One document matched: draft-ietf-dkim-ssp-requirements-02.txt
Differences from draft-ietf-dkim-ssp-requirements-01.txt
DKIM Working Group M. Thomas
Internet-Draft Cisco Systems
Intended status: Informational September 2006
Expires: March 5, 2007
Requirements for a DKIM Signing Practices Protocol
draft-ietf-dkim-ssp-requirements-02
Status of this Memo
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This Internet-Draft will expire on March 5, 2007.
Copyright Notice
Copyright (C) The Internet Society (2006).
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Abstract
DomainKeys Identified Mail [DKIM] [I-D.ietf-dkim-base] provides a
cryptographic mechanism for domains to assert responsibility for the
messages they handle. A related mechanism would allow an
administrator to publish various statements about their DKIM signing
practices. This draft defines the requirement for this mechanism.
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Requirements Language
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].
Table of Contents
1. Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 7
4. SSP Problem Scenarios . . . . . . . . . . . . . . . . . . . . 8
4.1. Problem Scenario 1: All Mail Signed with DKIM . . . . . . 8
4.2. Problem Scenario 2: Illegitimate Domain Name Use . . . . . 9
4.3. Problem Scenario 3: Domain Sends No Mail . . . . . . . . . 10
5. SSP Deployment Scenarios . . . . . . . . . . . . . . . . . . . 11
5.1. Deployment Scenario 1: Outsourced Signing . . . . . . . . 11
5.2. Deployment Scenario 2: Determinism in Lookup Mechanism . . 11
5.3. Deployment Scenario 3: Resent Original Mail . . . . . . . 11
5.4. Deployment Scenario 4: Incremental Deployment of
Signing . . . . . . . . . . . . . . . . . . . . . . . . . 12
5.5. Deployment Scenario 5: Transport Scenarios . . . . . . . . 12
5.6. Deployment Scenario 6: Human Legibility of Practices . . . 13
5.7. Deployment Scenario 7: Cryptographic Downgrade Attacks . . 13
5.8. Deployment Scenario 8: Extensibility . . . . . . . . . . . 13
5.9. Deployment Scenario 9: Security . . . . . . . . . . . . . 13
6. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 15
6.1. Discovery Requirements . . . . . . . . . . . . . . . . . . 15
6.2. Transport requirements . . . . . . . . . . . . . . . . . . 16
6.3. Practice and Expectation Requirements . . . . . . . . . . 16
6.4. Extensibility and Forward Compatibility Requirements . . . 19
7. Security Requirements . . . . . . . . . . . . . . . . . . . . 20
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21
9. Security Considerations . . . . . . . . . . . . . . . . . . . 22
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 23
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 24
11.1. Normative References . . . . . . . . . . . . . . . . . . . 24
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11.2. Informative References . . . . . . . . . . . . . . . . . . 24
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 25
Intellectual Property and Copyright Statements . . . . . . . . . . 26
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1. Preface
The purpose of this draft is get out into the open a range of issues
related to the perceived need for a signing practices information
service primarily focused on DKIM. This document is intended to
document well-agreed upon problems and requirements, in addition to
less well-agreed upon requirements in an attempt to capture the issue
as well as generalize the requirement as much as possible. These
latter requirements will be noted as "[PROVISIONAL]" to indicate that
there is not yet solid consensus, or that the problem is not well
understood. A winnowing process is envisioned where the more
difficult and/or speculative problems/requirement will be eliminated
unless concrete problems with proven constituencies can be
demonstrated, along with reasonable plausibility that they do not
contradict more well agreed upon requirements.
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2. Definitions
o Domain Holder: the entity that ultimately controls the contents of
the DNS subtree starting at the domain, either directly or by
delegation via NS records it controls.
o First Party Address: For DKIM, a first party address is defined to
be the [RFC2822].From address in the message header; a first party
address is also known as an Author address
o First Party Signature: a first party signature is a valid
signature where the domain tag (d= or the more specific identity
i= tag) matches the first party address. "Matches" in this
context is defined in [I-D.ietf-dkim-base]
o Third Party Signature: a third party signature is a valid
signature that does not qualify as a First Party Signature. Note
that a DKIM third party signature does is not required to
correspond to a third party address such as Sender or Listid, etc.
o DKIM Signer Complete: the state where the domain holder believes
that all legitimate mail purportedly from the domain was sent with
a valid DKIM signature.
o The Protocol: in this document, The Protocol is used as
placeholder for a protocol that will meet the requirements set in
this draft.
