wdiff draft-ietf-ippm-ipsec-01.txt draft-ietf-ippm-ipsec-02.txt

IPPM WG K. Pentikousis, Ed.
Internet-Draft EICT
Intended status: Standards Track Y. Cui
Expires: April 24, August 18, 2014 E. Zhang
Huawei Technologies
October 21, 2013
February 14, 2014

Network Performance Measurement for IPsec
draft-ietf-ippm-ipsec-01
draft-ietf-ippm-ipsec-02

Abstract

IPsec is

The O/TWAMP security mechanism requires that endpoints (i.e. both the
client and the server) possess a mature technology with several interoperable
implementations. Indeed, shared secret. Since the use currently-
standardized O/TWAMP security mechanism only supports a pre-shared
key mode, large scale deployment of IPsec tunnels O/TWAMP is increasingly
gaining popularity in several deployment scenarios, not hindered
significantly. At the least in
what used same time, recent trends point to be solely areas of traditional telecommunication
protocols. Wider IPsec deployment wider IKEv2
deployment, which in turn calls for mechanisms and methods that
enable tunnel end-users, as well as operators, to measure one-
way one-way and
two-way network performance in a standardized manner.
Unfortunately, however, standard IP performance measurement security
mechanisms cannot be readily used with IPsec. This document makes
the case for employing IPsec to protect
discusses the One-way and Two-Way
Active Measurement Protocols (O/TWAMP) and proposes a method which
combines IKEv2 and O/TWAMP use of keys derived from an IKE SA as defined the shared key in RFC 4656 and RFC 5357,
respectively. This specification aims, on
O/TWAMP. If the one hand, to ensure
that O/TWAMP shared key can be secured with the best mechanisms we have at our
disposal today while, on the other hand, it facilitates derived from the
applicability of IKE SA, O/TWAMP to networks that have already deployed
IPsec.
can support cert-based key exchange, which would allow for more
flexibility and efficiency. Such key derivation can also facilitate
automatic key management.

Status of This Memo

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provisions of BCP 78 and BCP 79.

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This Internet-Draft will expire on April 24, August 18, 2014.

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Motivation . . . O/TWAMP Security . . . . . . . . . . . . . . . . . . . . . . 4 3
3.1. O/TWAMP-Control Security . . . . . . . . . . . . . . . . 5 4
3.2. O/TWAMP-Test Security . . . . . . . . . . . . . . . . . . 6 5
3.3. O/TWAMP Security Root . . . . . . . . . . . . . . . . . . 7
3.4. O/TWAMP and IPsec . . . . . . . . . . . . . . . . . . . . 7 6
4. O/TWAMP for IPsec Networks . . . . . . . . . . . . . . . . . 8 6
4.1. Shared Key Derivation . . . . . . . . . . . . . . . . . . 8 6
4.2. Server Greeting Message Update . . . . . . . . . . . . . 9 7
4.3. Session Key Derivation . . . . . . . . . . . . . . . . . 11
4.3.1. Alternative 1 . . . . . . . . . . . . . . . . . . . . 12
4.3.2. Alternative 2 . . . Set-Up-Response Update . . . . . . . . . . . . . . . . . 14 9
5. Security Considerations . . . . . . . . . . . . . . . . . . . 15 10
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 10
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 16 10
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 16 10
8.1. Normative References . . . . . . . . . . . . . . . . . . 16 10
8.2. Informative References . . . . . . . . . . . . . . . . . 16 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16 11

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.

