Internet Engineering Task Force Tim Jenkins
IP Security Working Group TimeStep Corporation
Internet Draft October 20, 1999
IPSec Re-keying Issues
<draft-jenkins-ipsec-rekeying-02.txt>
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Copyright Notice
Copyright (C) Tim Jenkins (1999).
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Internet Draft IPSec Re-keying Issues October 1999
Table of Contents
1. Introduction...................................................3
2. Phase 2 SA Re-keying...........................................3
2.1 Phase 2 Re-keying Issues......................................3
2.1.1 Inconsistent SA Use Recommendation..........................4
2.1.2 Observed Behaviours.........................................5
2.1.3 SA Set-up Race Condition....................................5
2.1.4 Commit Bit Interaction......................................7
2.2 Solution Examination..........................................8
2.2.1 Responder Pre-Setup.........................................8
2.2.1.1 Normal Conditions.........................................9
2.2.1.2 Dropped Packet Conditions................................11
2.2.1.3 Failed Negotiation.......................................12
2.2.1.4 Responder Pre-Setup Security Hole........................13
2.2.2 Recommended Re-keying Method...............................13
2.2.2.1 Dropped Quick Mode 3 Message.............................15
2.2.2.2 Absence of Traffic.......................................15
2.2.2.3 Compatibility With Observed Behaviours...................16
2.2.2.4 Compatibility with Commit Bit............................16
2.2.2.5 Implementation Notes.....................................17
2.3 Conclusions..................................................17
3. Phase 1 SA Re-keying..........................................17
3.1 Phase 1 SA Re-keying Requirements............................18
3.2 Continuous Channel Implementations...........................19
3.2.1 Identity Perfect Forward Secrecy...........................22
3.3 Dangling Phase 2 SA Implementations..........................22
3.4 Other Phase 1 SA Re-keying Issues............................25
3.4.1 Multiple SA Usage..........................................25
3.4.2 INITIAL-CONTACT Notification...............................25
3.4.3 DELETE Notification........................................26
3.4.4 Re-keying Timing...........................................26
4. Next IPSec Version Recommendations............................26
4.1 Re-transmission Rules........................................27
4.1.1 Main Mode Re-Transmission Rules............................28
4.1.2 Aggressive Mode Re-Transmission Rules......................28
4.1.3 Quick Mode Re-Transmission Rules...........................28
4.2 Acknowledged SA Deletion.....................................28
4.3 Phase 1 Re-keying for IPSecond...............................30
4.4 Phase 2 Re-keying for IPSecond...............................30
4.4.1 Oldest Phase 2 SA First....................................31
4.4.2 Phase 2 Re-keying Illustration.............................31
4.5 Commit Bit Replacement.......................................35
4.5.1 DEFER_USAGE Notify Payload.................................35
4.5.2 ALLOW_USAGE Notify Payload.................................36
5. Acknowledgements..............................................37
6. References....................................................37
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1. Introduction
This document has three primary objectives.
The first objective is to illustrate problems and issues associated
with re-keying within the confines of the current set of IPSec
documents. For a number of reasons, re-keying in IPSec has become
problematic, such that packets can get dropped by IPSec
implementations during re-keying. Worse, there exists the
possibility that IPSec implementations from different vendors may
not be interoperable because of the way they re-key.
The second objective of this paper is to propose methods of
performing both phase 1 and phase 2 re-keying for IPSec
implementations in such a way as to minimise packet loss and to
maximize compatibility.
The initial focus of the first two objectives is on phase 2 re-
keying; it is then extended to phase 1 re-keying. The need for this
document in each case is initially discussed, followed by a
recommendation for re-keying within the protocol framework
established by the initial version of the IPSec documents.
Finally, the third objective of the document is to provide
recommendations for the next version of the IPSec protocols. These
recommendations are made to best solve the re-keying problems in a
manner that is not possible within the constraints of the existing
IPSec documents.
2. Phase 2 SA Re-keying
This section discusses phase 2 re-keying issues and makes
recommendations to minimise the impact of these issues within the
current IPSec document set.
2.1 Phase 2 Re-keying Issues
The issues associated with phase 2 re-keying are listed below. Some
of the points are expanded upon later.
1) There is no specification defining how re-keying is to be done.
2) The existing drafts appear contradictory in their
recommendations on the usage of multiple phase 2 SAs.
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3) Some recent implementations have shipped with a method of re-
keying that will not perform reliably under real world network
conditions.
4) The use of the DELETE notification is not required.
5) A variety of re-keying behaviours have been observed, some of
which are incompatible.
6) The commit bit is not yet widely implemented, and its use as
described is confusing. Further, while the documentation
requires its support, its use is not required.
7) A race condition exists at SA set up, exacerbating re-keying
issues.
2.1.1 Inconsistent SA Use Recommendation
The issue of inconsistent SA usage recommendations is examined
further here.
From paragraph 2 of Section 9 of [IKE]:
An implementation may wish to negotiate a range of SAs when
performing Quick Mode. By doing this they can speed up the "re-
keying". Quick Mode defines how KEYMAT is defined for a range of
SAs. When one peer feels it is time to change SAs they simply use
the next one within the stated range. A range of SAs can be
established by negotiating multiple SAs (identical attributes,
different SPIs) with one Quick Mode.
While the document does not define what "... the next one ..."
means, this paragraph strongly implies that there is no required
order for the use of phase 2 SAs that have been negotiated within a
phase 1 SA, and that multiple SAs may be pre-negotiated and used at
will.
However, this appears to be contradicted by paragraph 3 of section
4.3 of [ISAKMP]:
Modification of a Protocol SA (phase 2 negotiation) follows the
same procedure as creation of a Protocol SA. The creation of a new
SA is protected by the existing ISAKMP SA. There is no
relationship between the two Protocol SAs. A protocol
implementation SHOULD begin using the newly created SA for
outbound traffic and SHOULD continue to support incoming traffic
on the old SA until it is deleted or until traffic is received
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under the protection of the newly created SA. As stated previously
in this section, deletion of an old SA is then dependent on local
security policy.
Many implementations have interpreted this to mean that the new SA
should be used for outbound in preference to the old SA. In other
words, the old SA should be abandoned as soon as possible.
This interpretation of [ISAKMP] is in direct conflict with the usage
implied by [IKE], resulting in potential problems.
2.1.2 Observed Behaviours
The following behaviours have been observed by various vendors'
implementations when devices have set up a second phase 2 SA. The
behaviours listed below are not mutually exclusive.
1) The device continues to use the old SA until it naturally
expires, then switches to the new SA.
2) The device immediately begins using the new SA.
3) The device immediately drops the old SA.
4) The device never sends a DELETE notification.
