \
/ | | \ / | \
/ | | \ / | \
/ \ / \ / \
/ \ / \ / \
/ \ / \ / \
/ \ / \ / \
/ \ / \ / \
David Stuart Adversary
In that scenario, the collaborative application on one of the devices
will act as a server, and the application on the other device will
act as a client. The server wants to be discovered by the client but
has no desire to be discovered by anyone else. The adversary will be
listening to network traffic, attempting to discover the identity of
devices as in the first scenario and also attempting to discover the
patterns of traffic, as these patterns reveal the business and social
interactions between the owners of the devices.
The requirement in that scenario is that the discovery activity
should not disclose the identity of either the client or the server
nor reveal the business and social interactions between the owners of
the devices.
3.1.3. Wearable Client and Server
The third private discovery scenario involves wearable devices. A
typical example would be the watch on someone's wrist connecting to
the phone in their pocket.
( Taking notes:
( David is here. His watch is
( talking to his phone.
~~~~~~~~~~~
o
___ o ___
/ \ _|___|_
| | client |* *|
\_/ \_/
| _/ |
/|\ // /|\
/ | \__/ ^ / | \
/ |__ | Discovery / | \
/ |\ \ v / | \
/ \\_\ / \
/ \ server / \
/ \ / \
/ \ / \
/ \ / \
David Adversary
This third scenario is in many ways similar to the second scenario.
It involves two devices, one acting as server and the other acting as
client, and it leads to the same requirement of the discovery traffic
not disclosing the identity of either the client or the server. The
main difference is that the devices are managed by a single owner,
which can lead to different methods for establishing secure relations
between the devices. There is also an added emphasis on hiding the
type of devices that the person wears.
In addition to tracking the identity of the owner of the devices, the
adversary is interested in the characteristics of the devices, such
as type, brand, and model. Identifying the type of device can lead
to further attacks, from theft to device-specific hacking. The
combination of devices worn by the same person will also provide a
"fingerprint" of the person, risking identification.
This scenario also represents the general case of bringing private
Internet-of-Things (IoT) devices into public places. A wearable IoT
device might act as a DNS-SD/mDNS client, which allows attackers to
infer information about devices' owners. While the attacker might be
a person, as in the example figure, this could also be abused for
large-scale data collection installing stationary IoT-device-tracking
servers in frequented public places.
The issues described in Section 3.1.1, such as identifying people or
using the information for targeted attacks, apply here too.
3.2. DNS-SD Privacy Considerations
While the discovery process illustrated in the scenarios in
Section 3.1 most likely would be based on [RFC6762] as a means for
making service information available, this document considers all
kinds of means for making DNS-SD resource records available. These
means comprise of but are not limited to mDNS [RFC6762], DNS servers
([RFC1033], [RFC1034], and [RFC1035]), the use of Service
Registration Protocol (SRP) [SRP], and multi-link [RFC7558] networks.
The discovery scenarios in Section 3.1 illustrate three separate
abstract privacy requirements that vary based on the use case. These
are not limited to mDNS.
1. Client identity privacy: Client identities are not leaked during
service discovery or use.
2. Multi-entity, mutual client and server identity privacy: Neither
client nor server identities are leaked during service discovery
or use.
3. Single-entity, mutual client and server identity privacy:
Identities of clients and servers owned and managed by the same
legal person are not leaked during service discovery or use.
In this section, we describe aspects of DNS-SD that make these
requirements difficult to achieve in practice. While it is intended
to be thorough, it is not possible to be exhaustive.
Client identity privacy, if not addressed properly, can be thwarted
by a passive attacker (see Section 2). The type of passive attacker
necessary depends on the means of making service information
available. Information conveyed via multicast messages can be
obtained by an on-link attacker. Unicast messages are harder to
access, but if the transmission is not encrypted they could still be
accessed by an attacker with access to network routers or bridges.
Using multi-link service discovery solutions [RFC7558], external
attackers have to be taken into consideration as well, e.g., when
relaying multicast messages to other links.
Server identity privacy can be thwarted by a passive attacker in the
same way as client identity privacy. Additionally, active attackers
querying for information have to be taken into consideration as well.
This is mainly relevant for unicast-based discovery, where listening
to discovery traffic requires a MITM attacker; however, an external
active attacker might be able to learn the server identity by just
querying for service information, e.g., via DNS.
3.2.1. Information Made Available Via DNS-SD Resource Records
DNS-Based Service Discovery (DNS-SD) is defined in [RFC6763]. It
allows nodes to publish the availability of an instance of a service
by inserting specific records in the DNS ([RFC1033], [RFC1034], and
[RFC1035]) or by publishing these records locally using multicast DNS
(mDNS) [RFC6762]. Available services are described using three types
of records:
PTR Record
Associates a service type in the domain with an "instance" name of
this service type.
SRV Record
Provides the node name, port number, priority and weight
associated with the service instance, in conformance with
[RFC2782].
TXT Record
Provides a set of attribute-value pairs describing specific
properties of the service instance.
3.2.2. Privacy Implication of Publishing Service Instance Names
In the first phase of discovery, clients obtain all PTR records
associated with a service type in a given naming domain. Each PTR
record contains a Service Instance Name defined in Section 4 of
[RFC6763]:
Service Instance Name = <Instance> . <Service> . <Domain>
The <Instance> portion of the Service Instance Name is meant to
convey enough information for users of discovery clients to easily
select the desired service instance. Nodes that use DNS-SD over mDNS
[RFC6762] in a mobile environment will rely on the specificity of the
instance name to identify the desired service instance. In our
example of users wanting to upload pictures to a laptop in an
Internet cafe, the list of available service instances may look like:
Alice's Images . _imageStore._tcp . local
Alice's Mobile Phone . _presence._tcp . local
Alice's Notebook . _presence._tcp . local
Bob's Notebook . _presence._tcp . local
Carol's Notebook . _presence._tcp . local
Alice will see the list on her phone and understand intuitively that
she should pick the first item. The discovery will "just work".
(Note that our examples of service names conform to the specification
in Section 4.1 of [RFC6763] but may require some character escaping
when entered in conventional DNS software.)
However, DNS-SD/mDNS will reveal to anybody that Alice is currently
visiting the Internet cafe. It further discloses the fact that she
uses two devices, shares an image store, and uses a chat application
supporting the _presence protocol on both of her devices. She might
currently chat with Bob or Carol, as they are also using a _presence
supporting chat application. This information is not just available
to devices actively browsing for and offering services but to anybody
passively listening to the network traffic, i.e., a passive on-link
attacker.
There is, of course, also no authentication requirement to claim a
particular instance name, so an active attacker can provide resources
that claim to be Alice's but are not.
3.2.3. Privacy Implication of Publishing Node Names
The SRV records contain the DNS name of the node publishing the
service. Typical implementations construct this DNS name by
concatenating the "hostname" of the node with the name of the local
domain. The privacy implications of this practice are reviewed in
[RFC8117]. Depending on naming practices, the hostname is either a
strong identifier of the device or, at a minimum, a partial
identifier. It enables tracking of both the device and, by
extension, the device's owner.
3.2.4. Privacy Implication of Publishing Service Attributes
The TXT record's attribute-value pairs contain information on the
characteristics of the corresponding service instance. This in turn
reveals information about the devices that publish services. The
amount of information varies widely with the particular service and
its implementation:
* Some attributes, such as the paper size available in a printer,
are the same on many devices and thus only provide limited
information to a tracker.
* Attributes that have free-form values, such as the name of a
directory, may reveal much more information.
Combinations of individual attributes have more information power
than specific attributes and can potentially be used for
"fingerprinting" a specific device.
Information contained in TXT records not only breaches privacy by
making devices trackable but might directly contain private
information about the user. For instance, the _presence service
reveals the "chat status" to everyone in the same network. Users
might not be aware of that.
Further, TXT records often contain version information about
services, allowing potential attackers to identify devices running
exploit-prone versions of a certain service.
3.2.5. Device Fingerprinting
The combination of information published in DNS-SD has the potential
to provide a "fingerprint" of a specific device. Such information
includes:
* A list of services published by the device, which can be retrieved
because the SRV records will point to the same hostname.
* Specific attributes describing these services.
* Port numbers used by the services.
* Priority and weight attributes in the SRV records.
This combination of services and attributes will often be sufficient
to identify the version of the software running on a device. If a
device publishes many services with rich sets of attributes, the
combination may be sufficient to identify the specific device and
track its owner.
An argument is sometimes made that devices providing services can be
identified by observing the local traffic and that trying to hide the
presence of the service is futile. However, there are good reasons
for the discovery service layer to avoid unnecessary exposure:
1. Providing privacy at the discovery layer is of the essence for
enabling automatically configured privacy-preserving network
applications. Application layer protocols are not forced to
leverage the offered privacy, but if device tracking is not
prevented at the deeper layers, including the service discovery
layer, obfuscating a certain service's protocol at the
application layer is futile.
