SFC
Internet Engineering Task Force (IETF) M. Boucadair
Internet-Draft
Request for Comments: 9145 Orange
Intended status:
Category: Standards Track T. Reddy
Expires: March 24, 2022 Reddy.K
ISSN: 2070-1721 Akamai
D. Wing
Citrix
September 20,
December 2021
Integrity Protection for the Network Service Header (NSH) and Encryption
of Sensitive Context Headers
draft-ietf-sfc-nsh-integrity-09
Abstract
This specification presents an optional method to add integrity
protection directly to the Network Service Header (NSH) used for
Service Function Chaining (SFC). Also, this specification allows for
the encryption of sensitive metadata (MD) that is carried in the NSH.
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https://www.rfc-editor.org/info/rfc9145.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Assumptions and Basic Requirements . . . . . . . . . . . . . 5
4. Design Overview . . . . . . . . . . . . . . . . . . . . . . . 7
4.1. Supported Security Services . . . . . . . . . . . . . . . 7
4.1.1. Encrypt All or a Subset of Context Headers . . . . . 7
4.1.2. Integrity Protection . . . . . . . . . . . . . . . . 8
4.2. One Secret Key, Two Security Services . . . . . . . . . . 10
4.3. Mandatory-to-Implement Authenticated Encryption and HMAC
Algorithms . . . . . . . . . . . . . . . . . . . . . . . 11
4.4. Key Management . . . . . . . . . . . . . . . . . . . . . 11
4.5. New NSH Variable-Length Context Headers . . . . . . . . . 12
4.6. Encapsulation of NSH within NSH . . . . . . . . . . . . . 12
5. New NSH Variable-Length Context Headers . . . . . . . . . . . 13
5.1. MAC#1 Context Header . . . . . . . . . . . . . . . . . . 14
5.2. MAC#2 Context Header . . . . . . . . . . . . . . . . . . 16
6. Timestamp Format . . . . . . . . . . . . . . . . . . . . . . 18
7. Processing Rules . . . . . . . . . . . . . . . . . . . . . . 19
7.1. Generic Behavior . . . . . . . . . . . . . . . . . . . . 19
7.2. MAC NSH Data Generation . . . . . . . . . . . . . . . . . 20
7.3. Encrypted NSH Metadata Generation . . . . . . . . . . . . 21
7.4. Timestamp for Replay Attack Prevention . . . . . . . . . 21
7.5. NSH Data Validation . . . . . . . . . . . . . . . . . . . 22
7.6. Decryption of NSH Metadata . . . . . . . . . . . . . . . 23
8. MTU Considerations . . . . . . . . . . . . . . . . . . . . . 23
9. Security Considerations . . . . . . . . . . . . . . . . . . . 24
9.1. MAC#1 . . . . . . . . . . . . . . . . . . . . . . . . . . 26
9.2. MAC#2 . . . . . . . . . . . . . . . . . . . . . . . . . . 26
9.3. Time Synchronization . . . . . . . . . . . . . . . . . . 26
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 27
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 27
12.1.
11.1. Normative References . . . . . . . . . . . . . . . . . . 27
12.2.
11.2. Informative References . . . . . . . . . . . . . . . . . 28
Acknowledgements
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 30
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
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 logic and control its complexity while optimising optimizing 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 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, forcing a service
topology that requires security and privacy to use a transport
encapsulation that supports such features (Section 8.2 of [RFC8300]).
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 sensitive metadata (e.g., privacy-sensitive
information) will have access to the metadata. As a reminder, the
metadata referred to is 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]
[INTERNET-THREAT-MODEL] for a discussion on the need for more
awareness about attacks from within closed domains.
This specification fills that gap for SFC (that is, it defines the
"NSH Variable Header-Based Integrity" option mentioned in
Section 8.2.1 of [RFC8300]). Concretely, this document adds
integrity protection and optional encryption of sensitive metadata
directly to the NSH (Section 4). The integrity protection covers 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.
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
applicable to NSH MD Type 0x02 (Section 2.5 of [RFC8300]). MTU
considerations are discussed in Section 8. This specification is not
applicable to NSH MD Type 0x01 (Section 2.4 of [RFC8300]) because
that MD Type only allows a Fixed-Length Context Header whose size is
16-bytes;
16 bytes; that is not sufficient to accommodate both the metadata and
message integrity of the NSH data.
This specification limits access to NSH-supplied information along an
SFP to entities that have a need to interpret it.
The mechanism specified in this document does not preclude the use of
transport security. Such considerations are deployment-specific. deployment specific.
