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Internet Engineering Task Force                                Yang, Ed.
Internet-Draft                                                       Shi
Intended status: Informational                                     Xiang
Expires: September 12, 2017                                         Wang
                                                          Tsinghua Univ.
                                                          March 11, 2017

               Fast route attestation on AS Path Segment


   This draft proposes Fast Route Attestation (FRA), a mechanism for
   securing AS paths and preventing prefix hijacking by signing and
   verifying critical AS path segments (i.e., adjacent AS triples along
   AS path).  When full-deployed, FRA can achieve similar level of
   security as BGPSec, but with much higher efficiency.  When partial-
   deployed, FRA offers more security benefits than BGPSec.

Status of This Memo

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

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   This Internet-Draft will expire on September 12, 2017.

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   publication of this document.  Please review these documents

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   carefully, as they describe your rights and restrictions with respect
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Background  . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  FRA: Fast Route Attestation . . . . . . . . . . . . . . . . .   5
     4.1.  Neighbor Based Importing and Exporting  . . . . . . . . .   5
     4.2.  Signing Critical AS Path Segments efficiently . . . . . .   6
     4.3.  More benefits in partial-deployment scenario  . . . . . .   8
     4.4.  Other supports to FRA . . . . . . . . . . . . . . . . . .   8
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   7.  Conclusions . . . . . . . . . . . . . . . . . . . . . . . . .   9
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   In order to secure inter-domain routing, several extensions of BGP
   have been proposed, which fall into two categories: anomaly detection
   and cryptographic based authentication.  However, anomaly detection
   approaches [Whisper] [PGBGP] only detect and report routing
   anomalies.  They can not guarantee security in advance.
   Cryptographic approaches, like S-BGP [S-BGP] and BGPSec [RFC7353],
   use the Public Key Infrastructure (PKI) to authenticate routing
   announcements.  However, they may consume significant resources of
   computation and storage.  The other solutions either compromise in
   the security [IRV] [I-D.ng-sobgp-bgp-extensions] [psBGP] [SPV], or
   bring in more complexity on certification distribution [SA].

   Towards these unsolved issues, we propose an efficient approach, FRA
   (Fast Route Attestation), to secure AS path.  Through signing and
   verifying critical AS path segments (i.e., adjacent AS triples along
   AS path), FRA can achieve similar level of security as S-BGP/BGPSec,
   but with much higher efficiency.  Besides, when partial-deployed, FRA
   offers more security benefits than BGPSec, promoting ISPs to deploy
   the security mechanism.  It is the critical part of FS-BGP.
   Analysis, evaluations, and more discussions of FRA can be found in
   the recent technical report [TR-FSBGP].

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2.  Terminology

   (AS_i): AS i

   <AS_n, ..., AS_0>: AS path from AS n to the origin AS 0

   <AS_n, ..., AS_0>f: AS path of prefix f originated from AS 0

   <AS_i+1, AS_i, AS_i-1>: critical AS path segment, adjacent AS triple
   in a path

   <AS_1, AS_0, f>: origin critical AS path segment in a path of prefix

   {msg}i: signature on msg generated by AS i

3.  Background

   In BGP, UPDATE messages will not be validated, so neither the origin
   AS nor the AS path is guaranteed to be correct.  Secure BGP (S-BGP)
   [S-BGP] is the dominant solution to this problem, and it is based on
   RPKI [RFC6480] to help authenticating involved parties and messages.
   Specifically, S-BGP uses Route Attestations (RAs) for path
   authentication.  On the basis of S-BGP, BGPSec [RFC7353] was proposed
   to secure inter-domain routing, which has been standardized by IETF.

   As shown in Figure 1, an RA is all signatures signed by ASes along
   the path to authenticate the existence and position of ASes in the
   path.  We define {msg}i as the signature on msg generated with AS i's
   private key.  In Figure 1, each AS i equivalently signs the
   corresponding extended AS path <AS_i+1, AS_i, ..., AS_0> and the
   prefix f.  The inclusion of the recipient AS i+1 in each signature is
   necessary to prevent cut-and-paste attack.