Cryptographic

The currently-standardized O/TWAMP security mechanisms, such as IPsec, have been
considered during the early stage of the specification of the two
active measurement protocols mentioned above. However, due to
several reasons, it was decided to avoid tying mechanism [RFC4656]
[RFC5357] requires that endpoints (i.e. both the development client and
deployment of O/TWAMP to such security mechanisms. In practice, for
many networks, the issues listed in [RFC4656], Sec. 6.6 with respect
to IPsec are still valid. However, we expect that in
server) possess a shared secret. In today's network deployments,
however, the near future
IPsec will use of pre-shared keys may not be deployed in many more hosts and networks than today. optimal. For example, IPsec tunnels may be used to secure wireless channels.
In this case, what we are interested
in is measuring wireless infrastructure networks, certain network
performance specifically for the traffic carried by the secured
tunnel, not over elements, which
can be seen as the wireless channel in general. two endpoints from an O/TWAMP perspective, support
certificate-based security. This document
makes is the case that O/TWAMP should be cognizant when IPsec and other
security mechanisms are in place and can be leveraged upon. In other
words, it is now time one wants to specify how O/TWAMP is used in a network
environment where IPsec is already deployed. We expect that in such
an environment, measuring
measure IP performance over IPsec tunnels with O/
TWAMP is between an important tool eNB and SeGW, for operators.

For example, when considering instance. Since
the use of currently standardized O/TWAMP in networks with
IPsec deployed, we can take advantage of the IPsec security mechanism only supports
pre-shared key exchange
protocol [RFC5996]. In particular, we note that it mode, large scale deployment of O/TWAMP is not necessary
to use distinct keys in OWAMP-Control hindered
significantly. Furthermore, deployment and OWAMP-Test layers. One key management of "shared
secrets" for encryption massive equipment installation consumes a tremendous
amount of effort and another for authentication is sufficient for both
Control and Test layers. This obviates the need prone to generate two human error.

With IKEv2 widely used, using keys
for each layer and reduces derived from IKE SA as shared key
can be considered as a viable alternative. In mobile
telecommunication networks, the complexity deployment rate of O/TWAMP protocols in an IPsec environment. This observation comes from the fact that
separate session keys in exceeds 95%
with respect to the OWAMP-Control LTE serving network. In older-technology
cellular networks, such as UMTS and OWAMP-Test layers were
designed for preventing reflection attacks when employing the current
mechanism. Once GSM, IPsec use penetration is employed, such a potential threat
lower, but still quite significant. If the shared key can be derived
from the IKE 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
alleviated. orthogonal to the mechanism described in this document.

The remainder of this document is organized as follows. Section 3
motivates this work by revisiting the arguments made in [RFC4656]
against the use of IPsec; this section also
summarizes O/TWAMP protocol operation with respect to security.
Section 4 presents a method of binding O/TWAMP and IKEv2 for network
measurements between a sender the client and a receiver the server which both support IPsec.
IKEv2. Finally, Section 5 discusses the security considerations
arising from the proposed mechanisms.

2. Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].

3. Motivation

In order to motivate the solutions proposed O/TWAMP Security

Security for O/TWAMP-Control and O/TWAMP-Test are reviewed separately
in this document, let us
first revisit Section 6.6 of [RFC4656]. As we explain below, the
reasons originally listed therein may not apply in many cases today.

RFC 4656 opts against using IPsec and instead favors the use of "a section.

3.1. O/TWAMP-Control Security

O/TWAMP uses a simple cryptographic protocol (based which relies on a block cipher in CBC mode)".
The first argument justifying this decision in [RFC4656] is that
partial authentication

o AES in OWAMP Cipher Block Chaining (AES-CBC) for confidentiality

o HMAC-SHA1 truncated to 128 bits for message authentication mode is not possible
with IPsec. IPsec indeed cannot authenticate only a part

Three modes of a
packet. However, operation are supported in an environment where IPsec is already deployed the OWAMP-Control protocol:
unauthenticated, authenticated, and actively used, partial authentication for OWAMP contradicts encrypted. Besides the
operational reasons dictating above
three modes supported, the use of IPsec. It TWAMP-Control protocol also increases supports an
additional mode: mixed mode, i.e. the operational complexity of OWAMP (and TWAMP) TWAMP-Control protocol operates
in networks where
IPsec is actively used and may encrypted mode while TWAMP-Test protocol operates in practice limit its applicability.
unauthenticated mode. The second argument made authenticated, encrypted and mixed modes
require that endpoints possess a shared secret, typically a
passphrase. The secret key is derived from the need to keep separate deployment
paths between OWAMP and IPsec. In several currently deployed types
of networks IPsec is widely used to protect the data and signaling
planes. For example, in mobile telecommunication networks, passphrase using a
password-based key derivation function PBKDF2 (PKCS#5) [RFC2898].