2. Further, in the case of mDNS-based discovery, even if the
application layer does not protect privacy, services are
typically provided via unicast, which requires a MITM attacker,
whereas identifying services based on multicast discovery
messages just requires an on-link attacker.
The same argument can be extended to say that the pattern of services
offered by a device allows for fingerprinting the device. This may
or may not be true, since we can expect that services will be
designed or updated to avoid leaking fingerprints. In any case, the
design of the discovery service should avoid making a bad situation
worse and should, as much as possible, avoid providing new
fingerprinting information.
3.2.6. Privacy Implication of Discovering Services
The consumers of services engage in discovery and in doing so reveal
some information, such as the list of services they are interested in
and the domains in which they are looking for the services. When the
clients select specific instances of services, they reveal their
preference for these instances. This can be benign if the service
type is very common, but it could be more problematic for sensitive
services, such as some private messaging services.
One way to protect clients would be to somehow encrypt the requested
service types. Of course, just as we noted in Section 3.2.5, traffic
analysis can often reveal the service.
3.3. Security Considerations
For each of the operations described above, we must also consider
security threats we are concerned about.
3.3.1. Authenticity, Integrity, and Freshness
Can devices (both servers and clients) trust the information they
receive? Has it been modified in flight by an adversary? Can
devices trust the source of the information? Is the source of
information fresh, i.e., not replayed? Freshness may or may not be
required depending on whether the discovery process is meant to be
online. In some cases, publishing discovery information to a shared
directory or registry, rather than to each online recipient through a
broadcast channel, may suffice.
3.3.2. Confidentiality
Confidentiality is about restricting information access to only
authorized individuals. Ideally, this should only be the appropriate
trusted parties, though it can be challenging to define who are "the
appropriate trusted parties." In some use cases, this may mean that
only mutually authenticated and trusting clients and servers can read
messages sent for one another. The process of service discovery in
particular is often used to discover new entities that the device did
not previously know about. It may be tricky to work out how a device
can have an established trust relationship with a new entity it has
never previously communicated with.
3.3.3. Resistance to Dictionary Attacks
It can be tempting to use (publicly computable) hash functions to
obscure sensitive identifiers. This transforms a sensitive unique
identifier, such as an email address, into a "scrambled" but still
unique identifier. Unfortunately, simple solutions may be vulnerable
to offline dictionary attacks.
3.3.4. Resistance to Denial-of-Service Attacks
In any protocol where the receiver of messages has to perform
cryptographic operations on those messages, there is a risk of a
brute-force flooding attack causing the receiver to expend excessive
amounts of CPU time and, where applicable, battery power just
processing and discarding those messages.
Also, amplification attacks have to be taken into consideration.
Messages with larger payloads should only be sent as an answer to a
query sent by a verified client.
3.3.5. Resistance to Sender Impersonation
Sender impersonation is an attack wherein messages, such as service
offers, are forged by entities who do not possess the corresponding
secret key material. These attacks may be used to learn the identity
of a communicating party, actively or passively.
3.3.6. Sender Deniability
Deniability of sender activity, e.g., of broadcasting a discovery
request, may be desirable or necessary in some use cases. This
property ensures that eavesdroppers cannot prove senders issued a
specific message destined for one or more peers.
3.4. Operational Considerations
3.4.1. Power Management
Many modern devices, especially battery-powered devices, use power
management techniques to conserve energy. One such technique is for
a device to transfer information about itself to a proxy, which will
act on behalf of the device for some functions while the device
itself goes to sleep to reduce power consumption. When the proxy
determines that some action is required, which only the device itself
can perform, the proxy may have some way to wake the device, as
described for example in [SLEEP-PROXY].
In many cases, the device may not trust the network proxy
sufficiently to share all its confidential key material with the
proxy. This poses challenges for combining private discovery that
relies on per-query cryptographic operations with energy-saving
techniques that rely on having (somewhat untrusted) network proxies
answer queries on behalf of sleeping devices.
3.4.2. Protocol Efficiency
Creating a discovery protocol that has the desired security
properties may result in a design that is not efficient. To perform
the necessary operations, the protocol may need to send and receive a
large number of network packets or require an inordinate amount of
multicast transmissions. This may consume an unreasonable amount of
network capacity, particularly problematic when it is a shared
wireless spectrum. Further, it may cause an unnecessary level of
power consumption, which is particularly problematic on battery
devices and may result in the discovery process being slow.
It is a difficult challenge to design a discovery protocol that has
the property of obscuring the details of what it is doing from
unauthorized observers while also managing to perform efficiently.
3.4.3. Secure Initialization and Trust Models
One of the challenges implicit in the preceding discussions is that
whenever we discuss "trusted entities" versus "untrusted entities",
there needs to be some way that trust is initially established to
convert an "untrusted entity" into a "trusted entity".
The purpose of this document is not to define the specific way in
which trust can be established. Protocol designers may rely on a
number of existing technologies, including PKI, Trust On First Use
(TOFU), or the use of a short passphrase or PIN with cryptographic
algorithms, such as Secure Remote Password (SRP) [RFC5054] or a
Password-Authenticated Key Exchange like J-PAKE [RFC8236] using a
Schnorr Non-interactive Zero-Knowledge Proof [RFC8235].
Protocol designers should consider a specific usability pitfall when
trust is established immediately prior to performing discovery.
Users will have a tendency to "click OK" in order to achieve their
task. This implicit vulnerability is avoided if the trust
establishment requires more significant participation of the user,
such as entering a password or PIN.
3.4.4. External Dependencies
Trust establishment may depend on external parties. Optionally, this
might involve synchronous communication. Systems that have such a
dependency may be attacked by interfering with communication to
external dependencies. Where possible, such dependencies should be
minimized. Local trust models are best for secure initialization in
the presence of active attackers.
4. Requirements for a DNS-SD Privacy Extension
Given the considerations discussed in the previous sections, we state
requirements for privacy preserving DNS-SD in the following
subsections.
Defining a solution according to these requirements is intended to
lead to a solution that does not transmit privacy-violating DNS-SD
messages and further does not open pathways to new attacks against
the operation of DNS-SD.
However, while this document gives advice on which privacy protecting
mechanisms should be used on deeper-layer network protocols and on
how to actually connect to services in a privacy-preserving way,
stating corresponding requirements is out of the scope of this
document. To mitigate attacks against privacy on lower layers, both
servers and clients must use privacy options available at lower
layers and, for example, avoid publishing static IPv4 or IPv6
addresses or static IEEE 802 Media Access Control (MAC) addresses.
For services advertised on a single network link, link-local IP
addresses should be used; see [RFC3927] and [RFC4291] for IPv4 and
IPv6, respectively. Static servers advertising services globally via
DNS can hide their IP addresses from unauthorized clients using the
split mode topology shown in Encrypted Server Name Indication [ESNI].
Hiding static MAC addresses can be achieved via MAC address
randomization (see [RFC7844]).
4.1. Private Client Requirements
For all three scenarios described in Section 3.1, client privacy
requires DNS-SD messages to:
1. Avoid disclosure of the client's identity, either directly or via
inference, to nodes other than select servers.
2. Avoid exposure of linkable identifiers that allow tracing client
devices.
3. Avoid disclosure of the client's interest in specific service
instances or service types to nodes other than select servers.
When listing and resolving services via current DNS-SD deployments,
clients typically disclose their interest in specific services types
and specific instances of these types, respectively.
In addition to the exposure and disclosure risks noted above,
protocols and implementations will have to consider fingerprinting
attacks (see Section 3.2.5) that could retrieve similar information.
4.2. Private Server Requirements
Servers like the "printer" discussed in Section 3.1.1 are public, but
the servers discussed in Sections 3.1.2 and 3.1.3 are, by essence,
private. Server privacy requires DNS-SD messages to:
1. Avoid disclosure of the server's identity, either directly or via
inference, to nodes other than authorized clients. In
particular, servers must avoid publishing static identifiers,
such as hostnames or service names. When those fields are
required by the protocol, servers should publish randomized
values. (See [RFC8117] for a discussion of hostnames.)
2. Avoid exposure of linkable identifiers that allow tracing
servers.
3. Avoid disclosure to unauthorized clients of Service Instance
Names or service types of offered services.
4. Avoid disclosure to unauthorized clients of information about the
services they offer.
5. Avoid disclosure of static IPv4 or IPv6 addresses.
When offering services via current DNS-SD deployments, servers
typically disclose their hostnames (SRV, A/AAAA), instance names of
offered services (PTR, SRV), and information about services (TXT).
Heeding these requirements protects a server's privacy on the DNS-SD
level.
The current DNS-SD user interfaces present the list of discovered
service names to the users and let them pick a service from the list.
