Internet DRAFT - draft-bi-ippm-ipsec
draft-bi-ippm-ipsec
IPPM Y. Cui
Internet-Draft E. Bi
Intended status: Standards Track K. Pentikousis, Ed.
Expires: August 29, 2013 Huawei Technologies
February 25, 2013
Network Performance Measurement for IPsec
draft-bi-ippm-ipsec-01.txt
Abstract
IPsec is a mature technology with several interoperable
implementations. Indeed, the use of IPsec tunnels is increasingly
gaining popularity in several deployment scenarios, not the least in
what used to be solely areas of traditional telecommunication
protocols. Wider deployment calls for mechanisms and methods that
enable tunnel end-users, as well as operators, to measure one-way and
two-way network performance. Unfortunately, however, standard IP
performance measurement security mechanisms cannot be readily used
with IPsec. This document makes the case for employing IPsec to
protect O/TWAMP and proposes a method which combines IKEv2 and
O/TWAMP as defined in RFC 4656 and RFC 5357, respectively. This
specification aims, on the one hand, to ensure that O/TWAMP can be
secured, while on the other hand, it extends the applicability of
O/TWAMP to networks that have already deployed IPsec.
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 August 29, 2013.
Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology used in this document . . . . . . . . . . . . . . 4
3. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. O/TWAMP-Control Security . . . . . . . . . . . . . . . . . 5
3.2. O/TWAMP-Test Security . . . . . . . . . . . . . . . . . . 6
3.3. O/TWAMP Security Root . . . . . . . . . . . . . . . . . . 6
3.4. Co-existence of O/TWAMP and IPsec . . . . . . . . . . . . 6
4. O/TWAMP over IPsec . . . . . . . . . . . . . . . . . . . . . . 7
5. Others . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
6. Security Considerations . . . . . . . . . . . . . . . . . . . 11
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 11
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
9.1. Normative References . . . . . . . . . . . . . . . . . . . 11
9.2. Informative References . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
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1. Introduction
The active measurement protocols OWAMP [RFC4656] and 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 authenticity 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 security mechanisms, such as IPsec, have been
considered during the early stage of working towards the definition
of the two protocols mentioned above. However, due to several
reasons, it was preferred to avoid tying the development and
deployment of O/TWAMP protocols 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
the near future IPsec will be deployed in many more hosts and
networks than today. For example, IPsec tunnels may be used to
secure wireless channels. In this case, what we are interested in is
measuring network performance specifically for the traffic carried by
the tunnel, not in general over of the wireless channel. Therefore,
in this document we attempt to make the case that for networks where
wide deployment of IPsec and other security mechanisms is mandatory
for a variety of reasons, there are increasingly more use cases in
which IPsec and O/TWAMP protocols are needed simultaneously. In
other words, we argue that it is now time to specify how O/TWAMP can
be used in a network environment where IPsec is already deployed. In
such an environment, measuring IP performance over IPsec tunnels with
O/TWAMP is an important tool for operators.
Another advantage of IPsec key exchange protocol may be that it is
not necessary to use distinct keys in OWAMP-Control and OWAMP-Test
layers. One key for encryption and another for authentication is
sufficient for both the Control and Test layers. This obviates the
need to generate two keys and could reduce the complexity of O/TWAMP
protocols in this environment. This observation comes from the fact
that separate session keys in Control and Test layers are designed
for preventing reflection attacks when employing the current
mechanism. Once IPsec is employed, such a potential threat is
alleviated. Note that this will be very useful in the environments
where IPsec capability has been supported.
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2. Terminology used in this document
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
Let us first consider why the reasons originally listed in [RFC4656]
Sec. 6.6 may not apply today in many cases. First, the argument made
is that partial authentication in O/TWAMP authentication mode is not
possible with IPsec. IPsec indeed cannot authenticate only a part of
a packet. However, in an environment where IPsec is already deployed
and actively used, partial authentication of O/TWAMP contradicts the
operational reasons dictating the use of IPsec. At the same time,
this limits the applicability and use of O/TWAMP in networks using
IPsec.
The second argument made is the need to keep separate deployment
paths between O/TWAMP 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, 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.
Additionally, there is a great number of IPSec-based VPN applications
which are widely used in business applications to provide end-to-end,
or host-to-host security over IEEE 802.11 wireless LANs. At the same
time, lots of standardized protocols make use of IPsec/IKE, including
MIPv4/v6, HIP, SCTP, BGP, NAT and SIP, just to name a few.
Third, with respect to the support of IPsec in lightweight embedded
devices, nowadays, a large number of limited-resource and low-cost
devices, such as Ethernet switches, DSL modems, and other such
devices come with support for IPsec "out of the box". Therefore
concerns about implementation, although likely valid a decade ago,
are not well founded today.