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| (AS_n+1) <-- (AS_n) <-- ... <-- (AS_i) <-- ... <-- (AS_1) <-- (AS_0)            |
|          s_0                s_0                s_0        s_0                   |
|          s_1                s_1                s_1          \\                  |
|            .                  .                  \\          {AS_1, AS_0, f}0   |
|            .                  .                  {AS_2, AS_1, s_0}1             |
|            .                  .                   \\                            |
|          s_i                s_i                   {AS_2, AS_1, AS_0, f}1        |
|            .                  \\                                                |
|            .                  {AS_i+1, AS_i, s_i-1}i                            |
|            .                   \\                                               |
|          s_n                   {AS_i+1, AS_i, AS_i-1, ..., AS_1, AS_0, f}i      |
|            \\                                                                   |
|            {AS_n+1, AS_n, s_n-1}n                                               |
|             \\                                                                  |
|             {AS_n+1, AS_n, AS_n-1, ..., AS_1, AS_0, f}n                         |

                          Figure 1: RA in BGPSec.

   The main concern about deploying BGPSec in practice is its huge
   computational cost for signing and verifying signatures while
   authenticating AS path.  So there are a bunch of solutions for
   reducing the overhead of path authentication.

   soBGP [I-D.ng-sobgp-bgp-extensions] maintains all authenticated AS
   edges in a database, but faces the problem of forged paths.  IRV
   [IRV] builds an authentication server in each AS, but brings the
   problem of maintaining and inter-connecting these servers, and
   introduces query latencies.  SPV [SPV] accelerates the signing
   process by pre-generated one-time signatures based on a single root
   value, but involves a significant amount of state information, and
   its security can only be guaranteed probabilistically.  Signature
   Amortization (S-A) [SA] uses one bit vector for each neighbor of an
   AS to indicate the allowed recipients of a route, such that only for
   multiple recipients router only needs to sign once.  However, each AS
   will need to pre-establish a neighbor list corresponding to the bit
   vector, and to distribute it to all other ASes.

   As we can see, existing methods usually compromise security, and most
   of them only improve the performance of signing.  However,
   verification happens more frequently than signing, since one
   signature often needs to be verified at multiple places.

   Besides, when BGPSec is partial-deployed, it can only improve limited
   security benefits.  This influence the deployment of BGPSec
   seriously.  Many ISPs insist that unless majority of ASes deploys
   BGPSec, they would not benefit much from deploying BGPSec.

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   To overcome these weeknesses, Path-End Validation [PATH-END] has been
   proposed.  Since AS paths of BGP updates are usually very short, most
   attackers try to forge paths at their first two hops.  Path-End
   Validation aims to protect the two hops from modification.  The
   researchers show that if the first two hops of AS paths are
   authenticated, attackers can only attract little traffic by forging
   other parts of AS path.  That is, Path-End Validation provides less
   security protection than BGPSec when full-deployed.  However,
   according to simulation results, ASes can benefit more during the
   long partial-deployed period.  So Path-End Validation provides a
   tangible path to significant improvements in inter-domain routing
   security before BGPSec is fully deployed.

   Though Path-End Validation provides a way to improve inter-domain
   routing security, it has its own shortcoming.  When deployed widely,
   it cannot reach the security level of BGPSec.  Thus we wonder if
   there is a method which has higher computational efficiency than
   BGPSec with the similar security benefit when full-deployed.  In
   addition, the method improves security obviously like Path-End
   Validation during the long interim period.  Our solution, Fast Route
   Attestation (FRA), based on the assumption that RPKI has been used
   for origin authentication, focuses on path authentication.
   Importantly, FRA can satisfy such requirements well.

4.  FRA: Fast Route Attestation

4.1.  Neighbor Based Importing and Exporting

   BGP is a policy-based routing protocol.  An AS only exports a route
   to a neighbor if it is willing to forward traffic to the
   corresponding prefix from that neighbor.  Although complex policies
   (i.e. , route filters [RFC2622]) exist, AS usually does not
   differentiate with prefixes or nonadjacent ASes.  For example, in
   Figure 2, when AS n decides whether routes learned from AS n-1 can be
   exported to AS n+1, it only considers its relation with its two
   direct neighbors, but does not consider other ASes along the path
   (<AS_n-2, ..., AS_1, AS_0>).  We call this the Neighbor Based
   Importing and Exporting (NBIE).

