]> Independent

2386 Panoramic Circle Apopka Florida 32703 USA d3e3e3@gmail.com

Swedish Internet Foundation

johan.stenstam@internetstiftelsen.se

Internet Systems Consortium

PO Box 360 Newmarket NH 03857 USA marka@isc.org

Internet DNSSD This document specifies the SIGZERO and SIG(0) Domain Name System (DNS) Resource Records (RRs) which provide public key based authentication of DNS requests and transactions. SIGZERO is the RECOMMENDED option. This document obsoletes RFC 2931.

Introduction [[[ META COMMENTS: Comments within triple square brackets like this are discussion points or alternatives/options for the content of this draft. They are NOT text to be included in the final document. ]]] This document specifies the Domain Name System (DNS) SIGZERO and SIG(0) Resource Records (RRs) which provide public key based authentication of DNS requests and transactions. SIGZERO is patterned after the TSIG and RRSIG RRs. Use of SIGZERO is RECOMMENDED for this purpose. As discussed below, use of the SIG RR for this purpose is NOT RECOMMENDED. When a SIG RR is so used, it has a "type covered" field value of zero, and is called a "SIG(0)" RR. This document obsoletes .

Terminology The term "SIG Zero" is used in this document to refer to both the SIGZERO RR and the SIG(0) RR. General familiarity with DNS terminology is assumed. SRP is Service Registration Protocol . 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.

SIG Zero RR Design Rationale and Use The SIGZERO and SIG(0) (SIG Zero) Meta-RRs provide authentication and integrity protection for DNS transactions and requests that is not provided by the DNSSEC security specified in and . The authenticated data origin services of DNSSEC security provide either protected data resource records (RRs) or authenticatable denial of their existence. Those services provide no protection for the following:

• glue records,
• DNS requests,
• the DNS message headers on requests or responses, and
• the overall integrity of a transaction, that is to say, that the response was issued in response to the request sent and neither was tampered with in transit.

As Meta-RRs, SIGZERO and SIG(0) are not stored in zones. They accompany DNS messages in the Additional Information section of the message. (Meta-RRs are usually "one DNS server hop" and not forwarded by recursive servers but see for a discussion of forwarding SIG Zero RRs.) Transaction authentication can provide cryptographic assurance to a resolver that it is getting the DNS response message from the server to which it sent a request and that the received message is in response to that request. This is accomplished by adding either a TSIG RR or, as specified herein, a SIG Zero RR, at the end of the additional information section of the response which authenticates the concatenation of the corresponding resolver request and the server's response. Requests can be authenticated by including a SIG Zero RR at the end of the request's additional information section. This method of signing requests is primarily intended for authenticating requests for integrity protection and to demonstrate that the requester is authorized to make the request by its possession of the private key needed to generate the SIG Zero RR. Examples of such requests are dynamic update requests , use in the Service Registration Protocol (SRP) for DNS-Based Service Discovery , and TKEY requests . There may be additional requests specified in the future that require such authentication. The private keys used in public key based request security typically belong to the host composing the DNS request message or the other entity composing the request or to a zone to be affected by the request. The corresponding public key(s) can be stored in and retrieved from the DNS for verification as KEY RRs with a protocol byte of 3 or 255 (ANY).

Differences Between TSIG, SIGZERO, and SIG(0) A TSIG RR can also be used for request and transaction authentication. There are significant differences between TSIG and SIG Zero. Because TSIG involves secret keys available at both the requester and server the presence of such a key can imply that it is likely that the other party understands TSIG and has the same key installed. Furthermore, TSIG uses keyed hash authentication codes which are relatively compact and inexpensive to compute. Thus, if shared secret keys are in place and there is agreement to do so, it is relatively inexpensive to authenticate DNS requests and transactions with TSIG. SIGZERO and SIG(0) on the other hand, use public key authentication, where the public keys can be stored in DNS as KEY RRs and a private key is held by the signer. Existence of such a KEY RR does not necessarily imply that SIGZERO or SIG(0) are implemented or enabled. In addition, they involve relatively expensive public key cryptographic operations and their verification involves obtaining and verifying the corresponding KEY which can itself be an expensive operation. Indeed, a policy of using a SIGZERO or SIG(0) on all requests and verifying it before responding would, for some configurations, lead to a deadly embrace with the attempt to obtain and verify the KEY needed to authenticate the request resulting in additional requests accompanied by a SIGZERO or SIG(0) leading to further requests accompanied by a SIGZERO or SIG(0), etc. Furthermore, omitting these RRs when not required on requests halves the number of public key operations required by the transaction and saves space in requests. For these reasons, a SIG Zero RR SHOULD only be used on requests when necessary to authenticate that the requester has some required privilege or identity. SIG Zero on transactions is defined in such a way as to not require a SIG Zero on the corresponding request and still provide transaction protection. Which SIG Zero RRs are required to be authenticated by a server or requester should be a local configuration option.

