Diet-ESP: a flexible and compressed format for IPsec/ESP
draft-mglt-ipsecme-diet-esp-00
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|---|---|---|---|
| Authors | Daniel Migault , Tobias Guggemos , Daniel Palomares | ||
| Last updated | 2014-03-03 | ||
| Replaced by | draft-ietf-ipsecme-diet-esp | ||
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draft-mglt-ipsecme-diet-esp-00
IPSECME D. Migault (Ed)
Internet-Draft Orange
Intended status: Standards Track T. Guggemos
Expires: September 4, 2014 Orange / LMU Munich
D. Palomares
Orange / LIP6 - UMPC
March 3, 2014
Diet-ESP: a flexible and compressed format for IPsec/ESP
draft-mglt-ipsecme-diet-esp-00.txt
Abstract
IPsec/ESP has been designed to secure IP packets exchanged between
two nodes. IPsec implements security at the IP layer which makes
security transparent to the applications, as opposed to TLS or DTLS
that requires application to implement TLS/DTLS. As a result, IPsec
enable to define the security rules in a similar way one establishes
firewall rules.
One of the IPsec's drawbacks is that implementing security on a per
packet basis adds overhead to each IP packet. Considering IoT
devices, the data transmitted over an IP packet is expected to be
rather small, and the cost of sending extra bytes is so high that
IPsec/ESP can hardly be used for IoT as it is currently defined in
RFC 4303.
This document defines Diet-ESP, a protocol that compress and reduce
the ESP overhead of IPsec/ESP so that it can fit security and energy
efficient IoT requirements. Diet-ESP use already existing mechanism
like IKEv2 to negotiate the compression format. Furthermore a lot of
information, already existing for an IPsec Security Association, are
reused to offer light negotiation in addition to maximum compression.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 4, 2014.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Requirements notation . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Diet-ESP: Protocol Description . . . . . . . . . . . . . . . 5
5. Diet-ESP Context: Format Description . . . . . . . . . . . . 8
6. Difference between Diet-ESP and ESP . . . . . . . . . . . . . 11
6.1. Packet Alignment . . . . . . . . . . . . . . . . . . . . 11
6.2. SAD . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
6.2.1. Storing SPI SIZE SPI in the SAD . . . . . . . . . . . 11
6.2.2. Inbound Security Association Lookup . . . . . . . . . 12
6.2.3. Outgoing Security Association Lookup . . . . . . . . 16
6.3. Sequence Number . . . . . . . . . . . . . . . . . . . . . 16
6.4. Outgoing Packet processing . . . . . . . . . . . . . . . 16
6.5. Inbound Packet processing . . . . . . . . . . . . . . . . 17
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
8. Security Considerations . . . . . . . . . . . . . . . . . . . 18
9. NAT Considerations . . . . . . . . . . . . . . . . . . . . . 18
10. Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . 19
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 19
11.1. Normative References . . . . . . . . . . . . . . . . . . 19
11.2. Informational References . . . . . . . . . . . . . . . . 20
Appendix A. Comparison . . . . . . . . . . . . . . . . . . . . . 21
A.1. Transmitting 1 Byte without anti-replay . . . . . . . . . 21
A.2. Transmitting 1 Byte to multi directional connections. . . 23
Appendix B. Document Change Log . . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 26
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1. Requirements notation
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].
2. Introduction
The IPsec/ESP [RFC4303] is represented in Figure Figure 1 . It was
designed to: 1) provide high level of security as a basis, 2) favor
interoperability between implementations 3) scale on large
infrastructures.
In order to match these goals, ESP format favor mandatory fields with
fixed sizes that are designed for the worst case scenarios. This
results in a kind of "unique" packet format common to all considered
scenarios using ESP. These specific scenarios MAY result in carrying
"unnecessary" or "larger then required" fields. This cost of
additional bytes were than considered as negligible versus
interoperability, and this made ESP very successful over the years.
With IoT, requirements become slightly different. For most devices,
like sensors, sending extra bytes directly impacts the battery and so
the life time of the sensor. Furthermore, IoT scenarios MAY consider
that sensors MAY be designed not to interconnect between each other,
but instead to be connected to a specific Security Gateway. These
kind of dedicated connectivity, for example, does not impose the
sensors to be fully interoperable with any other IPsec/ESP
implementation. In contrast, it MAY be inter-operable with the
Security Gateway and those devices supporting the same sensor's
options.
In this document, we adapted ESP so IoT devices can use ESP designed
for their specific needs or applications. Diet-ESP allows to reduce
or remove all fields of the ESP format represented in figure 1. How
the fields are reduced is defined in the Diet-ESP Context. This
Diet-ESP Context MAY be announced or negotiated between the two
peers. How the two devices agree on using the same Diet-ESP Context
is out of scope of this document. Diet-ESP Context consist of a byte
that fully defines the parameters present in a Diet-ESP packet,
creating a Diet-ESP packet format agreement between compliant
devices.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ----
| Security Parameters Index (SPI) | ^Int.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Cov-
| Sequence Number | |ered
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ----
| Payload Data* (variable) | | ^
~ ~ | |
| | |Conf.
