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SFC                                                         M. Boucadair
Internet-Draft                                                    Orange
Intended status: Standards Track                                T. Reddy
Expires: December 20, 2020                                        McAfee
                                                                 D. Wing
                                                                  Citrix
                                                           June 18, 2020


Integrity Protection for the Network Service Header (NSH) and Encryption
                      of Sensitive Context Headers
                    draft-ietf-sfc-nsh-integrity-00

Abstract

   This specification adds integrity protection and optional encryption
   of sensitive metadata directly to the Network Service Header (NSH)
   used for Service Function Chaining (SFC).

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 https://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
   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 December 20, 2020.

Copyright Notice

   Copyright (c) 2020 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
   (https://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
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   include Simplified BSD License text as described in Section 4.e of



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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Assumptions and Basic Requirements  . . . . . . . . . . . . .   4
   4.  Design Overview . . . . . . . . . . . . . . . . . . . . . . .   6
     4.1.  Supported Security Services . . . . . . . . . . . . . . .   6
       4.1.1.  Encrypt All or a Subset of Context Headers  . . . . .   6
       4.1.2.  Integrity Protection  . . . . . . . . . . . . . . . .   7
     4.2.  One Secret Key, Two Security Services . . . . . . . . . .   9
     4.3.  Mandatory-to-Implement Authenticated Encryption and HMAC
           Algorithms  . . . . . . . . . . . . . . . . . . . . . . .  10
     4.4.  Key Management  . . . . . . . . . . . . . . . . . . . . .  10
     4.5.  New NSH Variable-Length Context Headers . . . . . . . . .  11
     4.6.  Encapsulation of NSH within NSH . . . . . . . . . . . . .  11
   5.  New NSH Variable-Length Context Headers . . . . . . . . . . .  12
     5.1.  MAC#1 Context Header  . . . . . . . . . . . . . . . . . .  13
     5.2.  MAC#2 Context Header  . . . . . . . . . . . . . . . . . .  15
   6.  Timestamp Format  . . . . . . . . . . . . . . . . . . . . . .  17
   7.  Processing Rules  . . . . . . . . . . . . . . . . . . . . . .  18
     7.1.  Generic Behavior  . . . . . . . . . . . . . . . . . . . .  18
     7.2.  MAC NSH Data Generation . . . . . . . . . . . . . . . . .  19
     7.3.  Encrypted NSH Metadata Generation . . . . . . . . . . . .  20
     7.4.  Timestamp for Replay Attack . . . . . . . . . . . . . . .  21
     7.5.  NSH Data Validation . . . . . . . . . . . . . . . . . . .  22
     7.6.  Decryption of NSH Metadata  . . . . . . . . . . . . . . .  22
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  22
     8.1.  MAC#1 . . . . . . . . . . . . . . . . . . . . . . . . . .  23
     8.2.  MAC#2 . . . . . . . . . . . . . . . . . . . . . . . . . .  24
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  24
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  24
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  24
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  24
     11.2.  Informative References . . . . . . . . . . . . . . . . .  25
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  26

1.  Introduction

   Many advanced Service Functions (SFs) are invoked for the delivery of
   value-added services.  Typically, SFs are used to meet various
   service objectives such as IP address sharing, avoiding covert
   channels, detecting Denial-of-Service (DoS) attacks and protecting
   network infrastructures against them, network slicing, etc.  Because
   of the proliferation of such advanced SFs together with complex
   service deployment constraints that demand more agile service



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   delivery procedures, operators need to rationalize their service
   delivery logics and master their complexity while optimising service
   activation time cycles.  The overall problem space is described in
   [RFC7498].

   [RFC7665] presents a data plane architecture addressing the
   problematic aspects of existing service deployments, including
   topological dependence and configuration complexity.  It also
   describes an architecture for the specification, creation, and
   maintenance of Service Function Chains (SFCs) within a network.  That
   is, how to define an ordered set of SFs and ordering constraints that
   must be applied to packets/flows selected as a result of traffic
   classification.  [RFC8300] specifies the SFC encapsulation: Network
   Service Header (NSH).

   The NSH data is unauthenticated and unencrypted [RFC8300], forcing a
   service topology that requires security and privacy to use a
   transport encapsulation that supports such features.  Note that some
   transport encapsulation (e.g., IPsec) only provide hop-by-hop
   security between two SFC data plane elements (e.g., two Service
   Function Forwarders (SFFs), SFF to SF) and do not provide SF-to-SF
   security of NSH metadata.  For example, if IPsec is used, SFFs or SFs
   within a Service Function Path (SFP) not authorized to access the
   privacy-sensitive metadata will have access to the metadata.  As a
   reminder, the metadata referred to is an information that is inserted
   by Classifiers or intermediate SFs and shared with downstream SFs;
   such information is not visible to the communication endpoints
   (Section 4.9 of [RFC7665]).

   The lack of such capability was reported during the development of
   [RFC8300] and [RFC8459].  The reader may refer to Section 3.2.1 of
   [I-D.arkko-farrell-arch-model-t] for a discussion on the need for
   more awareness about attacks from within closed domains.

   This specification fills that gap.  Concretely, this document adds
   integrity protection and optional encryption of sensitive metadata
   directly to the NSH (Section 4); integrity protects the packet
   payload, and provides replay protection (Section 7.4).  Thus, the NSH
   does not have to rely upon an underlying transport encapsulation for
   security and confidentiality.

   This specification introduces new Variable-Length Context Headers to
   carry fields necessary for integrity protected NSH headers and
   encrypted Context Headers (Section 5), and is therefore only
   applicable to NSH MD Type 0x02 (Section 2.5 of [RFC8300]).






