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Minimal ESP

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This is an older version of an Internet-Draft whose latest revision state is "Replaced".
Authors Daniel Migault , Tobias Guggemos
Last updated 2016-10-04
Replaced by draft-ietf-lwig-minimal-esp, draft-ietf-lwig-minimal-esp, RFC 9333
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Light-Weight Implementation Guidance (lwig)              D. Migault, Ed.
Internet-Draft                                                  Ericsson
Intended status: Informational                               T. Guggemos
Expires: April 7, 2017                                        LMU Munich
                                                         October 4, 2016

                              Minimal ESP


   This document describes a minimal version of the IP Encapsulation
   Security Payload (ESP) described in RFC 4303 which is part of the
   IPsec suite.

   ESP is used to provide confidentiality, data origin authentication,
   connectionless integrity, an anti-replay service (a form of partial
   sequence integrity), and limited traffic flow confidentiality.

   This document does not update or modify RFC 4303, but provides a
   compact description of how to implement the minimal version of the
   protocol.  If this document and RFC 4303 conflicts then RFC 4303 is
   the authoritative description.

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

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   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 April 7, 2017.

Copyright Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   ( 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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  Security Parameter Index (SPI) (32 bit) . . . . . . . . . . .   3
   4.  Sequence Number(SN) (32 bit)  . . . . . . . . . . . . . . . .   5
   5.  Padding . . . . . . . . . . . . . . . . . . . . . . . . . . .   6
   6.  Next Header (8 bit) . . . . . . . . . . . . . . . . . . . . .   6
   7.  ICV . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   7
   8.  Cryptographic Suites  . . . . . . . . . . . . . . . . . . . .   7
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   10. Security Considerations . . . . . . . . . . . . . . . . . . .   9
   11. Acknowledgment  . . . . . . . . . . . . . . . . . . . . . . .   9
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     12.1.  Normative References . . . . . . . . . . . . . . . . . .   9
     12.2.  Informative References . . . . . . . . . . . . . . . . .  10
   Appendix A.  Document Change Log  . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Requirements notation

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

2.  Introduction

   ESP [RFC4303]  is part of the IPsec suite protocol [RFC4301] .  It is
   used to provide confidentiality, data origin authentication,
   connectionless integrity, an anti-replay service (a form of partial
   sequence integrity) and limited traffic flow confidentiality.

   Figure 1 describes an ESP Packet.  Currently ESP is implemented in
   the kernel of IPsec aware devices.  This document provides a minimal
   ESP implementation guideline so that smaller devices like sensors
   without kernel and with hardware restrictions can implement ESP and
   benefit from IPsec.

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   For each field of the ESP packet represented in Figure 1 this
   document provides recommendations and guidance for minimal

 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.  Security Parameter Index (SPI) (32 bit)

   According to the [RFC4303], the SPI is a mandatory 32 bits field and
   is not allowed to be removed.

   The SPI is used to index the Security Association and as such is
   unidirectional.  The SPI MUST be unique so that any incoming ESP
   packet can appropriately be bound to its association.  Uniqueness of
   the SPI may be provided by random functions.  However, the SPI does
   not need to be unpredictable.  As a result, if random functions are
   too costly for some constraint devices, the SPI can be generated
   using predictable functions or even fixed values.

   A constraint device setting a unique ESP session with each remote
   peer may use a fix SPI value.  Such configuration may result in two
   kind of collisions.  SPI collision between inbound and outbound SPI
   of a given session with a given remote peer or SPI collision across
   sessions between different remote peers.

   Inbound and outbound SPI collision: when IKEv2 [RFC7296] or [RFC7815]
   is use to agree the session key materials, the SPI proposed by the
   constraint device will be used by the constraint device in order to

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   index its inbound traffic.  The use of a fixed value SPI may result
   in collision between inbound and outbound traffic if the remote peer
   proposes the same SPI value for its inbound traffic.  Such collisions
   are not an issue as for outbound traffic SPI value is not used by the
   sending device.  Instead, it will be used by the remote peer to bing
   the inbound traffic to the appropriated SA.

   Inter session SPI collisions: The SPI is mostly used for inbound
   traffic so the peer can identify the corresponding SA.  Binding
   between inbound traffic and SA should first consider the SPI and the
   IP addresses, so as long as the constraint device does not have more
   then one ESP session per IP address, the IP address is sufficient to
   bind incoming packets to the SA.

