a draft that missed the deadline

[Sandy Murphy <[e-mail]>]

Attached you will find an internet-draft describing the security
vulnerabilities in BGP, some possible solutions and the costs of those
solutions.  This is an item that I've been supposed to complete for an
unconscionable length of time.  Unfortunately, I did not get it done
in time for submission to the IETF by the Friday cutoff.

Yakov has suggested that I discuss this at the idr meeting in Washington.

--Sandy Murphy
  Trusted Information Systems
  Glenwood, MD  21738
-------------------------------------------------------------------------








Network Working Group                                       Sandra Murphy
INTERNET DRAFT                                Trusted Information Systems
draft-ietf-bgp-secr-00.txt                                  November 1997


                         BGP Security Analysis



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 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''.

To learn the current status of any Internet Draft, please check the
1id-abstracts.txt listing contained in one of the Internet Drafts Shadow
Directories on ds.internic.net (US East Coast), venera.isi.edu (US West
Coast), munnari.oz.au (Pacific Rim), or nic.nordu.net (Europe).

Abstract

BGP, along with a host of other infrastructure protocols designed before
the Internet environment became perilous, is designed with little
consideration for protection of the data it communicates or of its own
behavior.  There are no mechanisms in BGP to protect against attacks
that modify, delete, forge, or replay data, any of which has the
potential to be destructive of overall network routing behavior.

This internet draft discusses some of the security issues with BGP
routing data dissemination, and possible security solutions and the
costs of those solutions.  This internet draft does not discuss security
issues with forwarding of packets.

1.  Introduction

The two most common inter-domain routing protocols, BGP and IDRP, were
created when the Internet environment had not yet reached the present
contentious state.  Consequently, neither protocol was designed with





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protection against deliberate or accidental errors causing disruptions
of routing behavior.

We here discuss the vulnerabilities of BGP, based on the BGP RFC [1].
Vulnerabilities in IDRP should be similar.  We propose several different
security solutions to protect these vulnerabilities, discuss the
benefits derived from each solution and its cost.

It is clear that the Internet is vulnerable to attack through its
routing protocols.  BGP is no exception.  Faulty, misconfigured or
deliberately malicious sources can disrupt overall Internet behavior by
injecting bogus routing information into the BGP distributed routing
database (by modifying, forging, or replaying BGP packets).  The same
methods can also be used to disrupt local and overall network behavior
by breaking the distributed communication of information.  The sources
can be either external or internal to the protocol, i.e., non-BGP
speakers or true BGP speakers.  Under the present BGP/IDRP design, any
external source can inject believable BGP/IDRP packets into the
communication between BGP/IDRP peers and thereby inject bogus routing
information or break the peer to peer connection.  With IP spoofing, the
external sources of bogus BGP information can reside anywhere in the
world.  Furthermore, external sources can disrupt communications between
BGP peers by breaking their TCP connection with spoofed RST packets.
Internal sources, i.e., BGP speakers themselves, can inject bogus
routing information masquerading as information from any other
legitimate BGP speaker.  Bogus information from either external or
internal sources can affect routing behavior in the Internet over a
wide, possibly unbounded, area.

Bogus routing information can have many different effects on routing
behavior.  If the bogus information removes routing information for a
particular network, that network can become unreachable for the portion
of the Internet that accepts the bogus information.  If the bogus
information changes the route to a network, then packets destined for
that network may be forwarded by a sub-optimal path, or a path that does
not follow the expected policy, or a path that will not forward the
traffic.  If the bogus information makes it appear that an autonomous
system originates a network when it does not, then packets for that
network may not be deliverable for the portion of the Internet that
accepts the bogus information.  A false announcement that an autonomous
systems originates a network may also fragment aggregated address blocks
in other parts of the Internet and cause routing problems for other
networks.







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2.  Specific Vulnerabilities

Each message introduces certain different vulnerabilities:

2.1.  OPEN

Because receipt of a new OPEN message in the Established state will
cause the close of the BGP peering session and thereby induce the
release of all resources and deletion of all associated routes, the
ability to spoof this message can lead to a severe disruption of
routing.