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|                                       / ... (AS_x_0) ... \            |
|                                      /         .          \           |
|  (AS_n+1) <-- (AS_n) <-- (AS_n-1) <--   ...    .     ...  <-- (AS_0)  |
|                                      \         .          /           |
|                                       \ ... (AS_x_k) ... /            |

   Figure 2: In BGPSec, AS n signs k paths which share a mutual AS path
                          segment <n+1, n, n-1>.

   NBIE abstracts the basic functionality of BGP.  According to our
   measurement results in whois database, only a small portion of
   routing polices (route filters) violate NBIE assumption.
   Nevertheless, the purpose of route filters is to protect the routing
   system against distribution of inaccurate routing information
   [RFC2622].  In other words, the use of route filters is mainly due to
   security considerations rather than policy requirements.  We believe
   that under a security environment (i.e., FRA/FS-BGP or BGPSec), these
   ASes will not need filters any more.  In deed, our schema can also
   flexibly support complicated routing polices [TR-FSBGP].

4.2.  Signing Critical AS Path Segments efficiently

   Following NBIE assumption above, we propose Fast Route Attestation
   (FRA) to guarantee the authentication of AS paths.  Given a path
   p=<AS_n+1, AS_n, ..., AS_0>, we define its set of critical path
   segments as c_i, 0<i<=n, where

                      / <AS_1,AS_0,f>      , for i=0
                c_i =
                      \ <AS_i+1,AS_i,AS_i-1>  , for 0<i<=n

   We call AS i as the owner of c_i.  Particularly, c_0 is called the
   originating critical path segment owned by AS 0.  Under NBIE policy,
   a critical path segment <AS_i+1, AS_i, AS_i-1> actually describes an
   export policy of AS i, implying that AS i exports all routes imported
   from AS i-1 to AS i+1.

   More specifically, FRA uses Critical Segment Attestations (CSA) to
   authenticate paths.  A CSA is simply the signature of the critical
   path segment signed by its owner.  In a path p=<n+1, n, ..., 0>, the
   CSA s_i signed by AS i is defined as:

                          / {1,0,f}0      , for i=0
                    s_i =
                          \ {i+1,i,i-1}i  , for 0<i<=n

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   Importantly, the prefixes f in s_0 is necessary, because AS 0 might
   be multi-homing and can only announce part of its prefixes to AS 1 to
   balance traffic.

   Indeed, FRA have much higher efficiency than BGPSec.  Figure 3 and
   Figure 1 compare the signatures in FRA and BGPSec.  Obviously, the
   number of distinct critical path segments is far less than the number
   of distinct paths.  As a result, we can reduce the number of signing
   and verifying operations in FRA by using a small cache.  In Figure 2,
   AS n needs to sign each of the k paths individually in BGPSec.
   However, in FRA, all the k different paths can reuse one signature of
   the common critical segment <AS_n+1, AS_n, AS_n-1>.  Moreover, there
   are situations where several distinct prefixes can be reached along
   the same AS path.  As BGPSec is sensitive to prefix, one AS must sign
   several times if it deploys BGPSec.  While adopting FRA mechanism,
   the AS just signs critical path segment one time.

|  (AS_n+1) <-- (AS_n) <-- ... <-- (AS_i) <-- ... <-- (AS_1) <-- (AS_0)           |
|           s_0                s_0                s_0        s_0                  |
|           s_1                s_1                s_1          \\                 |
|             .                  .                 \\           {AS_1,AS_0,AS_f}0 |
|             .                  .                 {AS_2,AS_1,AS_0}1              |
|             .                  .                                                |
|           s_i                s_i                                                |
|             .                 \\                                                |
|             .                 {AS_i+1,AS_i,AS_i-1}i                             |
|             .                                                                   |
|           s_n                                                                   |
|            \\                                                                   |
|            {AS_n+1,AS_n,AS_n-1}n                                                |

                          Figure 3: CSAs in FRA.

