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Performing DNSKEY algorithm transitions with DNSSEC signing is unfortunately challenging to get right in practice without decent tooling support. This document weighs the correct, completely secure way of rolling keys against an alternate, significantly simplified, method that takes a zone through an insecure state first.

Introduction Performing DNSKEY algorithm transitions with DNSSEC signing is unfortunately challenging to get right in practice without decent tooling support. This document weighs the correct, completely secure way of rolling keys against an alternate, significantly simplified, method that takes a zone through an insecure state. Section 4.1.4 of describes the necessary steps required when a new signing key is published for a zone that uses a different signing algorithm than the currently published keys. These are the steps that MUST be followed when zone owners wish to have uninterrupted DNSSEC protection for their zones. The steps in this document are designed to ensure that all DNSKEY records and all DS records (and the rest of a zone records) are properly validatable by validating resolvers throughout the entire process. Whenever possible, this procedure SHOULD be followed. Unfortunately, there are a number of these steps that are challenging to accomplish either because the timing is tricky to get right or because current software doesn't support automating the process easily. Some examples:

1. The second step in Section 4.1.4 of requires that a new key with the new algorithm (which we refer to as K_new) be created, but not yet published. This step requires that both the old key (K_old) and K_new both sign and generate signatures for the zone, but without K_new actually being published in the zone even though its signatures. Put another way, only K_old can exist in the zone even though signatures from both keys must be included. After this odd mix has been published for a sufficient time length, based on the TTL, can K_new be safely introduced and published into the zone as well.
2. Sometimes one of the goals is to transfer zone management to new authoritative server software. But, if the newly desired algorithm isn't supported in the existing (to be replaced) DNSSEC signing software, then the transfer to the new software must be accomplished first. However, if there isn't an overlap between the algorithms available in both software sets, it becomes practically impossible to even transfer the zone since neither software set can use both K_old and K_new.

Although some DNSSEC signing solutions may automate the algorithm rollover steps (making operator involvement unnecessary), many other tools do not yet support automated algorithm updates. In these environments, the most challenging step is requiring that certain RRSIGs be published without the corresponding DNSKEYs that created them. This will likely require operators to use a text editor on the contents of a signed zone to carefully select zone records to extract before publication. This introduces potentially significant operator error(s). This document proposes an alternate approach that MAY be used to perform algorithm DNSKEY rollovers in these situations, which is potentially more operationally robust but less secure.

Requirements notation 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 when, and only when, they appear in all capitals, as shown here.

Transitioning temporarily through insecurity An alternate approach to properly rolling DNSKEYs to a new algorithm, is to intentionally make the zone become insecure while the DNSKEYs and algorithms are swapped. At a high level, this means removing all DS records from the parent zone first, then remove the old key and introduce the new key with its new algorithm during this period. Zone TTLs can be significantly shortened during this period to minimize the period of insecurity. Below are the enumerated steps required by this alternate transition mechanism. Note that there are still two critical waiting time requirements (steps 2 and 6) that must be followed carefully.

1. Optional: lower the TTLs of both the zone's DS record, and the TTL of the DNSKEY RRset. Note that in some operational deployments the parent zone may set the TTL of the DS record.
2. Remove all DS records from the parent zone.
3. Ensure the zone is considered unsigned by all validating resolvers by waiting 2 times the maximum TTL length for the DS record, and/or 2 times the largest TTL found in the zone (whichever is larger). This is the most critical timing as all records associated with K_old must be cleared from validating resolver caches. (The author of this document failed to wait the required time once. It was not pretty.)
4. Replace the old DNSKEY(s) using the old algorithm with new DNSKEY(s) using the new algorithm(s) in the zone and publish the zone.
5. Wait 2 times the largest TTL found in the zone to ensure the new DNSKEYs will be found by validating resolvers.
6. Add the DS record(s) for the new DNSKEYs to the parent zone.
7. If the TTLs were modified in the optional step 1, change them back to their preferred values.

