Path Computation Element                                        D. Lopez
Internet-Draft                                       O. Gonzalez de Dios
Intended status: Experimental                             Telefonica I+D
Expires: August 18, 2014                                           Q. Wu
                                                                D. Dhody
                                                       February 14, 2014

                       Secure Transport for PCEP


   The Path Computation Element Communication Protocol (PCEP) defines
   the mechanisms for the communication between a Path Computation
   Client (PCC) and a Path Computation Element (PCE), or among PCEs.
   This document describe the usage of Transport Layer Security (TLS) to
   enhance PCEP security, hence the PCEPS acronym proposed for it.  The
   additional security mechanisms are provided by the transport protocol
   supporting PCEP, and therefore they do not affect its flexibility and

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
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on August 18, 2014.

Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   ( in effect on the date of

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

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Requirements Language  . . . . . . . . . . . . . . . . . . . .  3
   3.  Applying PCEPS . . . . . . . . . . . . . . . . . . . . . . . .  4
     3.1.  TCP ports  . . . . . . . . . . . . . . . . . . . . . . . .  4
     3.2.  TLS Connection Establishment . . . . . . . . . . . . . . .  4
     3.3.  Peer Identity  . . . . . . . . . . . . . . . . . . . . . .  6
     3.4.  Connection Establishment Failure . . . . . . . . . . . . .  7
   4.  Discovery Mechanisms . . . . . . . . . . . . . . . . . . . . .  7
     4.1.  DANE Applicability . . . . . . . . . . . . . . . . . . . .  8
   5.  Backward Compatibility . . . . . . . . . . . . . . . . . . . .  8
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  8
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . .  8
   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  9
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  9
     9.1.  Normative References . . . . . . . . . . . . . . . . . . .  9
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 10
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11

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1.  Introduction

   PCEP [RFC5440] defines the mechanisms for the communication between a
   Path Computation Client (PCC) and a Path Computation Element (PCE),
   or between two PCEs.  These interactions include requests and replies
   that can be critical for a sustainable network operation and adequate
   resource allocation, and therefore appropriate security becomes a key
   element in the PCE infrastructure.  As the applications of the PCE
   framework evolves, and more complex service patterns emerge, the
   definition of a secure mode of operation becomes more relevant.

   [RFC5440] analyzes in its section on security considerations the
   potential threats to PCEP and their consequences, and discusses
   several mechanisms for protecting PCEP against security attacks,
   without making a specific recommendation on a particular one or
   defining their application in depth.  Moreover, [RFC6952] remarks the
   importance of ensuring PCEP communication privacy, especially when
   PCEP communication endpoints do not reside in the same AS, as the
   interception of PCEP messages could leak sensitive information
   related to computed paths and resources.

   Among the possible solutions mentioned in these documents, Transport
   Layer Security (TLS) [RFC5246] provides support for peer
   authentication, and message encryption and integrity.  TLS supports
   the usage of well-know mechanisms to support key configuration and
   exchange, and means to perform security checks on the results of PCE
   discovery procedures via IGP ([RFC5088] and [RFC5089]).

   This document describes a security container for the transport of
   PCEP requests and replies, and therefore it will not interfere with
   the protocol flexibility and extensibility.

   This document describes how to apply TLS in securing PCE
   interactions, including the TLS handshake mechanisms, the TLS methods
   for peer authentication, the applicable TLS ciphersuites for data
   exchange, and the handling of errors in the security checks.  In the
   rest of the document we will refer to this usage of TLS to provide a
   secure transport for PCEP as "PCEPS".

2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

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3.  Applying PCEPS

3.1.  TCP ports

   Since PCEP can operate either with or without TLS, it is necessary
   for the PCEP speaker to indicate whether it wants to set up a TLS
   connection or not.  There are two main ways of achieving this:

   o  One option is to use a different port number for TLS connections
      (for example, the port 443 used for HTTPS)

   o  The other is to use the regular port number and have the PCEP
      speaker request that the PCE switch the connection to TLS using a
      protocol-specific mechanism (for example, the STARTTLS for mail
      and news protocols)

   To avoid requiring a specific PCEP extension to request TLS, this
   document proposes the usage of the former solution to implement

   The default destination port number for PCEPS is TCP/XXXX.

   NOTE: This port has to be agreed and registered as PCEPS with IANA.