5) The device always sends a DELETE notification.
6) The device deletes the old SA some time after re-keying, but
before the end of its natural lifetime.
7) A device wants to keep more than one SA up all the time.
All of these behaviours are permitted under the current documents.
However, even when quick mode packets are not lost, it can be seen
that interoperability is not always possible with some combinations
of behaviours listed above.
2.1.3 SA Set-up Race Condition
Further, behaviour 2 above is not a good behaviour, as illustrated
below. In this example, the initiator is a gateway capable of
handling full T3 bandwidth rates, while the responder is a PC
running a software IPSec implementation, and it is overloaded.
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In the illustration, QM1 refers to the first quick mode message, QM2
to the second quick mode message and QM3 to the third quick mode
message.
By the time the responder has set up the new SA, packets protected
by that SA have already started arriving from the initiator. This
causes them to be dropped by the responder. This case is further
complicated by the possibility of packets taking different paths
through the network, so theoretically, the third quick mode message
could arrive after packets protected by the new SA.
Additionally, since all IKE packets are based on UDP, there is no
guarantee that QM3 even arrives at the peer, so making assumptions
about new SA use based on the transmission time of a packet will
still lead to failures in the field.
To reduce the effects of packet loss, some implementations were
observed to blindly transmit QM3 multiple times, back to back.
Initiator Responder
QM1 sent ----
-------
-------------
---------------> QM1 received
|
|
| QM1 processed
|
|
---------------- QM2 sent
-------------
-------
QM2 rec. <----
process |
QM3 sent -----
* -------
packet on new SA -------------
_____ ---------------> QM3 received
_______ |
_____________ | QM3 processing
_______________|
| packet dropped
|
* new SA set up
Figure 2-1 Race Condition Sequence Chart
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This can reduce the probability that the peer does not get QM3, but
cannot eliminate it. Nor can it eliminate race conditions due to
path differences or processing times.
If the behaviour of the initiator was to delay usage of the new SA
for outbound traffic, this would cause failures for those
implementations that immediately delete the old SA. Therefore, the
behaviour of delaying use of the new SA and immediately deleting the
old SA are incompatible.
2.1.4 Commit Bit Interaction
The use of the commit bit can solve the race condition illustrated
in the previous section when asserted by the responder during quick
mode. However, it suffers from the following problems:
1) Use of the commit bit is not well defined. The present
documentation ([ISAKMP]) specifies its use for phase 1 and
phase 2, but mentions phase 2 specific details. There are also
issues related to how the subsequent CONNECTED notification
fits in with the quick mode exchange.
2) While its support is required, its use is not.
3) Its use may make implementations susceptible to a denial of
service attack by forcing initiators to wait for a CONNECTED
notification that may never come. While this is only one of a
number of possible denial of service attacks on IKE, this is
not an excuse to leave the existing implementation as it is.
4) There is no defined way to recover from the loss of the
CONNECTED notification.
5) Some implementations are using the commit bit for the wrong
reasons.
Point 1 is being addressed by the working group; future versions of
the IPSec documents should clarify these issues. [IKEbis] has done
an excellent job of clarifying this issue.
Point 3 happens because the commit bit is in the ISAKMP header, and
the ISAKMP header is not authenticated, so is susceptible to
modification.
Point 5 above needs some elaboration. In a previous section, it was
mentioned that the loss of the third quick mode message can cause
problems, since the responder will not set up the SA at all. Because
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of this, some implementations have chosen to set the commit bit as a
mechanism to force the re-transmission of the third quick mode
message.
This is wrong for two reasons. First, it is not the stated purpose
of the commit bit. The purpose of the commit bit is to delay the
usage of an SA, for whatever reason. This implies that it is not a
good mechanism to cause re-transmission of the third quick mode
message.
Secondly, it does not solve the packet loss problem; it only defers
it. The logic of the improper usage is that the initiator will
resend the third quick mode message until it receives the CONNECTED
notification (which is now effectively the fourth quick mode
message).
The problem with this is that it leaves no mechanism for demanding
the re-transmission of the CONNECTED notification itself. It can be
dropped just as the third quick mode message can. This means that
the problem that was intended to be solved by the use of the commit
bit is simply pushed out to being the problem of solving the dropped
CONNECTED notification.
Sections 2.2.2.1 and 4.1 describe a mechanism for solving the
dropped third quick mode message problem.
2.2 Solution Examination
This section details the operation of some possible behaviours, with
the intent of arriving at a best possible phase 2 re-keying
mechanism under the constraints of the existing documents.
In all the examples, the term "sets up a new outbound SA" means that
the new outbound SA will be chosen in favour of the old one. Whether
the SA is actually created before that time or not is implementation
dependent.
2.2.1 Responder Pre-Setup
As a starting point, the responder pre-setup method of re-keying is
examined. Note that it will work with most of the behaviours
observed in the field.
In this method, SAs are treated separately as inbound and outbound,
as well as old and new. Further, it takes advantage of the fact that
the responder knows what the SA is going to be after the second
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quick mode message is sent. By using this information, it allows the
responder to set up the new inbound SA before having received the
third quick mode message.
Implicit acknowledgement of the reception of the third quick mode
message by the responder is provided by use of the new SA in the
initiator's inbound direction. The initiator should not use its new
outbound SA before that time.
Additionally, it does not require use of the CONNECTED notification
for prevention of the race condition, or the use of the DELETE
notification for removal of the old SA. This is important since,
even if they are always sent, they are unacknowledged UDP packets
and may be lost.
2.2.1.1 Normal Conditions
Figure 2-2 shows the operation under normal (successful) conditions.
While appearing complicated, it enables the lossless transfer from
one SA to another while supporting almost all other behaviours.
Support for and use of the DELETE notification is unchanged.
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Initiator Responder
Inbound Outbound Inbound Outbound
| | | |
1 ----------------- | |
| | ------------ | |
| | -------------------> 2
| | | | |
| | -------------------- 3
| | ------------ | *4 |
5 <--------------- | | |
| | | | | |
6 ---------------- | | |
| *7 | ------------ | | |
| | | -------------------> 8
| | | | | | |
| | | | | | *
| | | | | | *9
| | | | | *10 |
| | | | | |
| *11 | | | |
| | | *12 | | |
| | *13 | | | |
*14| | | | |
| | | *15 |
| | *16| |
| | | |
Figure 2-2 Phase 2 SA Pre-Setup Sequence Chart
Events
1) Initiator sends first quick mode message.
2) Responder receives first quick mode message.
3) Responder sends second quick mode message.
4) Responder sets up new inbound SA. This is to handle the case
where the initiator starts transmitting on the new SA
immediately after sending the third quick mode message.