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 term "transport encapsulation" used in this document
refers to the outer encapsulation (e.g., Generic Routing
Encapsulation (GRE), IPsec, and Generic Protocol Extension for VXLAN
Virtual eXtensible Local Area Network (VXLAN-GPE)) that is used to
carry NSH-encapsulated packets as per Section 4 of [RFC8300].
The document defines the following terms:
SFC data plane element: Refers to NSH-aware SF, SFF, the SFC Proxy,
or the 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 keys to authorized entities.
See, for example, 'kid' "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.
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 sharing context information (a.k.a., (a.k.a. metadata) with
downstream NSH-aware data plane elements on a per SFC/SFP per-SFC/SFP basis. To
that aim:
* The Classifier is instructed by an SFC control element about the
set of context information to be supplied for a given service
function chain.
* An NSH-aware SF is instructed by an SFC control element 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 by an SFC control element
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 by an SFC control element 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 Table 1,
o 1:
* 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
(Section 4.3 of [RFC7665]).
Thus, the following requirements:
o
* Only Classifiers, NSH-aware SFs, and SFC proxies must be able to
encrypt and decrypt a given Context Header.
o
* Both encrypted and unencrypted Context Headers may be included in
the same NSH.
o
* The solution must provide integrity protection for the Service
Path Header.
o
* The solution must provide optional integrity protection for the
Base Header. The implications of disabling such checks are
discussed in Section 9.1.
+----------------+-----------------------------+-------------------+
+=============+===========================+=======================+
| SFC Data | Insert, remove, or replace | Update the NSH |
| Plane | replace the NSH | |
| Element +========+========+=========+===========+===========+
| | Insert | Remove | SFC Data Plane +---------+---------+---------+---------+---------+
| Element | Replace | Decrement | |Decrement| Update |
| | Insert | Remove | Replace | Service | Context |
| | | | | Index |Header(s)|
+================+=========+=========+=========+=========+=========+ | Header(s) |
+=============+========+========+=========+===========+===========+
| Classifier | + | | + | | + |
+-------------+--------+--------+---------+-----------+-----------+
| Service | | + | | Classifier | |
| Function | | | | |
+----------------+---------+---------+---------+---------+---------+
|Service Function| | +
| Forwarder | | | | | |
|
|Forwarder (SFF) | | | | | |
+----------------+---------+---------+---------+---------+---------+
|Service Function|
+-------------+--------+--------+---------+-----------+-----------+
| Service | | | | + | + |
| Function | | | | | |
| (SF) | | | | | |
+----------------+---------+---------+---------+---------+---------+
+-------------+--------+--------+---------+-----------+-----------+
| Service | + | + | | + | + |
| SFC Function | | | | | |
| Chaining | | | | | |
| (SFC) Proxy | | | | | |
+----------------+---------+---------+---------+---------+---------+
+-------------+--------+--------+---------+-----------+-----------+
Table 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 encrypting all or a subset of NSH Context Headers
by Classifiers, NSH-aware SFs, and SFC proxies.
As depicted in Table 2, SFFs are not involved in data encryption.
+-----------------+------------------------------+------------------+
+====================+=======================+================+
| Data Plane Element | Base and Service Path | Context Header |
| Element | Headers Encryption | Encryption |
+-----------------+------------------------------+------------------+
+====================+=======================+================+
| Classifier | No | Yes |
+--------------------+-----------------------+----------------+
| SFF | No | No |
+--------------------+-----------------------+----------------+
| NSH-aware SF | No | Yes |
+--------------------+-----------------------+----------------+
| SFC Proxy | No | Yes |
+--------------------+-----------------------+----------------+
| NSH-unaware SF | No | No |
+-----------------+------------------------------+------------------+
+--------------------+-----------------------+----------------+
Table 2: 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,
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 the Service Index (SI) in conjunction with the
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 is where all NSH data except the Base
Header are integrity protected (Figure 1). In this case, the NSH
imposer may be a Classifier, an NSH-aware SF, or an SFC Proxy. SFFs
are not provided with authentication material. Further details are
discussed in Section 5.1.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Transport Encapsulation |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...
| Base Header | |
+->+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ N
| | Service Path Header | S
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ H
| | Context Header(s) | |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...
| | Original Packet |
+->+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
+------Scope of integrity protected integrity-protected data
Figure 1: First Level of Assurance
The second level of assurance is where all NSH data, including the
Base Header, are integrity protected (Figure 2). 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 integrity-protected data
Figure 2: Second Level of Assurance
The integrity protection integrity-protection scope is explicitly signaled to NSH-aware
SFs, SFFs, and SFC proxies in the NSH by means of a dedicated MD Type
(Section 5).