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   This specification limits thus access to an information within an SFP
   to entities that have a need to interpret it.  Particularly, SFFs
   should not act or process the Context Headers.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119][RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   This document makes use of the terms defined in [RFC7665] and
   [RFC8300].

   The document defines the following terms:

   o  SFC data plane element: Refers to SFC-aware SF, SFF, SFC Proxy, or
      Classifier as defined in the SFC data plane architecture [RFC7665]
      and further refined in [RFC8300].

   o  SFC control element: A logical entity that instructs one or more
      SFC data plane elements on how to process NSH packets within an
      SFC-enabled domain.

   o  Key Identifier: A key identifier used to identify and deliver keys
      to authorized entities.  See for example, 'kid' usage in
      [RFC7635].

   o  NSH data: The NSH is composed of a Base Header, a Service Path
      Header, and optional Context Headers.  NSH data refers to all the
      above headers and the packet or frame on which the NSH is imposed
      to realize an SFP.

   o  NSH imposer: Refers to the SFC data plane element that is entitled
      to impose the NSH with the Context Headers defined in this
      document.

3.  Assumptions and Basic Requirements

   Section 2 of [RFC8300] specifies that the NSH data can be spread over
   three headers:

   o  Base Header: Provides information about the service header and the
      payload protocol.

   o  Service Path Header: Provides path identification and location
      within an SFP.



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   o  Context Header(s): Carries metadata (i.e., context data) along a
      service path.

   The NSH allows to share context information (a.k.a., metadata) with
   downstream SFC-aware data elements on a per SFC/SFP basis.  To that
   aim:

      The control plane is used to instruct the Classifier about the set
      of context information to be supplied for a given service function
      chain.

      The control plane is also used to instruct an SFC-aware SF about
      any metadata it needs to attach to packets for a given service
      function chain.  This instruction may occur any time during the
      validity lifetime of an SFC/SFP.  The control plane may indicate,
      for a given service function chain, an order for consuming a set
      of contexts supplied in a packet.

      An SFC-aware SF can also be instructed about the behavior it
      should adopt after consuming a context information that was
      supplied in the NSH.  For example, the context can be maintained,
      updated, or stripped.

      An SFC Proxy may be instructed about the behavior it should adopt
      to process the context information that was supplied in the NSH on
      behalf of an SFC-unaware SF (e.g., the context can be maintained
      or stripped).  The SFC Proxy may also be instructed to add some
      new context information into the NSH on behalf of an SFC-unaware
      SF.

   In reference to Figure 1,

   o  Classifiers, SFC-aware SFs, and SFC proxies are entitled to update
      the Context Header(s).

   o  Only SFC-aware SFs and SFC proxies are entitled to update the
      Service Path Header.

   o  SFFs are entitled to modify the Base Path header (TTL value, for
      example).  Nevertheless, SFFs are not supposed to act on the
      Context Headers or look into the content of the Context Headers.

   Thus, the following requirements:

   o  Only Classifiers, SFC-aware SFs, and SFC proxies MUST be able to
      encrypt and decrypt a given Context Header.





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   o  Both encrypted and unecrypted Context Headers MAY be included in
      the same NSH.  That is, some Context Headers (TLVs) may be
      protected while others do not.

   o  The solution MUST provide integrity protection for the Service
      Path Header.

   o  The solution MAY provide integrity protection for the Base Header.
      The implications of disabling such checks are discussed in
      Section 8.1.

   +----------------+-----------------------------+-------------------+
   |                | Insert, remove, or replace  |  Update the NSH   |
   |                |          the NSH            |                   |
   |                |                             |                   |
   | SFC Data Plane +---------+---------+---------+---------+---------+
   |   Element      |         |         |         |Decrement| Update  |
   |                | Insert  | Remove  | Replace | Service | Context |
   |                |         |         |         |  Index  |Header(s)|
   +================+=========+=========+=========+=========+=========+
   |                |    +    |         |    +    |         |    +    |
   |   Classifier   |         |         |         |         |         |
   +----------------+---------+---------+---------+---------+---------+
   |Service Function|         |    +    |         |         |         |
   |Forwarder (SFF) |         |         |         |         |         |
   +----------------+---------+---------+---------+---------+---------+
   |Service Function|         |         |         |    +    |    +    |
   |      (SF)      |         |         |         |         |         |
   +----------------+---------+---------+---------+---------+---------+
   |                |    +    |    +    |         |    +    |    +    |
   |   SFC Proxy    |         |         |         |         |         |
   +----------------+---------+---------+---------+---------+---------+

                     Figure 1: Summary of NSH Actions

4.  Design Overview

4.1.  Supported Security Services

   This specification provides the functions described in the following
   subsections:

4.1.1.  Encrypt All or a Subset of Context Headers

   The solution allows to encrypt all or a subset of NSH Context Headers
   by Classifiers, SFC-aware SFs, and SFC proxies.





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   As depicted in Table 1, SFFs are not involved in data encryption.
   This document enforces this design approach by encrypting Context
   Headers with keys that are not supplied to SFFs, thus enforcing this
   limitation by protocol (rather than requirements language).