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Cov-
| | Padding (0-255 bytes) | |ered*
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |
| | Pad Length | Next Header | v v
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
| Integrity Check Value-ICV (variable) |
~ ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: ESP Packet Description
3. Terminology
This document uses the following terminology:
- IoT: Internet of Things
- ESP: ESP like described in [RFC4303].
- ESP-packet: The concatenation of the following fields:
- ESP-Header: The concatenation of the SPI and SN
- ESP Payload: The concatenation of the following two fields.
The ESP Payload is usually encrypted.
- Data Payload: The application payload. It MAY include
a transport layer header.
- ESP-Trailer: The Padding concatenated with the Pad
Length and Next Header fields.
- ESP ICV The ICV generated throw the specified algorithm.
- Diet-ESP: Diet version of ESP like described in this document.
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- Diet-ESP Context: The Context that describes the Diet-ESP packet
format (see Section 5).
- Diet-ESP-packet: The concatenation of the following fields:
- Diet-ESP-Header: The concatenation of the SPI and SN if they
appear in the packet.
- Diet-ESP Payload: The concatenation of the following two
fields. The Diet-ESP Payload is usually encrypted.
- Data Payload: The application payload. If the
transport layer header is present, it MAY be
removed.
- Diet-ESP-Trailer: The Padding concatenated with the
Pad Length and Next Header fields if they appear in
the packet.
- Diet-ESP ICV: The ICV generated throw the specified
algorithm and MAYBE truncated by Diet-ESP.
4. Diet-ESP: Protocol Description
This section describes how each field of the ESP can be compressed.
SPI SIZE: ESP Security Policy Index is 32 bits long. Diet-ESP omits,
leaves unchanged, or reduces the SPI to 8, 16 or 24 bits. The length
of the SPI should be guided by 1) the number of simultaneous inbound
SA the device is expected to handle and 2) reliability of the IP
addresses in order to identify the proper SA for incoming packets.
More specifically, a sensor with a single connection to a Security
Gateway, may bind incoming packets to the proper SA based only in its
IP addresses. In that case, the SPI MAY not be necessary. Other
scenarios may consider using the SPI to index the SAs or may consider
having multiple ESP channels with the same host from a single host.
In that case it may choose a reduced length for the SPI. Note that
reducing the size of the SPI may expose the system to security flows.
See Section 8 for more details. Note also that the value 0 for the
SPI is note allowed to be sent on the wire as described in [RFC4303].
For those cases where a regular SPI of 32 bits has been negotiated
(e.g. via IKEv2 [RFC5996]), the resulting SPI used for Diet-ESP
packets corresponds to the high order bits of that 32 bits SPI (see
Section 6 for further explanations).
SN SIZE: ESP Sequence Number is 32 bit and extended SN is 64 bit
long. Diet-ESP omits, leaves unchanged or reduces SN to 8, 16, 24
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bits. The length of the SN should be guided by 1) how the receiving
side handles the SN, 2) the number of packets expected to be sent
over Diet-ESP channel, and 3) how the node is willing to use IKEv2 to
re-key when SN are expired. SN are used to address replay attacks,
thus removing SN may expose the system to security flaws. See
Section 8 for more details. If SN is used, a 32 bits value may not
be required. Table 1 shows the lifetime of one SA before re-keying
is required in case the SN expires.
+----------+------------------+-------------------+-----------------+
| SN | 1 packet per | 1 packet per | 1 packet per |
| Length | second | minute | hour |
+----------+------------------+-------------------+-----------------+
| 8 bit | 4min 16sec | 4h 16min | 10 days 16h |
| 16 bit | 18h 12min 16sec | 6 weeks 3 days | ~7 years 25 |
| | | 12h | weeks |
| 24 bit | ~27 weeks 5 days | 31 years 47 weeks | ~1,915 years |
| 32 bit | ~136 years | ~8,171 years | ~490,293 years |
+----------+------------------+-------------------+-----------------+
Table 1: Lifetime of one Security Association with different sizes of
Sequence Numbers compared to different use cases.
Note that SN and SPI MUST be aligned to a multiple of the Alignment
value (ALIGN).
NH: Diet-ESP is able to remove the Next Header field from the ESP-
Trailer if the underlying protocol can be derived from the Traffic
Selector (TS) within the SA. More specifically, the next header
indicates whether the encrypted ESP payload is an IP packet, a UDP
packet, a TCP packet or no next header. The NH can only be removed
if this has been explicitly specified in the SA or if the device has
a single application. Suppose a device sets an ESP channel with
another peer only considering the IP addresses as TS without
specifying the transport protocols or (or upper layer protocols). If
the device uses this channel for multiple upper layer protocols (like
HTTP and tnftp), then the NH cannot be removed as the receiver would
not be able to determine whether incoming packets are HTTP or tnftp.