2.2.  KEEPALIVE

Receipt of a KEEPALIVE message when the peering connection is in the
OpenSent state can lead to a failure to establish a connection.  The
ability to spoof this message is a vulnerability, but difficult to
exploit deliberately, as it must be carefully timed in the sequence of
messages exchanged between the peers if it is to cause damage.

2.3.  NOTIFICATION

Receipt of a NOTIFICATION message will cause the close of the BGP
peering session and thereby induce the release of all resources and
deletion of all associated routes.  Therefore, the ability to spoof this
message can lead to a severe disruption of routing.

2.4.  UPDATE

The Update message carries the routing information.  The ability to
spoof any part of this message can lead to a disruption of routing.

2.4.1.  Unfeasible Routes Length, Total Path Attribute Length

There is a vulnerability arising from the ability to modify these
fields.  If a length is modified, the message is not likely to parse
properly, resulting in an error, the transmission of a NOTIFICATION
message and the close of the connection.  As a true BGP speaker is
always able to close a connection at any time, this vulnerability
represents an additional risk only when the source is external, i.e., it
presents no additional risk from internal sources.









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2.4.2.  Withdrawn Routes

An external source could cause the elimination of existing legitimate
routes by forging or modifying this field.  An external source could
also cause the elimination of reestablished routes by replaying this
withdrawal information from earlier packets.

A BGP speaker could "falsely" withdraw feasible routes using this field.
However, as the BGP speaker is authoritative for the routes it will
announce, it is allowed to withdraw any previously announced routes that
it wants.  As the receiving BGP speaker will only withdraw routes
associated with the sending BGP speaker, there is no opportunity for a
BGP speaker to withdraw another BGP speaker's routes.  Therefore, there
is no additional vulnerability from internal sources via this field.

2.4.3.  Path Attributes

The path attributes present many different vulnerabilities.

Attribute Flags, Attribute Type Codes, Attribute Length

An internal or external source could modify the attribute length or
attribute type (flags and type codes) so they did not reflect the
attribute values that followed.  If the length were modified, the likely
result would be that the UPDATE message would not parse correctly.  If
the flags were modified, the flags and type code could become
incompatible (i.e., a mandatory attribute marked as partial), or a
optional attribute could be interpreted as a mandatory attribute or vice
versa.  Modifying the type code could cause the attribute value to be
interpreted as if it were the data type and value of a different
attribute.  The most likely result from modifying the attribute flags or
type code would be a parse error of the UPDATE message.  A parse error
from any modification would cause the transmission of a NOTIFICATION
message and the close of the connection.  As a true BGP speaker is
always able to close a connection at any time, this vulnerability
represents an additional risk only when the source is external, i.e., it
presents no additional risk from internal sources.

ORIGIN

This field indicates whether the information was learned from IGP or EGP
information.  If the route is used in inter-AS multicast routing, a
values of INCOMPLETE may be used.  This field is not used in making
routing decisions, so there are no vulnerabilities arising from this
field, either from internal or external sources.





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AS_PATH

An internal or external source could announce an AS_PATH that was not
accurate for the associated NLRI.  Forwarding for the NLRI associated
with the AS_PATH could potentially be induced to follow a sub-optimal
path, a path that did not follow some intended policy, or even a path
that would not forward the traffic.

It is not clear how far an inaccurate AS_PATH could deviate from the
true AS_PATH.  It may be that the first AS in the AS_PATH, at least,
must be a legal hop.  The RFC states that a BGP speaker prepends its own
AS to an AS_PATH before announcing it to a neighbor.  If the BGP speaker
must prepend its own AS, then a BGP speaker that produced a bogus
AS_PATH could end up receiving the traffic for the associated NLRI.
This could be desirable if the error was deliberate and the intent was
to receive traffic that would not otherwise be received.  Receiving the
mis-routed traffic could be undesirable for the faulty BGP speaker if it
is not prepared to handle the extra (mis-routed) traffic.  So, if a
deliberately malicious speaker must prepend its own AS, it could be
motivated or discouraged from inventing an arbitrary AS_PATH.  If the
BGP speaker need not prepend its own AS, then it could announce a path
that begins with the AS of any BGP speaker.  Whether such an arbitrary
AS_PATH is a vulnerability would depend on whether BGP implementations
check the AS_PATH (to see if the first AS is the neighbor) and would
catch the error.  If there are legitimate situations in which a BGP
speaker could pass an AS_PATH to a neighbor without putting its own AS
at the head of the AS_PATH, then there is no way for implementations to
detect totally bogus AS_PATHs.