Why SIGZERO Is Preferred Over SIG(0) The SIGZERO RR was designed for this application and its use is RECOMMENDED. SIG(0) is an alternative use of the older SIG RR originally specified in and is NOT RECOMMENDED. Four reasons for this preference are as follows:

1. SIG(0) does not provide a convenient way to include an extended error code in a response reporting on the SIG Zero operation. SIGZERO has an Error field for this purpose.
2. SIG(0) does not provide a convenient way to forward the original DNS request message ID through a recursive server but this value is needed to validate a SIG(0) or SIGZERO signature. SIGZERO has a reserved field for this value (as does the TSIG RR). (See .)
3. There is no convenient way to extend SIG(0) while SIGZERO has an Other Data field for this purpose.
4. The SIG RR was used as a data RR for signatures and its RRTYPE is in the range normally used for data RRs, not Meta-RRs. That it is actually a Meta-RR if and only if a SIG RR's Type Covered field is zero might confuse a deficient DNS implementation.

Multiple TSIGs, SIGZEROs, and/or SIG(0)s [[[ This section currently preserves the tight restrictions on multiple TSIGs and/or SIG(0)s by themselves but is more liberal on SIGZERO and permits one or more SIGZEROs to be accompanied by a TSIG. Should this be yet further liberalized? ]]] A request or response may contain any one of the following but no other combinations are permitted:

• one TSIG,
• one SIG(0),
• one or more SIGZERO RRs, or
• one TSIG and one or more SIGZERO RRs.

It MUST NOT have both a TSIG and a SIG(0). It MUST NOT have more than one TSIG or more than one SIG(0). It MUST NOT have a SIG(0) along with a SIGZERO. A request with these prohibited combinations MUST be rejected with FORMERR and a response with such a combination is ignored. Since SIG Zero RRs in a DNS message do not sign each other, their order is not significant. They may be inserted into or removed from the message without affecting the validity of any other SIG Zeros in the message.

Indicating Support Support for the SIGZERO RR is indicated by the SZ bit in the EDNS(0) OPT RR. (See .)

The SIG Zero Resource Records The format of the SIGZERO and SIG(0) RRs are specified in the subsections below. All multi-octet integers in these RRs are sent in network byte order (see Section 2.3.2 of ). When SIG Zero authentication on a response is desired, the SIG Zero RR MUST be considered the highest priority of any additional information for inclusion in the response. If the SIG Zero RR cannot be added without causing the message to be truncated, the server MUST alter the response so that a SIG Zero can be included, set the TC bit, and return RCODE 0 (NOERROR). The client should at this point retry the request using an available transport that does not have UDP packet size restrictions.

SIGZERO RR Format The fields of the SIGZERO Meta-RR are described below. Most of these fields are similar or identical to the field in the TSIG or RRSIG RR with same field name.

SIGZERO RR Format 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ / Owner Name = Signer's Name | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | TYPE = TBD | CLASS = 0x00FF (ALL) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | TTL (MUST be zero) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | RDLENGTH | / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ RDATA / / / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

NAME:

The owner name of the KEY RR holding the public key that should verify the signature. If there is no such KEY RR owner name then, to avoid wasting bytes, this should be the name of the root, that is, a single zero byte.

TYPE:

This MUST be TBD [248 suggested] for SIGZERO

CLASS:

This MUST be 255 (ANY, 0x00FF).

TTL:

The TTL field MUST be zero and is ignored on receipt. The zero value minimizes the risk that a DNS implementation that does not understand SIGZERO will cache the RR.

RDLENGTH:

An unsigned integer giving the length of the RDATA.

RDATA:

The RDATA for a SIGZERO RR consists of a number of fields as described below and shown in .