Note that removing the Next Header impacts how encryption is
performed. For example, the use of AES-CBC [RFC3602] mode requires
the last block to be padded to reach a 128 bit alignment. In this
case removing the Next Header increases the padding by the Next
Header length, which is 8 bits. In this case, removing the Next
Header provides few advantages, as it does not reduce the ESP packet
length. With AES-CBC, the only advantage of removing the Next Header
would be for data with the last block of 15 bytes. In that case, ESP
pad with 15 modulo 16 bytes, set the 1 byte pad length field to 15
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and add the one byte Next Header field. This leads to 15 + 15 + 1 +
1 bytes to be sent. On the other hand, removing the Next Header
would require only the concatenation of the pad length byte with a 0
value, which leads to 16 bytes to be sent.
Other modes like AES-CTR [RFC3686] do not have block alignment
requirements. Using AES-CTR with ESP only requires the 32 bit
alignment - mostly for OS implementation. In fact if an n byte
alignment is required (for encryption or for packet format), data of
length k * n + n - 1 bytes, k an integer, takes advantage of removing
the Next Header and reduces the data to be sent over n bytes. In the
case of sensor network it is very likely that data of fixed size k *
n + n - 1 will be used. Furthermore, if 32 bits alignment is reduced
to 8 bits alignment, Next Header is always an additional unnecessary
byte being sent.
PAD: With ESP, all packets have a Pad Length field. This field is
usually present because ESP requires a 32 bits alignment which is
performed with padding. Diet-ESP considers that some devices may use
8 bits alignment, in which case padding is not necessary. Similarly,
sensors may send application data that has fixed length matching the
alignment. Note that alignment may be required by the device (8-bit,
16-bit, or more generally 32-bit), but it may also be required by the
encryption block size (AES-CBC uses 128 bit blocks). With ESP these
scenarios would result in an unnecessary Pad Length field always set
to zero. Diet-ESP considers those case with no padding, and thus the
Pad Length field can be omitted.
ALIGN: Alignment for Padding and Pad Length. ESP is designed for 32
bit alignment. This is mostly an OS implementation and hardware
design requirements for regular PC processors. IoT may not have
these requirements. Having no alignment requirements or a 16 bits
alignment requirement prevents or reduces the number of padding bytes
to be sent. As a result Diet-ESP considers alternative alignment
(8-bit, 16 bit, 32 bit) so to reduce the number of padding bytes.
Note that when PAD requires the Pad Length field to be present, ALIGN
provides the minimum alignment padding considers. More specifically,
ALIGN gives more priority to the hardware or OS implementation than
to the encryption algorithm used. In fact with AES-CTR padding will
be performed based on the value provided by ALIGN. However, AES-CBC
padding is performed on the AES block basis (128 bits). This value
overwrites the one provided by ALIGN.
IH: With ESP using the tunnel mode, the inner IP Header is sent in
every ESP Payload. This extra bytes sent do not carry relevant
information over sent packets. As a result Diet-ESP indicates the IP
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header has been omitted, and MUST be rebuilt by the receiver. These
information are negotiated via IKE and are stored in the SA.
TH: With ESP the transport header is transmitted in every packet.
This layer may not provide relevant information, especially for UDP
transport layer. The port parameters may be negotiated via IKE and
stored in the SA. As a result Diet-ESP indicates that the transport
protocol header (TH) has been removed from the encrypted ESP Payload.
This option can only be used if the header can be restored or if it
is unnecessary for the further packet procession. Other protocols
than UDP are considered out of scope of this document. TCP, for
example, includes information that are not as easy to restore, like
options, controls or windows. In order to use other transport layer
protocols within specific configuration, additional information may
be provided in the future.
ICV: ESP negotiates Authentication protocols. These protocols
generate an ICV of a length defined by the authentication protocol
negotiated for the SA. These authentication protocols do not provide
ways to perform weak authentication, as it only reduces the size of
the ICV. IoT is interested in weak authentication as it may sends a
small amount of bytes, and the trade-of between battery life time and
security may be worth. As a result Diet-ESP indicates the number of
bytes of the ICV. Diet-ESP considers sending the whole ICV or the
first 1 byte resp (2, 4, 8, 12, 16, 32) bytes. Note that Note that
reducing the size of the SPI may expose the system to security flows.
See Section 8 for more details.
5. Diet-ESP Context: Format Description
This section describes the Diet-ESP Context that contains all
necessary parameters for Diet-ESP.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
|SPI SIZE|SN SIZE |NH|P |ALIGN|TH|IH| ICV | X|
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
Figure 2: Diet-ESP Context
With the fields defined as below:
- SPI SIZE (3 bits): specifies the size of the SPI field length of
the Diet-ESP header in byte. Values can be from 0 to 4. A
zero value means the SPI does not appear in the Diet-ESP
packet. The size depends on the use case, the connection
should be used for.
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- 000: indicates a 0 bit SPI. The SPI is removed from the
packet.
- 001: indicates an 8 bit SPI in each Diet-ESP-packet.
- 010: indicates a 16 bit SPI in each Diet-ESP-packet.
- 011: indicates a 24 bit SPI in each Diet-ESP-packet.
- 100: indicates a 32 bit SPI in each Diet-ESP-packet. This
configuration is according to the RFC 4303 [RFC4303]
- 101: Unassigned
- 110: Unassigned
- 111: Unassigned
- SN SIZE (3 bits): specifies the size of the Sequence Number field
within the Diet-ESP header in byte. Values can be from 0 to 4.