Fourth, everyday use of IPsec applications by field technicians, on
the one hand, and good understanding of the IPsec API by many
programmers, on the other, should not be anymore 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 a certain level of expertise to deal with it, in practice,
most competent technical personnel and programmers have no problems
using it on a daily basis.
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O/TWAMP actually consists of two inter-related protocols: O/TWAMP-
Control and O/TWAMP-Test. O/TWAMP-Control is used to initiate,
start, and stop test sessions and to fetch their results, whereas
O/TWAMP-Test is used to exchange test packets between two measurement
nodes. In the following subsections we consider security for each
one separately and then make the case for using them over IPsec.
3.1. O/TWAMP-Control Security
O/TWAMP uses a simple cryptographic protocol which relies on AES-CBC
for confidentiality and on HMAC-SHA1 truncated to 128 bits for
message authentication. Three modes of operation are supported:
unauthenticated, authenticated, and encrypted. The authenticated and
encrypted 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 and encrypted modes, security parameters are
negotiated during the control connection establishment. Before the
client can send commands to a server, it has to establish a
connection to the server. Then, the client opens a TCP connection to
the server on the well-known port number 861. The server responds
with a server greeting, which contains the Challenge, Mode, Salt and
Count. If the client wants to establish the connection, it responds
with a Set-Up-Response message, wherein 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
itself is encrypted using AES in Cipher Block Chaining (AES-CBC).
Encryption is performed using a key derived from the shared secret
associated with KeyID. In the authenticated and encrypted modes, all
further communications are encrypted using the AES Session-key and
authenticated with the HMAC Session-key. 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
the block 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.
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3.2. O/TWAMP-Test Security
The O/TWAMP-Test protocol runs over UDP, using sender and receiver IP
and port numbers negotiated during the Request-Session exchange. As
with O/TWAMP-Control, O/TWAMP-Test has three modes: unauthenticated,
authenticated, and encrypted. All O/TWAMP-Test sessions that are
spawned by an O/TWAMP-Control session inherit its 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. In the case of O/TWAMP-Control, the keys are
generated by the client and communicated (as part of the Token)
during connection setup through the Set-Up-Response message. In the
case of O/TWAMP-Test, the keys are derived from the O/TWAMP-Control
keys and the session identifier (SID), as inputs of the key
derivation function (KDF). The O/TWAMP-Test AES Session-key is
generated by 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 by 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, key provision and management are
complicated and need to be taken care of appropriately.
Comparatively, a certificate-based approach in IKEv2/IPsec can
automatically manage the security root and solve this problem.
3.4. Co-existence of O/TWAMP and IPsec
According to [RFC4656] "[t]he deployment paths of IPsec and OWAMP
could be separate if OWAMP does not depend on IPsec." The problem
may occur in practice is that the security mechanism of O/TWAMP and
IPsec cannot co-exist at the same time. 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). Only
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integrity protection can be provided with AH. Both integrity and
encryption can be provided with ESP. The IKE Protocol is used for
dynamical key negotiation and automatic key management.
When the sender and receiver implement O/TWAMP over IPsec, they need
to agree on a shared key during the establishment of the IPsec
tunnel; subsequently all IP packets sent by the sender are protected.
If the AH protocol is used, IP packets are transmitted in plaintext.
The authentication part covers the entire packet. So all test
information, such as UDP port number, and the test results will be
visible to any attacker, which can intercept these test packets, and
introduce errors or forge packets that may be injected during the
transmission. In order to avoid this attack, the receiver must
validate the integrity of these packets with the negotiated secret
key. If ESP is used, IP packets are encrypted, and hence no other
than the receiver can use the IPsec secret key and decrypt the IP
packet, and then it can obtain the test data to assess the IP network
performance based on the measurements. So both the sender and
receiver must support IPsec to generate the security secret key of
IPsec.
In the current implementation of O/TWAMP, after the test packets are
received by the receiver, it cannot execute active measurement over
IPsec. That is because the receiver knows only the shared secret key
but not the IPsec key, while the test packets are protected by the
IPsec key ultimately. Therefore, it needs to be considered how to
measure IP network performance in an IPsec tunnel with O/TWAMP.
Without this functionality, the use of OWAMP and TWAMP over IPsec is
hindered.
Of course, backward compatibility should be considered, as well.
That is, the intrinsic security method based on shared key as
specified in the O/TWAMP standards can also fit the other platforms.
There should be no impact on the current security mechanisms defined
in O/TWAMP for other use cases. This document describes a possible
solution to this problem which takes advantage of the secret key
derived by IPsec, to provision the key needed in RFC 4656 and RFC
5357.
