Integrity Protection for the Network Service Header (NSH) and Encryption of Sensitive Context Headers
draft-ietf-sfc-nsh-integrity-05
SFC M. Boucadair
Internet-Draft Orange
Intended status: Standards Track T. Reddy
Expires: September 24, 2021 McAfee
D. Wing
Citrix
March 23, 2021
Integrity Protection for the Network Service Header (NSH) and Encryption
of Sensitive Context Headers
draft-ietf-sfc-nsh-integrity-05
Abstract
This specification adds integrity protection directly to the Network
Service Header (NSH) used for Service Function Chaining (SFC). Also,
this specification allows to encrypt sensitive metadata that is
carried in the NSH.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on September 24, 2021.
Copyright Notice
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document authors. All rights reserved.
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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. MTU Considerations . . . . . . . . . . . . . . . . . . . . . 22
9. Security Considerations . . . . . . . . . . . . . . . . . . . 23
9.1. MAC#1 . . . . . . . . . . . . . . . . . . . . . . . . . . 25
9.2. MAC#2 . . . . . . . . . . . . . . . . . . . . . . . . . . 25
9.3. Time Synchronization . . . . . . . . . . . . . . . . . . 25
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 26
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 26
12.1. Normative References . . . . . . . . . . . . . . . . . . 26
12.2. Informative References . . . . . . . . . . . . . . . . . 27
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 28
1. Introduction
Many advanced Service Functions (SFs) are enabled 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
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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
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 encapsulations (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) that are 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). This specification is only
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applicable to NSH MD Type 0x02 (Section 2.5 of [RFC8300]). MTU
considerations are discussed in Section 8.
This specification limits thus access to NSH-supplied information
along an SFP to entities that have a need to interpret it.
It is out of the scope of this document to specify an NSH-aware
control plane solution.
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:
SFC data plane element: Refers to NSH-aware SF, SFF, SFC Proxy, or
Classifier as defined in the SFC data plane architecture [RFC7665]
and further refined in [RFC8300].
SFC control element: Is a logical entity that instructs one or more
SFC data plane elements on how to process NSH packets within an
SFC-enabled domain.
Key Identifier: Is used to identify and deliver keys to authorized
entities. See, for example, 'kid' usage in [RFC7635].
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.
NSH imposer: Refers to an 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.
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o Service Path Header: Provides path identification and location
within an SFP.
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 NSH-aware data plane elements on a per SFC/SFP basis. To
that aim:
The Classifier is instructed about the set of context information
to be supplied for a given service function chain.
An NSH-aware SF is instructed 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. For a given service function chain, the NSH-aware SF is
also provided with an order for consuming a set of contexts
supplied in a packet.
An NSH-aware SF can also be instructed about the behavior it
should adopt after consuming context information that was supplied
in the NSH. For example, the context information 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 NSH-unaware SF (e.g., the context information 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 NSH-
unaware SF.
In reference to Figure 1,
o Classifiers, NSH-aware SFs, and SFC proxies are entitled to update
the Context Header(s).
o Only NSH-aware SFs and SFC proxies are entitled to update the
Service Path Header.
o SFFs are entitled to modify the Base 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, NSH-aware SFs, and SFC proxies MUST be able to
encrypt and decrypt a given Context Header.
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o Both encrypted and unencrypted Context Headers MAY be included in
the same NSH. That is, some Context Headers may be protected
while others do not need to be protected.
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 9.1.
+----------------+-----------------------------+-------------------+
| | 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, NSH-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 |
| NSH-aware SF | No | Yes |
| SFC Proxy | No | Yes |
| NSH-unaware SF | No | No |
+-----------------+------------------------------+------------------+
Table 1: Encryption Function Supported by SFC Data Plane Elements
Classifier(s), NSH-aware SFs, and SFC proxies are instructed with the
set of Context Headers (privacy-sensitive metadata, typically) that
must be encrypted. Encryption keying material is only provided to
these SFC data plane elements.
The control plane may 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.
The 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 NSH-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
The 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 NSH-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 NSH-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) |
| NSH-aware SF | Yes |
| SFC Proxy | Yes |
| NSH-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 protect the integrity of the NSH data.
The advantage of using the authenticated encryption algorithm is that
NSH-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 NSH-
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, NSH-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, NSH-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.
Note: The use of Advanced Encryption Standard (AES) in Galois/
Counter Mode (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 document 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 a certain amount of time, this document uses key identifiers to
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unambiguously identify the appropriate keying material. Doing so
allows to address the problem of synchronization of keying material.
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 NSH-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 include 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 Figure 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 (Variable) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: MAC and Encrypted Metadata Context Header
The "MAC and Encrypted Metadata" Context Headers are padded out to a
multiple of 4 bytes as per Section 2.2 of [RFC8300].
5.1. MAC#1 Context Header
MAC#1 Context Header is a variable-length Context Header 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 Context Header 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 9.1 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 (Variable) ~ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
~ Timestamp (8 bytes) ~ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| IV Length | Initialization Vector (Variable) ~ |
+->+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| ~ Encrypted Context Headers (opt.) ~ |
+->+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| ~ Message Authentication Code ~ |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | | |
| ~ 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:
Metadata Class: MUST be set to 0x0 (Section 2.5.1 of [RFC8300]).
