draft-ietf-dnsop-rfc2845bis-02.txt   draft-ietf-dnsop-rfc2845bis-03.txt 
Internet Engineering Task Force F. Dupont Internet Engineering Task Force F. Dupont
Internet-Draft S. Morris Internet-Draft S. Morris
Obsoletes: 2845, 4635 (if approved) ISC Obsoletes: 2845, 4635 (if approved) ISC
Intended status: Standards Track P. Vixie Intended status: Standards Track P. Vixie
Expires: May 23, 2019 Farsight Expires: September 8, 2019 Farsight
D. Eastlake 3rd D. Eastlake 3rd
Huawei Huawei
O. Gudmundsson O. Gudmundsson
CloudFlare CloudFlare
B. Wellington B. Wellington
Akamai Akamai
November 19, 2018 March 7, 2019
Secret Key Transaction Authentication for DNS (TSIG) Secret Key Transaction Authentication for DNS (TSIG)
draft-ietf-dnsop-rfc2845bis-02 draft-ietf-dnsop-rfc2845bis-03
Abstract Abstract
This protocol allows for transaction level authentication using This document describes a protocol for transaction level
shared secrets and one way hashing. It can be used to authenticate authentication using shared secrets and one way hashing. It can be
dynamic updates as coming from an approved client, or to authenticate used to authenticate dynamic updates as coming from an approved
responses as coming from an approved name server. client, or to authenticate responses as coming from an approved name
server.
No provision has been made here for distributing the shared secrets. No recommendation is made here for distributing the shared secrets:
it is expected that a network administrator will statically configure
name servers and clients using some out of band mechanism.
This document includes revised original TSIG specifications (RFC2845) This document obsoletes RFC2845 and RFC4635.
and its extension for HMAC-SHA (RFC4635).
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on May 23, 2019. This Internet-Draft will expire on September 8, 2019.
Copyright Notice Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
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skipping to change at page 2, line 35 skipping to change at page 2, line 35
Without obtaining an adequate license from the person(s) controlling Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other it for publication as an RFC or to translate it into languages other
than English. than English.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Key words . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Key Words . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. New Assigned Numbers . . . . . . . . . . . . . . . . . . . . 5 3. New Assigned Numbers . . . . . . . . . . . . . . . . . . . . 4
4. TSIG RR Format . . . . . . . . . . . . . . . . . . . . . . . 5 4. TSIG RR Format . . . . . . . . . . . . . . . . . . . . . . . 5
4.1. TSIG RR Type . . . . . . . . . . . . . . . . . . . . . . 5 4.1. TSIG RR Type . . . . . . . . . . . . . . . . . . . . . . 5
4.2. TSIG Calculation . . . . . . . . . . . . . . . . . . . . 5 4.2. TSIG Calculation . . . . . . . . . . . . . . . . . . . . 5
4.3. TSIG Record Format . . . . . . . . . . . . . . . . . . . 5 4.3. TSIG Record Format . . . . . . . . . . . . . . . . . . . 5
4.4. Example . . . . . . . . . . . . . . . . . . . . . . . . . 7 4.4. Example . . . . . . . . . . . . . . . . . . . . . . . . . 7
5. Protocol Operation . . . . . . . . . . . . . . . . . . . . . 7 5. Protocol Operation . . . . . . . . . . . . . . . . . . . . . 7
5.1. Effects of adding TSIG to outgoing message . . . . . . . 8 5.1. Effects of Adding TSIG to Outgoing Messages . . . . . . . 8
5.2. TSIG processing on incoming messages . . . . . . . . . . 8 5.2. TSIG Processing on Incoming Messages . . . . . . . . . . 8
5.3. Time values used in TSIG calculations . . . . . . . . . . 8 5.3. Time Values Used in TSIG Calculations . . . . . . . . . . 8
5.4. TSIG Variables and Coverage . . . . . . . . . . . . . . . 9 5.4. TSIG Variables and Coverage . . . . . . . . . . . . . . . 9
5.4.1. DNS Message . . . . . . . . . . . . . . . . . . . . . 9 5.4.1. DNS Message . . . . . . . . . . . . . . . . . . . . . 9
5.4.2. TSIG Variables . . . . . . . . . . . . . . . . . . . 9 5.4.2. TSIG Variables . . . . . . . . . . . . . . . . . . . 9
5.4.3. Request MAC . . . . . . . . . . . . . . . . . . . . . 10 5.4.3. Request MAC . . . . . . . . . . . . . . . . . . . . . 10
5.5. Component Padding . . . . . . . . . . . . . . . . . . . . 10 5.5. Component Padding . . . . . . . . . . . . . . . . . . . . 10
6. Protocol Details . . . . . . . . . . . . . . . . . . . . . . 10 6. Protocol Details . . . . . . . . . . . . . . . . . . . . . . 10
6.1. TSIG generation on requests . . . . . . . . . . . . . . . 10 6.1. TSIG Generation on Requests . . . . . . . . . . . . . . . 10
6.2. TSIG on Answers . . . . . . . . . . . . . . . . . . . . . 10 6.2. TSIG on Answers . . . . . . . . . . . . . . . . . . . . . 10
6.3. TSIG on TSIG Error returns . . . . . . . . . . . . . . . 11 6.3. TSIG on TSIG Error Returns . . . . . . . . . . . . . . . 11
6.4. TSIG on zone transfer over a TCP connection . . . . . . . 11 6.4. TSIG on Zone Transfer Over a TCP Connection . . . . . . . 11
6.5. Server TSIG checks . . . . . . . . . . . . . . . . . . . 12 6.5. Server TSIG checks . . . . . . . . . . . . . . . . . . . 12
6.5.1. Key check and error handling . . . . . . . . . . . . 12 6.5.1. Key Check and Error Handling . . . . . . . . . . . . 12
6.5.2. MAC check and error handling . . . . . . . . . . . . 12 6.5.2. MAC Check and Error Handling . . . . . . . . . . . . 12
6.5.3. Time check and error handling . . . . . . . . . . . . 13 6.5.3. Time Check and Error Handling . . . . . . . . . . . . 13
6.5.4. Truncation check and error handling . . . . . . . . . 13 6.5.4. Truncation Check and Error Handling . . . . . . . . . 13
6.6. Client processing of answer . . . . . . . . . . . . . . . 14 6.6. Client Processing of Answer . . . . . . . . . . . . . . . 14
6.6.1. Key error handling . . . . . . . . . . . . . . . . . 14 6.6.1. Key Error Handling . . . . . . . . . . . . . . . . . 14
6.6.2. MAC error handling . . . . . . . . . . . . . . . . . 14 6.6.2. MAC Error Handling . . . . . . . . . . . . . . . . . 14
6.6.3. Time error handling . . . . . . . . . . . . . . . . . 14 6.6.3. Time Error Handling . . . . . . . . . . . . . . . . . 14
6.6.4. Truncation error handling . . . . . . . . . . . . . . 14 6.6.4. Truncation Error Handling . . . . . . . . . . . . . . 14
6.7. Special considerations for forwarding servers . . . . . . 15 6.7. Special Considerations for Forwarding Servers . . . . . . 15
7. Algorithms and Identifiers . . . . . . . . . . . . . . . . . 15 7. Algorithms and Identifiers . . . . . . . . . . . . . . . . . 15
8. TSIG Truncation Policy . . . . . . . . . . . . . . . . . . . 16 8. TSIG Truncation Policy . . . . . . . . . . . . . . . . . . . 16
9. Shared Secrets . . . . . . . . . . . . . . . . . . . . . . . 17 9. Shared Secrets . . . . . . . . . . . . . . . . . . . . . . . 17