Using random identifiers for service names renders that UI flow
unusable. Privacy-respecting discovery protocols will have to solve
this issue, for example, by presenting authenticated or decrypted
service names instead of the randomized values.
4.3. Security and Operation
In order to be secure and feasible, a DNS-SD privacy extension needs
to consider security and operational requirements including:
1. Avoiding significant CPU overhead on nodes or significantly
higher network load. Such overhead or load would make nodes
vulnerable to denial-of-service attacks. Further, it would
increase power consumption, which is damaging for IoT devices.
2. Avoiding designs in which a small message can trigger a large
amount of traffic towards an unverified address, as this could be
exploited in amplification attacks.
5. IANA Considerations
This document has no IANA actions.
6. References
6.1. Normative References
[RFC6762] Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
DOI 10.17487/RFC6762, February 2013,
<https://www.rfc-editor.org/info/rfc6762>.
[RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service
Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013,
<https://www.rfc-editor.org/info/rfc6763>.
6.2. Informative References
[ESNI] Rescorla, E., Oku, K., Sullivan, N., and C. A. Wood, "TLS
Encrypted Client Hello", Work in Progress, Internet-Draft,
draft-ietf-tls-esni-07, June 1, 2020,
<https://tools.ietf.org/html/draft-ietf-tls-esni-07>.
[K17] Kaiser, D., "Efficient Privacy-Preserving
Configurationless Service Discovery Supporting Multi-Link
Networks", August 2017,
<https://nbn-resolving.de/urn:nbn:de:bsz:352-0-422757>.
[KW14a] Kaiser, D. and M. Waldvogel, "Adding Privacy to Multicast
DNS Service Discovery", DOI 10.1109/TrustCom.2014.107,
September 2014, <https://ieeexplore.ieee.org/xpl/
articleDetails.jsp?arnumber=7011331>.
[KW14b] Kaiser, D. and M. Waldvogel, "Efficient Privacy Preserving
Multicast DNS Service Discovery",
DOI 10.1109/HPCC.2014.141, August 2014,
<https://ieeexplore.ieee.org/xpl/
articleDetails.jsp?arnumber=7056899>.
[RFC1033] Lottor, M., "Domain Administrators Operations Guide",
RFC 1033, DOI 10.17487/RFC1033, November 1987,
<https://www.rfc-editor.org/info/rfc1033>.
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<https://www.rfc-editor.org/info/rfc1034>.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <https://www.rfc-editor.org/info/rfc1035>.
[RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782,
DOI 10.17487/RFC2782, February 2000,
<https://www.rfc-editor.org/info/rfc2782>.
[RFC3927] Cheshire, S., Aboba, B., and E. Guttman, "Dynamic
Configuration of IPv4 Link-Local Addresses", RFC 3927,
DOI 10.17487/RFC3927, May 2005,
<https://www.rfc-editor.org/info/rfc3927>.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, DOI 10.17487/RFC4291, February
2006, <https://www.rfc-editor.org/info/rfc4291>.
[RFC5054] Taylor, D., Wu, T., Mavrogiannopoulos, N., and T. Perrin,
"Using the Secure Remote Password (SRP) Protocol for TLS
Authentication", RFC 5054, DOI 10.17487/RFC5054, November
2007, <https://www.rfc-editor.org/info/rfc5054>.
[RFC7558] Lynn, K., Cheshire, S., Blanchet, M., and D. Migault,
"Requirements for Scalable DNS-Based Service Discovery
(DNS-SD) / Multicast DNS (mDNS) Extensions", RFC 7558,
DOI 10.17487/RFC7558, July 2015,
<https://www.rfc-editor.org/info/rfc7558>.
[RFC7844] Huitema, C., Mrugalski, T., and S. Krishnan, "Anonymity
Profiles for DHCP Clients", RFC 7844,
DOI 10.17487/RFC7844, May 2016,
<https://www.rfc-editor.org/info/rfc7844>.
[RFC8117] Huitema, C., Thaler, D., and R. Winter, "Current Hostname
Practice Considered Harmful", RFC 8117,
DOI 10.17487/RFC8117, March 2017,
<https://www.rfc-editor.org/info/rfc8117>.
[RFC8235] Hao, F., Ed., "Schnorr Non-interactive Zero-Knowledge
Proof", RFC 8235, DOI 10.17487/RFC8235, September 2017,
<https://www.rfc-editor.org/info/rfc8235>.
[RFC8236] Hao, F., Ed., "J-PAKE: Password-Authenticated Key Exchange
by Juggling", RFC 8236, DOI 10.17487/RFC8236, September
2017, <https://www.rfc-editor.org/info/rfc8236>.
[SLEEP-PROXY]
Cheshire, S., "Understanding Sleep Proxy Service",
December 2009,
<http://stuartcheshire.org/SleepProxy/index.html>.
[SRP] Lemon, T. and S. Cheshire, "Service Registration Protocol
for DNS-Based Service Discovery", Work in Progress,
Internet-Draft, draft-ietf-dnssd-srp-04, July 13, 2020,
<https://tools.ietf.org/html/draft-ietf-dnssd-srp-04>.
Acknowledgments
This document incorporates many contributions from Stuart Cheshire
and Chris Wood. Thanks to Florian Adamsky for extensive review and
suggestions on the organization of the threat model. Thanks to Barry
Leiba for an extensive review. Thanks to Roman Danyliw, Ben Kaduk,
Adam Roach, and Alissa Cooper for their comments during IESG review.
Authors' Addresses
Christian Huitema
Private Octopus Inc.
Friday Harbor, WA 98250
United States of America
Email: huitema@huitema.net
URI: http://privateoctopus.com/
Daniel Kaiser
University of Luxembourg
6, avenue de la Fonte
L-4364 Esch-sur-Alzette
Luxembourg
Email: daniel.kaiser@uni.lu
URI: https://secan-lab.uni.lu/

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Independent Submission V. Dolmatov, Ed.
Request for Comments: 8891 JSC "NPK Kryptonite"
Updates: 5830 D. Baryshkov
Category: Informational Auriga, Inc.
ISSN: 2070-1721 September 2020
GOST R 34.12-2015: Block Cipher "Magma"
Abstract
In addition to a new cipher with a block length of n=128 bits
(referred to as "Kuznyechik" and described in RFC 7801), Russian
Federal standard GOST R 34.12-2015 includes an updated version of the
block cipher with a block length of n=64 bits and key length of k=256
bits, which is also referred to as "Magma". The algorithm is an
updated version of an older block cipher with a block length of n=64
bits described in GOST 28147-89 (RFC 5830). This document is
intended to be a source of information about the updated version of
the 64-bit cipher. It may facilitate the use of the block cipher in
Internet applications by providing information for developers and
users of the GOST 64-bit cipher with the revised version of the
cipher for encryption and decryption.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This is a contribution to the RFC Series, independently of any other
RFC stream. The RFC Editor has chosen to publish this document at
its discretion and makes no statement about its value for
implementation or deployment. Documents approved for publication by
the RFC Editor are not candidates for any level of Internet Standard;
see 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/rfc8891.
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document.
Table of Contents
1. Introduction
2. General Information
3. Definitions and Notation
3.1. Definitions
3.2. Notation
4. Parameter Values
4.1. Nonlinear Bijection
4.2. Transformations
4.3. Key Schedule
5. Basic Encryption Algorithm
5.1. Encryption
5.2. Decryption
6. IANA Considerations
7. Security Considerations
8. References
8.1. Normative References
8.2. Informative References
Appendix A. Test Examples
A.1. Transformation t
A.2. Transformation g
A.3. Key Schedule
A.4. Test Encryption
A.5. Test Decryption
Appendix B. Background
Authors' Addresses
1. Introduction
The Russian Federal standard [GOSTR3412-2015] specifies basic block
ciphers used as cryptographic techniques for information processing
and information protection, including the provision of
confidentiality, authenticity, and integrity of information during
information transmission, processing, and storage in computer-aided
systems.
The cryptographic algorithms defined in this specification are
designed both for hardware and software implementation. They comply
with modern cryptographic requirements and put no restrictions on the
confidentiality level of the protected information.
This document is intended to be a source of information about the
updated version of the 64-bit cipher. It may facilitate the use of
the block cipher in Internet applications by providing information
for developers and users of a GOST 64-bit cipher with the revised
version of the cipher for encryption and decryption.
2. General Information
The Russian Federal standard [GOSTR3412-2015] was developed by the
Center for Information Protection and Special Communications of the
Federal Security Service of the Russian Federation, with
participation of the open joint-stock company "Information
Technologies and Communication Systems" (InfoTeCS JSC). GOST R
34.12-2015 was approved and introduced by Decree #749 of the Federal
Agency on Technical Regulating and Metrology on June 19, 2015.