Originating Routes

A special case of announcing a false AS_PATH occurs when the AS_PATH
advertises a direct path to a very specific network address.  An
internal or external source could disrupt routing to the network(s)
listed in the NLRI field by falsely advertising a direct path to the
network.  The NLRI would become unreachable to the portion of the
network that accepted this route, unless the BGP speaker undertook to
tunnel the packets it was forwarded for this NLRI on toward their
destination by a legal path.  But even when the BGP speaker tunnels the
packets on to the correct destination, the route followed may not be
optimal or may not follow the intended policy.  Additionally, routing
for other networks in the Internet could be affected if the false
advertisement fragmented an aggregated address block.







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NEXT_HOP

The NEXT_HOP attribute defines the IP address of the border router that
should be used as the next hop when forwarding the NLRI listed in the
UPDATE message.  If the recipient is an external peer, then the
recipient and the NEXT_HOP address must share a subnet.  It is clear
that an outside source modifying this field could disrupt the forwarding
of traffic between the two AS's.  In the case that the NEXT_HOP address
is an inter-AS peer and the recipient of the message is an inter-AS peer
of a different AS (this is one of two forms of "third party" NEXT_HOP),
then the BGP speaker advertising the route has the opportunity to direct
the recipient to forward traffic to a BGP speaker (the NEXT_HOP peer)
that may not be able to continue forwarding the traffic.  It is unclear
whether this would also require the advertising BGP speaker to construct
an AS_PATH mentioning the NEXT_HOP inter-AS peer's AS.

MULTI_EXIT_DISC

The MULTI_EXIT_DISC attribute is used in UPDATE messages transmitted
between inter-AS BGP peers.  While the MULTI_EXIT_DISC received from an
inter-AS peer may be propagated within an AS, it may not be propagated
to other AS's.  Consequently, this field is only used in making routing
decisions internal to one AS.  Modifying this field, whether by an
external source or an internal source, could influence routing within an
AS to be sub-optimal, but the effect should be limited in scope.

LOCAL_PREF

The LOCAL_PREF attribute must be included in all messages with internal
peers and excluded from messages with external peers.  Consequently,
modification of the LOCAL_PREF could effect the routing process within
the AS only.  Note that there is no requirement in the BGP RFC that the
LOCAL_PREF be consistent among the internal BGP speakers of an AS.  As
internal sources are free to choose the LOCAL_PREF as they wish,
modification of this field is a vulnerability with respect to external
sources only.

ATOMIC_AGGREGATE

The ATOMIC_AGGREGATE field indicates that an AS somewhere along the way
has received a more specific and a less specific route to the NLRI and
installed the aggregated route.  This route cannot be deaggregated
because it is not certain that the route to more specific prefixes will
follow the listed AS_PATH.  Consequently, BGP speakers receiving a route
with ATOMIC_AGGREGATE are restricted from making the NLRI any more





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specific.  Removing the ATOMIC_AGGREGATE attribute would remove the
restriction, possibly causing traffic intended for the more specific
NLRI to be routed incorrectly.   Adding the ATOMIC_AGGREGATE attribute
when no aggregation was done would have little effect, beyond
restricting the un-aggregated NLRI from being made more specific.  This
vulnerability exists whether the source is internal or external.

AGGREGATOR

This field may be included by a BGP speaker who has computed the routes
represented in the UPDATE message from aggregation of other routes.  The
field contains the AS number and IP address of the last aggregator of
the route.  It is not used in making any routing decisions, so it does
not represent a vulnerability.

