Network Working Group                                   M. Lepinski, Ed.Internet-Draft                                                       NCFIntended status: Standards Track                            July 6, 2015Expires: January 6, 2016                                                                     BGPsec Protocol Specification                   draft-ietf-sidr-bgpsec-protocol-13Abstract   This document describes BGPsec, an extension to the Border Gateway   Protocol (BGP) that provides security for the path of autonomous   systems through which a BGP update message passes.  BGPsec is   implemented via a new optional non-transitive BGP path attribute that   carries a digital signature produced by each autonomous system that   propagates the update message.Requirements Language   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and   "OPTIONAL" are to be interpreted as described in RFC 2119 [1] only   when they appear in all upper case.  They may also appear in lower or   mixed case as English words, without normative meaning.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 January 6, 2016.Copyright Notice   Copyright (c) 2015 IETF Trust and the persons identified as the   document authors.  All rights reserved.Lepinski                Expires January 6, 2016                 [Page 1]Internet-Draft              BGPsec Protocol                 July 6, 2015   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   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 . . . . . . . . . . . . . . . . . . . . . . . . .  2   2.  BGPsec Negotiation . . . . . . . . . . . . . . . . . . . . . .  3     2.1.  The BGPsec Capability  . . . . . . . . . . . . . . . . . .  3     2.2.  Negotiating BGPsec Support . . . . . . . . . . . . . . . .  4   3.  The BGPsec_Path Attribute  . . . . . . . . . . . . . . . . . .  6     3.1.  Secure_Path  . . . . . . . . . . . . . . . . . . . . . . .  7     3.2.  Signature_Block  . . . . . . . . . . . . . . . . . . . . .  8   4.  Generating a BGPsec Update . . . . . . . . . . . . . . . . . . 11     4.1.  Originating a New BGPsec Update  . . . . . . . . . . . . . 12     4.2.  Propagating a Route Advertisement  . . . . . . . . . . . . 15     4.3.  Processing Instructions for Confederation Members  . . . . 19     4.4.  Reconstructing the AS_PATH Attribute . . . . . . . . . . . 21   5.  Processing a Received BGPsec Update  . . . . . . . . . . . . . 22     5.1.  Overview of BGPsec Validation  . . . . . . . . . . . . . . 25     5.2.  Validation Algorithm . . . . . . . . . . . . . . . . . . . 26   6.  Algorithms and Extensibility . . . . . . . . . . . . . . . . . 30     6.1.  Algorithm Suite Considerations . . . . . . . . . . . . . . 30     6.2.  Extensibility Considerations . . . . . . . . . . . . . . . 30   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 31     7.1 Security Guarantees  . . . . . . . . . . . . . . . . . . . . 31     7.2 On the Removal of BGPsec Signatures  . . . . . . . . . . . . 32     7.3 Mitigation of Denial of Service Attacks  . . . . . . . . . . 35     7.4 Additional Security Considerations . . . . . . . . . . . . . 35   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 36   9.  Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 37     9.1.  Authors  . . . . . . . . . . . . . . . . . . . . . . . . . 37     9.2.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . 37   10.  Normative References  . . . . . . . . . . . . . . . . . . . . 38   11.  Informative References  . . . . . . . . . . . . . . . . . . . 38   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 391.  IntroductionLepinski                Expires January 6, 2016                 [Page 2]Internet-Draft              BGPsec Protocol                 July 6, 2015   This document describes BGPsec, a mechanism for providing path   security for Border Gateway Protocol (BGP) [2] route advertisements.   That is, a BGP speaker who receives a valid BGPsec update has   cryptographic assurance that the advertised route has the following   property: Every AS on the path of ASes listed in the update message   has explicitly authorized the advertisement of the route to the   subsequent AS in the path.   This document specifies a new optional (non-transitive) BGP path   attribute, BGPsec_Path.  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 is intended to be used to supplement BGP Origin Validation   [19] and when used in conjunction with origin validation, it is   possible to prevent a wide variety of route hijacking attacks against   BGP.   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 [12] and   the documents referenced therein.)  Any BGPsec speaker who wishes to   send, to external (eBGP) peers, BGP update messages containing the   BGPsec_Path needs to possess a private key associated with an RPKI   router certificate [9] that corresponds to the BGPsec speaker's AS   number.  Note, however, that a BGPsec speaker does not need such a   certificate in order to validate received update messages containing   the BGPsec_Path attribute.2.  BGPsec Negotiation   This document defines a new BGP capability [6] that allows a BGP   speaker to advertise to a neighbor the ability to send or to receive   BGPsec update messages (i.e., update messages containing the   BGPsec_Path attribute).2.1.  The BGPsec Capability   This capability has capability code : TBD   The capability length for this capability MUST be set to 3.   The three octets of the capability value are specified as follows.                       BGPsec Send Capability Value:Lepinski                Expires January 6, 2016                 [Page 3]Internet-Draft              BGPsec Protocol                 July 6, 2015                    0   1   2   3      4      5   6   7                 +---------------------------------------+                 | Version          | Dir |   Reserved   |                 +---------------------------------------+                 |                                       |                 +------           AFI              -----+                 |                                       |                 +---------------------------------------+   The first four bits 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.   The fifth bit of the first octet is a direction bit which indicates   whether the BGP speaker is advertising the capability to send BGPsec   update messages or receive BGPsec update messages. The BGP speaker   sets this bit to 0 to indicate the capability to receive BGPsec   update messages. The BGP speaker sets this bit to 1 to indicate the   capability to send BGPsec update messages.   The remaining three bits of the first octet are reserved for future   use.  These bits are set to zero by the sender of the capability and   ignored by the receiver of the capability.   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   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.2.2.  Negotiating BGPsec Support   In order to indicate that a BGP speaker is willing to send BGPsec   update messages (for a particular address family), a BGP speaker   sends the BGPsec Capability (see Section 2.1) with the Direction bit   (the fifth bit of the first octet) set to 1. In order to indicate   that the speaker is willing to receive BGP update messages containing   the BGPsec_Path attribute (for a particular address family), a BGP   speaker sends the BGPsec capability with the Direction bit set to 0.   In order to advertise the capability to both send and receive BGPsec   update messages, the BGP speaker sends two copies of the BGPsec   capability (one with the direction bit set to 0 and one with the   direction bit set to 1).Lepinski                Expires January 6, 2016                 [Page 4]Internet-Draft              BGPsec Protocol                 July 6, 2015   Similarly, if a BGP speaker wishes to use BGPsec with two different   address families (i.e., IPv4 and IPv6) over the same BGP session,   then the speaker includes two instances of this capability (one for   each address family) in the BGP OPEN message.  A BGP speaker MUST   support the BGP multiprotocol extension [3]. Additionally, a BGP   speaker MUST NOT advertise the capability of BGPsec support for a   particular AFI unless it has also advertised the multiprotocol   extension capability for the same AFI combination [3].   In a session where BGP session, a peer is permitted to send update   messages containing the BGPsec_Path attribute if, and only if:   o  The given peer sent the BGPsec capability for a particular version      of BGPsec and a particular address family with the Direction bit      set to 1; and   o  The other peer sent the BGPsec capability for the same version of      BGPsec and the same address family with the Direction bit set to      0.   In such a session, we say that the use of (the particular version of)   BGPsec has been negotiated (for a particular address family).  BGP   update messages without the BGPsec_Path attribute MAY be sent within   a session regardless of whether or not the use of BGPsec is   successfully negotiated.  However, if BGPsec is not successfully   negotiated, then BGP update messages containing the BGPsec_Path   attribute MUST NOT be sent.   This document defines the behavior of implementations in the case   where BGPsec version zero is the only version that has been   successfully negotiated.  Any future document which specifies   additional versions of BGPsec will need to specify behavior in the   case that support for multiple versions is negotiated.   