--- 1/draft-ietf-dprive-unauth-to-authoritative-03.txt 2021-09-28 12:14:09.784757932 -0700 +++ 2/draft-ietf-dprive-unauth-to-authoritative-04.txt 2021-09-28 12:14:09.812758637 -0700 @@ -1,95 +1,93 @@ Network Working Group P. Hoffman Internet-Draft ICANN Intended status: Experimental P. van Dijk -Expires: January 13, 2022 PowerDNS - July 12, 2021 +Expires: 1 April 2022 PowerDNS + 28 September 2021 Recursive to Authoritative DNS with Unauthenticated Encryption - draft-ietf-dprive-unauth-to-authoritative-03 + draft-ietf-dprive-unauth-to-authoritative-04 Abstract This document describes a use case and a method for a DNS recursive resolver to use unauthenticated encryption when communicating with authoritative servers. The motivating use case for this method is that more encryption on the Internet is better, and some resolver operators believe that unauthenticated encryption is better than no encryption at all. The method described here is optional for both - the recursive resolver and the authoritative server. This method - supports unauthenticated encryption using the same mechanism for - discovery of encryption support for the server as [FULL-AUTH]. + the recursive resolver and the authoritative server. 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 Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." - This Internet-Draft will expire on January 13, 2022. + This Internet-Draft will expire on 1 April 2022. Copyright Notice Copyright (c) 2021 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal - 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. + 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 1.1. Use Case for Unauthenticated Encryption . . . . . . . . . 3 1.2. Summary of Protocol . . . . . . . . . . . . . . . . . . . 3 1.3. Definitions . . . . . . . . . . . . . . . . . . . . . . . 4 2. Discovery of Authoritative Server Encryption . . . . . . . . 4 3. Processing Discovery Responses . . . . . . . . . . . . . . . 5 3.1. Resolver Process as Pseudocode . . . . . . . . . . . . . 6 3.2. Resolver Session Failures . . . . . . . . . . . . . . . . 7 - 4. Serving with Encryption . . . . . . . . . . . . . . . . . . . 7 + 4. Serving with Encryption . . . . . . . . . . . . . . . . . . . 8 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 6. Security Considerations . . . . . . . . . . . . . . . . . . . 8 - 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8 - 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 - 8.1. Normative References . . . . . . . . . . . . . . . . . . 8 - 8.2. Informative References . . . . . . . . . . . . . . . . . 9 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 + 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9 + 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 + 8.1. Normative References . . . . . . . . . . . . . . . . . . 9 + 8.2. Informative References . . . . . . . . . . . . . . . . . 10 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11 1. Introduction A recursive resolver using traditional DNS over port 53 may wish instead to use encrypted communication with authoritative servers in order to limit snooping of its DNS traffic by passive or on-path attackers. The recursive resolver can use unauthenticated encryption (defined in [OPPORTUN]) to achieve this goal. This document describes the use case for unauthenticated encryption in recursive resolvers in Section 1.1. The encryption method with - authoritative servers can be DNS-over-TLS [DNSOTLS] (DoT), DNS-over- - HTTPS [DNSOHTTPS] (DoH), and/or DNS-over-QUIC [DNSOQUIC] (DoQ). + authoritative servers can be DNS-over-TLS [DNS-OVER-TLS] (DoT), DNS- + over-HTTPS [DNS-OVER-HTTPS] (DoH), and/or DNS-over-QUIC + [DNS-OVER-QUIC] (DoQ). The document also describes a discovery method that shows if an authoritative server supports encryption in Section 2. See [FULL-AUTH] for a description of the use case and a proposed mechanism for fully-authenticated encryption. NOTE: The draft uses the SVCB record as a discovery mechanism for encryption by a particular authoritative server. Any record type that can show multiple types of encryption (currently DoT, DoH, and @@ -98,81 +96,85 @@ 1.1. Use Case for Unauthenticated Encryption The use case in this document for unauthenticated encryption is recursive resolver operators who are happy to use encryption with authoritative servers if doing so doesn't significantly slow down getting answers, and authoritative server operators that are happy to use encryption with recursive resolvers if it doesn't cost much. In this use case, resolvers do not want to return an error for requests that were sent over an encrypted channel if they would have been