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Versions: (draft-lepinski-bgpsec-protocol) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23

Network Working Group                                   M. Lepinski, Ed.
Internet-Draft                                                       BBN
Intended status: Standards Track                          March 12, 2012
Expires: September 13, 2012


                     BGPSEC Protocol Specification
                   draft-ietf-sidr-bgpsec-protocol-02

Abstract

   This document describes BGPSEC, an extension to the Border Gateway
   Protocol (BGP) that provides security for the AS-PATH attribute in
   BGP update messages.  BGPSEC is implemented via a new optional non-
   transitive BGP path attribute that carries a digital signature
   produced by each autonomous system on the AS-PATH.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [4].

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   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."

   This Internet-Draft will expire on September 13, 2012.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of



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   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  BGPSEC Negotiation . . . . . . . . . . . . . . . . . . . . . .  3
   3.  The BGPSEC_Path_Signatures Attribute . . . . . . . . . . . . .  6
   4.  Generating a BGPSEC Update . . . . . . . . . . . . . . . . . .  9
     4.1.  Originating a New BGPSEC Update  . . . . . . . . . . . . . 10
     4.2.  Propagating a Route Advertisement  . . . . . . . . . . . . 13
   5.  Processing a Received BGPSEC Update  . . . . . . . . . . . . . 16
     5.1.  Validation Algorithm . . . . . . . . . . . . . . . . . . . 17
   6.  Algorithms and Extensibility . . . . . . . . . . . . . . . . . 20
     6.1.  Algorithm Suite Considerations . . . . . . . . . . . . . . 21
     6.2.  Extensibility Considerations . . . . . . . . . . . . . . . 21
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 22
   8.  Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 25
     8.1.  Authors  . . . . . . . . . . . . . . . . . . . . . . . . . 25
     8.2.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . 26
   9.  Normative References . . . . . . . . . . . . . . . . . . . . . 26
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 27
























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1.  Introduction

   This document describes BGPSEC, a mechanism for providing path
   security for Border Gateway Protocol (BGP) [1] route advertisements.
   That is, a BGP speaker who receives a valid BGPSEC update has
   cryptographic assurance that the advertised route has the following
   two properties:

   1.  The route was originated by an AS that has been explicitly
       authorized by the holder of the IP address prefix to originate
       route advertisements for that prefix.

   2.  Every AS listed in the AS_Path attribute of the update explicitly
       authorized the advertisement of the route to the subsequent AS in
       the AS_Path.

   This document specifies a new optional (non-transitive) BGP path
   attribute, BGPSEC_Path_Signatures.  It also describes how a BGPSEC-
   compliant BGP speaker (referred to hereafter as a BGPSEC speaker) can
   generate, propagate, and validate BGP update messages containing this
   attribute to obtain the above assurances.

   BGPSEC relies on the Resource Public Key Infrastructure (RPKI)
   certificates that attest to the allocation of AS number and IP
   address resources.  (For more information on the RPKI, see [7] and
   the documents referenced therein.)  Any BGPSEC speaker who wishes to
   send BGP update messages to external peers (eBGP) containing the
   BGPSEC_Path_Signatures must have an RPKI end-entity certificate (as
   well as the associated private signing key) corresponding to the
   BGPSEC speaker's AS number.  Note, however, that a BGPSEC speaker
   does not require such a certificate in order to validate update
   messages containing the BGPSEC_Path_Signatures attribute.


2.  BGPSEC Negotiation

   This document defines a new BGP capability [3]that allows a BGP
   speaker to advertise to its neighbors the ability to send and/or
   receive BGPSEC update messages (i.e., update messages containing the
   BGPSEC_Path_Signatures attribute).

   This capability has capability code : TBD

   The capability length for this capability MUST be set to 5.

   The three octets of the capability value are specified as follows.





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                             Capability Value:

                    0        1        2  3       4 5 6 7
                 +---------------------------------------+
                 | Send | Receive | Reserved  |  Version |
                 +---------------------------------------+
                 |               AFI                     |
                 +---------------------------------------+
                 |                                       |
                 +---------------------------------------+
                 |             Reserved                  |
                 +---------------------------------------+
                 |               SAFI                    |
                 +---------------------------------------+


   The high order bit (bit 0) of the first octet is set to 1 to indicate
   that the sender is able to send BGPSEC update messages, and is set to
   zero otherwise.  The next highest order bit (bit 1) of this octet is
   set to 1 to indicate that the sender is able to receive BGPSEC update
   messages, and is set to zero otherwise.  The next two bits of the
   capability value (bits 2 and 3) are reserved for future use.  These
   reserved bits should be set to zero by the sender and ignored by the
   receiver.

   The four low order bits (4, 5, 6 and 7) of the first octet indicate
   the version of BGPSEC for which the BGP speaker is advertising
   support.  This document defines only BGPSEC version 0 (all four bits
   set to zero).  Other versions of BGPSEC may be defined in future
   documents.  A BGPSEC speaker MAY advertise support for multiple
   versions of BGPSEC by including multiple versions of the BGPSEC
   capability in its BGP OPEN message.

   If there does not exist at least one version of BGPSEC that is
   supported by both peers in a BGP session, then the use of BGPSEC has
   not been negotiated.  (That is, in such a case, messages containing
   the BGPSEC_Path_Signatures MUST NOT be sent.)

   If version 0 is the only version of BGPSEC for which both peers (in a
   BGP session) advertise support, then the use of BGPSEC has been
   negotiated and the BGPSEC peers MUST adhere to the specification of
   BGPSEC provided in this document.  (If there are multiple versions of
   BGPSEC which are supported by both peers, then the behavior of those
   peers is outside the scope of this document.)

   The second and third octets contain the 16-bit Address Family
   Identifier (AFI) which indicates the address family for which the
   BGPSEC speaker is advertising support for BGPSEC.  This document only



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   specifies BGPSEC for use with two address families, IPv4 and IPv6,
   AFI values 1 and 2 respectively.  BGPSEC for use with other address
   families may be specified in future documents.

   The fourth octet in the capability is reserved.  It is anticipated
   that this octet will not be used until such a time as the reserved
   octet in the Multi-protocol extensions capability advertisement [2]
   is specified for use.  The reserved octet should be set to zero by
   the sender and ignored by the receiver.

   The fifth octet in the capability contains the 8-bit Subsequent
   Address Family Identifier (SAFI).  This value is encoded as in the
   BGP multiprotocol extensions [2].