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3. Introduction
The DomainKeys Identified Mail working group is chartered to create a
base signing mechanism for email. This work is contained in
[I-D.ietf-dkim-base]. In addition there are two other documents
[I-D.ietf-dkim-overview] and [I-D.ietf-dkim-threats] which give an
overview and a threat analysis of the chartered work. This draft
reflects the requirements for the last part of the chartered work to
define a protocol to publish DKIM signing practices.
While the base signing document defines a mechanism for signing and
verifying DKIM signatures, there has been a great deal of interest in
a signing practices protocol. The most pressing case seems to be the
bid down attack inherent with almost all systems that allow optional
authentication: how does a receiver know whether or not it should
expect a message to contain authentication information? For email
this is an especially difficult problem since there is generally no a
priori knowledge of a sending domain's practices. If a protocol
could be developed for a domain to publish its DKIM signing
practices, a message verifier could take that into account when it
receives a unsigned piece of email.
This draft is organized into two main sections: a Problem and
Deployment Scenario section which describes the problems that The
Protocol is intended to address as well as the deployment issues
surrounding the base problems. The second section is the
Requirements that arise because of those scenarios.
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4. SSP Problem Scenarios
The email world is a diverse place with many deployment scenarios.
This section tries to outline some usage scenarios that it is
expected that DKIM signing/verifying will take place in, and how a
new protocol might be helpful to clarify the relevance of DKIM signed
mail.
4.1. Problem Scenario 1: All Mail Signed with DKIM
After auditing their outgoing mail and deploying DKIM signing for all
of their legitimate outgoing mail, a domain could be said to be DKIM
signing complete. That is, the domain has to the best of its ability
insured that all mail legitimately purporting to have come from that
domain contains a valid DKIM signature.
A receiver in the general case doesn't know what the practices are
for a given domain, or what their expectations are for unsigned mail.
Thus the receiver is at a disadvantage in that it does not know if it
should expect mail to be signed from a given domain or not. This
knowledge gap leads to a trivially exploitable bid-down attack where
the attacker merely sends unsigned mail; since the receiver doesn't
know the practices of the signing domain, it cannot treat the message
any more harshly for lack of a valid signature.
An information service which allowed a receiver to query for the
practices and expectations of the sending domain when no valid
signature is found could be useful in closing this gap. A receiver
could use this information to treat such questionable mail with
varying degrees of prejudice.
Note that for the foreseeable future, DKIM signature breakage for
unrestricted use patterns (eg where users are members of mailing
lists, etc) will likely suffer occasional non-malicious signature
failure in transit. While probably not a large percentage of total
traffic, the kind (quality) of breakage may be a significant concern
for those usage patterns. This scenario defines where the sender
cannot set any expectation as to whether an individual message will
arrive intact.
Even without that expectation, a receiver may be able to take
advantage of the knowledge that the domain's practice is to sign all
mail and bias filters against unsigned or damaged in transit mail.
This information should not be expected to be used in a binary yes/no
fashion, but instead as a data point among others in a filtering
system.
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1. Mail with a [RFC2822].From A purportedly sends to B with a
missing or broken DKIM signature from A
2. B would like to know whether that is an expected state of
affairs.
3. A provides information that it signs all outgoing mail, but
places no expectation on whether it will arrive with an intact
signature.
4. B could use this information to bias its filters such that it
looks somewhat more suspicious.
4.2. Problem Scenario 2: Illegitimate Domain Name Use
There seems to be a class of mail -- mostly transactional mail from
high value domains -- that are the target of phishing attacks. In
particular, many phishing scams forge the [RFC2822].From address in
addition to spoofing much of the content to trick unsuspecting users
into revealing sensitive information. Domain holders sending this
kind of mail would like the ability to give an enhanced guarantee
that mail sent in their name should always arrive with the provable
consent of the domain holder.
From a receiver's standpoint, knowing that a domain not only signs
all of its mail, but also expects that legitimate mail from the
domain will be received with a valid signature is quite interesting.