   Even though, the use of a single SPI value is possible as long as the
   device has only an single ESP session per remote node, it may also
   come with security or privacy drawbacks.  The use of a fix SPI value
   may identify the constraint device communications from a passive
   attacker.  This may provide such an attacker information such as the
   number of constraint devices connecting the remote peer, and in
   conjunction with data rate, the attacker may eventually determine the
   application the constraint device is associated to.  In addition, if
   the fix value SPI is fixed by a manufacturer or by some software
   application, the SPI may leak in an obvious way the type of sensor,
   the application involved or the model of the constraint device.  As a
   result, the use of a unpredictable SPI is preferred to provide better

   Similarly, the use of a fixed SPI value may also come with some
   security issues.  First of all, any information that reveals the type
   of application or model of the constraint device could be used to
   identify the vulnerabilities the constraint device is subject to.
   This is especially sensitive for constraint device where patches or
   software updates will be challenging to operate.  As a result, these
   devices may remain vulnerable for relatively long period.  In
   addition, predictable SPI enable an attacker to forge packets with a
   valid SPI.  Such packet will not be rejected due to an SPI mismatch,
   but instead after the signature check which requires more resource
   and thus make DoS more efficient, especially for devices powered by

   Values 0-255 SHOULD NOT be used.  Values 1-255 are reserved and 0 is
   only allowed to be used internal and it MUST NOT be send on the wire.

   [RFC4303] mentions :

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    -   "The SPI is an arbitrary 32-bit value that is used by a receiver
      to identify the SA to which an incoming packet is bound.  The SPI
      field is mandatory. [...]"

    -   "For a unicast SA, the SPI can be used by itself to specify an
      SA, or it may be used in conjunction with the IPsec protocol type
      (in this case ESP).  Because the SPI value is generated by the
      receiver for a unicast SA, whether the value is sufficient to
      identify an SA by itself or whether it must be used in conjunction
      with the IPsec protocol value is a local matter.  This mechanism
      for mapping inbound traffic to unicast SAs MUST be supported by
      all ESP implementations."

4.  Sequence Number(SN) (32 bit)

   According to [RFC4303], the sequence number is a mandatory 32 bits
   field in the packet.

   The SN is set by the sender so the receiver can implement anti-replay
   protection.  The SN is derived from any strictly increasing function
   that guarantees: if packet B is sent after packet A, then SN of
   packet B is strictly greater then the SN of packet A.

   In IoT, constraint devices are expected to establish communication
   with specific devices, like a specific gateway, or nodes similar to
   them.  As a result, the sender may know whereas the receiver
   implements anti-replay protection or not.  Even though the sender may
   know the receiver does not implement anti replay protection, the
   sender MUST implement a always increasing function to generate the

   Usually, SN is generated by incrementing a counter for each packet
   sent.  A constraint device may avoid maintaining this context.  If
   the device has a clock, it may use the time indicated by the clock
   has a SN.  This guarantees a strictly increasing function, and avoid
   storing any additional values or context related to the SN.  When the
   use of a clock is considered, one should take care that packets
   associated to a given SA are not sent with the same time value.

   [RFC4303] mentions :

    -   "This unsigned 32-bit field contains a counter value that
      increases by one for each packet sent, i.e., a per-SA packet
      sequence number.  For a unicast SA or a single-sender multicast
      SA, the sender MUST increment this field for every transmitted
      packet.  Sharing an SA among multiple senders is permitted, though
      generally not recommended. [...] The field is mandatory and MUST

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      always be present even if the receiver does not elect to enable
      the anti-replay service for a specific SA."

5.  Padding

   The purpose of padding is to respect the 32 byte alignment of ESP.
   Padding is not mandatory in ESP and may be performed by the
   encryption algorithm.  As a result, when ESP is designed with
   encryption algorithms that considers the padding, padding does not
   need to implement padding.  AES in CBC mode [RFC3602] is one of these
   algorithms.  Note that [RFC3602] does not specify how the padding
   bytes should be generated.

   On the other hand, encryption algorithms like AES in CTR [RFC3686] or
   GCM[RFC4106] or CCM [RFC4309] mode do not consider Padding.  As a
   result, when such algorithms are used, Padding must be done by ESP.
   ESP defines that padding bytes MUST be generated by a succession of
   unsigned bytes starting with 1, 2, 3 with the last byte set to Pad
   Length, where Pad Length designates the length of the padding bytes.
   Checking the padding structure is not mandatory, so the constraint
   device may not proceed to such checks, however, in order ton
   interoperate with existing ESP implementations, it MUST build the
   padding bytes as recommended by ESP.