In the
deployment rate of IPsec exceeds 95% with respect to unauthenticated mode, the LTE serving
network. security parameters are left unused.
In older technology cellular networks, such as UMTS the authenticated, encrypted and
GSM, IPsec use penetration is lower, but still quite significant.
Additionally, there is a great number of IPsec-based VPN applications
which are widely used in business applications to provide end-to-end mixed modes, the security over, for instance, publicly open or otherwise untrusted
IEEE 802.11 wireless LANs. At
parameters are negotiated during the same time, many IETF-standardized
protocols make use control connection
establishment.

Figure 1 illustrates the initiation stage of IPsec/IKE, including MIPv4/v6, HIP, SCTP, BGP,
NAT the O/TWAMP-Control
protocol between a client and SIP, just to name the server. In short, the client opens
a few.

The third argument in [RFC4656] is that, effectively, TCP connection to the adoption of
IPsec server in OWAMP may order to be problematic for "lightweight embedded devices."
However, since the publication of RFC 4656, able to send O/TWAMP-
Control commands. The server responds with a large number of
limited-resource and low-cost hardware, such as Ethernet switches,
DSL modems, set-top boxes Server Greeting, which
contains the Modes, Challenge, Salt, Count, and other such devices come with support
for IPsec "out MBZ fields (see
Section 3.1 of [RFC4656]). If the box". Therefore concerns about implementation,
although likely valid client-preferred mode is
available, the client responds with a decade ago, are not Set-Up- Response message,
wherein the selected Mode, as well founded today.

Finally, everyday use of IPsec applications by field technicians as the KeyID, Token and
good understanding of Client IV
are included. The Token is the IPsec API by many programmers should no
longer be concatenation of a reason for concern. On the contrary: By now, IPsec open
source code is available for anyone who wants to use it. Therefore,
although IPsec does need 16-octet
Challenge, a certain level of expertise to deal with
it, in practice, most competent technical personnel 16-octet AES Session-key used for encryption, and programmers
have no problems using it on a daily basis.

OWAMP and TWAMP actually consist of two inter-related protocols: O/
TWAMP-Control and O/TWAMP-Test. With respect to TWAMP, since "TWAMP
and OWAMP use the same protocol for establishment of Control and Test
procedures" [RFC5357] (Section 6), IPsec is also not considered. O/
TWAMP-Control is used to initiate, start, and stop test sessions and
to fetch their results, whereas O/TWAMP-Test is
32-octet HMAC-SHA1 Session-key used to exchange test
packets between two measurement nodes.

In the remainder of this section we review security for O/TWAMP-
Control and O/TWAMP-Test separately and then make the case for authentication. The Token is
encrypted using
them over IPsec.

3.1. 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 AES-CBC.

Three modes ----|
| |
|----- Set-Up-Response ---->|
| |
|<---- Server-Start --------|
| |

Figure 1: Initiation of operation are supported: unauthenticated,
authenticated, and encrypted. The authenticated and encrypted modes
require that endpoints possess a shared secret, typically O/TWAMP-Control

Encryption uses 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. shared secret associated with
KeyID. In the authenticated and authenticated, encrypted and mixed modes, security parameters are
negotiated during the control connection establishment.