BGPsec cannot provide meaningful security guarantees without support   for four-byte AS numbers.  Therefore, any BGP speaker that announces   the BGPsec capability, MUST also announce the capability for four-   byte AS support [4]. If a BGP speaker sends the BGPsec capability but   not the four-byte AS support capability then BGPsec has not been   successfully negotiated, and update messages containing the   BGPsec_Path attribute MUST NOT be sent within such a session.   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 [8].Lepinski                Expires January 6, 2016                 [Page 5]Internet-Draft              BGPsec Protocol                 July 6, 20153.  The BGPsec_Path Attribute   The BGPsec_Path 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 attribute carries the secured information regarding   the path of ASes through which an update message passes.  This   includes the digital signatures used to protect the path information.    We refer to those update messages that contain the BGPsec_Path   attribute as "BGPsec Update messages".  The BGPsec_Path attribute   replaces the AS_PATH attribute in a BGPsec update message.  That is,   update messages that contain the BGPsec_Path attribute MUST NOT   contain the AS_PATH attribute, and vice versa.   The BGPsec_Path attribute is made up of several parts.  The following   high-level diagram provides an overview of the structure of the   BGPsec_Path attribute:              High-Level Diagram of the BGPsec_Path Attribute        +---------------------------------------------------------+        |     +-----------------+                                 |        |     |   Secure Path   |                                 |        |     +-----------------+                                 |        |     |    AS X         |                                 |        |     |    pCount X     |                                 |        |     |    Flags X      |                                 |        |     |    AS Y         |                                 |        |     |    pCount Y     |                                 |        |     |    Flags Y      |                                 |        |     |      ...        |                                 |        |     +-----------------+                                 |        |                                                         |        |     +-----------------+       +-----------------+       |        |     | Sig Block 1     |       |  Sig Block 2    |       |        |     +-----------------+       +-----------------+       |        |     | Alg Suite 1     |       |  Alg Suite 2    |       |        |     | SKI X1          |       |  SKI X1         |       |        |     | Signature X1    |       |  Signature X1   |       |        |     | SKI Y1          |       |  SKI Y1         |       |        |     | Signature Y1    |       |  Signature Y1   |       |        |     |      ...        |       |      ....       |       |        |     +-----------------+       +-----------------+       |        |                                                         |        +---------------------------------------------------------+Lepinski                Expires January 6, 2016                 [Page 6]Internet-Draft              BGPsec Protocol                 July 6, 2015   The following is the specification of the format for the BGPsec_Path   attribute.                           BGPsec_Path Attribute         +-------------------------------------------------------+         | Secure_Path                             (variable)    |         +-------------------------------------------------------+         | Sequence of one or two Signature_Blocks (variable)    |         +-------------------------------------------------------+   The Secure_Path contains AS path information for the BGPsec update   message.  This is logically equivalent to the information that is   contained in a non-BGPsec AS_PATH attribute. The information in   Secure_Path is used by BGPsec speakers in the same way that   information from the AS_PATH is used by non-BGPsec speakers. The   format of the Secure_Path is described below in Section 3.1.   The BGPsec_Path attribute will contain one or two Signature_Blocks,   each of which corresponds to a different algorithm suite.  Each of   the Signature_Blocks will contain a signature segment for each AS   number (i.e., Secure_Path segment) in the Secure_Path.  In the most   common case, the BGPsec_Path attribute will contain only a single   Signature_Block.  However, in order to enable a transition from an   old algorithm suite to a new algorithm suite (without a flag day), it   will be necessary to include two Signature_Blocks (one for the old   algorithm suite and one for the new algorithm suite) during the   transition period.  (See Section 6.1 for more discussion of algorithm   transitions.)  The format of the Signature_Blocks is described below   in Section 3.2.3.1.  Secure_Path   Here we provide a detailed description of the Secure_Path information   in the BGPsec_Path attribute.                                Secure_Path             +-----------------------------------------------+             | Secure_Path Length                 (2 octets) |             +-----------------------------------------------+             | One or More Secure_Path Segments   (variable) |             +-----------------------------------------------+   The Secure_Path Length contains the length (in octets) of the entire   Secure_Path (including the two octets used to express this lengthLepinski                Expires January 6, 2016                 [Page 7]Internet-Draft              BGPsec Protocol                 July 6, 2015   field).  As explained below, each Secure_Path segment is six octets   long.  Note that this means the Secure_Path Length is two greater   than six times the number Secure_Path Segments (i.e., the number of   AS numbers in the path).   The Secure_Path contains one Secure_Path Segment for each (distinct)   Autonomous System in the path to the originating AS of the NLRI   specified in the update message.                            Secure_Path Segment                       +----------------------------+                       | AS Number      (4 octets)  |                       +----------------------------+                       | pCount         (1 octet)   |                       +----------------------------+                       | Flags          (1 octet)   |                       +----------------------------+   The AS Number is the AS number of the BGP speaker that added this   Secure_Path segment to the BGPsec_Path attribute.  (See Section 4 for   more information on populating this field.)   The pCount field contains 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 prepending   multiple copies of their AS to the AS_PATH without requiring the   speaker to generate multiple signatures. The pCount field is also   useful in managing route servers (see Section 4.2) and AS Number   migrations, see [18] for details.   The first bit of the Flags field is the Confed_Segment flag.  The   Confed_Segment flag is set to one to indicate that the BGPsec speaker   that constructed this Secure_Path segment is sending the update   message to a peer AS within the same Autonomous System confederation   [5].  (That is, the Confed_Segment flag is set in a BGPsec update   message whenever, in a non-BGPsec update message, the BGP speaker's   AS would appear in a AS_PATH segment of type AS_CONFED_SEQUENCE.)  In   all other cases the Confed_Segment flag is set to zero.   The remaining seven bits of the Flags MUST be set to zero by the   sender, and ignored by the receiver.  Note, however, that the   signature is computed over all eight bits of the flags field.3.2.  Signature_Block   Here we provide a detailed description of the Signature_Blocks in theLepinski                Expires January 6, 2016                 [Page 8]Internet-Draft              BGPsec Protocol                 July 6, 2015   BGPsec_Path attribute.Lepinski                Expires January 6, 2016                 [Page 9]Internet-Draft              BGPsec Protocol                 July 6, 2015                              Signature_Block              +---------------------------------------------+              | Signature_Block Length         (2 octets)   |              +---------------------------------------------+              | Algorithm Suite Identifier     (1 octet)    |              +---------------------------------------------+              | Sequence of Signature Segments (variable)   |              +---------------------------------------------+   The Signature_Block Length is the total number of octets in the   Signature_Block (including the two octets used to express this length   field).   The Algorithm Suite Identifier is a one-octet identifier specifying   the digest algorithm and digital signature algorithm used to produce   the digital signature in each Signature Segment.  An IANA registry of   algorithm identifiers for use in BGPsec is specified in the BGPsec   algorithms document [10].   A Signature_Block has exactly one Signature Segment for each   Secure_Path Segment in the Secure_Path portion of the BGPsec_Path   Attribute.  (That is, one Signature Segment for each distinct AS on   the path for the NLRI in the Update message.)                            