Network Working Group D. Wing
Internet-Draft Citrix
Intended status: Informational E. Nygren
Expires: 4 September 2025 Akamai Technologies
M. Richardson
Sandelman Software Works
3 March 2025
Requirements for HTTPS for Local Domains
draft-wing-settle-requirements-00
Abstract
When connecting to servers on their local network, users are
surprised to encounter user interfaces that display errors, show
insecure connections, and block some HTTP features when missing a
secure context. However, obtaining PKIX certificates for those
servers is difficult for a variety of reasons.
This document explores requirements for authenticating local servers.
About This Document
This note is to be removed before publishing as an RFC.
The latest revision of this draft can be found at
https://danwing.github.io/settle-requirements/draft-wing-settle-
requirements.html. Status information for this document may be found
at https://datatracker.ietf.org/doc/draft-wing-settle-requirements/.
Discussion of this document takes place on the SETTLE mailing list
(mailto:settle@ietf.org), which is archived at
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https://www.ietf.org/mailman/listinfo/settle/.
Source for this draft and an issue tracker can be found at
https://github.com/danwing/settle-requirements.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 4
3. Technical Requirements . . . . . . . . . . . . . . . . . . . 4
3.1. Naming . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.2. Cryptographic Binding . . . . . . . . . . . . . . . . . . 5
3.3. Abstract Naming . . . . . . . . . . . . . . . . . . . . . 5
3.4. Avoid Central Authority . . . . . . . . . . . . . . . . . 6
3.5. Multiple Application Protocols . . . . . . . . . . . . . 6
3.6. Cryptographic Agility . . . . . . . . . . . . . . . . . . 6
3.7. TLS Server Name Indication . . . . . . . . . . . . . . . 6
3.8. Localhost . . . . . . . . . . . . . . . . . . . . . . . . 7
3.9. W3C Private Network Access . . . . . . . . . . . . . . . 7
3.10. Constrain to Local Resources . . . . . . . . . . . . . . 7
3.11. Operate Standalone . . . . . . . . . . . . . . . . . . . 7
3.12. Miscellaneous . . . . . . . . . . . . . . . . . . . . . . 7
4. Human Factors Requirements . . . . . . . . . . . . . . . . . 8
4.1. Discoverable . . . . . . . . . . . . . . . . . . . . . . 8
4.2. Easy to Use . . . . . . . . . . . . . . . . . . . . . . . 8
4.3. Bookmarkable . . . . . . . . . . . . . . . . . . . . . . 8
4.4. Human-friendly Name . . . . . . . . . . . . . . . . . . . 8
5. Big Open Questions . . . . . . . . . . . . . . . . . . . . . 8
5.1. Key Rotation . . . . . . . . . . . . . . . . . . . . . . 8
5.2. Trust on First Use (TOFU) . . . . . . . . . . . . . . . . 9
5.3. User Experience . . . . . . . . . . . . . . . . . . . . . 9
5.4. Trust Relationship . . . . . . . . . . . . . . . . . . . 9
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5.5. Interaction with Matter/Thread . . . . . . . . . . . . . 9
6. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 9
7. Related . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
8. Security Considerations . . . . . . . . . . . . . . . . . . . 10
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
10.1. Normative References . . . . . . . . . . . . . . . . . . 10
10.2. Informative References . . . . . . . . . . . . . . . . . 11
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction
Servers on local networks have historically settled for unencrypted
communications -- printers, routers, network attached storage (NAS).
However, with the advent of HTTPS everywhere [everywhere], browsers
disadvantage unencrypted communications (e.g., [not-secure],
[sec-context]). This increases importance of a secure context
(HTTPS) to local domains.
In addition, it is recognized that home networks are not (and perhaps
have never been) the idyllic secure gardens that many think they are.
There are persistent threats in the home due to malware on devices
within the home, as well as malware that might arrive on guest
devices. Most home networks have little protection against various
kinds of (layer-2) spoofing attacks, which means that active on-path
attacks (MITM) must be assumed. Securing the administrative and
regular connections within the home network would result in
significant security gains for all devices in the home.