Figure 1 illustrates the initiation stage of all further
communication is encrypted using the O/TWAMP-Control
protocol between a client AES Session-key and
authenticated with the server. In short, the client opens
a TCP connection to HMAC Session-key. After receiving Set-Up-
Response the server in order to be able to send OWAMP-
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 and encrypted modes, all further
communication is encrypted using the AES Session-key and
authenticated with the HMAC Session-key. The client encrypts
everything it transmits through 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 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.

3.2. O/TWAMP-Test Security

The O/TWAMP-Test protocol runs over UDP, using the sender client and
receiver server
IP and port numbers that were negotiated during the Request-
Session Request-Session
exchange. O/TWAMP-Test O/TWAMP- Test has the same three modes as mode with O/
TWAMP-Control (unauthenticated, authenticated, and encrypted) 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 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.

3.3. O/TWAMP Security Root

As discussed above, the AES Session-key and HMAC Session-key used in
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/IPsec IKEv2 can automatically manage the
security root and solve this problem, as we explain in Section 4.

3.4.

4. O/TWAMP and IPsec

According to [RFC4656] the "deployment paths of for IPsec and OWAMP could
be separate if OWAMP does not depend on IPsec." However, the problem
that arises in practice is that the security mechanism Networks

This section presents a method of binding O/TWAMP and
IPsec cannot coexist at the same time without adding overhead or
increasing complexity.

IPsec provides confidentiality and data integrity to IP datagrams.
Distinct protocols are provided: Authentication Header (AH),
Encapsulating Security Payload (ESP) and Internet Key Exchange (IKE
v1/v2). AH provides only integrity protection, while ESP can also
provide encryption. IKE is used IKEv2 for dynamical key negotiation and
automatic key management.

When sender
network measurements between a client and receiver implement O/TWAMP over IPsec, they need to
agree on a server which both support
IPsec. In short, the shared secret key during the IPsec tunnel establishment.
Subsequently, all IP packets sent by the sender are protected. If
the AH protocol used for securing O/TWAMP traffic is used, IP packets are transmitted in plaintext.

The authentication part covers
derived using IKEv2 [RFC5996].

4.1. Shared Key Derivation

In the entire packet. So all test
information, such as UDP port number, authenticated, encrypted and mixed modes, the test results will be
visible to any attacker, which shared secret
key can intercept these test packets, and
introduce errors or forge packets that may be injected during derived from the
transmission. In order IKEv2 Security Association (SA). Note
that we explicitly opt to avoid this attack, derive the receiver must
validate shared secret key from the integrity of these packets with IKE
SA, rather than the negotiated secret
key. If ESP is used, IP packets are encrypted, and hence only child SA, since the
receiver can use case whereby an IKE SA
can be created without generating any child SA is possible [RFC6023].

If the IPsec shared secret key to decrypt is derived from the IP packet, IKE SA, SKEYSEED must be
generated first. SKEYSEED and
obtain the test data in order to assess the IP network performance
based on the measurements. Both the sender its derivatives are computed as per
[RFC5996], where prf is a pseudorandom function:

SKEYSEED = prf( Ni | Nr, g^ir )

Ni and receiver must support
IPsec to generate the security secret key of IPsec.

Currently, after Nr are, respectively, the test packets initiator and responder nonces,
which are received by negotiated during the receiver, it
cannot execute active measurement over IPsec. That initial exchange (see Section 1.2 of
[RFC5996]). g^ir is because the
receiver knows only shared secret from the ephemeral Diffie-
Hellman exchange and is represented as a string of octets.

