ComputerSurge/bind9
3
0
Fork 0
Code Pull Requests 1 Activity
Files
fd6574dbc551faac89ae2ce6f3549fed51c24e49
bind9/doc/draft/draft-ietf-dnsext-nsec3-01.txt
Mark Andrews 4f7f21e50d new draft
2005-02-24 03:22:23 +00:00

1010 lines
36 KiB
Plaintext
Raw Blame History

This file contains invisible Unicode characters
This file contains invisible Unicode characters that are indistinguishable to humans but may be processed differently by a computer. If you think that this is intentional, you can safely ignore this warning. Use the Escape button to reveal them.
Network Working Group B. Laurie
Internet-Draft G. Sisson
Expires: August 2, 2005 Nominet
R. Arends
Telematica Instituut
february 2005
DNSSEC Hash Authenticated Denial of Existence
draft-ietf-dnsext-nsec3-01
Status of this Memo
This document is an Internet-Draft and is subject to all provisions
of section 3 of RFC 3667. By submitting this Internet-Draft, each
author represents that any applicable patent or other IPR claims of
which he or she is aware have been or will be disclosed, and any of
which he or she become aware will be disclosed, in accordance with
RFC 3668.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as
Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on August 2, 2005.
Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
The DNS Security (DNSSEC) NSEC resource record (RR) is intended to be
used to provide authenticated denial of existence of DNS ownernames
and types; however, it permits any user to traverse a zone and obtain
a listing of all ownernames.
Laurie, et al. Expires August 2, 2005 [Page 1]
Internet-Draft nsec3 february 2005
A complete zone file can be used either directly as a source of
probable e-mail addresses for spam, or indirectly as a key for
multiple WHOIS queries to reveal registrant data which many
registries (particularly in Europe) may be under strict legal
obligations to protect. Many registries therefore prohibit copying
of their zone file; however the use of NSEC RRs makes renders
policies unenforceable.
This document proposes a scheme which obscures original ownernames
while permitting authenticated denial of existence of non-existent
names. Non-authoritative delegation point NS RR types may be
excluded.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1 Rationale . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2 Reserved Words . . . . . . . . . . . . . . . . . . . . . . 4
1.3 Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. The NSEC3 Resource Record . . . . . . . . . . . . . . . . . . 5
2.1 NSEC3 RDATA Wire Format . . . . . . . . . . . . . . . . . 5
2.1.1 The Authoritative Only Flag Field . . . . . . . . . . 6
2.1.2 The Hash Function Field . . . . . . . . . . . . . . . 6
2.1.3 The Iterations Field . . . . . . . . . . . . . . . . . 6
2.1.4 The Salt Length Field . . . . . . . . . . . . . . . . 6
2.1.5 The Salt Field . . . . . . . . . . . . . . . . . . . . 6
2.1.6 The Next Hashed Ownername Field . . . . . . . . . . . 7
2.1.7 The list of Type Bit Map(s) Field . . . . . . . . . . 7
2.2 The NSEC3 RR Presentation Format . . . . . . . . . . . . . 8
3. Creating Additional NSEC3 RR for Empty Non Terminals . . . . . 9
4. Calculation of the Hash . . . . . . . . . . . . . . . . . . . 9
5. Including NSEC3 RRs in a Zone . . . . . . . . . . . . . . . . 9
6. Special Considerations . . . . . . . . . . . . . . . . . . . . 10
6.1 delegation points . . . . . . . . . . . . . . . . . . . . 10
6.1.1 Unsigned Delegations . . . . . . . . . . . . . . . . . 11
6.2 Additional Complexity Caused by Wildcards . . . . . . . . 11
6.3 Salting . . . . . . . . . . . . . . . . . . . . . . . . . 12
6.4 Hash Collision . . . . . . . . . . . . . . . . . . . . . . 12
6.4.1 Avoiding Hash Collisions during generation . . . . . . 12
6.4.2 Second Preimage Requirement Analysis . . . . . . . . . 12
6.4.3 Possible Hash Value Truncation Method . . . . . . . . 13
7. Performance Considerations . . . . . . . . . . . . . . . . . . 13
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
9. Security Considerations . . . . . . . . . . . . . . . . . . . 14
10. Requirements notation . . . . . . . . . . . . . . . . . . . 14
11. Security Considerations . . . . . . . . . . . . . . . . . . 14
A. Example Zone . . . . . . . . . . . . . . . . . . . . . . . . . 14
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 15
Laurie, et al. Expires August 2, 2005 [Page 2]
Internet-Draft nsec3 february 2005
12.1 Normative References . . . . . . . . . . . . . . . . . . . . 15
12.2 Informative References . . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 16
Intellectual Property and Copyright Statements . . . . . . . . 18
Laurie, et al. Expires August 2, 2005 [Page 3]
Internet-Draft nsec3 february 2005
1. Introduction
The DNS Security Extensions (DNSSEC) introduced the NSEC Resource
Record (RR) for Authenticated Denial of Existence. This document
introduces a new RR as an alternative to NSEC that provides measures
against zone traversal and allows for gradual expansion of
delegation-centric zones.