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
11. Security Considerations . . . . . . . . . . . . . . . . . . . 18 11. Security Considerations . . . . . . . . . . . . . . . . . . . 18
11.1. Issue fixed in this document . . . . . . . . . . . . . . 19 11.1. Issue Fixed in this Document . . . . . . . . . . . . . . 19
11.2. Why not DNSSEC? . . . . . . . . . . . . . . . . . . . . 19 11.2. Why not DNSSEC? . . . . . . . . . . . . . . . . . . . . 19
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 20 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 20
12.1. Normative References . . . . . . . . . . . . . . . . . . 20 12.1. Normative References . . . . . . . . . . . . . . . . . . 20
12.2. Informative References . . . . . . . . . . . . . . . . . 20 12.2. Informative References . . . . . . . . . . . . . . . . . 20
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . 22 Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . 22
Appendix B. Change History (to be removed before publication) . 23 Appendix B. Change History (to be removed before publication) . 23
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 25 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 25
1. Introduction 1. Introduction
The Domain Name System (DNS) [RFC1034], [RFC1035] is a replicated The Domain Name System (DNS) [RFC1034], [RFC1035] is a replicated
hierarchical distributed database system that provides information hierarchical distributed database system that provides information
fundamental to Internet operations, such as name <=> address fundamental to Internet operations, such as name <=> address
translation and mail handling information. translation and mail handling information.
In 2017, security problems in two nameservers strictly following In 2017, two nameservers strictly following [RFC2845] and [RFC4635]
[RFC2845] and [RFC4635] (i.e., TSIG and its HMAC-SHA extension) (i.e., TSIG and its HMAC-SHA extension) specifications were
specifications were discovered. The implementations were fixed but, discovered to have security problems related to this feature. The
to avoid similar problems in the future, the two documents were implementations were fixed but, to avoid similar problems in the
updated and merged, producing this revised specification for TSIG. future, the two documents were updated and merged, producing this
revised specification for TSIG.
This document specifies use of a message authentication code (MAC), This document specifies use of a message authentication code (MAC),
either HMAC-MD5 or HMAC-SHA (keyed hash functions), to provide an generated using certain keyed hash functions, to provide an efficient
efficient means of point-to-point authentication and integrity means of point-to-point authentication and integrity checking for DNS
checking for DNS transactions. transactions. Such transactions include DNS update requests and
responses for which this can provide a lightweight alternative to the
The second area where the secret key based MACs specified in this
document can be used is to authenticate DNS update requests as well
as transaction responses, providing a lightweight alternative to the
protocol described by [RFC3007]. protocol described by [RFC3007].
A further use of this mechanism is to protect zone transfers. In A further use of this mechanism is to protect zone transfers. In
this case the data covered would be the whole zone transfer including this case the data covered would be the whole zone transfer including
any glue records sent. The protocol described by DNSSEC does not any glue records sent. The protocol described by DNSSEC does not
protect glue records and unsigned records unless SIG(0) (transaction protect glue records and unsigned records unless SIG(0) (transaction
signature) is used. signature) is used.
The authentication mechanism proposed in this document uses shared The authentication mechanism proposed in this document uses shared
secret keys to establish a trust relationship between two entities. secret keys to establish a trust relationship between two entities.
Such keys must be protected in a fashion similar to private keys, Such keys must be protected in a manner similar to private keys, lest
lest a third party masquerade as one of the intended parties (by a third party masquerade as one of the intended parties (by forging
forging the MAC). There is an urgent need to provide simple and the MAC). There is an urgent need to provide simple and efficient
efficient authentication between clients and local servers and this authentication between clients and local servers and this proposal
proposal addresses that need. The proposal is unsuitable for general addresses that need. The proposal is unsuitable for general server
server to server authentication for servers which speak with many to server authentication for servers which speak with many other
other servers, since key management would become unwieldy with the servers, since key management would become unwieldy with the number
number of shared keys going up quadratically. But it is suitable for of shared keys going up quadratically. But it is suitable for many
many resolvers on hosts that only talk to a few recursive servers. resolvers on hosts that only talk to a few recursive servers.
A server acting as an indirect caching resolver -- a "forwarder" in A server acting as an indirect caching resolver -- a "forwarder" in
common usage -- might use transaction-based authentication when common usage -- might use transaction-based authentication when
communicating with its small number of preconfigured "upstream" communicating with its small number of preconfigured "upstream"
servers. Other uses of DNS secret key authentication and possible servers. Other uses of DNS secret key authentication and possible
systems for automatic secret key distribution may be proposed in systems for automatic secret key distribution may be proposed in
separate future documents. separate future documents.
Note that use of TSIG presumes prior agreement between the two Note that use of TSIG presumes prior agreement between the two
parties involved (e.g., resolver and server) as to any algorithm and parties involved (e.g., resolver and server) as to any algorithm and
key to be used. key to be used.
Since the publication of first version of this document ([RFC2845]) a Since the publication of first version of this document ([RFC2845]) a
mechanism based on asymmetric signatures using the SIG RR was mechanism based on asymmetric signatures using the SIG RR was
specified (SIG(0) [RFC2931]) whereas this document uses symmetric specified (SIG(0) [RFC2931]) whereas this document uses symmetric
authentication codes calculated by HMAC [RFC2104] using strong hash authentication codes calculated by HMAC [RFC2104] using strong hash
functions. functions.