The shared secret key but not can be generated as follows:

Shared secret key = PRF{ SKEYSEED, "IPPM" }

The shared secret key is derived in the IPsec key,
while the test packets are protected by layer. Thus, the IPsec key ultimately.
Therefore, it needs to
keying material is not be considered how exposed to measure IP network
performance in an IPsec tunnel with O/TWAMP. Without this
functionality, the use of OWAMP O/TWAMP client. Note that
the interaction between the O/TWAMP and TWAMP over IPsec implementations is hindered.
outside the scope of this document, which focuses on the interaction
between the O/TWAMP client and server. Of course, backward compatibility should be considered as well. That
is, extracting the intrinsic security method based on
shared secret key as specified in from the O/TWAMP standards IPsec layer can also still be suitable for other network
settings. There should be no impact depend on the current security
mechanisms defined in O/TWAMP for other use cases. This document
describes
implementation. One possible solutions to this problem which take advantage of way could be the secret key derived by IPsec, in order to provision following: at the key needed
for active network measurements based on [RFC4656] and [RFC5357].

4. O/TWAMP for IPsec Networks

This section presents
client side, the IPSec layer can perform a method lookup in the Security
Association Database (SAD) using the IP address of binding O/TWAMP and IKEv2 for
network measurements between a client the server and a
thus match the corresponding IKE SA. At the server which both support
IPsec. In short, side, the shared key used for securing O/TWAMP traffic is
derived using IKEv2 [RFC5996].

4.1. Shared Key Derivation

If IPSec
layer can look up the AH protocol is used, corresponding IKE SA by using the IP packets are transmitted in
plaintext, but all O/TWAMP traffic is integrity-protected SPIs sent by IPsec.
Therefore, even if
the peers choose to opt client, and therefore extract the shared secret key.

If rekeying for the unauthenticated
mode, IPsec integrity protection is extended to O/TWAMP. In IKE SA or deletion of the
authenticated and encrypted modes, IKE SA occurs, the
corresponding shared secret key generated from the SA can continue to
be derived
from used until the IKEv2 Security Association (SA), or IPsec SA.

If lifetime of the shared secret key is derived from expires.

4.2. Server Greeting Message Update

To achieve a binding association between the IKEv2 SA, SKEYSEED must
be key generated firstly. SKEYSEED from IKE
and its derivatives are computed as
per [RFC5996], where prf is a pseudorandom function:

SKEYSEED = prf( Ni | Nr, g^ir )

Ni and Nr are, respectively, the initiator and responder nonces,
which are negotiated during the initial exchange (see Section 1.2 of
[RFC5996]). g^ir is the shared secret from the ephemeral Diffie-
Hellman exchange and is represented as a string of octets. Note that
this SKEYSEED can be used as the O/TWAMP shared secret key directly.

Alternatively, the shared secret key can be generated as follows:

Shared secret key = PRF{ SKEYSEED, Session ID }

wherein the Session ID is the O/TWAMP-Test SID.

If the shared secret key is derived from the IPsec SA, instead, the
shared secret key can be equal to KEYMAT, wherein

KEYMAT = prf+( SK_d, Ni | Nr )

The term "prf+" stands for a function that outputs a pseudorandom
stream based on the inputs to a prf, while SK_d is defined in
[RFC5996] (Sections 2.13 and 1.2, respectively). The shared secret
key can alternatively be generated as follows:

Shared secret key = PRF{ KEYMAT, Session ID }

wherein the session ID is is the O/TWAMP-Test SID.

If rekeying for the IKE SA and IPsec SA occurs, the corresponding key
of the SA is updated. Generally, ESP and AH SAs always exist in
pairs, with one SA in each direction. If the SA is deleted, the key
generated from the IKE SA or IPsec SA should also be updated.

4.2. Server Greeting Message Update

As discussed above, a binding association between the key generated
from IPsec and the O/TWAMP shared secret key needs to be considered.
The Security Association (SA) can be identified by the Security
Parameter Index (SPI) and protocol uniquely for a given sender and
receiver pair. Therefore, these parameters should be agreed upon
during the initiation stage of O/TWAMP-Control. At the stage that
the sender and receiver negotiate the integrity key, the IPsec
protocol and SPI MUST be checked. Only if the two parameters are
matched with the IPsec information, MUST the O/TWAMP connection be
established.