   +-----------------+------------------------------+------------------+
   | Data Plane      | Base and Service Headers     | Metadata         |
   | Element         | Encryption                   | Encryption       |
   +-----------------+------------------------------+------------------+
   | Classifier      | No                           | Yes              |
   | SFF             | No                           | No               |
   | SFC-aware SF    | No                           | Yes              |
   | SFC Proxy       | No                           | Yes              |
   | SFC-unaware SF  | No                           | No               |
   +-----------------+------------------------------+------------------+

     Table 1: Encryption Function Supported by SFC Data Plane Elements

   The SFC control plane is assumed to instruct the Classifier(s), SFC-
   aware SFs, and SFC proxies with the set of Context Headers (privacy-
   sensitive metadata, typically) that must be encrypted.  Encryption
   keying material is only provided to these SFC data elements.

   The control plane may also indicate the set of SFC data plane
   elements that are entitled to supply a given context header (e.g., in
   reference to their identifiers as assigned within the SFC-enabled
   domain).  It is out of the scope of this document to elaborate on how
   such instructions are provided to the appropriate SFC data plane
   elements, nor to detail the structure used to store the instructions.

   The Service Path Header (Section 2 of [RFC8300]) is not encrypted
   because SFFs use Service Index (SI) in conjunction with Service Path
   Identifier (SPI) for determining the next SF in the path.

4.1.2.  Integrity Protection

   The solution provides integrity protection for the NSH data.  Two
   levels of assurance (LoAs) are supported.

   A first level of assurance where all NSH data except the Base Header
   are integrity protected (Figure 2).  In this case, the NSH imposer
   may be a Classifier, an SFC-aware SF, or an SFC Proxy.  SFFs are not
   thus provided with authentication material.  Further details are
   discussed in Section 5.1.







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      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                Transport Encapsulation                |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...
      |                Base Header                            |  |
   +->+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  N
   |  |                Service Path Header                    |  S
   |  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  H
   |  |                Context Header(s)                      |  |
   |  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...
   |  |                Original Packet                        |
   +->+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |
   +------Scope of integrity protected data

                    Figure 2: First Level of Assurance

   A second level of assurance where all NSH data, including the Base
   Header, are integrity protected (Figure 3).  In this case, the NSH
   imposer may be a Classifier, an SFC-aware SF, an SFF, or an SFC
   Proxy.  Further details are provided in Section 5.2.

      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                Transport Encapsulation                |
   +->+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...
   |  |                Base Header                            |  |
   |  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  N
   |  |                Service Path Header                    |  S
   |  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  H
   |  |                Context Header(s)                      |  |
   |  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...
   |  |                Original Packet                        |
   +->+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |
   +----Scope of integrity protected data


                    Figure 3: Second Level of Assurance

   The integrity protection scope is explicitly signaled to SFC-aware
   SFs and SFC proxies in the NSH by means of a dedicated MD Type
   (Section 5).

   In both levels of assurance, the unencrypted Context Headers and the
   packet on which the NSH is imposed are subject to integrity
   protection.

   Table 2 lists the roles of SFC data plane elements in providing
   integrity protection for the NSH.



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         +--------------------+----------------------------------+
         | Data Plane Element | Integrity Protection             |
         +--------------------+----------------------------------+
         | Classifier         | Yes                              |
         | SFF                | No (first LoA); Yes (second LoA) |
         | SFC-aware SF       | Yes                              |
         | SFC Proxy          | Yes                              |
         | SFC-unaware SF     | No                               |
         +--------------------+----------------------------------+

    Table 2: Integrity Protection Supported by SFC Data Plane Elements

4.2.  One Secret Key, Two Security Services

   The authenticated encryption algorithm defined in [RFC7518] is used
   to provide NSH data integrity and to encrypt the Context Headers that
   carry privacy-sensitive metadata.

   The authenticated encryption algorithm provides a unified encryption
   and authentication operation which turns plaintext into authenticated
   ciphertext and vice versa.  The generation of secondary keys MAC_KEY
   and ENC_KEY from the secret key (K) is discussed in Section 5.2.2.1
   of [RFC7518]:

   o  The ENC_KEY is used for encrypting the Context Headers and the
      message integrity of the NSH data is calculated using the MAC_KEY.

   o  If the Context Headers are not encrypted, the Hashed Message
      Authentication Mode (HMAC) algorithm discussed in [RFC4868] is
      used to integrity protect the NSH data.

   The advantage of using the authenticated encryption algorithm is that
   SFC-aware SFs and SFC proxies only need to re-compute the message
   integrity of the NSH data after decrementing the Service Index (SI)
   and do not have to re-compute the ciphertext.  The other advantage is
   that SFFs do not have access to the ENC_KEY and cannot act on the
   encrypted Context Headers and, only in case of the second level of
   assurance, SFFs do have access to the MAC_KEY.  Similarly, an SFC-
   aware SF or SFC Proxy not allowed to decrypt the Context Headers will
   not have access to the ENC_KEY.

   The authenticated encryption algorithm or HMAC algorithm to be used
   by SFC data plane elements is typically controlled using the SFC
   control plane.  Mandatory to implement authenticated encryption and
   HMAC algorithms are listed in Section 4.3.

   The authenticated encryption process takes as input four octet
   strings: a secret key (K), a plaintext (P), Additional Authenticated



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   Data (A) (which contains the data to be authenticated, but not
   encrypted), and an Initialization Vector (IV).  The ciphertext value
   (E) and the Authentication Tag value (T) are provided as outputs.

   In order to decrypt and verify, the cipher takes as input K, IV, A,
   T, and E.  The output is either the plaintext or an error indicating
   that the decryption failed as described in Section 5.2.2.2 of
   [RFC7518].

4.3.  Mandatory-to-Implement Authenticated Encryption and HMAC
      Algorithms

   Classifiers, SFC-aware SFs, and SFC proxies MUST implement the
   AES_128_CBC_HMAC_SHA_256 algorithm and SHOULD implement the
   AES_192_CBC_HMAC_SHA_384 and AES_256_CBC_HMAC_SHA_512 algorithms.