Type: TBD1 (See Section 10)
U: Unassigned bit (Section 2.5.1 of [RFC8300]).
Length: Variable. Padding considerations are discussed in
Section 2.5.1 of [RFC8300].
Key Length: Variable. Carries the length of the key identifier.
Key Identifier: Carries a variable-length Key Identifier object used
to identify and deliver keys to SFC data plane elements. This
identifier is helpful to accommodate deployments relying upon
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keying material per SFC/SFP. The key identifier helps in
resolving the problem of synchronization of keying material.
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.
IV Length: Carries the length of the IV (Section 5.2 of [RFC7518]).
If encryption is not used, IV length is set to zero (that is, no
"Initialization Vector" is included).
Initialization Vector: Carries the IV for authenticated encryption
algorithm as discussed in Section 5.2 of [RFC7518].
Encrypted Context Headers: Carries the optional encrypted Context
Headers.
Message Authentication Code: Covers the entire NSH data, excluding
the Base header. 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.
5.2. MAC#2 Context Header
MAC#2 Context Header is a variable-length Context Header 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 Context Header 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 (Variable) ~ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
~ Timestamp (8 bytes) ~ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| IV Length | Initialization Vector (Variable) ~ |
+->+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| ~ Encrypted Context Headers (opt.) ~ |
+->+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| ~ Message Authentication Code ~ |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | | |
| ~ 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:
Metadata Class: MUST be set to 0x0 (Section 2.5.1 of [RFC8300]).
Type: TBD2 (See Section 10)
U: Unassigned bit (Section 2.5.1 of [RFC8300]).
Length: Variable. Padding considerations are discussed in
Section 2.5.1 of [RFC8300].
Key Length: See Section 5.1.
Key Identifier: See Section 5.1.
Timestamp: See Section 6.
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IV Length: See Section 5.1.
Initialization Vector: See Section 5.1.
Encrypted Context Headers: Carries the optional encrypted Context
Headers.
Message Authentication Code: Coves the entire NSH data. 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.
6. Timestamp Format
This section follows the template provided in Section 3 of [RFC8877].
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.
Epoch:
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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 (i.e., to strip the entire NSH, including Context Headers).
Failures of a classifier to inject the Context Headers defined in
this document SHOULD be logged locally while a notification alarm MAY
be sent to an SFC control element. Failures of an NSH-aware node 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. The details of sending notification alarms (i.e., the
parameters affecting the transmission of the notification alarms
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depend on the information in the context header such as frequency,
thresholds, and content in the alarm) SHOULD be configurable.
NSH-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 NSH-aware nodes is to maintain such Context
Headers so that the information can be passed to next NSH-aware hops.
NSH-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 NSH-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 NSH-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
plane 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 8.
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.
The Message Authentication Code (T) computation process can be
illustrated as follows:
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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 (Sections 6 and 7).
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, for example, in 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 Context Header carrying a privacy-
sensitive 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
Note that "||" denotes the concatenation of two values.
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 NSH-aware SF or SFC Proxy that only has access to the
MAC_KEY, but not the ENC_KEY, computes the message Authentication Tag
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(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 NSH-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 Timestamp imposed by an initial Classifier is left untouched
along an SFP. However, it can be updated when reclassification
occurs (Section 4.8 of [RFC7665]). The same considerations for
setting the Timestamp are followed in both initial classification and
reclassification (Section 6).
The received NSH is accepted by an NSH-aware node 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 Delta interval is a configurable parameter. The default value
for the allowed Delta is 2 seconds. Special care should be taken
when setting very low Delta values as this may lead to dropping
legitimate traffic. If the timestamp is not within the boundaries,
then the SFC data plane element receiving such packet MUST discard
the NSH message.
Replay attacks within the Delta window may be detected by an NSH-
aware node by recording a unique value derived, for example, from the
NSH data and Original packet (e.g., using SHA2). Such NSH-aware node
will detect and reject duplicates. If for legitimate service
reasons, some flows have to be duplicated but still share portion of
an SFP with the original flow, legitimate duplicate packets will be
tagged by NSH-aware nodes involved in that segment as replay packets
unless sufficient entropy is added to the duplicate packet.
Note: Within the timestamp delta window, defining a sequence
number to protect against replay attacks may be considered. In
such mode, NSH-aware nodes must discard packets with duplicate
sequence numbers within the timestamp delta window. However, in
deployments with several instances of the same SF (e.g., cluster
or load-balanced SFs), a mechanism to coordinate among those
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instances to discard duplicate sequence numbers is required.
Because the coordination mechanism to comply with this requirement
is service-specific, this document does not include this
protection.
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 successfully passed, the SFC data plane
element proceeds 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 NSH-
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. MTU Considerations
The SFC architecture prescribes that additional information be added
to packets to:
o Identify SFPs: this is typically the NSH Base Header and Service
Path Header.
o Carry metadata such as those defined in Section 5.
o Steer the traffic along the SFPs: transport encapsulation.
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This added information increases the size of the packet to be carried
along an SFP.