The Security Parameter Index (SPI) and protocol type (see [RFC4301]
[RFC5996]) will need to be included in the Server Greeting of the O/
TWAMP-Control protocol depicted in Figure 1. After the client
receives the greeting, it MUST close the connection if it receives a
greeting with an erroneous SPI and protocol value (Figure 2).
Otherwise, the client SHOULD generate the shared secret key as
discussed in Section 4.1 and respond with the server-expected Set-Up-
Response message.

The Modes field in Figure 2 will need to allow for support of key
derivation as discussed in Section 4.1. As such, pending discussion
in the IPPM WG, Modes value 8 MUST be supported by compatible
implementations, indicating support for IPsec. Server
implementations compatible with this document MUST set the first 28
bits of the Modes field to zero. A client compatible with this
specification MUST ignore the first 28 bits of the Modes field. For
backward compatibility, the server is obviously allowed to indicate
support for the Modes defined in [RFC4656]

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Protocol |
|+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SPIi |
|+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SPIr |
|+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Modes |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Challenge (16 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Salt (16 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Count (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| MBZ (12 octets) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 2: Server Greeting format

A compatible O/TWAMP client implementation would then interpret the
originally unused 12 bits of the Server Greeting (see sec. 3.1 of
[RFC4656]) as follows: The first 4 octets of the Server Greeting
message indicate the protocol type, while the following 8 octets
indicate the initiator (SPIi) and responder (SPIr) SPIs as
illustrated in Figure 2. Note that in this case, the remaining
fields of the Server Greeting message remain as per [RFC4656].

EDITOR'S NOTE:
We expect that this implementation option would pose the least
backwards compatibility problems to existing O/TWAMP clients.
Robust client implementations of [RFC4656] would disregard that
the 29th Modes bit in the Server Greeting is set, and should
ignore the information contained in the newly defined fields
(Protocol, SPIi, SPIr). If the server supports other Modes, as
one would assume, the client would then indicate any of the
Modes defined in [RFC4656] and effectively indicate that it
does not support the IPsec mode. At this point, the Server
would need to use the Modes defined in [RFC4656] only.

When using ESP, all IP packets are encrypted, and therefore only the
receiver can use the IPsec key to decrypt the IP active measurement
packets. In this case, the IPsec tunnel between the sender and
receiver provides additional security: even if the peers choose the
unauthenticated mode, IPsec encryption and integrity protection is
provided to O/TWAMP. If the sender and receiver decide to use the
authenticated or encrypted mode, the shared secret can also be
derived from IKE SA or IPsec SA. The method for key generation and
binding association is the same discussed above for the AH protocol
mode.

There is an encryption-only configuration in ESP, though this is not
recommended due to its limitations. Since it does not produce
integrity key in this case, either encryption-only ESP should be
prohibited for O/TWAMP, or a decryption failure should be
distinguished due to possible integrity attack.

4.3. Session Key Derivation

Section 4.1 described a method for deriving the shared key for O/
TWAMP by capitalizing on IPsec. This is a step forward in terms of
facilitating O/TWAMP deployment at scale in IPsec networks as it
allows for greater and secure automation of standardized network
performance measurements. We note, however, that the O/TWAMP
protocol uses distinct encryption and integrity keys for O/TWAMP-
Control and O/TWAMP-Test. Consequently, four keys are generated to
protect O/TWAMP-Control and O/TWAMP-Test messages.

In fact, once IPsec is employed, one key for encryption and another
for authentication is sufficient for both the Control and Test
protocols. Therefore, in an IPsec environment we can further reduce
the operational complexity of O/TWAMP protocols in a straightforward
manner, as discussed below.

EDITOR'S NOTE:
We expect that both session key derivation proposals and
optimization alternatives will be discussed in the IPPM working
group and we are looking forward to community comments and
feedback.

