IPPM WG                                              K. Pentikousis, Ed.
Internet-Draft                                                      EICT
Intended status: Standards Track                                E. Zhang
Expires: March 23, May 14, 2015                                             Y. Cui
                                                     Huawei Technologies
                                                      September 19,
                                                       November 10, 2014

               IKEv2-based Shared Secret Key for O/TWAMP


   The O/TWAMP security mechanism requires that both the client and
   server endpoints possess a shared secret.  Since the currently-
   standardized O/TWAMP security mechanism only supports a pre-shared
   key mode, large scale deployment of O/TWAMP is hindered
   significantly.  At the same time, recent trends point to wider IKEv2
   deployment which, in turn, calls for mechanisms and methods that
   enable tunnel end-users, as well as operators, to measure one-way and
   two-way network performance in a standardized manner.  This document
   discusses the use of keys derived from an IKEv2 SA as the shared key
   in O/TWAMP.  If the shared key can be derived from the IKEv2 SA, O/
   TWAMP can support certificate-based key exchange, which would allow
   for more operational flexibility and efficiency.  The key derivation
   presented in this document can also facilitate automatic key

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Scope and Applicability . . . . . . . . . . . . . . . . . . .   4
   4.  O/TWAMP Security  . . . . . . . . . . . . . . . . . . . . . .   4
     4.1.  O/TWAMP-Control Security  . . . . . . . . . . . . . . . .   4
     4.2.  O/TWAMP-Test Security . . . . . . . . . . . . . . . . . .   5
     3.3.   6
     4.3.  O/TWAMP Security Root . . . . . . . . . . . . . . . . . .   6
   4.   7
   5.  O/TWAMP for IPsec Networks  . . . . . . . . . . . . . . . . .   6
     4.1.   7
     5.1.  Shared Key Derivation . . . . . . . . . . . . . . . . . .   6
     4.2.   7
     5.2.  Server Greeting Message Update  . . . . . . . . . . . . .   7
     4.3.   8
     5.3.  Set-Up-Response Update  . . . . . . . . . . . . . . . . .   9
     5.4.  O/TWAMP over an IPsec tunnel  . . . . . . . . . . . . . .  10
   5.  11
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   6.  11
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   7.  11
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  11
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  11
     8.2.  12
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  11  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   The One-way Active Measurement Protocol (OWAMP) [RFC4656] and the
   Two-Way Active Measurement Protocol (TWAMP) [RFC5357] can be used to
   measure network performance parameters, such as latency, bandwidth,
   and packet loss by sending probe packets and monitoring their
   experience in the network.  In order to guarantee the accuracy of
   network measurement results, security aspects must be considered.
   Otherwise, attacks may occur and the authenticity of the measurement
   results may be violated.  For example, if no protection is provided,
   an adversary in the middle may modify packet timestamps, thus
   altering the measurement results.

   The currently-standardized O/TWAMP security mechanism [RFC4656]
   [RFC5357] requires that endpoints (i.e. both the client and the
   server) possess a shared secret.  In today's network deployments,
   however, the use of pre-shared keys is far from optimal.  For
   example, in wireless infrastructure networks, certain network
   elements, which can be seen as the two endpoints from an O/TWAMP
   perspective, support certificate-based security.  For instance,
   consider the case in which one wants to measure IP performance
   between an eNB and SeGW.  Both eNB and SeGW are 3GPP LTE nodes and
   support certificate mode and IKEv2.  Since the currently standardized
   O/TWAMP security mechanism only supports pre-shared key mode, large
   scale deployment of O/TWAMP is hindered significantly.  Furthermore,
   deployment and management of "shared secrets" for massive equipment
   installation consumes a tremendous amount of effort and is prone to
   human error.

   With IKEv2 widely used, employing keys derived from IKEv2 SA as
   shared key can be considered as a viable alternative.  In mobile
   telecommunication networks, the deployment rate of IPsec exceeds 95%
   with respect to the LTE serving network.  In older-technology
   cellular networks, such as UMTS and GSM, IPsec use penetration is
   lower, but still quite significant.  If the shared key can be derived
   from the IKEv2 SA, O/TWAMP can support cert-based key exchange and
   make it more flexible in practice and more efficient.  The use of
   IKEv2 also makes it easier to extend automatic key management.  In
   general, O/TWAMP measurement packets can be transmitted inside the
   IPsec tunnel, as it occurs with typical user traffic, or transmitted
   outside the IPsec tunnel.  This may depend on the operator's policy
   and is orthogonal to the mechanism described in this document.