SIGZERO RR Format 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Algorithm | Flags | Original ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Error | Fudge | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | Time Signed +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | Signature Size | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Key Tag | / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Signature / / / / / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Other Length | / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Other Data / / / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Algorithm:

The signature algorithm used. Values in this field have the same meaning as they do in the RRSIG RR and use the same IANA registry

Flags:

Reserved for flags to be specified in the future. MUST be sent as zero and ignored on receipt.

Original ID:

An unsigned 16-bit integer holding the DNS message ID of the original message. For a SIGZERO RR added to a DNS message being originated, it is set equal to the DNS message ID. When a SIGZERO RR is being forwarded as discussed in , the Original ID field is forwarded as received.

Error:

In responses, an unsigned 16-bit integer containing the extended RCODE covering SIGZERO processing. In requests, this MUST be zero and is ignored on receipt of the request.

Fudge:

An unsigned 16-bit integer specifying the allowed time difference in seconds permitted from the Time Signed field.

Time Signed:

An unsigned 48-bit integer containing the time the message was signed as seconds since 00:00 on 1970-01-01 UTC, ignoring leap seconds.

Signature Size:

An unsigned integer giving the size of the Signature field in bytes.

Key Tag:

The Key Tag field contains the key tag value of the public key that is to be used to validate this signature. In the case of multiple possible KEY RRs, the Key Tag usually allows a heuristic reduction the number of KEY RRs to try. Appendix B of specifies how to calculate Key Tag values.

Signature:

The Signature field contains the cryptographic signature that covers the DNS request or transaction. The format of this field depends on the algorithm in use, and these formats are described in separate companion documents referenced from the IANA registry . The data signed is specified in .

Other Length:

An unsigned 16-bit integer specifying the length of the Other Data field in octets. If it would be zero, this field SHOULD be omitted to save space.

Other Data:

Additional data relevant to the TSIG record to be specified in later extensions.

The Time Signed and the Fudge form a time bracket, that is, the Time Signed plus/minus the Fudge, for the purpose of limiting replay attacks. Signatures received outside that bracket are considered invalid. In IP networks, the value of Fudge should normally not be more than 5 minutes. [[[ Should the Other Length / Other Data construct copied from TSIG and TKEY be replaced by TLVs, which would be more flexible? ]]]

The SIG(0) RR Format The structure of the SIG(0) resource record (RR) is the same as the structure of the RRSIG RR in Section 4 except as provided below.

SIG(0) RR Format 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ / Owner Name (not used, SHOULD be 0x0) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | TYPE = 24 | CLASS = 0x00FF (ALL) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | TTL (MUST be zero) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | RDLENGTH | / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ RDATA / / / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The type of the SIG RR is 24. The structure of a SIG(0) RDATA is shown in . For SIG(0) RRs, the above Owner Name, CLASS, and TTL fields are meaningless. To conserve space, the owner name SHOULD be root (a single zero octet). The TTL field MUST be zero. The CLASS field MUST be 255 (ANY), These fields are ignored on receipt. A TTL of zero decreases the risk that a DNS implementation that does not understand SIG(0) will cache such an RR. The RDATA for a SIG(0) RR consists of a number of fields as described below.

SIG(0) RDATA Format from 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type Covered = 0 | Algorithm | Labels = 0 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Original TTL = 0 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Signature Expiration | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Signature Inception | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Key Tag | / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Signer's Name / / / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ / / / Signature / / / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Type Covered:

MUST be zero which is what makes the SIG RR a SIG(0).

Algorithm:

The signature algorithm used. Values in this field have the same meaning as they do in the RRSIG RR and use the same IANA registry

Labels:

Not used, MUST be zero.

Original TTL:

Not used, MUST be zero.

Signature Inception and Expiration:

These times in SIG(0)s are for the purpose of limiting replay attacks. They form a time bracket and messages received outside that bracket are ignored. In IP networks, this time bracket SHOULD NOT normally extend further than 5 minutes into the past or 5 minutes into the future from the time the SIG(0) is added to the message.

Key Tag:

The Key Tag field contains the key tag value of the public key that is to be used to validate this signature. In the case of multiple possible KEY RRs, the Key Tag usually allows a heuristic reduction the number of KEY RRs to try. Appendix B of specifies how to calculate Key Tag values.

Signer's Name:

The owner name of the KEY RR holding the public key that should verify the signature. If there is no such KEY RR owner name then, to avoid wasting bytes, this should be the name of the root, that is, a single zero byte.