A zero value means the SN does not appear in the Diet-ESP
packet. The size depends on the use case, the connection
should be used for.
- 000: indicates a 0 bit SN. The SN is removed from the
packet and anti-replay is disabled on the receiver.
- 001: indicates an 8 bit SN in each Diet-ESP-packet.
- 010: indicates a 16 bit SN in each Diet-ESP-packet.
- 011: indicates a 24 bit SN in each Diet-ESP-packet.
- 100: indicates a 32 bit SN in each Diet-ESP-packet. This
configuration is according to the RFC 4303 [RFC4303]
- 101: Unassigned
- 110: Unassigned
- 111: Unassigned
- NH (1 bit): specifies if the Next Header field appears in the
Diet-ESP trailer. NH unset to 0 indicates the Next Header
field is present and NH set to 1 indicates the Next Header is
omitted.
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- P (1 bit): specifies if the Pad Length field appears in the Diet-
ESP trailer. P unset to 0 indicates the Pad Length field is
present and P set to 1 indicates the Pad Length is omitted.
- ALIGN (2 bits): specifies Padding, Padding Length as follows:
- 00: indicates an 8 bit alignment. The field Pad Length is
omitted and the Diet-ESP packet never has Padding.
- 01: indicates a 16 bit alignment. The field Pad Length is
always present.
- 10: indicates a 32 bit alignment. The field Pad Length is
always present.
- 11: Unassigned
- TH (1 bit): specifies if the transport layer field appears in the
Diet-ESP Payload Data. TH unset to 0 indicates the Transport
header field is present and TH set to 1 indicates the transport
header is omitted. In this case, the transport protocol MUST
be specified in the SA with its associated port. If a non
unique port or a non unique transport protocol is specified,
this bit MUST be unset to 0. Otherwise, the device will not be
able to rebuilt the transport header. This document only
considers UDP.
- IH (1 bit): specifies if the inner IP address field appears in the
Diet-ESP Payload Data. This bit is only significant for the
tunnel mode. With IPsec transport mode, IH SHOULD be set to 0
and ignored. With tunnel mode IH unset to 0 indicates the
inner IP header field is present and IH set to 1 indicates the
inner IP header is omitted.
- ICV (2 bits): specifies the transmitted number of bytes to
authenticate the Diet-ESP packet. Note that ICV is optional so
if one chose not to perform authentication, it SHOULD negotiate
the authentication algorithm to NULL as defined in [RFC4835].
The minimum length greater than 0 for ICV is 96 bits and can be
generated with the following hash functions: HMAC-MD5-96
[RFC2403], HMAC-SHA1-96 [RFC2404], AES-CMAC-96 [RFC4494], AES-
XCBC-MAC-96 [RFC3566]. As a result ICV only specifies size
lower than 96 bits.
- 000: ICV is left untouched as it is specified by the
authentication algorithm.
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- 001: Diet-ESP ICV consists of the 8 most significant bits of
ESP ICV.
- 010: Diet-ESP ICV consists of the 16 most significant bits
of ESP ICV.
- 011: Diet-ESP ICV consists of the 32 most significant bits
of ESP ICV.
- 100: Diet-ESP ICV consists of the 64 most significant bits
of ESP ICV.
- 101: Unassigned
- 110: Unassigned
- 111: Unassigned
- X (1 bit): Extension bit. When set to 1, this bit indicates an
additional byte carry information. In this document, this bit
MUST be set to 0.
6. Difference between Diet-ESP and ESP
This section details how to use Diet-ESP to send and receive
messages. The use of Diet-ESP is based on the IPsec architecture
[RFC4301] and ESP [RFC4303]. We suppose the reader is familiar with
these documents and list here the adaptation that MAY be involved by
Diet-ESP.
6.1. Packet Alignment
In ESP each packet has a fixed alignment to 32 bits. For Diet-ESP
each device has an internal parameter that defines the minimal kernel
alignment that is acceptable. ALIGN SHOULD be a the maximum of the
peer's minimal alignment.
Diet-ESP Context with SPI SIZE + SN SIZE that is not a multiple of
ALIGN MUST be rejected.
6.2. SAD
6.2.1. Storing SPI SIZE SPI in the SAD
For devices using a single SPI SIZE value (e.g. sensors), the SA will
be indexed with the SPI as described in ESP. More specifically, SPI
is used as the index in the SAD. The only difference is that it has
smaller size in the ESP header. If the only supported SPI SIZE is
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zero, the lookup has to be performed with the IP address. Some
implementations MAY use a specific SPI value in their SAD for
unspecified SPIs.
For devices that allow multiple SPI SIZE, like some IoT generic end
points or IoT Security Gateways, SAD lookup has to deal with SPI of
different sizes. The SPI stored in the SAD MAY be converted from an
SPI of any size to a standard 4 bytes SPI. This means that for
inbound packets a conversion from SPI SIZE byte SPI to 4 byte SPI is
performed before the SAD lookup.
The SPI of the SA may be negotiated using IKEv2 [RFC5996]. Regular
IKEv2 implementation negotiate a 4 byte SPI. In order to be able to
use regular IKEv2 for Diet-ESP, the following convention is used.
