One document matched: draft-ietf-rsvp-md5-06.txt
Differences from draft-ietf-rsvp-md5-05.txt
Internet Draft Fred Baker
Expiration: February 1999 Cisco
File: draft-ietf-rsvp-md5-06.txt Bob Lindell
USC/ISI
Mohit Talwar
USC/ISI
RSVP Cryptographic Authentication
Status of this Memo
This document is an Internet-Draft. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas,
and its working groups. Note that other groups may also distribute
working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress". Comments
should be made on the list rsvp@isi.edu.
To view the entire list of current Internet-Drafts, please check the
"1id-abstracts.txt" listing contained in the Internet-Drafts Shadow
Directories on ftp.is.co.za (Africa), ftp.nordu.net (Northern
Europe), ftp.nis.garr.it (Southern Europe), munnari.oz.au (Pacific
Rim), ftp.ietf.org (US East Coast), or ftp.isi.edu (US West Coast).
Abstract
This document describes the format and use of RSVP's INTEGRITY object
to provide hop-by-hop integrity and authentication of RSVP messages.
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1. Introduction
The Resource ReSerVation Protocol RSVP [1] is a protocol for setting
up distributed state in routers and hosts, and in particular for
reserving resources to implement integrated service. RSVP allows
particular users to obtain preferential access to network resources,
under the control of an admission control mechanism. Permission to
make a reservation will depend both upon the availability of the
requested resources along the path of the data, and upon satisfaction
of policy rules.
To protect the integrity of this admission control mechanism, RSVP
requires the ability to protect its messages against corruption and
spoofing. This document defines a mechanism to protect RSVP message
integrity hop-by-hop. The proposed scheme transmits an
authenticating digest of the message, computed using a secret
Authentication Key and a keyed-hash algorithm. This scheme provides
protection against forgery or message modification. The INTEGRITY
object of each RSVP message is tagged with a one time use sequence
number. This allows the message receiver to identify playbacks and
hence to thwart replay attacks. The proposed mechanism does not
afford confidentiality, since messages stay in the clear; however,
the mechanism is also exportable from most countries, which would be
impossible were a privacy algorithm to be used. Note: this document
uses the terms "sender" and "receiver" differently from [1]. They
are used to refer to systems which face each other across an RSVP
hop, the "sender" being the system generating RSVP messages.
The message replay prevention algorithm is quite simple. The sender
generates packets with increasing sequence numbers. In turn, the
receiver only accepts packets which have a larger sequence number
than the previous packet. To get this process started, a receiver
handshakes with the sender to get a starting sequence number. This
memo discusses ways to relax the strictness of the in order delivery
of messages as well as techniques to generate monotonically
increasing sequence numbers that are robust across sender failures
and restarts.
The proposed mechanism is independent of a specific cryptographic
algorithm, but the document describes the use of Keyed-Hashing for
Message Authentication using HMAC-MD5 [8]. As noted in [8], there
exist stronger hashes, such as HMAC-SHA1; where warranted,
implementations will do well to make them available. However, in the
general case, [8] suggests that HMAC-MD5 is adequate to the purpose
at hand and has preferable performance characteristics. [8] also
offers source code and test vectors for this algorithm, a boon to
those who would test for interoperability. HMAC-MD5 is required as a
baseline to be universally included in RSVP implementations providing
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cryptographic authentication, with other proposals optional (see the
section on Conformance Requirements below).
The RSVP checksum may be disabled (set to zero) if HMAC-MD5
authentication is used, as the HMAC-MD5 digest is a much stronger
integrity check.
Two uses are envisioned for INTEGRITY objects: authentication of RSVP
messages (or message fragments, should a fragmentation procedure be
defined in the future), and authentication of policy data objects
[10]. The INTEGRITY object used in both is the same, and is defined
in this document. The use of the INTEGRITY object for those purposes
is defined in other documents [1] [7].
1.1. Conventions used in this document
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 [9].
1.2. Why not use the Standard IPSEC Authentication Header?
One obvious question is why, since there exists a standard mechanism,
IPSEC, for authentication [5], we would choose not to use it. This
was discussed at length in the working group, and the use of IPSEC
was rejected for the following reasons.
The security associations in IPSEC are based on destination address.