This assertion from the signing domain is quite a bit stronger than
the assertion in Problem Scenario 1; even though a signer can never
know the true path mail will take before delivery, the implication is
that if the message is lacking a valid signature the message is
either malicious or is the responsibility of the signing domain to
avoid whatever broke the signature.
[Informative Note: in terms of a receiving filter, one may choose
to treat scenario 2 much more harshly than scenario 1; where
scenario 1 looks odd, scenario 2 looks like something is very
wrong]
1. Mail with a [RFC2822].From A purportedly sends to B with a
missing or broken DKIM signature from A
2. B would like to know whether that is an expected state of
affairs.
3. A provides information that it signs all outgoing mail, but
places an expectation that it should arrive with an intact
signature, and that the receiver should be suspicious if it does
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not.
4. B could use this information to bias its filters such that it
looks much more suspicious.
4.3. Problem Scenario 3: Domain Sends No Mail
A domain may not intend to send mail at all. In such a case, it
could be advantageous for a receiver to know the domain's intent and
would be likely to treat such mail very suspiciously. It has been
noted that a solution to Problem Scenario 2 could potentially be used
to emulate this practice. In reality, they are close but not
precisely the same semantics. That is, a piece of email purporting
to come from a domain which claims to send none is illegitimate on
its face, whereas there may be some lingering doubt with Problem
Scenario 2 given the possibility in deployments between whether one
should publish scenario 1 and 2, etc.
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5. SSP Deployment Scenarios
Given the problems enumerated above for which we'd like The Protocol
to provide information to recipients, there are a number of scenarios
that are not related to the problems that are to be solved, per se,
but the actual mechanics of implementing/deploying the information
service that The Protocol would provide.
5.1. Deployment Scenario 1: Outsourced Signing
Many domains do not run their own mail infrastructure, or may
outsource parts of it to third parties. It is desirable for a domain
holder to have the ability delegate to other entities the ability to
sign for the domain holder. One obvious use scenario is a domain
holder from a small domain that needs to have the ability for their
outgoing ISP to sign all of their mail on behalf of the domain
holder. Other use scenarios include outsourced bulk mail for
marketing campaigns, as well as outsourcing various business
functions such as insurance benefits, etc.
5.2. Deployment Scenario 2: Determinism in Lookup Mechanism
The Protocol's client will generally be deployed on incoming mail
streams to provide the information as proposed in the problem
scenarios. As such, it is envisioned that the RFC2822.From address
would be used as a basis for the lookup. In particular, the domain
part of the address would be consulted in some manner to fetch the
published information. There is a fairly trivial attack against a
naive use of this algorithm which is called the subdomain attack:
that is, a domain needs to not only publish a policy for a given DNS
label it controls, but it also may need to protect all subdomains of
that label as well. If this characteristic is not met, an attacker
would need only create a possibly fictitious subdomain which was not
covered by The Protocol's information service
In widening the scope to have the possibility of all subdomains
inherit the parent practice, a number of algorithms could be employed
-- all seemingly with their own set of engineering tradeoffs. A
common theme in the production of this draft was that the number of
lookups, on average should be small, and that the discovery process
should always be bound to some small finite number of queries.
5.3. Deployment Scenario 3: Resent Original Mail
Resent mail is a common occurrence in many scenarios in the email
world of today. For example, Alice sends a DKIM signed message with
a published practice of signing all messages to Bob's mailing list.
Bob, being a good net citizen, wants to be able to take his part of
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the responsibility of the message in question, so he DKIM signs the
message, perhaps corresponding to the Sender address.
Note that this scenario is completely orthogonal to whether Alice's
signature survived Bob's mailing list: Bob merely wants to assert his
part in the chain of accountability for the benefit of the ultimate
receivers. It would be useful for this practice to be encouraged as
it gives a more accurate view of who handled the message. It also
has the side benefit that remailers that are not friendly to DKIM
first party signatures (ie, break them) can be potentially assessed
by the receiver based on the receiver's opinion of the signing
domains that actually survived.