The SPI considered in Diet-ESP consists in the SPI SIZE low power
bytes of 32 bit SPI negotiated with IKEv2. Only this value should be
considered in the SAD. How the SPI SIZE SPI is represented in the
SAD is another issue addressed above.
6.2.2. Inbound Security Association Lookup
For devices that are configured with a single SPI SIZE value can
process inbound packet as defined in [RFC4301]. As such, no
modifications is required by Diet-ESP.
Detecting Inbound Security Association: Identifying the SA for
incoming packets is a one of the main reasons the SPI is send in each
packet on the wire. For regular ESP (and AH) packets, the Security
Association is detected as follows:
1. Search the SAD for a match on {SPI, destination address, source
address}. If an SAD entry matches, then process the inbound ESP
packet with that matching SAD entry. Otherwise, proceed to step
2.
2. Search the SAD for a match on {SPI, destination address}. If the
SAD entry matches, then process the inbound ESP packet with that
matching SAD entry. Otherwise, proceed to step 3.
3. Search the SAD for a match on only {SPI} if the receiver has
chosen to maintain a single SPI space for AH and ESP, or on {SPI,
protocol} otherwise. If an SAD entry matches, then process the
inbound ESP packet with that matching SAD entry. Otherwise,
discard the packet and log an auditable event.
For device that are dealing with different SPI SIZE SPI, the way
inbound packets are handled differs from the [RFC4301]. In fact,
when a inbound packet is received, the peer does not know the SPI
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SIZE. As a result, it does not know the SPI that applies to the
incoming packet. The different values could be the 0 (resp. 1, 2, 3
and 4) first bytes of the IP payload.
Since the size of the SPI is not known for incoming packets, the
detection of inbound SAs has to be redefined in a Diet-ESP
environment. In order to ensure a detection of a SA the above
described regular detection have to be done for each supported SPI
size (in most cases 5 times). In most common cases this will return
a unique Security Association.
If there is more than one SA matching the lookup, the authentication
MUST be performed for all found SAs to detect the SA with the correct
key. In case there is no match, the packet MUST be dropped. Of
course this can lead into DoS vulnerability as an attacker recognizes
an overlap of one or more IP-SPI combinations. Therefore it is
highly recommended to avoid different values of the SPI SIZE for one
tuple of Source and Destination IP address. Furthermore this
recommendation becomes mandatory if NULL authentication is supported.
This is easy to implement as long as the sensors are not mobile and
do not change their IP address.
The following optimizations MAY be considered for sensor that are not
likely to perform mobility or multihoming features provided by MOBIKE
[RFC4555] or any change of IP address during the lifetime of the SA.
Optimization 1 - SPI SIZE is mentioned inside the SPI: The SPI SIZE
is defined as part of the SPI sent in each packet. Therefore the
receiver has to choose the most significant 2 bits of the SPI in the
following way in order to recognize the right size for incoming Diet-
ESP packets:
00: SPI SIZE of 1 byte is used.
01: SPI SIZE of 2 byte is used.
10: SPI SIZE of 3 byte is used.
11: SPI SIZE of 4 byte is used.
If the the value 0 is chosen for the SPI SIZE this option does not
feasible.
Optimization 2 - IP address based lookup: IP addressed based search
is one optimization one MAY choose to avoid several SAD lookups. It
is based on the IP address and the stored SPI SIZE, which MUST be the
same value for each SA of one IP address. Otherwise it can't neither
be ensured that an SA is found nor that the correct one is found.
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Note that in case of mobile IP the SPI SIZE MUST be updated for all
SAs related to the new IP address which may cause in renegotiation.
Figure Figure 3 shows this lookup described below.
1. Search most significant SA as follows:
1.1 Search the first SA for a match on {destination address,
source address}. If an SA entry matches, then process to step
2. Otherwise, proceed to step 1.2.
1.2 Search the first SA for a match on {source address}. If an SA
entry matches, then process to step 2. Otherwise, drop the
packet.
2. Identify the size of the compressed SPI for the found SA, stored
in the Diet-ESP context. Note that all SAs to one IP address MUST
have the same value for the SPI SIZE. Then go to step 3.
3. If the SPI SIZE is NOT zero, read the SPI SIZE SPI from the packet
and perform a regular SAD lookup as described in [RFC4301]. If
the SPI SIZE is zero, the SA from step 1 is unique and can be
used.
Note that some implementation MAY collect all SPI matching the IP
addresses in step 2 to avoid an additional lookup over the whole SAD.
This is implementation dependant.
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+-----------+
| START |
+-----------+
|
V
+-----------------+
| find 1st SA to |
| IP address |------------------+
+-----------------+ |
| |
____V____ V
yes / \ +-----+
+------/ SPI_SIZE \ /----->|'---'|
| \ = 0 ? / / | SAD |
| \_________/ / + +
| |no / '---'
| V /
| +-----------------+ /
| | find 1st SA to |--/
| | SPI +IP |
| | address |
| +-----------------+
| |
| V
| +-----------------+
| | Diet-ESP packet |
+-->| procession |
+-----------------+
Figure 3: SAD lookup for incoming packets.