   Note that if the BGPSEC speaker wishes to use BGPSEC with two
   different address families (i.e., IPv4 and IPv6) over the same BGP
   session, then the speaker must include two instances of this
   capability (one for each address family) in the BGP OPEN message.  A
   BGPSEC speaker SHOULD NOT advertise the capability of BGPSEC support
   for any <AFI, SAFI> combination unless it has also includes the
   multiprotocol extension capability for the same <AFI, SAFI>
   combination [2].

   By indicating support for receiving BGPSEC update messages, a BGP
   speaker is, in particular, indicating that the following are true:

   o  The BGP speaker understands the BGPSEC_Path_Signatures attribute
      (see Section 3).

   o  The BGP speaker supports 4-byte AS numbers (see RFC 4893).

   Note that BGPSEC update messages can be quite large, therefore any
   BGPSEC speaker announcing the capability to receive BGPSEC messages
   SHOULD also announce support for the capability to receive BGP
   extended messages [5].

   A BGP speaker MUST NOT send an update message containing the
   BGPSEC_Path_Signatures attribute within a given BGP session unless
   both of the following are true:

   o  The BGP speaker indicated support for sending BGPSEC update
      messages in its open message.

   o  The peer of the BGP speaker indicated support for receiving BGPSEC
      update messages in its open message.






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3.  The BGPSEC_Path_Signatures Attribute

   The BGPSEC_Path_Signatures attribute is a new optional (non-
   transitive) BGP path attribute.

   This document registers a new attribute type code for this attribute
   : TBD

   The BGPSEC_Path_Signatures attribute has the following structure:

                     BGPSEC_Path_Signatures Attribute
        +---------------------------------------------------------+
        | Flags Octet                     (1 octet)               |
        +---------------------------------------------------------+
        | Algorithm Suite Identifier 1    (1 octet)               |
        +---------------------------------------------------------+
        | Algorithm Suite Identifier 2    (1 octet)               |
        +---------------------------------------------------------+
        | Reserved                       (8 octets)               |
        +---------------------------------------------------------+
        | Sequence of Signature-Segments (variable)               |
        +---------------------------------------------------------+


   The flags octet is an unsigned octet that contains flags to aid in
   receiver processing.

                 Flags Octet in Path_Signatures Attribute

                     0               1  2  3  4  5  6  7
               +-------------------------------------------+
               | Two Algorithms  |        Reserved         |
               +-------------------------------------------+


   The first bit in the Flags octet is set to zero in the common case
   that each Signature-Segment contains a single signature.  The first
   bit of the Flags octet is set to one in the case that each Signature-
   Segment contains two signatures, produced by two different algorithm
   suites.  (Note that this second case is necessary to support a
   transition between two algorithm suites, see Section 8.)  The
   remaining 7 bits of the Flags octet are reserved for future use.
   These bits should be set to zero by the sender and ignored by the
   receiver.

   Algorithm Suite Identifier 1 contains a one-octet identifier
   specifying the digest algorithm and digital signature algorithm used
   to produce the first signature in each Signature-Segment.  An IANA



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   registry of algorithm identifiers for use in BGPSEC is created in the
   BGPSEC algorithms document[10].

   Algorithm Suite Identifier 2 contains a one-octet identifier
   specifying the digest algorithm and digital signature algorithm used
   to produce the second signature in each Signature-Segment.  This
   field is ignored by the receiver if the first bit in the Flags octet
   is set to zero (indicating that only one signature algorithm is used
   in this BGPSEC update).  An IANA registry of algorithm identifiers
   for use in BGPSEC is created in the BGPSEC algorithms document[10].

   There are eight octets reserved for future use.  These octets are
   digitally signed (see Section 4 below).

   EDITOR'S NOTE: In a previous version of this document there was an
   Expire Time that was used to provide protection against replay of old
   (stale) digital signatures or failure to propagate a withdrawal
   message.  This mechanism was removed from the current version of the
   document.  Please see the SIDR mailing list for discussions related
   to protection against replay attacks.  Depending on the result of
   discussions within the SIDR working group this reserved field could
   at some future point be used to re-introduce Expire Time, or some
   other octets used in a future replay protection mechanism.

   The BGPSEC_Path_Signatures attribute contains one Signature-Segment
   for each AS along the path of the route advertisement in this update
   message.  (For a detailed explanation of how an AS processes a BGPSEC
   update message and adds a new Signature_Segment, see Section 4.)  A
   Signature-Segment has the following structure:






















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                            Signature Segments

              +-------------------------------------------- +
              | AS Number                       (4 octets)  |
              +---------------------------------------------+
              | pCount                           (1 octet)  |
              +---------------------------------------------+
              | Subject Key Identifier 1 Length  (1 octet)  |
              +---------------------------------------------+
              | Subject Key Identifier 1        (variable)  |
              +---------------------------------------------+
              | Signature 1 Length               (1 octet)  |
              +---------------------------------------------+
              | Signature 1                     (variable)  |
              +---------------------------------------------+
              | Subject Key Identifier 2 Length  (1 octet)  |
              +---------------------------------------------+
              | Subject Key Identifier 2        (variable)  |
              +---------------------------------------------+
              | Signature Length 2               (1 octet)  |
              +---------------------------------------------+
              | Signature 2                     (variable)  |
              +---------------------------------------------+


   The AS Number is the Autonomous System Number of the BGPSEC speaker
   that produced the digital signature(s) in this Signature Segment.

   The pCount field contains an unsigned integer indicating the number
   of repetitions of the associated autonomous system number that the
   signature covers.  This field enables a BGPSEC speaker to mimic the
   semantics of adding multiple copies of their AS to the AS-PATH
   without requiring the speaker to generate multiple signatures.

   The Subject Key Identifier 1 Length field contains the size (in
   octets) of the value in the Subject Key Identifier 1 field of the
   Signature-Segment.  The Subject Key Identifier 1 field contains the
   value in the Subject Key Identifier extension of the RPKI end-entity
   certificate that is used to verify the first signature in the
   Signature-Segment (see Section 5 for details on validity of BGPSEC
   update messages).

   The Signature 1 Length field contains the size (in octets) of the
   value in the Signature 1 field.  The Signature 1 field contains a
   digital signature that protects the NLRI and the
   BGPSEC_Path_Signatures attribute (see Sections 4 and 5 for details on
   generating and verifying this signature, respectively).




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   The Subject Key Identifier 2 Length field contains the size (in
   octets) of the value in the Subject Key Identifier 2 field of the
   Signature-Segment.  This length field SHOULD be zero if the first bit
   in the Flags octet is zero (indicating that only one algorithm suite
   is being used to generate signatures for this update message).  The
   Subject Key Identifier 2 field contains the value in the Subject Key
   Identifier extension of the RPKI end-entity certificate that is used
   to verify the second signature in the Signature-Segment (see Section
   5 for details on validity of BGPSEC update messages).  This field is
   ignored by the receiver when the first bit in the Flags octet is zero
   (indicating that only one algorithm suite is being used to generate
   signatures for this update message).