   [RFC4303] mentions :

    -   "If Padding bytes are needed but the encryption algorithm does
      not specify the padding contents, then the following default
      processing MUST be used.  The Padding bytes are initialized with a
      series of (unsigned, 1-byte) integer values.  The first padding
      byte appended to the plaintext is numbered 1, with subsequent
      padding bytes making up a monotonically increasing sequence: 1, 2,
      3, .... When this padding scheme is employed, the receiver SHOULD
      inspect the Padding field.  (This scheme was selected because of
      its relative simplicity, ease of implementation in hardware, and
      because it offers limited protection against certain forms of "cut
      and paste" attacks in the absence of other integrity measures, if
      the receiver checks the padding values upon decryption.)"

6.  Next Header (8 bit)

   According to [RFC4303], the Next Header is a mandatory 8 bits field
   in the packet.  In some cases, devices are dedicated to a single
   application or a single transport protocol, in which case, the Next
   Header has a fix value.

   [RFC4303] mentions :

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    -   "The Next Header is a mandatory, 8-bit field that identifies the
      type of data contained in the Payload Data field, e.g., an IPv4 or
      IPv6 packet, or a next layer header and data. [...] the protocol
      value 59 (which means "no next header") MUST be used to designate
      a "dummy" packet.  A transmitter MUST be capable of generating
      dummy packets marked with this value in the next protocol field,
      and a receiver MUST be prepared to discard such packets, without
      indicating an error."

7.  ICV

   The ICV is an optional value with variable length.  Unless the
   crypto-suite provides authentication without the use of the ICV
   field, the ICV field is used to host the authentication part of the

   As detailed in Section 8 we recommend to use authentication, the ICV
   field is expected to be present that is to say with a size different
   from zero.  This makes it a mandatory field which size is defined by
   the security recommendations only.

   [RFC4303] mentions :

    -   "The Integrity Check Value is a variable-length field computed
      over the ESP header, Payload, and ESP trailer fields.  Implicit
      ESP trailer fields (integrity padding and high-order ESN bits, if
      applicable) are included in the ICV computation.  The ICV field is
      optional.  It is present only if the integrity service is selected
      and is provided by either a separate integrity algorithm or a
      combined mode algorithm that uses an ICV.  The length of the field
      is specified by the integrity algorithm selected and associated
      with the SA.  The integrity algorithm specification MUST specify
      the length of the ICV and the comparison rules and processing
      steps for validation."

8.  Cryptographic Suites

   Light implementations of ESP will probably implement a reduced number
   of cipher suites.  When choosing the cipher suites it is recommended
   to balance the number of cipher suites as well as the cipher itself
   with other criteria.  This section attempts to provide some generic
   guidances for choosing the appropriated cipher suites.  Some
   recommended and for IoT relevant ciphers are marked in
   [I-D.mglt-ipsecme-rfc7321bis] with the tag "IoT"

   This section lists some of the criteria that may be considered.  The
   list is not expected to be exhaustive and may also evolve overtime.
   As a result, the list is provided as indicative:

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   - Security :   Security is the criteria that should be considered
         first when a selection of cipher suites is performed.  The
         security of cipher suites is expected to evolve over time, and
         it is of primary importance to follow up-to-date security
         guidances and recommendations.  The chosen cipher suites MUST
         NOT be known vulnerable or weak (see
         [I-D.mglt-ipsecme-rfc7321bis] for outdated ciphers).  ESP can
         be used to authenticate only or to encrypt the communication.
         In the later case, encryption should be always considered in
         conjunction with authentication.  [I-D.mglt-ipsecme-rfc7321bis]
         allows combined encryption and authentication ciphers, which
         enables the use of modes like GCM [RFC4106]  or CCM [RFC4309].

   - Interoperability :   Interoperability considers the cipher suites
         shared by the greatest number of nodes.  Note that it is not
         because a cipher suite is widely deployed that is secured.  As
         a result, security SHOULD NOT be weaken for interoperability.
         Life cycle of cipher suites is expected to be long enough so
         interoperability can still be provided with secure cipher
         suites.  Cipher sweets marked with "MUST" in
         [I-D.mglt-ipsecme-rfc7321bis] are considered to be deployed in
         all ESP applications and therefore mostly interoperable.  On
         the other hand, constraint devices may have limited
         interoperability requirements which makes possible to reduces
         the number of cipher suites to implement.