Today, a secure context is obtained with a PKIX certificate
([RFC5280]) signed by a Certification Authority (CA) that is trusted
by the client.
However, servers on a local network cannot easily get PKIX
certificates signed by a Certification Authority because: they are
not directly reachable from the outside (due to firewall or NAPT),
lack of domain name delegation, and need for ongoing certificate
renewal.
The problem has been well recognized since about 2017 and several
proposals have been suggested to solve this problem, each with their
own drawbacks. This document is not intended to summarize these
proposals or their drawbacks; for that detail see the pointers to
previous work in Section 7. At a high level, the proposals have
involved solutions such as:
* pre-shared secrets (scanned, printed, or displayed by the server)
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* Public DNS pointing at local domain's IP address (e.g., [plex])
* Local Certification Authority, where a CA is added to client's
certificate trust list and that CA signs certificates for devices
within the local network
* Trust On First Use (TOFU), where a user verifies the first
connection to a server and the client remembers that verification,
similar to common use of ssh
* WebRTC and WebTransport, where a PKI-signed server provides a
public key fingerprint of another server that it has previously
bootstrapped
* Encoding server's public key into the hostname [thomson-hld]
This document explores IETF requirements for an alternative server
authentication system for local hosts.
2. Conventions and Definitions
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.
3. Technical Requirements
The goal is to work out the engineering tradeoff around
[zookotriangle]. Specifically it says there are three aspects that
must be traded off:
* Human-meaningful
* Secure
* Decentralized
3.1. Naming
PKIX certificates are a centralized naming scheme derived from DNS.
These names have (the possibility of) having human-readable names.
But the most significant property is uniqueness -- each name has its
own identity and that identity can be proven.
A system that does not rely on centralized naming lacks this
inherient uniqueness property.
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Without a centralized naming scheme, name collisions are possible and
likely. For example, it is likely that many networks will have a
printer named, simply, "printer", much like many people might share a
common name such as "John". Humans prefer simple, human-readable
names, but a strong identity cannot be created with such names.
Two networks both have a printer named "printer", they are
indistinguishable. This would not be as much of a problem were
personal devices not mobile. A person's smartphone could easily
visit my networks on which there is a device named "printer", and the
user might well wish to actually use those printers. At the time
time, if those names are not secured, then a simple attack against
the user is possible, leading to them printing to a malicious device.
Worse, if there are symmetric credentials (such as passwords)
involved, then the user might well disclose their password to the
attacker. This would be unacceptable.
R-UNIQUE-NAME: The system MUST have a way to uniquely identify
servers.
3.2. Cryptographic Binding
A server's name has to be mapped to its cryptographic identity.
R-BINDING: The Web Origin MUST be cryptographically bound to one
or more key pairs, where the private keying material is on the
service endpoint and where an attacker without the private key(s)
is unable to access any state associated with the Web Origin.
A client has to be able to validate the name maps to the
cryptographic identity.
R-VALIDATE: Clients MUST be able to cryptographically validate
that the authenticating server matches the identity in the URI /
Web Origin.
Web browsers and modern users both expect a URI.
R-URI: It MUST be possible to construct a URI that encapsulates a
Web Origin and its cryptographically-bound identity information.
3.3. Abstract Naming
Using IP addresses in names is problematic if the server's IP address
changes due to ISP renumbering or internal network DHCP server
reconfiguration.
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Given common NAT44 (NAPT), many many networks will share the same
IPv4 addresses.
R-ABSTRACT: The solution SHOULD abstract names from IP addresses.
Any given name should be resolvable to a mixture of IPv4, IPv6 Link-
Local (on an Interface), IPv6 ULA, and IPv6 Globally-Routable
addresses. Operating a local DNS is beyond the scope of many
administrators, so being able to advertise the server using [DNS-SD]
is necessary.
R-DNS-SD: The name MUST be advertisable using [DNS-SD]
3.4. Avoid Central Authority
A solution needs to be self-contained and not use the central
authority of PKIX.