   When IPsec is deployed, protecting O/TWAMP traffic in unauthenticated
   mode using IPsec is one option.  Another option is to protect O/TWAMP
   traffic using O/TWAMP layer security established using the PSK
   derived from IKEv2 but bypassing the IPsec tunnel.  Protecting
   unauthenticated O/TWAMP control and/or test traffic via AH or ESP
   cannot provide various security options, e.g. it cannot authenticate
   part of a O/TWAMP packet as mentioned in [RFC4656].  For measuring
   latency, timestamp is carried in O/TWAMP traffic.  The sender has to
   fetch the timestamp, encrypt it, and send it.  In this case, the
   middle step can be skipped, potentially improving accuracy as the
   sequence number can be encrypted and authenticated before the
   timestamp is fetched.  It is the same case for the receiver since it
   can obtain the timstamp timestamp by skipping the decryption step.  In such
   cases, protecting O/TWAMP traffic using O/TWAMP layer security but
   bypassing IPsec tunnel has its advantages.  This document describes
   how to derive the shared secret key from the IKEv2 SA and employ the
   security service at the O/TWAMP layer.  This method SHOULD be used
   when O/TWAMP traffic is bypassing IPsec protection and is running
   over an external network exactly between two IKEv2 systems.


   After clarifying the terminology and scope in the subsequent
   sections, the remainder of this document is organized as follows.
   Section 3 4 summarizes O/TWAMP protocol operation with respect to
   security.  Section 4 5 presents a the method of for binding O/TWAMP TWAMP and IKEv2
   for network measurements between the client and the server which both
   support IKEv2.  Finally, Section 5 6 discusses the security
   considerations arising from the proposed mechanisms.

2.  Terminology

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

3.  Scope and Applicability

   This document specifies a method for enabling network measurements
   between a TWAMP client and a TWAMP server which both support IPsec.
   In short, the shared key used for securing TWAMP traffic is derived
   using IKEv2 [RFC7296].  This document reserves from the TWAMP-Modes
   registry the Mode value IANA.TBA.TWAMP.IKEv2Derived which MUST be
   used by TWAMP implementations compatible with this specification.

   Although the control procedures described in this document are
   applicable to OWAMP per se, the lack of an established IANA registry
   for OWAMP Mode values technically prevents us from extending OWAMP
   Mode values.  Therefore, independent OWAMP implementations SHOULD be
   checked for full compatibility with respect to the use of this Mode
   value.  Until an IANA registry for OWAMP Mode values is established,
   the use this feature in OWAMP implementations MUST be arranged
   privately among consenting OWAMP users.

4.  O/TWAMP Security

   Security for O/TWAMP-Control and O/TWAMP-Test are briefly reviewed in
   the following subsections.


4.1.  O/TWAMP-Control Security

   O/TWAMP uses a simple cryptographic protocol which relies on

   o  AES in Cipher Block Chaining (AES-CBC) for confidentiality
   o  HMAC-SHA1 truncated to 128 bits for message authentication

   Three modes of operation are supported in the OWAMP-Control protocol:
   unauthenticated, authenticated, and encrypted.  In addition to these
   modes, the TWAMP-Control protocol also supports a mixed mode, i.e.
   the TWAMP-Control protocol operates in encrypted mode while TWAMP-
   Test protocol operates in unauthenticated mode.  The authenticated,
   encrypted and mixed modes require that endpoints possess a shared
   secret, typically a passphrase.  The secret key is derived from the
   passphrase using a password-based key derivation function PBKDF2
   (PKCS#5) [RFC2898].

   In the unauthenticated mode, the security parameters are left unused.
   In the authenticated, encrypted and mixed modes, the security
   parameters are negotiated during the control connection

   Figure 1 illustrates the initiation stage of the O/TWAMP-Control
   protocol between a client and the server.  In short, the client opens
   a TCP connection to the server in order to be able to send O/TWAMP-
   Control commands.  The server responds with a Server Greeting, which
   contains the Modes, Challenge, Salt, Count, and MBZ fields (see
   Section 3.1 of [RFC4656]).  If the client-preferred mode is
   available, the client responds with a Set-Up- Response message,
   wherein the selected Mode, as well as the KeyID, Token and Client IV
   are included.  The Token is the concatenation of a 16-octet
   Challenge, a 16-octet AES Session-key used for encryption, and a
   32-octet HMAC-SHA1 Session-key used for authentication.  The Token is
   encrypted using AES-CBC.

