< draft-xu-tictoc-ipsec-security-for-synchronization-01.txt   draft-xu-tictoc-ipsec-security-for-synchronization-02.txt >
TICTOC Y. Xu TICTOC Y. Xu
Internet-Draft Huawei Technologies Internet-Draft Huawei Technologies
Intended status: Standards Track July 5, 2011 Intended status: Standards Track September 16, 2011
Expires: January 6, 2012 Expires: March 19, 2012
IPsec security for packet based synchronization IPsec security for packet based synchronization
draft-xu-tictoc-ipsec-security-for-synchronization-01.txt draft-xu-tictoc-ipsec-security-for-synchronization-02.txt
Abstract Abstract
Cellular networks often use Internet standard technologies to handle Cellular networks often use Internet standard technologies to handle
synchronization. This document defines a extension based on WESP. synchronization. This document defines an extension based on WESP.
Usually, several traffic flows are carried in one IPsec tunnel, for Usually, several traffic flows are carried in one IPsec tunnel, for
some applications, such as, 1588 or NTP, the packets need to be some applications, such as, 1588 or NTP, the packets need to be
identified after IPsec encryption to handle specially. In order to identified after IPsec encryption to handle specially. In order to
achieve high scalability in implement, a separate IPsec tunnel will achieve high scalability in implement, a separate IPsec tunnel will
not be established for some special traffic. This document analyses not be established for some special traffic. This document analyses
the need for security methods for synchronization messages the need for security methods for synchronization messages
distributed over the Internet. This document also gives a solution distributed over the Internet. This document also gives a solution
on how to mark the synchronization message when IPSec is implemented on how to mark the synchronization message when IPSec is implemented
in end to end frequency synchronization." in end to end frequency synchronization."
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8. Security Considerations . . . . . . . . . . . . . . . . . . . 14 8. Security Considerations . . . . . . . . . . . . . . . . . . . 14
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 15 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 15
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
11.1. Normative References . . . . . . . . . . . . . . . . . . . 15 11.1. Normative References . . . . . . . . . . . . . . . . . . . 15
11.2. Informative References . . . . . . . . . . . . . . . . . . 15 11.2. Informative References . . . . . . . . . . . . . . . . . . 15
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 15 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 15
1. Introduction 1. Introduction
When transfering timing in internet, a shared infrastructure is used, When transferring timing in internet, a shared infrastructure is used,
and hence the path is no longer physically deterministic. It leaves and hence the path is no longer physically deterministic. It leaves
open the possibility to disrupt, corrupt or even spoof the timing open the possibility to disrupt, corrupt or even spoof the timing
flow, where a timing signal purports to come from a higher quality flow, where a timing signal purports to come from a higher quality
clock than it actually does. In the extreme, this may be used to clock than it actually does. In the extreme, this may be used to
attack the integrity of the network, to disrupt the synchronization attack the integrity of the network, to disrupt the synchronization
flow, or cause authentication failures. On the other hand, it may be flow, or cause authentication failures. On the other hand, it may be
possible for unauthorized users to request service from a clock possible for unauthorized users to request service from a clock
server. This may overload a clock server and compromise its ability server. This may overload a clock server and compromise its ability
to deliver timing to authorized users. to deliver timing to authorized users.
For the cellular backhaul applications, two kinds of synchronization For the cellular backhaul applications, two kinds of synchronization
is needed, one is the recovery of an accurate and stable frequency are needed, one is the recovery of an accurate and stable frequency
synchronization signal as a reference for the radio signal (e.g. synchronization signal as a reference for the radio signal (e.g.
GSM, UMTS FDD, LTE FDD). In addition to frequency synchronization, GSM, UMTS FDD, LTE FDD). In addition to frequency synchronization,
phase/time synchronization are also needed in Mobile technologies, phase/time synchronization are also needed in Mobile technologies,
This is the case for the TDD technologies such as UMTS TDD,LTE TDD. This is the case for the TDD technologies such as UMTS TDD,LTE TDD.