1.1 Rationale
The DNS Security Extensions included the NSEC RR to provide
authenticated denial of existence. Though the NSEC RR meets the
requirements for authenticated denial of Existence, it introduced a
side-effect in that the contents of a zone can be enumerated. This
property introduces undesired policy issues.
A second requirement was that the existence of all record types in a
zone -including delegation point NS record types- can be accounted
for, despite the fact that delegation point NS RRsets are not
authoritative and not signed. This requirement has a side-effect
that the overhead of delegation centric signed zones is not related
to the increase in security of subzones. This requirement does not
allow delegation centric zones size to grow in relation to the growth
of signed subzones.
In the past, solutions have been proposed as a measure against these
side effects but at the time were regarded as secondary over the need
to have a stable DNSSEC specification. With (draft-vixie-dnssec-ter)
a graceful transition path to future enhancements is introduced,
while current DNSSEC deployment can continue. This document
accumulates measures against the side effects introduced by NSEC, and
presents the NSEC3 Resource Record.
The reader is assumed to be familiar with the basic DNS concepts
described in RFC1034 [RFC1034], RFC1035 [RFC1035] and subsequent RFCs
that update them: RFC2136 [RFC2136], RFC2181 [RFC2181] and RFC2308
[RFC2308].
1.2 Reserved Words
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
1.3 Terminology
In this document the term "original ownername" refers to a standard
ownername. Because this proposal uses the result of a hash function
Laurie, et al. Expires August 2, 2005 [Page 4]
Internet-Draft nsec3 february 2005
over the original (unmodified) ownername, this result is referred to
as "hashed ownername".
2. The NSEC3 Resource Record
The NSEC3 RR provides Authenticated Denial of Existence for DNS
Resource Record Sets.
The NSEC3 Resource Record lists RR types present at the NSEC3 RR's
original ownername. It includes the next hashed ownername in the
canonical ordering of the zone. The complete set of NSEC3 RRs in a
zone indicates which RRsets exist for the original ownername of the
RRset and form a chain of hashed ownernames in the zone. This
information is used to provide authenticated denial of existence for
DNS data, as described in RFC 2535 [RFC2535]. Unsigned delegation
point NS RR sets can optionally be excluded. To provide protection
against zone traversal, the ownernames used in the NSEC3 RR are
cryptographic hash-value prepended to the name of the zone. The
NSEC3 RR record indicates which Hash Function is used to construct to
hash, which Salt is used, and how many iterations of the Hash
Function are performed over the original ownername.
The type value for the NSEC3 RR is XX.
The NSEC3 RR RDATA format is class independent.
The NSEC3 RR SHOULD have the same TTL value as the SOA minimum TTL
field. This is in the spirit of negative caching [RFC2308].
2.1 NSEC3 RDATA Wire Format
The RDATA of the NSEC3 RR is as shown below:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|A|Hash Function| Iterations |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Salt Length | Salt /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ Next Hashed Ownername /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ Type Bit Maps /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Laurie, et al. Expires August 2, 2005 [Page 5]
Internet-Draft nsec3 february 2005
2.1.1 The Authoritative Only Flag Field
The Authoritative Only Flag field indicates whether the Type Bit Maps
include delegation point NS record types.