It is not clear that RSVP messages are well defined for either source
or destination based security associations, as a router must forward
PATH and PATH TEAR messages using the same source address as the
sender listed in the SENDER TEMPLATE. RSVP traffic may otherwise not
follow exactly the same path as data traffic. Using either source or
destination based associations would require opening a new security
association among the routers that a flow traverses for each flow
making reservations.
In addition, it was noted that neighbor relationships between RSVP
systems are not limited to those which face one another across a
communication channel. RSVP relationships across non-RSVP clouds,
such as those described in section 2.8 of [1], are not necessarily
visible to the sending system, suggesting that key management based
on RSVP router to RSVP router associations may allow a simpler key
management strategy.
2. Data Structures
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2.1. INTEGRITY Object Format
An RSVP Message consists of a sequence of "objects," which are type-
length-value encoded fields having specific purposes. The
information required for hop-by-hop integrity checking is carried in
an INTEGRITY object. The same INTEGRITY object type is used for both
IPv4 and IPv6.
The contents of an INTEGRITY object are defined as a "Keyed Message
Digest" structure, with the following format:
Keyed Message Digest INTEGRITY Object: Class = 4,
C-Type = 1
+-------------+-------------+-------------+-------------+
| Key Identifier |
| |
+-------------+-------------+-------------+-------------+
| Sequence Number |
| |
+-------------+-------------+-------------+-------------+
| |
+ +
| |
+ Keyed Message Digest |
| |
+ +
| |
+-------------+-------------+-------------+-------------+
(1) Key Identifier
An unsigned 64-bit number that acts as a key selector. With
the key, the system stores an algorithm for its application.
Senders SHOULD pick globally unique key identifiers. This
can be accomplished by using an IP address, a hash of an IP
address, or a globally unique MAC address concatenated with a
key number.
(2) Sequence Number
An unsigned 64-bit monotonically increasing, unique sequence
number.
Any monotonically increasing sequence of numbers, that
provides the INTEGRITY object of each RSVP message with a
unique tag, may be used as Sequence Number values. Details
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on sequence number generation are presented in the next
section.
(3) Keyed Message Digest
The digest must be a multiple of 4 octets long. For HMAC-
MD5, it will be 16 bytes long.
3. Generating Sequence Numbers
In this section we describe methods which could be chosen to generate
the sequence numbers used in the INTEGRITY object of an RSVP message.
As previous stated, there are two important properties that MUST be
satisfied by the generation procedure. The first property is that
the sequence numbers are unique, or one time, for the lifetime of the
integrity key that is in current use. A receiver can use this
property to unambiguously distinguish between a new or a replayed
message. The second property is that the sequence numbers are
generated in monotonically increasing order. This is required to
greatly simplify the message processing rules, since a receiver only
needs to save the value of the highest sequence number seen to avoid
a replay attack.
The size of the sequence number field is chosen to be a 64-bit
unsigned quantity. This is large enough to avoid exhaustion over the
key lifetime. For example, if a key lifetime was conservatively
defined as one year, there would be enough sequence number values to
send RSVP messages at an average rate of about 585 gigaMessages per
second. A 32-bit sequence number would limit this average rate to
about 136 messages per second.
The ability to generate unique monotonically increasing sequence
numbers across a failure and restart implies some form of stable
storage, either local to the device or remotely over the network.
Three state-based sequence number generation procedures are described
below.
3.1. Simple Sequence Numbers
The most straight forward approach would be to generate a unique
sequence number using a message counter. Each time a message is
transmitted for a given key, the sequence number counter is
incremented. The current value of this counter is continually or
periodically saved to stable storage. Recovery of this counter after
a restart is accomplished by using this stable storage. If the
counter was saved periodically to stable storage, the count should be
recovered by increasing the saved value to be larger than any
possible value of the counter at the time of the failure. This can
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be computed knowing the interval at which the counter was saved to
stable storage and incrementing the stored value by that amount.
3.2. Sequence Numbers Based on a Real Time Clock
Most devices will probably not have the capability to save sequence
number counters to stable storage for each key. A more universal
solution is to base sequence numbers on the stable storage of a real
time clock. Many computing devices have a real time clock module
that includes stable storage of the clock. These modules generally
include some form of nonvolatile memory to retain clock information
in the event of a power failure.
In this approach, we use an NTP based timestamp value as the sequence
number. The rollover period of an NTP timestamp is about 136 years,
much longer than any reasonable lifetime of a key. In addition, the
granularity of the NTP timestamp is fine enough to allow the
generation of an RSVP message every 200 picoseconds for a given key.