   The Signature 2 Length field contains the size (in octets) of the
   value in the Signature 2 field.  This length field SHOULD be zero if
   the first bit in the Flags octet is zero (indicating that only one
   algorithm suite is being used to generate signatures for this update
   message).  The Signature 2 field contains a digital signature that
   protects the NLRI and the BGPSEC_Path_Signatures attribute (see
   Sections 4 and 5 for details on generating and verifying this
   signature, respectively).  This field is ignored by the receiver when
   the first bit in the Flags octet is zero (indicating that only one
   algorithm suite is being used to generate signatures for this update
   message).


4.  Generating a BGPSEC Update

   Sections 4.1 and 4.2 cover two cases in which a BGPSEC speaker may
   generate an update message containing the BGPSEC_Path_Signatures
   attribute.  The first case is that in which the BGPSEC speaker
   originates a new route advertisement (Section 4.1).  That is, the
   BGPSEC speaker is constructing an update message in which the only AS
   to appear in the AS_PATH attribute is the speaker's own AS (normally
   appears once but may appear multiple times if AS prepending is
   applied).  The second case is that in which the BGPSEC speaker
   receives a route advertisement from a peer and then decides to
   propagate the route advertisement to an external (eBGP) peer (Section
   4.2).  That is, the BGPSEC speaker has received a BGPSEC update
   message and is constructing a new update message for the same NLRI in
   which the AS_PATH attribute will contain AS number(s) other than the
   speaker's own AS.

   In the remaining case where the BGPSEC speaker is sending the update
   message to an internal (iBGP) peer, the BGPSEC speaker populates the
   BGPSEC_Path_Signatures attribute by copying the
   BGPSEC_Path_Signatures attribute from the received update message.
   That is, the BGPSEC_Path_Signatures attribute is copied verbatim.



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   Note that in the case that a BGPSEC speaker chooses to forward to an
   iBGP peer a BGPSEC update message that has not been successfully
   validated (see Section 5), the BGPSEC_Path_Signatures attribute
   SHOULD NOT be removed.  (See Section 7 for the security ramifications
   of removing BGPSEC signatures.)

   The information protected by the signature on a BGPSEC update message
   includes the AS number of the peer to whom the update message is
   being sent.  Therefore, if a BGPSEC speaker wishes to send a BGPSEC
   update to multiple BGP peers, it MUST generate a separate BGPSEC
   update message for each unique peer AS to which the update message is
   sent.

   A BGPSEC update message MUST advertise a route to only a single NLRI.
   This is because a BGPSEC speaker receiving an update message with
   multiple NLRI is unable to construct a valid BGPSEC update message
   (i.e., valid path signatures) containing a subset of the NLRI in the
   received update.  If a BGPSEC speaker wishes to advertise routes to
   multiple NLRI, then it MUST generate a separate BGPSEC update message
   for each NLRI.

   Note that in order to create or add a new signature to a BGPSEC
   update message with a given algorithm suite, the BGPSEC speaker must
   possess a private key suitable for generating signatures for this
   algorithm suite.  Additionally, this private key must correspond to
   the public key in a valid Resource PKI end-entity certificate whose
   AS number resource extension includes the BGPSEC speaker's AS number
   [11].  Note also new signatures are only added to a BGPSEC update
   message when a BGPSEC speaker is generating an update message to send
   to an external peer (i.e., when the AS number of the peer is not
   equal to the BGPSEC speaker's own AS number).  Therefore, a BGPSEC
   speaker who only sends BGPSEC update messages to peers within its own
   AS, it does not need to possess any private signature keys.

4.1.  Originating a New BGPSEC Update

   In an update message that originates a new route advertisement (i.e.,
   an update whose AS_Path contains a single AS number), a BGPSEC
   speaker will use only a single algorithm suite.  That is, the BGPSEC
   speaker will set the Two_Algorithms flag to 0 in the
   BGPSEC_Path_Signatures attribute and include only a single signature
   in the Signature-Segment (setting the Signature 2 Length and Subject
   Key Identifier 2 Lengths to zero).  However, to ensure backwards
   compatibility during a period of transition from a 'current'
   algorithm suite to a 'new' algorithm suite, it will be necessary to
   originate update messages containing both the 'current' and the 'new'
   algorithm suites (see Section 6.1).  In such a case the BGPSEC
   speaker will set the Two_Algorithms flag to 1 in the



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   BGPSEC_Path_Signatures attribute and include two separate digital
   signatures (one for each algorithm suite).  For the remainder of this
   section we describe the common case where the Two_Algorithms flag is
   set to one.  However, the construction of the second signature is
   completely analogous (the only change is the replacement of 1 by 2 in
   the field names corresponding to the second signature).

   The Resource PKI enables the legitimate holder of IP address
   prefix(es) to issue a signed object, called a Route Origination
   Authorization (ROA), that authorizes a given AS to originate routes
   to a given set of prefixes (see [6]).  Note that validation of a
   BGPSEC update message will fail (i.e., the validation algorithm,
   specified in Section 5.1, returns 'Not Good') unless there exists a
   valid ROA authorizing the first AS in the AS PATH attribute to
   originate routes to the prefix being advertised.  Therefore, a BGPSEC
   speaker SHOULD NOT originate a BGPSEC update advertising a route for
   a given prefix unless a ROA has previously been created (and
   published in the repository system) that authorizing the BGPSEC
   speaker's AS to originate routes to this prefix.

   EDITOR'S NOTE: In a previous version of this document there was a
   description here of a mechanism that used that used periodic
   repetition of update messages (aka "beaconing") to protect against
   replay of old (stale) digital signatures or failure to propagate a
   withdrawal message.  This mechanism was removed from the current
   version of the document.  Please see the SIDR mailing list for
   discussions related to protection against replay attacks.  Depending
   on the result of discussions within the SIDR working group a
   mechanism for protection against replay of digital signatures may be
   re-introduced into BGPSEC in the future.

   When originating a new route advertisement, the
   BGPSEC_Path_Signatures attribute MUST contain a single Signature-
   Segment.  The following describes how the BGPSEC speaker populates
   the fields of the Signature-Segment (see Section 3 for more
   information on the syntax of the Signature-Segment).

   The AS field is set to the AS number of the BGPSEC speaker.  That is,
   the AS number that the BGPSEC speaker advertised in the Open message
   of the current BGP session.