   +--------+                  +--------+
   | Client |                  | Server |
   +--------+                  +--------+
       |                           |
       |<---- TCP Connection ----->|
       |                           |
       |<---- Greeting message ----|
       |                           |
       |----- Set-Up-Response ---->|
       |                           |
       |<---- Server-Start --------|
       |                           |

                  Figure 1: Initiation of O/TWAMP-Control

   Encryption uses a key derived from the shared secret associated with
   KeyID.  In the authenticated, encrypted and mixed modes, all further
   communication is encrypted using the AES Session-key and
   authenticated with the HMAC Session-key.  After receiving Set-Up-
   Response the server responds with a Server-Start message containing
   Server-IV.  The client encrypts everything it transmits through the
   just-established O/TWAMP-Control connection using stream encryption
   with Client- IV as the IV.  Correspondingly, the server encrypts its
   side of the connection using Server-IV as the IV.  The IVs themselves
   are transmitted in cleartext.  Encryption starts with the block
   immediately following that containing the IV.

   The AES Session-key and HMAC Session-key are generated randomly by
   the client.  The HMAC Session-key is communicated along with the AES
   Session-key during O/TWAMP-Control connection setup.  The HMAC
   Session-key is derived independently of the AES Session-key.


4.2.  O/TWAMP-Test Security

   The O/TWAMP-Test protocol runs over UDP, using the client and server
   IP and port numbers that were negotiated during the Request-Session
   exchange.  O/TWAMP- Test has the same mode with O/TWAMP-Control and
   all O/TWAMP-Test sessions inherit the corresponding O/TWAMP-Control
   session mode except when operating in mixed mode.

   The O/TWAMP-Test packet format is the same in authenticated and
   encrypted modes.  The encryption and authentication operations are,
   however, different.  Similarly with the respective O/TWAMP-Control
   session, each O/TWAMP-Test session has two keys: an AES Session-key
   and an HMAC Session-key.  However, there is a difference in how the
   keys are obtained:

   O/TWAMP-Control:  the keys are generated by the client and
           communicated to the server during the control connection
           establishment with the Set-Up-Response message (as part of
           the Token).

   O/TWAMP-Test:  the keys are derived from the O/TWAMP-Control keys and
           the session identifier (SID), which serve as inputs of the
           key derivation function (KDF).  The O/TWAMP-Test AES Session-
           key is generated using the O/TWAMP- Control AES Session-key,
           with the 16-octet session identifier (SID), for encrypting
           and decrypting the packets of the particular O/TWAMP-Test
           session.  The O/TWAMP-Test HMAC Session-key is generated
           using the O/TWAMP-Control HMAC Session-key, with the 16-octet
           session identifier (SID), for authenticating the packets of
           the particular O/TWAMP-Test session.


4.3.  O/TWAMP Security Root

   As discussed above, the AES Session-key and HMAC Session-key used by
   the O/TWAMP-Test protocol are derived from the AES Session-key and
   HMAC Session-key which are used in O/TWAMP-Control protocol.  The AES
   Session-key and HMAC Session-key used in the O/TWAMP-Control protocol
   are generated randomly by the client, and encrypted with the shared
   secret associated with KeyID.  Therefore, the security root is the
   shared secret key.  Thus, for large deployments, key provision and
   management may become overly complicated.  Comparatively, a
   certificate-based approach using IKEv2 can automatically manage the
   security root and solve this problem, as we explain in Section 4.

4. 5.

5.  O/TWAMP for IPsec Networks

   This section presents a method of binding O/TWAMP and IKEv2 for
   network measurements between a client and a server which both support
   IPsec.  In short, the shared key used for securing O/TWAMP traffic is
   derived using IKEv2 [RFC5996].

4.1. [RFC7296].

5.1.  Shared Key Derivation

   In the authenticated, encrypted and mixed modes, the shared secret
   key MUST be derived from the IKEv2 Security Association (SA).  Note
   that we explicitly opt to derive the shared secret key from the IKEv2
   SA, rather than the child SA, since the use case whereby an IKEv2 SA
   can be created without generating any child SA is possible [RFC6023].

   When the shared secret key is derived from the IKEv2 SA, SK_d must be
   generated first.  SK_d MUST be computed as per [RFC5996]. [RFC7296].