   Classifiers, SFC-aware SFs, and SFC proxies MUST implement the HMAC-
   SHA-256-128 algorithm and SHOULD implement the HMAC-SHA-384-192 and
   HMAC-SHA-512-256 algorithms.

   SFFs MAY implement the aforementioned cipher suites and HMAC
   algorithms.

   o  Note: The use of AES-GCM + HMAC may have CPU and packet size
      implications (need for a second 128-bit authentication tag).

4.4.  Key Management

   The procedure for the allocation/provisioning of secret keys (K) and
   authenticated encryption algorithm or MAC_KEY and HMAC algorithm is
   outside the scope of this specification.  As such, this specification
   does not mandate the support of any specific mechanism.

   The documents does not assume nor preclude the following:

   o  The same keying material is used for all the service functions
      used within an SFC-enabled domain.

   o  Distinct keying material is used per SFP by all involved SFC data
      path elements.

   o  Per-tenant keys are used.

   In order to accommodate deployments relying upon keying material per
   SFC/SFP and also the need to update keys after encrypting NSH data
   for certain amount of time, this document uses key identifier (kid)
   to unambiguously identify the appropriate keying material.  Doing so
   allows to address the problem of synchronization of keying material.



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   Additional information on manual vs. automated key management and
   when one should be used over the other can be found in [RFC4107].

4.5.  New NSH Variable-Length Context Headers

   New NSH Variable-Length Context Headers are defined in Section 5 for
   NSH data integrity protection and, optionally, encryption of Context
   Headers carrying privacy-sensitive metadata.  Concretely, an NSH
   imposer includes (1) the key identifier to identify the keying
   material, (2) the timestamp to protect against replay attacks
   (Section 7.4), and (3) the Message Authentication Code (MAC) for the
   target NSH data (depending on the integrity protection scope)
   calculated using the MAC_KEY and optionally Context Headers encrypted
   using ENC_KEY.

   An SFC data plane element that needs to check the integrity of the
   NSH data uses MAC_KEY and the HMAC algorithm for the key identifier
   being carried in the NSH.

   An SFC-aware SF or SFC Proxy that needs to decrypt some Context
   Headers uses ENC_Key and the decryption algorithm for the key
   identifier being carried in the NSH.

   Section 7 specifies the detailed procedure.

4.6.  Encapsulation of NSH within NSH

   As discussed in [RFC8459], an SFC-enabled domain (called, upper-level
   domain) may be decomposed into many sub-domains (called, lower-level
   domains).  In order to avoid maintaining state to restore back upper-
   lower NSH information at the boundaries of lower-level domains, two
   NSH levels are used: an Upper-NSH which is imposed at the boundaries
   of the upper-level domain and a Lower-NSH that is pushed by the
   Classifier of a lower-level domain in front of the original NSH
   (Figure 4).  As such, the Upper-NSH information is carried along the
   lower-level chain without modification.  The packet is forwarded in
   the top-level domain according to the Upper-NSH, while it is
   forwarded according to the Lower-NSH in a lower-level domain.













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                       +---------------------------------+
                       |     Transport Encapsulation     |
                    +->+---------------------------------+
                    |  |        Lower-NSH Header         |
                    |  +---------------------------------+
                    |  |        Upper-NSH Header         |
                    |  +---------------------------------+
                    |  |          Original Packet        |
                    +->+---------------------------------+
                    |
                    |
                    +----Scope of NSH security protection
                         provided by a lower-level domain

                 Figure 4: Encapsulation of NSH within NSH

   SFC data plane elements of a lower-level domain includes the Upper-
   NSH when computing the MAC.

   Keying material used at the upper-level domain SHOULD NOT be the same
   as the one used by a lower-level domain.

5.  New NSH Variable-Length Context Headers

   This section specifies the format of new Variable-Length Context
   headers that are used for NSH integrity protection and, optionally,
   Context Headers encryption.

   In particular, this section defines two "MAC and Encrypted Metadata"
   Context Headers; each having specific deployment constraints.  Unlike
   Section 5.1, the level of assurance provided in Section 5.2 requires
   sharing MAC_KEY with SFFs.  Both Context headers have the same format
   as shown in Section 5.


















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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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |          Metadata Class       |      Type     |U|    Length   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | Key Length  |         Key Identifier (Variable)               ~
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       ~                      Timestamp (8 bytes)                      ~
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | IV Length     |     Initialization Vector  (Variable)         ~
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       |     Message Authentication Code and optional Encrypted        |
       ~                   Context Headers                             ~
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

            Figure 5: MAC and Encrypted Metadata Context Header

5.1.  MAC#1 Context Header

   MAC#1 Context Header is a variable-length TLV that carries the
   Message Authentication Code (MAC) for the Service Path Header,
   Context Headers, and the inner packet on which NSH is imposed,
   calculated using MAC_KEY and optionally Context Headers encrypted
   using ENC_KEY.  The scope of the integrity protection provided by
   this TLV is depicted in Figure 6.

   This MAC scheme does not require sharing MAC_KEY with SFFs.  It does
   not require to re-compute the MAC by each SFF because of TTL
   processing.  Section 8.1 discusses the possible threat associated
   with this level of assurance.



