Signature Segments              +---------------------------------------------+              | Subject Key Identifier        (20 octets)   |              +---------------------------------------------+              | Signature Length              (2 octets)    |              +---------------------------------------------+              | Signature                     (variable)    |              +---------------------------------------------+   The Subject Key Identifier contains the value in the Subject Key   Identifier extension of the RPKI router certificate [9] that is used   to verify the signature (see Section 5 for details on validity of   BGPsec update messages).   The Signature Length field contains the size (in octets) of the value   in the Signature field of the Signature Segment.   The Signature contains a digital signature that protects the NLRI and   the BGPsec_Path attribute (see Sections 4 and 5 for details on   signature generation and validation, respectively).Lepinski                Expires January 6, 2016                [Page 10]Internet-Draft              BGPsec Protocol                 July 6, 20154.  Generating a BGPsec Update   Sections 4.1 and 4.2 cover two of the cases in which a BGPsec speaker   generates an update message containing the BGPsec_Path 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   BGPsec_Path is the speaker's own AS.  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 BGPsec_Path attribute will contain AS   number(s) other than the speaker's own AS.   The remaining case is where the BGPsec speaker sends the update   message to an internal (iBGP) peer.  When originating a new route   advertisement and sending it to an internal peer, the BGPsec speaker   omits the BGPsec_Path attribute.  When propagating a received route   advertisement to an internal peer, the BGPsec speaker typically   populates the BGPsec_Path attribute by copying the BGPsec_Path   attribute from the received update message.  That is, the BGPsec_Path   attribute is copied verbatim. However, in the case that the BGPsec   speaker is performing an AS Migration, the BGPsec speaker may add an   additional signature on ingress before copying the BGPsec_Path   attribute (see [18] for more details).   Note that when a BGPsec speaker chooses to forward a BGPsec update   message to an iBGP peer, the BGPsec attribute SHOULD NOT be removed,   unless the peer doesn't support BGPsec. In particular, the BGPsec   attribute SHOULD NOT be removed even in the case where the BGPsec   update message has not been that has not successfully validated. (See   Section 5 for more information on validation, and 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 whom 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 would be 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 BGPsecLepinski                Expires January 6, 2016                [Page 11]Internet-Draft              BGPsec Protocol                 July 6, 2015   update message for each NLRI. Additionally, a BGPsec update message   MUST use the MP_REACH_NLRI [3] attribute to encode the NLRI.   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 [9]. Note   also that 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.   Section 4.3 contains special processing instructions for members of   an autonomous system confederation [5]. A BGPsec speaker that is not   a member of such a confederation MUST set the Flags field of the   Secure_Path Segment to zero in all BGPsec update messages it sends.   Section 4.4 contains instructions for reconstructing the AS_Path   attribute in cases where a BGPsec speaker receives an update message   with a BGPsec_Path attribute and wishes to propagate the update   message to a peer who does not support BGPsec.4.1.  Originating a New BGPsec Update   In an update message that originates a new route advertisement (i.e.,   an update whose path will contain only a single AS number), when   sending the route advertisement to an external, BGPsec-speaking peer,   the BGPsec speaker creates a new BGPsec_Path attribute as follows.   First, the BGPsec speaker constructs the Secure_Path with a single   Secure_Path Segment.  The AS in this path is the BGPsec speaker's own   AS number.  In particular, this AS number MUST match an AS number in   the AS number resource extension field of the Resource PKI router   certificate(s) [9] that will be used to verify the digital   signature(s) constructed by this BGPsec speaker.   The BGPsec_Path attribute and the AS_Path attribute are mutually   exclusive.  That is, any update message containing the BGPsec_Path   attribute MUST NOT contain the AS_Path attribute.  The information   that would be contained in the AS_Path attribute is instead conveyed   in the Secure_Path portion of the BGPsec_Path attribute.   The Resource PKI enables the legitimate holder of IP address   prefix(es) to issue a signed object, called a Route OriginationLepinski                Expires January 6, 2016                [Page 12]Internet-Draft              BGPsec Protocol                 July 6, 2015   Authorization (ROA), that authorizes a given AS to originate routes   to a given set of prefixes (see [7]). It is expected that most   relying parties will utilize BGPsec in tandem with origin validation   (see [19] and [20]). Therefore, it is RECOMMENDED that a BGPsec   speaker only originate a BGPsec update advertising a route for a   given prefix if there exists a valid ROA authorizing the BGPsec   speaker's AS to originate routes to this prefix.   The pCount field of the Secure_Path Segment 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 repetition.   Typically, a BGPsec speaker will use only a single algorithm suite,   and thus create only a single Signature_Block in the BGPsec_Path   attribute.  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   that contain a Signature_Block for both the 'current' and the 'new'   algorithm suites (see Section 6.1).   When originating a new route advertisement, each Signature_Block MUST   consist of a single Signature Segment.  The following describes how   the BGPsec speaker populates the fields of the Signature_Block.   The Subject Key Identifier field (see Section 3) is populated with   the identifier contained in the Subject Key Identifier extension of   the RPKI router certificate corresponding to the BGPsec speaker [9].   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 Signature field contains a digital signature that binds the NLRI   and BGPsec_Path attribute to the RPKI router certificate   corresponding to the BGPsec speaker.  The digital signature is   computed as follows:   o  Construct a sequence of octets by concatenating the Target AS      Number, the Secure_Path (Origin AS, pCount, and Flags), and the      Algorithm Suite Identifier. Then append to this sequence the      Address Family Identifier (AFI), Subsequent Address Family      Identifier (SAFI), and Network Layer Reachability Information      (NLRI) fields from the MP_REACH_NLRI attribute. Additionally, inLepinski                Expires January 6, 2016                [Page 13]Internet-Draft              BGPsec Protocol                 July 6, 2015      the Prefix field of the NLRI (from MP_REACH_NLRI), all of the      trailing bits MUST be set to zero when constructing this sequence.      In this sequence, 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.)Lepinski                Expires January 6, 2016                [Page 14]Internet-Draft              BGPsec Protocol                 July 6, 2015                      Sequence of Octets to be Signed        +------------------------------------+        | Target AS Number      (4 octets)   |        +------------------------------------+        | Origin AS Number      (4 octets)   |  ---\        +------------------------------------+      \        | pCount                (1 octet)    |       >  Secure_Path        +------------------------------------+      /        | Flags                 (1 octet)    |  ---/        +------------------------------------+        | Algorithm Suite Id.   (1 octet)    |        +------------------------------------+        | AFI                   (2 octets)   |  ---\        +------------------------------------+      \        | SAFI                  (1 octet)    |       >  MP_REACH_NLRI        +------------------------------------+      /        | NLRI                  (variable)   |  ---/        +------------------------------------+   o  Apply to this octet sequence the digest algorithm (for the      algorithm suite of this Signature_Block) to obtain a digest value.   o  Apply to this digest value the signature algorithm, (for the      algorithm suite of this Signature_Block) to obtain the digital      signature.  Then populate the Signature Field with this digital      signature.   The Signature Length field is populated with the length (in octets)   of the Signature field.4.2.  Propagating a Route Advertisement   When a BGPsec speaker receives a BGPsec update message containing a   BGPsec_Path attribute (with one or more signatures) from an (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.   If a BGPsec router has received only a non-BGPsec update message   (without the BGPsec_Path attribute), containing the AS_Path   attribute, from a peer for a given prefix then it MUST NOT attach a   BGPsec_Path attribute when it propagates the update message.  (Note   that a BGPsec router may also receive a non-BGPsec update message   from an internal peer without the AS_Path attribute, i.e., with just   the NLRI in it.  In that case, the prefix is originating from that AS   and hence the BGPsec speaker SHOULD sign and forward the update to   its external peers, as specified in Section 4.1.)Lepinski                Expires January 6, 2016                [Page 15]Internet-Draft              BGPsec Protocol                 July 6, 2015   Conversely, if a BGPsec router has received a BGPsec update message   (with the BGPsec_Path attribute) from a peer for a given prefix and   it chooses to propagate that peer's route for the prefix, then it   SHOULD propagate the route as a BGPsec update message containing the   BGPsec_Path attribute.   Note that removing BGPsec signatures (i.e., propagating a route   advertisement without the BGPsec_Path attribute) has significant   security ramifications.  (See Section 7 for discussion of 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 attribute   is NOT RECOMMENDED, unless the message is sent to a peer that did not   advertise the capability to receive BGPsec update messages (see   Section 4.4).   Furthermore, note that when a BGPsec speaker propagates a route   advertisement with the BGPsec_Path attribute it 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 would, in   the absence of BGPsec, contain an AS_SET (e.g., the BGPsec speaker is   performing proxy aggregation), then the BGPsec speaker MUST NOT   include the BGPsec_Path attribute.  In such a case, the BGPsec   speaker must remove any existing BGPsec_Path in the received   advertisement(s) for this prefix and produce a traditional (non-   BGPsec) update message.  It should be noted that BCP 172 [13]   recommends against the use of AS_SET and AS_CONFED_SET in the AS_PATH   of BGP updates.   To generate the BGPsec_Path attribute on the outgoing update message,   the BGPsec speaker first prepends a new Secure_Path Segment (places   in first position) to the Secure_Path.  The AS number in this   Secure_Path segment MUST match the AS number in the AS number   resource extension field of the Resource PKI router certificate(s)   that will be used to verify the digital signature(s) constructed by   this BGPsec speaker [9].   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 theLepinski                Expires January 6, 2016                [Page 16]Internet-Draft              BGPsec Protocol                 July 6, 2015   effective length of the AS path.  (Note that BGPsec speakers compute   the effective length of the AS path by summing the pCount values in   the BGPsec_Path attribute, see Section 5.)  However, when a route   server sets the pCount value to 0, it still inserts its AS number   into the Secure_Path segment, as this information is needed to   validate the signature added by the route server. (See [18] for a   discussion of setting pCount to 0 to facilitate AS Number Migration.)   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. (That is, pCount is only to be set to zero in   cases such as route servers or AS Number Migration where the BGPsec   speaker's peer expects pCount to be set to zero.)   If the received BGPsec update message contains two Signature_ Blocks   and the BGPsec speaker supports both of the corresponding algorithms   suites, then the new update message generated by the BGPsec speaker   SHOULD include both of the Signature_Blocks.  If the received BGPsec   update message contains two Signature_Blocks and the BGPsec speaker   only supports one of the two corresponding algorithm suites, then the   BGPsec speaker MUST remove the Signature_Block corresponding to the   algorithm suite that it does not understand.  If the BGPsec speaker   does not support the algorithm suites in any of the Signature_Blocks   contained in the received update message, then the BGPsec speaker   MUST NOT propagate the route advertisement with the BGPsec_Path   attribute.  (That is, if it chooses to propagate this route   advertisement at all, it must do so as an unsigned BGP update   message).   Note that in the case where the BGPsec_Path has two Signature_Blocks   (corresponding to different algorithm suites), the validation   algorithm (see Section 5.2) deems a BGPsec update message to be   'Valid' if there is at least one supported algorithm suite (and   corresponding Signature_Block) that is deemed 'Valid'.  This means   that a 'Valid' BGPsec update message may contain a Signature_Block   which is not deemed 'Valid' (e.g., contains signatures that the   BGPsec does not successfully verify).  Nonetheless, such   Signature_Blocks MUST NOT be removed.  (See Section 7 for a   discussion of the security ramifications of this design choice.)   For each Signature_Block corresponding to an algorithm suite that the   BGPsec speaker does support, the BGPsec speaker adds a new Signature   Segment to the Signature_Block.  This Signature Segment is prepended   to the list of Signature Segments (placed in the first position) so   that the list of Signature Segments appear in the same order as the   corresponding Secure_Path segments.  The BGPsec speaker populates the   fields of this new signature segment as follows.   The Subject Key Identifier field in the new segment is populated withLepinski                Expires January 6, 2016                [Page 17]Internet-Draft              BGPsec Protocol                 July 6, 2015   the identifier contained in the Subject Key Identifier extension of   the RPKI router certificate corresponding to the BGPsec speaker [9].    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 Signature field in the new segment contains a digital signature   that binds the NLRI and BGPsec_Path attribute to the RPKI router   certificate corresponding to the BGPsec speaker.  The digital   signature is computed as follows:   o  Construct a sequence of octets by concatenating the Target AS      number, the Secure_Path segment that is being added by the BGPsec      speaker constructing the signature, and the signature field of the      most recent Signature Segment (the one corresponding to AS from      whom the BGPsec speaker's AS received the announcement).  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.                      Sequence of Octets to be Signed       +--------------------------------------+       | Target AS Number        (4 octets)   |       +--------------------------------------+       | Signer's AS Number      (4 octets)   |  ---\       +--------------------------------------+      \       | pCount                  (1 octet)    |       >  Secure_Path       +--------- ----------------------------+      /       | Flags                   (1 octet)    |  ---/       +--------------------------------------+       | Most Recent Sig Field   (variable)   |       +--------------------------------------+   o  Apply to this octet sequence the digest algorithm (for the      algorithm suite of this Signature_Block) to obtain a digest value.   o  Apply to this digest value the signature algorithm, (for the      algorithm suite of this Signature_Block) to obtain the digital      signature.  Then populate the Signature Field with this digital      signature.   The Signature Length field is populated with the length (in octets)   of the Signature field.Lepinski                Expires January 6, 2016                [Page 18]Internet-Draft              BGPsec Protocol                 July 6, 20154.3.  Processing Instructions for Confederation Members   Members of autonomous system confederations [5] MUST additionally   follow the instructions in this section for processing BGPsec update   messages.   When a confederation member sends a BGPsec update message to a peer   that is a member of the same confederation, the confederation member   puts its (private) Member-AS Number (as opposed to the public AS   Confederation Identifier) in the AS Number field of the Secure_Path   Segment that it adds to the BGPsec update message.  Furthermore, when   a confederation member sends a BGPsec update message to a peer that   is a member of the same confederation, the BGPsec speaker that   generates the Secure_Path Segment sets the Confed_Segment flag to   one.  This means that in a BGPsec update message, an AS number   appears in a Secure_Path Segment with the Confed_Segment flag set   whenever, in a non-BGPsec update message, the AS number would appear   in a segment of type AS_CONFED_SEQUENCE in a non-BGPsec update   message.   Within a confederation, the verification of BGPsec signatures added   by other members of the confederation is optional.  If a   confederation chooses not to have its members verify signatures added   by other confederation members, then when sending a BGPsec update   message to a peer that is a member of the same confederation, the   confederation members MAY set the Signature field within the   Signature_Segment that it generates to be zero (in lieu of   calculating the correct digital signature as described in Sections   4.1 and 4.2).  Note that if a confederation chooses not to verify   digital signatures within the confederation, then BGPsec is able to   provide no assurances about the integrity of the (private) Member-AS   Numbers placed in Secure_Path segments where the Confed_Segment flag   is set to one.   