If the flag is set to 1, the NS RR type bit for a delegation point
ownername SHOULD be clear when the NSEC3 RR is generated. The NS RR
type bit MUST be ignored during processing of the NSEC3 RR. The NS
RR type bit has no meaning in this context (it is not authoritative),
hence the NSEC3 does not contest the existence of a NS RR type record
for this ownername. When a delegation is not secured, there exist no
DS RR type nor any other authoritative types for this delegation,
hence the unsecured delegation has no NSEC3 record associated.
Please see the Special Consideration section for implications for
unsigned delegations.
If the flag is set to 0, the NS RR type bit for a delegation point
ownername MUST be set if the NSEC3 covers a delegation, even though
the NS RR itself is not authoritative. This implies that all
delegations, signed or unsigned, have an NSEC3 record associated.
This behaviour is identical to NSEC behaviour.
2.1.2 The Hash Function Field
The Hash Function field identifies the cryptographic hash function
used to construct the hash-value.
This document defines Value 1 for SHA-1 and Value 127 for
Experimental. All other values are reserved.
On reception, a resolver MUST discard an NSEC3 RR with an unknown
Hash Function value.
2.1.3 The Iterations Field
The Iterations field defines the number of times the hash has been
iterated. More iterations results in greater resiliency of the hash
value against dictionary attacks, but at a higher cost for both the
server and resolver.
2.1.4 The Salt Length Field
The Salt Length Field defines the length of the salt in octets.
2.1.5 The Salt Field
The salt field is not present when the Salt Length Field has a value
of 0.
Laurie, et al. Expires August 2, 2005 [Page 6]
Internet-Draft nsec3 february 2005
The salt field is prepended to the original ownername before hashing
in order to defend against precalculated dictionary attacks.
The salt is not prepended during iterations of the hash function.
The Salt field value MUST be identical for all NSEC3 RRs generated
for the zone. If the salt were different for each NSEC3 RR,
collisions could occur where an NSEC3 denies the existence of
existing RRs due to the application of different salt values.
2.1.6 The Next Hashed Ownername Field
The Next Hashed Ownername Field contains the hash of the ownername of
the next RR in the canonical ordering of the hashed ownernames of the
zone. The value of the Next Hashed Ownername Field in the last NSEC3
record in the zone is the same as the ownername of the first NSEC3 RR
in the zone in canonical order.
A sender MUST NOT use DNS name compression on the Next Hashed
Ownername field when transmitting an NSEC3 RR.
Hashed ownernames of RRsets not authoritative for the given zone
(such as glue records) MUST NOT be listed in the Hash of Next Domain
Name unless at least one authoritative RRset exists at the same owner
name.
2.1.7 The list of Type Bit Map(s) Field
The Type Bit Maps field identifies the RRset types which exist at the
NSEC3 RR's ownername.
The Type bit for the NSEC3 and RRSIG MUST be set during generation,
and MUST be ignored during processing.
The RR type space is split into 256 window blocks, each representing
the low-order 8 bits of the 16-bit RR type space. Each block that
has at least one active RR type is encoded using a single octet
window number (from 0 to 255), a single octet bitmap length (from 1
to 32) indicating the number of octets used for the window block's
bitmap, and up to 32 octets (256 bits) of bitmap.
Blocks are present in the NSEC3 RR RDATA in increasing numerical
order.
"|" denotes concatenation
Type Bit Map(s) Field = ( Window Block # | Bitmap Length | Bitmap ) +
Laurie, et al. Expires August 2, 2005 [Page 7]
Internet-Draft nsec3 february 2005
Each bitmap encodes the low-order 8 bits of RR types within the
window block, in network bit order. The first bit is bit 0. For
window block 0, bit 1 corresponds to RR type 1 (A), bit 2 corresponds
to RR type 2 (NS), and so forth. For window block 1, bit 1
corresponds to RR type 257, bit 2 to RR type 258. If a bit is set to
1, it indicates that an RRset of that type is present for the NSEC3
RR's ownername. If a bit is set to 0, it indicates that no RRset of
that type is present for the NSEC3 RR's ownername.
The RR type 2 (NS) is authoritative at the apex of a zone and is not
authoritative at delegation points. If the Authoritative Only Flag
is set to 1, the delegation point NS RR type MUST NOT be included in
the type bit maps. If the Authoritative Only Flag is set to 0, the
NS RR type at a delegation point MUST be included in the type bit
maps.