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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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Ver|O|U|    TTL    |   Length  |U|U|U|U|MD Type| Next Protocol |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<--+
   |          Service Path Identifier              | Service Index |   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |
   |                                                               |   |
   ~       Variable-Length Unencrypted Context Headers  (opt.)     ~   |
   |                                                               |   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |
   |          Metadata Class       |      Type     |U|    Length   |   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |
   | Key Length  |              Key Identifier                     ~   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |
   ~                      Timestamp (8 bytes)                      ~   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |
   | IV Length   |           Initialization Vector                 ~   |
+->+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |
|  ~             Context Header TLVs to encrypt (opt.)             ~   |
+->+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |
|  |                                                               |   |
|  ~               Inner Packet on which NSH is imposed            ~   |
|  |                                                               |   |
|  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<--|
|                                                                      |
|                                                                      |
|                                                                      |
|                                       Integrity Protection Scope ----+
+----Encrypted Data

                         Figure 6: Scope of MAC#1

   In reference to Figure 5, the description of the fields is as
   follows:

   o  Metadata Class: MUST be set to 0x0 (Section 2.5.1 of [RFC8300]).

   o  Type: TBD1 (See Section 9)

   o  U: Unassigned bit (Section 2.5.1 of [RFC8300]).

   o  Length: Variable.

   o  Key Length: Variable.  Carries the length of the key identifier.

   o  Key Identifier: Carries a variable length Key Identifier object
      used to identify and deliver keys to SFC data plane elements.



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      This identifier is helpful to accommodate deployments relying upon
      keying material per SFC/SFP.  The key identifier helps in
      resolving the problem of synchronization of keying material.

   o  Timestamp: Carries an unsigned 64-bit integer value that is
      expressed in seconds relative to 1970-01-01T00:00Z in UTC time.
      See Section 6 for more details.

   o  IV Length: Carries the length of the IV (Section 5.2 of
      [RFC7518]).  If HMAC algorithm is used, IV length is set to zero.

   o  Initialization Vector: Carries the IV for authenticated encryption
      algorithm as discussed in Section 5.2 of [RFC7518].

   o  The Additional Authenticated Data (defined in [RFC7518]) MUST be
      the Service Path header, the unencrypted Context headers, and the
      inner packet on which the NSH is imposed .

   o  Message Authentication Code covering the entire NSH data excluding
      the Base header.

5.2.  MAC#2 Context Header

   MAC#2 Context Header is a variable-length TLV that carries the MAC
   for the entire NSH data calculated using MAC_KEY and optionally
   Context Headers encrypted using ENC_KEY.  The scope of the integrity
   protection provided by this TLV is depicted in Figure 7.
























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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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<--+
   |Ver|O|U|    TTL    |   Length  |U|U|U|U|MD Type| Next Protocol |   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |
   |          Service Path Identifier              | Service Index |   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |
   |                                                               |   |
   ~       Variable-Length Unencrypted Context Headers  (opt.)     ~   |
   |                                                               |   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |
   |          Metadata Class       |      Type     |U|    Length   |   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |
   | Key Length  |              Key Identifier                     ~   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |
   ~                      Timestamp (8 bytes)                      ~   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |
   | IV Length   |           Initialization Vector                 |   |
+->+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |
|  ~             Context Header TLVs to encrypt (opt.)             ~   |
+->+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   |
|  |                                                               |   |
|  ~               Inner Packet on which NSH is imposed            ~   |
|  |                                                               |   |
|  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<--|
|                                                                      |
|                                                                      |
|                                                                      |
|                                       Integrity Protection Scope ----+
+----Encrypted Data

                         Figure 7: Scope of MAC#2

   In reference to Figure 5, the description of the fields is as
   follows:

   o  Metadata Class: MUST be set to 0x0 (Section 2.5.1 of [RFC8300]).

   o  Type: TBD2 (See Section 9)

   o  U: Unassigned bit (Section 2.5.1 of [RFC8300]).

   o  Length: Variable.

   o  Key Length: See Section 5.1.

   o  Key Identifier: See Section 5.1.




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   o  Timestamp: See Section 6.

   o  IV Length: See Section 5.1.

   o  Initialization Vector: See Section 5.1.

   o  The Additional Authenticated Data (defined in [RFC7518]) MUST be
      the entire NSH data (i.e., including the Base Header) excluding
      the Context Headers to be encrypted.

   o  Message Authentication Code covering the entire NSH data and
      optional encrypted Context Headers.

6.  Timestamp Format

   This section follows the template provided in
   [I-D.ietf-ntp-packet-timestamps].

   The format of the Timestamp field introduced in Section 5 is depicted
   in Figure 8.

        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                            Seconds                            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                           Fraction                            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                     Figure 8: Timestamp Field Format

   Timestamp field format:

      Seconds: specifies the integer portion of the number of seconds
      since the epoch.

      + Size: 32 bits.

      + Units: seconds.

      Fraction: specifies the fractional portion of the number of
      seconds since the epoch.

      + Size: 32 bits.

      + Units: the unit is 2^(-32) seconds, which is roughly equal to
      233 picoseconds.




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   Epoch:

      The epoch is 1970-01-01T00:00Z in UTC time.

   Leap seconds:

      This timestamp format is affected by leap seconds.  The timestamp
      represents the number of seconds elapsed since the epoch minus the
      number of leap seconds.

   Resolution:

      The resolution is 2^(-32) seconds.

   Wraparound:

      This time format wraps around every 2^32 seconds, which is roughly
      136 years.  The next wraparound will occur in the year 2106.