3.2.  TLS Connection Establishment

   PCEPS has no notion of negotiating TLS in an established connection.
   PCEP peers MAY either discover that the other PCEP endpoint supports
   PCEPS or can be preconfigured to use PCEPS for a given peer (see
   section Section 4 for more details).  The connection establishment
   SHALL follow the following steps:

   1.  After completing the TCP handshake, immediately negotiate TLS
       sessions according to [RFC5246].  The following restrictions

       *  Support for TLS v1.2 [RFC5246] or later is REQUIRED.

       *  Support for certificate-based mutual authentication is

       *  Negotiation of mutual authentication is REQUIRED.

       *  Negotiation of a ciphersuite providing for integrity
          protection is REQUIRED.

       *  Negotiation of a ciphersuite providing for confidentiality is

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       *  Support for and negotiation of compression is OPTIONAL.

       *  PCEPS implementations MUST, at a minimum, support negotiation
          of the TLS_RSA_WITH_3DES_EDE_CBC_SHA, and SHOULD support
          TLS_RSA_WITH_RC4_128_SHA and TLS_RSA_WITH_AES_128_CBC_SHA as
          well.  In addition, PCEPS implementations MUST support
          negotiation of the mandatory-to-implement ciphersuites
          required by the versions of TLS that they support.

   2.  Peer authentication can be performed in any of the following two
       REQUIRED operation models:

       *  TLS with X.509 certificates using PKIX trust models:

          +  Implementations MUST allow the configuration of a list of
             trusted Certification Authorities (CAs) for incoming

          +  Certificate validation MUST include the verification rules
             as per [RFC5280].

          +  Implementations SHOULD indicate their trusted CAs.  For TLS
             1.2, this is done using [RFC5246], Section 7.4.4,
             "certificate_authorities" (server side) and [RFC6066],
             Section 6 "Trusted CA Indication" (client side).

          +  Peer validation always SHOULD include a check on whether
             the locally configured expected DNS name or IP address of
             the peer that is contacted matches its presented
             certificate.  DNS names and IP addresses can be contained
             in the Common Name (CN) or subjectAltName entries.  For
             verification, only one of these entries is to be
             considered.  The following precedence applies: for DNS name
             validation, subjectAltName:DNS has precedence over CN; for
             IP address validation, subjectAltName:iPAddr has precedence
             over CN.

          +  NOTE: Consider here whether peer validation MAY be extended
             by means of the DANE procedures, including its specs as
             informative references.

          +  Implementations MAY allow the configuration of a set of
             additional properties of the certificate to check for a
             peer's authorization to communicate (e.g., a set of allowed
             values in subjectAltName:URI or a set of allowed X509v3
             Certificate Policies)

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       *  TLS with X.509 certificates using certificate fingerprints:
          Implementations MUST allow the configuration of a list of
          trusted certificates, identified via fingerprint of the
          Distinguished Encoding Rules (DER) encoded certificate octets.
          Implementations MUST support SHA-256 as the hash algorithm for
          the fingerprint.

   3.  Start exchanging PCEP messages.

   To support TLS re-negotiation both peers MUST support the mechanism
   described in [RFC5746].  Any attempt of initiate a TLS handshake to
   establish new cryptographic parameters not aligned with [RFC5746]
   SHALL be considered a TLS negotiation failure.

3.3.  Peer Identity

   Depending on the peer authentication method in use, PCEPS supports
   different operation modes to establish peer's identity and whether it
   is entitled to perform requests or can be considered authoritative in
   its replies.  PCEPS implementations SHOULD provide mechanisms for
   associating peer identities with different levels of access and/or
   authoritativeness, and they MUST provide a mechanism for establish a
   default level for properly identified peers.  Any connection
   established with a peer that cannot be properly identified SHALL be
   terminated before any PCEP exchange takes place.

   In TLS-X.509 mode using fingerprints, a peer is uniquely identified
   by the fingerprint of the presented client certificate.