If the sensor is likely to change its IP address, the outcome MAY be
a given IP address associated to different SPI SIZE. This case MAY
occur if one IP address has been used by a device not anymore online,
but the SA has not been removed. The IP has then been provided to
another device. In this case the Diet-ESP Context SHOULD NOT be
accepted by the Security Gateway when the new Diet-ESP Context is
provided to the Security Gateway. At least the Security Gateway can
check the previous peer is reachable and then delete the SA before
accepting the new SA.
Another case MAY be that a sensor got two interfaces with different
IP addresses, negotiates a different SPI SIZE on each interface and
then use MOBIKE to move the IPsec channels from one interface to the
other. In this case, the Security Gateway SHOULD NOT accept the
update, or force a renegotiation of the SPI SIZE for all SAs,
basically by re-keying the SAs.
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6.2.3. Outgoing Security Association Lookup
Outgoing lookups for the SPI are performed in the same way as it is
done in ESP. The Traffic Selector for the packet is searched and the
right SA is read from the SA. The SPI used in the packet MUST be
reduced to the value stored in SPI SIZE.
6.3. Sequence Number
Sequence number in ESP [RFC4303] can be of 4 bytes or 8 bytes for
extended ESP. Diet-ESP introduces different sizes. One way to deal
with this is to add a MAX_SN value that stores the maximum value the
SN can have. Any new value of the SN will be check against this
MAX_SN.
6.4. Outgoing Packet processing
NH, TH, IH, P indicate fields or payloads that are removed from the
Diet-ESP packet. How the Diet-ESP packet is generated depends on the
Payload Data of lPD bytes, BLCK the block size of the encryption
algorithm and the device alignment ALIGN. We note M = MAX(BLCK,
ALIGN). Although not normative the resulting Diet-ESP packet should
be and explained below. We consider the Diet-ESP Payload as
described in Section 3
- 1: if TH is set to 1, then remove the transport layer of the
Payload Data.
- 2: if IH is set to 1, and the IPsec mode is tunnel, then remove
the inner IP address of the Payload Data.
- 3: if PAD is set to 0 and NH is set to 0: Diet-ESP considers both
fields Pad Length and Next Header. The Diet-ESP Payload is the
encryption of the following clear text: Payload Data | Padding
of Pad Length bytes | Pad Length field | Next Header field.
The Pad Length value is such that lPD + 2 + Pad Length = 0 [M].
- 4: if PAD is set to 0 and NH is set to 1: Diet-ESP considers the
Pad Length field but removes the Next Header field. The ESP
Payload is the encryption of the following clear text: Payload
Data | Padding of Pad Length bytes | Pad Length field | Next
Header field. The Pad Length value is such that lPD + 1 + Pad
Length = 0 [M].
- 5: if PAD is set to 1 and NH is set to 0: Diet-ESP considers the
Next Header but do not consider the Pad Length field or the
Padding Field. This is valid as long as lPD + 1 = 0 [M]. If M
= 1 as it is the case for AES-CTR this equation is always true.
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On the other hand the use of specific block size requires the
application to send specific length of application data.
- 6: if PAD is set to 1 and NH is set to 1: Diet-ESP does consider
neither the Next Header field nor the Pad Length field nor the
Padding Field. This is valid as long as lAD = 0 [M]. If M = 1
as it is the case for AES-CTR this equation is always true. On
the other hand the use of specific block size requires the
application to send specific length of application data.
6.5. Inbound Packet processing
Decryption is for performed the other way around.
After SAD lookup, authenticating and decrypting the Diet-ESP payload
the original packet is rebuild as follows:
- 1: if PAD is set to 1 and NH is set to 1: Diet-ESP does consider
neither the Next Header field nor the Pad Length field nor the
Padding Field. The Next Header field of the IP packet is set
to the protocol defined for incoming traffic within the Traffic
Selector of the SA. Because there is no Padding it is
disregarded.
- 2: if PAD is set to 1 and NH is set to 0: Diet-ESP considers the
Next Header but do not consider the Pad Length field or the
Padding Field. The Next Header field of the IP packet is set
to the value within the Diet-ESP trailer.
- 3: if PAD is set to 0 and NH is set to 1: Diet-ESP considers the
Pad Length field but removes the Next Header field. The Next
Header field of the IP packet is set to the protocol defined
for incoming traffic within the Traffic Selector of the SA.
The Pad Length field is read and the Padding is removed from
the Data Payload which results the original Data Payload.
- 4: if PAD is set to 0 and NH is set to 0: Diet-ESP considers both
fields Pad Length and Next Header. The Next Header field of
the IP packet is set to the value within the Diet-ESP trailer.
The Pad Length field is read and the Padding is removed from
the Data Payload which results the original Data Payload.
- 5: if IH is set to 1, and the IPsec mode is tunnel and the IP
header is reconstructed. The source and destination address
and the Next Header field are read from the Traffic Selector.
The Payload Length is calculated including the size of the
transport header, regardless if it is removed with TH or not.
All other IP-header values are set to common defaults or have
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to be negotiated otherwise which is out of scope of this
document.