Signature:

The Signature field contains the cryptographic signature that covers the DNS request or transaction. The format of this field depends on the algorithm in use, and these formats are described in separate companion documents referenced from the IANA registry . The data signed is specified in .

For transaction SIG(0)s, there MUST be a KEY RR associated with the signer name with the public key corresponding to the private key used to calculate the signature. For general transaction authentication and integrity, the Signer's Name field is a name of the originating host; for example, the host domain name used may be the inverse IP address mapping name for an IP address of the host if the relevant KEY is stored there. For SIG(0)s on requests requiring authentication, the signer relates to the authority being requested such as authority to update a zone.

Calculating Request and Transaction SIG Zero RRs This section specifies the exact data over which request and transaction SIG Zero RRs are calculated. In the case of more than one SIGZERO RR, there is no significance to their order and a SIGZERO RR does not sign any other SIGZERO RR in that DNS message.

Calculating Request SIGZERO RRs A DNS request may be optionally signed by including one or more SIGZERO RRs at the end of the request additional information section. These RRs are calculated for and sign the "data" consisting of the following:

1. The SIGZERO RR with the Signature field set to all zero bytes.
2. The DNS request message, including the DNS header, but not any earlier headers such as UDP/IP headers, and before any SIG Zero RRs have been added so that, for example, the RR counts have not yet been adjusted for SIG Zero inclusion.

That is data = (SIGZERO RR with zero Signature) | (request message without SIG Zero RRs) where "|" is concatenation and RR is a SIGZERO RR with the signature field set to zero.

Calculating Request SIG(0) RRs A DNS request may be optionally signed by including a single SIG(0) RR) at the end of the request additional information section. This RR is calculated for and signs the "data" consisting of the following:

1. For the SIG(0), its RDATA section completely omitting the signature subfield itself, not just zeroing its value.
2. The DNS request message, including DNS header, but not any earlier headers such as UDP/IP headers and before the SIG(0) RR has been added so that, for example, the RR counts have not yet been adjusted for SIG(0) inclusion.

That is data = (SIG(0) RDATA with Signature omitted) | (request without SIG(0)) where "|" is concatenation and RDATA is the RDATA of a SIG(0) being calculated completely omitting the Signature itself.

Calculating Transaction SIGZERO RRs A SIGZERO can be used to secure a transaction consisting of a response and the request that produced it. Such a transaction signature SIGZERO, to be included in the response, is calculated over data consisting of the following:

1. That SIGZERO RR with the signature field set to all zero bytes.
2. The DNS request message that produced this response, with the following changes: (1) Omit any SIG Zeros that were present in the request including appropriate RR count reduction. (2) Including the request's DNS header with the Message ID replaced by the Original ID field of the SIGZERO but not any preceding headers such as UDP or IP.
3. The DNS response message, including the DNS header but not any preceding headers such as TCP or IP and before any SIGZEROs have been added so that, for example, the response RR counts have not yet been adjusted for such inclusion.

data = (SIGZERO RR with signature zeroed) | (request message without SIG Zeros) | (response message without SIG Zeros) where "|" is concatenation. With appropriate configuration, successful verification of a response SIGZERO cryptographically confirms that the query and response were not tampered with in transit, that the response corresponds to the intended query, and that the response comes from the queried server.

Calculating a Transaction SIG(0) RR A SIG(0) can be used to secure a transaction consisting of a response and the request that produced it. Such a transaction signature is calculated by using data consisting of

1. For the SIG(0), the RDATA section omitting (not just zeroing) the signature itself.
2. The DNS request message that produced this response, including the request's DNS header and any SIG(0) that was present but not any preceding headers such as UDP or IP.
3. The DNS response message, including DNS header but not any preceding headers such as TCP or IP and before any SIG(0) has been added so that, for example, the response RR counts have not yet been adjusted for such inclusion.

data = (SIG(0) RDATA omitting signature) | (request message) | (response message without SIG Zeros) where "|" is concatenation and RDATA is the RDATA of a SIG(0) being calculated omitting the signature itself. With appropriate configuration, successful verification of a response SIG(0) cryptographically confirms that the query and response were not tampered with in transit, that the response corresponds to the intended query, and that the response comes from the queried server.