2.4.4.  NLRI

By modifying or forging this field, either an external or internal
source could cause disruption of routing to the announced network,
overwhelm a router along the announced route, cause data loss when the
announced route will not forward traffic to the announced network, route
traffic by a sub-optimal route, etc.

3.  Possible Protections

3.1.  External sources

External sources can be prevented from disrupting routing by providing
cryptographic protection of the BGP peer connection.  The cryptography
chosen should protect the authenticity and integrity of the message and
should also protect against replay.  As the protection is only of the
peer-peer communications, asymmetric cryptography is not needed.  The
protection could be provided at the IP level by using existing IPSEC
mechanisms.  If IPSEC is not available, using cryptographic protection
within BGP or TCP would be necessary (but is not as yet defined).  Note
that applying the cryptographic protection within BGP does not provide
the same protection as applying it within TCP, as TCP information other
than the payload (BGP) data (e.g., the RST field) could still be spoofed
in ways that would harm the connection.

Prevention of spoofing completely removes any risk associated with bogus
OPEN, KEEPALIVE, or NOTIFICATION messages, as the only vulnerabilities
from these messages come from external sources.  It also protects
against all threats from bogus UPDATE messages arising from external
sources.





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3.2.  Internal sources

Protection of the communication between BGP peers does nothing to
protect against errors introduced by the BGP speakers themselves.  BGP
speakers can introduce bogus routing information, e.g., invalid
AS_PATHs, incorrect ORIGINs, etc., at any time.  Furthermore, detecting
the internal source of bogus information (if and when the bogus-ness is
detected) can be difficult if not impossible.

There are several possible solutions to prevent a BGP speaker from
inserting bogus information in its advertisements to its peers.

(1)  sign the originating AS.

(2)  sign the originating AS and predecessor information

(3)  sign the originating AS, and nest signatures of AS_PATHs to the
     number of consecutive bad routers you want to prevent from causing
     damage.

(4)  rely on a registry to say if AS_PATH and originating AS are valid

3.3.  Sign Originating AS

It would be beneficial to know which AS has first advertised a route to
a NLRI.  This could be done by including a new field which would contain
the originating AS number and the originating AS's digital signature [3]
of that plus the NLRI advertised. A digital signature is required
because the number and identities of all eventual recipients could not
be known and because non-repudiation would be desired.  This field could
be verified against an Internet registry, if a complete and accurate
registry existed.  If routing was disturbed by the presence of this
advertisement, then the culprit could be determined.

If a structure exists representing ownership of network addresses, then
the owner as well as the advertiser could sign.  A representation of an
owner could be useful when Internet service providers transfer sub-
blocks of their owned addresses to smaller ISP's.  The ISP's could
advertise NLRI but the ownership of the network could still be
determined.

If routes are aggregated by a BGP speaker and the aggregated route
advertised, then the idea of "originator" and "owner" become less
useful.  There might be several "originators" and "owners" represented
among the aggregated routes.  We suggest that the AGGREGATOR field





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become mandatory and that an aggregating BGP speaker append its
signature of the AGGREGATOR field and the aggregated NLRI.
Unfortunately, aggregation prevents identification of the specific
culprit should it be discovered that a network is being originated in
error.

3.4.  Sign Originating AS and Predecessor Information

Reference [2] suggests several different types of cryptographic
protection of BGP.  The suggested protection against possibly faulty BGP
speakers introduces some link state topology information (see [4]) that
can be used to verify AS_PATHs.

To protect against the need to trust BGP speakers regarding NLRI
information not specific to their own AS, [2] suggests adding the
following information to the UPDATE message:

-    the AS originating the information (either the aggregator or the
     advertiser of a direct route) and

-    the predecessor of the originating AS (i.e., the neighbor to which
     the NLRI is first advertised).

This field is digitally signed along with the NLRI, the
ATOMIC_AGGREGATOR, and other fields of the UPDATE message.  The
signature and the predecessor information must be included as the route
in the UPDATE message propagates across the network, i.e., it is
transitive.