Many real time clock modules do not have the resolution of an NTP
timestamp. In these cases, the least significant bits of the
timestamp can be generated using a message counter, which is reset
every clock tick. For example, when the real time clock provides a
resolution of 1 second, the 32 least significant bits of the sequence
number can be generated using a message counter. The remaining 32
bits are filled with the 32 least significant bits of the timestamp.
Assuming that the recovery time after failure takes longer than one
tick of the real time clock, the message counter for the low order
bits can be reset to zero.
3.3. Sequence Numbers Based on a Network Recovered Clock
If the device does not contain any stable storage, it could recover
the real time clock from the network using NTP. Once the clock has
been recovered, following a restart, the sequence number generation
procedure would be identical to the procedure described in section
6.2.
3.4. Sequence Number Wraparound
Sequence numbers might roll over within some key's lifetime. To
accomodate this behavior, each receiver MUST accept monotonically
increasing sequence numbers, modulo 2^64. In addition, we assume
that a key's lifetime is short enough for the key to expire within
half the sequence number space. With this assumption, receivers MUST
reject sequence numbers which lie in the wrong half of the sequence
number space. This solution draws directly from the TCP sequence
number algorithm [11].
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4. Message Processing Rules
4.1. Message Generation
An RSVP message is created as specified in [1], with these
exceptions:
(1) The RSVP checksum field is set to zero. If required, an RSVP
checksum can be calculated after step (7), when the processing
of the INTEGRITY object is complete.
(2) The INTEGRITY object is inserted in the appropriate place, and
its location in the message is remembered for later use.
(3) The current sequence number must be updated, if required, to
ensure a unique, monotonically increasing number. It is then
placed in the Sequence Number field of the INTEGRITY object.
(4) The Keyed Message Digest field is set to zero.
(5) The Key Identifier is placed into the INTEGRITY object.
(6) An authenticating digest of the is computed using the
appropriate Authentication Key in conjunction with the keyed-
hash algorithm. When the HMAC-MD5 algorithm is used, the hash
calculation is described in [8].
(7) The digest is written into the Cryptographic Digest field of the
INTEGRITY object.
In the sender, Authentication Key selection is based on the interface
through which the message is sent, there being a key configured per
interface. While administrations may configure all the routers and
hosts on a subnet (or for that matter, in their network) with the
same key, implementations MUST assume that each sender may send with
a different key on each interface (be it numbered or unnumbered), and
that the keys are simplex - the key that a system uses to sign its
messages need not be same key that its receivers use to sign theirs.
Implementations SHOULD maintain a separate key per interface they
send on. User interfaces SHOULD provide convenient ways to configure
these keys.
An RSVP router may have unnumbered interfaces which carry a common IP
address but distinct Logical Interface Handles (LIHs) for RSVP. In
these cases, an implementation SHOULD maintain a separate key per
LIH. In addition, Key Identifier values should be formed using some
combination of the common IP address, the LIH, and the key number in
an attempt to produce a global unique value.
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4.2. Message Reception
When the message is received, the process is reversed:
(1) The RSVP checksum field is set to zero.
(2) The Cryptographic Digest field of the INTEGRITY object is set
aside.
(3) The Key Identifier field is used to determine the Authentication
Key and the hash algorithm to be used. In the rare event that
the key identifier is not unique, each matching Authentication
Key and associated hash algorithm is applied in an attempt to
find a match.
(4) The sequence number is validated to prevent replay attacks, and
messages with invalid sequence numbers are ignored by the
receiver.
Every time a message is accepted, the sequence number of that
message updates the stored value corresponding to the largest
sequence number received to date. Each subsequent message must
have a larger sequence number to be accepted (see section 3.4).
This simple processing rule prevents message replay attacks, it
must be modified to be tolerant to limited out of order message
delivery.
If several messages were sent simultaneously (for example, in a
periodic refresh generated by a router, or as a result of a tear
down function), a reordering problem might arise either due to
the use of CBQ/WFQ queuing algorithms in the sender, or due to
reordering in an intervening non-RSVP cloud. Therefore, the
sequence number received may not be higher than the number last
seen.