   The shared secret key MUST be generated as follows:

      Shared secret key = PRF( SK_d, "IPPM" )

   Wherein the string "IPPM" comprises four ASCII characters and prf is
   a pseudorandom function.  It is recommended that the shared secret
   key is derived in the IPsec layer.  This way, the IPsec keying
   material is not exposed to the O/TWAMP client.  Note, however, that
   the interaction between the O/TWAMP and IPsec layers is host-internal
   and implementation-specific.  Therefore, this is clearly outside the
   scope of this document, which focuses on the interaction between the
   O/TWAMP client and server.  That said, one possible way could be the
   following: at the client side, the IPSec layer can perform a lookup
   in the Security Association Database (SAD) using the IP address of
   the server and thus match the corresponding IKEv2 SA.  At the server
   side, the IPSec layer can look up the corresponding IKEv2 SA by using
   the SPIs sent by the client, and therefore extract the shared secret
   key.  In case that both client and server do support IKEv2 but there
   is no current IKEv2 SA, two alternative ways could be considered.
   First, the O/TWAMP client initiates the establishment of the IKEv2
   SA, logs this operation, and selects the mode which supports IKEv2.
   Alternatively, the O/TWAMP client does not initiate the establishment
   of the IKEv2 SA, logs an error for operational management purposes,
   and proceeds with the modes defined in [RFC4656][RFC5357][RFC5618].
   Again, although both alternatives are feasible, they are in fact

   If rekeying for the IKEv2 SA or deletion of the IKEv2 SA occurs, the
   corresponding shared secret key generated from the SA can continue to
   be used until the O/TWAMP session terminates.


5.2.  Server Greeting Message Update

   To achieve a binding association between the key generated from IKEv2
   and the O/TWAMP shared secret key, Server Greeting Message should be
   updated as in Figure 2.

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   |                                                               |
   |                       Unused (12 octets)                      |
   |                                                               |
   |                           Modes                               |
   |                                                               |
   |                     Challenge (16 octets)                     |
   |                                                               |
   |                                                               |
   |                                                               |
   |                        Salt (16 octets)                       |
   |                                                               |
   |                                                               |
   |                        Count (4 octets)                       |
   |                                                               |
   |                        MBZ (12 octets)                        |
   |                                                               |

                     Figure 2: Server Greeting format

   The Modes field in Figure 2 will need to allow for support of key
   derivation as discussed in Section 4.1. 5.1.  As such, the Modes value
   extension MUST be supported by implementations compatible with this
   document, indicating support for deriving the shared key from the
   IKEv2 SA.  The new Modes value indicating support for this
   specification is IANA.TBA.TWAMP.IKEv2Derived (note to IANA: 128 is
   preferred, i.e. bit in position 7).  Clearly, an implementation
   compatible with this specification MUST support the authenticated,
   encrypted and mixed modes as per [RFC4656][RFC5357][RFC5618].

   The choice of this set of Modes values poses no backwards
   compatibility problems to existing O/TWAMP clients.  Robust legacy
   client implementations would disregard the fact that the
   IANA.TBA.TWAMP.IKEv2Derived Modes bit in the Server Greeting is set.
   On the other hand, a client compatible with this specification can
   easily identify that the O/TWAMP server contacted does not support
   this specification.  If the server supports other Modes, as one could
   assume, the client would then decide which Mode to use and indicate
   such accordingly as per [RFC4656][RFC5357].  A client compatible with
   this specification which decides not to employ IKEv2 derivation, can
   simply behave as a purely [RFC4656]/[RFC5357] compatible client.


5.3.  Set-Up-Response Update

   The Set-Up-Response Message should be updated as in Figure 3.  When a
   O/TWAMP client compatible with this specification receives a Server
   Greeting indicating support for Mode IANA.TBA.TWAMP.IKEv2Derived it
   SHOULD reply to the O/TWAMP server with a Set-Up response that
   indicates so.  For example, a compatible O/TWAMP client choosing the
   authenticated mode with IKEv2 shared secret key derivation should set
   Mode to 130, i.e. set the bits in positions 1 and 7 (TBD IANA) to

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   |                            Mode                               |
   |                                                               |
   |                     Key ID (80 octets)                        |
   |                                                               |
   |                                                               |
   |                                                               |
   |                     Token (16 octets)                         |
   |                                                               |
   |                                                               |
   |                                                               |
   |                    Client-IV (12 octets)                      |
   |                                                               |

                     Figure 3: Set-Up-Response Message

   The Security Parameter Index (SPI)(see [RFC4301] [RFC5996]) [RFC7296]) can
   uniquely identify the Security Association (SA).  If the client
   supports the derivation of shared secret key from IKEv2 SA, it will
   choose the corresponding mode value and carry SPIi and SPIr in the
   Key ID field.  SPIi and SPIr MUST be included in the Key ID field of
   Set-Up-Response Message to indicate the IKEv2 SA from which the O/
   TWAMP shared secret key derived from.  The length of SPI is 4 octets.
   Therefore, the first 4 octets of Key ID field MUST carry SPIi and the
   second 4 octets MUST carry SPIr.  The remaining bits of the Key ID
   field MUST set to zero.

