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Versions: 00

DICE                                                     D. Migault (Ed)
Internet-Draft                                                    Orange
Intended status: Standards Track                             T. Guggemos
Expires: August 4, 2014                              Orange / LMU Munich
                                                            D. Palomares
                                                    Orange / LIP6 - UMPC
                                                        January 31, 2014


        Diet-ESP: a flexible and compressed format for IPsec/ESP
                    draft-mglt-dice-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 August 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 . . . . . . . . . . . . . . . . . . . .   2
   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
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  14
   9.  Acknowledgment  . . . . . . . . . . . . . . . . . . . . . . .  15
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  15
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  15
     10.2.  Informational References . . . . . . . . . . . . . . . .  16
   Appendix A.  Comparison . . . . . . . . . . . . . . . . . . . . .  16
     A.1.  Transmitting 1 Byte without anti-replay . . . . . . . . .  16
     A.2.  Transmitting 1 Byte to multi directional connections. . .  18
   Appendix B.  Document Change Log  . . . . . . . . . . . . . . . .  20
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  21

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].






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2.  Introduction

   The IPsec/ESP [RFC4303] is represented in 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.

   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
   bits.  The length of the SN should be guided by 1) how the receiving



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   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
   and add the one byte Next Header field.  This leads to 15 + 15 + 1 +



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   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
   header has been omitted, and MUST be rebuilt by the receiver.  These
   information are negotiated via IKE and are stored in the SA.



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   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.

         - 000:  indicates a 0 bit SPI.  The SPI is removed from the
               packet.



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         - 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.

   - 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.




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   - 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.

         - 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.



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         - 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.

   Each device has an internal parameter that defines the minimal kernel
   alignment that is acceptable.  The value HARD-ALIGN defines the
   minimum alignment allowed by the devices.

   Diet-ESP Context with SPI SIZE + SN SIZE that is not a multiple of
   ALIGN MUST be rejected.

   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.

   For devices that allow multiple SPI SIZE, like some IoT generic end
   points or IoT Security Gateways, SAD lookup has to deal with indexes
   of different sizes.  One way would be to convert SPI of any size to a
   standard 4 bytes SPI.  This means that for inbound packets a
   conversion from SPI SIZE bytes SPI to 4 bytes SPI is performed before
   the SAD lookup is performed.  Similarly, a 4 bytes SPI to SPI SIZE
   bytes SPI conversion is performed before inserting the SPI into the
   Diet-ESP packet.  A possible implementation may consist in using the
   SPI SIZE bytes SPI as the low order bytes of the 4 byte SPI and fill
   with NULL bytes the remaining high order bytes.  This also means that
   any negotiated SPI must not start with NULL bytes.  Another way could
   consist in adding the SPI SIZE argument in the SAD lookup.  This



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   means that instead of looking at the SPI, implementations will
   consider looking at the (SPI, SPI SIZE).

   The SPI of the SA may be negotiated using IKEv2 [RFC5996].  Regular
   IKEv2 implementation negotiate a 4 byte SPI.  The SPI considered in
   Diet-ESP consists in the SPI SIZE low power bytes of this SPI.  Only
   the value should be considered in the SAD.  How the SPI SIZE SPI is
   represented in the SAD is another issue addressed above.

   When the SPI is omitted, the device must be able to perform a SAD
   lookup that is not based on a SPI value, but only the IP addresses.
   This is specific to Diet-ESP, and one way to make Diet-ESP compliant
   with the IPsec architecture is to generate a SPI from the IP
   addresses.  Most likely, no collision will occur.  To avoid all
   collision cases, one can introduce a check function that proceed to
   the SPI and IP address match.  If SPI matches but the IP address does
   not match then the hash function can be performed again over the
   previous SPI, until a match is found.  Of course the system should
   define the maximum number of hashes that should be performed.

   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.

   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



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         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.
         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.

   Decryption is performed the other way around.

   After authenticating and encrypting 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.



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   - 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
         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.




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9.  Acknowledgment

10.  References

10.1.  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.

   [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.

   [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.

   [RFC4835]  Manral, V., "Cryptographic Algorithm Implementation
              Requirements for Encapsulating Security Payload (ESP) and
              Authentication Header (AH)", RFC 4835, April 2007.




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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.

10.2.  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.

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 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 does not offer the possibility of removing the Sequence
   number.  Therefore the minimum number of 16 bit has to be sent in
   each packet, even if it is not going to be used.  If a SN of 8 or 24
   bit should be used, similar characteristics can be recognized.

   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 3a and 3b 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 3a) 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    |0 |SP|SN|NH|           SN          |
                  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
                16|           SN          | initialization vector |
                  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
                32|             initialization vector             |
                  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
                48|             initialization vector             |
                  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
                64|             initialization vector             |
                  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
                80| initialization vector |source port| dest port |
                  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
                96|                     length                    |
                  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
               112|      1 byte data      |       pad length      |
                  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
               128|     Id    |0 |C |  P  |          ICV          |
                  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
               144|                      ICV                      |
                  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
               160|                      ICV                      |
                  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
               176|                      ICV                      |
                  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
               192|                      ICV                      |
                  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
               208|                      ICV                      |
                  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
               224|          ICV          |
                  +--+--+--+--+--+--+--+--+

               Figure 3b) 1 byte data payload with 6LoWPAN ESP.
                          (no SPI, 16 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.  Using 6LoWPAN ESP there
   is no possibility of reducing the SPI, it is only possible to remove
   it completely.  Diet ESP allows the reduction to 8, 16 and 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.  This advantage remains as
   long as there is no usage of the whole range of the 32 bit SPI, which



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   is extraordinary for sensors.  Since there is no possibility to
   remove the SN with 6LoWPAN it has to be at least 16 Bit.

   6LoWPAN does not offer the possibility of removing the Sequence
   number.  Therefore the minimum number of 16 bit has to be sent in
   each packet, even if it is not going to be used.  If a SN of 8 or 24
   bit should be used, similar characteristics can be recognized.

   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.  In case of an 8 bit SPI the
   advantage is 120 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 4a) 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    |0 |SP|SN|NH|          SPI          |
                  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
                16|                      SPI                      |
                  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
                32|          SPI          |           SN          |
                  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
                48|           SN          | initialization vector |
                  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
                64|             initialization vector             |
                  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
                80|             initialization vector             |
                  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
                96|             initialization vector             |
                  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
               112| initialization vector |source port| dest port |
                  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
               128|                     length                    |
                  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
               144|      1 byte data      |       pad length      |
                  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
               160|     Id    |0 |C |  P  |          ICV          |
                  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
               176|                      ICV                      |
                  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
               192|                      ICV                      |
                  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
               208|                      ICV                      |
                  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
               224|                      ICV                      |
                  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
               240|                      ICV                      |
                  +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
               256|          ICV          |
                  +--+--+--+--+--+--+--+--+

               Figure 4b) 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

   [RFC Editor: This section is to be removed before publication]

   -00: First version published.




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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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