5.4. Deployment Scenario 4: Incremental Deployment of Signing
As a practical matter, it may be difficult for a domain to roll out
DKIM signing such that they can publish the DKIM Signing Complete
practice given the complexities of the user population, outsourced
vendors sending on its behalf, etc. This leaves open an exploit that
high-value mail such as in Problem Scenario 2 must be classified to
the least common denominator of the published practices. It would be
desirable to allow a domain holder to publish a list of exceptions
which would have a stronger practices statement.
For example, bigbank.example.com might be ready to say that
statements@bigbank.example.com is always signed, but the rest of the
domain, say, is not. Another situation is that the practices of some
address local parts in a given domain are not the same as practices
of other local parts. Using the same example of
statements@bigbank.example.com being a transactional kind of email
which would like to publish very strong practices, mixed in with the
rest of the user population local parts which may go through mailing
lists, etc, for which a less strong statement is appropriate.
It should be said that DKIM, through the use of subdomains, can
already support this kind of differentiation. That is, in order to
publish a strong practice, one only has to segregate those cases into
different subdomains. For example: *@accounts.bigbank.example.com
would publish a strong practice while *@bigbank.example.com could
publish a more permissive practice.
5.5. Deployment Scenario 5: Transport Scenarios
Email service provides an any-any mesh of potential connections: all
that is required is the publication of an MX record and a SMTP
listener to receive mail. Thus the use of The Protocol is likely to
fall into two main scenarios, the first of which are large, well
known domains who are in constant contact with one another. In this
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case caching of records is essential for performance, including the
caching of the non-existence of records (ie, negative caching).
The second main scenario is when a domain exchanges mail with a much
smaller volume domain. This scenario can be both perfectly normal as
with the case of vanity domains, and sadly a vector for those sending
mail for anti-social reasons. In this case we'd like the burden to
The Protocol querier to be low, since many of the lookups will not
provide a useful answer. Likewise, it would be advantageous to have
upstream caching here as well so that, say, a mailing list exploder
on a small domain does not result in an explosion of queries back at
the root server for the small domain.
5.6. Deployment Scenario 6: Human Legibility of Practices
While The Protocol records are likely to be primarily consumed by an
automaton, for the foreseeable future they are also likely to be
inspected by hand. It would be nice to have the practices stated in
a fashion which is also intuitive to the human inspectors.
[Author's $.02: it's been amply demonstrated that simple human
readable labels are often misconstrued. Opaque symbols do have
the advantage that you need to consult the definition to determine
its meaning rather than just intuiting what it "ought" to mean.
/mat]
5.7. Deployment Scenario 7: Cryptographic Downgrade Attacks
There is a downgrade attack possible where a DKIM signature is hashed
with a previously acceptable but now insecure hash algorithm. This
could allow attackers to send their chosen text which is apparently
signed by the targeted domain. It would be advantageous for a domain
to publish what the allowable signing/hashing algorithms are to
prevent this downgrade attack.
5.8. Deployment Scenario 8: Extensibility
While this document pertains only to requirements surrounding DKIM
signing practices, it would be beneficial for the protocol to be able
to extend to other protocols.
5.9. Deployment Scenario 9: Security
The protocol must be able to withstand life in a hostile open
internet environment. These include DoS attacks, and especially DoS
attacks that leverage themselves through amplification inherent in
the protocol. In addition, while a useful protocol may be built
without strong source authentication provided by the information
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service, a path to strong source authentication should be provided by
the protocol, or underlying protocols.
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6. Requirements
This section defines the requirements for The Protocol. As with most
requirements drafts, these requirements define the MINIMUM
requirements that a candidate protocol must provide. It should also
be noted that The Protocol must fulfill all of the requirements.
[Informative Note: it's not clear to the author that all of the
provisional requirements can fulfill the harder requirements. If
this is determined to be true, the provisional requirement should
either be dropped or the harder requirements revised]
6.1. Discovery Requirements
Receivers need a means of obtaining information about a sender's DKIM
practices. This requires a means of discovering where the
information is and what it contains.
1. The author is the first-party sender of a message, as specified
in the [rfc2822].From field. The Protocol's information is
associated with the author's domain name and is published
subordinate to that domain name.
2. In order to limit the cost of its use, any query service
supplying The Protocol's information must provide a definitive
responsive within a small, deterministic number of query
exchanges.