R-AVOID-CENTRAL: A solution SHOULD NOT (MUST NOT?) rely on central
trust hierarchy.
Vendors go out of business or lose interest in continuing to service
old products. The products may still be operational.
R-AVOID-VENDOR: A solution SHOULD NOT (MUST NOT?) have continued
reliance on a service operated by a vendor, including if the
device is reset to factory defaults (e.g., reset for
troubleshotting or because sold).
3.5. Multiple Application Protocols
R-HTTPS: A solution MUST support HTTPS.
R-MULT-APP: A solution SHOULD support other application-level
protocols such as IPPS [RFC7472], DoT [RFC7858], SMB over QUIC
[smb-quic], IMAP [RFC8314], and SIP [RFC3261], as those protocols
are routinely served with a local domain.
3.6. Cryptographic Agility
R-AGILITY: A solution SHOULD support crypto agility (such as
supporting more than one active key type).
3.7. TLS Server Name Indication
R-TLS-SNI: A solution SHOULD support TLS SNI so a server knows
which key pair/cert is expected.
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3.8. Localhost
R-LOCALHOST: A solution SHOULD support "localhost" (e.g., for
sending a user to connect to a local service)
3.9. W3C Private Network Access
R-PNA: A solution SHOULD integrate well with an evolution of
[w3c-pna] and both allow for an improved model there but should
also provide more robust solutions to vulnerabilities that it
tries to address
3.10. Constrain to Local Resources
R-LOCAL: A solution SHOULD be constrained to .local and .internal.
Discuss: MAY constrain to the DHCP domain-search value?? Should
we also allow any arbitrary name if the IP address is local
(RFC1918 address), too?
3.11. Operate Standalone
After configuration, the system needs to operate without a connection
to the Internet. This is necessary because Internet connectivity is
sometimes flaky or unavailable (e.g., cabin in the woods).
R-STANDALONE: MUST operate securely while Internet connectivity is
unavailable.
3.12. Miscellaneous
1. It SHOULD be possible to have a way to represent a URI that
includes a single specific IP address and the cryptographic
identity of the service endpoint.
Discuss: the above requirement needs to be re-written.
1. SHOULD support key rotation (even if via 301 redirect)
* Q: is it acceptable to state to be lost here? Note: likely cannot
do 301 if doing TLS (HTTPS). Is this suggestion to start HTTP and
upgrade to HTTPS? Could be useful for HTTPS but redirect
unavailable for IPP, SMB, DoH.
Discuss: the above requirement needs to be re-written.
1. SHOULD support building trust relationships within devices in the
local environment
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Discuss: the above requirement needs to be re-written.
1. Could this help with HTTPS access to Wi-Fi login portals
([RFC8952], [RFC8910])?
Discuss: the above requirement needs to be re-written.
4. Human Factors Requirements
4.1. Discoverable
R-DISCOVER: A solution SHOULD have a way to do discovery of
endpoints and their identities (for example, via [DNS-SD]).
4.2. Easy to Use
R-EASY: A solution SHOULD have human factors and adversarial
testing on proposed solutions to make sure that this solution
provides a reasonable experience to average and novice end-users
and does not introduce new security exploitation vectors
4.3. Bookmarkable
R-BOOKMARK: A solution SHOULD have a URI that users can Bookmark
to create an association to a friendly name.
Discussion: Can URL bar of the browser honor mDNS/DNSSD advertised
names, or give a pull-down of them similar to how the "add
printer" dialog does for printers? This would help ease the use
of long FQDN so it's almost as easy as router.local. Especially
if it could show a nickname that is configured by the printer.
4.4. Human-friendly Name
R-CONSISTENT: A solution SHOULD represent these URIs to humans in
a consistent, readable, and non-confusing fashion. (In a browser,
users shouldn't see the key fingerprint by default but rather a
representation of its presence)
5. Big Open Questions
5.1. Key Rotation
1. Is it acceptable for the Web Origin to change as part of key
rotations? A: no, this does not happen today and changing the
web origin would violate the principle of least surprise.