When a confederation member receives a BGPsec update message from a   peer within the confederation and propagates it to a peer outside the   confederation, it needs to remove all of the Secure_Path Segments   added by confederation members as well as the corresponding Signature   Segments.  To do this, the confederation member propagating the route   outside the confederation does the following:   o  First, starting with the most recently added Secure_Path segment,      remove all of the consecutive Secure_Path segments that have the      Confed_Segment flag set to one.  Stop this process once a      Scure_Path segment is reached which has its Confed_Segment flag      set to zero.  Keep a count of the number of segments removed in      this fashion.Lepinski                Expires January 6, 2016                [Page 19]Internet-Draft              BGPsec Protocol                 July 6, 2015   o  Second, starting with the most recently added Signature Segment,      remove a number of Signature Segments equal to the number of      Secure_Path Segments removed in the previous step.  (That is,      remove the K most recently added signature segments, where K is      the number of Secure_Path Segments removed in the previous step.)   o  Finally, add a Secure_Path Segment containing, in the AS field,      the AS Confederation Identifier (the public AS number of the      confederation) as well as a corresponding Signature Segment.  Note      that all fields other that the AS field are populated as per      Sections 4.1 and 4.2.   When validating a received BGPsec update message, confederation   members need to make the following adjustment to the algorithm   presented in Section 5.2.  When a confederation member processes   (validates) a Signature Segment and its corresponding Secure_Path   Segment, the confederation member must note the following. For a   signature produced by a peer BGPsec speaker outside of a   confederation, the Target AS will always be the AS Confederation   Identifier (the public AS number of the confederation) as opposed to   the Member-AS Number.   To handle this case, when a BGPsec speaker (that is a confederation   member) processes a current Secure_Path Segment that has the   Confed_Segment flag set to zero, if the next most recently added   Secure_Path segment has the Confed_Segment flag set to one then, when   computing the digest for the current Secure_Path segment, the BGPsec   speaker takes the Target AS Number to be the AS Confederation   Identifier of the validating BGPsec speaker's own confederation.   (Note that the algorithm in Section 5.2 processes Secure_Path   Segments in order from most recently added to least recently added,   therefore this special case will apply to the first Secure_Path   segment that the algorithm encounters that has the Confed_Segment   flag set to zero.)   Finally, as discussed above, an AS confederation may optionally   decide that its members will not verify digital signatures added by   members.  In such a federation, when a confederation member runs the   algorithm in Section 5.2, the confederation member, during processing   of a Signature_Segment, first checks whether the Confed_Sequence flag   in the corresponding Secure_Path segment is set to one.  If the   Confed_Sequence flag is set to one in the corresponding Secure_Path   segment, the confederation member does not perform any further checks   on the Signature_Segment and immediately moves on to the next   Signature_Segment (and checks its corresponding Secure_Path segment).   Note that as specified in Section 5.2, it is an error when a BGPsec   speaker receives from a peer, who is not in the same AS   confederation, a BGPsec update containing a Confed_Sequence flag setLepinski                Expires January 6, 2016                [Page 20]Internet-Draft              BGPsec Protocol                 July 6, 2015   to one.  (As discussed in Section 5.2, any error in the BGPsec_Path   attribute MUST be handled using the "treat-as-withdraw", approach as   defined in RFC WXYZ [11].)4.4.  Reconstructing the AS_PATH Attribute   BGPsec update messages do not contain the AS_PATH attribute. However,   the AS_PATH attribute can be reconstructed from the BGPsec_Path   attribute.  This is necessary in the case where a route advertisement   is received via a BGPsec update message and then propagated to a peer   via a non-BGPsec update message (e.g., because the latter peer does   not support BGPsec). Note that there may be additional cases where an   implementation finds it useful to perform this reconstruction.   The AS_PATH attribute can be constructed from the BGPsec_Path   attribute as follows.  Starting with an empty AS_PATH attribute,   process the Secure_Path segments in order from least-recently added   (corresponding to the origin) to most-recently added.  For each   Secure_Path segment perform the following steps:   1.  If the Confed_Segment flag in the Secure_Path segment is set to       one, then look at the most-recently added segment in the AS_PATH.       *  In the case where the AS_PATH is empty or in the case where          the most-recently added segment is of type AS_SEQUENCE then          add (prepend to the AS_PATH) a new AS_PATH segment of type          AS_CONFED_SEQUENCE.  This segment of type AS_CONFED_SEQUENCE          shall contain a number of elements equal to the pCount field          in the current Secure_Path segment.  Each of these elements          shall be the AS number contained in the current Secure_Path          segment.  (That is, if the pCount field is X, then the segment          of type AS_CONFED_SEQUENCE contains X copies of the          Secure_Path segment's AS Number field.)       *  In the case where the most-recently added segment in the          AS_PATH is of type AS_CONFED_SEQUENCE then add (prepend to the          segment) a number of elements equal to the pCount field in the          current Secure_Path segment.  The value of each of these          elements shall be the AS number contained in the current          Secure_Path segment.  (That is, if the pCount field is X, then          add X copies of the Secure_Path segment's AS Number field to          the existing AS_CONFED_SEQUENCE.)Lepinski                Expires January 6, 2016                [Page 21]Internet-Draft              BGPsec Protocol                 July 6, 2015   2.  If the Confed_Segment flag in the Secure_Path segment is set to       zero, then look at the most-recently added segment in the       AS_PATH.       *  In the case where the AS_PATH is empty, and the pCount field          in the Secure_Path segment is greater than zero, add (prepend          to the AS_PATH) a new AS_PATH segment of type AS_SEQUENCE.          This segment of type AS_SEQUENCE shall contain a number of          elements equal to the pCount field in the current Secure_Path          segment.  Each of these elements shall be the AS number          contained in the current Secure_Path segment.  (That is, if          the pCount field is X, then the segment of type AS_SEQUENCE          contains X copies of the Secure_Path segment's AS Number          field.)       *  In the case where the most recently added segment in the          AS_PATH is of type AS_SEQUENCE then add (prepend to the          segment) a number of elements equal to the pCount field in the          current Secure_Path segment.  The value of each of these          elements shall be the AS number contained in the current          Secure_Path segment.  (That is, if the pCount field is X, then          add X copies of the Secure_Path segment's AS Number field to          the existing AS_SEQUENCE.)5.  Processing a Received BGPsec Update   Upon receiving a BGPsec update message from an external (eBGP) peer,   a BGPsec speaker SHOULD validate the message to determine the   authenticity of the path information contained in the BGPsec_Path   attribute. Typically, a BGPsec speaker will also wish to perform   origin validation (see [19] and [20]) on an incoming BGPsec update   message, but such validation is independent of the validation   described in this section.   Section 5.1 provides an overview of BGPsec validation and Section 5.2   provides a specific algorithm for performing such validation.  (Note   that an implementation need not follow the specific algorithm in   Section 5.2 as long as the input/output behavior of the validation is   identical to that of the algorithm in Section 5.2.)  During   exceptional conditions (e.g., the BGPsec speaker receives an   incredibly large number of update messages at once) a BGPsec speaker   MAY temporarily defer validation of incoming BGPsec update messages.   The treatment of such BGPsec update messages, whose validation has   been deferred, is a matter of local policy. However, an   implementation SHOULD ensure that deferment of validation and status   of deferred messages is visible to the operator.Lepinski                Expires January 6, 2016                [Page 22]Internet-Draft              BGPsec Protocol                 July 6, 2015   The validity of BGPsec update messages is a function of the current   RPKI state.  When a BGPsec speaker learns that RPKI state has changed   (e.g., from an RPKI validating cache via the RTR protocol), the   BGPsec speaker MUST re-run validation on all affected update messages   stored in its ADJ-RIB-IN.  