In both levels of assurance, the Context Headers and the packet on
which the NSH is imposed are subject to integrity protection.
Table 3 classifies the data plane elements as being involved or not
involved in providing integrity protection for the NSH or not.
+--------------------+----------------------------------+ NSH.
+====================+==================================+
| 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 3: Integrity Protection Supported by SFC Data
Plane Elements
4.2. One Secret Key, Two Security Services
The Authenticated Encryption with Associated Data (AEAD) interface
defined in Section 5 of [RFC5116] is used to encrypt the Context
Headers that carry sensitive metadata and to provide integrity
protection for the encrypted Context Headers.
The secondary keys MAC_KEY "MAC_KEY" and ENC_KEY "ENC_KEY" are generated from the
input secret key (K) as follows; each of these two keys is an octet
string:
MAC_KEY: consists Consists of the initial MAC_KEY_LEN octets of K, in order.
The MAC_KEY is used for calculating the message integrity of the
NSH data. In other words, the integrity protection provided by
the cryptographic mechanism is extended to also provide protection
for the unencrypted Context Headers and the packet on which the
NSH is imposed.
ENC_KEY: consists Consists of the final ENC_KEY_LEN octets of K, in order.
The ENC_KEY is used as the symmetric encryption key for encrypting
the Context Headers.
The Hashed Message Authentication Mode Code (HMAC) algorithm discussed in
[RFC4868] is used to protect the integrity of the NSH data. The
algorithm for implementing and validating HMACs is provided in
[RFC2104].
The advantage of using both AEAD and HMAC algorithms (instead of just
AEAD) is that NSH-aware SFs and SFC proxies only need to re-compute recompute
the message integrity of the NSH data after decrementing the Service
Index (SI) SI and
do not have to re-compute recompute the ciphertext. The other advantage is that
SFFs do not have access to the ENC_KEY and cannot act on the
encrypted Context Headers Headers, and (in the case of the second level of
assurance) SFFs do have access to the MAC_KEY. Similarly, an NSH-aware 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 Mandatory-to-implement authenticated encryption and
HMAC algorithms are listed in Section 4.3.
The authenticated encryption process takes four inputs, each of which
is an octet string: a secret key (ENC_KEY, referred to as K "K" in
[RFC5116]), a plaintext (P), associated data (A) (which contains the
data to be authenticated, authenticated but not encrypted), and a nonce (N). A
ciphertext (C) is generated as an output as discussed in Section 2.1
of [RFC5116].
In order to decrypt and verify, the cipher takes as input ENC_KEY, N, A, and C. C
as input. The output is either the plaintext or an error indicating
that the decryption failed as described in Section 2.2 of [RFC5116].
4.3. Mandatory-to-Implement Authenticated Encryption and HMAC
Algorithms
Classifiers, NSH-aware SFs, and SFC proxies MUST implement the
AES_128_GCM [GCM][RFC5116] algorithm and SHOULD implement the
AES_192_GCM and AES_256_GCM 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 the AES_128_CBC_HMAC_SHA_256 algorithm would have
avoided the need for a second 128-bit authentication tag, but due
to the nature of how Cipher Block Chaining (CBC) mode operates,
AES_128_CBC_HMAC_SHA_256 allows for the malleability of
plaintexts. This malleability allows for attackers that know the MAC
Message Authentication Code (MAC) key but not the encryption key
to make changes in the ciphertext and, if parts of the plaintext
are known, create arbitrary blocks of plaintext. This
specification mandates the use of separate AEAD and MAC
protections to prevent this type of attack.
4.4. Key Management
The procedure for the allocation/provisioning of secret keys (K) and
the 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
unambiguously identify the appropriate keying material and associated
algorithms for MAC and encryption. This use of in-band identifiers
addresses the problem of the 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].
The risk involved in using a group-shared symmetric key increases
with the size of the group to which it is shared. Additional
security issues are discussed in Section 9.
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 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) MAC for the target NSH data (depending on the integrity integrity-
protection scope) calculated using the MAC_KEY and optionally and, optionally, Context
Headers encrypted using ENC_KEY.
An SFC data plane element that needs to check the integrity of the
NSH data uses the 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 Section 3 of [RFC8459], an SFC-enabled domain
(called, (called
an upper-level domain) may be decomposed into many sub-domains
(called,
(called lower-level domains). In order to avoid maintaining state to
restore back upper-level NSH information at the boundaries of lower-level
domains, two NSH levels are used: an Upper-NSH which that 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 3). 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.