   There are numerous trust models in Public-Key Infrastructure (PKI)
   environments, and it is beyond the scope of this document to define
   how a particular deployment determines whether a client is
   trustworthy.  Implementations that want to support a wide variety of
   trust models should expose as many details of the presented
   certificate to the administrator as possible so that the trust model
   can be implemented by the administrator.  As a suggestion, at least
   the following parameters of the X.509 client certificate should be

   o  Peer's IP address

   o  Peer's fully qualified domain name (FQDN)

   o  Certificate Fingerprint

   o  Issuer

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   o  Subject

   o  All X509v3 Extended Key Usage

   o  All X509v3 Subject Alternative Name

   o  All X509v3 Certificate Policies

   In addition, a PCC MAY apply the procedures described in [RFC6698]
   (DANE) to verify its peer identity when using DNS discovery.  See
   section Section 4.1 for further details.

3.4.  Connection Establishment Failure

   In case the initial TLS negotiation or the peer identity check fail
   according to the procedures listed in this document, the peer MUST
   immediately terminate the session.  It SHOULD follow the procedure
   listed in [RFC5440] to retry session setup along with an exponential
   back-off session establishment retry procedure.

4.  Discovery Mechanisms

   A PCE can advertise its capability to support PCEPS using the IGP
   advertisement and discovery mechanism.  The PCE-CAP-FLAGS sub-TLV is
   an optional sub-TLV used to advertise PCE capabilities.  It MAY be
   present within the PCED sub-TLV carried by OSPF or IS-IS.  [RFC5088]
   and [RFC5089] provide the description and processing rules for this
   sub-TLV when carried within OSPF and IS-IS, respectively.  PCE
   capability bits are defined in [RFC5088].  A new capability flag bit
   for the PCE-CAP-FLAGS sub-TLV that can be announced as attribute to
   distribute PCEP security support information is proposed in

   NOTE: A new bit must be added here to advertise the PCEPS capability.

   When DNS is used by a PCC (or a PCE acting as a client, for the rest
   of the section, PCC refers to both) willing to use PCEPS to locate an
   appropriate PCE [I-D.wu-pce-dns-pce-discovery], the PCC as initiating
   entity chooses at least one of the returned FQDNs to resolve, which
   it does by performing DNS "A" or "AAAA" lookups on the FDQN.  This
   will eventually result in an IPv4 or IPv6 address.  The PCC SHALL use
   the IP address(es) from the successfully resolved FDQN (with the
   corresponding port number returned by the DNS SRV lookup) as the
   connection address(es) for the receiving entity.

   If the PCC fails to connect using an IP address but the "A" or "AAAA"
   lookups returned more than one IP address, then the PCC SHOULD use

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   the next resolved IP address for that FDQN as the connection address.
   If the PCC fails to connect using all resolved IP addresses for a
   given FDQN, then it SHOULD repeat the process of resolution and
   connection for the next FQDN returned by the SRV lookup based on the
   priority and weight.

   If the PCC receives a response to its SRV query but it is not able to
   establish a PCEPS connection using the data received in the response,
   as initiating entity it MAY fall back to lookup a PCE that uses TCP
   as transport.

4.1.  DANE Applicability

   DANE [RFC6698] defines a secure method to associate the certificate
   that is obtained from a TLS server with a domain name using DNS,
   i.e., using the TLSA DNS resource record (RR) to associate a TLS
   server certificate or public key with the domain name where the
   record is found, thus forming a "TLSA certificate association".  The
   DNS information needs to be protected by DNSSEC.  A PCC willing to
   apply DANE to verify server identity MUST conform to the rules
   defined in section 4 of [RFC6698].

5.  Backward Compatibility

   Since the procedure described in this document describes a security
   container for the transport of PCEP requests and replies carried on a
   newly allocated TCP port there will be no impact on the base PCEP
   and/or any further extensions.

6.  IANA Considerations

   NOTE: PCEPS has to be registered as TCP port XXXX.

   No new PCEP messages or other objects are defined.

7.  Security Considerations

   While the application of TLS satisfies the requirement on privacy as
   well as fine-grained, policy-based peer authentication, there are
   security threats that it cannot address.  It is advisable to apply
   additional protection measures, in particular in what relates to
   attacks specifically addressed to forging the TCP connection
   underpinning TLS.  TCP-AO (TCP Authentication Option [RFC5925]) is
   fully compatible with and deemed as complementary to TLS, so its
   usage is to be considered as a security enhancement whenever any of

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   the PCEPS peers require it, especially in the case of long-lived
   connections.  The mechanisms to configure the requirements to use
   TCP-AO and other lower-layer protection measures, as well as the
   association of the required crypto material (MKT in the case of
   TCP-AO) with a particular peer are outside the scope of this
   document.  [I-D.chunduri-karp-using-ikev2-with-tcp-ao] defines a
   method to perform such association.