   Synchronization aspects:

      It is assumed that SFC data plane elements are synchronized to UTC
      using a synchronization mechanism that is outside the scope of
      this document.  In typical deployments SFC data plane elements use
      NTP [RFC5905] for synchronization.  Thus, the timestamp may be
      derived from the NTP-synchronized clock, allowing the timestamp to
      be measured with respect to the clock of an NTP server.  Since the
      NTP time format is affected by leap seconds, the current timestamp
      format is similarly affected.  Therefore, the value of a timestamp
      during or slightly after a leap second may be temporarily
      inaccurate.

7.  Processing Rules

   The following subsections describe the processing rules for integrity
   protected NSH and optionally encrypted Context Headers.

7.1.  Generic Behavior

   This document adheres to the recommendations in [RFC8300] for
   handling the Context Headers at both ingress and egress SFC boundary
   nodes.  That is, to strip such context headers.

   Failures to inject or validate the Context Headers defined in this
   document SHOULD be logged locally while a notification alarm MAY be
   sent to an SFC control element.  Similarly, failure to validate the
   integrity of the NSH data MUST cause that packet to be discarded
   while a notification alarm MAY be sent to an SFC control element.



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   The details of sending notification alarms (i.e., the parameters
   affecting the transmission of the notification alarms depend on the
   information in the context header such as frequency, thresholds, and
   content in the alarm) SHOULD be configurable by the SFC control
   plane.

   SFC-aware SFs and SFC proxies MAY be instructed to strip some
   encrypted Context Headers from the packet or to pass the data to the
   next SF in the service function chain after processing the content of
   the Context Headers.  If no instruction is provided, the default
   behavior for intermediary SFC-aware nodes is to maintain such Context
   Headers so that the information can be passed to next SFC-aware hops.
   SFC-aware SFs and SFC proxies MUST re-apply the integrity protection
   if any modification is made to the Context Headers (strip a Context
   Header, update the content of an existing Context Header, insert a
   new Context Header).

   An SFC-aware SF or SFC Proxy that is not allowed to decrypt any
   Context Headers MUST NOT be given access to the ENC_KEY.

   Otherwise, an SFC-aware SF or SFC Proxy that receives encrypted
   Context Headers, for which it is not allowed to consume a specific
   Context Header it decrypts (but consumes others), MUST keep that
   Context Header unaltered when forwarding the packet upstream.

   Only one instance of "MAC and Encrypted Metadata" Context Header
   (Section 5) is allowed.  If multiple instances of "MAC and Encrypted
   Metadata" Context Header are included in an NSH packet, the SFC data
   element MUST process the first instance and ignore subsequent
   instances, and MAY log or increase a counter for this event as per
   Section 2.5.1 of [RFC8300].

   MTU and fragmentation considerations are discussed in Section 5 of
   [RFC8300].  Those considerations are not reiterated here.

7.2.  MAC NSH Data Generation

   If the Context Headers are not encrypted, the HMAC algorithm
   discussed in [RFC4868] is used to integrity protect the target NSH
   data.  An NSH imposer inserts a "MAC and Encrypted Metadata" Context
   Header for integrity protection (Section 5).

   The NSH imposer computes the message integrity for the target NSH
   data (depending on the integrity protection scope discussed in
   Section 5) using MAC_KEY and HMAC algorithm.  It inserts the MAC in
   the "MAC and Encrypted Metadata" Context Header.  The length of the
   MAC is decided by the HMAC algorithm adopted for the particular key
   identifier.



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   The Message Authentication Code (T) computation process can be
   illustrated as follows:

         T = HMAC-SHA-256-128(MAC_KEY, A)

   An entity in the SFP that intends to update the NSH MUST follow the
   above behavior to maintain message integrity of the NSH for
   subsequent validations.

7.3.  Encrypted NSH Metadata Generation

   An NSH imposer can encrypt Context Headers carrying privacy-sensitive
   metadata, i.e., encrypted and unencrypted metadata may be carried
   simultaneously in the same NSH packet (Figure 9).

        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |Ver|O|U|    TTL    |   Length  |U|U|U|U|MD Type| Next Protocol |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |          Service Path Identifier              | Service Index |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       ~       Variable-Length Unencrypted Context Headers  (opt.)     ~
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       ~                      Key Identifier                           ~
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       ~                      Timestamp                                ~
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       ~                   MAC and Encrypted Context Headers           ~
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

           Figure 9: NSH with Encrypted and Unencrypted Metadata

   In an SFC-enabled domain where pervasive monitoring [RFC7258] is
   possible, all Context Headers carrying privacy-sensitive metadata
   MUST be encrypted; doing so privacy-sensitive metadata is not
   revealed to attackers.  Privacy specific threats are discussed in
   Section 5.2 of [RFC6973].

   Using K and authenticated encryption algorithm, the NSH imposer
   encrypts the Context Headers (as set by the control plane Section 3),
   computes the message integrity for the target NSH data, and inserts
   the resulting payload in the "MAC and Encrypted Metadata" Context
   Header (Section 5).  The entire TLV carrying a privacy-sensitive



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   metadata is encrypted (that is, including the MD Class, Type, Length,
   and associated metadata of each Context Header).

   The message Authentication Tag (T) and ciphertext (E) computation
   process can be illustrated as follows:

         MAC_KEY = initial MAC_KEY_LEN octets of K,
         ENC_KEY = final ENC_KEY_LEN octets of K,
         E = CBC-PKCS7-ENC(ENC_KEY, P),
         M = MAC(MAC_KEY, A || IV || E || AL),
         T = initial T_LEN octets of M.
         MAC and Encrypted Metadata = E || T

   As specified in [RFC7518], the octet string (AL) is equal to the
   number of bits in the Additional Authenticated Data (A) expressed as
   a 64-bit unsigned big-endian integer.