able - to give a correct answer using unencrypted transport. + to give a correct answer using unencrypted transport. Ultimately, + this effort has two two goals: to protect queries from failing in + case authenticated encryption is not available, and to enable + recursive resolver operators to encrypt without server + authentication. Resolvers and authoritative servers understand that using encryption costs something, but are willing to absorb the costs for the benefit of more Internet traffic being encrypted. The extra costs (compared to using traditional DNS on port 53) include: - o Extra round trips to establish TCP for every session (but not + * Extra round trips to establish TCP for every session (but not necessarily for every query) - o Extra round trips for TLS establishment + * Extra round trips for TLS establishment - o Greater CPU use for TLS establishment + * Greater CPU use for TLS establishment - o Greater CPU use for encryption after TLS establishment + * Greater CPU use for encryption after TLS establishment - o Greater memory use for holding TLS state + * Greater memory use for holding TLS state This use case is not expected to apply to all resolvers or authoritative servers. For example, according to [RSO_STATEMENT], some root server operators do not want to be the early adopters for DNS with encryption. The protocol in this document explicitly allows authoritative servers to signal when they are ready to begin offering DNS with encryption. 1.2. Summary of Protocol This summary gives an overview of how the parts of the protocol work together. - o The resolver discovers whether any authoritative server of + * The resolver discovers whether any authoritative server of interest supports DNS with encryption by querying for the SVCB records [SVCB]. As described in [DNS-SVCB], SVCB records can indicate that a server supports encrypted transport of DNS queries. NOTE: In this document, the term "SVCB record" is used _only_ for SVCB records that indicate encryption as described in [DNS-SVCB]. SVCB records that do not have these indicators in the RDATA are not included in the term "SVCB record" in this document. - o The resolver uses any authoritative server with a SVCB record that + * The resolver uses any authoritative server with a SVCB record that indicates encryption to perform unauthenticated encryption. - o The resolver does not fail to set up encryption if the + * The resolver does not fail to set up encryption if server authentication in the TLS session fails. 1.3. Definitions The terms "recursive resolver", "authoritative server", and "classic DNS" are defined in [DNS-TERM]. "DNS with encryption" means transport of DNS over any of DoT, DoH, or DoQ. A server that supports DNS with encryption supports transport over one or more of DoT, DoH, or DoQ. 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 [MUSTSHOULD1] [MUSTSHOULD2] when, and only when, they appear in - all capitals, as shown here. + 14 [MUST-SHOULD-1] [MUST-SHOULD-2] when, and only when, they appear + in all capitals, as shown here. 2. Discovery of Authoritative Server Encryption An authoritative server that supports DNS with encryption makes itself discoverable by publishing one or more DNS SVCB records that contain "alpn" parameter keys. SVCB records are defined in [SVCB], and the DNS extension to those records is defined in [DNS-SVCB]. A recursive resolver discovers whether an authoritative server supports DNS with encryption by looking for cached SVCB records for @@ -213,58 +215,62 @@ those authoritative servers in the cache are negative responses, the resolver MUST use classic (unencrypted) DNS instead of encryption. Similarly, if none of the DNS SVCB records for the authoritative servers in the cache have supported "alpn" parameters, the resolver MUST use classic (unencrypted) DNS instead of encryption. If there are any DNS SVCB records in the cache for the authoritative servers for a zone with supported "alpn" parameters, the resolver MUST try each indicated authoritative server using DNS with encryption until it successfully sets up a connection. The resolver - only attempts to use the encrypted transports that are in the - associated SVCB record for the authoritative server. (( Note that - this completely prohibits "simple port 853 probing" even though that - is what some operators are currently doing. Does the WG want to be - this strict? )) + attempts to use the encrypted transports that are in the associated + SVCB record for the authoritative server. A resolver SHOULD keep a DNS with encryption session to a particular server open if it expects to send additional queries to that server in a short