   Since computational resources required by TLS handshake and
   ciphersuite are higher than unencrypted TCP, clients connecting to a
   PCEPS server can more easily create high load conditions and a
   malicious client might create a Denial-of-Service attack more easily.

   Some TLS ciphersuites only provide integrity validation of their
   payload, and provide no encryption.  This specification does not
   forbid the use of such ciphersuites, but administrators must weight
   carefully the risk of relevant internal data leakage that can occur
   in such a case, as explicitly stated by [RFC6952].

   When using certificate fingerprints to identify PCEPS peers, any two
   certificates that produce the same hash value will be considered the
   same peer.  Therefore, it is important to make sure that the hash
   function used is cryptographically uncompromised so that attackers
   are very unlikely to be able to produce a hash collision with a
   certificate of their choice.  This document mandates support for SHA-
   256, but a later revision may demand support for stronger functions
   if suitable attacks on it are known.

8.  Acknowledgements

   This specification relies on the analysis and profiling of TLS
   included in [RFC6614].

9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC5088]  Le Roux, JL., Vasseur, JP., Ikejiri, Y., and R. Zhang,
              "OSPF Protocol Extensions for Path Computation Element
              (PCE) Discovery", RFC 5088, January 2008.

   [RFC5089]  Le Roux, JL., Vasseur, JP., Ikejiri, Y., and R. Zhang,
              "IS-IS Protocol Extensions for Path Computation Element

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              (PCE) Discovery", RFC 5089, January 2008.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246, August 2008.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, May 2008.

   [RFC5440]  Vasseur, JP. and JL. Le Roux, "Path Computation Element
              (PCE) Communication Protocol (PCEP)", RFC 5440,
              March 2009.

   [RFC5746]  Rescorla, E., Ray, M., Dispensa, S., and N. Oskov,
              "Transport Layer Security (TLS) Renegotiation Indication
              Extension", RFC 5746, February 2010.

   [RFC5925]  Touch, J., Mankin, A., and R. Bonica, "The TCP
              Authentication Option", RFC 5925, June 2010.

   [RFC6066]  Eastlake, D., "Transport Layer Security (TLS) Extensions:
              Extension Definitions", RFC 6066, January 2011.

   [RFC6698]  Hoffman, P. and J. Schlyter, "The DNS-Based Authentication
              of Named Entities (DANE) Transport Layer Security (TLS)
              Protocol: TLSA", RFC 6698, August 2012.

9.2.  Informative References

              Chunduri, U., Tian, A., and J. Touch, "A framework for RPs
              to use IKEv2 KMP",
              draft-chunduri-karp-using-ikev2-with-tcp-ao-06 (work in
              progress), February 2014.

              Lopez, D., Wu, Q., Dhody, D., and D. King, "IGP extension
              for PCEP security capability support in the PCE
              discovery", draft-wu-pce-discovery-pceps-support-00 (work
              in progress), February 2014.

              Wu, W., Dhody, D., King, D., and D. Lopez, "Path
              Computation Element (PCE) Discovery using Domain Name
              System(DNS)", draft-wu-pce-dns-pce-discovery-04 (work in
              progress), January 2014.

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   [RFC6614]  Winter, S., McCauley, M., Venaas, S., and K. Wierenga,
              "Transport Layer Security (TLS) Encryption for RADIUS",
              RFC 6614, May 2012.

   [RFC6952]  Jethanandani, M., Patel, K., and L. Zheng, "Analysis of
              BGP, LDP, PCEP, and MSDP Issues According to the Keying
              and Authentication for Routing Protocols (KARP) Design
              Guide", RFC 6952, May 2013.

Authors' Addresses

   Diego R. Lopez
   Telefonica I+D
   Don Ramon de la Cruz, 82
   Madrid,   28006

   Phone: +34 913 129 041

   Oscar Gonzalez de Dios
   Telefonica I+D
   Don Ramon de la Cruz, 82
   Madrid,   28006

   Phone: +34 913 129 041

   Qin Wu
   101 Software Avenue, Yuhua District
   Nanjing, Jiangsu  210012


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   Dhruv Dhody
   Leela Palace
   Bangalore, KA  560008


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