Handling Multipacket DNS Messages In the case of a DNS message split into multiple packets via a stream transport (e.g. TCP, DoT, etc.), a SIG Zero on the first data packet is calculated with "data" as above but using data only from the first packet. For each subsequent packet, it is calculated as follows: data = ( (SIG(0) RDATA) or (SIGZERO RR) ) | (DNS payload without SIG Zeros) | (previous packet) where "|" is concatenations, RDATA and SIGZERO RR are as above, and previous packet is the previous DNS payload including DNS header but not any preceding headers such as TCP or IP and including the SIG(0) RR if one was present but not any SIGZERO RRs. This does not apply to fragmented UDP where the message is just signed once at the end and then fragmented. Except where needed to authenticate an update, TKEY, SRP registration or similar request, servers are not required to verify a request SIG Zero.

Processing SIG Zero RRs and Responses If the time when a SIG Zero on a request is received is outside the interval indicated (by the Inception and Expiration Times for a SIG(0) or the Time Signed and Fudge for a SIGZERO), the BADTIME error is returned. If this applies to a response, the response is ignored. If one or more SIG Zero RRs are at the end of the additional information section of a response, they are transaction signatures covering the response and the request that produced that response. If a response's SIG Zero check succeeds, such a transaction authentication does NOT directly authenticate the validity of any data RRs in the message. However, it can increase confidence that they were sent by the queried server and have not been altered in transit. (Only an RRSIG RR signed by the zone or a key tracing its authority to the zone or to resolver configuration can directly authenticate data RRs, depending on resolver policy.) If a resolver or server does not implement transaction and/or request SIG Zeros, it MUST ignore them without error where they are optional and treat them as failing where they are required. If a response has multiple SIGZERO RRs and verification of some succeeds and other fail, the appropriate action is dependent on local policy and configuration.

Considerations for Forwarding Servers A server acting as a forwarding (recursive) server of a DNS message such as an Update or an SRP registration SHOULD check for the existence of SIG Zero RRs. If it implements SIG Zero RRs but cannot verify a SIG Zero RR, the server MUST include that SIG Zero RR when forwarding the message. If a SIG Zero passes all checks and verifies, the forwarding server SHOULD remove it and if possible, add a SIG Zero of its own to the destination or the next forwarder. If no transaction security is available to the destination and the message is a request, and if the corresponding response has the AD flag (see ) set, the forwarder MUST clear the AD flag before adding a SIG Zero to the response and returning the result to the host from which it received the request. The transit of a DNS request between the originating client and final server through one or more forwarding servers and the similar handling of its response introduces additional potential failure and/or compromise points. Thus, when practical, requests with a SIG Zero RR should be sent directly to the final server that will verify that SIG Zero. [[[ This section probably need some more work. ]]]

Security Considerations Private keys used to create SIG Zero RRs are very sensitive information and all available steps should be taken to protect them on every host on which they are stored. Such hosts may need to be physically protected. If they are multi-user machines, great care should be taken so that unprivileged users have no access to private keying material. The inclusion of the SIG Zero Inception and Expiration Time and the SIGZERO Time Signed and Fudge under the signature improves resistance to replay attacks.

IANA Considerations IANA is requested to make the assignments specified in the following sections.

SIGZERO RR Type Number IANA is requested to assign a SIGZERO RRTYPE number in the "Resource Record (RR) TYPEs" registry in the range for meta-RRs as requested in . [Value 248 is suggested] The resulting entry would be as follows:

TYPE	Value	Meaning	Reference
SIGZERO	TBD	Public key request or transaction signature.	[this document]

SIGZERO Support EDNS OPT Bit IANA is requested to assign an EDNS Header flag in the EDNS Header Flags registry in the Domain Name System (DNS) Registry Group as follows:

Bit	Flag	Description	Reference
TBD2	SZ	SIGZERO supported	[this document]