2. Key words 2. Key Words
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
3. New Assigned Numbers 3. New Assigned Numbers
RRTYPE = TSIG (250) RRTYPE = TSIG (250)
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<id>.B.example.net, and <id>.A.site.example.B.example.net. It <id>.B.example.net, and <id>.A.site.example.B.example.net. It
should be possible for more than one key to be in simultaneous should be possible for more than one key to be in simultaneous
use among a set of interacting hosts. The name only needs to use among a set of interacting hosts. The name only needs to
be meaningful to the communicating hosts but a meaningful be meaningful to the communicating hosts but a meaningful
mnemonic name as above is strongly recommended. mnemonic name as above is strongly recommended.
The name may be used as a local index to the key involved and The name may be used as a local index to the key involved and
it is recommended that it be globally unique. Where a key is it is recommended that it be globally unique. Where a key is
just shared between two hosts, its name actually need only be just shared between two hosts, its name actually need only be
meaningful to them but it is recommended that the key name be meaningful to them but it is recommended that the key name be
mnemonic and incorporate the resolver and server host names in mnemonic and incorporates the names of participating agents or
that order. resources.
TYPE TSIG (250: Transaction SIGnature)
CLASS ANY TYPE This MUST be TSIG (250: Transaction SIGnature)
CLASS This MUST be ANY
TTL 0 TTL This MUST be 0
RdLen (variable) RdLen (variable)
RDATA The RDATA for a TSIG RR consists of an octet stream Algorithm RDATA The RDATA for a TSIG RR consists of an octet stream Algorithm
Name field, a uint48_t Time Signed field, a uint16_t Fudge Name field, a uint48_t Time Signed field, a uint16_t Fudge
field, a uint16_t MAC Size field, a octet stream MAC field, a field, a uint16_t MAC Size field, a octet stream MAC field, a
uint16_t Original ID, a uint16_t Error field, a uint16_t Other uint16_t Original ID, a uint16_t Error field, a uint16_t Other
Len field and an octet stream of Other Data. Len field and an octet stream of Other Data.
1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
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| Original ID | Error | | Original ID | Error |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Other Len | / | Other Len | /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Other Data / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Other Data /
/ / / /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The contents of the RDATA fields are: The contents of the RDATA fields are:
* Algorithm Name - identifies the TSIG algorithm name in the * Algorithm Name - identifies the TSIG algorithm name in the
domain name syntax. domain name syntax. (Allowed names are listed in Table 1.)
The name is stored in the DNS name wire format as described
in [RFC1034]. As per [RFC3597], this name MUST NOT be
compressed.
* Time Signed - time signed as seconds since 00:00 on * Time Signed - time signed as seconds since 00:00 on
1970-01-01 UTC ignoring leap seconds. 1970-01-01 UTC ignoring leap seconds.
* Fudge - specifies the allowed time difference in seconds * Fudge - specifies the allowed time difference in seconds
permitted in the Time Signed field. permitted in the Time Signed field.
* MAC Size - the length of MAC field in octets. Truncation is * MAC Size - the length of MAC field in octets. Truncation is
indicated by a MAC size less than the size of the keyed hash indicated by a MAC size less than the size of the keyed hash
produced by the algorithm specified by the Algorithm Name. produced by the algorithm specified by the Algorithm Name.
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TYPE TSIG TYPE TSIG
CLASS ANY CLASS ANY
TTL 0 TTL 0
RdLen As appropriate RdLen As appropriate
RDATA RDATA
Field Name Contents Field Name Contents
-------------- ------------------- -------------- ------------------------
Algorithm Name SAMPLE-ALG.EXAMPLE. Algorithm Name HMAC-MD5.SIG-ALG.REG.INT
Time Signed 853804800 Time Signed 853804800
Fudge 300 Fudge 300
MAC Size As appropriate MAC Size As appropriate
MAC As appropriate MAC As appropriate
Original ID As appropriate Original ID As appropriate
Error 0 (NOERROR) Error 0 (NOERROR)
Other Len 0 Other Len 0
Other Data Empty Other Data Empty
5. Protocol Operation 5. Protocol Operation
5.1. Effects of adding TSIG to outgoing message 5.1. Effects of Adding TSIG to Outgoing Messages
Once the outgoing message has been constructed, the HMAC computation Once the outgoing message has been constructed, the HMAC computation
can be performed. The resulting MAC will then be stored in a TSIG can be performed. The resulting MAC will then be stored in a TSIG
which is appended to the additional data section (the ARCOUNT is which is appended to the additional data section (the ARCOUNT is
incremented to reflect this). If the TSIG record cannot be added incremented to reflect the extra RR). If the TSIG record cannot be
without causing the message to be truncated, the server MUST alter added without causing the message to be truncated, the server MUST
the response so that a TSIG can be included. This response consists alter the response so that a TSIG can be included. This response
of only the question and a TSIG record, and has the TC bit set and consists of only the question and a TSIG record, and has the TC bit
RCODE 0 (NOERROR). The client SHOULD at this point retry the request set and RCODE 0 (NOERROR). The client SHOULD at this point retry the
using TCP (per [RFC1035] 4.2.2). request using TCP (per [RFC1035] 4.2.2).
5.2. TSIG processing on incoming messages 5.2. TSIG Processing on Incoming Messages
If an incoming message contains a TSIG record, it MUST be the last If an incoming message contains a TSIG record, it MUST be the last
record in the additional section. Multiple TSIG records are not record in the additional section. Multiple TSIG records are not
allowed. If a TSIG record is present in any other position, the DNS allowed. If a TSIG record is present in any other position, the DNS
message is dropped and a response with RCODE 1 (FORMERR) MUST be message is dropped and a response with RCODE 1 (FORMERR) MUST be
returned. Upon receipt of a message with exactly one correctly returned. Upon receipt of a message with exactly one correctly
placed TSIG RR, the TSIG RR is copied to a safe location, removed placed TSIG RR, the TSIG RR is copied to a safe location, removed
from the DNS Message, and decremented out of the DNS message header's from the DNS Message, and decremented out of the DNS message header's
ARCOUNT. At this point the keyed hash (HMAC) computation is ARCOUNT. At this point the keyed hash (HMAC) computation is
performed. performed.