5) Initiator receives second quick mode message.
6) Initiator sends third quick mode message.
7) Initiator sets up new inbound SA.
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8) Responder receives third quick mode message.
9) Responder sets up new outbound SA.
10) Responder deletes old outbound SA.
11) Traffic from responder to initiator arrives at initiator on new
SA.
12) Initiator sets up new outbound SA.
13) Initiator deletes old outbound SA.
14) Initiator deletes old inbound SA.
15) Traffic from initiator to responder arrives at responder on new
SA.
16) Responder deletes old inbound SA.
2.2.1.2 Dropped Packet Conditions
In this case, the event list is modified to show what happens when
each packet is dropped once. The event numbers refer to those
illustrated in Figure 2-2.
1) Initiator sends first quick mode message.
e) Packet is dropped during transmission.
1b) Initiator times out waiting for second quick mode message.
1) Initiator re-sends first quick mode message.
2) Responder receives first quick mode message.
3) Responder sends second quick mode message.
4) Responder sets up new inbound SA. This is to handle the case
where the initiator starts transmitting on the new SA
immediately after sending the third quick mode message.
e) Packet is dropped during transmission.
1b) or 7b) Responder times out waiting for third quick mode
message.
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1) or 3) Responder re-sends second quick mode message.
5) Initiator receives second quick mode message.
6) Initiator sends third quick mode message.
7) Initiator sets up new inbound SA.
e) Packet is dropped during transmission.
7b) Responder times out waiting for third quick mode message.
3) Responder re-sends second quick mode message.
5) Initiator receives second quick mode message again.
6) Initiator re-sends third quick mode message.
8) Responder receives third quick mode message.
and so on, as for normal operation.
2.2.1.3 Failed Negotiation
In this case, the second quick mode packet has an invalid hash, and
the initiator sends the notification to the peer. Again, the event
numbers refer to those illustrated in Figure 2-2.
1) Initiator sends first quick mode message.
2) Responder receives first quick mode message.
3) Responder sends second quick mode message.
4) Responder sets up new inbound SA. This is to handle the case
where the initiator starts transmitting on the new SA
immediately after sending the third quick mode message.
5) Initiator receives second quick mode message.
e) Hash (or other parameter) fails.
e1) Initiator sends notification to responder.
e2) Responder receives notification.
e3) Responder deletes new inbound SA.
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A similar operation would occur if retry counters expire for packet
re-transmissions.
2.2.1.4 Responder Pre-Setup Security Hole
In the failed negotiation case, the need to delete the invalid
inbound SA raises the issue of a temporary hole, in that the
responder allows inbound packets while waiting for the third quick
mode message. However, if the inbound SA is not set up ahead of
time, initiators that immediately transmit on the new outbound SA
will cause packets to be dropped.
It also illustrates why the proposal above made the usage of the
outbound SA by the initiator wait until there is an indication of
the use of the SA by the responder.
Note that this security hole is exactly what would result from an
attacker replaying the first quick mode message of an exchange.
2.2.2 Recommended Re-keying Method
In this method, the previous method is modified to remove the risk
of the security hole. It also simplifies the operation somewhat, but
at the expense of lost packets if the initiator's behaviour is such
that it immediately uses the new SA for its outbound traffic.
Note that deletion of the old inbound SA by the initiator could be
further delayed if protection against loss of packets using the old
SA on different and slower network paths is desired.
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Initiator Responder
Inbound Outbound Inbound Outbound
| | | |
1 ----------------- | |
| | ------------ | |
| | -------------------> 2
| | | | |
| | -------------------- 3
| | ------------ | |
4 <--------------- | |
| | | | |
5 ---------- | | |
| *6 ------------------ | |
| | | -------------------> 7
| | | | | |
| | | | | *
| | | | *8 |
| | | | | | *9
| | | | | *10 |
| | | | | |
| *11 | | | |
| | | *12 | | |
| | *13 | | | |
*14| | | | |
| | | *15 |
| | *16| |
| | | |
Figure 2-3 Recommended Phase 2 Re-key Sequence Chart
1) Initiator sends first quick mode message.
2) Responder receives first quick mode message.
3) Responder sends second quick mode message.
4) Initiator receives second quick mode message.
5) Initiator sends third quick mode message.
6) Initiator sets up new inbound SA.
7) Responder receives third quick mode message.
8) Responder sets up new inbound SA.
9) Responder sets up new outbound SA.
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10) Responder deletes old outbound SA.
11) Traffic from responder to initiator arrives at initiator on new
SA.
12) Initiator sets up new outbound SA.
13) Initiator deletes old outbound SA.
14) Initiator deletes old inbound SA.
15) Traffic from initiator to responder arrives at responder on new
SA.
16) Responder deletes old inbound SA.
2.2.2.1 Dropped Quick Mode 3 Message
In cases where the third quick mode message is dropped, the
responder must request re-transmission of it by re-sending the
second quick mode message. The existence of traffic on the new
inbound SA at the initiator should not be used as an implicit
acknowledgement for the following reasons:
1) There may be no traffic for the responder to send.
2) The responder may be designed to use the old SA until its
natural expiration.
This implies that implementations must be able to respond to the re-
transmission of the second quick mode message even after having sent
the third quick mode message.
2.2.2.2 Absence of Traffic
The proposed implementation uses the presence of traffic from the
responder on new SAs to provide an implied acknowledgement for the
purposes of switching to the new SA. However, if there is no traffic
from the responder, the implied acknowledgement will not appear.
A similar behaviour is exhibited by implementations that continue to
use old SAs until their natural expiration.
However, due to the number of implementations that delete old SAs 30
seconds after negotiating a new one, the same behaviour has the best
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chance of interoperability, and of not dropping packets when traffic
does restart.
Therefore, it is recommended that implementations delete old SAs and
start using new SAs 30 seconds after negotiating new SAs in the
absence of traffic. Use of the DELETE notification is strongly
recommended in cases where the peer implementation is continuing to
use the old SA.
2.2.2.3 Compatibility With Observed Behaviours
When operating with behaviours that use the new SA immediately, this
method performs equivalently when this method is used by the
responder. When used by the initiator, the performance will depend
on when the responder deletes the old inbound SA.
When operating with behaviours that continue to use the old SA, this
method performs as described in the dropped quick mode three example
above when used by the initiator. When used by the responder, there
is no change in operation, since the responder will wait until the
new SA is used before deleting the old SA.
However, as stated in a previous section, it is recommended that the
initiator keep the old SA (both inbound and outbound) for only 30
seconds after creation of the new SA in cases where traffic is not
detected on the new SA.