   An authorized entity in the SFP that intends to update the content of
   an encrypted Context Header or needs to add a new encrypted Context
   Header MUST also follow the aforementioned behavior.

   An SFF or SFC-aware SF or SFC Proxy that only has access to the
   MAC_KEY, but not the ENC_KEY, computes the message Authentication Tag
   (T) after decrementing the TTL (by the SFF) or SI (by an SF or SFC
   Proxy) and replaces the Authentication Tag in the NSH with the
   computed Authentication Tag. Similarly, an SFC-aware SF (or SFC
   Proxy) that does not modify the encrypted Context headers also
   follows the aforementioned behavior.

   The message Authentication Tag (T) computation process can be
   illustrated as follows:

         M = MAC(MAC_KEY, A || IV || E || AL),
         T = initial T_LEN octets of M.

7.4.  Timestamp for Replay Attack

   The received NSH is accepted if the Timestamp (TS) in the NSH is
   recent enough to the reception time of the NSH (TSrt).  The following
   formula is used for this check:

             -Delta < (TSrt ? TS) < +Delta

   The RECOMMENDED value for the allowed Delta is 2 seconds.  If the
   timestamp is not within the boundaries, then the SFC data plane
   element receiving such packet MUST discard the NSH message.





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   All SFC data plane elements must be synchronized among themselves.
   These elements may be synchronized to a global reference time.

7.5.  NSH Data Validation

   When an SFC data plane element receives an NSH packet, it MUST first
   ensure that a "MAC and Encrypted Metadata" Context Header is
   included.  It MUST silently discard the message if the timestamp is
   invalid (Section 7.4).  It MUST log an error at least once per the
   SPI for which the "MAC and Encrypted Metadata" Context Header is
   missing.

   If the timestamp check is successfuly passed, the SFC data plane
   element proceeds then with NSH data integrity validation.  The SFC
   data plane element computes the message integrity for the target NSH
   data (depending on the integrity protection scope discussed in
   Section 5) using the MAC_KEY and HMAC algorithm for the key
   identifier.  If the value of the newly generated digest is identical
   to the one enclosed in the NSH, the SFC data plane element is certain
   that the NSH data has not been tampered and validation is therefore
   successful.  Otherwise, the NSH packet MUST be discarded.

7.6.  Decryption of NSH Metadata

   If entitled to consume a supplied encrypted Context Header, an SFC-
   aware SF or SFC Proxy decrypts metadata using (K) and decryption
   algorithm for the key identifier in the NSH.

   Authenticated encryption algorithm has only a single output, either a
   plaintext or a special symbol (FAIL) that indicates that the inputs
   are not authentic (Section 5.2.2.2 of [RFC7518]).

8.  Security Considerations

   NSH security considerations are discussed in Section 8 of [RFC8300].
   The guidelines for cryptographic key management are discussed in
   [RFC4107].

   The interaction between the SFC-aware data plane elements and a key
   management system MUST NOT be transmitted in clear since this would
   completely destroy the security benefits of the integrity protection
   solution defined in this document.  The secret key (K) must have an
   expiration time assigned as the latest point in time before which the
   key may be used for integrity protection of NSH data and encryption
   of Context Headers.  Prior to the expiration of the secret key, all
   participating service function nodes SHOULD have the control plane
   distribute an new key identifier and associated keying material, so
   that when the secret key is expired those nodes are prepared with the



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   new secret key.  This allows the NSH Imposer to switch to the new key
   identifier as soon as necessary.  It is RECOMMENDED that the next key
   identifier be distributed by the control plane well prior to the
   secret key expiration time.

   NSH data are exposed to several threats:

   o  A man-in-the-middle attacker modifying NSH data.

   o  Attacker spoofing NSH data.

   o  Attacker capturing and replaying NSH data.

   o  Metadata in Context Headers revealing privacy-sensitive
      information to attackers.

   o  Attacker replacing the packet on which NSH is imposed with a bogus
      or malicious packet.

   In an SFC-enabled domain where the above attacks are possible, NSH
   data MUST be integrity-protected and replay-protected, and privacy-
   sensitive NSH metadata MUST be encrypted for confidentiality
   preservation purposes.  The Base and Service Path headers are not
   encrypted.

   MACs with two levels of assurance are defined in Section 5.
   Considerations specific to each level of assurance are discussed in
   the following subsections.

   The attacks discussed in [I-D.nguyen-sfc-security-architecture] are
   handled owing to the solution specified in this document, except for
   attacks dropping packets.  Such attacks can be detected relying upon
   statistical analysis; such analysis is out of scope of this document.
   Also, if SFFs are not involved in the integrity checks, a misbehaving
   SFF which decrements SI while this should be done by an SF (SF bypass
   attack) will be detected by an upstream SF because the integrity
   check will fail.

8.1.  MAC#1

   An active attacker can potentially modify the Base header (e.g.,
   decrement the TTL so the next SFF in the SFP discards the NSH
   packet).  In the meantime, an active attacker can also drop NSH
   packets.  As such, this attack is not considered an attack against
   the security mechanism specified in the document.

   No device other than the SFC-aware SFs in the SFC-enabled domain
   should be able to update the integrity protected NSH data.



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   Similarly, no device other than the SFC-aware SFs and SFC proxies in
   the SFC-enabled domain be able to decrypt and update the Context
   Headers carrying privacy-sensitive metadata.  In other words, if the
   SFC-aware SFs and SFC proxies in the SFC-enabled domain are
   considered fully trusted to act on the NSH data, only they can have
   access to privacy-sensitive NSH metadata and the keying material used
   to integrity protect NSH data and encrypt Context Headers.