If the algorithm name or key name is unknown to the recipient, or if If the algorithm name or key name is unknown to the recipient, or if
the MACs do not match, the whole DNS message MUST be discarded. If the MACs do not match, the whole DNS message MUST be discarded. If
the message is a query, a response with RCODE 9 (NOTAUTH) MUST be the message is a query, a response with RCODE 9 (NOTAUTH) MUST be
sent back to the originator with TSIG ERROR 17 (BADKEY) or TSIG ERROR sent back to the originator with TSIG ERROR 17 (BADKEY) or TSIG ERROR
16 (BADSIG). If no key is available to sign this message it MUST be 16 (BADSIG). If no key is available to sign this message it MUST be
sent unsigned (MAC size == 0 and empty MAC). Algorithm name and time sent unsigned (MAC size == 0 and empty MAC). The algorithm name,
signed and fudge fields SHOULD be copied to the response to provide time signed, and fudge fields SHOULD be copied to the response to
off path spoof protection. A message to the system operations log provide off path spoof protection. A message to the system
SHOULD be generated, to warn the operations staff of a possible operations log SHOULD be generated, to warn the operations staff of a
security incident in progress. Care should be taken to ensure that possible security incident in progress. Care should be taken to
logging of this type of event does not open the system to a denial of ensure that logging of this type of event does not open the system to
service attack. a denial of service attack.
Until these error checks are successfully passed, concluding that the Until these error checks are successfully passed, concluding that the
signature is valid, the signature MUST be considered to be invalid. signature is valid, the signature MUST be considered to be invalid.
5.3. Time values used in TSIG calculations 5.3. Time Values Used in TSIG Calculations
The data digested includes the two timer values in the TSIG header in The data digested includes the two timer values in the TSIG header in
order to defend against replay attacks. If this were not done, an order to defend against replay attacks. If this were not done, an
attacker could replay old messages but update the "Time Signed" and attacker could replay old messages but update the "Time Signed" and
"Fudge" fields to make the message look new. This data is named "Fudge" fields to make the message look new. This data is named
"TSIG Timers", and for the purpose of MAC calculation they are hashed "TSIG Timers", and for the purpose of MAC calculation, they are
in their "on the wire" format, in the following order: first Time hashed in their "on the wire" format, in the following order: first
Signed, then Fudge. For example: Time Signed, then Fudge. For example:
Field Name Value Wire Format Meaning Field Name Value Wire Format Meaning
----------- --------- ----------------- ------------------------ ----------- --------- ----------------- ------------------------
Time Signed 853804800 00 00 32 e4 07 00 Tue Jan 21 00:00:00 1997 Time Signed 853804800 00 00 32 e4 07 00 Tue Jan 21 00:00:00 1997
Fudge 300 01 2C 5 minutes Fudge 300 01 2C 5 minutes
5.4. TSIG Variables and Coverage 5.4. TSIG Variables and Coverage
When generating or verifying the contents of a TSIG record, the When generating or verifying the contents of a TSIG record, the
following data are passed as input to MAC computation, in network following data are passed as input to MAC computation, in network
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The request's MAC is digested in wire format, including the following The request's MAC is digested in wire format, including the following
fields: fields:
Field Type Description Field Type Description
---------- ------------ ---------------------- ---------- ------------ ----------------------
MAC Length uint16_t in network byte order MAC Length uint16_t in network byte order
MAC Data octet stream exactly as transmitted MAC Data octet stream exactly as transmitted
5.5. Component Padding 5.5. Component Padding
Digested components (i.e., inputs to keyed hash computation) are fed Digested components (i.e., inputs to the keyed hash computation) are
into the hashing function as a continuous octet stream with no fed into the hashing function as a continuous octet stream with no
interfield separator or padding. interfield separator or padding.
6. Protocol Details 6. Protocol Details
6.1. TSIG generation on requests 6.1. TSIG Generation on Requests
Client performs the keyed hash (HMAC) computation and appends a TSIG The client performs the keyed hash (HMAC) computation and appends a
record to the additional data section and transmits the request to TSIG record to the additional data section and transmits the request
the server. The client MUST store the MAC from the request while to the server. The client MUST store the MAC from the request while
awaiting an answer. The digest components for a request are: awaiting an answer. The digest components for a request are:
DNS Message (request) DNS Message (request)
TSIG Variables (request) TSIG Variables (request)
Note that some older name servers will not accept requests with a Note that some older name servers will not accept requests with a
nonempty additional data section. Clients SHOULD only attempt signed nonempty additional data section. Clients SHOULD only attempt signed
transactions with servers who are known to support TSIG and share transactions with servers who are known to support TSIG and share
some algorithm and secret key with the client -- so, this is not a some algorithm and secret key with the client -- so, this is not a
problem in practice. problem in practice.
skipping to change at page 11, line 17 skipping to change at page 11, line 17
Signing responses to unsigned TKEY requests MUST be explicitly Signing responses to unsigned TKEY requests MUST be explicitly
specified in the description of an individual secret key specified in the description of an individual secret key
establishment algorithm [RFC3645]. establishment algorithm [RFC3645].
The digest components are: The digest components are:
Request MAC Request MAC
DNS Message (response) DNS Message (response)
TSIG Variables (response) TSIG Variables (response)
6.3. TSIG on TSIG Error returns 6.3. TSIG on TSIG Error Returns
When a server detects an error relating to the key or MAC, the server When a server detects an error relating to the key or MAC, the server
SHOULD send back an unsigned error message (MAC size == 0 and empty SHOULD send back an unsigned error message (MAC size == 0 and empty
MAC). It MUST NOT send back a signed error message. MAC). It MUST NOT send back a signed error message.
If an error is detected relating to the TSIG validity period or the If an error is detected relating to the TSIG validity period or the
MAC is too short for the local policy, the server SHOULD send back a MAC is too short for the local policy, the server SHOULD send back a
signed error message. The digest components are: signed error message. The digest components are:
Request MAC (if the request MAC validated) Request MAC (if the request MAC validated)
DNS Message (response) DNS Message (response)
TSIG Variables (response) TSIG Variables (response)
The reason that the request is not included in this MAC in some cases The reason that the request is not included in this MAC in some cases
is to make it possible for the client to verify the error. If the is to make it possible for the client to verify the error. If the
error is not a TSIG error the response MUST be generated as specified error is not a TSIG error the response MUST be generated as specified
in Section 6.2. in Section 6.2.
6.4. TSIG on zone transfer over a TCP connection 6.4. TSIG on Zone Transfer Over a TCP Connection
A zone transfer over a DNS TCP session can include multiple DNS A zone transfer over a DNS TCP session can include multiple DNS
messages. Using TSIG on such a connection can protect the connection messages. Using TSIG on such a connection can protect the connection
from hijacking and provide data integrity. The TSIG MUST be included from hijacking and provide data integrity. The TSIG MUST be included
on the first and last DNS messages, and SHOULD be placed on all on the first and last DNS messages, and SHOULD be placed on all
intermediary messages. For backward compatibility, a client which intermediary messages. For backward compatibility, a client which
receives DNS messages and verifies TSIG MUST accept up to 99 receives DNS messages and verifies TSIG MUST accept up to 99
intermediary messages without a TSIG. The first envelope is intermediary messages without a TSIG. The first message is processed
processed as a standard answer, and subsequent messages have the as a standard answer (see Section 6.2) and subsequent messages have
following digest components: the following digest components:
Prior MAC (running) Prior MAC (running)
DNS Messages (any unsigned messages since the last TSIG) DNS Messages (any unsigned messages since the last TSIG)
TSIG Timers (current message) TSIG Timers (current message)
This allows the client to rapidly detect when the session has been This allows the client to rapidly detect when the session has been
altered; at which point it can close the connection and retry. If a altered; at which point it can close the connection and retry. If a
client TSIG verification fails, the client MUST close the connection. client TSIG verification fails, the client MUST close the connection.