An implementation SHOULD allow administrative configuration
which sets the tolerance to out of order message delivery. A
simple approach would allow administrators to specify a message
window corresponding to the worst case reordering behavior. For
example, one might specify that packets reordered within a 32
message window would be accepted. If no reordering can occur,
the window is set to one. Since sequence numbers might not be
strictly sequential, it is necessary to store a list of all
sequence numbers seen during the reordering window. Acceptance
of a sequence number implies adding it to the list and removing
a number from the lower end of the list.
A received sequence number is valid if (a) it is greater than
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the maximum sequence number received as yet or (b) a past
sequence number lying within the reordering window and not
recorded in the list. Messages received with sequence numbers
lying below the lower end of the window or marked seen in the
list are silently discarded.
(5) The Cryptographic Digest field of the INTEGRITY object is set to
zero.
(6) A new keyed-digest is calculated using the indicated algorithm
and the Authentication Key.
(7) If the calculated digest does not match the received digest, the
message is discarded without further processing.
4.3. Handshake at Restart or Initialization of the Receiver
During initialization or restart, a receiver must obtain a starting
sequence number for a sender whose messages require an integrity
check. The receiver SHOULD initiate a handshake with the sender to
attain this information.
An RSVP capable device challenges another device with an RSVP
handshake message containing a unique sequence number generated by
the standard methods outlined earlier. The remote device receives
the challenge and returns an INTEGRITY-checked RSVP handshake message
which contains the original sequence number. The response is
accepted only if the original sequence number matches the returned
sequence number in the message. This prevents replay of old
handshake responses. If the sequence number matches, the device
saves the remote sequence number from the INTEGRITY object, along
with the key for the remote device. If a response is not received
within a given period of time, the challenge is repeated. When the
handshake is successfully completed, a device will begin accepting
normal RSVP signaling messages from that sender and ignore any other
handshake responses.
An RSVP handshake message will carry a message type of 11. The
message format is as follows:
<INTEGRITY Handshake message> ::= <Common Header> [ <INTEGRITY> ]
<CHALLENGE>
The contents of a CHALLENGE object is defined with the following
format:
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CHALLENGE Object: Class = 16,
C-Type = 1
+-------------+-------------+-------------+-------------+
| Sequence Number |
| |
+-------------+-------------+-------------+-------------+
The use of a handshake may not be necessary in all environments. A
common use of RSVP integrity will be between peering domain routers,
which are likely to be processing a steady stream of RSVP messages
due to aggregation effects. If a router crashes and restarts, there
will probably be valid RSVP messages from peering senders arriving
within a short duration of restart. Assuming that replay messages
are injected into the stream of valid RSVP messages, there may only
be a small window of opportunity for a replay attack before a valid
message is processed. This valid message will set the largest
sequence number seen to a value greater than any number that had been
stored prior to the crash, preventing any further replays.
On the other hand, not using a handshake could allow exposure to
replay attacks if there is a long period of silence from a given
sender following a restart of a receiver. It SHOULD be an
administrative decision whether or not a handshake is performed.
That decision will be based on assumptions related to a particular
network environment.
5. Key Management
It is likely that the IETF will define a standard key management
protocol. It is strongly desirable to use that key management
protocol to distribute RSVP Authentication Keys among communicating
RSVP implementations. Such a protocol would provide scalability and
significantly reduce the human administrative burden. The Key ID can
be used as a hook between RSVP and such a future protocol. Key
management protocols have a long history of subtle flaws that are
often discovered long after the protocol was first described in
public. To avoid having to change all RSVP implementations should
such a flaw be discovered, integrated key management protocol
techniques were deliberately omitted from this specification.
5.1. Key Management Procedures
Each key has a lifetime associated with it. In general, no key is
ever used outside its lifetime (but see section 5.3). If more than
one key is currently alive, then the youngest key (the key whose
lifetime most recently started) should be sent.
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Possible mechanisms for managing key lifetime include: the use of the
Network Time Protocol, hardware time-of-day clocks, or waiting some
time before emitting the first message to determine what key other
systems are signing with. The matter is left for the implementor.
Note that the concept of a "key lifetime" does not require a hardware
time-of-day clock or the use of NTP, although one or the other is
advised; it merely requires that the earliest and latest times that
the key is valid must be programmable in a way the system
understands.
To maintain security, it is advisable to change the RSVP
Authentication Key on a regular basis. It should be possible to
switch the RSVP Authentication Key without loss of RSVP state or
denial of reservation service, and without requiring people to change
all the keys at once. This requires the RSVP implementation to
support the storage and use of more than one RSVP Authentication Key
on a given interface at the same time.