Frequency synchronization is normally implemented in an end-to-end Frequency synchronization is normally implemented in an end-to-end
scenario where none of the intermediate nodes in the network have to scenario where none of the intermediate nodes in the network have to
recognize and process the synchronization packets. However In phase/ recognize and process the synchronization packets. However In phase/
time synchronization, a hop-by-hop scenario will request intermediate time synchronization, a hop-by-hop scenario will request intermediate
nodes to process the synchronization packets If very accurate phase/ nodes to process the synchronization packets If very accurate phase/
time is needed (e.g. sub-microsecond accuracy). time is needed (e.g. sub-microsecond accuracy).
Femtocell is the typical cellular backhaul application that requires Femtocell is the typical cellular backhaul application that requires
time synchronization. A Femtocell is defined as a wireless base time synchronization. A Femtocell is defined as a wireless base
station for deployment in residential environments and is typically station for deployment in residential environments and is typically
connected to the mobile core network via a public broadband connected to the mobile core network via a public broadband
connection (eg., DSL modem, cable modem). Femtocell improves connection (eg., DSL modem, cable modem). Femtocell improves
cellular network coverage and saves cost for operators. Just like a cellular network coverage and saves cost for operators. Just like a
typical macrocell (larger base station), Femtocells (residential base typical macrocell (larger base station), a Femtocell (residential base
stations) require a certain level of synchronization (frequency or station) requires a certain level of synchronization (frequency or
phase/time) on the air interface, predominantly frequency phase/time) on the air interface, predominantly frequency
requirements. requirements.
The [3GPP.33.320] specification defines some of the high-level The [3GPP.33.320] specification defines some of the high-level
network architecture aspects of a Home NodeB (3G UMTS) and a Home network architecture aspects of a Home NodeB (3G UMTS) and a Home
eNodeB (4G LTE). In addition, the Femto Forum organization also eNodeB (4G LTE). In addition, the Femto Forum organization also
provides a network reference model very similar to 3GPP. Both provides a network reference model very similar to 3GPP. Both
architectures have commonalities as illustrated in Figure 1. architectures have commonalities as illustrated in Figure 1.
+-------------+ +-------------+
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be performed in the synchronization device itself, or it might be be performed in the synchronization device itself, or it might be
performed in a separate device, e.g. a secure gateway. An example performed in a separate device, e.g. a secure gateway. An example
might be where the timing packets have to pass through an encrypted might be where the timing packets have to pass through an encrypted
tunnel (e.g. an IPSec tunnel). Full encryption might be required for tunnel (e.g. an IPSec tunnel). Full encryption might be required for
various reasons. The contents of the packet may be considered various reasons. The contents of the packet may be considered
secret, such as might be the case where accuracy of the time secret, such as might be the case where accuracy of the time
distribution is being sold as a service. Alternatively, it may be distribution is being sold as a service. Alternatively, it may be
because other traffic from a device is considered secret, and hence because other traffic from a device is considered secret, and hence
it is easier to encrypt all traffic. it is easier to encrypt all traffic.
IPsec,as a popular security mechanism, is being considered in some IPsec, as a popular security mechanism, is being considered in some
mobile applications, especially in case of unsecure backhaul links mobile applications, especially in case of unsecure backhaul links
(e.g. Femtocells, [3GPP.33.320]) being involved. IPsec can provide (e.g. Femtocells, [3GPP.33.320]) being involved. IPsec can provide
data source authentication, confidentiality, integrity that is data source authentication, confidentiality, integrity that is
suitable to end to end synchronization without intermediate nodes. suitable to end to end synchronization without intermediate nodes.
It provides security services by Authentication header (AH) and It provides security services by Authentication header (AH) and
Encapsulating security payload (ESP). Authentication Header provides Encapsulating security payload (ESP). Authentication Header provides
integrity protection and data origin authentication. Moreover, ESP integrity protection and data origin authentication. Moreover, ESP
can be used to provide confidentiality besides data origin can be used to provide confidentiality besides data origin
authentication, connectionless integrity. For the time packet authentication, connectionless integrity. For the time packet
protection, the critical issue is the precision of the timestamps. protection, the critical issue is the precision of the timestamps.
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packets as defined in [IEEE1588]as the port is encrypted by IPsec. packets as defined in [IEEE1588]as the port is encrypted by IPsec.