Operational considerations The process of replacing a DNSKEY with an older algorithm , such as RSAMD5 or RSASHA1 with a more modern one such as RSASHA512 or ECDSAP256SHA256 can be a daunting task if the zone's current tooling doesn't provide an easy-to-use solution. For example, this may be the case for zone owners using command line tools integrated into their zone production environment. This document describes an alternative approach to rolling DNSKEY algorithms that may be significantly less prone to operational mistakes. However, it is paramount that operators understand of the security considerations of using this approach. The document recommends waiting 2 times TTL values in certain cases for added assurance that the waiting period is long enough for caches to expire. In reality, waiting slightly longer than 1 TTL may be sufficient but requires accepting added risks with propagation timing and clock synchronization.

Security considerations DNSSEC provides data integrity protection for DNS data. This document specifically calls out a reason why a zone owner may desire to deliberately turn off this protection while changing the zone's DNSKEY's cryptographic algorithms. Thus, this technique is potentially harmful if an attacker knows when this will occur and can use that time window to launch DNS modification attacks (for example, cache poisoning attacks) against validating resolvers or other validating DNS infrastructure. Most importantly, this will deliberately break certain types of DNS records that must be validatable for them to be effective. This includes for example, but not limited to, all DS records for the zone's own children, DANE , PGP key fingerprints , and SSHFP fingerprints. Zone owners must carefully consider which records within their zone and their zone's children depend on DNSSEC being available before using the procedure outlined in this document. Given all of this, it leaves the question of: "why would a zone owner want to deliberately turn off security temporarily then?", to which there is one principal answer: if the the complexity of executing an algorithm role the correct way is difficult (or impossible), then the chances of introducing an error that causes an operational outage may be significantly higher than the chances of the zone being attacked during the insecure transition period. Simply put, an invalid zone created by a botched algorithm roll is potentially worse than an unsigned but still available zone.