If the client does not receive TSIG records frequently enough (as If the client does not receive TSIG records frequently enough (as
specified above) it SHOULD assume the connection has been hijacked specified above) it SHOULD assume the connection has been hijacked
and it SHOULD close the connection. The client SHOULD treat this the and it SHOULD close the connection. The client SHOULD treat this the
same way as they would any other interrupted transfer (although the same way as they would any other interrupted transfer (although the
exact behavior is not specified). exact behavior is not specified here).
6.5. Server TSIG checks 6.5. Server TSIG checks
Upon receipt of a message, server will check if there is a TSIG RR. Upon receipt of a message, server will check if there is a TSIG RR.
If one exists, the server is REQUIRED to return a TSIG RR in the If one exists, the server is REQUIRED to return a TSIG RR in the
response. The server MUST perform the following checks in the response. The server MUST perform the following checks in the
following order, check KEY, check MAC, check TIME values, check following order, check KEY, check MAC, check TIME values, check
Truncation policy. Truncation policy.
6.5.1. Key check and error handling 6.5.1. Key Check and Error Handling
If a non-forwarding server does not recognize the key used by the If a non-forwarding server does not recognize the key used by the
client, the server MUST generate an error response with RCODE 9 client, the server MUST generate an error response with RCODE 9
(NOTAUTH) and TSIG ERROR 17 (BADKEY). This response MUST be unsigned (NOTAUTH) and TSIG ERROR 17 (BADKEY). This response MUST be unsigned
as specified in Section 6.3. The server SHOULD log the error. as specified in Section 6.3. The server SHOULD log the error.
(Special considerations apply to forwarding servers, see (Special considerations apply to forwarding servers, see
Section 6.7.) Section 6.7.)
6.5.2. MAC check and error handling 6.5.2. MAC Check and Error Handling
If a TSIG fails to verify, the server MUST generate an error response If a TSIG fails to verify, the server MUST generate an error response
as specified in Section 6.3 with RCODE 9 (NOTAUTH) and TSIG ERROR 16 as specified in Section 6.3 with RCODE 9 (NOTAUTH) and TSIG ERROR 16
(BADSIG). This response MUST be unsigned as specified in (BADSIG). This response MUST be unsigned as specified in
Section 6.3. The server SHOULD log the error. Section 6.3. The server SHOULD log the error.
6.5.2.1. Specifying Truncation 6.5.2.1. Specifying Truncation
When space is at a premium and the strength of the full length of a When space is at a premium and the strength of the full length of a
MAC is not needed, it is reasonable to truncate the keyed hash and MAC is not needed, it is reasonable to truncate the keyed hash and
skipping to change at page 13, line 29 skipping to change at page 13, line 29
TSIG MAC for a reply is the truncated request MAC. TSIG MAC for a reply is the truncated request MAC.
4. "MAC size" field is less than the larger of 10 (octets) and half 4. "MAC size" field is less than the larger of 10 (octets) and half
the length of the hash function in use: the length of the hash function in use:
With the exception of certain TSIG error messages described in With the exception of certain TSIG error messages described in
Section 6.3, where it is permitted that the MAC size be zero, Section 6.3, where it is permitted that the MAC size be zero,
this case MUST NOT be generated and, if received, MUST cause the this case MUST NOT be generated and, if received, MUST cause the
DNS message to be dropped and RCODE 1 (FORMERR) to be returned. DNS message to be dropped and RCODE 1 (FORMERR) to be returned.
6.5.3. Time check and error handling 6.5.3. Time Check and Error Handling
If the server time is outside the time interval specified by the If the server time is outside the time interval specified by the
request (which is: Time Signed, plus/minus Fudge), the server MUST request (which is: Time Signed, plus/minus Fudge), the server MUST
generate an error response with RCODE 9 (NOTAUTH) and TSIG ERROR 18 generate an error response with RCODE 9 (NOTAUTH) and TSIG ERROR 18
(BADTIME). The server SHOULD also cache the most recent time signed (BADTIME). The server SHOULD also cache the most recent time signed
value in a message generated by a key, and SHOULD return BADTIME if a value in a message generated by a key, and SHOULD return BADTIME if a
message received later has an earlier time signed value. A response message received later has an earlier time signed value. A response
indicating a BADTIME error MUST be signed by the same key as the indicating a BADTIME error MUST be signed by the same key as the
request. It MUST include the client's current time in the time request. It MUST include the client's current time in the time
signed field, the server's current time (a uint48_t) in the other signed field, the server's current time (a uint48_t) in the other
data field, and 6 in the other data length field. This is done so data field, and 6 in the other data length field. This is done so
that the client can verify a message with a BADTIME error without the that the client can verify a message with a BADTIME error without the
verification failing due to another BADTIME error. The data signed verification failing due to another BADTIME error. The data signed
is specified in Section 6.3. The server SHOULD log the error. is specified in Section 6.3. The server SHOULD log the error.
6.5.4. Truncation check and error handling 6.5.4. Truncation Check and Error Handling
If a TSIG is received with truncation that is permitted under If a TSIG is received with truncation that is permitted under
Section 6.5.2.1 above but the MAC is too short for the local policy Section 6.5.2.1 above but the MAC is too short for the local policy
in force, an RCODE 9 (NOTAUTH) and TSIG ERROR 22 (BADTRUNC) MUST be in force, an RCODE 9 (NOTAUTH) and TSIG ERROR 22 (BADTRUNC) MUST be
returned. The server SHOULD log the error. returned. The server SHOULD log the error.
6.6. Client processing of answer 6.6. Client Processing of Answer
When a client receives a response from a server and expects to see a When a client receives a response from a server and expects to see a
TSIG, it first checks if the TSIG RR is present in the response. TSIG, it first checks if the TSIG RR is present in the response.