It becomes complicated when processing IPsec packets as the nodes It becomes complicated when processing IPsec packets as the nodes
will not be able to identify the 1588 packets that need to be time will not be able to identify the 1588 packets that need to be time
stamped any more. This document describes a method to resolve this stamped any more. This document describes a method to resolve this
problem. For time packets, some identifiers that can be used to problem. For time packets, some identifiers that can be used to
recognize all such packet at the physical layer are defined in WESP, recognize all such packet at the physical layer are defined in WESP,
and all of these are provided with data integrity protection. For and all of these are provided with data integrity protection. For
example, if only frequency synchronization is needed, an end-to-end example, if only frequency synchronization is needed, an end-to-end
scenario where none of the intermediate nodes in the network have to scenario where none of the intermediate nodes in the network have to
recognise and process the synchronization packets might be suitable recognise and process the synchronization packets might be suitable
to use IPsec security mechansim. In this case, the synchronization to use IPsec security mechanism. In this case, the synchronization
packets will be encrypted if the packed is transported in the IPSec packets will be encrypted if the packed is transported in the IPSec
tunnel. tunnel.
IPsec can meet synchronization rquirement 1 and 2 in section 3. IPsec can meet synchronization requirement 1 and 2 in section 3.
However IPsec still need some enhancement to meet requirement 3. However IPsec still need some enhancement to meet requirement 3.
Normally, device will decrypt IPSec message in IP layer, but in order Normally, device will decrypt IPSec message in IP layer, but in order
to improve the synchronization accuracy, some synchronization to improve the synchronization accuracy, some synchronization
protocol (e.g. [IEEE1588]) requests to process the synchronization protocol (e.g. [IEEE1588]) requests to process the synchronization
message in hardware, therefore the synchronization device may need to message in hardware, therefore the synchronization device may need to
identify synchronization messages in physical layer before the identify synchronization messages in physical layer before the
message is decrypted. How to identify the synchronization messages message is decrypted. How to identify the synchronization messages
in IPsec becomes the most important issue to keep the synchronization in IPsec becomes the most important issue to keep the synchronization
accuracy in IPsec synchronization scenario. accuracy in IPsec synchronization scenario.
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header is an empty field initialized to zero if using ESP with header is an empty field initialized to zero if using ESP with
encryption. encryption.
o HdrLen is identical with the definition in [RFC5840]. It is the o HdrLen is identical with the definition in [RFC5840]. It is the
offset from the beginning of the WESP header to the beginning of offset from the beginning of the WESP header to the beginning of
the Rest of Payload Data (i.e., past the IV, if present and any the Rest of Payload Data (i.e., past the IV, if present and any
other WESP options defined in the future) within the encapsulated other WESP options defined in the future) within the encapsulated
ESP header, in octets. HdrLen MUST be set to zero when using ESP ESP header, in octets. HdrLen MUST be set to zero when using ESP
with encryption. with encryption.
o TrailerLen contains the size of the Integrity Check Value (ICV) o TrailerLen contains the size of the Integrity Check Value (ICV)
being used by the negotiated algorithms within the IPsec SA. being used by the negotiated algorithms within the IPsec SA.
TrailerLen MUST be set to zero when using ESP with encryption.One TrailerLen MUST be set to zero when using ESP with encryption. One
issue must be taken into account that if using ESP with issue must be taken into account that if using ESP with
encryption, TrailerLen has lost the significance of ICV, as any encryption, TrailerLen has lost the significance of ICV, as any
attacker could juggle the field definition above, Next Header, attacker could juggle the field definition above, Next Header,
HdrLen, TrailerLen to zero, and forward the modified packet to the HdrLen, TrailerLen to zero, and forward the modified packet to the
receiver. The receiver will deal with the dummy encrypted packet receiver. The receiver will deal with the dummy encrypted packet
falsely. falsely.
o Authentication cotains extended data type, extended data length, o Authentication contains extended data type, extended data length,
the optional Algorithm ID field and extended data and ICV when the optional Algorithm ID field and extended data and ICV when
using ESP with encryption. This part will be depicted in next using ESP with encryption. This part will be depicted in next
section. section.