That is, when a given RPKI certificate   ceases to be valid (e.g., it expires or is revoked), all update   messages containing a signature whose SKI matches the SKI in the   given certificate must be re-assessed to determine if they are still   valid. If this reassessment determines that the validity state of an   update has changed then, depending on local policy, it may be   necessary to re-run best path selection.   BGPsec update messages do not contain an AS_PATH attribute.   Therefore, a BGPsec speaker MUST utilize the AS path information in   the BGPsec_Path attribute in all cases where it would otherwise use   the AS path information in the AS_PATH attribute.  The only exception   to this rule is when AS path information must be updated in order to   propagate a route to a peer (in which case the BGPsec speaker follows   the instructions in Section 4).  Section 4.4 provides an algorithm   for constructing an AS_PATH attribute from a BGPsec_Path attribute.   Whenever the use of AS path information is called for (e.g., loop   detection, or use of AS path length in best path selection) the   externally visible behavior of the implementation shall be the same   as if the implementation had run the algorithm in Section 4.4 and   used the resulting AS_PATH attribute as it would for a non-BGPsec   update message.   Many signature algorithms are non-deterministic.  That is, many   signature algorithms will produce different signatures each time they   are run (even when they are signing the same data with the same key).   Therefore, if an implementation receives a BGPsec update from a peer   and later receives a second BGPsec update message from the same peer,   the implementation SHOULD treat the second message as a duplicate   update message if it differs from the first update message only in   the Signature fields (within the BGPsec_Path attribute).  That is, if   all the fields in the second update are identical to the fields in   the first update message, except for the Signature fields, then the   second update message should be treated as a duplicate of the first   update message.  Note that if other fields (e.g., the Subject Key   Identifier field) within a Signature segment differ between two   update messages then the two updates are not duplicates.   With regards to the processing of duplicate update messages, if the   first update message is valid, then an implementation SHOULD NOT run   the validation procedure on the second, duplicate update message   (even if the bits of the signature field are different).  If the   first update message is not valid, then an implementation SHOULD run   the validation procedure on the second duplicate update message (asLepinski                Expires January 6, 2016                [Page 23]Internet-Draft              BGPsec Protocol                 July 6, 2015   the signatures in the second update may be valid even though the   first contained a signature that was invalid).Lepinski                Expires January 6, 2016                [Page 24]Internet-Draft              BGPsec Protocol                 July 6, 20155.1.  Overview of BGPsec Validation   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   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 router certificate, 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.  (For example,   the trusted cache could deliver the necessary validity information to   the BGPsec speaker using the router key PDU [16] for the RTR protocol   [15].)   To validate a BGPsec update message containing the BGPsec_Path   attribute, the recipient performs the validation steps specified in   Section 5.2.  The validation procedure results in one of two states:   'Valid' and 'Not Valid'.   It is expected that the output of the validation procedure will be   used as an input to BGP route selection.  That said, BGP route   selection, and thus the handling of the validation states is a matter   of local policy, and is handled using local policy mechanisms.   Implementations SHOULD enable operators to set such local policy on a   per-session basis. (That is, we expect some operators will choose to   treat BGPSEC validation status differently for update messages   received over different BGP sessions.)   It is expected that BGP peers will generally prefer routes received   via 'Valid' BGPsec update messages over both routes received via 'Not   Valid' BGPsec update messages and routes received via update messages   that do not contain the BGPsec_Path attribute.  However, BGPsec   specifies no changes to the BGP decision process.  (See [17] for   related operational considerations.)   BGPsec validation needs only be performed at the 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 via some   mechanism, according to local policy within an AS.  As discussed in   Section 4, when a BGPsec speaker chooses to forward a (syntacticallyLepinski                Expires January 6, 2016                [Page 25]Internet-Draft              BGPsec Protocol                 July 6, 2015   correct) BGPsec update message, it SHOULD be forwarded with its   BGPsec_Path attribute intact (regardless of the validation state of   the update message).  Based entirely on local policy, an egress   router receiving a BGPsec update message from within its own AS MAY   choose to perform its own validation.5.2.  Validation Algorithm   This section specifies an algorithm for validation of BGPsec update   messages.  A conformant implementation MUST include a BGPsec update   validation algorithm that is functionally equivalent to the   externally visible behavior of this algorithm.   First, the recipient of a BGPsec update message performs a check to   ensure that the message is properly formed.  Specifically, the   recipient performs the following checks:   1.  Check to ensure that the entire BGPsec_Path attribute is       syntactically correct (conforms to the specification in this       document).   2.  Check that each Signature_Block contains one Signature segment       for each Secure_Path segment in the Secure_Path portion of the       BGPsec_Path attribute.  (Note that the entirety of each       Signature_Block must be checked to ensure that it is well formed,       even though the validation process may terminate before all       signatures are cryptographically verified.)   3.  Check that the update message does not contain an AS_PATH       attribute.   4.  If the update message was received from a peer that is not a       member of the BGPsec speaker's AS confederation, check to ensure       that none of the Secure_Path segments contain a Flags field with       the Confed_Sequence flag set to one.   5.  If the update message was received from a peer that is not       expected to set pCount equal to zero (see Section 4.2) then check       to ensure that the pCount field in the most-recently added       Secure_Path segment is not equal to zero.   If any of these checks fail, it is an error in the BGPsec_Path   attribute. Any of these errors in the BGPsec_Path attribute are   handled as per RFC WXYZ [11]. BGPsec speakers MUST handle these   errors using the "treat-as-withdraw" approach as defined in RFC WXYZ   [11].   Next, the BGPsec speaker examines the Signature_Blocks in theLepinski                Expires January 6, 2016                [Page 26]Internet-Draft              BGPsec Protocol                 July 6, 2015   BGPsec_Path attribute.  A Signature_Block corresponding to an   algorithm suite that the BGPsec speaker does not support is not   considered in validation.  If there is no Signature_Block   corresponding to an algorithm suite that the BGPsec speaker supports,   then the BGPsec speaker MUST treat the update message in the same   manner that the BGPsec speaker would treat an (unsigned) update   message that arrived without a BGPsec_Path attribute.   For each remaining Signature_Block (corresponding to an algorithm   suite supported by the BGPsec speaker), the BGPsec speaker iterates   through the Signature segments in the Signature_Block, starting with   the most recently added segment (and concluding with the least   recently added segment).  Note that there is a one-to-one   correspondence between Signature segments and Secure_Path segments   within the BGPsec_Path attribute.  The following steps make use of   this correspondence.   o  (Step I): Locate the public key needed to verify the signature (in      the current Signature segment).  To do this, consult the valid      RPKI router certificate data and look up all valid (AS, SKI,      Public Key) triples in which the AS matches the AS number in the      corresponding Secure_Path segment.  Of these triples that match      the AS number, check whether there is an SKI that matches the      value in the Subject Key Identifier field of the Signature      segment.  If this check finds no such matching SKI value, then      mark the entire Signature_Block as 'Not Valid' and proceed to the      next Signature_Block.   o  (Step II): Compute the digest function (for the given algorithm      suite) 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:Lepinski                Expires January 6, 2016                [Page 27]Internet-Draft              BGPsec Protocol                 July 6, 2015                      Sequence of Octets to be Hashed     +-------------------------------------------+     | AS Number of Target AS         (4 octets) |     +-------------------------------------------+     | AS Number                      (4 octets) |  ---\     +-------------------------------------------+      \     | pCount                         (1 octet)  |       >  Secure_Path     +-------------------------------------------+      /     | Flags                          (1 octet)  |  ---/     +-------------------------------------------+     | Sig Field in the Next Segment  (variable) |     +-------------------------------------------+   For the first segment to be processed (the most recently added   segment), the 'AS Number of Target 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 Target AS' is the   AS number in the Secure_Path segment that corresponds to the   Signature Segment added immediately after the one being processed.   (That is, in the Secure_Path segment that corresponds to the   Signature segment that the validator just finished processing.)   The AS Number, pCount and Flags fields are taken from the Secure_Path   segment that corresponds to the Signature segment currently being   processed.  The 'Signature Field in the Next Segment' is the   Signature field found in the Signature segment that is next to be   processed (that is, the next most recently added Signature Segment).   Alternatively, if the segment being processed corresponds to the   origin AS (i.e., if it is the least recently added segment), then the   digest function should be computed on the following sequence of   octets:Lepinski                Expires January 6, 2016                [Page 28]Internet-Draft              BGPsec Protocol                 July 6, 2015                      Sequence of Octets to be Hashed        +------------------------------------+        | AS Number of Target AS (4 octets)  |        +------------------------------------+        | Origin AS Number       (4 octets)  |  ---\        +------------------------------------+      \        | pCount                 (1 octet)   |       >  Secure_Path        +------------------------------------+      /        | Flags                  (1 octet)   |  ---/        +------------------------------------+        | Algorithm Suite Id.    (1 octet)   |        +------------------------------------+        | AFI                   (2 octets)   |  ---\        +------------------------------------+      \        | SAFI                  (1 octet)    |       >  MP_REACH_NLRI        +------------------------------------+      /        | NLRI                  (variable)   |  ---/        +------------------------------------+   The Address Family Identifier (AFI), Subsequent Address Family   Identifier (SAFI), and Network Layer Reachability Information (NLRI)   are obtained directly from the MP_REACH_NLRI attribute of the update   message. However, in the Prefix field of the NLRI (from   MP_REACH_NLRI), all of the trailing bits MUST be set to zero for the   purpose of signature verification. The Algorithm Suite Identifier is   obtained from the BGPsec_Path attribute being validated.  The Origin   AS Number, pCount, and Flags fields are taken from the Secure_Path   segment corresponding to the Signature Segment currently being   processed.   The 'AS Number of Target AS' is the AS Number from the Secure_Path   segment that was added immediately after the Secure_Path segment   containing the Origin AS Number.  (That is, the Secure_Path segment   corresponding to the Signature segment that the receiver just   finished processing prior to the current Signature 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, then mark the entire Signature_Block as 'Not      Valid' and proceed to the next Signature_Block.  If the signature      validation algorithm determines that the signature is valid, then      continue processing Signature Segments (within the current      Signature_Block).Lepinski                Expires January 6, 2016                [Page 29]Internet-Draft              BGPsec Protocol                 July 6, 2015   If all Signature Segments within a Signature_Block pass validation   (i.e., all segments are processed and the Signature_Block has not yet   been marked 'Not Valid'), then the Signature_Block is marked as   'Valid'.   If at least one Signature_Block is marked as 'Valid', then the   validation algorithm terminates and the BGPsec update message is   deemed to be 'Valid'.  (That is, if a BGPsec update message contains   two Signature_Blocks then the update message is deemed 'Valid' if the   first Signature_Block is marked 'Valid' OR the second Signature_Block   is marked 'Valid'.)6.  Algorithms and Extensibility6.1.  Algorithm Suite Considerations   Note that there is currently no support for bilateral negotiation   (using BGP capabilities) between BGPsec peers to use of a particular   (digest and signature) algorithm suite. 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 [10].   We anticipate that, in the future, the mandatory algorithm suites   document will be updated to specify a transition from the 'current'   algorithm suite to a '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 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 single Signature_Block (corresponding   to the 'new' algorithm).6.2.  Extensibility ConsiderationsLepinski                Expires January 6, 2016                [Page 30]Internet-Draft              BGPsec Protocol                 July 6, 2015   This section discusses potential changes to BGPsec that would require   substantial changes to the processing of the BGPsec_Path and thus   necessitate a new version of BGPsec.  Examples of such changes   include:   o  A new type of signature algorithm that produces signatures of      variable length   o  A new type of signature algorithm for which the number of      signatures in the Signature_Block is not equal to the number of      ASes in the Secure_Path (e.g., aggregate signatures)   o  Changes to the data that is protected by the BGPsec signatures      (e.g., attributes other than the 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   that this version of BGPsec would specify a new BGP path attribute,   let's call it BGPsec_PATH_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 6.1.  During the transition   period all BGPsec speakers SHOULD simultaneously include both the   BGPsec_Path attribute and the new BGPsec_PATH_TWO attribute.  Once   the transition is complete, the use of BGPsec_Path could then be   deprecated, at which point BGPsec speakers SHOULD include only the   new BGPsec_PATH_TWO attribute.  Such a process could facilitate a   transition to a new BGPsec semantics in a backwards compatible   fashion.7.  Security Considerations   For a discussion of the BGPsec threat model and related security   considerations, please see [14].7.1 Security Guarantees   When used in conjunction with Origin Validation (see [19] and [20]),   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 hasLepinski                Expires January 6, 2016                [Page 31]Internet-Draft              BGPsec Protocol                 July 6, 2015      been authorized, in the RPKI, by the IP address space holder to      originate route advertisements for the given prefix.   o  For each AS in the path, a BGPsec speaker authorized by the holder      of the AS number intentionally chose (in accordance with local      policy) to propagate the route advertisement to the subsequent AS      in the path.   That is, the recipient of a valid BGPsec Update message is assured   that the Secure_Path portion of the BGPsec_Path attribute 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 that BGPsec does not offer any guarantee that the   data packets would flow 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.   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).7.2 On the Removal of BGPsec Signatures   There may be cases where a BGPsec speaker deems 'Valid' (as per the   validation algorithm in Section 5.2) a BGPsec update message that   contains both a 'Valid' and a 'Not Valid' Signature_Block.  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 a BGPsec speaker choosing to propagate the   route advertisement in such an update message SHOULD add its   signature to each of the Signature_Blocks. Thus the BGPsec speaker   creates a signature using both algorithm suites and creates a new   update message that contains both the 'Valid' and the 'Not Valid' set   of signatures (from its own vantage point).   To understand the reason for such a design decision consider the caseLepinski                Expires January 6, 2016                [Page 32]Internet-Draft              BGPsec Protocol                 July 6, 2015   where the BGPsec speaker receives an update message with both a set   of algorithm A signatures which are 'Valid' and a set of algorithm B   signatures which are 'Not Valid'.  In such a case it is possible   (perhaps even likely, depending on the state of the algorithm   transition) 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   Valid' set of signatures corresponding to algorithm B, such entities   would treat the message as though it were unsigned.  By including the   'Not Valid' 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   differently from BGPsec updates that contain a single set of 'Not   Valid' signatures.  That is, by removing the set of 'Not Valid'   signatures the BGPsec speaker might actually cause a downstream   entity to 'upgrade' the status of a route advertisement from 'Not   Valid' to unsigned.  