References Normative References This RFC is the revised specification of the protocol and format used in the implementation of the Domain Name System. It obsoletes RFC-883. This memo documents the details of the domain name client - server communication. In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. The Domain Name System Security Extensions (DNSSEC) add data origin authentication and data integrity to the Domain Name System. This document introduces these extensions and describes their capabilities and limitations. This document also discusses the services that the DNS security extensions do and do not provide. Last, this document describes the interrelationships between the documents that collectively describe DNSSEC. [STANDARDS-TRACK] This document is part of a family of documents that describe the DNS Security Extensions (DNSSEC). The DNS Security Extensions are a collection of new resource records and protocol modifications that add data origin authentication and data integrity to the DNS. This document describes the DNSSEC protocol modifications. This document defines the concept of a signed zone, along with the requirements for serving and resolving by using DNSSEC. These techniques allow a security-aware resolver to authenticate both DNS resource records and authoritative DNS error indications. This document obsoletes RFC 2535 and incorporates changes from all updates to RFC 2535. [STANDARDS-TRACK] This document specifies how to use the SHA-256 digest type in DNS Delegation Signer (DS) Resource Records (RRs). DS records, when stored in a parent zone, point to DNSKEYs in a child zone. [STANDARDS-TRACK] This document describes a set of practices for operating the DNS with security extensions (DNSSEC). The target audience is zone administrators deploying DNSSEC. The document discusses operational aspects of using keys and signatures in the DNS. It discusses issues of key generation, key storage, signature generation, key rollover, and related policies. This document obsoletes RFC 4641, as it covers more operational ground and gives more up-to-date requirements with respect to key sizes and the DNSSEC operations. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. This document is part of a family of documents that describe the DNS Security Extensions (DNSSEC). The DNS Security Extensions are a collection of resource records and protocol modifications that provide source authentication for the DNS. This document defines the public key (DNSKEY), delegation signer (DS), resource record digital signature (RRSIG), and authenticated denial of existence (NSEC) resource records. The purpose and format of each resource record is described in detail, and an example of each resource record is given. This document obsoletes RFC 2535 and incorporates changes from all updates to RFC 2535. [STANDARDS-TRACK] Informative References OpenPGP is a message format for email (and file) encryption that lacks a standardized lookup mechanism to securely obtain OpenPGP public keys. DNS-Based Authentication of Named Entities (DANE) is a method for publishing public keys in DNS. This document specifies a DANE method for publishing and locating OpenPGP public keys in DNS for a specific email address using a new OPENPGPKEY DNS resource record. Security is provided via Secure DNS, however the OPENPGPKEY record is not a replacement for verification of authenticity via the "web of trust" or manual verification. The OPENPGPKEY record can be used to encrypt an email that would otherwise have to be sent unencrypted. This document clarifies and updates the DNS-Based Authentication of Named Entities (DANE) TLSA specification (RFC 6698), based on subsequent implementation experience. It also contains guidance for implementers, operators, and protocol developers who want to use DANE records. This memo describes a downgrade-resistant protocol for SMTP transport security between Message Transfer Agents (MTAs), based on the DNS-Based Authentication of Named Entities (DANE) TLSA DNS record. Adoption of this protocol enables an incremental transition of the Internet email backbone to one using encrypted and authenticated Transport Layer Security (TLS). Encrypted communication on the Internet often uses Transport Layer Security (TLS), which depends on third parties to certify the keys used. This document improves on that situation by enabling the administrators of domain names to specify the keys used in that domain's TLS servers. This requires matching improvements in TLS client software, but no change in TLS server software. [STANDARDS-TRACK] This document describes a method of verifying Secure Shell (SSH) host keys using Domain Name System Security (DNSSEC). The document defines a new DNS resource record that contains a standard SSH key fingerprint. [STANDARDS-TRACK] The DNSSEC protocol makes use of various cryptographic algorithms to provide authentication of DNS data and proof of nonexistence. To ensure interoperability between DNS resolvers and DNS authoritative servers, it is necessary to specify both a set of algorithm implementation requirements and usage guidelines to ensure that there is at least one algorithm that all implementations support. This document replaces and obsoletes RFC 8624 and moves the canonical source of algorithm implementation requirements and usage guidance for DNSSEC from RFC 8624 to the IANA DNSSEC algorithm registries. This is done to allow the list of requirements to be more easily updated and referenced. Extensions to these registries can be made in future RFCs. This document also updates RFC 9157 and incorporates the revised IANA DNSSEC considerations from that RFC. This document does not change the recommendation status (MUST, MAY, RECOMMENDED, etc.) of the algorithms listed in RFC 8624; that is the work of future documents. This document deprecates the use of the RSASHA1 and RSASHA1-NSEC3-SHA1 algorithms for the creation of DNS Public Key (DNSKEY) and Resource Record Signature (RRSIG) records. It updates RFCs 4034 and 5155 as it deprecates the use of these algorithms. This document describes how to produce RSA/SHA-256 and RSA/SHA-512 DNSKEY and RRSIG resource records for use in the Domain Name System Security Extensions (RFC 4033, RFC 4034, and RFC 4035). [STANDARDS TRACK] This document describes how to specify Elliptic Curve Digital Signature Algorithm (DSA) keys and signatures in DNS Security (DNSSEC). It lists curves of different sizes and uses the SHA-2 family of hashes for signatures. [STANDARDS-TRACK]

Acknowledgments The author has discussed the pros and cons of this approach with multiple people, including:

• Vladimír Čunát
• Peter van Dijk
• Viktor Dukhovni
• Warren Kumari.
• Scott Rose
• Tuomo Soini
• Paul Wouters

Github Version of this document While this document is under development, it can be viewed, tracked, issued, pushed with PRs, ... here: https://github.com/hardaker/draft-hardaker-dnsop-intentionally-temporarily-insecure