Since bit 0 in window block 0 refers to the non-existing RR type 0,
it MUST be set to 0. After verification, the validator MUST ignore
the value of bit 0 in window block 0.
Bits representing Meta-TYPEs or QTYPEs as specified in RFC 2929 [4]
(section 3.1) or within the range reserved for assignment only to
QTYPEs and Meta-TYPEs MUST be set to 0, since they do not appear in
zone data. If encountered, they must be ignored upon reading.
Blocks with no types present MUST NOT be included. Trailing zero
octets in the bitmap MUST be omitted. The length of each block's
bitmap is determined by the type code with the largest numerical
value, within that block, among the set of RR types present at the
NSEC3 RR's actual ownername. Trailing zero octets not specified MUST
be interpreted as zero octets.
2.2 The NSEC3 RR Presentation Format
The presentation format of the RDATA portion is as follows:
The Authoritative Only Field is represented as an unsigned decimal
integer. The value are either 0 or 1.
The Hash field is presented as the name of the hash or as an unsigned
decimal integer. The value has a maximum of 127.
The Iterations field is presented as an unsigned decimal integer.
The Salt Length field is not presented.
The Salt field is represented as a sequence of case-insensitive
hexadecimal digits. Whitespace is not allowed within the sequence.
Laurie, et al. Expires August 2, 2005 [Page 8]
Internet-Draft nsec3 february 2005
The Salt Field is represented as 00 when the Salt Length field has
value 0.
The Hash of Next Domain Name field is represented as a sequence of
case-insensitive base32 digits. Whitespace is allowed within the
sequence.
The List of Type Bit Map(s) Field is represented as a sequence of RR
type mnemonics. When the mnemonic is not known, the TYPE
representation as described in RFC 3597 [5] (section 5) MUST be used.
3. Creating Additional NSEC3 RR for Empty Non Terminals
In order to prove the non-existence of a record that might be covered
by a wildcard, it is necessary to prove the existence of its closest
encloser. A closest encloser might be an Empty Non Terminal.
Additional NSEC3 RRs cover every existing intermediate label level.
Additional NSEC3 RRs are identical in format to NSEC3 RRs that cover
existing RRs in the zone. The difference is that the type-bit-maps
only indicate the existence of an NSEC3 RR and a RRSIG type.
4. Calculation of the Hash
Define H(x) to be the hash of x using the hash function selected by
the NSEC3 record and || to indicate concatenation. Then define:
IH(salt,x,0)=H(x || salt)
IH(salt,x,k)=H(IH(salt,x,k-1) || salt) if k > 0
Then the calculated hash of an ownername is
IH(salt,ownername,iterations-1), where the ownername is the canonical
form.
The canonical form of the ownername is the wire format of the
ownername where:
1. The ownername is fully expanded (no DNS name compression) and
fully qualified;
2. All uppercase US-ASCII letters are replaced by the corresponding
lowercase US-ASCII letters;
3. If the ownername is a wildcard name, the ownername is in its
original unexpanded form, including the "*" label (no wildcard
substitution);
5. Including NSEC3 RRs in a Zone
Each owner name in the zone which has authoritative data or a secured
Laurie, et al. Expires August 2, 2005 [Page 9]
Internet-Draft nsec3 february 2005
delegation point NS RRset MUST have an NSEC3 resource record.
An unsecured delegation point NS RRset MAY have an NSEC3 resource
record. This is different from NSEC records where an unsecured
delegation point NS RRset MUST have an NSEC record.
The TTL value for any NSEC3 RR SHOULD be the same as the minimum TTL
value field in the zone SOA RR.
The type bitmap of every NSEC3 resource record in a signed zone MUST
indicate the presence of both the NSEC3 record itself and its
corresponding RRSIG record.
The bitmap for the NSEC3 RR at a delegation point requires special
attention. Bits corresponding to the delegation NS RRset and any
RRsets for which the parent zone has authoritative data MUST be set;
bits corresponding to any non-NS RRset for which the parent is not
authoritative MUST be clear.
The following steps describe the proper construction of NSEC3
records.