Aligned with Section 5 of [RFC8300], it is RECOMMENDED for network
operators to increase the underlying MTU so that NSH traffic is
forwarded within an SFC-enabled domain without fragmentation. The
available underlying MTU should be taken into account by network
operators when providing SFs with the required Context Headers to be
injected per SFP and the size of the data to be carried in these
Context Headers.
If the underlying MTU cannot be increased to accommodate the NSH
overhead, network operators may rely upon a transport encapsulation
protocol with the required fragmentation handling. The impact of
activating such feature on SFFs should be carefully assessed by
network operators (Section 5.6 of [RFC7665]).
When dealing with MTU issues, network operators should consider the
limitations of various transport encapsulations such as those
discussed in [I-D.ietf-intarea-tunnels].
9. Security Considerations
Data plane SFC-related security considerations, including privacy,
are discussed in Section 6 of [RFC7665] and Section 8 of [RFC8300].
In particular, Section 8.2.2 of [RFC8300] states that attached
metadata (i.e., Context Headers) should be limited to that necessary
for correct operation of the SFP. Also, that section indicates that
[RFC8165] discusses metadata considerations that operators can take
into account when using NSH.
The guidelines for cryptographic key management are discussed in
[RFC4107].
The interaction between the SFC 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 NSH-aware nodes SHOULD have the control plane
distribute a new key identifier and associated keying material so
that when the secret key is expired, those nodes are prepared with
the 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 and associated keying material be distributed by the
control plane well prior to the secret key expiration time.
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NSH data are exposed to several threats:
o A man-in-the-middle attacker modifying the NSH data.
o Attacker spoofing the NSH data.
o Attacker capturing and replaying the NSH data.
o Data carried in Context Headers revealing privacy-sensitive
information to attackers.
o Attacker replacing the packet on which the NSH is imposed with a
bogus packet.
In an SFC-enabled domain where the above attacks are possible, (1)
NSH data MUST be integrity-protected and replay-protected, and (2)
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
Sections 9.1 and 9.2.
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 the 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.
Some events are logged locally with notification alerts sent by NSH-
aware nodes to a Control Element. These events SHOULD be rate-
limited.
The solution specified in this document does not provide data origin
authentication.
In order to detect compromised nodes, it is assumed that appropriate
mechanisms to monitor and audit an SFC-enabled domain to detect
misbehavior and to deter misuse are in place. Compromised nodes can
thus be withdrawn from active service function chains using
appropriate control plane mechanisms.
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9.1. 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 NSH-aware SFs in the SFC-enabled domain
should be able to update the integrity protected NSH data.
Similarly, no device other than the NSH-aware SFs and SFC proxies in
the SFC-enabled domain should be able to decrypt and update the
Context Headers carrying privacy-sensitive metadata. In other words,
if the NSH-aware SFs and SFC proxies in the SFC-enabled domain are
considered fully trusted to act on the NSH data, only these elements
can have access to privacy-sensitive NSH metadata and the keying
material used to integrity protect NSH data and encrypt Context
Headers.
9.2. 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 (see Section 7.1).
9.3. Time Synchronization
Section 5.6 of [RFC8633] describes best current practices to be
considered in deployments where SFC data plane elements use NTP for
time synchronization purposes.
Also, a mechanism to provide cryptographic security for NTP is
specified in [RFC8915].
10. 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] |
+-------+-------------------------------+----------------+
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11. 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, Diego Lopez, Greg Mirsky, and Dhruv Dhody
for the comments.
Many thanks to Steve Hanna for the valuable security directorate
review.
Thanks to Greg Mirsky for the Shepherd review.
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,
<https://www.rfc-editor.org/info/rfc2119>.
[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>.
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[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>.
12.2. 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-04 (work in progress), July 2020.
[I-D.ietf-intarea-tunnels]
Touch, J. and M. Townsley, "IP Tunnels in the Internet
Architecture", draft-ietf-intarea-tunnels-10 (work in
progress), September 2019.
[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.
[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>.
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[RFC8165] Hardie, T., "Design Considerations for Metadata
Insertion", RFC 8165, DOI 10.17487/RFC8165, May 2017,
<https://www.rfc-editor.org/info/rfc8165>.
[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>.
[RFC8633] Reilly, D., Stenn, H., and D. Sibold, "Network Time
Protocol Best Current Practices", BCP 223, RFC 8633,
DOI 10.17487/RFC8633, July 2019,
<https://www.rfc-editor.org/info/rfc8633>.
[RFC8877] Mizrahi, T., Fabini, J., and A. Morton, "Guidelines for
Defining Packet Timestamps", RFC 8877,
DOI 10.17487/RFC8877, September 2020,
<https://www.rfc-editor.org/info/rfc8877>.
[RFC8915] Franke, D., Sibold, D., Teichel, K., Dansarie, M., and R.
Sundblad, "Network Time Security for the Network Time
Protocol", RFC 8915, DOI 10.17487/RFC8915, September 2020,
<https://www.rfc-editor.org/info/rfc8915>.
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
Dan Wing
Citrix Systems, Inc.
USA
Email: dwing-ietf@fuggles.com
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