Otherwise, the response is treated as having a format error and Otherwise, the response is treated as having a format error and
discarded. The client then extracts the TSIG, adjusts the ARCOUNT, discarded. The client then extracts the TSIG, adjusts the ARCOUNT,
and calculates the MAC in the same way as the server, applying the and calculates the MAC in the same way as the server, applying the
same rules to decide if truncated MAC is valid. If the TSIG does not same rules to decide if truncated MAC is valid. If the TSIG does not
validate, that response MUST be discarded, unless the RCODE is 9 validate, that response MUST be discarded, unless the RCODE is 9
(NOTAUTH), in which case the client SHOULD attempt to verify the (NOTAUTH), in which case the client SHOULD attempt to verify the
response as if it were a TSIG Error response, as specified in response as if it were a TSIG Error response, as specified in
Section 6.3. A message containing an unsigned TSIG record or a TSIG Section 6.3. A message containing an unsigned TSIG record or a TSIG
record which fails verification SHOULD NOT be considered an record which fails verification SHOULD NOT be considered an
acceptable response; the client SHOULD log an error and continue to acceptable response; the client SHOULD log an error and continue to
wait for a signed response until the request times out. wait for a signed response until the request times out.
6.6.1. Key error handling 6.6.1. Key Error Handling
If an RCODE on a response is 9 (NOTAUTH), and the response TSIG If an RCODE on a response is 9 (NOTAUTH), and the response TSIG
validates, and the TSIG key is different from the key used on the validates, and the TSIG key is different from the key used on the
request, then this is a Key error. The client MAY retry the request request, then this is a Key error. The client MAY retry the request
using the key specified by the server. This should never occur, as a using the key specified by the server. This should never occur, as a
server MUST NOT sign a response with a different key than signed the server MUST NOT sign a response with a different key than signed the
request. request.
6.6.2. MAC error handling 6.6.2. MAC Error Handling
If the response RCODE is 9 (NOTAUTH) and TSIG ERROR is 16 (BADSIG), If the response RCODE is 9 (NOTAUTH) and TSIG ERROR is 16 (BADSIG),
this is a MAC error, and client MAY retry the request with a new this is a MAC error, and client MAY retry the request with a new
request ID but it would be better to try a different shared key if request ID but it would be better to try a different shared key if
one is available. Clients SHOULD keep track of how many MAC errors one is available. Clients SHOULD keep track of how many MAC errors
are associated with each key. Clients SHOULD log this event. are associated with each key. Clients SHOULD log this event.
6.6.3. Time error handling 6.6.3. Time Error Handling
If the response RCODE is 9 (NOTAUTH) and the TSIG ERROR is 18 If the response RCODE is 9 (NOTAUTH) and the TSIG ERROR is 18
(BADTIME), or the current time does not fall in the range specified (BADTIME), or the current time does not fall in the range specified
in the TSIG record, then this is a Time error. This is an indication in the TSIG record, then this is a Time error. This is an indication
that the client and server clocks are not synchronized. In this case that the client and server clocks are not synchronized. In this case
the client SHOULD log the event. DNS resolvers MUST NOT adjust any the client SHOULD log the event. DNS resolvers MUST NOT adjust any
clocks in the client based on BADTIME errors, but the server's time clocks in the client based on BADTIME errors, but the server's time
in the other data field SHOULD be logged. in the other data field SHOULD be logged.
6.6.4. Truncation error handling 6.6.4. Truncation Error Handling
If the response RCODE is 9 (NOTAUTH) and the TSIG ERROR is 22 If the response RCODE is 9 (NOTAUTH) and the TSIG ERROR is 22
(BADTRUNC) then this is a Truncation error. The client MAY retry (BADTRUNC) then this is a Truncation error. The client MAY retry
with a lesser truncation up to the full HMAC output (no truncation), with a lesser truncation up to the full HMAC output (no truncation),
using the truncation used in the response as a hint for what the using the truncation used in the response as a hint for what the
server policy allowed (Section 8). Clients SHOULD log this event. server policy allowed (Section 8). Clients SHOULD log this event.
6.7. Special considerations for forwarding servers 6.7. Special Considerations for Forwarding Servers
A server acting as a forwarding server of a DNS message SHOULD check A server acting as a forwarding server of a DNS message SHOULD check
for the existence of a TSIG record. If the name on the TSIG is not for the existence of a TSIG record. If the name on the TSIG is not
of a secret that the server shares with the originator the server of a secret that the server shares with the originator the server
MUST forward the message unchanged including the TSIG. If the name MUST forward the message unchanged including the TSIG. If the name
of the TSIG is of a key this server shares with the originator, it of the TSIG is of a key this server shares with the originator, it
MUST process the TSIG. If the TSIG passes all checks, the forwarding MUST process the TSIG. If the TSIG passes all checks, the forwarding
server MUST, if possible, include a TSIG of his own, to the server MUST, if possible, include a TSIG of its own, to the
destination or the next forwarder. If no transaction security is destination or the next forwarder. If no transaction security is
available to the destination and the response has the AD flag (see available to the destination and the message is a query then, if the
[RFC4035]), the forwarder MUST unset the AD flag before adding the corresponding response has the AD flag (see [RFC4035]) set, the
TSIG to the answer. forwarder MUST clear the AD flag before adding the TSIG to the
response and returning the result to the system from which it
received the query.
7. Algorithms and Identifiers 7. Algorithms and Identifiers
The only message digest algorithm specified in the first version of The only message digest algorithm specified in the first version of
these specifications [RFC2845] was "HMAC-MD5" (see [RFC1321], these specifications [RFC2845] was "HMAC-MD5" (see [RFC1321],
[RFC2104]). The "HMAC-MD5" algorithm is mandatory to implement for [RFC2104]). The "HMAC-MD5" algorithm is mandatory to implement for
interoperability. interoperability.
The use of SHA-1 [FIPS180-4], [RFC3174], (which is a 160-bit hash as The use of SHA-1 [FIPS180-4], [RFC3174], (which is a 160-bit hash as
compared to the 128 bits for MD5), and additional hash algorithms in compared to the 128 bits for MD5), and additional hash algorithms in
skipping to change at page 16, line 15 skipping to change at page 16, line 15
Requirement Name Requirement Name
----------- ------------------------ ----------- ------------------------
Mandatory HMAC-MD5.SIG-ALG.REG.INT Mandatory HMAC-MD5.SIG-ALG.REG.INT
Optional gss-tsig Optional gss-tsig
Mandatory hmac-sha1 Mandatory hmac-sha1
Optional hmac-sha224 Optional hmac-sha224
Mandatory hmac-sha256 Mandatory hmac-sha256
Optional hmac-sha384 Optional hmac-sha384
Optional hmac-sha512 Optional hmac-sha512
Table 1
SHA-1 truncated to 96 bits (12 octets) SHOULD be implemented. SHA-1 truncated to 96 bits (12 octets) SHOULD be implemented.