1. Sort the zone in canonical order.
2. For each unique original owner name, add a NSEC3 RRset, where the
ownername of the NSEC3 RR is the hashed equivalent of the
original owner name, prepended to the zone name.
3. For each RRset at the original owner, set the corresponding bit
in the type bit map. If the RRset signifies an unsecured
delegation point, and the policy is to have Authoritative Only
RRsets, mark this NSEC3 RR.
4. If the difference in labels between the apex and the original
ownername is greater then 1, additional NSEC3 need to be added
for every intermediate label level between the apex and the
original ownername.
5. sort the set of NSEC3 RRs.
6. In each NSEC3 RR, insert the Next Hashed Ownername. If the next
hashed ownername is a marked NSEC3 (from step 3), delete the
marked NSEC3 from the zone, set the Authoritative Only bit in the
current NSEC3 RRs, and repeat this step. The last NSEC3 in the
zone will contain the value of the first NSEC3 in the zone.
6. Special Considerations
The following paragraphs clarify specific behaviour explain special
considerations for implementations.
6.1 delegation points
This proposal introduces the Authoritative Only Flag which indicates
Laurie, et al. Expires August 2, 2005 [Page 10]
Internet-Draft nsec3 february 2005
whether non authoritative delegation point NS records are included in
the type bit Maps. As discussed in paragraph 2.1.1, a flag value of
0 indicates that the interpretation of the type bit maps is identical
to NSEC records.
The following subsections describe behaviour when the flag value is
1.
6.1.1 Unsigned Delegations
Delegation point NS records are not authoritative. They are
authoritative in the delegated zone. No other data exists at the
ownername of an unsigned delegation point.
Since no authoritative data exist at this ownername, it is excluded
from the NSEC3 chain. This is an optimization since it relieves the
zone of including an NSEC3 record and its associated signature for
this name.
An NSEC3 that denies existence of ownernames between X and X' with
the Authoritative Only Flag set to 1 can not be used to proof
presence nor absence of the delegation point NS records for unsigned
delegations in the interval X, X'. The Authoritative Only Flag
effectively states No Contest on the presence of delegation point NS
resource records.
Since proof is absent, there exists a new attack vector. Unsigned
delegation point NS records can be deleted during a man in the middle
attack, effectively denying existence of the delegation. This is a
form of Denial of Service, where the victim has no information it is
under attack, since all signatures are valid and the fabricated
response form is a known type of response.
The only possible mitigation is to either not use this method, hence
proving existence or absence of unsigned delegations, or signing the
delegated zone, changing the unsigned delegation into a signed
delegation.
A second attack vector exists in that an adversary is able to
successfully fabricate a response claiming a not existent delegation
to exist, though unsigned.
The only possible mitigation is to either not use this method, hence
proving absence of unsigned delegations.
6.2 Additional Complexity Caused by Wildcards
If a wildcard ownername appears in a zone, the wildcard label ("*")
Laurie, et al. Expires August 2, 2005 [Page 11]
Internet-Draft nsec3 february 2005
is treated as a literal symbol and is treated in the same way as any
other ownername for purposes of generating NSEC3 RRs. RFC 2535
[RFC2525] describes the impact of wildcards on authenticated denial
of existence.
In order to prove there are no wildcards for a domain, as well as no
RRs that match directly, an RR must be shown for the closest
encloser, and non-existence must be shown for all enclosers that
could be closer.
6.3 Salting
Augmenting original ownernames with salt before hashing increases the
cost of a dictionary of pre-generated hash-values. For every bit of
salt, the cost of the dictionary doubles. The NSEC3 RR can use
maximum 2040 bits of salt, multiplying the cost by 2^2040.
The salt value for each NSEC3 RR MUST be equal for a single version
of the zone.
6.4 Hash Collision
Hash collisions occur when different messages have the same hash
value. The expected number of domain names needed to give a 1 in 2
chance of a single collision is about 2^80. Though this probability
is extremely low, the following paragraphs deal with avoiding
collisions and assessing possible damage in the event of an attack
using Hash collisions.
6.4.1 Avoiding Hash Collisions during generation
During generation of NSEC3 RRs, hash values are supposedly unique.
