DS Algorithms for Securing NS and GlueGoDaddybrian.peter.dickson@gmail.com
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DNSOP Working GroupInternet-DraftThis Internet Draft proposes a mechanism to encode relevant data for NS records (and optionally A and AAAA records) on the parental side of a zone cut, by encoding them in new DS algorithms.Since DS records are signed by the parent, this creates a method for validation of the otherwise unsigned delegation and glue records.This is beneficial if the name server names are in a DNSSEC signed zone.There are new privacy goals and DNS server capability discovery goals, which cannot be met without the ability to validate the name of the name servers for a given domain at the delegation point.Specifically, a query for NS records over an unprotected transport path returns results which do not have protection from tampering by an active on-path attacker, or against successful cache poisoning attackes.This is true regardless of the DNSSEC status of the domain containing the authoritative information for the name servers for the queried domain.For example, querying for the NS records for “example.com”, at the name servers for the “com” TLD, where the published com zone has “example.com NS ns1.example.net”, is not protected against MITM attacks, even if the domain “example.net” (the domain serving records for “ns1.example.net”) is DNSSEC signed.More infomation can be found in . (An exmple
of an informative reference to a draft in the middle of text. Note that
referencing an Internet draft involves replacing “draft-“ in the name with
“I-D.”)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.The methods developed for adding security to the Domain Name System, collectively refered to as DNSSEC, had as a primary requirement that they be backward compatible. The original specifications for DNS used the same Resourc Record Type (RRTYPE) on both the parent and child side of a zone cut (the NS record). The main goal of DNSSEC was to ensure data integrity by using cryptographic signatures. However, owing to this overlap in the NS record type where the records above and below the zone cut have the same owner name created an inherent conflict, as only the child zone is authoritative for these records.The result is that the parental side of the zone cut has records needed for DNS resolution which are not signed and not validatable.This has no impact on DNS zones which are fully DNSSEC signed (anchored at the IANA DNS Trust Anchor), but does impact unsigned zones regardless of where the transition from secure to insecure occurs.These new DNSKEY algorithms conform to the structure requirements from , but are not themselves used as actual DNSKEY algorithms. They are assigned values from the DNSKEY algorithm table. No DNSKEY records are published with these algorithms.They are used only as the input to the corresponding DS hashes published in the parent zone.This algorithm is used to validate the NS records of the delegation for the owner name.The NS records are canonicalized and sorted according to the DNSSEC signing process section 6, including removing any label compression, and normalizing the character cases to lower case. The RDATA fields of the records are concatenated, and the result is hashed using the selected digest algorithm(s), e.g. SHA2-256 for DS digest algorithm 1.Consider the delegation in the COM zone:
example.com NS ns1.example.net
example.com NS ns2.example.netThese two records have RDATA, which after canonicalization and sorting, would be
ns1.example.net
ns2.example.netThe input to the digest is the concatenation of those values in wire format.
For example, if the NS set’s RDATA are “ns1.example.net” and “ns2.example.net”,
the wire format would beThe Key Tag is calculated per using this value as the RDATA.The resulting DS record isThis algorithm is used to validate the glue A records required as glue for the delegation NS set associated with the owner name.The glue A records are canonicalized and sorted according to the DNSSEC signing process , including removing any label compression, and normalizing the character cases. The entirety of the records are concatenated, and the result is hashed using the selected hash type(s), e.g. SHA2-256 for DS type 2.For example, if the original “glue” (unsigned) A records are:There would be one DS record for each of the glue “A” records, with the canonicalized
wire format of the entire record provided as input to the hash function.Then the resulting DS record isThis algorithm is used to validate the glue AAAA records required as glue for the delegation NS set associated with the owner name.The glue AAAA records are canonicalized and sorted according to the DNSSEC signing process , including removing any label compression, and normalizing the character cases. The entirety of the records are concatenated, and the result is hashed using the selected hash type(s), e.g. SHA2-256 for DS type 2.For example, if the original “glue” (unsigned) AAAA records are:There would be one DS record for each of the glue “A” records, with the canonicalized
wire format of the entire record provided as input to the hash function.Then the resulting DS record isThese new DS records are used to validate corresponding delegation records and glue, as follows:
- NS records are validated using {TBD1}
- Glue A records (if present) are validated using {TBD2}
- Glue AAAA records (if present) are validated using {TBD3}The same method used for constructing the DS records, is used to validate their contents. The algorithm is replicated with the corresponding inputs, and the hash compared to the published DS record(s).As outlined above, there could be security issues in various use
cases.This document has no IANA actions.
(Well, actually, TBD1, TBD2, and TBD3 need to be assigned from the DNSSEC DNSKEY Algorithm Table.)Key words for use in RFCs to Indicate Requirement LevelsIn 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.Ambiguity of Uppercase vs Lowercase in RFC 2119 Key WordsRFC 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.Resource Records for the DNS Security ExtensionsThis 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]The Internet is for End Users This document explains why the IAB believes the IETF should consider
end-users as its highest priority concern, and how that can be done.
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