This information distributes a bit of link state topology information,
concerning just the last hop before the destination network's AS, into
the usual BGP distance vector (some say "path vector") protocol.  Each
BGP speaker, even those who are transit only and originate no UPDATE
messages with NLRI contained in their own AS, will transmit this
"predecessor" information.  From all the signed predecessor information
received, it would be possible to verify that each of the adjacencies
represented in an AS_PATH is legitimate.  When a segment of an AS_PATH
is a sequence, each adjacent pair in the sequence must correspond to a
received signed predecessor tuple.

The protection provided by the signed predecessor information becomes
more difficult to use past an aggregation point where a BGP speaker
advertises a less specific route which includes the NLRI.  In
particular, the rules for verifying an AS_PATH containing a segment that
is a set would be either very lenient or very complex.





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While this predecessor information assures that each adjacency in a
sequence of an AS_PATH is valid, it does not ensure that the AS_PATH as
a whole is valid.  Each AS's decision regarding routes it will advertise
and traffic it will transit is individual and totally unconstrained.
The fact that a valid path of ASs exists to a destination does not
ensure that the corresponding AS_PATH is valid.  This mechanism also
does not assure that any information which comes from one router alone
(LOCAL_PREF, NEXT_HOP, AGGREGATOR, etc.) is accurate.  A router, then,
can still falsely announce that its neighbor should be forwarded the
traffic for an NLRI.

3.5.  Sign Originating AS and AS_PATH

A protection against possibly faulty BGP speakers that does provide some
assurance that the AS_PATH is valid involves nested digital signatures
of the AS_PATH.

Each BGP speaker would receive signed AS_PATH information (including the
ATOMIC_AGGREGATOR and NLRI attributes) from its peer.  After making its
routing decision, it would augment the chosen AS_PATH with its own AS
and sign the result.  The BGP speaker would pass to its peers the
augmented AS_PATH, its signature, and the signature of its peer over the
base AS_PATH from which the augmented AS_PATH was formed.  The peer
receiving this information can verify that the received AS_PATH was
indeed constructed with some basis in reality by verifying the signature
of the BGP speaker's peer over the tail of the received AS_PATH.  The
BGP speaker's signature will be passed on by the peer to provide similar
assurance that it constructed its advertised AS_PATH legitimately.

This procedure as described protects against one consecutive faulty
router in the path.  If it is desired to protect against more possibly
faulty routers in the path, then the procedure can be nested
arbitrarily.  To protect against n consecutive faulty routers, each
router would receive signed AS_PATH information from its neighbor along
with n signatures of the preceding n BGP speakers in the path, each
successive signature covering a shorter suffix of the path.  It would
pass on a newly constructed AS_PATH along with its own signature, its
neighbor's signature and n-1 of the included nested signatures.

A BGP speaker could snip out a suffix of the data it received as well as
the associated signatures and pass those on as the proof that its
AS_PATH was based on reality.  To prevent this, the signatures generated
should cover not only the AS_PATH but the intended receiver as well.







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For example, consider a case where it was decided to protect against
only one faulty BGP speaker.  Suppose AS1 receives an AS_PATH from AS2
of "AS2 AS3 ... ASk".  Then it should also receive AS2's signature of
"AS1, 'AS2 AS3 ... ASk'" and AS3's signature of "AS2, 'AS3 ... ASk'".
AS1 would compute a path "AS1 AS2 AS3 ... ASk", and pass on to AS0 this
path along with its signature of "AS0, 'AS1 AS2 AS3 ... ASk'" and AS2's
signature of "AS1, 'AS2 AS3 ... ASk'".

Note that this scheme becomes more complicated when one of the BGP
speakers performs aggregation of a set of routes.  To assure recipients
of the validity of the aggregated route, it would be necessary to pass
on the text and signatures of each of the aggregated component routes.
This means an enormous increase in transmission bandwidth and
verification time at each aggregation point, rather than a decrease.
This cost would not have to be passed on to further neighbors, but it
does violate the spirit of aggregation.