In the (academic) case of a collision occurring, an alternative salt
SHOULD be chosen and all hash values SHOULD be regenerated.
If hash values are not regenerated on collision, the NSEC3 RR MUST
list all authoritative RR types that exist for both owners, to avoid
a replay attack, spoofing an existing type as non-existent.
6.4.2 Second Preimage Requirement Analysis
A collision resistant hash function has a second-preimage resistance
property. The second-preimage resistance property means that it is
computationally infeasible to find another message with the same hash
value as a given message, i.e. given preimage X, to find a second
preimage X' <> X such that hash(X) = hash(X'). The probability of
finding a second preimage is 1 in 2^160 for SHA-1 on average. To
mount an attack using an existing NSEC3 RR, an adversary needs to
Laurie, et al. Expires August 2, 2005 [Page 12]
Internet-Draft nsec3 february 2005
find a second preimage.
Assuming an adversary is capable of mounting such an extreme attack,
the actual damage is that a response message can be generated which
claims that a certain QNAME (i.e. the second pre-image) does exist,
while in reality QNAME does not exist (a false positive), which will
either cause a security aware resolver to re-query for the
non-existent name, or to fail the initial query. Note that the
adversary can't mount this attack on an existing name but only on a
name that the adversary can't choose and does not yet exist.
6.4.3 Possible Hash Value Truncation Method
The previous sections outlined the low probability and low impact of
a second-preimage attack. When impact and probability are low, while
space in a DNS message is costly, truncation is tempting. Truncation
might be considered to allow for shorter ownernames and rdata for
hashed labels. In general, if a cryptographic hash is truncated to n
bits, then the expected number of domains required to give a 1 in 2
probability of a single collision is approximately 2^(n/2) and the
work factor to produce a second preimage resistance is 2^n.
An extreme hash value truncation would be truncating to the shortest
possible unique label value. Considering that hash values are
presented in base32, which represents 5 bits per label character,
truncation must be done on a 5 bit boundary. This would be unwise,
since the work factor to produce collisions would then approximate
the size of the zone.
Though the mentioned truncation can be maximized to a certain
extreme, the probability of collision increases exponentially for
every truncated bit. Given the low impact of hash value collisions
and limited space in DNS messages, the balance between truncation
profit and collision damage may be determined by local policy.
7. Performance Considerations
Iterated hashes will obviously impose a performance penalty on both
authoritative servers and resolvers. Therefore, the number of
iterations should be carefully chosen.
8. IANA Considerations
IANA has to create a new registry for NSEC3 Hash Functions. The
range for this registry is 0-127. Value 1 is marked as SHA-1.
Values 0, 2-126 are marked as Reserved For Future Use. Value 127 is
marked as Experimental.
Laurie, et al. Expires August 2, 2005 [Page 13]
Internet-Draft nsec3 february 2005
9. Security Considerations
The NSEC3 records are still susceptible to dictionary attacks (i.e.
the attacker retrieves all the NSEC3 records, then calculates the
hashes of all likely domain names, comparing against the hashes found
in the NSEC3 records, and thus enumerating the zone). These are
substantially more expensive than traversing the original NSEC
records would have been, and in any case, such an attack could also
be used directly against the name server itself by performing queries
for all likely names. The expense of this attack can be chosen by
setting the iterations in the NSEC3 RR.
High-value domains are also susceptible to a precalculated dictionary
attack - that is, a list of hashes for all likely names is computed
once, then NSEC3 is scanned periodically and compared against the
precomputed hashes. This attack is prevented by changing the salt on
a regular basis.
Walking the NSEC3 RRs will reveal the total number of records in the
zone, and also what types they are. This could be mitigated by
adding dummy entries, but certainly an upper limit can always be
found.
Hash collisions may occur. If they do, it will be impossible to
prove the non-existence of the colliding domain - however, this is
fantastically unlikely, and, in any case, DNSSEC already relies on
SHA-1 to not collide.
10. Requirements notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
11. Security Considerations
Appendix A. Example Zone
This is a zone showing its NSEC3 records. They can also be used as
test vectors for the hash algorithm. RRSIG records have been elided.