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5.2. Trust on First Use (TOFU)
Is TOFU acceptable?
Note: TOFU is arguably what we have today with self-signed
certificates which can be trusted (after the user accepts the
warning message and adds the certificate to their client's trust
store).
5.3. User Experience
For a solution, what is the User Experience for any trust
relationship / web-of-trust?
5.4. Trust Relationship
For a solution, what is the nature of the trust relationship?
* Peer trust web?
* Central CA within the local environment / trust clearing house?
* Client establishes its own trust to the server
5.5. Interaction with Matter/Thread
How does a solution tie into systems like Matter/Thread that have
their own trust establishment frameworks?
6. Use Cases
For the below, "Secure communications" means being able to make a TLS
connection to a service such that the service is able to authenticate
itself in a way to prevent MitM attacks. The security model must be
TOFU at a minimum, but when the identity of a service is none it
should be possible to send it as a URI in such as a way to present a
secure association rooted in the connection that sent it:
* Secure communications via HTTPS to admin interfaces on CPEs for
both initial and ongoing configuration tasks of various servers
(router, printer, NAS, etc.).
* Secure communications to DoH/DoT servers on CPEs
* Secure communications to printers (IPPS [RFC7472] printing)
* Secure communications to other local services (SMB over QUIC to
another workstation or a NAS) and IoT devices
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* Secure communications to localhost processes from a browser (e.g.,
admin tools)
7. Related
Martin Thomson wrote a document on HTTPS for Local Domains which
covers requirements, discusses several solutions and their tradeoffs,
and suggests a solution with hostnames encoding the server's public
key [thomson-hld] in November 2017.
W3C worked on this problem from 2017 through 2021 [w3c-httpslocal].
More recently, W3C had a workshop on the problem in September 2024
[tpac].
The boundaries of a limited domain -- such as the local domain
described in this document -- are explored in Section 6 of [RFC8799].
The IOTOPS working group and the associated IOT Security Foundation
[iotsf] discussed the problem and some requirements in their white
paper [iotops-suib] and presentation to IOTOPS working group at
IETF112 [iotops-suib-prezo].
A threshold key system is described and implemented at [phb-mesh]
with the following description:
The Mesh is designed to provide users with the highest level of
security that is possible without asking them to do anything at
all. For this to become possible, the Mesh will have to be
shipped to users as part of the machine Operating System.
A summary of the problem and analysis of several solutions (Locally-
installed CAs, Plex, WebRTC and WebTransport, TOFU, shared secrets)
and some drawbacks of those solutions is at [stark].
A method using PAKE and a shared secret (displayed on the server) is
explained at [shared].
8. Security Considerations
TODO Security
9. IANA Considerations
This document has no IANA actions.
10. References
10.1. Normative References
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[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/rfc/rfc2119>.
[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/rfc/rfc8174>.
10.2. Informative References
[DNS-SD] Cheshire, S. and M. Krochmal, "DNS-Based Service
Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013,
<https://www.rfc-editor.org/rfc/rfc6763>.
[everywhere]
EFF, "HTTPS Everywhere", March 2025,
<https://www.eff.org/https-everywhere>.
[iotops-suib]
IOT Security Foundation, "SUIB: Router and IoT
Vulnerabilities: Insecure by Design", August 2021,
<https://iotsecurityfoundation.org/wp-
content/uploads/2021/08/ManySecured-SUIB-White-Paper.pdf>.
[iotops-suib-prezo]
Geertsma, J., Amsüss, C., Richardson, M., and N. Allott,
"SUIB: Browsing local web resources in a secure usable
manner", November 2021,
<https://datatracker.ietf.org/meeting/112/materials/
slides-112-iotops-suib-browsing-local-web-resources-in-a-
secure-usable-manner-iot-device-configuration-as-a-
special-case-00.pdf>. Presentation of IOT Security
Foundation SUIB to IETF112 IOTOPS working group
[iotsf] "IOT Security Foundation", September 2015,
<https://iotsecurityfoundation.org>.