Terms and concepts in the specification comply with the following
international standards:
* ISO/IEC 10116 [ISO-IEC10116]
* series of standards ISO/IEC 18033 [ISO-IEC18033-1][ISO-IEC18033-3]
3. Definitions and Notation
The following terms and their corresponding definitions are used in
the specification.
3.1. Definitions
encryption algorithm: process that transforms plaintext into
ciphertext (Clause 2.19 of [ISO-IEC18033-1])
decryption algorithm: process that transforms ciphertext into
plaintext (Clause 2.14 of [ISO-IEC18033-1])
basic block cipher: block cipher that, for a given key, provides a
single invertible mapping of the set of fixed-length plaintext
blocks into ciphertext blocks of the same length
block: string of bits of a defined length (Clause 2.6 of
[ISO-IEC18033-1])
block cipher: symmetric encipherment system with the property that
the encryption algorithm operates on a block of plaintext -- i.e.,
a string of bits of a defined length -- to yield a block of
ciphertext (Clause 2.7 of [ISO-IEC18033-1])
Note: In GOST R 34.12-2015, it is established that the terms
"block cipher" and "block encryption algorithm" are synonyms.
encryption: reversible transformation of data by a cryptographic
algorithm to produce ciphertext -- i.e., to hide the information
content of the data (Clause 2.18 of [ISO-IEC18033-1])
round key: sequence of symbols that is calculated from the key and
controls a transformation for one round of a block cipher
key: sequence of symbols that controls the operation of a
cryptographic transformation (e.g., encipherment, decipherment)
(Clause 2.21 of [ISO-IEC18033-1])
Note: In GOST R 34.12-2015, the key must be a binary sequence.
plaintext: unencrypted information (Clause 3.11 of [ISO-IEC10116])
key schedule: calculation of round keys from the key,
decryption: reversal of a corresponding encipherment (Clause 2.13 of
[ISO-IEC18033-1])
symmetric cryptographic technique: cryptographic technique that uses
the same secret key for both the originator's and the recipient's
transformation (Clause 2.32 of [ISO-IEC18033-1])
cipher: alternative term for encipherment system (Clause 2.20 of
[ISO-IEC18033-1])
ciphertext: data that has been transformed to hide its information
content (Clause 3.3 of [ISO-IEC10116])
3.2. Notation
The following notation is used in the specification:
V* the set of all binary vector strings of a finite length
(hereinafter referred to as the strings), including the empty
string
V_s the set of all binary strings of length s, where s is a
nonnegative integer; substrings and string components are
enumerated from right to left, starting from zero
U[*]W direct (Cartesian) product of two sets U and W
|A| the number of components (the length) of a string A belonging to
V* (if A is an empty string, then |A| = 0)
A||B concatenation of strings A and B both belonging to V* -- i.e.,
a string from V_(|A|+|B|), where the left substring from V_|A| is
equal to A and the right substring from V_|B| is equal to B
A<<<_11 cyclic rotation of string A belonging to V_32 by 11
components in the direction of components having greater indices
Z_(2^n) ring of residues modulo 2^n
(xor) exclusive-or of two binary strings of the same length
[+] addition in the ring Z_(2^32)
Vec_s: Z_(2^s) -> V_s bijective mapping that maps an element from
ring Z_(2^s) into its binary representation; i.e., for an element
z of the ring Z_(2^s), represented by the residue z_0 + (2*z_1) +
... + (2^(s-1)*z_(s-1)), where z_i in {0, 1}, i = 0, ..., n-1, the
equality Vec_s(z) = z_(s-1)||...||z_1||z_0 holds
Int_s: V_s -> Z_(2^s) the mapping inverse to the mapping Vec_s,
i.e., Int_s = Vec_s^(-1)
PS composition of mappings, where the mapping S applies first
P^s composition of mappings P^(s-1) and P, where P^1=P
4. Parameter Values
4.1. Nonlinear Bijection
The bijective nonlinear mapping is a set of substitutions:
Pi_i = Vec_4 Pi'_i Int_4: V_4 -> V_4,
where
Pi'_i: Z_(2^4) -> Z_(2^4), i = 0, 1, ..., 7.
The values of the substitution Pi' are specified below as arrays.
Pi'_i = (Pi'_i(0), Pi'_i(1), ... , Pi'_i(15)), i = 0, 1, ..., 7:
Pi'_0 = (12, 4, 6, 2, 10, 5, 11, 9, 14, 8, 13, 7, 0, 3, 15, 1);
Pi'_1 = (6, 8, 2, 3, 9, 10, 5, 12, 1, 14, 4, 7, 11, 13, 0, 15);
Pi'_2 = (11, 3, 5, 8, 2, 15, 10, 13, 14, 1, 7, 4, 12, 9, 6, 0);
Pi'_3 = (12, 8, 2, 1, 13, 4, 15, 6, 7, 0, 10, 5, 3, 14, 9, 11);
Pi'_4 = (7, 15, 5, 10, 8, 1, 6, 13, 0, 9, 3, 14, 11, 4, 2, 12);
Pi'_5 = (5, 13, 15, 6, 9, 2, 12, 10, 11, 7, 8, 1, 4, 3, 14, 0);
Pi'_6 = (8, 14, 2, 5, 6, 9, 1, 12, 15, 4, 11, 0, 13, 10, 3, 7);
Pi'_7 = (1, 7, 14, 13, 0, 5, 8, 3, 4, 15, 10, 6, 9, 12, 11, 2);
4.2. Transformations
The following transformations are applicable for encryption and
decryption algorithms:
t: V_32 -> V_32
t(a) = t(a_7||...||a_0) = Pi_7(a_7)||...||Pi_0(a_0), where
a=a_7||...||a_0 belongs to V_32, a_i belongs to V_4, i=0, 1, ...,
7.
g[k]: V_32 -> V_32
g[k](a) = (t(Vec_32(Int_32(a) [+] Int_32(k)))) <<<_11, where k, a
belong to V_32
G[k]: V_32[*]V_32 -> V_32[*]V_32
G[k](a_1, a_0) = (a_0, g[k](a_0) (xor) a_1), where k, a_0, a_1
belong to V_32
G^*[k]: V_32[*]V_32 -> V_64
G^*[k](a_1, a_0) = (g[k](a_0) (xor) a_1) || a_0, where k, a_0, a_1
belong to V_32.
4.3. Key Schedule
Round keys K_i belonging to V_32, i=1, 2, ..., 32 are derived from
key K = k_255||...||k_0 belonging to V_256, k_i belongs to V_1, i=0,
1, ..., 255, as follows:
K_1 = k_255||...||k_224;
K_2 = k_223||...||k_192;
K_3 = k_191||...||k_160;
K_4 = k_159||...||k_128;
K_5 = k_127||...||k_96;
K_6 = k_95||...||k_64;
K_7 = k_63||...||k_32;
K_8 = k_31||...||k_0;
K_(i+8) = K_i, i = 1, 2, ..., 8;
K_(i+16) = K_i, i = 1, 2, ..., 8;
K_(i+24) = K_(9-i), i = 1, 2, ..., 8.
5. Basic Encryption Algorithm
5.1. Encryption
Depending on the values of round keys K_1,...,K_32, the encryption
algorithm is a substitution E_(K_1,...,K_32) defined as follows:
E_(K_1,...,K_32)(a)=G^*[K_32]G[K_31]...G[K_2]G[K_1](a_1, a_0),
where a=(a_1, a_0) belongs to V_64, and a_0, a_1 belong to V_32.
5.2. Decryption
Depending on the values of round keys K_1,...,K_32, the decryption
algorithm is a substitution D_(K_1,...,K_32) defined as follows:
D_(K_1,...,K_32)(a)=G^*[K_1]G[K_2]...G[K_31]G[K_32](a_1, a_0),
where a=(a_1, a_0) belongs to V_64, and a_0, a_1 belong to V_32.
6. IANA Considerations
This document has no IANA actions.
7. Security Considerations
This entire document is about security considerations.
Unlike [RFC5830] (GOST 28147-89), but like [RFC7801], this
specification does not define exact block modes that should be used
together with the updated Magma cipher. One is free to select block
modes depending on the protocol and necessity.
8. References
8.1. Normative References
[GOSTR3412-2015]
Federal Agency on Technical Regulating and Metrology,
"Information technology. Cryptographic data security.
Block ciphers.", GOST R 34.12-2015, 2015.
[RFC5830] Dolmatov, V., Ed., "GOST 28147-89: Encryption, Decryption,
and Message Authentication Code (MAC) Algorithms",
RFC 5830, DOI 10.17487/RFC5830, March 2010,
<https://www.rfc-editor.org/info/rfc5830>.
[RFC7801] Dolmatov, V., Ed., "GOST R 34.12-2015: Block Cipher
"Kuznyechik"", RFC 7801, DOI 10.17487/RFC7801, March 2016,
<https://www.rfc-editor.org/info/rfc7801>.