For each key there will be a locally-stored Key Identifier. The
combination of the Key Identifier and the interface associated with
the message identifies the cryptographic algorithm and Authentication
Key in use by RSVP. As noted above, the sender will select a valid
key from the set of valid keys for that interface. The receiver will
use the Key Identifier to determine which key to use for
authentication of the received message. More than one key may be
associated with an interface at the same time.
To ensure a smooth switch-over, each communicating RSVP system must
be updated with the new key before the current key will expire and
before the new key lifetime begins. The new key should have a
lifetime that starts several minutes before the old key expires.
This gives time for each system to learn of the new RSVP
Authentication Key before that key will be used. It also ensures
that at the time that the current key's lifetime has expired, all
systems have prepared to send and receive data using the new key.
For the duration of the overlap in key lifetimes, a system may
receive messages using either key and authenticate the message.
There are four important times for each key:
+ KeyStartReceive: the time the system starts accepting received
packets signed with the key.
+ KeyStartSign: the time the system starts signing packets with the
key.
+ KeyStopSign: the time the system stops signing packets with the
key, which implies that it starts signing with the next key, if
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any.
+ KeyStopReceive: the time the system stops accepting received
packets signed with the key.
The times in the order listed SHOULD form a non-decreasing sequence.
There needs to be some distance between start times and stop times,
to achieve a seamless transition.
5.2. Key Management Requirements
Requirements on an implementation are as follows.
(1) It is strongly desirable that a hypothetical security breach in
one Internet protocol not automatically compromise other
Internet protocols. The Authentication Key of this
specification SHOULD NOT be stored using protocols or algorithms
that have known flaws.
(2) An implementation MUST support the storage of more than one key
at the same time, although normally only one key will be active
on an interface.
(3) An implementation MUST associate a specific lifetime (i.e.,
KeyStartSign and KeyStopSign) with each key and corresponding
Key Identifier.
(4) An implementation MUST support manual key distribution (e.g.,
the privileged user manually typing in the key, key lifetime,
and key identifier on the console). The lifetime may be
infinite.
(5) If more than one algorithm is supported, then the implementation
MUST require that the algorithm be specified for each key at the
time the other key information is entered.
(6) Keys that are out of date MAY be deleted at will by the
implementation without requiring human intervention.
(7) Manual deletion of active keys SHOULD also be supported.
(8) Key storage SHOULD persist across a system restart, warm or
cold, to avoid operational issues.
5.3. Pathological Cases
An implementation of this document must handle two pathological
cases. Both of these should be exceedingly rare.
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(1) During key switch-over, devices may exist which have not yet
been successfully configured with the new key.
If a key is shared with multiple receivers, there is a region of
uncertainty around the time of key switch-over during which some
receivers may still be using the old key and others have
switched to the new key. The size of this uncertainity region
is related to clock synchrony of the receivers. Administrators
should configure the overlap between the expiration time of the
old key (KeyStopReceive) and the validity of the new key
(KeyStartReceive) to be at least twice the size of this
uncertainity interval. This will allow a sender to make the key
switch-over at the midpoint of this interval and be confident
that all receivers are now accepting the new key.
(2) It is possible that the last key associated with an interface
may expire.
When this happens, it is unacceptable to revert to an
unauthenticated condition, and not advisable to disrupt current
reservations. Therefore, the system should send a "last
authentication key expiration" notification to the network
manager and treat the key as having an infinite lifetime until
the lifetime is extended, the key is deleted by network
management, or a new key is configured.
6. Conformance Requirements
To conform to this specification, an implementation MUST support all
of its aspects. The HMAC-MD5 authentication algorithm defined in [8]
MUST be implemented by all conforming implementations. A conforming
implementation MAY also support other authentication algorithms such
as NIST's Secure Hash Algorithm (SHA). Manual key distribution as
described above MUST be supported by all conforming implementations.
All implementations MUST support the smooth key roll over described
under "Key Change Procedures."
The user documentation provided with the implementation MUST contain
clear instructions on how to ensure that smooth key roll over occurs.
Implementations SHOULD support a standard key management protocol for
secure distribution of RSVP Authentication Keys once such a key
management protocol is standardized by the IETF.