4. O/TWAMP over IPsec
A security method based on a shared secret key has been defined in
O/TWAMP [RFC4656][RFC5357]. In this section, in order to employ
O/TWAMP over IPsec, a method of binding O/TWAMP and IKEv2 is
described, for those both the sender and receiver supporting the
IPsec protocols. The shared key used in the security of O/TWAMP is
derived from IPsec [RFC5996]. If the AH protocol is used, the IP
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packets are transmitted in plaintext. All of O/TWAMP is integrity-
protected by IPsec. Even if the peers choose to opt for the
unauthenticated mode, IPsec integrity protection is extended to
O/TWAMP. In the authenticated and encrypted modes, the shared secret
can be derived from IKE SA or IPsec SA. If the shared secret key is
derived from IKE SA, SKEYSEED must be generated firstly. SKEYSEED
and its derivatives are computed as per [RFC5996], where prf is a
pseudorandom function:
SKEYSEED = prf(Ni | Nr, g^ir)
Ni and Nr are nonces, negotiated during initial exchange. g^ir is the
shared secret from the ephemeral Diffie-Hellman exchange and is
represented as a string of octets. SKEYSEED can be used as the
shared secret key directly, then the shared key is equal to SKEYSEED.
Alternatively, the shared secret key can be generated as follows:
Shared secret key=PRF{ SKEYSEED, Session ID}
wherein the session ID is the SID agreed during the O/TWAMP-Test
protocol.
If the shared secret key is derived from IPsec SA, the shared secret
key can be equal to KEYMAT, wherein
KEYMAT = prf+(SK_d, Ni | Nr)
The term "prf+" describes a function that outputs a pseudorandom
stream based on the inputs to a prf [RFC5996]; or the shared secret
key can be generated as follows:
Shared secret key=PRF{ KEYMAT, Session ID}
wherein the session ID is the SID agreed during the O/TWAMP-Test
protocol.
There are some cases for rekeying IKE SA and IPsec SA, after which
the corresponding key of 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.
As discussed above, a binding association between the key generated
from IPsec and the shared secret key needs to be considered. SA can
be identified by SPI and protocol uniquely for a given sender and a
receiver. So these parameters should be agreed upon during the
O/TWAMP protocol. When the sender and receiver execute O/TWAMP
protocol to negotiate integrity key, the IPsec protocol and SPI
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should be checked. Only if two parameters are matched with the
information of IPsec, should the O/TWAMP connection be established.
As illustrated in Fig. 1, the SPI and protocol type are included in
the server greeting of the O/TWAMP-Control protocol. After the
client receives the greeting, it closes the connection if it receives
a greeting with an erroneous SPI and protocol value. Otherwise, the
client responds with the following Set-Up-Response message and
generates the shared secret key. This message exchange flow is
illustrated as Fig. 1.
+--------+ +--------+
| Client | | Server |
+--------+ +--------+
| |
| TCP Connection |
|<------------------------->|
| |
| Greeting message |
|<--------------------------|
| |
| Set-Up-Response |
|-------------------------->|
| |
| |
| Server-Start |
|<--------------------------|
| |
Figure 1. The procedure of O/TWAMP-Control
The format of server greeting is illustrated in Fig. 2. The unused
12 octets are used to carry the new parameter: protocol and SPIs.
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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. The format of server greeting
In ESP, when the IP packets are encrypted, no other than the receiver
can use the IPsec key and decrypt the IP packets. It gains the test
data to process measurement IP performance. 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 also want to use authenticated or encrypted mode, the shared
secret can be also derived from IKE SA or IPsec SA. The method of
key generation and binding association is the same as AH protocol
mode.
Besides, there is encryption-only configuration in ESP, though 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.
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5. Others
The 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 O/TWAMP.
6. Security Considerations
As the shared secret key is derived from IPsec, 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 DoS attacks are as
defined in [RFC5996].
7. IANA Considerations
There may be IANA considerations for allocating additional value for
these options. The values of the protocol field needed to be
assigned from the numbering space.
8. Acknowledgments
We would like to thank Eric Chen and Yakov Stein for their comments,
and Al Morton for pointing to previous work discussed in IPPM WG.
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.
[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.
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[RFC5996] Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen,
"Internet Key Exchange Protocol Version 2 (IKEv2)",
RFC 5996, September 2010.
9.2. Informative References
[RFC2898] Kaliski, B., "PKCS #5: Password-Based Cryptography
Specification Version 2.0", RFC 2898, September 2000.
Authors' Addresses
Yang Cui
Huawei Technologies
Huawei Building, Q20, No.156, Rd. BeiQing
Haidian District, Beijing 100095
P. R. China
Email: cuiyang@huawei.com
Emily Bi
Huawei Technologies
Huawei Building, Q20, No.156, Rd. BeiQing
Haidian District, Beijing 100095
P. R. China
Phone: +86-10-82881907
Email: bixiaoyu@huawei.com
Kostas Pentikousis (editor)
Huawei Technologies
Carnotstrasse 4
10587 Berlin
Germany
Email: k.pentikousis@huawei.com
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