8. TSIG Truncation Policy 8. TSIG Truncation Policy
As noted above, two DNS agents (e.g., resolver and server) must As noted above, two DNS agents (e.g., resolver and server) must
mutually agree to use TSIG. Implicit in such an "agreement" are mutually agree to use TSIG. Implicit in such an "agreement" are
criteria as to acceptable keys and algorithms and, with the criteria as to acceptable keys and algorithms and, with the
extensions in this document, truncations. Note that it is common for extensions in this document, truncations. Note that it is common for
implementations to bind the TSIG secret key or keys that may be in implementations to bind the TSIG secret key or keys that may be in
place at two parties to particular algorithms. Thus, such place at two parties to particular algorithms. Thus, such
skipping to change at page 17, line 25 skipping to change at page 17, line 25
A name server usually runs privileged, which means its configuration A name server usually runs privileged, which means its configuration
data need not be visible to all users of the host. For this reason, data need not be visible to all users of the host. For this reason,
a host that implements transaction-based authentication should a host that implements transaction-based authentication should
probably be configured with a "stub resolver" and a local caching and probably be configured with a "stub resolver" and a local caching and
forwarding name server. This presents a special problem for forwarding name server. This presents a special problem for
[RFC2136] which otherwise depends on clients to communicate only with [RFC2136] which otherwise depends on clients to communicate only with
a zone's authoritative name servers. a zone's authoritative name servers.
Use of strong random shared secrets is essential to the security of Use of strong random shared secrets is essential to the security of
TSIG. See [RFC4086] for a discussion of this issue. The secret TSIG. See [RFC4086] for a discussion of this issue. The secret
SHOULD be at least as long as the keyed hash output, i.e., 16 bytes SHOULD be at least as long as the keyed hash output [RFC2104].
for HMAC-MD5 or 20 bytes for HMAC-SHA1.
10. IANA Considerations 10. IANA Considerations
IANA maintains a registry of algorithm names to be used as "Algorithm IANA maintains a registry of algorithm names to be used as "Algorithm
Names" as defined in Section 4.3. Algorithm names are text strings Names" as defined in Section 4.3. Algorithm names are text strings
encoded using the syntax of a domain name. There is no structure encoded using the syntax of a domain name. There is no structure
required other than names for different algorithms must be unique required other than names for different algorithms must be unique
when compared as DNS names, i.e., comparison is case insensitive. when compared as DNS names, i.e., comparison is case insensitive.
Previous specifications [RFC2845] and [RFC4635] defined values for Previous specifications [RFC2845] and [RFC4635] defined values for
HMAC MD5 and SHA. IANA has also registered "gss-tsig" as an HMAC MD5 and SHA. IANA has also registered "gss-tsig" as an
skipping to change at page 18, line 12 skipping to change at page 18, line 12
Section 4.3. New error codes are assigned and specified as in Section 4.3. New error codes are assigned and specified as in
[RFC6895]. [RFC6895].
11. Security Considerations 11. Security Considerations
The approach specified here is computationally much less expensive The approach specified here is computationally much less expensive
than the signatures specified in DNSSEC. As long as the shared than the signatures specified in DNSSEC. As long as the shared
secret key is not compromised, strong authentication is provided secret key is not compromised, strong authentication is provided
between two DNS systems, e.g., for the last hop from a local name between two DNS systems, e.g., for the last hop from a local name
server to the user resolver, or between primary and secondary server to the user resolver, or between primary and secondary
nameservers.. nameservers.
Secret keys should be changed periodically. If the client host has Recommendations for choosing and maintaining secret keys can be found
been compromised, the server should suspend the use of all secrets in [RFC2104]. If the client host has been compromised, the server
known to that client. If possible, secrets should be stored in should suspend the use of all secrets known to that client. If
encrypted form. Secrets should never be transmitted in the clear possible, secrets should be stored in encrypted form. Secrets should
over any network. This document does not address the issue on how to never be transmitted in the clear over any network. This document
distribute secrets except that it mentions the possibilities of does not address the issue on how to distribute secrets except that
manual configuration and the use of TKEY [RFC2930]. Secrets SHOULD it mentions the possibilities of manual configuration and the use of
NOT be shared by more than two entities. TKEY [RFC2930]. Secrets SHOULD NOT be shared by more than two
entities.
This mechanism does not authenticate source data, only its This mechanism does not authenticate source data, only its
transmission between two parties who share some secret. The original transmission between two parties who share some secret. The original
source data can come from a compromised zone master or can be source data can come from a compromised zone master or can be
corrupted during transit from an authentic zone master to some corrupted during transit from an authentic zone master to some
"caching forwarder." However, if the server is faithfully performing "caching forwarder." However, if the server is faithfully performing
the full DNSSEC security checks, then only security checked data will the full DNSSEC security checks, then only security checked data will
be available to the client. be available to the client.
A fudge value that is too large may leave the server open to replay A fudge value that is too large may leave the server open to replay
attacks. A fudge value that is too small may cause failures if attacks. A fudge value that is too small may cause failures if
machines are not time synchronized or there are unexpected network machines are not time synchronized or there are unexpected network
delays. The recommended value in most situations is 300 seconds. delays. The RECOMMENDED value in most situations is 300 seconds.
For all of the message authentication code algorithms listed in this For all of the message authentication code algorithms listed in this
document, those producing longer values are believed to be stronger; document, those producing longer values are believed to be stronger;
however, while there have been some arguments that mild truncation however, while there have been some arguments that mild truncation
can strengthen a MAC by reducing the information available to an can strengthen a MAC by reducing the information available to an
attacker, excessive truncation clearly weakens authentication by attacker, excessive truncation clearly weakens authentication by
reducing the number of bits an attacker has to try to break the reducing the number of bits an attacker has to try to break the
authentication by brute force [RFC2104]. authentication by brute force [RFC2104].
Significant progress has been made recently in cryptanalysis of hash Significant progress has been made recently in cryptanalysis of hash
functions of the types used here, all of which ultimately derive from functions of the types used here. While the results so far should
the design of MD4. While the results so far should not effect HMAC, not affect HMAC, the stronger SHA-1 and SHA-256 algorithms are being
the stronger SHA-1 and SHA-256 algorithms are being made mandatory made mandatory as a precaution.
due to caution. Note that today SHA-3 [FIPS202] is available as an
alternative to SHA-2 using a very different design.
See also the Security Considerations section of [RFC2104] from which See also the Security Considerations section of [RFC2104] from which
the limits on truncation in this RFC were taken. the limits on truncation in this RFC were taken.