+---------------------------------+
| Transport Encapsulation |
+->+---------------------------------+
| | Lower-NSH Header |
| +---------------------------------+
| | Upper-NSH Header |
| +---------------------------------+
| | Original Packet |
+->+---------------------------------+
|
|
+----Scope of NSH security protection
provided by a lower-level domain
Figure 3: 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
Headers that are used for NSH integrity protection and, optionally,
Context Headers Header encryption.
In particular, this section defines two "MAC and Encrypted Metadata"
Context Headers; 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 Headers have the same format
as shown in Figure 4.
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 Id Len | Key Identifier (Variable) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Timestamp (8 bytes) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Nonce Length | Nonce (Variable) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message Authentication Code and optional Encrypted |
~ Context Headers (Variable) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: 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]. The "MAC and
Encrypted Metadata" Context Header, if included, MUST always be the
last Context Header.
5.1. MAC#1 Context Header
The MAC#1 Context Header is a variable-length Variable-Length Context Header that
carries
the Message Authentication Code (MAC) MAC for the Service Path Header, Context Headers, and the
inner packet on which NSH is imposed, calculated using MAC_KEY, and optionally 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 5.
This MAC scheme does not require sharing MAC_KEY with SFFs. It does
not require to re-compute recomputing the MAC by each SFF because of TTL
processing. Section 9.1 discusses the possible threat associated
with this level of assurance.
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 Id Len | Key Identifier (Variable) ~ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
~ Timestamp (8 bytes) ~ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| Nonce Length | Nonce (Variable) ~ |
+->+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| ~ Encrypted Context Headers (opt.) ~ |
+->+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| ~ Message Authentication Code ~ |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | | |
| ~ Inner Packet on which NSH is imposed ~ |
| | | |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<--|
| |
| Integrity Protection Integrity-Protection Scope ----+
+----Encrypted Data
Figure 5: Scope of MAC#1
In reference to Figure 4, the description of the fields is as
follows:
Metadata Class: MUST be set to 0x0 (Section 2.5.1 2.2 of [RFC8300]).
Type: TBD1 (See 0x02 (see Section 10) 10).
U: Unassigned bit (Section 2.5.1 of [RFC8300]).
Length: Indicates the length of the variable-length metadata, metadata in
bytes. Padding considerations are discussed in
Section 2.5.1 of [RFC8300].
Key Id Len: Variable. Carries the length of the key identifier, identifier in
octets.
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 for accommodating deployments
relying upon keying material per SFC/SFP. The key
identifier helps in
resolving to resolve the problem of
synchronization of keying material. A single key
identifier is used to lookup look up both the ENC_KEY and the
MAC_KEY associated with a key, and the corresponding
encryption and MAC algorithms used with those keys.
Timestamp: Refer to Section 6 for more details about the structure
of this field.
Nonce Length: Carries the length of the Nonce. If the Context
Headers are only integrity protected, "Nonce Length" is
set to zero (that is, no "Nonce" is included).
Nonce: Carries the Nonce for the authenticated encryption
operation (Section 3.1 of [RFC5116]).
Encrypted Context Headers: Carries the optional encrypted Context
Headers.
Message Authentication Code: Covers the entire NSH data, excluding
the Base header. Header.
5.2. MAC#2 Context Header
The MAC#2 Context Header is a variable-length Variable-Length Context Header that
carries the MAC for the entire NSH data calculated using MAC_KEY and
optionally and,
optionally, Context Headers encrypted using ENC_KEY. The scope of
the integrity protection provided by this Context Header is depicted
in Figure 6.
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 Id Len | Key Identifier (Variable) ~ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
~ Timestamp (8 bytes) ~ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| Nonce Length | Nonce (Variable) ~ |
+->+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| ~ Encrypted Context Headers (opt.) ~ |
+->+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| ~ Message Authentication Code ~ |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | | |
| ~ Inner Packet on which NSH is imposed ~ |
| | | |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+<--|
| |
| Integrity Protection Integrity-Protection Scope ----+
+----Encrypted Data
Figure 6: Scope of MAC#2
In reference to Figure 4, the description of the fields is as
follows:
Metadata Class: MUST be set to 0x0 (Section 2.5.1 2.2 of [RFC8300]).
Type: TBD2 (See 0x03 (see Section 10) 10).
U: Unassigned bit (Section 2.5.1 of [RFC8300]).
Length: Indicates the length of the variable-length metadata, metadata in
bytes. Padding considerations are discussed in
Section 2.5.1 of [RFC8300].