[Informative Note: this, for all intents and purposes is a
prohibition on anything that might produce loops or result in
extended delays and overhead; also though "deterministic"
doesn't specify how many exchanges, the expectation is "few".]
[Refs: Deployment Scenario 2]
3. The Protocol's publishing mechanism MUST be defined to produce
unambiguous semantics, particularly with respect to other
information that might share the publication mechanism.
[Informative note: An example of ambiguity is sharing resource
record types within a common DNS leaf. Hence, uniquely
defined leaf names or uniquely defined resource record types
will ensure unambiguous reference.]
[Refs: Deployment Scenario 2]
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6.2. Transport requirements
1. Widespread deployment of the transport layer would be highly
desirable, especially if riding on top of a true transport layer
(eg, TCP, UDP).
[Refs: Deployment Scenario 5, 8]
2. A low-cost query/response in terms of latency time and the number
of packets involved is highly desirable.
[Refs: Deployment Scenario 5]
3. If the infrastructure doesn't provide caching (ala DNS), the
records retrieved will need time-to-live values to allow querying
verifiers to maintain their own caches. Existing caching
infrastructure is, however, highly desirable.
[Refs: Deployment Scenario 5]
4. Multiple geographically and topologically diverse servers must be
supported for high availability
[Refs: Deployment Scenario 5, 8]
6.3. Practice and Expectation Requirements
In this section, a Practice is defined as a true statement according
to the [RFC2822].From domain holder of its intended externally
visible behavior. An Expectation combines with a Practice to convey
what the domain holder considers the likely outcome of the
survivability of the Practice for a receiver. For example, a
Practice that X is true when it leaves the domain, and an Expectation
that it will|will-not|may|may-not remain true for some/all receivers.
1. The Protocol MUST be able to make Practices and Expectation
assertions about the [RFC2822].From address in the context of
DKIM. The Protocol will not make assertions about other
addresses for DKIM at this time.
[Refs: Problem Scenario 1,2]
2. [PROVISIONAL] The Protocol MUST be able to publish a Practice
which is indicative that domain doesn't send mail.
[Refs: Problem Scenario 3]
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3. If the Discovery process would be shortened by publication of a
"null" practice, the protocol SHOULD provide a mechanism to
publish such a practice.
[INFORMATIVE NOTE: there seems to be widespread consensus
that a "neutral" or "I sign some mail" practice is useless to
receivers. However, a null practice may help to cut short
the policy lookup mechanism if it's published, and if that's
the case it seems worthwhile. Also, a null policy may have
some forensic utility, such as gaging the number of domains
considering/using DKIM for example.]
[Refs: Deployment Scenario 2]
4. The Protocol MUST be able to publish a Practice that the
domain's signing behavior is "DKIM Signing Complete"
[Refs: Problem Scenario 1]
5. The Protocol MUST be able to publish an Expectation that a
verifiable First Party DKIM Signature should be expected on
receipt of a message.
[Refs: Problem Scenario 2]
6. Practices and Expectations MUST be presented in the Protocol
syntax using as intuitive a descriptor as possible. For
example, p=? would be better represented as p=unknown.
[Refs: Deployment Scenario 6]
7. The Protocol MUST NOT invent a different means of allowing
affiliated parties to sign on a domain's behalf. Because DKIM
uses DNS to store selectors, there is always the ability for a
domain holder to delegate all or parts of the _domainkey
subdomain to an affiliated party of the domain holder's
choosing. That is, the domain holder may be able to set a NS
record for _domainkey.example.com to, say, an email provider who
manages that namespace. There is also the ability for the
domain holder to partition its namespace into subdomains to
further constrain how third parties. For example, a domain
holder could delegate only _domainkey.benefits.example.com to a
third party to constrain the third party to only be able to
produce valid signatures in the benefits.example.com subdomain.
Last, a domain holder can even use CNAME's to delegate
individual leaf nodes.
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8. [PROVISIONAL] The protocol MUST have the ability to provide
practices and expectations keyed off of the local part of the
[RFC2822].From address. As with all provisional requirements,
this requirement must not be in conflict with other
requirements, including DNS considerations, etc.