-6: if TH is set to 1, the Transport layer header is restored with
the information in the Security Association. Section 4
describes some differences between the different protocols. In
this document we focus on UDP which can be easily restored with
the ports inside the Traffic Selector. The Length field can be
calculated and the checksum can be left as 0 according to
[RFC0768]
7. IANA Considerations
There are no IANA consideration for this document.
8. Security Considerations
This section lists security considerations related to the Diet-ESP
protocol.
Small SPI SIZE exposes the device to DoS. For a device, the number
of SA is related to the number of SPI. For systems using small SPI
SIZE values as index of their database, the number of simultaneous
communications is limited by the SPI SIZE. This means that a given
device initiating SPI SIZE communications can isolate the system. In
order to leverage this vulnerability, one can consider receiving
systems that generate 32 bits SPI with a hash function that considers
different parameters associated to the reduced SPI. For example, if
one use the IP addresses as well as the reduced SPI, the number of
SPI becomes SPI SIZE per IP address. This may be sufficient as
sensors are not likely to perform multiple communications.
Small size of ICV reduces the authentication strength. For example 8
bits mean that authentication can be spoofed with a probability of 1/
256. Standard value considers a length of 96 bit for reliable
authentication. If specified, the ICV field is truncated after the
given number of bits which, for sure, has to be mentioned while
incoming packet procession as well. For removing authentication ESP
NULL has to be negotiated, as described in RFC4303.
Removing the SN prevents protection against replay attack.
9. NAT Considerations
This section lists considerations related to the use of Diet-ESP in
NAT environments.
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Diet-ESP is a protocol designed for the IoT, assuming to work in an
IPv6 environment. However, ESP is designed to work in every IP
environment whereas Diet-ESP can be delivered in other IP
environments like IPv4 as well. This environment MAY cause the need
of NAT. In IPsec, UDP encapsulation is used to deal with NAT
environments as described in [RFC3948]. Because UDP cannot define
the underlying protocol with a Next Header, IKEv2 traffic is
distinguished from ESP or AH traffic by sending the Non-ESP Marker (4
bytes ZERO) after the UDP header. As the SPI is considered to never
be ZERO this clearly identifies IKEv2 traffic.
In context of Diet-ESP the SPI MAY not be present in the Diet-ESP-
header, which MAY corrupt this mechanism in case:
- the 4 byte SN is ZERO
- the SN is absent and the first 4 byte of the encrypted payload are
ZERO
- the compressed SN is ZERO AND the remaining bytes of the encrypted
payload are ZERO
Therefore an implementer has to define a way to ensure the first 4
bytes are NOT zero. We suggest the negotiated SPI to be at least 1
byte if UDP encapsulation is enabled.
10. Acknowledgment
Diet-ESP is a joint work between Orange and Ludwig-Maximilians-
Universitaet Munich.
11. References
11.1. Normative References
[I-D.raza-6lowpan-ipsec]
Raza, S., Duquennoy, S., and G. Selander, "Compression of
IPsec AH and ESP Headers for Constrained Environments",
draft-raza-6lowpan-ipsec-01 (work in progress), September
2013.
[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
August 1980.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
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[RFC2403] Madson, C. and R. Glenn, "The Use of HMAC-MD5-96 within
ESP and AH", RFC 2403, November 1998.
[RFC2404] Madson, C. and R. Glenn, "The Use of HMAC-SHA-1-96 within
ESP and AH", RFC 2404, November 1998.
[RFC3566] Frankel, S. and H. Herbert, "The AES-XCBC-MAC-96 Algorithm
and Its Use With IPsec", RFC 3566, September 2003.
[RFC3602] Frankel, S., Glenn, R., and S. Kelly, "The AES-CBC Cipher
Algorithm and Its Use with IPsec", RFC 3602, September
2003.
[RFC3686] Housley, R., "Using Advanced Encryption Standard (AES)
Counter Mode With IPsec Encapsulating Security Payload
(ESP)", RFC 3686, January 2004.
[RFC3948] Huttunen, A., Swander, B., Volpe, V., DiBurro, L., and M.
Stenberg, "UDP Encapsulation of IPsec ESP Packets", RFC
3948, January 2005.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, December 2005.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)", RFC
4303, December 2005.
[RFC4494] Song, JH., Poovendran, R., and J. Lee, "The AES-CMAC-96
Algorithm and Its Use with IPsec", RFC 4494, June 2006.
[RFC4555] Eronen, P., "IKEv2 Mobility and Multihoming Protocol
(MOBIKE)", RFC 4555, June 2006.
[RFC4835] Manral, V., "Cryptographic Algorithm Implementation
Requirements for Encapsulating Security Payload (ESP) and
Authentication Header (AH)", RFC 4835, April 2007.
[RFC5996] Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen,
"Internet Key Exchange Protocol Version 2 (IKEv2)", RFC
5996, September 2010.
11.2. Informational References
[RFC5856] Ertekin, E., Jasani, R., Christou, C., and C. Bormann,
"Integration of Robust Header Compression over IPsec
Security Associations", RFC 5856, May 2010.