Note that this scheme does not assure that the received route is the
best route the peer could have computed.  In particular, it does not
guard against a peer that does not announce the best result of its
decision process - a peer that replays previous announcements, perhaps,
or does not change its announcements when it receives withdrawn routes.
These are a matter for the internal correct operation of the router and
cannot be induced by security protection.  This mechanism also does not
assure that any information which comes from one router alone
(LOCAL_PREF, NEXT_HOP, AGGREGATOR, etc.) is accurate.  A router, then,
can still falsely announce that its neighbor should be forwarded the
traffic for an NLRI.

This discussion is predicated on the use of asymmetric cryptography.
Each autonomous system would be required to possess an asymmetric key
pair.  The public key would have to be accessible to all recipients of
the digital signature.  The private key would have to be available to
all BGP speakers in the autonomous system, but protected from exposure.
Alternatively, each BGP speaker could possess its own asymmetric key
pair, at the cost of further complicating the protocol.  The protocol
would have to be altered to include the identity of the BGP speaker
within the AS who produces the AS_PATH and signature so that the
signature verification procedure could choose the correct public key to
use.

Symmetric cryptography could be used to protect the information by using
a keyed cryptographic hash instead of a digital signature.  However, in
order to provide the same level of protection against faulty routing,
each BGP speaker would have to share a different secret key with each of





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its neighbors and each of its neighbors' neighbors.  (In the case that
it is desired to protect against n>1 faulty BGP speakers, the number of
keys would grow exponentially - a different key with all 1-hop-away
neighbors, 2-hop-away neighbors, ..., and n+1-hop-away neighbors.) This
is obviously not a scalable solution.  It may also require autonomous
systems to reveal their peering agreements where they would not wish to
do so.

3.6.  Rely on Registries

The Internet registries can provide data that will help to assure that
AS_PATHS and NLRI origination data are correct.  If the data registered
in the Internet registries can be assumed to be correct, then the
peering information in the database can be used to verify each pair of
AS's in an AS_PATH sequence segment are truly peers.  Depending on the
sophistication of the information recorded in the registry, the
registries might also be used to verify that the AS_PATH as a whole was
valid.

The assurance provided by this protection would rely on the completeness
of the registry, on the authenticity of the registry data and on the
protection it received in storage and transit.  The protection is useful
if data from the registry is either available locally or retrievable
with an acceptable lag time.

The assurance provided by this protection also relies on the openness of
the data recorded in the registries.  To be truly useful, each
autonomous system's policy would have to be recorded in the registry, in
order that the AS_PATH as a whole can be verified to be valid.
Information about policy, however, can be sensitive to an autonomous
system and not openly available to every other autonomous system.  Any
restrictions on the availability of information stored in the registry
will restrict its applicability as a protection mechanism.

4.  Security Costs

Choosing the protection to apply in any situation depends on the
perception of the risk of attack, of the damage that can result, of the
benefits derived from providing the protection, and of the cost of
providing the protection.  This section discusses the cost of each of
the protection options mentioned above.









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4.1.  Protecting the Peer-Peer Link   The cost of this protection is the
processing required for the cryptography and the need to establish and
manage the cryptographic keys.  The cryptography need not be
computationally expensive; HMAC or similar algorithms can be used.
Shared secret keys are adequate for this protection, as the protection
applies only to the communication between peers, so the key management
cost is low.  Ideally, a separate key should be used for each BGP
peering.  One key might be used for multiple peerings with a reduction
in the level of protection that is provided.  However, it is best to
remember that apocryphally, the more places know a secret, the more
chances it will be exposed.

This level of protection is low cost and protects against the vast
number of possible adversaries (i.e., any non-BGP speaker in the
internet).

4.2.  Sign Originating AS

The cost of signing the originating AS of each route is the cost of
providing a public key infrastructure to generate an asymmetric key pair
for each autonomous system and to distribute and maintain the public
keys associated with each autonomous system.  The Internet registries
might be sufficient to serve as an authorization structure for
advertising each NLRI, but the authorization of ownership of network
addresses would either have to come from the IANA or from some new
authorization structure.