Laurie, et al. Expires August 2, 2005 [Page 14]
Internet-Draft nsec3 february 2005
example.com. 1000 IN SOA localhost.
postmaster.localhost.example.com. (
1 ; serial
3600 ; refresh (1 hour)
1800 ; retry (30 minutes)
604800 ; expire (1 week)
3600 ; minimum (1 hour)
)
1000 NS ns1.example.com.
1000 NS ns2.example.com.
f519593e82969842a136e0f47814c881fa163833.example.com. 3600 IN NSEC3 \
SHA-1 200 31323334 4EF8239D95C18403A509D7C336A5D0FA48FD1107 \
NS SOA RRSIG DNSKEY NSEC3
a.example.com. 1000 IN A 1.2.3.4
1000 IN A 1.2.3.5
1000 TXT "An example"
bfe6ea21dee9d228889ae11fa58c4bd551d15801.example.com. 3600 IN NSEC3 \
SHA-1 200 31323334 F519593E82969842A136E0F47814C881FA163833 \
A TXT RRSIG NSEC3
b.example.com. 1000 IN A 1.2.3.7
83c06d3b7d01fbc9576c71af2bec1a1163435153.example.com. 3600 IN NSEC3 \
SHA-1 200 31323334 A33559360EECB02F36B5C1B72C109126CA4F5A0D \
A RRSIG NSEC3
a.b.c.example.com. 1000 IN A 1.2.3.6
a33559360eecb02f36b5c1b72c109126ca4f5a0d.example.com. 3600 IN NSEC3 \
SHA-1 200 31323334 BFE6EA21DEE9D228889AE11FA58C4BD551D15801 \
A RRSIG NSEC3
ns1.example.com. 1000 IN A 1.2.3.8
4ef8239d95c18403a509d7c336a5d0fa48fd1107.example.com. 3600 IN NSEC3 \
SHA-1 200 31323334 50016B56FD2F0FFC7B563C50FAF0E34259763BBB \
A RRSIG NSEC3
ns2.example.com. 1000 IN A 1.2.3.9
50016b56fd2f0ffc7b563c50faf0e34259763bbb.example.com. 3600 IN NSEC3 \
SHA-1 200 31323334 83C06D3B7D01FBC9576C71AF2BEC1A1163435153 \
A RRSIG NSEC3
12. References
12.1 Normative References
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, November 1987.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Laurie, et al. Expires August 2, 2005 [Page 15]
Internet-Draft nsec3 february 2005
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2136] Vixie, P., Thomson, S., Rekhter, Y. and J. Bound, "Dynamic
Updates in the Domain Name System (DNS UPDATE)", RFC 2136,
April 1997.
[RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS
Specification", RFC 2181, July 1997.
[RFC2308] Andrews, M., "Negative Caching of DNS Queries (DNS
NCACHE)", RFC 2308, March 1998.
[RFC2535] Eastlake, D., "Domain Name System Security Extensions",
RFC 2535, March 1999.
12.2 Informative References
[RFC2026] Bradner, S., "The Internet Standards Process -- Revision
3", BCP 9, RFC 2026, October 1996.
[RFC2418] Bradner, S., "IETF Working Group Guidelines and
Procedures", BCP 25, RFC 2418, September 1998.
[rollover]
Ihren, J., Kolkman, O. and B. Manning, "An In-Band
Rollover Algorithm and a Out-Of-Band Priming Method for
DNS Trust Anchors.", July 2004.
Authors' Addresses
Ben Laurie
Nominet
17 Perryn Road
London W3 7LR
England
Phone: +44 (20) 8735 0686
EMail: ben@algroup.co.uk
Geoffrey Sisson
Nominet
Laurie, et al. Expires August 2, 2005 [Page 16]
Internet-Draft nsec3 february 2005
Roy Arends
Telematica Instituut
Brouwerijstraat 1
7523 XC Enschede
The Netherlands
Phone: +31 (53) 485 0485
EMail: roy.arends@telin.nl
Laurie, et al. Expires August 2, 2005 [Page 17]
Internet-Draft nsec3 february 2005
Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Disclaimer of Validity
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Copyright Statement
Copyright (C) The Internet Society (2005). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society.
Laurie, et al. Expires August 2, 2005 [Page 18]
View Git Blame Copy Permalink