o Flags: The bits are defined most-significant-bit (MSB) first, so o Flags: The bits are defined most-significant-bit (MSB) first, so
bit 0 is the most significant bit of the flags octet. The four bit 0 is the most significant bit of the flags octet. The four
bits "Rsvd" are used for the future, the least significant bit of bits "Rsvd" are used for the future, the least significant bit of
the four bit to indicate the some extended information is included the four bit to indicate the some extended information is included
when using ESP not only integrity but also with encryption, i.e., when using ESP not only integrity but also with encryption, i.e.,
if the least significant bit is set to one, the corresponding if the least significant bit is set to one, the corresponding
extended information will be contained in Authentication payload. extended information will be contained in Authentication payload.
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| | | | | |
| message with time packets | | | message with time packets | |
|<----------------------------------|-------------------| |<----------------------------------|-------------------|
| | | | | |
+--------------+ | | +--------------+ | |
|identify the | | | |identify the | | |
|timing packet | | | |timing packet | | |
| | | | | | | |
+--------------+ | | +--------------+ | |
Figure 5. example procedure Figure 7. Example Procedure
In the Security Gateway scenario, The IPsec with tunnel mode is In the Security Gateway scenario, The IPsec with tunnel mode is
established between Femtocell and Security Gateway. After Femtocell established between Femtocell and Security Gateway. After Femtocell
and Clock server exchange the Sync Request and Sync Response, the and Clock server exchange the Sync Request and Sync Response, the
clock server will send the time packets to Femtocell to implement clock server will send the time packets to Femtocell to implement
frequency synchronization with the protection of IPsec tunnel. When frequency synchronization with the protection of IPsec tunnel. When
Femtocell receives the message, it can identify whether it is time Femtocell receives the message, it can identify whether it is time
packet, and can also identify whether the time packet is the event packet, and can also identify whether the time packet is the event
message by the time packet information in the unencryped field as message by the time packet information in the unencrypted field as
defined in the new ESP format. If the message is time packet and defined in the new ESP format. If the message is time packet and
identifies that it is the event message, Femtocell will do special identifies that it is the event message, Femtocell will do special
process for the event message, such as recording the message process for the event message, such as recording the message
receiving time. On the server side, When Security Gateway receives receiving time. On the server side, When Security Gateway receives
the message, it identifies the time packet at first, then put the message, it identifies the time packet at first, then put
appropriate value to Data type field to identify the message type in appropriate value to Data type field to identify the message type in
Payload Data, after that, it could put more packet information into Payload Data, after that, it could put more packet information into
Authentication Payload, such as UDP port number or timestamps, then Authentication Payload, such as UDP port number or timestamps, then
Extended Data Length, Algorithm ID, Extended Data integrity Check Extended Data Length, Algorithm ID, Extended Data integrity Check
value, could also be filled consequently. value, could also be filled consequently.
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This document describes the modification or extension for the WESP This document describes the modification or extension for the WESP
for the additional application. The approach described in this for the additional application. The approach described in this
document requires the ESP endpoints to be modified to support the new document requires the ESP endpoints to be modified to support the new
protocol. It allows the ESP receiver or intermediate node not only protocol. It allows the ESP receiver or intermediate node not only
to distinguish encrypted and unencrypted traffic deterministically, to distinguish encrypted and unencrypted traffic deterministically,
but also identify whether the encrypted packets are the common but also identify whether the encrypted packets are the common
packets or the time packets by a simpler implementation for the packets or the time packets by a simpler implementation for the
transport node. transport node.
Note that whether the time packets identified by the defined mark
or tag are transparent or not, there is always a possibility for
attackers to employ interception attacks to block transmission.
How to prevent interception attack is out of scope of this draft.
9. IANA Considerations 9. IANA Considerations
There have been no IANA considerations so far in this document. There have been no IANA considerations so far in this document.
10. Acknowledgments 10. Acknowledgments
The authors appreciate the valuable work and contribution done to The authors appreciate the valuable work and contribution done to
this document by Marcus Wong. this document by Marcus Wong.
11. References 11. References
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