period of time. [DNS-OVER-TCP] says "both clients and servers SHOULD support connection reuse" for TCP connections, and that advice could apply as well for DNS with encryption, especially as DNS with encryption has far greater overhead for re-establishing a connection. If the server closes the DNS with encryption session, the resolver can possibly re-establish a DNS with encryption session - using encrypted session resumption. + using encrypted session resumption. Configuration for the maximum + timeout, minimum timeout, and duration of encrypted sessions should + take into consideration the recommendations given in [TCP-TIMEOUT], + [EDNS-TCP], and (for DoH) [HTTP-1.1]. For any DNS with encryption protocols, TLS version 1.3 [TLS-13] or later MUST be used. A resolver following this protocol does not need to authenticate TLS servers. Thus, when setting up a TLS connection, if the server's authentication credentials do not match those expected by the resolver, the resolver continues with the TLS connection. Privacy- oriented resolvers (defined in [PRIVACY-REC]) following this protocol MUST NOT indicate that they are using encryption because this protocol is susceptible to on-path attacks. + If the resolver gets a TLS failure (such as those listed in + Section 3.2, the resolver instead uses classic DNS on any of the + authoritative servers. + 3.1. Resolver Process as Pseudocode This section is meant as an informal clarification of the protocol, and is not normative. The pseudocode here is designed to show the intent of the protocol, so it is not optimized for things like intersection of sets and other shortcuts. - In this code, "signal_rrset(this_name)" means an "SVCB" query for the - "'_dns'" prefix of "this_name". The "Query over secure transport - until successful" section ignores differences in name server - selection and retry behaviour in different resolvers. + In this code, signal_rrset(this_name) means an SVCB query for the + '_dns' prefix of this_name. The Query over secure transport until + successful section ignores differences in name server selection and + retry behaviour in different resolvers. # Inputs ns_names = List of NS Rdatas from the NS RRset for the queried name can_do_secure = List of secure transports supported by resolver secure_names_and_transports = Empty list, filled in below # Fill secure_names_and_transports with (name, transport) tuples for this_name in ns_names: if signal_rrset(this_name) is in the resolver cache: if signal_rrset(this_name) positively does not exist: @@ -276,36 +282,36 @@ queue a query for signal_rrset(this_name) for later caching # Query over secure transport until successful for (this_name, this_transport) tuple in secure_names_and_transports: query using this_transport on this_name if successful: finished # Got here if no this_name/this_transport query was successful # or if secure_names_and_transports was empty - query using classic DNS on any/all ns_names; finished + query using classic DNS; finished 3.2. Resolver Session Failures The following are some of the reasons that a DNS with encryption session might fail to be set up: - o The resolver receives a TCP RST response + * The resolver receives a TCP RST response - o The resolver does not receive replies to TCP or TLS setup (such as + * The resolver does not receive replies to TCP or TLS setup (such as getting the TCP SYN message, the first TLS message, or completing TLS handshakes) - o The TLS handshake gets a definitive failure + * The TLS handshake gets a definitive failure - o The encrypted session fails for reasons other than for + * The encrypted session fails for reasons other than for authentication, such as incorrect algorithm choices or TLS record failures 4. Serving with Encryption An operator of an authoritative server following this protocol SHOULD publish SVCB records as described in Section 2. If they cannot publish such records, the security properties of their authoritative servers will not be found. If an operator wants to test serving using encryption, they can publish SVCB records with short TTLs and @@ -344,102 +350,150 @@ The method described in this document explicitly allows a resolver to perform DNS communications over traditional unencrypted, unauthenticated DNS on port 53, if it cannot find an authoritative server that advertises that it supports encryption. The method described in this document explicitly allows a resolver using encryption to choose to allow unauthenticated encryption. In either of these cases, the resulting communication will be susceptible to obvious and well-understood attacks from an attacker in the path of the communications. + [TLS-1.3] specifically