   The pCount field is typically set to the value 1.  However, a BGPSEC
   speaker may set the pCount field to a value greater than 1.  Setting
   the pCount field to a value greater than one has the same semantics
   as repeating an AS number multiple times in the AS_PATH of a non-
   BGPSEC update message (e.g., for traffic engineering purposes).
   Setting the pCount field to a value greater than one permits this
   repetition without requiring a separate digital signature for each



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   repetition.

   The Subject Key Identifier 1 field (see Section 3) is populated with
   the identifier contained in the Subject Key Identifier extension of
   the RPKI end-entity certificate (containing keys suitable for use
   with Algorithm Suite 1) used by the BGPSEC speaker.  This Subject Key
   Identifier will be used by recipients of the route advertisement to
   identify the proper certificate to use in verifying the signature.

   The Subject Key Identifier 1 Length field is populated with the
   length (in octets) of the Subject Key Identifier 1 field.

   The Signature 1 field contains a digital signature that binds the
   NLRI, AS_Path attribute and BGPSEC_Path_Signatures attribute to the
   RPKI end-entity certificate used by the BGPSEC speaker.  The digital
   signature is computed as follows:

   o  Construct a sequence of octets by concatenating the Target AS
      Number, AS Number (from the Signature_Segment), pCount, Algorithm
      Suite Identifier 1, Reserved field of the BGPSEC_Path_Signatures
      attribute and NLRI.  The Target AS Number is the AS to whom the
      BGPSEC speaker intends to send the update message.  (Note that the
      Target AS number is the AS number announced by the peer in the
      OPEN message of the BGP session within which the update is sent.)

                      Sequence of Octets to be Signed
                 +----------------------------------------+
                 | Target AS Number (4 octets)            |
                 +----------------------------------------+
                 | AS Number        (4 octets)            |
                 +----------------------------------------+
                 | pCount          (1 octet)              |
                 +----------------------------------------+
                 | Algorithm Suite Identifier 1 (1 octet) |
                 +----------------------------------------+
                 | Expire Time     (8 octets)             |
                 +----------------------------------------+
                 | NLRI Length     (1 octet)              |
                 +----------------------------------------+
                 | NLRI Prefix    (variable)              |
                 +----------------------------------------+

   o  Apply to this octet sequence the digest algorithm (for Algorithm
      Suite 1) to obtain a digest value.

   o  Apply to this digest value the signature algorithm, (for Algorithm
      Suite 1) to obtain the digital signature.  Then populate the
      Signature 1 field with this digital signature.



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   The Signature 1 Length field is populated with the length (in octets)
   of the Signature 1 field.

4.2.  Propagating a Route Advertisement

   When a BGPSEC speaker receives a BGPSEC update message containing a
   BGPSEC_Path_Signatures algorithm (with one or more signatures) from a
   (internal or external) peer, it may choose to propagate the route
   advertisement by sending to its (internal or external) peers by
   creating a new BGPSEC advertisement for the same prefix.

   A BGPSEC speaker MUST NOT generate an update message containing the
   BGPSEC_Path_Signatures attribute unless it has selected, as the best
   route to the given prefix, a route that it received in an update
   message containing the BGPSEC_Path_Signatures attribute.  In
   particular, this means that whenever a BGPSEC speaker generates an
   update message with a BGPSEC_Path_Signatures attribute that it will
   possess a received update message for the same prefix that also
   contains a BGPSEC_Path_Signatures attribute.

   Additionally, whenever a BGPSEC speaker selects as the best route to
   a given prefix a route that it received in an update message
   containing the BGPSEC_Path_Signatures attribute, it is RECOMMENDED
   that if the BGPSEC speaker chooses to propagate the route that it
   generate an update message containing the BGPSEC_Path_Signatures
   attribute.  However, a BGPSEC speaker MAY propagate a route
   advertisement by generating a (non-BGPSEC) update message that does
   not contain the BGPSEC_Path_Signatures attribute.  Note that if a
   BGPSEC speaker receives a route advertisement containing the
   BGPSEC_Path_Signatures attribute and chooses for any reason (e.g.,
   its peer is a non-BGPSEC speaker) to propagate the route
   advertisement as a non-BGPSEC update message without the
   BGPSEC_Path_Signatures attribute, then it MUST follow the
   instructions in Section 4.2.1.

   The Subject Key Identifier 1 field (see Section 3) is populated with
   the identifier contained in the Subject Key Identifier extension of
   the RPKI end-entity certificate (containing keys suitable for use
   with Algorithm Suite 1) used by the BGPSEC speaker.  This Subject Key
   Identifier will be used by recipients of the route advertisement to
   identify the proper certificate to use in verifying the signature.

   The Subject Key Identifier 1 Length field is populated with the
   length (in octets) of the Subject Key Identifier 1 field.

   Note that removing BGPSEC signatures (i.e., propagating a route
   advertisement without the BGPSEC_Path_Signatures attribute) has
   significant security ramifications.  (See Section 7 for discussion of



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   the security ramifications of removing BGPSEC signatures.)
   Therefore, when a route advertisement is received via a BGPSEC update
   message, propagating the route advertisement without the
   BGPSEC_Path_Signatures attribute is NOT RECOMMENDED.  Furthermore,
   note that when a BGPSEC speaker propagates a route advertisement with
   the BGPSEC_Path_Signatures attribute it is attesting to the fact
   that: (1) it received a BGPSEC update message that advertised this
   route; and (2) it chose this route as its best path to the given
   prefix.  That is, the BGPSEC speaker is not attesting to the
   validation state of the update message it received.  (See Section 7
   for more discussion of the security semantics of BGPSEC signatures.)

   If the BGPSEC speaker is producing an update message which contains
   an AS-SET (e.g., the BGPSEC speaker is performing proxy aggregation),
   then the BGPSEC speaker MUST NOT include the BGPSEC_Path_Signatures
   attribute.  In such a case, the BGPSEC speaker must remove any
   existing BGPSEC_Path_Signatures in the received advertisement(s) for
   this prefix and produce a standard (non-BGPSEC) update message.

   If the received BGPSEC update message uses two algorithm suites
   (i.e., the Two_Algorithms flag is set to 1) and the BGPSEC speaker
   supports both of the corresponding algorithms suites, then the BGPSEC
   speaker SHOULD generate a new update message that uses both algorithm
   suites (i.e., set the Two_Algorithms flag to 1).  If the received
   BGPSEC update message that uses two algorithm suites and the BGPSEC
   speaker does not support the second algorithm suite, then the BGPSEC
   speaker MUST set the Two_Algorithms flag to 1 and remove the
   Signature 2 and Subject Key Identifier 2 fields from each Signature-
   Segment in the BGPSEC_Path_Signatures attribute (and set the
   corresponding lengths to zero).  Note that this case can happen
   during an algorithm transition when the BGPSEC speaker has not yet
   been updated to support the new algorithm, see Section 6 for more
   details.  If the BGPSEC speaker does not support the first algorithm
   suite in a BGPSEC update message, then the BGPSEC speaker MUST NOT
   propagate the route advertisement with the BGPSEC_Path_Signatures
   attribute.  (Note that if this case occurs, something has gone wrong,
   as algorithm transitions are designed to never produce this case.)