4.3.  Sign Originating AS and Predecessor Information

This scheme requires the same public key infrastructure as is needed if
one simply signs the originating AS information.  It also requires that
each adjacency for a BGP speaker be signed (the "predecessor"
information) and transmitted along with an AS_PATH.  Essentially, each
BGP speaker must announce its peers, something that does not currently
occur in the BGP protocol.  Each BGP speaker must compute one signature
for each UPDATE message transmitted and must verify one signature for
each UPDATE message received.  (Each UPDATE message must be separately
signed because the mechanism described in [2] includes a sequence
number, the Withdrawn Routes and the Unfeasible Route Length fields, so
the information to be signed changes with each message.  These fields
are protected from external sources by the peer-peer communication
protection and so do not need to be digitally signed.  If only the NLRI,
ATOMIC_AGGREGATE and predecessor information were signed each time, then
the signature might not have to be computed with each new UPDATE
message.)  The predecessor information in each route must be stored





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indefinitely.  Each route received must be verified by comparison to
predecessor information previously received.

4.4.  Sign Originating AS and AS_PATH

This scheme requires the same public key infrastructure as is needed if
one simply signs the originating AS information.  For each UPDATE
message received, n signatures (the level of protection from consecutive
faulty routers) must be verified.  For each UPDATE message transmitted,
one signature must be computed.  Note that the signature includes the
recipient, so computing one signature per AS_PATH and NLRI announced is
insufficient.

4.5.  Rely on Registries

The cost of relying on registries would vary considerably depending on
the protection provided to the information in storage and in transit.
Any latency, above that caused by the use of cryptography, would depend
on the mechanism used to protect the registry information (e.g.,
anything from frequent complete download to real-time query and
response).

5.  Security Considerations

This entire memo is about security considerations.

6.  References

[1]  RFC1771, A Border Gateway Protocol 4 (BGP-4). Y. Rekhter & T. Li.
     March 1995.

[2]  B. Smith and J.J. Garcia-Luna-Aceves, ``Securing the Border Gateway
     Routing Protocol,'' Proc. Global Internet'96, London, UK, 20-21
     November 1996.

[3]  Bruce Schneier.  Applied Cryptography Protocols, Algorithms, and
     Source Code in C, John Wiley & Sons, Inc 1994

[4]  John Moy.  OSPF Version 2.  RFC 1583, March 1994

7.  Author's Address

Sandra Murphy
Trusted Information Systems
3060 Washington Road





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Glenwood, MD  21738
EMail: [e-mail]
















































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Table of Contents


 Status of this Memo ..............................................    1
 Abstract .........................................................    1
1 Introduction ....................................................    1
2 Specific Vulnerabilities ........................................    3
2.1 OPEN ..........................................................    3
2.2 KEEPALIVE .....................................................    3
2.3 NOTIFICATION ..................................................    3
2.4 UPDATE ........................................................    3
2.4.1 Unfeasible Routes Length, Total Path Attribute Length .......    3
2.4.2 Withdrawn Routes ............................................    4
2.4.3 Path Attributes .............................................    4
 Attribute Flags, Attribute Type Codes, Attribute Length ..........    4
 ORIGIN ...........................................................    4
 AS_PATH ..........................................................    5
 Originating Routes ...............................................    5
 NEXT_HOP .........................................................    6
 MULTI_EXIT_DISC ..................................................    6
 LOCAL_PREF .......................................................    6
 ATOMIC_AGGREGATE .................................................    6
 AGGREGATOR .......................................................    7
2.4.4 NLRI ........................................................    7
3 Possible Protections ............................................    7
3.1 External sources ..............................................    7
3.2 Internal sources ..............................................    8
3.3 Sign Originating AS ...........................................    8
3.4 Sign Originating AS and Predecessor Information ...............    9
3.5 Sign Originating AS and AS_PATH ...............................   10
3.6 Rely on Registries ............................................   12
4 Security Costs ..................................................   12
4.1 Protecting the Peer-Peer Link .................................   13
4.2 Sign Originating AS ...........................................   13
4.3 Sign Originating AS and Predecessor Information ...............   13
4.4 Sign Originating AS and AS_PATH ...............................   14
4.5 Rely on Registries ............................................   14
5 Security Considerations .........................................   14
6 References ......................................................   14
7 Author's Address ................................................   14










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