warns against anonymous connections because + such connections only provide protection against passive + eavesdropping while failing to protect against active on-path + attacks. Section C.5 of [TLS-1.3] explicitly states applications + MUST NOT use TLS with unverifiable server authentication unless there + is explicit configuration or a specific application profile to do so. + This document is such an application profile. + + Encrypting the traffic between resolvers and authoritative servers + does not solve all the privacy issues for resolution. See + [PRIVACY-REC] and [PRIVACY-CONS] for in-depth discussion of the + associated privacy issues. + 7. Acknowledgements Puneet Sood contributed many ideas to early drafts of this document. The DPRIVE Working Group has contributed many ideas that keep shifting the focus and content of this document. 8. References 8.1. Normative References - [DNS-SVCB] - Schwartz, B., "Service Binding Mapping for DNS Servers", - draft-schwartz-svcb-dns-03 (work in progress), April 2021. + [DNS-SVCB] Schwartz, B., "Service Binding Mapping for DNS Servers", + Work in Progress, Internet-Draft, draft-schwartz-svcb-dns- + 04, 26 July 2021, . - [DNS-TERM] - Hoffman, P. and K. Fujiwara, "DNS Terminology", draft- - ietf-dnsop-rfc8499bis-02 (work in progress), June 2021. + [DNS-TERM] Hoffman, P. and K. Fujiwara, "DNS Terminology", Work in + Progress, Internet-Draft, draft-ietf-dnsop-rfc8499bis-03, + 28 September 2021, . [FULL-AUTH] Pauly, T., Rescorla, E., Schinazi, D., and C. A. Wood, - "Signaling Authoritative DNS Encryption", draft-rescorla- - dprive-adox-latest-00 (work in progress), February 2021. + "Signaling Authoritative DNS Encryption", Work in + Progress, Internet-Draft, draft-rescorla-dprive-adox- + latest-00, 26 February 2021, + . - [MUSTSHOULD1] + [MUST-SHOULD-1] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . - [MUSTSHOULD2] + [MUST-SHOULD-2] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . - [OPPORTUN] - Dukhovni, V., "Opportunistic Security: Some Protection + [OPPORTUN] Dukhovni, V., "Opportunistic Security: Some Protection Most of the Time", RFC 7435, DOI 10.17487/RFC7435, December 2014, . [SVCB] Schwartz, B., Bishop, M., and E. Nygren, "Service binding and parameter specification via the DNS (DNS SVCB and - HTTPS RRs)", draft-ietf-dnsop-svcb-https-06 (work in - progress), June 2021. + HTTPS RRs)", Work in Progress, Internet-Draft, draft-ietf- + dnsop-svcb-https-07, 5 August 2021, + . [TLS-13] Rescorla, E., "The Transport Layer Security (TLS) Protocol Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, . 8.2. Informative References + [DNS-OVER-HTTPS] + Hoffman, P. and P. McManus, "DNS Queries over HTTPS + (DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018, + . + + [DNS-OVER-QUIC] + Huitema, C., Dickinson, S., and A. Mankin, "Specification + of DNS over Dedicated QUIC Connections", Work in Progress, + Internet-Draft, draft-ietf-dprive-dnsoquic-04, 3 September + 2021, . + [DNS-OVER-TCP] Dickinson, J., Dickinson, S., Bellis, R., Mankin, A., and D. Wessels, "DNS Transport over TCP - Implementation Requirements", RFC 7766, DOI 10.17487/RFC7766, March 2016, . - [DNSOHTTPS] - Hoffman, P. and P. McManus, "DNS Queries over HTTPS - (DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018, - . - - [DNSOQUIC] - Huitema, C., Mankin, A., and S. Dickinson, "Specification - of DNS over Dedicated QUIC Connections", draft-ietf- - dprive-dnsoquic-02 (work in progress), February 2021. - - [DNSOTLS] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D., + [DNS-OVER-TLS] + 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, . + [EDNS-TCP] Wouters, P., Abley, J., Dickinson, S., and R. Bellis, "The + edns-tcp-keepalive EDNS0 Option", RFC 7828, + DOI 10.17487/RFC7828, April 2016, + . + + [HTTP-1.1] 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, + . + + [PRIVACY-CONS] + Wicinski, T., Ed., "DNS Privacy Considerations", RFC 9076, + DOI 10.17487/RFC9076, July 2021, + . + [PRIVACY-REC] Dickinson, S., Overeinder, B., van Rijswijk-Deij, R., and A. Mankin, "Recommendations for DNS Privacy Service Operators", BCP 232, RFC 8932, DOI 10.17487/RFC8932, October 2020, . [RSO_STATEMENT] "Statement on DNS Encryption", 2021, . + [TCP-TIMEOUT] + Kristoff, J. and D. Wessels, "DNS Transport over TCP - + Operational Requirements", Work in Progress, Internet- + Draft, draft-ietf-dnsop-dns-tcp-requirements-12, 18 August + 2021, . + + [TLS-1.3] Rescorla, E., "The Transport Layer Security (TLS) Protocol + Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, + . + Authors' Addresses Paul Hoffman ICANN Email: paul.hoffman@icann.org Peter van Dijk PowerDNS