4.3.1. Alternative 1

If an IPsec SA is established between the server and the client, or
both server and client support IPsec, the root key for O/TWAMP-based
active network measurements can be derived from the IKE or IPsec SA.

If the root key that will be used in O/TWAMP network performance
measurements is derived from the IKE SA, SKEYSEED must be generated
first. SKEYSEED and its derivatives are computed as per [RFC5996].
SKEYSEED can be used as the root key of O/TWAMP directly; then the
root key of O/TWAMP is equal to SKEYSEED. If the root key of O/TWAMP
is derived from the IPsec SA, the shared secret key can be equal to
KEYMAT. KEYMAT and its derivatives are computed as per usual
[RFC5996].

Then, the session keys for encryption and authentication can be
derived from the root key of O/TWAMP, wherein:

Session key for enc = PRF{ root key of O/TWAMP, "O/TWAMP enc" }

Session key for auth = PRF{ root key of O/TWAMP, "O/TWAMP auth" }

The former can provide encryption protection for O/TWAMP-Control and
O/TWAMP-Test messages, while the latter can provide integrity
protection.

Note that there are cases where rekeying the IKE SA and IPsec SA is
necessary, and after which the corresponding key of SA is updated.
If the SA is deleted, the O/TWAMP shared key generated from the IKE
SA or IPsec SA should also be updated.

EDITOR'S NOTE:

In addition to optimizing session key derivation, we can also
reduce the verbosity of the Server Greeting and Set-Up-Response
messages, as explained below. Note, however, that such O/TWAMP
message simplification poses backward compatibility challenges,
which should be discussed in the IPPM WG.

In this optimization, the O/TWAMP-Control message exchange flow
remains as per Figure 1. However, the optimized Server Greeting
(Figure 3) can do without the Salt and Count parameters (cf. Figure
2) since the root key of O/TWAMP is derived from IKE SA or IPsec SA.
O/TWAMP security can rely on IPsec and the SPI can uniquely identify
the IPsec SA from which the root key was derived from.

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Protocol |
|+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SPIi |
|+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SPIr |
|+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Modes |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Challenge (16 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| MBZ (12 octets) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 3: Optimized the O/TWAMP shared secret key, Server Greeting format

The format of the Set-Up-Response is illustrated in Figure 4. The
Token carried in the Set-Up-Response is calculated Message should be
updated as follows:

Token = Enc_root-key( Challenge )

where Challenge is the value received earlier in the Server Greeting
(Figure 3) 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mode |
| Unused (12 octets) |
| |
|+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Modes |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Token Challenge (16 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Client-IV Salt (16 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Count (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| MBZ (12 octets) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 4: Set-Up-Response 2: Server Greeting format

The Modes field in Alternative 1

If the server authenticates the token successfully, then the O/TWAMP-
Control message exchange flow can continue.

4.3.2. Alternative Figure 2

Another way will need to allow for optimizing support of key
derivation as discussed in Section 4.1. As such, pending discussion
in the IPPM WG, Modes value 8 extension MUST be supported by
implementations compatible with this document, indicating support for
deriving shared key use is to set the O/TWAMP
session keys equal to from IKE SA. Modes value 16 indicates
authenticated mode; Modes value 32 indicates encrypted mode; and
Modes value 64 indicates mixed mode over IKEv2.

Authenticated mode over IKEv2 means that the keys of client and server
operate in authenticated mode with the IPsec SA directly, i.e:

Session key for enc = encryption shared secret key of derived from
IKE SA. Encrypted mode over IKEv2 means that the IPsec SA

Session key for auth = integrity key of client and server
operate in encrypted mode with the IPsec SA

The former session shared secret key can provide encryption protection for O/TWAMP-
Control derived from IKE
SA. Mixed mode over IKEv2 means that the client and O/TWAMP-Test messages, while server operate
in encrypted mode for the latter can provide
integrity protection. The point made O/TWAMP-Control protocol while operating in
unauthenticated mode for the previous subsection
about rekeying O/TWAMP-Test protocol with shared secret
key derived from IKE SA.

