Internet-Draft NAMEHACK June 2021
Schwartz & Kumari Expires 10 December 2021 [Page]
Intended Status:
B. Schwartz
Google LLC
W. Kumari
Google LLC

Nameserver Access Modes with Encryption Held in Alphanumeric Configuration Keys


Some recent proposals to the DPRIVE working group rely on the use of SVCB records to provide instructions about how to reach an authoritative nameserver over an encrypted transport. These proposals will be difficult to deploy until the parent domain's delegation software has been modified to support these records. As an interim solution for these domains, this draft proposes encoding relevant signals in the child's NS-name.

Discussion Venues

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Status of This Memo

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This Internet-Draft will expire on 10 December 2021.

Table of Contents

1. 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.

2. Background

[I-D.draft-schwartz-svcb-dns] defines how to use SVCB records to describe the secure transport protocols supported by a DNS server. [I-D.draft-ietf-dprive-unauth-to-authoritative] describes the use of such records on the names of nameservers (the "NS name") to enable opportunistic encryption of recursive-to-authoritative DNS queries. Resolvers are permitted to fetch SVCB records asynchronously and cache them, resulting in "partial opportunistic encryption": even without an active adversary forcing a downgrade, queries will sometimes be sent in cleartext. Participating authoritative nameservers and recursive resolvers would have to be modified to make use of these records.

When the child zone is DNSSEC-signed, publishing a SVCB record of this kind is technically sufficient to enable authenticated encryption. However, in order to support reliable authentication, recursive resolvers would have to query for a SVCB record on every signed delegation, and wait for a response before issuing their intended query. We call this behavior a "synchronous binding check".

Many validating resolvers might not be willing to enable a "synchronous binding check" behavior, as this would slow down resolution of many existing domains in order to enable a new feature (authenticated encryption) that is not yet used at all. To enable authenticated encryption without this general performance loss, [I-D.draft-rescorla-dprive-adox-latest] proposes to deliver the SVCB records from the parent, in the delegation response. This avoids the need for a binding check, at the cost of additionally requiring modifications to the parent nameserver, which must provide these extra records in delegation responses.

Providing these additional records is sufficient to enable "full opportunistic encryption": the transport is always encrypted in the absence of an active adversary. However, these records are not protected by DNSSEC, so the child can only achieve fully authenticated encryption if the parent also implements fully authenticated encryption or otherwise protects the delivery of these records.

Even if this approach is standardized, many parent zones may not support delivery of SVCB records in delegation responses in the near future. To enable the broadest use of encrypted transport, we may need an interim solution that can be deployed more easily.

3. Proposal

We propose to indicate a nameserver's support for encrypted transports using a signal encoded in its name. This signal takes two forms: a "flag" and a "menu".

We note that encoding semantics in DNS labels is a hack, but believe that the privacy benefits outweigh the ick factor.

In either form, the signal helps resolvers to acquire a SVCB RRSet for the nameserver. Resolvers use this RRSet as specified in [I-D.draft-rescorla-dprive-adox-latest].

3.1. Flag form

If the NS name's first label is svcb, this is regarded as a "flag". When contacting a flagged nameserver, participating resolvers SHOULD perform a synchronous binding check, and upgrade to a secure transport if appropriate, before issuing the query.

The presence of this flag does not guarantee that the corresponding SVCB records are actually present.

3.3. Implementation requirements

Resolvers that implement support for "menu" mode MUST also support the "flag" mode. Resolvers that support either mode MUST also support [I-D.draft-rescorla-dprive-adox-latest], and ignore the in-name signal if any SVCB records are included in a delegation response.

When possible, zones SHOULD use SVCB records in the delegation response and omit any in-name signal.

4. Security Considerations

NS names received during delegation are not protected by DNSSEC. Therefore, just like in [I-D.draft-rescorla-dprive-adox-latest], this scheme only enables authenticated encryption if the parent domain can provide authentication without DNSSEC validation, e.g. using a secure transport or Zone Digest [RFC8976].

5. Operational Considerations

It is possible that an existing NS name already matches the "flag" pattern. Such a "false positive flag" will result in a small performance loss due to the unnecessary synchronous binding check, but will not otherwise impair functionality.

If a pre-existing NS name contains the menu pattern, that nameserver will become unreachable by resolvers implementing this specification. The authors believe that no such nameservers are currently deployed, and such servers are unlikely to be deployed by accident.

6. IANA Considerations

IANA is requested to create a new registry entitled "Authoritative Server Transport In-Name Signal Characters", with the following fields:

The registry policy is TBD.

The initial contents (DO NOT USE, subject to change) are as follows:

Table 1
Character SvcParams
t alpn=dot
h alpn=h2 dohpath=/dns-query{?dns}
3 alpn=h3 dohpath=/dns-query{?dns}
q alpn=doq

7. References

7.1. Normative References

Schwartz, B., "Service Binding Mapping for DNS Servers", Work in Progress, Internet-Draft, draft-schwartz-svcb-dns-03, , <>.
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <>.
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <>.

7.2. Informative References

Bretelle, E., "Encoding DNS-over-TLS (DoT) Subject Public Key Info (SPKI) in Name Server name", Work in Progress, Internet-Draft, draft-bretelle-dprive-dot-spki-in-ns-name-00, , <>.
Fujiwara, K., "Delegation Information (Referrals) Signer for DNSSEC", Work in Progress, Internet-Draft, draft-fujiwara-dnsop-delegation-information-signer-00, , <>.
Hoffman, P. and P. V. Dijk, "Recursive to Authoritative DNS with Unauthenticated Encryption", Work in Progress, Internet-Draft, draft-ietf-dprive-unauth-to-authoritative-01, , <>.
Levine, J., "Signaling That an Authoritative DNS server offers DoT", Work in Progress, Internet-Draft, draft-levine-dprive-signal-02, , <>.
Pauly, T., Rescorla, E., Schinazi, D., and C. A. Wood, "Signaling Authoritative DNS Encryption", Work in Progress, Internet-Draft, draft-rescorla-dprive-adox-latest-00, , <>.
Dijk, P. V., "The VERBATIM Digest Algorithm for DS records", Work in Progress, Internet-Draft, draft-vandijk-dnsop-ds-digest-verbatim-00, , <>.
Dijk, P. V., Geuze, R., and E. Bretelle, "Signalling Authoritative DoT support in DS records, with key pinning", Work in Progress, Internet-Draft, draft-vandijk-dprive-ds-dot-signal-and-pin-01, , <>.
Wessels, D., Barber, P., Weinberg, M., Kumari, W., and W. Hardaker, "Message Digest for DNS Zones", RFC 8976, DOI 10.17487/RFC8976, , <>.



Authors' Addresses

Benjamin M. Schwartz
Google LLC
Warren Kumari
Google LLC