2.2.2.4 Compatibility with Commit Bit
If the commit bit is set by the responder with this proposal, some
of the problems described in Section 0 may occur. To reduce the
effects of these problems, following rules should be followed:
1) The initiator should set up its inbound SA immediately after
sending the third quick mode message regardless of the state of
the commit bit.
2) Sensing of traffic on the initiator's new inbound SA should
trigger the use of the new outbound SA to detect cases when the
CONNECTED notification is dropped.
The recommended proposal does not allow built-in support of the
commit bit. It does allow responders that use the commit bit to
detect reception of the CONNECTED notification by the initiator due
to the presence of traffic on its new inbound SA. However, this
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works only if there is traffic, so it cannot be considered a useful
method to perform this function.
The recommended proposal does cause the initiator to delay usage of
a new SA until it is set up. This is the primary use of the commit
bit, so use of this proposal makes the use of the commit bit
unnecessary except for the setting up of the first phase 2 SA.
2.2.2.5 Implementation Notes
The presence of traffic on the new SA can be part of the expiration
checking operation, and does not need to occur instantaneously,
although it must occur before the 30 second no traffic SA deletion
criteria. As long as the new SA is negotiated with enough time
before the expiration of the old one, the detection of traffic on
the new SA can be on the order of seconds with no ill effects.
Since SAs will likely have traffic counters anyway, this method
requires only the addition of a flag that indicates it is a new SA.
When the expiration process checks for ageing and expired SAs, it
can also check for new SAs with a non-zero traffic count. When
detected, the SA is marked as non-new, and the remaining operations
can be performed.
2.3 Conclusions
The final re-keying method is the best compromise for
interoperability within the framework of the current IPSec documents
without compromising security.
3. Phase 1 SA Re-keying
This section makes a proposal for phase 1 SA re-keying. This
proposal is necessary for many of the same reasons a phase 2 SA re-
keying proposal is necessary.
1) The rules for phase 1 SA re-keying are not specified in the
drafts.
2) Adhoc implementations have lead to poor implementations and
possible interoperability issues.
The goal of the proposed phase 1 SA re-keying method is to provide
secure, lossless communications. This means that there should be no
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dropped traffic during re-keying, but also that there should be no
further traffic if re-keying fails.
3.1 Phase 1 SA Re-keying Requirements
The two reasons for re-keying a phase 1 SA are for freshness (time
or traffic) of the phase 1 SA keying material (affecting its ability
to protect phase 2 SA negotiations) and for re-authentication (and
therefore authorisation) of the encrypting devices.
The second reason stated above has been deemed unimportant by the
working group as a factor in determining phase 1 SA re-keying for
two reasons:
1) System administrators understand IPsec well enough to configure
the combination of phase 1 and phase 2 SA lifetimes such that
terminating phase 2 SAs when authentication ends means the
unauthorised usage period is insignificant.
2) Many implementation will be required to produce a mechanism to
tear down SAs created by entities that are no longer authorised.
Originally, this document made the assumption that there must always
be a valid phase 1 SA in existence between entities to allow the
phase 2 SAs to continue to exist. This was driven primarily by the
desire to bound the authorised lifetime of phase 2 SAs by the
authorised lifetime of the phase 1 SA. However, as stated above,
this requirement has been considered unnecessary by the working
group.
Without that requirement, it was decided by the working group that a
valid phase 1 SA does not have to exist between two peers that have
valid phase 2 SAs.
In spite of this, this document asserts that there is still value in
making sure that a valid phase 1 SA exists at all times. This value
comes about from the fact that the existence of phase 1 SAs between
two entities creates a logical control channel for phase 2 SA
management between those entities. This method of phase 1 re-keying
will be called the continuous channel method.
The continuous channel method is implicitly recommended by RFC2408.
The following quote is from paragraph six of [ISAKMP]:
Third, having an ISAKMP SA in place considerably reduces the cost
of ISAKMP management activity - without the "trusted path" that
an ISAKMP SA gives you, the entities (e.g. ISAKMP servers) would
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have to go through a complete re-authentication for each error
notification or deletion of an SA.
Unfortunately, the downside of this implementation is that it must
be aware of dangling phase 2 SA implementations due to the decision
of the working group. This document uses the term "dangling" to
describe phase 2 SAs that have no valid phase 1 SA between the two
peers. The differences between the two methods are further discussed
here.
3.2 Continuous Channel Implementations
Continuous channel implementations are those implementations that
attempt to always maintain at least one valid phase 1 SA between any
peers that have phase 2 SAs.
The primary advantage of the continuous existence of the logical
channel is that it allows cleaner management of phase 2 SAs,
particular if the two entities become unsynchronised for any reason.
Therefore, re-keying of phase 1 SAs requires that peers negotiate a
new phase 1 SA before the old phase 1 SA expires, at some percentage
of the SA's lifetime.
Note that this automatic re-keying of phase 1 SAs means that SAs
could live independent of traffic, since re-keying of both phase 1
and phase 2 SAs takes place with no traffic triggers (if they expire
by time). In other words, SAs that are no longer necessary may never
disappear.
This suggests that a traffic monitoring capability should be part of
implementations that need to delete idle or unused SAs. As such, it
is not given further consideration, since it is beyond the scope of
this document.
The existence of the INITIAL-CONTACT notification determines whether
it should delete any phase 2 SAs it has with the peer.
Summarised, the rules for phase 1 re-keying for continuous channel
implementations are:
Initial Phase 1 SA Negotiation:
-initiator MUST use INITIAL-CONTACT notification
-responder SHOULD use INITIAL-CONTACT notification (when
possible)
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-responder deletes any pre-existing phase 1 SA with the peer when
authentication of peer complete
-responder deletes all previously existing phase 2 SAs with the
peer, if any
Phase 1 SA Ages:
-end point that first detects this negotiates new phase 1 SA;
becomes new initiator
New Phase 1 SA Negotiation:
-initiator MUST NOT use INITIAL-CONTACT notification
-responder MUST detect that this is a re-key and MUST NOT use
INITIAL-CONTACT notification
-responder SHOULD mark its existing phase 1 SA as re-keyed, so as
to not re-key again
-since no INITIAL-CONTACT notification is used by either end;
phase 2 SAs are kept
Phase 1 SA Expiration:
-DELETE notification SHOULD be sent for phase 1 SA only
Note that any information that may be associated with pre-existing
phase 1 SAs should be carried over into the new SA. Examples of this
type of information are addresses passed using the Configuration
Exchange mode.
Also, continuous channel implementations MUST delete all phase 2 SAs
with a peer when the last phase 1 SA between them expires. This
could happen due to administrative shut-down of the link between the
peers, or a policy change that caused the phase 1 SA re-keying to
fail, leaving no valid phase 1 SAs between them when the existing
phase 1 expired.