8.2. Informative References
[GOST28147-89]
Government Committee of the USSR for Standards,
"Cryptographic Protection for Data Processing System, GOST
28147-89, Gosudarstvennyi Standard of USSR", 1989.
[ISO-IEC10116]
ISO/IEC, "Information technology -- Security techniques --
Modes of operation for an n-bit block cipher", ISO/
IEC 10116, 2017.
[ISO-IEC18033-1]
ISO/IEC, "Information technology -- Security techniques --
Encryption algorithms -- Part 1: General", ISO/
IEC 18033-1:2015, 2015.
[ISO-IEC18033-3]
ISO/IEC, "Information technology -- Security techniques --
Encryption algorithms -- Part 3: Block ciphers", ISO/
IEC 18033-3:2010, 2010.
[RFC7836] Smyshlyaev, S., Ed., Alekseev, E., Oshkin, I., Popov, V.,
Leontiev, S., Podobaev, V., and D. Belyavsky, "Guidelines
on the Cryptographic Algorithms to Accompany the Usage of
Standards GOST R 34.10-2012 and GOST R 34.11-2012",
RFC 7836, DOI 10.17487/RFC7836, March 2016,
<https://www.rfc-editor.org/info/rfc7836>.
Appendix A. Test Examples
This section is for information only and is not a normative part of
the specification.
A.1. Transformation t
t(fdb97531) = 2a196f34,
t(2a196f34) = ebd9f03a,
t(ebd9f03a) = b039bb3d,
t(b039bb3d) = 68695433.
A.2. Transformation g
g[87654321](fedcba98) = fdcbc20c,
g[fdcbc20c](87654321) = 7e791a4b,
g[7e791a4b](fdcbc20c) = c76549ec,
g[c76549ec](7e791a4b) = 9791c849.
A.3. Key Schedule
With key set to
K = ffeeddccbbaa99887766554433221100f0f1f2f3f4f5f6f7f8f9fafbfcfdfeff,
the following round keys are generated:
K_1 = ffeeddcc,
K_2 = bbaa9988,
K_3 = 77665544,
K_4 = 33221100,
K_5 = f0f1f2f3,
K_6 = f4f5f6f7,
K_7 = f8f9fafb,
K_8 = fcfdfeff,
K_9 = ffeeddcc,
K_10 = bbaa9988,
K_11 = 77665544,
K_12 = 33221100,
K_13 = f0f1f2f3,
K_14 = f4f5f6f7,
K_15 = f8f9fafb,
K_16 = fcfdfeff,
K_17 = ffeeddcc,
K_18 = bbaa9988,
K_19 = 77665544,
K_20 = 33221100,
K_21 = f0f1f2f3,
K_22 = f4f5f6f7,
K_23 = f8f9fafb,
K_24 = fcfdfeff,
K_25 = fcfdfeff,
K_26 = f8f9fafb,
K_27 = f4f5f6f7,
K_28 = f0f1f2f3,
K_29 = 33221100,
K_30 = 77665544,
K_31 = bbaa9988,
K_32 = ffeeddcc.
A.4. Test Encryption
In this test example, encryption is performed on the round keys
specified in Appendix A.3. Let the plaintext be
a = fedcba9876543210,
then
(a_1, a_0) = (fedcba98, 76543210),
G[K_1](a_1, a_0) = (76543210, 28da3b14),
G[K_2]G[K_1](a_1, a_0) = (28da3b14, b14337a5),
G[K_3]...G[K_1](a_1, a_0) = (b14337a5, 633a7c68),
G[K_4]...G[K_1](a_1, a_0) = (633a7c68, ea89c02c),
G[K_5]...G[K_1](a_1, a_0) = (ea89c02c, 11fe726d),
G[K_6]...G[K_1](a_1, a_0) = (11fe726d, ad0310a4),
G[K_7]...G[K_1](a_1, a_0) = (ad0310a4, 37d97f25),
G[K_8]...G[K_1](a_1, a_0) = (37d97f25, 46324615),
G[K_9]...G[K_1](a_1, a_0) = (46324615, ce995f2a),
G[K_10]...G[K_1](a_1, a_0) = (ce995f2a, 93c1f449),
G[K_11]...G[K_1](a_1, a_0) = (93c1f449, 4811c7ad),
G[K_12]...G[K_1](a_1, a_0) = (4811c7ad, c4b3edca),
G[K_13]...G[K_1](a_1, a_0) = (c4b3edca, 44ca5ce1),
G[K_14]...G[K_1](a_1, a_0) = (44ca5ce1, fef51b68),
G[K_15]...G[K_1](a_1, a_0) = (fef51b68, 2098cd86)
G[K_16]...G[K_1](a_1, a_0) = (2098cd86, 4f15b0bb),
G[K_17]...G[K_1](a_1, a_0) = (4f15b0bb, e32805bc),
G[K_18]...G[K_1](a_1, a_0) = (e32805bc, e7116722),
G[K_19]...G[K_1](a_1, a_0) = (e7116722, 89cadf21),
G[K_20]...G[K_1](a_1, a_0) = (89cadf21, bac8444d),
G[K_21]...G[K_1](a_1, a_0) = (bac8444d, 11263a21),
G[K_22]...G[K_1](a_1, a_0) = (11263a21, 625434c3),
G[K_23]...G[K_1](a_1, a_0) = (625434c3, 8025c0a5),
G[K_24]...G[K_1](a_1, a_0) = (8025c0a5, b0d66514),
G[K_25]...G[K_1](a_1, a_0) = (b0d66514, 47b1d5f4),
G[K_26]...G[K_1](a_1, a_0) = (47b1d5f4, c78e6d50),
G[K_27]...G[K_1](a_1, a_0) = (c78e6d50, 80251e99),
G[K_28]...G[K_1](a_1, a_0) = (80251e99, 2b96eca6),
G[K_29]...G[K_1](a_1, a_0) = (2b96eca6, 05ef4401),
G[K_30]...G[K_1](a_1, a_0) = (05ef4401, 239a4577),
G[K_31]...G[K_1](a_1, a_0) = (239a4577, c2d8ca3d).
Then the ciphertext is
b = G^*[K_32]G[K_31]...G[K_1](a_1, a_0) = 4ee901e5c2d8ca3d.
A.5. Test Decryption
In this test example, decryption is performed on the round keys
specified in Appendix A.3. Let the ciphertext be
b = 4ee901e5c2d8ca3d,
then
(b_1, b_0) = (4ee901e5, c2d8ca3d),
G[K_32](b_1, b_0) = (c2d8ca3d, 239a4577),
G[K_31]G[K_32](b_1, b_0) = (239a4577, 05ef4401),
G[K_30]...G[K_32](b_1, b_0) = (05ef4401, 2b96eca6),
G[K_29]...G[K_32](b_1, b_0) = (2b96eca6, 80251e99),
G[K_28]...G[K_32](b_1, b_0) = (80251e99, c78e6d50),
G[K_27]...G[K_32](b_1, b_0) = (c78e6d50, 47b1d5f4),
G[K_26]...G[K_32](b_1, b_0) = (47b1d5f4, b0d66514),
G[K_25]...G[K_32](b_1, b_0) = (b0d66514, 8025c0a5),
G[K_24]...G[K_32](b_1, b_0) = (8025c0a5, 625434c3),
G[K_23]...G[K_32](b_1, b_0) = (625434c3, 11263a21),
G[K_22]...G[K_32](b_1, b_0) = (11263a21, bac8444d),
G[K_21]...G[K_32](b_1, b_0) = (bac8444d, 89cadf21),
G[K_20]...G[K_32](b_1, b_0) = (89cadf21, e7116722),
G[K_19]...G[K_32](b_1, b_0) = (e7116722, e32805bc),
G[K_18]...G[K_32](b_1, b_0) = (e32805bc, 4f15b0bb),
G[K_17]...G[K_32](b_1, b_0) = (4f15b0bb, 2098cd86),
G[K_16]...G[K_32](b_1, b_0) = (2098cd86, fef51b68),
G[K_15]...G[K_32](b_1, b_0) = (fef51b68, 44ca5ce1),
G[K_14]...G[K_32](b_1, b_0) = (44ca5ce1, c4b3edca),
G[K_13]...G[K_32](b_1, b_0) = (c4b3edca, 4811c7ad),
G[K_12]...G[K_32](b_1, b_0) = (4811c7ad, 93c1f449),
G[K_11]...G[K_32](b_1, b_0) = (93c1f449, ce995f2a),
G[K_10]...G[K_32](b_1, b_0) = (ce995f2a, 46324615),
G[K_9]...G[K_32](b_1, b_0) = (46324615, 37d97f25),
G[K_8]...G[K_32](b_1, b_0) = (37d97f25, ad0310a4),
G[K_7]...G[K_32](b_1, b_0) = (ad0310a4, 11fe726d),
G[K_6]...G[K_32](b_1, b_0) = (11fe726d, ea89c02c),
G[K_5]...G[K_32](b_1, b_0) = (ea89c02c, 633a7c68),
G[K_4]...G[K_32](b_1, b_0) = (633a7c68, b14337a5),
G[K_3]...G[K_32](b_1, b_0) = (b14337a5, 28da3b14),
G[K_2]...G[K_32](b_1, b_0) = (28da3b14, 76543210).