   Then we explain that FRA mechanism can achieve similar level of
   security as S-BGP/BGPSec.  For every secure path in BGPSec, it is
   also authenticated in FRA.  For instance, <AS_n, AS_n-1, ..., AS_0>
   is secure in BGPSec.  That is to say, ASes along the path all deploy
   BGPSec, signing and verifying the path.  If they adopt FRA, they also
   sign its corresponding critical path segment.  Since ASes along the
   path are fully-deployed, the critical path segments can constitute
   the complete path.  If some attacker k intends to forge a link
   between k and AS i, receivers will verify the CSA.  Because the CSA
   s_i (i.e. {AS_i+1,AS_i,AS_i-1}i) means i+1 is the true next-hop, the
   forged update will be dropped.

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   In this section, we argue that under the NBIE rule, if every AS along
   a path signs its critical path segment, the path can be
   authenticated.  So as long as all the ASes along an AS path adopt FRA
   mechanism, the path must be authenticated.  Considering its
   efficiency we discussed above, FRA can achieve similar level of
   security as BGPSec with less time cost.

4.3.  More benefits in partial-deployment scenario

   As BGPSec is likely to coexist with legacy BGP for a long time, we
   must consider the effects of them in partial-deployment period.  In
   general, when not fully deployed, FRA can prevent more attacks than

   In BGPSec, one AS regards a route secure/insecure according to those
   ASes along the path.  Only if they all have deployed BGPSec, this
   route is regarded as a secure route.  However, if there is any AS
   which still runs legacy BGP, it would be regarded as an insecure one.

   But under FRA mechanism, this changes.  A route will not be regarded
   secure/insecure roughly.  Instead, FRA can provide different levels
   of protections to authenticate AS path.  For instance, suppose that
   <AS_n, ..., AS_0> is a path of prefix f.  If an attacker a intends to
   forge a path <AS_n, ..., AS_i+1, AS_a, AS_i-1, ..., AS_0> but a is
   not AS i-1's true neighbor, the forged path may be dropped by FRA
   authentication.  Specifically, if AS i-1 deploys FRA mechanism, it
   should sign a critical path segment <AS_a, AS_i-1, AS_i-2>.  Since AS
   a is not AS i-1's neighbor, the critical path segment will not appear
   in UPDATE messages.  Thus, the attacker has to forge the CSA, which
   can be detected by FRA adopters.  Briefly speaking, even if it is
   during partial-deployment period, FRA can provide more benefit than
   BGPSec.  According to the example aforementioned, the isolated
   deployment on AS i-1 can prevent attackers from forging path to it.
   However, the same benefit with BGPSec needs the deployment on all
   ASes along the true path.

   Since full-deployed BGPSec is not a short-term job, FRA makes sense
   because of its better benefit in interim period.  When majority still
   runs legacy BGP, FRA guarantees users better security than BGPSec.
   Besides, because FRA authenticates the whole path of BGP updates when
   fully deployed, it can provide a similar security benefit as BGPSec.

4.4.  Other supports to FRA

   FRA uses certificates to handle UPDATE messages.  As FRA takes effect
   even if some ASes along the path don't deploy it, the certificates of
   FRA must involve extra info.

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   Based on RPKI [RFC6480], FRA can also validate source address of BGP.
   Thus, FRA certificates must include ASNs, prefixes and their maximum
   length, which are similar to RPKI's ROAs.

   In order to sign critical AS path segments, any AS must be accessible
   to public keys of all ASes.  They are stored in some public
   repositories.  Relying parties can download them to their local
   caches and validate UPDATEs with FRA.

   Besides, ASNs of all the ASes having deployed FRA are also involved
   in certificates.  When FRA is partial-deployed, ASes can check all
   adopters' CSAs along the path.  Thus, attackers cannot remove any
   CSAs to forge path.