Server implementations compatible with this document MUST set the IPsec SA applies here too.

EDITOR'S NOTE:
As noted in
first 25 bits of the previous subsection, here too we can reduce Modes field to zero. A client compatible with
this specification MUST ignore the
verbosity first 25 bits of the Server Greeting and Set-Up-Response messages
even further, as explained below. Note, however, that such O/
TWAMP message simplification poses Modes field.

For backward compatibility
challenges, which should be discussed in compatibility, the IPPM WG. server is obviously allowed to
indicate support for the Modes defined in [RFC4656]

The choice of this set of Modes values poses the least backwards
compatibility problems to existing O/TWAMP control message exchange flow remains clients. Robust client
implementations of [RFC4656] would disregard that the same (i.e. as
per Figure 1), while first 29 Modes
bits in the Server Greeting format is illustrated in
Figure 5. The Challenge, Salt, and Count parameters can be
eliminated since set. If the session keys of O/TWAMP are equal to server supports other
Modes, as one would assume, the keys client would then indicate any of
an IPsec SA directly. SPI can identify the IPsec SA where
Modes defined in [RFC4656] and effectively indicate that it does not
support key derivation from IKE. At this point, the
session keys derived from. Server would
need to use the Modes defined in [RFC4656] only.

4.3. Set-Up-Response Update

The similarly optimized Set-Up-Response
message is illustrated in Figure 6.

Figure 5: Optimized Server Greeting format Message should be updated as in Figure 3.

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 6: 3: Set-Up-Response Message

The Security Parameter Index (SPI)(see [RFC4301] [RFC5996]) can
uniquely identify the Security Association (SA). If the client
supports the derivation of shared secret key from IKE SA, it will
choose the corresponding mode value and carry SPIi and SPIr in Alternative 2 the
KeyID field. SPIi and SPIr are included in Key ID field of Set-Up-
Response Message to indicate the IKE SA which O/TWAMP shared secret
key derived from. The length of SPI is 4 octets. The first 4 octets
of Key ID field carries SPIi and the second 4 octets carries SPIr.
The rest bits of the Key ID field is set to zero.

A server which supports deriving shared secret from an IKE SA can
obtain the SPIi and SPIr from the first 8 octets and ignore the rest
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 server can not find the IKE SA corresponding to the SPIi and
SPIr, the Accept field of Server-Start message is extended to
indicate that. Accept value 6 can be used to indicate that server is
not willing to conduct further transactions in this OWAMP-Control
session since it can not find the corresponding IKE SA.

5. Security Considerations

As the shared secret key is derived from IPsec, the IKE SA, the key
derivation algorithm strength and limitations are as per [RFC5996].
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].

EDITOR'S NOTE:

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]
[RFC5357].

6. IANA Considerations

IANA may will need to allocate additional values for the Modes options
presented in this document. The values of the protocol field may
need to be assigned from the numbering space.

7. Acknowledgments

Emily Bi contributed to an earlier version of this document.

We thank Eric Chen and Chen, Yakov Stein Stein, and John Mattsson for their comments
on this draft, and Al Morton for the discussion on related earlier
work in IPPM WG.

8. References

8.1. Normative References

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

[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.

[RFC5996] Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen,
"Internet Key Exchange Protocol Version 2 (IKEv2)", RFC
5996, September 2010.

8.2. 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
2010.

Authors' Addresses

Kostas Pentikousis (editor)
EICT GmbH
Torgauer Strasse 12-15
10829 Berlin
Germany

Email: k.pentikousis@eict.de

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

Email: cuiyang@huawei.com
Emma Zhang
Huawei Technologies
Huawei Building, Q20, No.156, Rd. BeiQing
Haidian District , Beijing 100095
P. R. China

Email: emma.zhanglijia@huawei.com