Then the plaintext is
a = G^*[K_1]G[K_2]...G[K_32](b_1, b_0) = fedcba9876543210.
Appendix B. Background
This specification is a translation of relevant parts of the
[GOSTR3412-2015] standard. The order of terms in both parts of
Section 3 comes from the original text. Combining [RFC7801] with
this document will create a complete translation of [GOSTR3412-2015]
into English.
Algorithmically, Magma is a variation of the block cipher defined in
[RFC5830] ([GOST28147-89]) with the following clarifications and
minor modifications:
1. S-BOX set is fixed at id-tc26-gost-28147-param-Z (see Appendix C
of [RFC7836]);
2. key is parsed as a single big-endian integer (compared to the
little-endian approach used in [GOST28147-89]), which results in
different subkey values being used;
3. data bytes are also parsed as a single big-endian integer
(instead of being parsed as little-endian integer).
Authors' Addresses
Vasily Dolmatov (editor)
JSC "NPK Kryptonite"
Spartakovskaya sq., 14, bld 2, JSC "NPK Kryptonite"
Moscow
105082
Russian Federation
Email: vdolmatov@gmail.com
Dmitry Baryshkov
Auriga, Inc.
office 1410
Torfyanaya Doroga, 7F
Saint-Petersburg
197374
Russian Federation
Email: dbaryshkov@gmail.com

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Internet Engineering Task Force (IETF) R. Shekh-Yusef
Request for Comments: 8898 Auth0
Updates: 3261 C. Holmberg
Category: Standards Track Ericsson
ISSN: 2070-1721 V. Pascual
Nokia
September 2020
Third-Party Token-Based Authentication and Authorization for Session
Initiation Protocol (SIP)
Abstract
This document defines the "Bearer" authentication scheme for the
Session Initiation Protocol (SIP) and a mechanism by which user
authentication and SIP registration authorization is delegated to a
third party, using the OAuth 2.0 framework and OpenID Connect Core
1.0. This document updates RFC 3261 to provide guidance on how a SIP
User Agent Client (UAC) responds to a SIP 401/407 response that
contains multiple WWW-Authenticate/Proxy-Authenticate header fields.
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/rfc8898.
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction
1.1. Terminology
1.2. Applicability
1.3. Token Types and Formats
1.4. Example Flows
1.4.1. Registration
1.4.2. Registration with Preconfigured AS
2. SIP Procedures
2.1. UAC Behavior
2.1.1. Obtaining Tokens and Responding to Challenges
2.1.2. Protecting the Access Token
2.1.3. REGISTER Request
2.1.4. Non-REGISTER Request
2.2. User Agent Server (UAS) and Registrar Behavior
2.3. Proxy Behavior
3. Access Token Claims
4. WWW-Authenticate Response Header Field
5. Security Considerations
6. IANA Considerations
6.1. New Proxy-Authenticate Header Field Parameters
6.2. New WWW-Authenticate Header Field Parameters
7. Normative References
8. Informative References
Acknowledgments
Authors' Addresses
1. Introduction
The Session Initiation Protocol (SIP) [RFC3261] uses the same
framework as HTTP [RFC7230] to authenticate users: a simple
challenge-response authentication mechanism that allows a SIP User
Agent Server (UAS), proxy, or registrar to challenge a SIP User Agent
Client (UAC) request and allows the UAC to provide authentication
information in response to that challenge.
OAuth 2.0 [RFC6749] defines a token-based authorization framework to
allow an OAuth client to access resources on behalf of its user.
The OpenID Connect Core 1.0 specification [OPENID] defines a simple
identity layer on top of the OAuth 2.0 protocol, which enables OAuth/
OpenID clients to verify the identity of the user based on the
authentication performed by a dedicated authorization server (AS),
referred to as OpenID Provider (OP), as well as to obtain basic
profile information about the user.
This document defines the "Bearer" authentication scheme for SIP and
a mechanism by which user authentication and SIP registration
authorization is delegated to a third party, using the OAuth 2.0
framework and OpenID Connect Core 1.0. This kind of user
authentication enables single sign-on, which allows the user to
authenticate once and gain access to both SIP and non-SIP services.
This document also updates [RFC3261] by defining the UAC procedures
when a UAC receives a 401/407 response with multiple WWW-
Authenticate/Proxy-Authenticate header fields, providing challenges
using different authentication schemes for the same realm.
1.1. Terminology
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.
1.2. Applicability
This document covers cases where grants that allow the UAC to obtain
an access token from the AS are used. Cases where the UAC is not
able to obtain an access token (e.g., in the case of an authorization
code grant) are not covered.
1.3. Token Types and Formats
The tokens used in third-party authorization depend on the type of
AS.
An OAuth AS provides the following tokens to a successfully
authorized UAC:
Access Token:
The UAC will use this token to gain access to services by
providing the token to a SIP server.
Refresh Token:
The UAC will present this token to the AS to refresh a stale
access token.
An OP returns an additional token:
ID Token:
This token contains a SIP URI associated with the user and other
user-specific details that will be consumed by the UAC.
Tokens can be represented in two different formats:
Structured Token:
A token that consists of a structured object that contains the
claims associated with the token, e.g., JSON Web Token (JWT), as
defined in [RFC7519].
Reference Token:
A token that consists of an opaque string that is used to obtain
the details of the token and its associated claims, as defined in
[RFC6749].
Access tokens are represented in one of the above two formats.
Refresh tokens usually are represented in a reference format, as this
token is consumed only by the AS that issued the token. The ID token
is defined as a structured token in the form of a JWT.
1.4. Example Flows
1.4.1. Registration
Figure 1 below shows an example of a SIP registration where the
registrar informs the UAC about the AS from which the UAC can obtain
an access token.
UAC Registrar AS/OP
---------------------------------------------------------------------
| | |
| [1] REGISTER | |
|------------------------------>| |
| | |
| [2] 401 Unauthorized | |
| WWW-Authenticate: Bearer "authz_server"="<authz_server>" |
|<------------------------------| |
| | |
| [3] The UAC interacts with the AS and obtains tokens using |
| some out-of-scope mechanism. |
|<=============================================================>|
| | |
| [4] REGISTER | |
| Authorization: Bearer <access_token> |
|------------------------------>| |
| | [5] HTTP POST /introspect |
| | {access_token} |
| | (OPTIONAL) |
| |------------------------------>|
| | |
| | [6] 200 OK {metadata} |
| | (OPTIONAL) |
| |<------------------------------|
| | |
| [7] 200 OK | |
|<------------------------------| |
| | |
Figure 1: Example Registration Flow
In step [1], the UAC starts the registration process by sending a SIP
REGISTER request to the registrar without any credentials.
In step [2], the registrar challenges the UA by sending a SIP 401
(Unauthorized) response to the REGISTER request. In the response,
the registrar includes information about the AS to contact in order
to obtain a token.
In step [3], the UAC interacts with the AS via an out-of-scope
mechanism, potentially using the OAuth Native App mechanism defined
in [RFC8252]. The AS authenticates the user and provides the UAC
with the tokens needed to access the SIP service.
In step [4], the UAC retries the registration process by sending a
new REGISTER request that includes the access token that the UAC
obtained in the step above.
The registrar validates the access token. If the access token is a
reference token, the registrar MAY perform an introspection
[RFC7662], as in steps [5] and [6], in order to obtain more
information about the access token and its scope, per [RFC7662].
Otherwise, after the registrar validates the token, it inspects its
claims and acts upon it.
In step [7], once the registrar has successfully verified and
accepted the access token, it sends a 200 (OK) response to the
REGISTER request.
1.4.2. Registration with Preconfigured AS
Figure 2 shows an example of a SIP registration where the UAC has
been preconfigured with information about the AS from which to obtain
the access token.
UAC Registrar AS/OP
---------------------------------------------------------------------
| | |
| [1] The UAC interacts with the AS and obtains tokens using |
| some out-of-scope mechanism. |
|<=============================================================>|
| | |
| [2] REGISTER | |
| Authorization: Bearer <access_token> |
|------------------------------>| |
| | [3] HTTP POST /introspect |
| | {access_token} |
| | (OPTIONAL) |
| |------------------------------>|
| | |
| | [4] 200 OK {metadata} |
| | (OPTIONAL) |
| |<------------------------------|
| | |
| [5] 200 OK | |
|<------------------------------| |
| | |
Figure 2: Example Registration Flow - AS Information Preconfigured
In step [1], the UAC interacts with the AS using an out-of-scope
mechanism, potentially using the OAuth Native App mechanism defined
in [RFC8252]. The AS authenticates the user and provides the UAC
with the tokens needed to access the SIP service.