5.  IANA Considerations

   This document includes no request to IANA.

6.  Security Considerations

   The entire document is about security consideration.  More
   theoretical analysis and experiment results can be found in our
   technical report [TR-FSBGP].

7.  Conclusions

   This draft proposes Fast Route Attestation (FRA), an efficient
   mechanism for securing AS paths and preventing prefix hijacking by
   signing critical AS path segments with cache machenism.  FRA can
   achieve provide higher security benefits than BGPSec even in very
   limited partial adoption.  Also, we believe it can achieve higher
   level of security than Path-End validation when full-deployed.

8.  References

8.1.  Normative References

              Ng, J., "Extensions to BGP to Support Secure Origin BGP
              (soBGP)", 2004.

   [IRV]      Goodell, G., Aiello, W., Griffin, T., Ioannidis, J.,
              McDaniel, P., and A. Rubin, "Working around BGP: An
              Incremental Approach to Improving Security and Accuracy in
              Interdomain Routing", 2003.

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              Cohen, Avichai., Gilad, Yossi., Herzberg, Amir., and
              Michael. Schapira, "Jumpstarting BGP Security with Path-
              End Validation", 2016.

   [psBGP]    van Oorschot, P., Wan, T., and E. Kranakis, "On
              interdomain routing security and pretty secure BGP
              (psBGP)", 2007.

   [RFC2622]  Alaettinoglu, C., Villamizar, C., Gerich, E., Kessens, D.,
              Meyer, D., Bates, T., Karrenberg, D., and M. Terpstra,
              "Routing Policy Specification Language (RPSL)", RFC 2622,
              DOI 10.17487/RFC2622, June 1999,

   [RFC4271]  Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
              Border Gateway Protocol 4 (BGP-4)", RFC 4271,
              DOI 10.17487/RFC4271, January 2006,

   [RFC6480]  Lepinski, M. and S. Kent, "An Infrastructure to Support
              Secure Internet Routing", RFC 6480, DOI 10.17487/RFC6480,
              February 2012, <http://www.rfc-editor.org/info/rfc6480>.

   [RFC7353]  Bellovin, S., Bush, R., and D. Ward, "Security
              Requirements for BGP Path Validation", RFC 7353,
              DOI 10.17487/RFC7353, August 2014,

   [S-BGP]    Kent, S., Lynn, C., Mikkelson, J., and K. Seo, "Secure
              Border Gateway Protocol (S-BGP)", 2000.

   [SA]       Nicol, D., Smith, S., and M. Zhao, "Evaluation of
              efficient security for BGP route announcements using
              parallel simulation", 2004.

   [SPV]      Hu, Y., Perrig, A., and M. Sirbu, "SPV: secure path vector
              routing for securing BGP", 2004.

              Xiang, Yang., Wang, Zhiliang., Yin, Xia., Shi, Xingang.,
              and Jianping. Wu, "FS-BGP: An Efficient Approach to
              Securing AS Paths", 2011.

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8.2.  Informative References

   [PGBGP]    Karlin, J., Forrest, S., and J. Rexford, "Pretty Good BGP:
              Improving BGP by Cautiously Adopting Routes", 2006.

   [Whisper]  Subramanian, L., Roth, V., Stoica, I., Shenker, S., and R.
              Katz, "Listen and Whisper: Security Mechanisms for BGP",

Authors' Addresses

   Yan Yang (editor)
   Tsinghua Univ.

   Email: yangyan15@mails.tsinghua.edu.cn

   Xingang Shi
   Tsinghua Univ.

   Email: shixg@cernet.edu.cn

   Yang Xiang
   Tsinghua Univ.

   Email: xiangy08@csnet1.cs.tsinghua.edu.cn

   Zhiliang Wang
   Tsinghua Univ.

   Email: wzl@csnet1.cs.tsinghua.edu.cn

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   Jianping Wu
   Tsinghua Univ.

   Email: jianping@csnet1.cs.tsinghua.edu.cn

   Xia Yin
   Tsinghua Univ.

   Email: yxia@csnet1.cs.tsinghua.edu.cn

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