   A O/TWAMP server which supports the specification of this document,
   MUST obtain the SPIi and SPIr from the first 8 octets and ignore the
   remaining octets of the Key ID field.  Then, the client and the
   server can derive the shared secret key based on the mode value and
   SPI.  If the O/TWAMP server cannot find the IKEv2 SA corresponding to
   the SPIi and SPIr received, it MUST log the event for operational
   management purposes.  In addition, the O/TWAMP server SHOULD set the
   Accept field of the Server-Start message to the value 6 to indicate
   that server is not willing to conduct further transactions in this O/
   TWAMP-Control session since it can not find the corresponding IKEv2


5.4.  O/TWAMP over an IPsec tunnel

   IPsec AH [RFC4302] and ESP [RFC4303]  provide confidentiality and
   data integrity to IP datagrams.  Thus an IPsec tunnel can be used to
   provide the protection needed for O/TWAMP Control and Test packets,
   even if the peers choose the unauthenticated mode of operation.  If
   the two endpoints are already connected through an IPSec tunnel it is
   RECOMMENDED that the O/TWAMP measurement packets are forwarded over
   the IPSec tunnel if the peers choose the unauthenticated mode in
   order to ensure authenticity and security.


6.  Security Considerations

   As the shared secret key is derived from the IKEv2 SA, the key
   derivation algorithm strength and limitations are as per [RFC5996]. [RFC7296].
   The strength of a key derived from a Diffie-Hellman exchange using
   any of the groups defined here depends on the inherent strength of
   the group, the size of the exponent used, and the entropy provided by
   the random number generator employed.  The strength of all keys and
   implementation vulnerabilities, particularly Denial of Service (DoS)
   attacks are as defined in [RFC5996]. [RFC7296].

   As a more general note, the IPPM community may want to revisit the
   arguments listed in [RFC4656], Sec. 6.6.  Other widely-used Internet
   security mechanisms, such as TLS and DTLS, may also be considered for
   future use over and above of what is already specified in [RFC4656]


7.  IANA Considerations

   IANA is requested to allocate the IANA.TBA.TWAMP.IKEv2Derived Modes
   value in the TWAMP-Modes registry.


8.  Acknowledgments

   We thank Eric Chen, Yaakov Stein, Brian Trammell, Emily Bi, John
   Mattsson, and Steve Baillargeon for their comments and text

   Al Morton deserves a special mention for his thorough reviews and
   text contributions and the good discussion and pointers to earlier related
   work in this document as well as the constructive
   discussions over several IPPM WG.

8. meetings.

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.

   [RFC4302]  Kent, S., "IP Authentication Header", RFC 4302, December

   [RFC4303]  Kent, S., "IP Encapsulating Security Payload (ESP)", RFC
              4303, December 2005.

   [RFC4656]  Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M.
              Zekauskas, "A One-way Active Measurement Protocol
              (OWAMP)", RFC 4656, September 2006.

   [RFC5357]  Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J.
              Babiarz, "A Two-Way Active Measurement Protocol (TWAMP)",
              RFC 5357, October 2008.

   [RFC5618]  Morton, A. and K. Hedayat, "Mixed Security Mode for the
              Two-Way Active Measurement Protocol (TWAMP)", RFC 5618,
              August 2009.


   [RFC7296]  Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen, P., and T.
              Kivinen, "Internet Key Exchange Protocol Version 2
              (IKEv2)", STD 79, RFC
              5996, September 2010.

8.2. 7296, October 2014.

9.2.  Informative References

   [RFC2898]  Kaliski, B., "PKCS #5: Password-Based Cryptography
              Specification Version 2.0", RFC 2898, September 2000.

   [RFC4301]  Kent, S. and K. Seo, "Security Architecture for the
              Internet Protocol", RFC 4301, December 2005.

   [RFC6023]  Nir, Y., Tschofenig, H., Deng, H., and R. Singh, "A
              Childless Initiation of the Internet Key Exchange Version
              2 (IKEv2) Security Association (SA)", RFC 6023, October

Authors' Addresses
   Kostas Pentikousis (editor)
   EICT GmbH
   EUREF-Campus Haus 13
   Torgauer Strasse 12-15
   10829 Berlin

   Email: k.pentikousis@eict.de

   Emma Zhang
   Huawei Technologies
   Huawei Building, Q20, No.156, Rd. BeiQing
   Haidian District , Beijing   100095
   P. R. China

   Email: emma.zhanglijia@huawei.com

   Yang Cui
   Huawei Technologies
   Otemachi First Square 1-5-1 Otemachi
   Chiyoda-ku, Tokyo   100-0004

   Email: cuiyang@huawei.com