   The Reserved field from the BGPSEC_Path_Signatures attribute is
   copied directly from the Reserved field in the received update
   message.

   The BGPSEC speaker then creates a new Signature-Segment.  This
   Signature-Segment is prepended to the list of Signature-Segments
   (placed in the first position) so that the list of Signature-Segments
   appears in the same order as the corresponding AS numbers in the
   AS_PATH attribute.  The BGPSEC speaker populates the fields of this
   new Signature-Segment as follows.



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   The AS field is set to the AS number of the BGPSEC speaker.  That is,
   the AS number that the BGPSEC speaker advertised in the Open message
   of the current BGP session.

   The pCount is typically set to the value 1.  A BGPSEC speaker may set
   the pCount field to a value greater than 1.  (See Section 4.1 for a
   discussion of setting pCount to a value greater than 1.)  A route
   server that participates in the BGP control path, but does not act as
   a transit AS in the data plane, may choose to set pCount to 0.  This
   option enables the route server to participate in BGPSEC and obtain
   the associated security guarantees without increasing the effective
   length of the AS_PATH.  (Note that the Signature_Segmenet still
   contains the AS Number of the route server as this information is
   necessary for signature verification.)  Note that the option of
   setting pCount to 0 is intended only for use by route servers that
   desire not to increase the effective AS-PATH length of routes they
   advertise.  The pCount field SHOULD NOT be set to 0 in other
   circumstances.  BGPSEC speakers SHOULD drop incoming update messages
   with pCount set to zero in cases where the BGPSEC speaker does not
   expect its peer to set pCount to zero (i.e., cases where the peer is
   not acting as a route server).

   The Subject Key Identifier 1 field (see Section 3) is populated with
   the identifier contained in the Subject Key Identifier extension of
   the RPKI end-entity certificate (containing keys suitable for use
   with Algorithm Suite 1) used by the BGPSEC speaker.  This Subject Key
   Identifier will be used by recipients of the route advertisement to
   identify the proper certificate to use in verifying the signature.

   The Subject Key Identifier 1 Length field is populated with the
   length (in octets) of the Subject Key Identifier 1 field.

   The Signature 1 field in the new segment contains a digital signature
   that binds the NLRI, AS_Path attribute and BGPSEC_Path_Signatures
   attribute to the RPKI end-entity certificate used by the BGPSEC
   speaker.  The digital signature is computed as follows:

   o  Construct a sequence of octets by concatenating the Signature 1
      Length and Signature 1 fields of the most recent Signature-Segment
      (the one corresponding to AS from whom the BGPSEC speaker's AS
      received the announcement) with the pCount field inserted by the
      signer, and the Target AS (the AS to whom the BGPSEC speaker
      intends to send the update message).  Note that the Target AS
      number is the AS number announced by the peer in the OPEN message
      of the BGP session within which the BGPSEC update message is sent.






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                      Sequence of Octets to be Signed

      +-------------------------------------------------------------+
      | Most Recent Signature 1 Length Field      (1 octet)         |
      +-------------------------------------------------------------+
      | Most Recent Signature 1 Field             (variable)        |
      +-------------------------------------------------------------+
      | pCount Field of Signer        (1 octet)                     |
      +-------------------------------------------------------------+
      | Target AS Number              (4 octets)                    |
      +-------------------------------------------------------------+

   o  Apply to this octet sequence the digest algorithm (for the
      algorithm suite of this Signature-List) to obtain a digest value.

   o  Apply to this digest value the signature algorithm, (for the
      algorithm suite of this Signature-List) to obtain the digital
      signature.  Then populate the Signature Field with this digital
      signature.

   The Subject Key Identifier 1 Length field is populated with the
   length (in octets) of the Subject Key Identifier 1 field.


5.  Processing a Received BGPSEC Update

   Validation of a BGPSEC update messages makes use of data from RPKI
   certificates and signed Route Origination Authorizations (ROA).  In
   particular, to validate update messages containing the
   BGPSEC_Path_Signatures attribute, it is necessary that the recipient
   have access to the following data obtained from valid RPKI
   certificates and ROAs:

   o  For each valid RPKI end-entity certificate containing an AS Number
      extension, the AS Number, Public Key and Subject Key Identifier
      are required

   o  For each valid ROA, the AS Number and the list of IP address
      prefixes

   Note that the BGPSEC speaker could perform the validation of RPKI
   certificates and ROAs on its own and extract the required data, or it
   could receive the same data from a trusted cache that performs RPKI
   validation on behalf of (some set of) BGPSEC speakers.  (The latter
   case in analogous to the use of the RPKI-RTR protocol [12] for origin
   validation.)

   To validate a BGPSEC update message containing the



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   BGPSEC_Path_Signatures attribute, the recipient performs the
   validation steps specified in Section 5.1.  The validation procedure
   results in one of two states: 'Good' and 'Not Good'.

   It is expected that the output of the validation procedure will be
   used as an input to BGP route selection.  However, BGP route
   selection and thus the handling of the two validation states is a
   matter of local policy, and shall be handled using existing local
   policy mechanisms.  It is expected that BGP peers will generally
   prefer routes received via 'Good' BGPSEC update messages over routes
   received via 'Not Good' BGPSEC update messages as well as routes
   received via update messages that do not contain the
   BGPSEC_Path_Signatures attribute.  However, BGPSEC specifies no
   changes to the BGP decision process and leaves to the operator the
   selection of an appropriate policy mechanism to achieve the
   operator's desired results within the BGP decision process.

   BGPSEC validation need only be performed at eBGP edge.  The
   validation status of a BGP signed/unsigned update MAY be conveyed via
   iBGP from an ingress edge router to an egress edge router.  Local
   policy in the AS determines the specific means for conveying the
   validation status through various pre-existing mechanisms (e.g.,
   modifying an attribute).  As discussed in Section 4, when a BGPSEC
   speaker chooses to forward a (syntactically correct) BGPSEC update
   message, it SHOULD be forwarded with its BGPSEC_Path_Signatures
   attribute intact (regardless of the validation state of the update
   message).  Based entirely on local policy settings, an egress router
   MAY trust the validation status conveyed by an ingress router or it
   MAY perform its own validation.