[not-secure]
Google, "A secure web is here to stay", 2018,
<https://blog.chromium.org/2018/02/a-secure-web-is-here-
to-stay.html>.
[phb-mesh] Hallam-Baker, P., "Mathematical Mesh", 2022,
<https://github.com/hallambaker/Mathematical-Mesh>.
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[plex] Valsorda, F., "How Plex Is Doing Https for All Its Users",
June 2015, <https://words.filippo.io/how-plex-is-doing-
https-for-all-its-users/>.
[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/rfc/rfc3261>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/rfc/rfc5280>.
[RFC7472] McDonald, I. and M. Sweet, "Internet Printing Protocol
(IPP) over HTTPS Transport Binding and the 'ipps' URI
Scheme", RFC 7472, DOI 10.17487/RFC7472, March 2015,
<https://www.rfc-editor.org/rfc/rfc7472>.
[RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D.,
and P. Hoffman, "Specification for DNS over Transport
Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May
2016, <https://www.rfc-editor.org/rfc/rfc7858>.
[RFC8314] Moore, K. and C. Newman, "Cleartext Considered Obsolete:
Use of Transport Layer Security (TLS) for Email Submission
and Access", RFC 8314, DOI 10.17487/RFC8314, January 2018,
<https://www.rfc-editor.org/rfc/rfc8314>.
[RFC8799] Carpenter, B. and B. Liu, "Limited Domains and Internet
Protocols", RFC 8799, DOI 10.17487/RFC8799, July 2020,
<https://www.rfc-editor.org/rfc/rfc8799>.
[RFC8910] Kumari, W. and E. Kline, "Captive-Portal Identification in
DHCP and Router Advertisements (RAs)", RFC 8910,
DOI 10.17487/RFC8910, September 2020,
<https://www.rfc-editor.org/rfc/rfc8910>.
[RFC8952] Larose, K., Dolson, D., and H. Liu, "Captive Portal
Architecture", RFC 8952, DOI 10.17487/RFC8952, November
2020, <https://www.rfc-editor.org/rfc/rfc8952>.
[sec-context]
W3C, "Secure Contexts", 2023,
<https://w3c.github.io/webappsec-secure-contexts/>.
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[shared] W3C, "APPROACH-2: Using Shared Secret", September 2019,
<https://httpslocal.github.io/proposals/#approach-2>.
[smb-quic] Microsoft, "SMB over QUIC", December 2024,
<https://learn.microsoft.com/en-us/windows-server/storage/
file-server/smb-over-quic>.
[stark] Stark, E. M., "When a web PKI certificate won't cut it",
December 2021, <https://emilymstark.com/2021/12/24/when-a-
web-pki-certificate-wont-cut-it.html>.
[thomson-hld]
Thomson, M., "HTTPS for Local Domains", September 2017,
<https://docs.google.com/document/u/0/
d/170rFC91jqvpFrKIqG4K8Vox8AL4LeQXzfikBQXYPmzU/edit>.
[tpac] IL, C., "HTTPS for Local Networks", September 2024,
<https://github.com/w3c/tpac2024-breakouts/issues/78>.
[w3c-httpslocal]
W3C, "HTTPS in Local Network Community Group", 2019,
<https://github.com/httpslocal>.
[w3c-pna] W3C, "Private Network Access", September 2024,
<https://wicg.github.io/private-network-access/>.
[zookotriangle]
Wikipedia, "Zooko's triangle", March 2025,
<https://en.wikipedia.org/wiki/Zooko%27s_triangle>.
Acknowledgments
TODO acknowledge.
Authors' Addresses
Dan Wing
Cloud Software Group, Inc.
Email: danwing@gmail.com
Erik Nygren
Akamai Technologies
Email: erik+ietf@nygren.org
URI: http://erik.nygren.org/
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Michael Richardson
Sandelman Software Works
Email: mcr+ietf@sandelman.ca
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