A difficulty arises here due to the optional and unacknowledged
transmission of the delete notification and the need to be dangling
SA aware. If the delete notification for any existing phase 2 SA is
dropped, the implementation must attempt to determine if the peer
uses the continuous channel method, or is an SA dangler.
A possible state machine for continuous channel implementations is
shown in Table 1. Note that this state machine does not cover error
conditions, simultaneous SA negotiations and other events, and is
provided for illustration only. It should not be considered a
complete design.
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# SAs
P1 P2 Event Actions
=======================================================================
0 0 -phase 1 negotiation -initiate phase 1 negotiation
from peer -use initial contact if allowed
-phase 1 SA needed
=======================================================================
1 0 -phase 1 SA negotiation -respond to phase 1 negotiation
from peer -do not use initial contact
-----------------------------------------------------------------------
-phase 1 SA deletion -delete phase 1 SA
from peer
-----------------------------------------------------------------------
-phase 1 SA ages -re-key phase 1 SA (or not)
-----------------------------------------------------------------------
-phase 1 SA expires -send delete notification for phase 1 SA
-delete phase 1 SA
=======================================================================
1 1+ -phase 1 SA negotiation -respond to phase 1 negotiation
from peer -do not use initial contact
-----------------------------------------------------------------------
-phase 1 SA ages -re-key phase 1 SA
-----------------------------------------------------------------------
-phase 1 SA deletion -re-key phase 1 SA (1)
from peer -delete phase 1 SA
-----------------------------------------------------------------------
-phase 1 SA expires -send deletes for all phase 2 SAs
-delete all phase 2 SAs
-send delete notification for phase 1 SA
-delete phase 1 SA
=======================================================================
2+ 1+ -phase 1 SA negotiation -respond to phase 1 negotiation
from peer -do not use initial contact
-----------------------------------------------------------------------
-phase 1 SA ages -re-key the phase 1 SA
-----------------------------------------------------------------------
-phase 1 SA deletion -delete phase 1 SA
from peer
-----------------------------------------------------------------------
-phase 1 SA expires -send delete notification for phase 1 SA
-delete phase 1 SA
=======================================================================
0 1+ -phase 1 negotiation -delete all phase 2 SAs (3)
fails (2) -send no delete notifications
=======================================================================
Table 1 Continuous Channel State/Event Table
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Table Notes:
(1) This event's actions are a result of dangling SA awareness.
In a pure continuous channel system, the action here would be to
delete all phase 2 SAs and the phase 1 SA.
(2) This event may result from the action associated with the
previous note. Thus, this event is the result of a continuous
channel implementation attempting to be dangling SA aware.
(3) Implementations could choose to do nothing here, and behave
as an SA dangling implementation. However, if phase 1 SA negotiation
fails, in general it means that the control channel between the
peers cannot be maintained, suggesting that phase 2 SAs should also
be deleted.
3.2.1 Identity Perfect Forward Secrecy
Identity PFS is normally done by allowing the use of only a single
quick mode in a phase 1 SA. This is controlled by the deletion of
the phase 1 after a quick mode.
In a dangling SA implementation, this is not a problem, since the
absence of a valid phase 1 SA is permitted. However, in a continuous
channel implementation, this can lead to the absence of the channel.
This is solved by creating two phase 1 SAs before the first quick
mode is done. The first of these SAs is assigned the role of channel
management, and thus performs SA deletion and notification transfer.
The second SA is used to perform the quick mode, and is immediately
deleted.
The phase 1 SA that is assigned to channel management is re-keyed as
described here. Since it is the oldest phase 1 SA, it will naturally
be used for all management traffic even if another phase 1 SA
temporarily exists only for the purpose of performing a quick modes.
These other phase 1 SAs are created and used to generate phase 2
SAs, then immediately deleted.
3.3 Dangling Phase 2 SA Implementations
These implementations allow phase 2 SAs to exist without a valid
phase 1 SA between peers. They do this by allowing phase 1 SAs to
expire without re-keying them, and then re-keying them only when
necessary, such as when a phase 2 SA needs re-keying.
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Unfortunately, this can lead to situations where phase 2 SAs cannot
be properly cleaned up. For example, if an implementation's policy
is changed to disallow a user access to a network, all SAs between
that user and the network should be terminated. However, if there
are no phase 1 SAs between them, none can be re-keyed, so the DELETE
notifications for the phase 2 SAs cannot be sent. This can lead to
the existence of invalid phase 2 SAs on one end, with the result
that encrypted traffic is send from that end that cannot be used.
Since phase 1 SAs cannot be created, the SAs cannot be explicitly
deleted by the peer.
(If this was a continuous channel implementation, the phase 2 SAs
could have been deleted when the change in authorisation was
discovered, or when the existing phase 1 SA expired.)
Summarised, the rules for phase 1 re-keying for dangling SA
implementations are:
Initial Phase 1 SA Negotiation:
-initiator MUST use INITIAL-CONTACT notification
-responder SHOULD use INITIAL-CONTACT notification (when
possible)
-responder deletes any pre-existing phase 1 SA with the peer when
authentication of peer complete
-responder deletes all previously existing phase 2 SAs with the
peer, if any
New Phase 1 SA Negotiation:
-initiator MUST NOT use INITIAL-CONTACT notification
-responder MUST detect that this is a re-key and MUST NOT use
INITIAL-CONTACT notification
-responder SHOULD mark all existing phase 1 SAs with same peer as
re-keyed, so as to not re-key again
-since no INITIAL-CONTACT notification is used by either end;
phase 2 SAs are kept
Phase 1 SA Expiration:
-DELETE notification SHOULD be sent for phase 1 SA only
Phase 2 SA Ages, and no existing phase 1 SA
-attempt New Phase 1 SA Negotiation
-if that succeeds, attempt new phase 2 SA negotiation
A possible state machine for continuous channel implementations is
shown in Table 2. Note that this state machine does not cover error
conditions, simultaneous SA negotiations and other events, and is
provided for illustration only. It should not be considered a
complete design.