Normative References Informative References

SIGZERO RRTYPE Assignment Application A. Submission Date: tbd B.1 Submission Type: [X] New RRTYPE [ ] Modification to RRTYPE B.2 Kind of RR: [ ] Data RR [X] Meta-RR C. Contact Information for submitter (will be publicly posted): Name: Donald Eastlake Email Address: d3e3e3@gmail.com International telephone number: +1-508-333-2270 Other contact handles: D. Motivation for the new RRTYPE application. SIG(0) has been found to have a number of deficiencies which are fixed in the specification for this new RRTYPE. E. Description of the proposed RR type. See draft-eastlake-dnssd-rfc2931bis-sigzero F. What existing RRTYPE or RRTYPEs come closest to filling that need and why are they unsatisfactory? The SIG RR (RFC 2536) with type covered of zero. Deficiencies are listed in draft-eastlake-dnssd-rfc2931bis-sigzero G. What mnemonic is requested for the new RRTYPE (optional)? SIGZERO H. Does the requested RRTYPE make use of any existing IANA registry or require the creation of a new IANA subregistry in DNS Parameters? Does not create any new registries and does not add entries to existing registries other than the allocation of the RRTYPE. I. Does the proposal require/expect any changes in DNS servers/resolvers that prevent the new type from being processed as an unknown RRTYPE (see RFC 3597)? It can be ignored but then you do not get its security benefits. J. Comments: See draft-eastlake-dnssd-rfc2931bis-sigzero

Changes from

1. Specify a new RR, SIGZERO, designed for the SIG Zero purpose which overcomes the deficiencies of SIG(0). RECOMMEND use of SIGZERO and make SIG(0) be NOT RECOMMENDED. Add RRTYPE assignment template for SIGZERO.
2. Add section on considerations for forwarding servers. Add paragraph suggesting the avoidance of forwarding servers where practical to eliminate a potential point of failure or compromise.
3. Remove statement that TCP support for SIG(0) is OPTIONAL.
4. Editorial changes including updates to meet current Internet draft format requirements. Update references. Convert source to XMLv3.

Change History RFC Editor: Please delete this section before publication. Note: This draft was initially targetted to the DNSOP WG but, after discussion with the Chairs and draft authors, was re-targetted to the DNSSD WG.

From to dnsop-00

1. Change to require KEY RRs used in connection with SIG(0) to have a protocol byte of 255 (ANY). ( also permits a protocol byte of 3.
2. Change implementation requirement for the TTL and CLASS field of SIG(0) RRs from SHOULD be zero and 255, respectively, to MUST have those values and are ignored on receipt.
3. Add section on considerations for forwarding servers.
4. Remove statement that TCP support for SIG(0) is OPTIONAL.
5. Specify an EDNS option to convey the original ID and return an extended error code.
6. Editorial changes including updates to meet current Internet draft format requirements. Update references. Convert source to XMLv3.

From dnsop-00 to dnsop-01

1. Add section on error return via EDNS and add IANA request for an EDNS OPT number.
2. Clarify that a SIG(0) public key can be associated with a zone or otherwise indicate authorization.
3. Add author.
4. Editorial Changes.

From dnsop-01 to dnsop-02

1. Permit multiple SIG(0)s.
2. Back out change requiring protocol 255 in SIG(0)s and again permit protocol 3 or 255.
3. Add reference to SIG(0) usage in SRP (Service Registration Protocol).
4. Editorial changes.

From dnsop-02 to dnsop-03

1. Generalize TCP references to include mentions of other stream protocols.
2. Update reference to DNSSD SRP from draft to .
3. Editorial changes.

From dnsop-03 to dnssd-00

1. Change to specify a new RR (SIGZERO) patterned more like TSIG. Drop EDNS(0) stuff.
2. Add paragraph suggesting the avoidance of forwarding servers where practical to eliminate a potential point of failure.
3. Add paragraph about Time Signed and Fudge for SIGZERO specifying a time interval similar to the Inception and Expiration times for SIG(0).
4. Omit request SIGZEROs from data for response SIGZERO to avoid breaking transaction security if a forwarder, for example, adds a second SIGZERO.
5. Numerous editorial changes.

From dnssd-00 to dnssd-01

1. Correct intended status to Standards Track from Informational.
2. Note that passage through a forwarding server may also be a potential point of compromise.
3. Soften assertions of "assurance" to "increase confidence".
4. Minor editorial changes.

From dnssd-01 to dnssd-02

1. Add an ENDS(0) OPT bit to announce support of SIGZRO.
2. Allow a TSIG with one or more SIGZEROs.
3. Provde that the Other Length field in a SIGZERO SHOULD be omitted if its value would be zero.
4. Eliminate key state from SIGZERO since it has nothing to do with the needed signature data, just the KEY RR.
5. Editorial changes.

Acknowledgements The comments and suggestions of the following are gratefully acknowledged: Stuart Cheshire The comments and suggestions of the following persons were incorporated into , which was the previous version of this document, and are gratefully acknowledged: Olafur Gudmundsson, Ed Lewis, Erik Nordmark, Brian Wellington.