8.2.  MAC#2

   SFFs can detect whether an illegitimate node has altered the content
   of the Base header.  Such messages MUST be discarded with appropriate
   logs and alarms generated.

9.  IANA Considerations

   This document requests IANA to assign the following types from the
   "NSH IETF-Assigned Optional Variable-Length Metadata Types" (0x0000
   IETF Base NSH MD Class) registry available at:
   https://www.iana.org/assignments/nsh/nsh.xhtml#optional-variable-
   length-metadata-types.

   +-------+-------------------------------+----------------+
   | Value | Description                   | Reference      |
   +=======+===============================+================+
   | TBD1  | MAC and Encrypted Metadata #1 | [ThisDocument] |
   | TBD2  | MAC and Encrypted Metadata #2 | [ThisDocument] |
   +-------+-------------------------------+----------------+

10.  Acknowledgements

   This document was edited as a follow up to the discussion in
   IETF#104: https://datatracker.ietf.org/meeting/104/materials/slides-
   104-sfc-sfc-chair-slides-01 (slide 7).

   Thanks to Joel Halpern, Christian Jacquenet, Dirk von Hugo, Tal
   Mizrahi, Daniel Migault, and Diego Lopez for the comments.

11.  References

11.1.  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,
              <https://www.rfc-editor.org/info/rfc2119>.





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   [RFC4107]  Bellovin, S. and R. Housley, "Guidelines for Cryptographic
              Key Management", BCP 107, RFC 4107, DOI 10.17487/RFC4107,
              June 2005, <https://www.rfc-editor.org/info/rfc4107>.

   [RFC4868]  Kelly, S. and S. Frankel, "Using HMAC-SHA-256, HMAC-SHA-
              384, and HMAC-SHA-512 with IPsec", RFC 4868,
              DOI 10.17487/RFC4868, May 2007,
              <https://www.rfc-editor.org/info/rfc4868>.

   [RFC7518]  Jones, M., "JSON Web Algorithms (JWA)", RFC 7518,
              DOI 10.17487/RFC7518, May 2015,
              <https://www.rfc-editor.org/info/rfc7518>.

   [RFC7665]  Halpern, J., Ed. and C. Pignataro, Ed., "Service Function
              Chaining (SFC) Architecture", RFC 7665,
              DOI 10.17487/RFC7665, October 2015,
              <https://www.rfc-editor.org/info/rfc7665>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8300]  Quinn, P., Ed., Elzur, U., Ed., and C. Pignataro, Ed.,
              "Network Service Header (NSH)", RFC 8300,
              DOI 10.17487/RFC8300, January 2018,
              <https://www.rfc-editor.org/info/rfc8300>.

11.2.  Informative References

   [I-D.arkko-farrell-arch-model-t]
              Arkko, J. and S. Farrell, "Challenges and Changes in the
              Internet Threat Model", draft-arkko-farrell-arch-model-
              t-03 (work in progress), March 2020.

   [I-D.ietf-ntp-packet-timestamps]
              Mizrahi, T., Fabini, J., and A. Morton, "Guidelines for
              Defining Packet Timestamps", draft-ietf-ntp-packet-
              timestamps-09 (work in progress), March 2020.

   [I-D.nguyen-sfc-security-architecture]
              Nguyen, T. and M. Park, "A Security Architecture Against
              Service Function Chaining Threats", draft-nguyen-sfc-
              security-architecture-00 (work in progress), November
              2019.







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   [RFC5905]  Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch,
              "Network Time Protocol Version 4: Protocol and Algorithms
              Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010,
              <https://www.rfc-editor.org/info/rfc5905>.

   [RFC6973]  Cooper, A., Tschofenig, H., Aboba, B., Peterson, J.,
              Morris, J., Hansen, M., and R. Smith, "Privacy
              Considerations for Internet Protocols", RFC 6973,
              DOI 10.17487/RFC6973, July 2013,
              <https://www.rfc-editor.org/info/rfc6973>.

   [RFC7258]  Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an
              Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May
              2014, <https://www.rfc-editor.org/info/rfc7258>.

   [RFC7498]  Quinn, P., Ed. and T. Nadeau, Ed., "Problem Statement for
              Service Function Chaining", RFC 7498,
              DOI 10.17487/RFC7498, April 2015,
              <https://www.rfc-editor.org/info/rfc7498>.

   [RFC7635]  Reddy, T., Patil, P., Ravindranath, R., and J. Uberti,
              "Session Traversal Utilities for NAT (STUN) Extension for
              Third-Party Authorization", RFC 7635,
              DOI 10.17487/RFC7635, August 2015,
              <https://www.rfc-editor.org/info/rfc7635>.

   [RFC8459]  Dolson, D., Homma, S., Lopez, D., and M. Boucadair,
              "Hierarchical Service Function Chaining (hSFC)", RFC 8459,
              DOI 10.17487/RFC8459, September 2018,
              <https://www.rfc-editor.org/info/rfc8459>.

Authors' Addresses

   Mohamed Boucadair
   Orange
   Rennes  35000
   France

   Email: mohamed.boucadair@orange.com


   Tirumaleswar Reddy
   McAfee, Inc.
   Embassy Golf Link Business Park
   Bangalore, Karnataka  560071
   India

   Email: TirumaleswarReddy_Konda@McAfee.com



Boucadair, et al.       Expires December 20, 2020              [Page 26]


Internet-Draft      Integrity Protection for the NSH           June 2020


   Dan Wing
   Citrix Systems, Inc.
   USA

   Email: dwing-ietf@fuggles.com














































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