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Appendix A. Comparison
This section compares the proposed Diet ESP with 6LoWPAN ESP
[I-D.raza-6lowpan-ipsec] related to IoT use cases. It shows the
different ESP packet sent with the two compression methods. In each
case the maximum possible compression is used and the underlying UDP
header is compressed as much as possible. The big advantage of Diet
ESP compression removing the UDP header appears. Furthermore there
are no additional compression configuration bytes to be sent in each
packet, like done in 6LoWPAN compression, because the configuration
is negotiated at the beginning of the communication the during the
IKEv2 [RFC5996] negotiation. Diet ESP uses the idea of ROHC[RFC5856]
compression removing the disadvantage that the whole packet has to be
sent once at the beginning of the connection, because it considers
that a lot of information of the Security Association can be reused
to decompress the packet.
Both comparisons are using 8 bits alignment. The figures are aligned
to 16 bits to improve the readability.
A.1. Transmitting 1 Byte without anti-replay
6LoWPAN offers compression of the Sequence Number to 8, 16, 24 bit
has to be sent in each packet, even if it is not going to be used.
6LoWPAN does not offer to reduce the ICV as it is not removed with
NULL-authentication. Diet-ESP offers reducing to fair securely 64
bits.
AES-CTR is used for encryption.
Figure 4a and 4b show this comparison. The advantage of Diet ESP for
this example is 96 bits.
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0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
0| initialization vector |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
16| initialization vector |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
32| initialization vector |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
48| initialization vector |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
64| 1 byte data | ICV |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
80| ICV |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
96| ICV |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
112| ICV |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
128| ICV |
+--+--+--+--+--+--+--+--+
Figure 4a) 1 byte Data Payload with Diet-ESP. (no SPI, no SN, no PAD,
no NH)
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0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
0| Id | SPI | SN | SN |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
16| initialization vector |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
32| initialization vector |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
48| initialization vector |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
64| initialization vector |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
80| Id |0 |C | P |source port| dest port |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
96| length |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
112| 1 byte data | pad length |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
128| next header | ICV |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
144| ICV |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
160| ICV |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
176| ICV |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
192| ICV |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
208| ICV |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
224| ICV |
+--+--+--+--+--+--+--+--+
Figure 4b) 1 byte data payload with 6LoWPAN ESP. (no SPI, 8 bits SN,
8 bits pad length, 8 bits 6LoWPAN NH)
A.2. Transmitting 1 Byte to multi directional connections.
Having multiple connections to one host implies the use of the SPI to
identify the correct Security Association. Diet ESP allows the
reduction to 8, 16 and 24 bit. 6LoWPAN ESP offers quite the same
reductions, except 24 bit. In most sensor use cases 254 possible
connection are more than enough, whereas the following two pictures
show the advantage of Diet ESP against 6LoWPAN ESP for an 8 bit SPI.
Since there is no possibility to remove the SN with 6LoWPAN it has to
be at least 8 Bit.
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6LoWPAN offers compression of the Sequence Number to 8, 16, 24 bit
has to be sent in each packet, even if it is not going to be used.
6LoWPAN does not offer to reduce the ICV as it is not removed with
NULL-authentication. Diet-ESP offers reducing to fair securely 64
bits.
AES-CTR is used for encryption.
Figure 5a and 5b show this comparison. In case of an 8 bit SPI the
advantage is 96 bits. For a 24 bit SPI the advantage would be 104
bits.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
0| SPI | initialization vector |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
16| initialization vector |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
32| initialization vector |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
48| initialization vector |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
64| initialization vector | 1 byte data |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
80| ICV |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
96| ICV |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
112| ICV |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
128| ICV |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
Figure 5a) 1 byte Data Payload with Diet-ESP. (8 bits SPI, no SN, no
PAD, no NH)
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0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
0| Id | SPI | SN | SPI |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
16| SN | initialization vector |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
32| initialization vector |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
48| initialization vector |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
64| initialization vector |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
80| initialization vector | Id |0 |C | P |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
96|source port| dest port | length |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
112| length | 1 byte data |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
128| pad length | next header |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
144| ICV |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
160| ICV |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
176| ICV |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
192| ICV |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
208| ICV |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
224| ICV |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
Figure 5b) 1 byte data payload with 6LoWPAN ESP. (32 bits SPI, 16
bits SN, 8 bits pad length, 8 bits 6LoWPAN NH)
Appendix B. Document Change Log
[draft-mglt-dice-diet-esp-00.txt]: First version published.
[draft-mglt-ipsecme-diet-esp-00.txt]:
NAT consideration added.
Comparison actualized to new Version of 6LoWPAN ESP.
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Authors' Addresses
Daniel Migault
Orange
38 rue du General Leclerc
92794 Issy-les-Moulineaux Cedex 9
France
Phone: +33 1 45 29 60 52
Email: daniel.migault@orange.com
Tobias Guggemos
Orange / LMU Munich
Am Osteroesch 9
87637 Seeg, Bavaria
Germany
Email: tobias.guggemos@gmail.com
Daniel Palomares
Orange / LIP6 - UMPC
10, Rue du Moulin
92170 Vanves, Ille-de-France
France
Email: daniel.palomares@orange.com
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