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# SAs
P1 P2 Event Actions
=======================================================================
0 0 -phase 1 negotiation -initiate phase 1 negotiation
from peer -use initial contact if allowed
-phase 1 SA needed
=======================================================================
1 0 -phase 1 SA negotiation -respond to phase 1 negotiation
from peer -do not use initial contact
-----------------------------------------------------------------------
-phase 1 SA deletion -delete phase 1 SA
from peer
-----------------------------------------------------------------------
-phase 1 SA expires -send delete notification for phase 1 SA
-delete phase 1 SA
=======================================================================
1+ 1+ -phase 1 SA negotiation -respond to phase 1 negotiation
from peer -do not use initial contact
-----------------------------------------------------------------------
-phase 1 SA deletion -delete phase 1 SA
from peer
-----------------------------------------------------------------------
-phase 1 SA expires -send delete notification for phase 1 SA
-delete phase 1 SA
=======================================================================
0 1+ -phase 1 SA negotiation -respond to phase 1 negotiation
from peer -do not use initial contact
-----------------------------------------------------------------------
-phase 2 SA ages -attempt to re-negotiate phase 1 SA
-re-key phase 2 SA if successful
-----------------------------------------------------------------------
-phase 2 SA expires -attempt to re-negotiate phase 1 SA
-send delete notification for phase 2 SA
if successful
-delete phase 2 SA unconditionally
=======================================================================
Table 2 Dangling SA State/Event Table
The differences between Table 1 and Table 2 are the following:
-ageing detection of phase 1 SAs is unnecessary
-the state table is not split based on having 1 or more than 1
phase 1 SA for the event where a phase 1 SA deletion is received
-the state table now depends on phase 2 SA events
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While there is more complexity in the continuous channel
implementation, it is not excessive, and some of it is required to
support the dangling SA implementation.
3.4 Other Phase 1 SA Re-keying Issues
This section describes other issues associated with phase 1 SA re-
keying that are independent of the whether the implementation
dangles phase 2 SAs or not.
3.4.1 Multiple SA Usage
When there is more than one phase 1 SA between peers, it is
recommended that the oldest SA be used for subsequent traffic
requiring phase 1 SAs. This allows full use of the keying material
generated and reduces race conditions. It also means that no special
expiration conditions are required when the phase 1 SAs expire by
traffic only, as the old SA will eventually expire on its own due to
usage.
3.4.2 INITIAL-CONTACT Notification
As stated above, the INITIAL-CONTACT notification should be used
only on the very first phase 1 that is negotiated between two peers.
If used on subsequent negotiations, it means that all pre-existing
SAs (phase 1 and phase 2) held between the peers should be deleted.
As an example, this is the mechanism used to detect when an SA end
point has crashed and is now alive again.
The use of INITIAL-CONTACT may be restricted by the mode used to
negotiate phase 1 SAs. For these reasons, implementation may want to
avoid the use of aggressive mode when possible. When it is used, it
is recommended that the third aggressive mode message be encrypted
so that the INITIAL-CONTACT notification can be added to it when
needed. Note that the responder during aggressive mode is never
allowed to use any notification, and this document's suggestion that
the use of INITIAL-CONTACT is permitted by the initiator if the
third aggressive mode packet is encrypted is possibly contrary to
RFC2408.
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3.4.3 DELETE Notification
As currently defined by the IPSec documents, the DELETE notification
is advisory only and is optional and unacknowledged.
Given that it is optional, UDP based, and not used by some existing
implementations, it should never be considered necessary.
However, even though its use is of dubious value, it SHOULD be sent
when any SA (phase 1 or phase 2) is deleted, since the expiration of
SAs may not occur at the same time at both ends to increase the
probability that both ends are synchronised with respect to SA
usage.
Further, implementations should attempt to use the acknowledged
notify exchange as described in [IKEbis].
3.4.4 Re-keying Timing
To reduce the probability of simultaneous re-keying, each device
should re-key at a variable time with respect to the SA's expiration
limit, in case they are the same. These recommendations apply to
both phase 1 and phase 2 SAs.
An example of this is that the end with the higher IP address re-
keys at 95% of the lifetime, while the end with lower IP address re-
keys at 85% of the lifetime.
Whatever rule is chosen, it is recommended that the rule be
deterministic in order to have predictable and consistent behaviour
between peers. If the rule had used the SPI as the determining
factor (as an example did in the first version of this document),
different peers would be doing the re-keying at different times.
In any case, simultaneous attempts at re-keying should be supported
in one form or another, since it can never be guaranteed that this
will not happen under all circumstances.
4. Next IPSec Version Recommendations
The recommendations made in sections 2 and 3 of this document have
limitations in their ability to provide lossless, reliable and
interoperable SA re-keying due to restrictions of existing
implementations and the existing IPSec documentation.
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This section makes recommendations for explicit re-transmission
rules, phase 1 and phase 2 re-keying, and describes the use of a new
mode for reliable SA deletion in order to better provide reliable,
lossless and interoperable re-keying.
Also, a replacement for the commit bit is proposed.
4.1 Re-transmission Rules
In systems that use exchanges that have an even number of packets,
the rules for re-transmission are relatively obvious. Simply put, a
packet is re-sent if the expected response to it is not received
within a certain period of time.
However, IPSec has a number of modes that have an odd number of
packets. This can lead to confusion as to when the re-transmission
rules should be applied, depending how the re-transmission rules are
applied to the packets in the echange. This in turn can lead to the
dropping of aggressive and quick modes' third messages. It is
recommended that each of these modes have specific rules applied to
them to avoid re-transmission issues.
These rules will be applied based on request-response pairs. Packets
are defined as a request or a response in an exchange. The requestor
is responsible for re-sending the request in order to solicit the
response. The responder (not to be confused with an SA negotiation
responder) is responsible for re-sending the response as it receives
the initial and subsequent transmissions of the request. Note that
the responder must exist after transmitting a response in case that
response is dropped.
In the modes with an odd number of packets, the request-response
pair must be applied across the odd number of packets. This means
that at least one packet must be considered the response to the
previous packet, and must also be considered the request of the next
request-response pair.
This means that an implementation must be able to perform re-
transmission of packets after it normally would have considered
itself to be done with an exchange or a mode. Further, any timers
set by the transmission of the final message of an exchange should
be reset when re-transmission occurs.
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4.1.1 Main Mode Re-Transmission Rules
In main mode, there are effectively three completely separate
exchanges. The first request-response pair contains the SA
proposals, the second pair contains the keying material, and the
third pair contains the authentication material. (These descriptions
are generalised for the purposes of stating what the exchanges are,
and are not intended to create discussion on the actual contents of
the exchanges.)
As an example of the separation of the exchanges, there is no need
to re-send the second main message to solicit the third main mode
message, since the responder should not send the fourth main mode
message until receiving the third main mode message. The absence of
the fourth main mode message will cause the initiator to re-send the
third main mode message.
Keeping the exchanges separate from a re-transmission point of view
should simplify implementations.
4.1.2 Aggressive Mode Re-Transmission Rules
In aggressive mode, the second message is the message that is both a
response and a request. Therefore, the responder in a phase 1
negotiation that uses aggressive mode must re-transmit the second
aggressive mode message to solicit a third aggressive mode message
that it perceives as lost.