   EDITOR'S NOTE: Text will be inserted here for dealing with the
   AS_PATH attribute.  Note that the BGPGSEC_Path_Signatures attribute
   now contains all of the information needed to construct the AS_PATH
   attribute.  Therefore, there seem to be two options.  One option the
   BGPSEC speaker checks the AS_PATH attribute against the information
   in the BGPSEC_Path_Signatures attribute and returns "Not Good" if the
   two do not match.  The other option is that the BGPSEC speaker
   discards anything in the AS_PATH attribute and reconstructs the
   AS_PATH from the data in the BGPSEC_Path_Signatures attribute.  I
   believe that there are no interoperability problems if the choice
   between these two options is left up to the BGPSEC speaker.

5.1.  Validation Algorithm

   This section specifies an algorithm for validation of BGPSEC update
   messages.  A conformant implementation MUST include an BGPSEC update
   validation algorithm that is functionally equivalent to the external
   behavior of this algorithm.



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   First, the recipient of a BGPSEC update message performs a check to
   ensure that the message is properly formed.  Specifically, the
   recipient checks that the BGPSEC_Path_Signatures attribute is
   properly formed (as specified in Section 3).  If the
   BGPSEC_Path_Signatures attribute is not properly formed, then the
   recipient should log that an error occurred and drop the update
   message containing the error.

   Second, the BGPSEC speaker verifies that the origin AS is authorized
   to advertise the prefix in question.  To do this, consult the valid
   ROA data to obtain a list of AS numbers that are associated with the
   given IP address prefix in the update message.  Then locate the last
   (least recently added) AS number in the AS-Path.  If the origin AS in
   the AS-Path is not in the set of AS numbers associated with the given
   prefix, then BGPSEC update message is 'Not Good' and the validation
   algorithm terminates.

   Third, the BGPSEC speaker examines the Algorithm Suite identifiers
   and the Two-Algorithms flag in the BGPSEC_Path_Signatures attribute.
   If the BGPSEC speaker does not support the first Algorithm Suite,
   then the BGPSEC speaker MUST treat the update message in the same
   manner that the BGPSEC speaker would treat an update message that
   arrived without a BGPSEC_Path_Signatures attribute.  (Note that
   algorithm transitions are designed so that this case will never
   happen, therefore if this case occurs the BGPSEC speaker SHOULD log
   an error message.)  If the Two-Algorithms flag is set to 1 and the
   BGPSEC speaker supports only the first algorithm suite then it
   follows the instructions below to validate the signatures using the
   first algorithm suite, and ignore Signature 2 in each Signature-
   Segment.  If the Two-Algorithms flag is set to 1 and the BGPSEC
   speaker supports both algorithm suites, then the BGPSEC speaker
   follows the instructions below to validate the signatures using the
   first algorithm suite.  The BGPSEC speaker MAY then analogously
   validate the second set of signatures using Algorithm Suite 2.  If
   the BGPSEC speaker chooses to validate both sets of signatures, it
   returns "Good" if either the first or the second set of signatures
   successfully validate.

   o  (Step I): Locate the public key needed to verify the signature (in
      the current Signature-Segment).  To do this, consult the valid
      RPKI end-entity certificate data and look for an SKI that matches
      the value in the Subject Key Identifier 1 field of the Signature-
      Segment.  If no such SKI value is found in the valid RPKI data
      then validation fails and returns "Not Good".  Similarly, if the
      SKI exists but the AS Number associated with the SKI does NOT
      match the AS Number in the Signature-Segment, then validation
      fails and returns "Not Good".




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   o  (Step II): Compute the digest function (for Algorithm Suite 1) on
      the appropriate data.  If the segment is not the (least recently
      added) segment corresponding to the origin AS, then the digest
      function should be computed on the following sequence of octets:

                      Sequence of Octets to be Hashed

        +----------------------------------------------------------+
        | Signature 1 Length Field in the Next Segment  (1 octet) |
        +----------------------------------------------------------+
        | Signature 1 Field in the Next Segment         (variable) |
        +----------------------------------------------------------+
        | pCount Field in the Current Segment           (1 octet)  |
        +----------------------------------------------------------+
        | AS Number of Previous AS                      (4 octets) |
        +----------------------------------------------------------+

   The 'Signature 1 Field in the Next Segment' and 'Signature 1 Length
   Field in Next Segment' are the Signature 1 field and Signature 1
   Length fields found in the Signature-Segment that is next to be
   processed (that is, the next most recently added Signature- Segment).
   The 'pCount Field in the Current Segment' is the pCount field found
   in the Signature-Segment that is currently being processed.

   For the first segment to be processed (the most recently added
   segment), the 'AS Number of Subsequent AS' is the AS number of the
   BGPSEC speaker validating the update message.  Note that if a BGPSEC
   speaker uses multiple AS Numbers (e.g., the BGPSEC speaker is a
   member of a confederation), the AS number used here MUST be the AS
   number announced in the OPEN message for the BGP session over which
   the BGPSEC update was received.

   For each other Signature-Segment, the 'AS Number of Previous AS' is
   the AS number in the Signature-Segment that was most recently
   processed.

   Alternatively, if the segment being processed corresponds to the
   origin AS, then the digest function should be computed on the
   following sequence of octets:












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                      Sequence of Octets to be Hashed
                -------------------------------------------+
                | AS Number of Previous AS    (4 octets)   |
                +------------------------------------------+
                | Origin AS Number            (4 octets)   |
                +------------------------------------------+
                | Algorithm Suite 1 Identifier  (1 octet)  |
                +------------------------------------------+
                | pCount       (1 octet)                   |
                +------------------------------------------+
                | NLRI Length  (1 octet)                   |
                +------------------------------------------+
                | NLRI Prefix  (variable)                  |
                +------------------------------------------+

   The NLRI Length, NLRI Prefix, Expire Time, and Algorithm Suite
   Identifier are all obtained in a straight forward manner from the
   NLRI of the update message or the BGPSEC_Path_Signatures attribute
   being validated.  The pCount field is taken from the Signature-
   Segment currently being processed.

   The Origin AS Number is the same Origin AS Number that was located in
   Step I above.  (That is, the AS number in the least recently added
   Signature-Segment.)

   The 'AS Number of Previous AS' is the AS Number in the Signature-
   Segment that was most recently processed (i.e., processed before the
   current segment).

   o  (Step III): Use the signature validation algorithm (for the given
      algorithm suite) to verify the signature in the current segment.
      That is, invoke the signature validation algorithm on the
      following three inputs: the value of the Signature field in the
      current segment; the digest value computed in Step II above; and
      the public key obtained from the valid RPKI data in Step I above.
      If the signature validation algorithm determines that the
      signature is invalid, validation has failed and return 'Not Good'.
      If the signature validation algorithm determines that the
      signature is valid, then continue processing Signature-Segments.