[INFORMATIVE NOTE: this requirement seems to have rather weak
support. It's mainly been added so that it can be issue-
tracked. /mat]
[Refs: Deployment Scenario 4]
9. Practices and Expectations MUST be presented as an information
service from the signing domain to be consumed as an added
factor to the receiver's local policy. In particular, a
Practice or Expectation MUST NOT mandate any disposition stance
on the receiver.
[Refs: Problem Scenario 1, 2, 3]
10. There is no requirement that The Protocol publish a Practices of
any/all third parties that MUST NOT sign on the domain holder's
behalf. This should be considered out of scope.
[INFORMATIVE NOTE: this is essentially saying that the
protocol doesn't have to concern itself with being a
blacklist repository.]
[Refs: Problem Scenario 1-2]
11. The Protocol MUST NOT be required to be invoked if a valid first
party signature is found.
[Refs: Deployment Scenario 2]
12. [PROVISIONAL] A domain holder MUST be able to publish a Practice
which enumerates the acceptable cryptographic algorithms for
signatures purportedly from that domain.
[Refs: Deployment Scenario 7]
13. The protocol MUST NOT provide a mechanism which impugns the
existence of non-first party signatures in a message. A
corollary of this requirement is that the protocol MUST NOT link
practices of first party signers with the practices of third
party signers.
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[INFORMATIVE NOTE: the main thrust of this requirement is
that practices should only be published for that which the
publisher has control, and should not meddle in what is
ultimately the local policy of the receiver.]
[Refs: Deployment Scenario 3]
6.4. Extensibility and Forward Compatibility Requirements
1. The Protocol MUST NOT extend to any other protocol than DKIM for
email at this time. The Protocol SHOULD be able to extend for
protocols other than DKIM.
[Refs: Deployment Scenario 8]
2. The Protocol MUST be able to add new Practices and Expectations
within the existing discovery/transport/practices in a backward
compatible fashion.
[Refs: Deployment Scenario 8]
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7. Security Requirements
1. Minimize DoS potential: The Protocol for a high-value domain is
potentially a high-value DoS target, especially since the
unavailability of The Protocol's record could make unsigned
messages less suspicious.
2. Amplification Attacks: The Protocol MUST NOT make highly
leveraged amplification or make-work attacks possible. In
particular any amplification must be O(1).
[Author's question: is it really O(1)? or O(n)?]
[Refs: Deployment Scenario 9]
3. Authenticity: The Protocol MUST have the ability for a domain
holder to provide The Protocol's data such that a receiver can
determine that it is authentically from the domain holder with a
large degree of certainty. The Protocol may provide means which
provide less certainty in trade off for ease of deployment.
[Refs: Deployment Scenario 9]
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8. IANA Considerations
This document makes no request of IANA.
Note to RFC Editor: this section may be removed on publication as an
RFC.
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9. Security Considerations
This draft defines requirements for a new protocol and the security
related requirements are defined above. There is an expectation that
The Protocol will not always be required to have source
authentication of the practices information which is noteworthy.
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10. Acknowledgments
Due to flipping in the market and raising interest rates, this home
is no longer free. Dave Crocker and Jim Fenton helped me raise the
walls on this draft and are accorded a room at the inn. The inn is
not yet full, however.
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11. References
11.1. Normative References
[I-D.ietf-dkim-base]
Allman, E., "DomainKeys Identified Mail (DKIM)
Signatures", draft-ietf-dkim-base-04 (work in progress),
July 2006.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2822] Resnick, P., "Internet Message Format", RFC 2822,
April 2001.
11.2. Informative References
[I-D.ietf-dkim-overview]
Hansen, T., "DomainKeys Identified Mail (DKIM) Service
Overview", draft-ietf-dkim-overview-01 (work in progress),
June 2006.
[I-D.ietf-dkim-threats]
Fenton, J., "Analysis of Threats Motivating DomainKeys
Identified Mail (DKIM)", draft-ietf-dkim-threats-03 (work
in progress), May 2006.
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Author's Address
Michael Thomas
Cisco Systems
606 Sanchez St
San Francisco, California 94114
USA
Phone: +1-408-525-5386
Fax: +1-408-525-5386
Email: mat@cisco.com
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Full Copyright Statement
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