4.1.3 Quick Mode Re-Transmission Rules
In quick mode, the second message is the message that is both a
response and a request. Therefore, the responder in a phase 1
negotiation must re-transmit the second quick mode message to
solicit a third quick mode message that it perceives as lost.
These rules must apply independently of the state of the commit bit,
since there are currently no timing restrictions on the transmission
of the CONNECTED notification.
4.2 Acknowledged SA Deletion
A previous version of this document described a new mode called
Delete Mode. This mode is no longer necessary, as the new proposed
Acknowledged Informational exchange can be used with the delete
payload to perform the same thing. (See section 6.4.2 of [IKEbis].)
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This section describes in detail how the Acknowledged Informational
exchange is used when deleting SAs.
The Acknowledged Informational exchange consists of two packets. The
first packet is the transmission of a notify or delete payload. The
second is the acknowledgement of that packet.
When used with a delete payload, it is interpreted to mean the
following:
"I am not sending anymore traffic on this SA (or these SA pairs).
Would you please stop sending traffic on it (or them), and send me
an acknowledgement when you are done?"
The receiver of the delete request then switches his outbound
traffic to another SA, deletes both inbound and outbound SAs and
sends the delete acknowledgement.
This is interpreted to mean:
"I am also not sending anymore traffic on this SA (or these SA
pairs). You may delete it (or them)."
The receiver of the delete acknowledgement may then delete the
inbound SA. The outbound SA should have already been deleted or
somehow not used before the sending of the delete request.
Note that re-transmission rules apply to the request-acknowledge
pair. That is, if the initiator of the delete mode does not get the
delete acknowledgement, the delete request should be re-transmitted.
Similarly, if the responder of the delete request receives multiple
copies, multiple copies of the delete acknowledgement should be
sent.
If the retry counter for the delete request expires, the SAs
indicated in the request should be unilaterally deleted.
Note that there is a race condition for the delete request and
delete acknowledgement packets if an implementation sends them
immediately after sending a packet on one of the SAs to be deleted.
The race occurs if the packet order gets changed in the network and
the delete mode packets arrive before packets sent on the SAs to
which the deletes refer.
The delete request-acknowledgement pair should also be applied to
phase 1 SAs. In this case, the phase 1 SA is not completely torn
down until the reception of the delete acknowledgement message.
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As a specific clarification, the binding between the inbound and the
outbound phase 2 SAs is not weakened. In the messages used, the SA
specified in the delete request is that of the sender's inbound SA.
In other words, the SPI sent to be deleted is the SPI that was
generated by the sender. When phase 1 SAs are being deleted, the SPI
values used are the cookies of the phase 1 SA to be deleted.
The use of the Acknowledged Informational does not eliminate the use
for the existing DELETE notification. It could still be used if an
implementation determines it needs to immediately (and impolitely)
delete an SA. Implementations must still recognise that it is sent
over UDP and may be dropped.
4.3 Phase 1 Re-keying for IPSecond
The phase 1 re-keying method described in Section 3 requires only
one change for IPSecond. That is the required use of the
Acknowledged Informational exchange when deleting SAs.
4.4 Phase 2 Re-keying for IPSecond
The phase 2 re-keying proposal described in Section 2, while
necessary under the circumstances, is not the ideal method of re-
keying. It forces the specific transfer times of SAs, thus making
the intent of paragraph 2, section 9 of [IKE] impossible.
This section describes proposals related to re-keying for the next
version of the IPSec protocols. The purpose is to precisely define
re-keying so that implementations are lossless and perfectly
interoperable during re-keying. It also allows the spirit of
paragraph 2, section 9 of [IKE] to be used. Further, it meets the
requirements of paragraph 3 of section 4.3 of [ISAKMP].
A summary of the recommendations is:
1) Define and require that the normal procedure is to use the
oldest phase 2 SA first, and to use it until its natural
expiration.
2) Use the recommended re-transmission request rules for quick
mode.
3) Make use of the Acknowledged Informational exchange a
requirement for SA deletion.
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4.4.1 Oldest Phase 2 SA First
The concept of using the oldest phase 2 SA first for outbound
traffic allows the maximum use of negotiated keys and allows for the
pre-negotiation of an arbitrary number of phase 2 SAs to be made
available for later use.
Additionally, it decouples new phase 2 SA negotiation from old phase
2 SA deletion, and the need to transfer to the new SA during re-
keying.
It also eliminates the race condition that occurs during SA set up
during re-keying. This means that use of the commit bit to avoid the
race condition is not necessary except when the very first phase 2
SA is set up.
The oldest SA is defined as the first negotiated of the available
SAs. In cases of simultaneous and near simultaneous SA negotiation,
the use of the delete mode and the ability to overlap SAs for an
arbitrary period of time should make this condition manageable.
4.4.2 Phase 2 Re-keying Illustration
This section illustrates the events when re-keying occurs using the
above proposals. Note the simplifications due to the decoupling of
SA negotiation and old SA deletion.
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Initiator Responder
Inbound Outbound Inbound Outbound
| | | |
1 ----------------- | |
| | ------------ | |
| | -------------------> 2
| | | | |
| | -------------------- 3
| | ------------ | |
4 <--------------- | |
| | | | |
5 ---------------- | |
| *6 | ------------ | |
| | | ------------------> 7
| | | | |
| | | | *8 |
| | | | | |
9
| | | | | |
| | *10 *10 | | |
11 ----------------- | | | |
| | ------------ | | |
| | | -------------------> 12
| | | | | |
| | | | | *13 * 13
| | | | | |
| | | | | |
| | | -------------------- 14
| | ------------ *15| |
16 <--------------- | | |
| | | | |
*17| | | |
| | | |
Figure 4-1 Recommended IPSecond Phase 2 Re-key Sequence Chart,
Initiator Expiration
1) Initiator sends first quick mode message.
2) Responder receives first quick mode message.
3) Responder sends second quick mode message.
4) Initiator receives second quick mode message.
5) Initiator sends third quick mode message.
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6) Initiator sets up new inbound SA. Implementations may choose to
set up the new outbound SA at this time, as long as they do not
use it.
7) Responder receives third quick mode message.
8) Responder set up new inbound SA. Implementations may choose to
set up the new outbound SA at this time, as long as they do not
use it.
9) Initiator's old SA pair expires.
10) Initiator starts using new outbound SA and stops using old
outbound SA.
11) Initiator sends first Acknowledged Informational exchange
message with a delete payload.
12) Responder receives first Acknowledged Informational exchange
message.
13) Responder sets up new outbound SA.
13) Responder deletes old outbound SA and starts using new outbound
SA.
14) Responder sends second Acknowledged Informational exchange
message.