Finally, note that in the above scenario, the   BGPsec speaker might have deemed algorithm A signatures 'Valid' only   because 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 Valid' (due to the   revocation) and not as 'unsigned' (which would happen if the 'Not   Valid' Signature_Blocks 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   path (to a given prefix) a route obtained via a 'Not Valid' BGPsec   update message. In such a case, the BGPsec speaker should propagate a   signed BGPsec update message, adding his signature to the 'Not Valid'   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 should also be noted   that due to possible differences in RPKI data observed at different   vantage points in the network, a BGPsec update deemed 'Not Valid' at   an upstream BGPsec speaker may be deemed 'Valid' by another BGP   speaker downstream.   Indeed, 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:   o  The BGPsec speaker received the given route advertisement with theLepinski                Expires January 6, 2016                [Page 33]Internet-Draft              BGPsec Protocol                 July 6, 2015      indicated NLRI and Secure_Path; and   o  The BGPsec speaker chose to propagate an advertisement for this      route to the peer (implicitly) indicated by the 'Target AS'Lepinski                Expires January 6, 2016                [Page 34]Internet-Draft              BGPsec Protocol                 July 6, 20157.3 Mitigation of Denial of Service Attacks   The BGPsec update validation procedure is a potential target for   denial of service attacks against a BGPsec speaker. Here we consider   the mitigation only of denial of service attacks that are specific to   BGPsec.   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   performing less expensive checks (e.g., syntax checks).  The   validation algorithm specified in Section 5.2 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 5.2 may not provide the best   denial of service protection for all implementations.   Additionally, sending update messages with very long AS paths (and   hence a large number of signatures) is a potential mechanism to   conduct denial of service attacks. For this reason, it is important   that an implementation of the validation algorithm stops attempting   to verify signatures as soon as an invalid signature is found. (This   ensures that long sequences of invalid signatures cannot be used for   denial of service attacks.) Furthermore, implementations can mitigate   such attacks by only performing validation on update messages that,   if valid, would be selected as the best path. That is, if an update   message contains a route that would lose out in best path selection   for other reasons (e.g., a very long AS path) then it is not   necessary to determine the BGPsec-validity status of the route.7.4 Additional Security Considerations   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 within which an upstream entity   two or more hops away has set pCount to zero is unable to verify for   themselves whether pCount was set to zero legitimately.   BGPsec does not provide protection against attacks at the transport   layer.  As with any BGP session, an adversary on the path between aLepinski                Expires January 6, 2016                [Page 35]Internet-Draft              BGPsec Protocol                 July 6, 2015   BGPsec speaker and its peer is able to perform attacks such as   modifying valid BGPsec updates to cause them to fail validation,   injecting (unsigned) BGP update messages without   BGPsec_Path_Signature attributes, injecting BGPsec update messages   with BGPsec_Path_Signature attributes that fail validation, or   causing the peer to tear-down the BGP session. The use of BGPsec does   nothing to increase the power of an on-path adversary -- in   particular, even an on-path adversary cannot cause a BGPsec speaker   to believe a BGPsec-invalid route is valid. However, as with any BGP   session, BGPsec sessions SHOULD be protected by appropriate transport   security mechanisms.   One might be concerned about a potential attack in which an adversary   replays a valid signature on an origin Secure_Path segment as though   it were a signature on later Secure_Path segment (in a different   update message). The only way such an attack could succeed would be   if a structure of bits to be signed in Section 4.1 (origin segment)   could also be parsed as a valid sequence of bits to be signed in   Section 4.2 (later segment). This, in particular, would require that   the length of the two structures match exactly, which cannot happen   given the current choice of algorithms in [10]. We do not expect this   to be a problem with future signature algorithms, as it is likely   that signatures will get longer (instead of shorter) over time.   However, authors of future revisions of the algorithms document [10]   should take care to ensure that this attack remains infeasible.8.  IANA Considerations   This document registers a new capability in the registry of BGP   Capabilities. The description for the new capability is "BGPsec   Capability". The reference for the new capability is this document   (i.e., the RFC that replaces draft-ietf-sidr-bgpsec-protocol).   This document registers a new path attribute in the registry of BGP   Path Attributes. The code for this new attribute is "BGPsec_PATH".   The reference for the new capability is this document (i.e., the RFC   that replaces draft-ietf-sidr-bgpsec-protocol).     This document does not create any new IANA registries.Lepinski                Expires January 6, 2016                [Page 36]Internet-Draft              BGPsec Protocol                 July 6, 20159.  Contributors9.1.  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   New College of Florida   mlepinski.ietf@gmail.com   Stephen Kent   BBN Technologies   kent@bbn.com   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   Parsons   weiler+ietf@watson.org9.2.  Acknowledgements   The authors would like to thank Michael Baer, Luke Berndt, Sharon   Goldberg, Ed Kern, Chris Morrow, Doug Maughan, Pradosh Mohapatra,Lepinski                Expires January 6, 2016                [Page 37]Internet-Draft              BGPsec Protocol                 July 6, 2015   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.10.  Normative References   [1]   Bradner, S., "Key words for use in RFCs to Indicate Requirement         Levels", BCP 14, RFC 2119, March 1997.   [2]   Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A Border         Gateway Protocol 4", RFC 4271, January 2006.   [3]   Bates, T., Chandra, R., Katz, D., and Y. Rekhter,         "Multiprotocol Extensions for BGP-4", RFC 4760, January 2007.   [4]   Vohra, Q. and E. Chen, "BGP Support for Four-octet AS Number         Space", RFC 6793, December 2012.   [5]   Traina, P., McPherson, D., and J. Scudder, "Autonomous System         Confederations for BGP", RFC 5065, August 2007.   [6]   Scudder, J. and R. Chandra, "Capabilities Advertisement with         BGP-4", RFC 5492, February 2009.   [7]   Lepinski, M., Kent, S., and D. Kong, "A Profile for Route         Origin Authorizations (ROAs)", RFC 6482, February 2012.   [8]   Patel, K., Ward, D., and R. Bush, "Extended Message support for         BGP", draft-ietf-idr-bgp-extended-messages (work in progress),         January 2015.   [9]  Reynolds, M., Turner, S., and S. Kent, "A Profile for BGPsec         Router Certificates, Certificate Revocation Lists, and         Certification Requests", draft-ietf-sidr-bgpsec-pki-profiles         (work in progress), November 2014.   [10]  Turner, S., "BGP Algorithms, Key Formats, & Signature Formats",         draft-ietf-sidr-bgpsec-algs (work in progress), July 2014.   [11]  Scudder, J., Chen, E., Mohapatra, P., and K. Patel, "Revised         Error Handling for BGP UPDATE Messages", draft-ietf-idr-error-         handling (work in progress), December 2014.11.  Informative References   [12]   Lepinski, M. and S. Kent, "An Infrastructure to Support Secure         Internet Routing", RFC 6480, February 2012.Lepinski                Expires January 6, 2016                [Page 38]Internet-Draft              BGPsec Protocol                 July 6, 2015   [13]  Kumari, W. and K. Sriram, "Recommendation for Not Using AS_SET         and AS_CONFED_SET in BGP", RFC 6472, December 2011.   [14]  Kent, S. and A. Chi, "Threat Model for BGP Path Security", RFC         7132, February 2014.   [15]  Bush, R. and R. Austein, "The Resource Public Key         Infrastructure (RPKI) to Router Protocol", RFC 6810, January         2013.   [16]  Bush, R., Patel, K., and S. Turner, "Router Key PDU for RPKI-         Router Protocol", draft-ymbk-rpki-rtr-keys (work in progress),         April 2013.   [17]  Bush, R., "BGPsec Operational Considerations", draft-ietf-sidr-         bgpsec-ops (work in progress), May 2012.   [18]  George, W. and S. Murphy, "BGPsec Considerations for AS         Migration", draft-ietf-sidr-as-migration (work in progress),         July 2014.   [19] Huston, G. and G. Michaelson, "Validation of Route Origination         Using the Resource Certificate Public Key Infrastructure (PKI)         and Route Origin Authorizations (ROAs)", RFC 6483, February         2013.   [20] Mohapatra, P., Scudder, J., Ward, D., Bush, R., and R. Austein,         "BGP Prefix Origin Validation", RFC 6811, January 2013.Author's Address   Matthew Lepinski (editor)   BBN Technologies   10 Moulton St   Cambridge, MA  55409   US   Phone: +1 617 873 5939   Email: mlepinski.ietf@gmail.comLepinski                Expires January 6, 2016                [Page 39]