11.1. Issue fixed in this document 11.1. Issue Fixed in this Document
When signing a DNS reply message using TSIG, the MAC computation uses When signing a DNS reply message using TSIG, the MAC computation uses
the request message's MAC as an input to cryptographically relate the the request message's MAC as an input to cryptographically relate the
reply to the request. The original TSIG specification [RFC2845] reply to the request. The original TSIG specification [RFC2845]
required that the TIME values be checked before the request's MAC. required that the TIME values be checked before the request's MAC.
If the TIME was invalid, some implementations failed to carry out If the TIME was invalid, some implementations failed to carry out
further checks and could use an invalid request MAC in the signed further checks and could use an invalid request MAC in the signed
reply. reply.
This document proposes the principle that the request MAC must be This document makes it a madatory that the request MAC is considered
considered to be invalid until it has been validated: until then, any to be invalid until it has been validated: until then, any answer
answer must be unsigned. For this reason, the request MAC is now must be unsigned. For this reason, the request MAC is now checked
checked before the TIME value. before the TIME value.
11.2. Why not DNSSEC? 11.2. Why not DNSSEC?
This section from the original document [RFC2845] analyzes DNSSEC in This section from the original document [RFC2845] analyzes DNSSEC in
order to justify the introduction of TSIG. order to justify the introduction of TSIG.
DNS has recently been extended by DNSSEC ([RFC4033], [RFC4034] and DNS has recently been extended by DNSSEC ([RFC4033], [RFC4034] and
[RFC4035]) to provide for data origin authentication, and public key [RFC4035]) to provide for data origin authentication, and public key
distribution, all based on public key cryptography and public key distribution, all based on public key cryptography and public key
based digital signatures. To be practical, this form of security based digital signatures. To be practical, this form of security
skipping to change at page 20, line 31 skipping to change at page 20, line 31
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC2845] Vixie, P., Gudmundsson, O., Eastlake 3rd, D., and B. [RFC2845] Vixie, P., Gudmundsson, O., Eastlake 3rd, D., and B.
Wellington, "Secret Key Transaction Authentication for DNS Wellington, "Secret Key Transaction Authentication for DNS
(TSIG)", RFC 2845, DOI 10.17487/RFC2845, May 2000, (TSIG)", RFC 2845, DOI 10.17487/RFC2845, May 2000,
<https://www.rfc-editor.org/info/rfc2845>. <https://www.rfc-editor.org/info/rfc2845>.
[RFC3597] Gustafsson, A., "Handling of Unknown DNS Resource Record
(RR) Types", RFC 3597, DOI 10.17487/RFC3597, September
2003, <https://www.rfc-editor.org/info/rfc3597>.
[RFC4635] Eastlake 3rd, D., "HMAC SHA (Hashed Message Authentication [RFC4635] Eastlake 3rd, D., "HMAC SHA (Hashed Message Authentication
Code, Secure Hash Algorithm) TSIG Algorithm Identifiers", Code, Secure Hash Algorithm) TSIG Algorithm Identifiers",
RFC 4635, DOI 10.17487/RFC4635, August 2006, RFC 4635, DOI 10.17487/RFC4635, August 2006,
<https://www.rfc-editor.org/info/rfc4635>. <https://www.rfc-editor.org/info/rfc4635>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
12.2. Informative References 12.2. Informative References
[FIPS202] National Institute of Standards and Technology, "SHA-3
Standard", FIPS PUB 202, August 2015.
[RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321, [RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
DOI 10.17487/RFC1321, April 1992, DOI 10.17487/RFC1321, April 1992,
<https://www.rfc-editor.org/info/rfc1321>. <https://www.rfc-editor.org/info/rfc1321>.
[RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed- [RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
Hashing for Message Authentication", RFC 2104, Hashing for Message Authentication", RFC 2104,
DOI 10.17487/RFC2104, February 1997, DOI 10.17487/RFC2104, February 1997,
<https://www.rfc-editor.org/info/rfc2104>. <https://www.rfc-editor.org/info/rfc2104>.
[RFC2136] Vixie, P., Ed., Thomson, S., Rekhter, Y., and J. Bound, [RFC2136] Vixie, P., Ed., Thomson, S., Rekhter, Y., and J. Bound,
skipping to change at page 22, line 34 skipping to change at page 22, line 39
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26, Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017, RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>. <https://www.rfc-editor.org/info/rfc8126>.
Appendix A. Acknowledgments Appendix A. Acknowledgments
This document consolidates and updates the earlier documents by the This document consolidates and updates the earlier documents by the
authors of [RFC2845] (Paul Vixie, Olafur Gudmundsson, Donald E. authors of [RFC2845] (Paul Vixie, Olafur Gudmundsson, Donald E.
Eastlake 3rd and Brian Wellington) and [RFC4635] (Donald E. Eastlake Eastlake 3rd and Brian Wellington) and [RFC4635] (Donald E. Eastlake
3rd). It would not be possible without their original work. 3rd).
The security problem addressed by this document was reported by The security problem addressed by this document was reported by
Clement Berthaux from Synacktiv. Clement Berthaux from Synacktiv.
Note for the RFC Editor (to be removed before publication): the first Note for the RFC Editor (to be removed before publication): the first
'e' in Clement is a fact a small 'e' with acute, unicode code U+00E9. 'e' in Clement is a fact a small 'e' with acute, unicode code U+00E9.
I do not know if xml2rfc supports non ASCII characters so I prefer to I do not know if xml2rfc supports non ASCII characters so I prefer to
not experiment with it. BTW I am French too so I can help if you not experiment with it. BTW I am French too so I can help if you
have questions like correct spelling... have questions like correct spelling...
skipping to change at page 25, line 5 skipping to change at page 24, line 51
Many improvements in the wording. Many improvements in the wording.
Added RFC 2845 authors as co-authors of this document. Added RFC 2845 authors as co-authors of this document.
draft-ietf-dnsop-rfc2845bis-02 draft-ietf-dnsop-rfc2845bis-02
Added a recommendation to copy time fields in BADKEY errors. Added a recommendation to copy time fields in BADKEY errors.
(Mark Andrews) (Mark Andrews)
draft-ietf-dnsop-rfc2845bis-03
Further changes as a result of comments by Mukund Sivaraman.
Miscellaneous changes to wording.
Authors' Addresses Authors' Addresses
Francis Dupont Francis Dupont
Internet Software Consortium Internet Software Consortium
950 Charter Street 950 Charter Street
Redwood City, CA 94063 Redwood City, CA 94063
United States of America United States of America
Email: Francis.Dupont@fdupont.fr Email: Francis.Dupont@fdupont.fr
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