In step [2], the UAC initiates the registration process by sending a
new REGISTER request that includes the access token that the UAC
obtained in the step above.
The registrar validates the access token. If the access token is a
reference token, the registrar MAY perform an introspection
[RFC7662], as in steps [4] and [5], in order to obtain more
information about the access token and its scope, per [RFC7662].
Otherwise, after the registrar validates the token, it inspects its
claims and acts upon it.
In step [5], once the registrar has successfully verified and
accepted the access token, it sends a 200 (OK) response to the
REGISTER request.
2. SIP Procedures
Section 22 of [RFC3261] defines the SIP procedures for the Digest
authentication mechanism. The same procedures apply to the "Bearer"
authentication mechanism, with the changes described in this section.
2.1. UAC Behavior
2.1.1. Obtaining Tokens and Responding to Challenges
When a UAC sends a request without credentials (or with invalid
credentials), it could receive either a 401 (Unauthorized) response
with a WWW-Authenticate header field or a 407 (Proxy Authentication
Required) response with a Proxy-Authenticate header field. If the
WWW-Authenticate or Proxy-Authenticate header field indicates
"Bearer" scheme authentication and contains an address to an AS, the
UAC contacts the AS in order to obtain tokens and includes the
requested scopes, based on a local configuration (Figure 1). The UAC
MUST check the AS URL received in the 401/407 response against a list
of trusted ASs configured on the UAC in order to prevent several
classes of possible vulnerabilities when a client blindly attempts to
use any provided AS.
The detailed OAuth2 procedure to authenticate the user and obtain
these tokens is out of scope of this document. The address of the AS
might already be known to the UAC via configuration. In such cases,
the UAC can contact the AS for tokens before it sends a SIP request
(Figure 2). Procedures for native applications are defined in
[RFC8252]. When using the mechanism defined in [RFC8252], the user
of the UAC will be directed to interact with the AS using a web
browser, which allows the AS to prompt the user for multi-factor
authentication, to redirect the user to third-party identity
providers, and to enable the use of single sign-on sessions.
The tokens returned to the UAC depend on the type of AS; an OAuth AS
provides an access token and, optionally, a refresh token [RFC6749].
The refresh token is only used between the UAC and the AS. If the AS
provides a refresh token to the UAC, the UAC uses it to request a new
access token from the AS before the currently used access token
expires ([RFC6749], Section 1.5). If the AS does not provide a
refresh token, the UAC needs to reauthenticate the user in order to
get a new access token before the currently used access token
expires. An OP returns an additional ID token that contains claims
about the authentication of the user by an authorization server. The
ID token can potentially include other optional claims about the
user, e.g., the SIP URI, that will be consumed by the UAC and later
used to register with the registrar.
If the UAC receives a 401/407 response with multiple WWW-
Authenticate/Proxy-Authenticate header fields, providing challenges
using different authentication schemes for the same realm, the UAC
provides credentials for one of the schemes that it supports, based
on local policy.
| NOTE: At the time of writing, detailed procedures for the cases
| where a UAC receives multiple different authentication schemes
| had not been defined. A future specification might define such
| procedures.
| NOTE: The address of the AS might be known to the UAC, e.g.,
| using means of configuration, in which case the UAC can contact
| the AS in order to obtain the access token before it sends SIP
| request without credentials.
2.1.2. Protecting the Access Token
[RFC6749] mandates that access tokens are protected with TLS when in
transit. However, SIP makes use of intermediary SIP proxies, and TLS
only guarantees hop-to-hop protection when used to protect SIP
signaling. Therefore, the access token MUST be protected in a way so
that only authorized SIP servers will have access to it. SIP
endpoints that support this document MUST use encrypted JWTs
[RFC7519] for encoding and protecting access tokens when they are
included in SIP requests, unless some other mechanism is used to
guarantee that only authorized SIP endpoints have access to the
access token. TLS can still be used for protecting traffic between
SIP endpoints and the AS, as defined in [RFC6749].
2.1.3. REGISTER Request
The procedures in this section apply when the UAC has received a
challenge that contains a "Bearer" scheme and the UAC has obtained a
token, as specified in Section 2.1.1.
The UAC sends a REGISTER request with an Authorization header field
containing the response to the challenge, including the "Bearer"
scheme carrying a valid access token in the request, as specified in
[RFC6750].
Note that if there were multiple challenges with different schemes,
then the UAC may be able to successfully retry the request using
non-"Bearer" credentials.
Typically, a UAC will obtain a new access token for each new binding.
However, based on local policy, a UAC MAY include an access token
that has been used for another binding associated with the same
Address Of Record (AOR) in the request.
If the access token included in a REGISTER request is not accepted
and the UAC receives a 401 response or a 407 response, the UAC
follows the procedures in Section 2.1.1.
2.1.4. Non-REGISTER Request
The procedures in this section apply when the UAC has received a
challenge that contains a "Bearer" scheme and the UAC has obtained a
token, as specified in Section 2.1.1.
When the UAC sends a request, it MUST include an Authorization header
field with a "Bearer" scheme carrying a valid access token obtained
from the AS indicated in the challenge in the request, as specified
in [RFC6750]. Based on local policy, the UAC MAY include an access
token that has been used for another dialog, or for another stand-
alone request, if the target of the new request is the same.
If the access token included in a request is not accepted and the UAC
receives a 401 response or a 407 response, the UAC follows the
procedures in Section 2.1.1.
2.2. User Agent Server (UAS) and Registrar Behavior
When a UAS or registrar receives a request that fails to contain
authorization credentials acceptable to it, the UAS/registrar SHOULD
challenge the request by sending a 401 (Unauthorized) response. If
the UAS/registrar chooses to challenge the request and is willing to
accept an access token as a credential, it MUST include a WWW-
Authenticate header field in the response that indicates a "Bearer"
scheme and includes an AS address, encoded as an https URI [RFC7230],
from which the UAC can obtain an access token.
When a UAS or registrar receives a SIP request that contains an
Authorization header field with an access token, the UAS/registrar
MUST validate the access token using the procedures associated with
the type of access token (structured or reference) used, e.g.,
[RFC7519]. If the token provided is an expired access token, then
the UAS/registrar MUST reply with a 401 (Unauthorized) response, as
defined in Section 3 of [RFC6750]. If the validation is successful,
the UAS/registrar can continue to process the request using normal
SIP procedures. If the validation fails, the UAS/registrar MUST
reply with a 401 (Unauthorized) response.
2.3. Proxy Behavior
When a proxy receives a request that fails to contain authorization
credentials acceptable to it, it SHOULD challenge the request by
sending a 407 (Proxy Authentication Required) response. If the proxy
chooses to challenge the request and is willing to accept an access
token as a credential, it MUST include a Proxy-Authenticate header
field in the response that indicates a "Bearer" scheme and includes
an AS address, encoded as an https URI [RFC7230], from which the UAC
can obtain an access token.
When a proxy wishes to authenticate a received request, it MUST
search the request for Proxy-Authorization header fields with 'realm'
parameters that match its realm. It then MUST successfully validate
the credentials from at least one Proxy-Authorization header field
for its realm. When the scheme is "Bearer", the proxy MUST validate
the access token using the procedures associated with the type of
access token (structured or reference) used, e.g., [RFC7519].
3. Access Token Claims
The type of services to which an access token grants access can be
determined using different methods. The methods used and the access
provided by the token are based on local policy agreed between the AS
and the registrar.
If an access token is encoded as a JWT, it will contain a list of
claims [RFC7519], including both registered and application-specific
claims. The registrar can grant access to services based on such
claims, some other mechanism, or a combination of claims and some
other mechanism. If an access token is a reference token, the
registrar will grant access based on some other mechanism. Examples
of such other mechanisms are introspection [RFC7662] and user profile
lookups.
4. WWW-Authenticate Response Header Field
This section uses ABNF [RFC5234] to describe the syntax of the WWW-
Authenticate header field when used with the "Bearer" scheme to
challenge the UAC for credentials by extending the 'challenge'
parameter defined by [RFC3261].
challenge =/ ("Bearer" LWS bearer-cln *(COMMA bearer-cln))
bearer-cln = realm / scope-param / authz-server-param / error-param /
auth-param
realm = <defined in RFC 3261>
scope-param = "scope" EQUAL DQUOTE scope DQUOTE
scope = <defined in RFC 6749>
authz-server-param = "authz_server" EQUAL DQUOTE authz-server DQUOTE
authz-server = https-URI
https-URI = <defined in RFC 7230>
error-param = "error" EQUAL DQUOTE error DQUOTE
error = <defined in RFC 6749>
auth-param = <defined in RFC 3261>
Figure 3: "Bearer" Scheme Syntax
The authz_server parameter contains the HTTPS URI, as defined in
[RFC7230], of the AS. The UAC can discover metadata about the AS
using a mechanism like the one defined in [RFC8414].