   If all Signature-Segments pass validation (i.e., all segments are
   processed and the algorithm has not yet returned 'Not Good'), then
   validation succeeds and returns 'Good'.


6.  Algorithms and Extensibility





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6.1.  Algorithm Suite Considerations

   Note that there is currently no support for bilateral negotiation
   between BGPSEC peers to use of a particular (digest and signature)
   algorithm suite using BGP capabilities.  This is because the
   algorithm suite used by the sender of a BGPSEC update message must be
   understood not only by the peer to whom he is directly sending the
   message, but also by all BGPSEC speakers to whom the route
   advertisement is eventually propagated.  Therefore, selection of an
   algorithm suite cannot be a local matter negotiated by BGP peers, but
   instead must be coordinated throughout the Internet.

   To this end, a mandatory algorithm suites document will be created
   which specifies a mandatory-to-use 'current' algorithm suite for use
   by all BGPSEC speakers.  Additionally, the document specifies an
   additional 'new' algorithm suite that is recommended to implement.

   It is anticipated that in the future the mandatory algorithm suites
   document will be updated to specify a transition from the 'current'
   algorithm suite to the 'new' algorithm suite.  During the period of
   transition (likely a small number of years), all BGPSEC update
   messages SHOULD simultaneously use both the 'current' algorithm suite
   and the 'new' algorithm suite.  (Note that Sections 3 and 4 specify
   how the BGPSEC_Path_Signatures attribute can contain signatures, in
   parallel, for two algorithm suites.)  Once the transition is
   complete, use of the old 'current' algorithm will be deprecated, use
   of the 'new' algorithm will be mandatory, and a subsequent 'even
   newer' algorithm suite may be specified as recommend to implement.
   Once the transition has successfully been completed in this manner,
   BGPSEC speakers SHOULD include only a signatures corresponding to the
   'new' algorithm.

6.2.  Extensibility Considerations

   This section discusses potential changes to BGPSEC that would require
   substantial changes to the processing of the BGPSEC_Path_Signatures
   and thus necessitate a new version of BGPSEC.  Examples of such
   changes include

   o  A new type of signature algorithm for which the number of
      signatures in the Signature-List Block is not equal to the number
      of ASes in the AS_PATH (e.g., aggregate signatures)

   o  Changes to the data that is protected by the BGPSEC signatures
      (e.g., protection of attributes other than AS_PATH)

   In the case that such a change to BGPSEC were deemed desirable, it is
   expected that a subsequent version of BGPSEC would be created and



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   that this version of BGPSEC would specify a new BGP Path Attribute,
   let's call it BGPSEC_PATH_SIG_TWO, which is designed to accommodate
   the desired changes to BGPSEC.  In such a case, the mandatory
   algorithm suites document would be updated to specify algorithm
   suites appropriate for the new version of BGPSEC.

   At this point a transition would begin which is analogous to the
   algorithm transition discussed in Section 6.2.  During the transition
   period all BGPSEC speakers SHOULD simultaneously include both the
   BGPSEC_PATH_SIGNATURES attribute and the new BGPSEC_PATH_SIG_TWO
   attribute.  Once the transition is complete, the use of
   BGPSEC_PATH_SIGNATURES could then be deprecated, at which point
   BGPSEC speakers SHOULD include only the new BGPSEC_PATH_SIG_TWO
   attribute.  Such a process could facilitate a transition to a new
   BGPSEC semantics in a backwards compatible fashion.


7.  Security Considerations

   For discussion of the BGPSEC threat model and related security
   considerations, please see [8].

   A BGPSEC speaker who receives a valid BGPSEC update message,
   containing a route advertisement for a given prefix, is provided with
   the following security guarantees:

   o  The origin AS number corresponds to an autonomous system that has
      been authorized by the IP address space holder to originate route
      advertisements for the given prefix.

   o  For each subsequent AS number in the AS-Path, a BGPSEC speaker
      authorized by the holder of the AS number selected the given route
      as the best route to the given prefix.

   o  For each AS number in the AS Path, a BGPSEC speaker authorized by
      the holder of the AS number intentionally propagated the route
      advertisement to the next AS in the AS-Path.

   That is, the recipient of a valid BGPSEC Update message is assured
   that the AS-Path corresponds to a sequence of autonomous systems who
   have all agreed in principle to forward packets to the given prefix
   along the indicated path.  (It should be noted BGPSEC does not offer
   a precise guarantee that the data packets would propagate along the
   indicated path; it only guarantees that the BGP update conveying the
   path indeed propagated along the indicated path.)  Furthermore, the
   recipient is assured that this path terminates in an autonomous
   system that has been authorized by the IP address space holder as a
   legitimate destination for traffic to the given prefix.



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   Note that although BGPSEC provides a mechanism for an AS to validate
   that a received update message has certain security properties, the
   use of such a mechanism to influence route selection is completely a
   matter of local policy.  Therefore, a BGPSEC speaker can make no
   assumptions about the validity of a route received from an external
   BGPSEC peer.  That is, a compliant BGPSEC peer may (depending on the
   local policy of the peer) send update messages that fail the validity
   test in Section 5.  Thus, a BGPSEC speaker MUST completely validate
   all BGPSEC update messages received from external peers.  (Validation
   of update messages received from internal peers is a matter of local
   policy, see Section 5).

   Note that there may be cases where a BGPSEC speaker deems 'Good' (as
   per the validation algorithm in Section 5.1) a BGPSEC update message
   that contains two sets of signatures, one 'Good' and one 'Not Good'.
   That is, the update message contains two sets of signatures
   corresponding to two algorithm suites, and one set of signatures
   verifies correctly and the other set of signatures fails to verify.
   In this case, the protocol specifies that if the BGPSEC speaker
   propagates the route advertisement received in such an update message
   then the BGPSEC speaker SHOULD add its signature using both the
   algorithm suites.  Thus the BGPSEC speaker creates a signature using
   both algorithm suites and creates a new update message that contains
   both the 'Good' and the 'Not Good' set of signatures (from its own
   vantage point).

   To understand the reason for such a design decision consider the case
   where the BGPSEC speaker receives an update message with both a set
   of algorithm A signatures which are 'Good' and a set of algorithm B
   signatures which are 'Not Good'.  In such a case it is possible
   (perhaps even quite likely) that some of the BGPSEC speaker's peers
   (or other entities further 'downstream' in the BGP topology) do not
   support algorithm A. Therefore, if the BGPSEC speaker were to remove
   the 'Not Good' set of signatures corresponding to algorithm B, such
   entities would treat the message as though it were unsigned.  By
   including the 'Not Good' set of signatures when propagating a route
   advertisement, the BGPSEC speaker ensures that 'downstream' entities
   have as much information as possible to make an informed opinion
   about the validation status of a BGPSEC update.