   - Power Consumption and Cipher Suite Complexity :   Complexity of the
         cipher suite or the energy associated to it are especially
         considered when devices have limited resources or are using
         some batteries, in which case the battery determine the life of
         the device.  The choice of a cryptographic function may
         consider re-using specific libraries or to take advantage of
         hardware acceleration provided by the device.  For example if
         the device benefits from AES hardware modules and uses AES-CTR,
         it may prefer AUTH_AES-XCBC for its authentication.  In
         addition, some devices may also embed radio modules with
         hardware acceleration for AES-CCM, in which case, this mode may
         be preferred.

   - Power Consumption and Bandwidth Consumption :   Similarly to the
         cipher suite complexity, reducing the payload sent, may
         significantly reduce the energy consumption of the device.  As
         a result, cipher suites with low overhead may be considered.
         To reduce the overall payload size one may for example, one MAY

         a  Use of counter-based ciphers without fixed block length
               (e.g.  AES-CTR, or ChaCha20-Poly1305)

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         b  Use of ciphers with capability of using implicit IVs

         c  Use of ciphers recommended for IoT
               [I-D.mglt-ipsecme-rfc7321bis].  Note that the size of the
               ICV must not be performed at the expense of acceptable
               security.  As a result, reducing the size of the ICV MUST
               follow the security recommendations.

         d  Sending payload data which are aligned to the cipher block
               length -2 for the ESP trailer

9.  IANA Considerations

   There are no IANA consideration for this document.

10.  Security Considerations

   Security considerations are those of [RFC4303].

11.  Acknowledgment

12.  References

12.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC3602]  Frankel, S., Glenn, R., and S. Kelly, "The AES-CBC Cipher
              Algorithm and Its Use with IPsec", RFC 3602,
              DOI 10.17487/RFC3602, September 2003,

   [RFC3686]  Housley, R., "Using Advanced Encryption Standard (AES)
              Counter Mode With IPsec Encapsulating Security Payload
              (ESP)", RFC 3686, DOI 10.17487/RFC3686, January 2004,

   [RFC4106]  Viega, J. and D. McGrew, "The Use of Galois/Counter Mode
              (GCM) in IPsec Encapsulating Security Payload (ESP)",
              RFC 4106, DOI 10.17487/RFC4106, June 2005,

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   [RFC4301]  Kent, S. and K. Seo, "Security Architecture for the
              Internet Protocol", RFC 4301, DOI 10.17487/RFC4301,
              December 2005, <>.

   [RFC4303]  Kent, S., "IP Encapsulating Security Payload (ESP)",
              RFC 4303, DOI 10.17487/RFC4303, December 2005,

   [RFC4309]  Housley, R., "Using Advanced Encryption Standard (AES) CCM
              Mode with IPsec Encapsulating Security Payload (ESP)",
              RFC 4309, DOI 10.17487/RFC4309, December 2005,

   [RFC7296]  Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.
              Kivinen, "Internet Key Exchange Protocol Version 2
              (IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October
              2014, <>.

   [RFC7815]  Kivinen, T., "Minimal Internet Key Exchange Version 2
              (IKEv2) Initiator Implementation", RFC 7815,
              DOI 10.17487/RFC7815, March 2016,

12.2.  Informative References

              Migault, D., Guggemos, T., and Y. Nir, "Implicit IV for
              Counter-based Ciphers in IPsec", draft-mglt-ipsecme-
              implicit-iv-00 (work in progress), June 2016.

              Migault, D., Mattsson, J., Wouters, P., and Y. Nir,
              "Cryptographic Algorithm Implementation Requirements and
              Usage Guidance for Encapsulating Security Payload (ESP)
              and Authentication Header (AH)", draft-mglt-ipsecme-
              rfc7321bis-00 (work in progress), March 2016.

Appendix A.  Document Change Log

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

   -00: First version published.

   -01: Clarified description

   -02: Clarified description

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Authors' Addresses

   Daniel Migault (editor)
   8400 boulevard Decarie
   Montreal, QC H4P 2N2


   Tobias Guggemos
   LMU Munich
   Oettingenstr. 67
   80538 Munich, Bavaria


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