The realm and auth-param parameters are defined in [RFC3261].
Per [RFC3261], "the realm string alone defines the protection
domain". [RFC3261] states that the realm string must be globally
unique and recommends that the realm string contain a hostname or
domain name. It also states that the realm string should be a human-
readable identifier that can be rendered to the user.
The scope and error parameters are defined in [RFC6749].
The scope parameter can be used by the registrar/proxy to indicate to
the UAC the minimum scope that must be associated with the access
token to be able to get service. As defined in [RFC6749], the value
of the scope parameter is expressed as a list of space-delimited,
case-sensitive strings. The strings are defined by the AS. The
values of the scope parameter are out of scope of this document. The
UAC will use the scope provided by the registrar to contact the AS
and obtain a proper token with the requested scope.
The error parameter could be used by the registrar/proxy to indicate
to the UAC the reason for the error, with possible values of
"invalid_token" or "invalid_scope".
5. Security Considerations
The security considerations for OAuth are defined in [RFC6749]. The
security considerations for "Bearer" tokens are defined in [RFC6750].
The security considerations for JWTs are defined in [RFC7519]. These
security considerations also apply to SIP usage of access tokens, as
defined in this document.
[RFC6749] mandates that access tokens are protected with TLS when in
transit. However, SIP makes use of intermediary SIP proxies, and TLS
only guarantees hop-to-hop protection when used to protect SIP
signaling. Therefore, the access token MUST be protected in a way so
that only authorized SIP servers will have access to it. SIP
endpoints that support this document MUST use encrypted JWTs
[RFC7519] for encoding and protecting access tokens when they are
included in SIP requests, unless some other mechanism is used to
guarantee that only authorized SIP endpoints have access to the
access token. TLS can still be used for protecting traffic between
SIP endpoints and the AS, as defined in [RFC6749].
Single Sign-On (SSO) enables the user to use one set of credentials
to authenticate once and gain access to multiple SIP and non-SIP
services using access token(s). If the SSO login is compromised,
that single point of compromise has a much broader effect than is the
case without SSO. Further, an attacker can often use a compromised
account to set up Single Sign-On for other services that the victim
has not established an account with and sometimes can even switch a
dedicated account into SSO mode, creating a still broader attack.
Because of that, it is critical to make sure that extra security
measures be taken to safeguard credentials used for Single Sign-On.
Examples of such measures include a long passphrase instead of a
password, enabling multi-factor authentication, and the use of the
native platform browser when possible, as defined in [RFC8252].
Although this is out of scope for this document, it is important to
carefully consider the claims provided in the tokens used to access
these services to make sure of the privacy of the user accessing
these services. As mentioned above, this document calls for
encrypting JWTs representing the access token.
It is important that both parties participating in SSO provide
mechanisms for users to sever the SSO relationship so that it is
possible without undue difficulty to mitigate a compromise that has
already happened.
The operator of an SSO authentication system has access to private
information about sites and services that their users log into and
even, to some extent, their usage patterns. It's important to call
these out in privacy disclosures and policies and to make sure that
users can be aware of the trade-offs between convenience and privacy
when they choose to use SSO.
When a registrar chooses to challenge a REGISTER request, if the
registrar can provide access to different levels of services, it is
RECOMMENDED that the registrar include a scope in the response in
order to indicate the minimum scope needed to register and access
basic services. The access token might include an extended scope
that gives the user access to more advanced features beyond basic
services. In SIP, the AS administrator will typically decide what
level of access is provided for a given user.
The UAC MUST check the AS URL received in the 401/407 response
against a list of trusted ASs configured on the UAC in order to
prevent several classes of possible vulnerabilities when a client
blindly attempts to use any provided AS.
6. IANA Considerations
6.1. New Proxy-Authenticate Header Field Parameters
This section defines new SIP header field parameters in the "Header
Field Parameters and Parameter Values" subregistry of the "Session
Initiation Protocol (SIP) Parameters" registry:
<https://www.iana.org/assignments/sip-parameters>
+================+===================+===========+
| Parameter Name | Predefined Values | Reference |
+================+===================+===========+
| authz_server | No | RFC 8898 |
+----------------+-------------------+-----------+
| error | No | RFC 8898 |
+----------------+-------------------+-----------+
| scope | No | RFC 8898 |
+----------------+-------------------+-----------+
Table 1: Header Field: Proxy-Authenticate
6.2. New WWW-Authenticate Header Field Parameters
This section defines new SIP header field parameters in the "Header
Field Parameters and Parameter Values" subregistry of the "Session
Initiation Protocol (SIP) Parameters" registry:
<https://www.iana.org/assignments/sip-parameters>
+================+===================+===========+
| Parameter Name | Predefined Values | Reference |
+================+===================+===========+
| authz_server | No | RFC 8898 |
+----------------+-------------------+-----------+
| error | No | RFC 8898 |
+----------------+-------------------+-----------+
| scope | No | RFC 8898 |
+----------------+-------------------+-----------+
Table 2: Header Field: WWW-Authenticate
7. Normative References
[OPENID] Sakimura, N., Bradley, J., Jones, M., de Medeiros, B., and
C. Mortimore, "OpenID Connect Core 1.0", February 2014.
[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>.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
DOI 10.17487/RFC3261, June 2002,
<https://www.rfc-editor.org/info/rfc3261>.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<https://www.rfc-editor.org/info/rfc5234>.
[RFC6749] Hardt, D., Ed., "The OAuth 2.0 Authorization Framework",
RFC 6749, DOI 10.17487/RFC6749, October 2012,
<https://www.rfc-editor.org/info/rfc6749>.
[RFC6750] Jones, M. and D. Hardt, "The OAuth 2.0 Authorization
Framework: Bearer Token Usage", RFC 6750,
DOI 10.17487/RFC6750, October 2012,
<https://www.rfc-editor.org/info/rfc6750>.
[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing",
RFC 7230, DOI 10.17487/RFC7230, June 2014,
<https://www.rfc-editor.org/info/rfc7230>.
[RFC7519] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
(JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
<https://www.rfc-editor.org/info/rfc7519>.
[RFC7662] Richer, J., Ed., "OAuth 2.0 Token Introspection",
RFC 7662, DOI 10.17487/RFC7662, October 2015,
<https://www.rfc-editor.org/info/rfc7662>.
[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>.
8. Informative References
[RFC8252] Denniss, W. and J. Bradley, "OAuth 2.0 for Native Apps",
BCP 212, RFC 8252, DOI 10.17487/RFC8252, October 2017,
<https://www.rfc-editor.org/info/rfc8252>.
[RFC8414] Jones, M., Sakimura, N., and J. Bradley, "OAuth 2.0
Authorization Server Metadata", RFC 8414,
DOI 10.17487/RFC8414, June 2018,
<https://www.rfc-editor.org/info/rfc8414>.
Acknowledgments
The authors would like to specially thank Paul Kyzivat for his
multiple detailed reviews and suggested text that significantly
improved the quality of the document.
The authors would also like to thank the following for their review
and feedback on this document:
Olle Johansson, Roman Shpount, Dale Worley, and Jorgen Axell.
The authors would also like to thank the following for their review
and feedback of the original document that was replaced with this
document:
Andrew Allen, Martin Dolly, Keith Drage, Paul Kyzivat, Jon Peterson,
Michael Procter, Roy Radhika, Matt Ryan, Ivo Sedlacek, Roman Shpount,
Robert Sparks, Asveren Tolga, Dale Worley, and Yehoshua Gev.
Roman Danyliw, Benjamin Kaduk, Erik Kline, Barry Leiba, Eric Vyncke,
and Magnus Westerlund provided feedback and suggestions for
improvements as part of the IESG evaluation of the document. Special
thanks to Benjamin Kaduk for his detailed and comprehensive reviews
and comments.
The authors would also like to specially thank Jean Mahoney for her
multiple reviews, editorial help, and the conversion of the XML
source file from v2 to v3.
Authors' Addresses
Rifaat Shekh-Yusef
Auth0
Ottawa Ontario
Canada
Email: rifaat.s.ietf@gmail.com
Christer Holmberg
Ericsson
Hirsalantie 11
FI-02420 Jorvas
Finland
Email: christer.holmberg@ericsson.com
Victor Pascual
Nokia
Barcelona
Spain
Email: victor.pascual_avila@nokia.com

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