   Note also that during a period of partial BGPSEC deployment, a
   'downstream' entity might reasonably treat unsigned messages
   different from BGPSEC updates that contain a single set of 'Not Good'
   signatures.  That is, by removing the set of 'Not Good' signatures
   the BGPSEC speaker might actually cause a downstream entity to
   'upgrade' the status of a route advertisement from 'Not Good' to
   unsigned.  Finally, note that in the above scenario, the BGPSEC
   speaker might have deemed algorithm A signatures 'Good' only because



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   of some issue with RPKI state local to his AS (for example, his AS
   might not yet have obtained a CRL indicating that a key used to
   verify an algorithm A signature belongs to a newly revoked
   certificate).  In such a case, it is highly desirable for a
   downstream entity to treat the update as 'Not Good' (due to the
   revocation) and not as 'unsigned' (which would happen if the 'Not
   Good' signatures were removed).

   A similar argument applies to the case where a BGPSEC speaker (for
   some reason such as lack of viable alternatives) selects as his best
   route to a given prefix a route obtained via a 'Not Good' BGPSEC
   update message.  (That is, a BGPSEC update containing only 'Not Good'
   signatures.)  In such a case, the BGPSEC speaker should propagate a
   signed BGPSEC update message, adding his signature to the 'Not Good'
   signatures that already exist.  Again, this is to ensure that
   'downstream' entities are able to make an informed decision and not
   erroneously treat the route as unsigned.  It may also be noted here
   that due to possible differences in RPKI data at different vantage
   points in the network, a BGPSEC update that was deemed 'Not Good' at
   an upstream BGPSEC speaker may indeed be deemed 'Good' at another BGP
   speaker downstream.

   Therefore, it is important to note that when a BGPSEC speaker signs
   an outgoing update message, it is not attesting to a belief that all
   signatures prior to its are valid.  Instead it is merely asserting
   that:

   1.  The BGPSEC speaker received the given route advertisement with
       the indicated NLRI and AS Path;

   2.  The BGPSEC speaker selected this route as the best route to the
       given prefix; and

   3.  The BGPSEC speaker chose to propagate an advertisement for this
       route to the peer (implicitly) indicated by the 'Target AS'

   The BGPSEC update validation procedure is a potential target for
   denial of service attacks against a BGPSEC speaker.  To mitigate the
   effectiveness of such denial of service attacks, BGPSEC speakers
   should implement an update validation algorithm that performs
   expensive checks (e.g., signature verification) after less expensive
   checks (e.g., syntax checks).  The validation algorithm specified in
   Section 5.1 was chosen so as to perform checks which are likely to be
   expensive after checks that are likely to be inexpensive.  However,
   the relative cost of performing required validation steps may vary
   between implementations, and thus the algorithm specified in Section
   5.1 may not provide the best denial of service protection for all
   implementations.



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   Finally, the mechanism of setting the pCount field to zero is
   included in this specification to enable route servers in the control
   path to participate in BGPSEC without increasing the effective length
   of the AS_PATH.  However, entities other than route servers could
   conceivably use this mechanism (set the pCount to zero) to attract
   traffic (by reducing the effective length of the AS_PATH)
   illegitimately.  This risk is largely mitigated if every BGPSEC
   speaker drops incoming update messages that set pCount to zero but
   come from a peer that is not a route server.  However, note that a
   recipient of a BGPSEC update message in which an upstream entity that
   is two or more hops away set pCount to zero is unable to verify for
   themselves whether pCount was set to zero legitimately.


8.  Contributors

8.1.  Authors

   Rob Austein
   Dragon Research Labs
   sra@hactrn.net


   Steven Bellovin
   Columbia University
   smb@cs.columbia.edu


   Randy Bush
   Internet Initiative Japan
   randy@psg.com


   Russ Housley
   Vigil Security
   housley@vigilsec.com


   Matt Lepinski
   BBN Technologies
   lepinski@bbn.com



   Stephen Kent
   BBN Technologies
   kent@bbn.com




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   Warren Kumari
   Google
   warren@kumari.net


   Doug Montgomery
   USA National Institute of Standards and Technology
   dougm@nist.gov


   Kotikalapudi Sriram
   USA National Institute of Standards and Technology
   kotikalapudi.sriram@nist.gov


   Samuel Weiler
   Cobham
   weiler+ietf@watson.org

8.2.  Acknowledgements

   The authors would like to thank Luke Berndt, Wes George, Sharon
   Goldberg, Ed Kern, Chris Morrow, Doug Maughan, Pradosh Mohapatra,
   Russ Mundy, Sandy Murphy, Keyur Patel, Mark Reynolds, Heather
   Schiller, Jason Schiller, John Scudder, Ruediger Volk and David Ward
   for their valuable input and review.


9.  Normative References

   [1]   Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A Border
         Gateway Protocol 4", RFC 4271, January 2006.

   [2]   Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
         "Multiprotocol Extensions for BGP-4", RFC 4760, January 2007.

   [3]   Scudder, J. and R. Chandra, "Capabilities Advertisement with
         BGP-4", RFC 5492, February 2009.

   [4]   Bradner, S., "Key words for use in RFCs to Indicate Requirement
         Levels", BCP 14, RFC 2119, March 1997.

   [5]   Patel, K., Ward, D., and R. Bush, "Extended Message support for
         BGP", March 2011.

   [6]   Lepinski, M., Kent, S., and D. Kong, "A Profile for Route
         Origin Authorizations", February 2011.




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   [7]   Lepinski, M. and S. Kent, "An Infrastructure to Support Secure
         Internet Routing", February 2011.

   [8]   Kent, S., "Threat Model for BGP Path Security", June 2011.

   [9]   Bush, R., "BGPsec Operational Considerations", October 2011.

   [10]  Turner, S., "BGP Algorithms, Key Formats, & Signature Formats",
         December 2011.

   [11]  Reynolds, M., Turner, S., and S. Kent, "A Profile for BGPSEC
         Router Certificates, Certificate Revocation Lists, and
         Certification Requests", December 2011.

   [12]  Bush, R. and R. Austein, "The RPKI/Router Protocol",
         October 2011.


Author's Address

   Matthew Lepinski (editor)
   BBN
   10 Moulton St
   Cambridge, MA  55409
   US

   Phone: +1 617 873 5939
   Email: mlepinski@bbn.com























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