7. Acknowledgments
This document is derived directly from similar work done for OSPF and
RIP Version II, jointly by Ran Atkinson and Fred Baker. Significant
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editing was done by Bob Braden, resulting in increased clarity. (if
you think this document was hard to read, think about what Bob read).
Significant comments were submitted by Steve Bellovin, who actually
understands this stuff. Matt Crawford and Dan Harkins helped revise
the document.
8. References
[1] Braden, R., Ed., Zhang, L., Estrin, D., Herzog, S., and S.
Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
Functional Specification". Internet Draft draft-ietf-rsvp-
spec-14.ps, January 1997.
[2] S. Bellovin, "Security Problems in the TCP/IP Protocol Suite",
ACM Computer Communications Review, Volume 19, Number 2, pp.32-
48, April 1989.
[3] N. Haller, R. Atkinson, "Internet Authentication Guidelines",
Request for Comments 1704, October 1994.
[4] R. Braden, D. Clark, S. Crocker, & C. Huitema, "Report of
IAB Workshop on Security in the Internet Architecture", Request
for Comments 1636, June 1994.
[5] R. Atkinson, "IP Authentication Header", Request for Comments
1826, August 1995.
[6] R. Atkinson, "IP Encapsulating Security Payload", Request for
Comments 1827, August 1995.
[7] S. Herzog, "RSVP Extensions for Policy Control", draft-ietf-
rsvp-policy-ext-02.txt, March 1997.
[8] Krawczyk, Bellare, and Canetti, "HMAC: Keyed-Hashing for Message
Authentication", Request for Comments 2104, March 1996.
[9] [RFC-2119], Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, Harvard University, March 1997.
[10] R. Yavatkar, D. Pendarakis, R. Guerin, "A Framework for
Policy-based Admission Control", draft-ietf-rap-framework-00.txt
November 1997.
[11] Postel, Jon, "Transmission Control Protocol", Request for
Comments 793, September 1981.
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9. Security Considerations
This entire memo describes and specifies an authentication mechanism
for RSVP that is believed to be secure against active and passive
attacks. Passive attacks are widespread in the Internet at present.
Protection against active attacks is also needed even though such
attacks are not as widespread.
Users need to understand that the quality of the security provided by
this mechanism depends completely on the strength of the implemented
authentication algorithms, the strength of the key being used, and
the correct implementation of the security mechanism in all
communicating RSVP implementations. This mechanism also depends on
the RSVP Authentication Keys being kept confidential by all parties.
If any of these assumptions are incorrect or procedures are
insufficiently secure, then no real security will be provided to the
users of this mechanism.
While the handshake response is required to be INTEGRITY-checked, the
handshake challenge is not. This was done intentionally to eliminate
a dependency on an integrity key in the opposite direction.
Hence an intruder could generate fake handshaking challenges with a
certain sequence number. It could then save the response and attempt
to play it against a receiver that is in recovery. If it was lucky
enough to have guessed the sequence number used by the receiver at
recovery time it could use the saved response. This response would
be accepted, since it is properly signed, and would have a smaller
sequence number for the sender because it was an old message. This
opens the receiver up to replays.
This seems very difficult to exploit. Not only does it require
guessing the challenge sequence number in advance, but also being
able to masquerade as the receiver to generated a handshake request
with the proper IP address and not being caught. Moreover, since
messages flow back and forth there might be keys in both directions.
In such cases the receiver can also sign its challenge for the sender
to authenticate and cover this attack.
Confidentiality is not provided by this mechanism; if this is
required, IPSEC ESP [6] may be the best approach, although it is
subject to the same criticisms as IPSEC Authentication, and therefore
would be applicable only in specific environments. Protection
against traffic analysis is also not provided. Mechanisms such as
bulk link encryption might be used when protection against traffic
analysis is required.
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10. Authors' Addresses
Fred Baker
Cisco Systems
519 Lado Drive
Santa Barbara,
California 93111
Phone: (408) 526-4257
Email: fred@cisco.com
Bob Lindell
USC Information Sciences Institute
4676 Admiralty Way
Marina del Rey, CA 90292
Phone: (310) 822-1511
EMail: lindell@ISI.EDU
Mohit Talwar
USC Information Sciences Institute
4676 Admiralty Way
Marina del Rey, CA 90292
Phone: (310) 822-1511
EMail: mtalwar@ISI.EDU
Baker, et. al. Expiration: February 1999 [Page 16]
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