15) Responder deletes old inbound SA.
16) Initiator receives second Acknowledged Informational exchange
message.
17) Initiator deletes old inbound SA.
If the responder's old SA expires first, the events are as follows.
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Initiator Responder
Inbound Outbound Inbound Outbound
| | | | | |
9
| | | | | |
| | | | | *10 *10
| | | | | |
| | | -------------------< 11
| | | ------------ | | |
12 <--------------- | | |
| | | | | |
| | *13 *13 | | |
| | | | | |
| | | | | |
| | | | | |
14 >--------------- | | | |
15 * | ------------ | | |
| | -------------------> 16
| | | | |
| | 17 * | |
| | | |
Figure 4-2 Recommended IPSecond Phase 2 Re-key Sequence Chart,
Responder Expiration
9) Responder's old SA pair expires.
10) Responder starts using new outbound SA and stops using old
outbound SA.
11) Responder sends first Acknowledged Informational exchange
message with a delete payload.
12) Initiator receives first Acknowledged Informational exchange
message.
13) Initiator sets up new outbound SA.
13) Initiator deletes old outbound SA and starts using new outbound
SA.
14) Initiator sends second Acknowledged Informational exchange
message.
15) Initiator deletes old inbound SA.
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16) Responder receives second Acknowledged Informational exchange
message.
17) Responder deletes old inbound SA.
4.5 Commit Bit Replacement
The intent of this section is to propose a mechanism to allow
implementations to delay the usage of negotiated SAs. Its use may
eliminate the need for the commit bit, and will not suffer from any
of the problems of the commit bit. While the commit bit usage is
much better defined by [IKEbis], it is unable to solve all the
difficulties associated with it.
Replacement of the commit bit is done by introducing a new mechanism
to indicate to a peer that usage of a newly negotiated SA should be
deferred. Then, depending on the deferral time intended, one of two
mechanisms is introduced to indicate that the SA may be used.
These mechanisms are preferred over the commit bit for the following
reasons:
o They receive the full protection of phase 1 SAs, and as such
provide the maximum resistance to denial of service attacks.
o Their use is clearly and unambiguously defined.
o They are resistant to the possibilities of dropped packets.
4.5.1 DEFER_USAGE Notify Payload
The indication that an SA should not be made available for use
immediately by peer can be indicated by the addition of a new
notify payload to the quick mode that negotiated the SA. To allow a
single quick mode to negotiate multiple SAs, the DEFER_USAGE notify
payload explicitly names the SA whose use is to be deferred, in the
same manner as the current DELETE payload.
The DEFER_USAGE notify payload should be added by the peer wishing
to delay usage of an SA.
On reception of the DEFER_USAGE notify payload, the newly negotiated
SA should be set aside until reception of the ALLOW_USAGE notify
payload, described in the next section, or the reception of the
CONNECTED notification.
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The expected response depends on which type of DEFER_USAGE
notification is sent. These types are termed long and short. A short
DEFER_USAGE notification causes a quick mode to become four messages
in length, as with the intended use of the commit bit. A long
DEFER_USAGE notification causes quick mode to proceed normally, with
usage of the specified SA deferred until the sender of the
DEFER_USAGE notification sends the ALLOW_USAGE notify.
Implementations should be prepared to received the long DEFER_USAGE
notification for the same SA (pair) that they send it for; in other
words, usage of both SAs (inbound and outbound) of the negotiated
pairs may be deferred simultaneously by both peers.
There are no time constraints associated with the sending of the
long DEFER_USAGE notification and the subsequent reception of the
allow usage mode.
Usage of the short DEFER_USAGE notification is restricted to quick
mode responders only. It causes the transmission of a CONNECTED
notification as a fourth quick mode message in the same way that the
commit bit does.
4.5.2 ALLOW_USAGE Notify Payload
The purpose of this notify is to indicate to a peer that an SA may
now be used. Normally, usage of the SA by the peer would have been
deferred by the use of the long DEFER_USAGE notify payload,
described in the previous section. However, reception of this notify
for an SA whose usage has not been deferred is not considered an
error.
This payload MUST be used only with the Acknowledged Informational
exchange.
The initiator of the exchange must start usage of the inbound SA of
the pair when sending the first packet of the exchange. Usage of the
initiator's outbound SA must wait until reception of the
acknowledgement packet of the exchange.
The responder of the exchange must start usage of its inbound SA of
the pair before sending the acknowledgement, and may start usage of
its outbound SA of the pair any time after receiving the first
packet of the exchange.
The initiator of the exchange re-transmits the ALLOW_USAGE
notification until it receives the acknowledgement packet or exceeds
its re-try counter.
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If use of the SA was deferred by both peers, two transactions of the
ALLOW_USAGE notification are required (one in each direction) before
the SAs involved may be used.
5. Acknowledgements
Some of the concepts presented in this document are based on work
done by TimeStep Corporation's engineering group.
Others are taken from concepts discussed within the IPSec working
group, particularly some of the concerns expressed about problems
with the commit bit.
6. References
[IKE] Harkins, D., Carrel, D., "The Internet Key Exchange (IKE)",
RFC2409, November 1998
[ISAKMP]Maughan, D., Schertler, M., Schneider, M., and Turner, J.,
"Internet Security Association and Key Management Protocol
(ISAKMP)", RFC2408, November 1998
[IKEbis]Harkins, D., Carrel, D., "The Internet Key Exchange (IKE)",
draft-ietf-ipsec-ike-01.txt, May 1999
Revision History
September 23, 1998 Initial Release
April 7, 1999 -clarification of objectives of document
-more commit bit comments
-change phase 1 re-keying discussion to explicitly
allow multiple phase 1 SAs between peers; previous
version explicitly allowed only 1 phase 1 between
peers
-other miscellaneous changes
October 20, 1999 -separation of phase 1 re-keying into continuous
channel and dangling SA implementations
-use of Acknowledged Information exchange used
where possible
-other changes
Jenkins [Page 37]
Internet Draft IPSec Re-keying Issues October 1999
Security Considerations
This document is associated with the IPSec family of documents. As
such, security considerations permeate the document.
Author's Address
Tim Jenkins
tjenkins@timestep.com
TimeStep Corporation
362 Terry Fox Drive
Kanata, ON
Canada
K2K 2P5
+1 (613) 599-3610
The IPSec working group can be contacted via the IPSec working
group's mailing list (ipsec@lists.tislabs.com) or through its
chairs:
Robert Moskowitz
rgm@icsa.net
International Computer Security Association
Theodore Y. Ts'o
tytso@MIT.EDU
Massachusetts Institute of Technology
This document expires April 20, 2000
Jenkins [Page 38]