Key Id Len: See Section 5.1.
Key Identifier: See Section 5.1.
Timestamp: See Section 6.
Nonce Length: See Section 5.1.
Nonce: See Section 5.1.
Encrypted Context Headers: Carries the optional encrypted Context
Headers.
Message Authentication Code: Covers the entire NSH data.
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 7.
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 7: Timestamp Field Format
Timestamp field format:
Seconds: specifies Specifies the integer portion of the number of seconds
since the epoch.
+ Size: 32 bits. bits
+ Units: seconds. Seconds
Fraction: specifies Specifies the fractional portion of the number of
seconds since the epoch.
+ Size: 32 bits. bits
+ Units: the The unit is 2^(-32) seconds, which is roughly equal to
233 picoseconds.
Epoch:
The epoch is 1970-01-01T00:00 in UTC time. Note that this epoch
value is different from the one used in Section 6 of [RFC5905]
(which will wrap around in 2036).
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
this time format is specified in terms of UTC, it is affected by
leap seconds (in a manner analogous to the NTP time format, which
is similar). 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
integrity-protected NSH and optionally and, optionally, encrypted Context Headers.
7.1. Generic Behavior
This document adheres to the recommendations in Section 8.1 of
[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 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 that affect the transmission of the notification alarms
depending on the information in the context header 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 the next NSH-aware
hops. NSH-aware SFs and SFC proxies MUST re-apply reapply the integrity
protection if any modification is made to the Context Headers (e.g.,
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 a "MAC and Encrypted Metadata" Context Header
(Section 5) is allowed in an NSH level. If multiple instances of a
"MAC and Encrypted Metadata" Context Header are included in an NSH
level, the SFC data plane element MUST process the first instance and
ignore subsequent instances, instances and MAY log or increase a counter for
this event as per Section 2.5.1 of [RFC8300]. If NSH-in-NSH NSH within NSH is
used (Section 4.6), distinct LoAs may be used for each NSH level.
MTU and fragmentation considerations are discussed in Section 8.
7.2. MAC NSH Data Generation
After performing any Context Header encryption, 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 sets the MAC field to zero and then computes the
message integrity for the target NSH data (depending on the integrity
protection
integrity-protection scope discussed in Section 5) using the MAC_KEY
and HMAC algorithm. It inserts the computed digest in the MAC field
of 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 for the
target NSH data with HMAC-SHA-256-128() can be illustrated as
follows:
T = HMAC-SHA-256-128(MAC_KEY, target NSH data)
An entity in the SFP that updates 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 sensitive
metadata, i.e., encrypted and unencrypted metadata may be carried
simultaneously in the same NSH packet (Sections 5 and 6).
In order to prevent pervasive monitoring [RFC7258], it is RECOMMENDED
to encrypt all Context Headers. All Context Headers carrying
privacy-sensitive metadata MUST be encrypted; by doing so, privacy-
sensitive metadata is not revealed to attackers. Privacy specific Privacy-specific
threats are discussed in Section 5.2 of [RFC6973].
Using the secret key (ENC_KEY) and authenticated encryption
algorithm, the NSH imposer encrypts the Context Headers (as set, for
example, in Section 3) and inserts the resulting payload in the "MAC
and Encrypted Metadata" Context Header (Section 5). The additional
authenticated data input to the AEAD function is a zero-length byte
string. The entire Context Header carrying a sensitive metadata is
encrypted (that is, including the MD Class, Type, Length, and
associated metadata of each Context Header).
More details about the exact encryption procedure are provided in
Section 2.1 of [RFC5116]. In this case, the associated data (A)
input is zero-length zero length for AES-GCM. AES Galois/Counter Mode (AES-GCM).
An authorized entity in the SFP that updates the content of an
encrypted Context Header or needs to add a new encrypted Context
Header MUST also follow the aforementioned behavior.
7.4. Timestamp for Replay Attack Prevention
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 packets 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 from the packet, for
example, such
as a unique value from the MAC field value. Such an NSH-aware node
will detect and reject duplicates. If for legitimate service
reasons, reasons
some flows have to be duplicated but still share a 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. How such an
entropy is added is implementation-specific. implementation specific.
Note: Within the timestamp delta Delta window, defining a sequence
number to protect against replay attacks may be considered. In
such a mode, NSH-aware nodes must discard packets with duplicate
sequence numbers within the timestamp delta 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
instances to discard duplicate sequence numbers is required.
Because the coordination mechanism to comply with this requirement
is service-specific, 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 that conforms to this specification
needs to check the validity of the NSH data, it MUST ensure that a
"MAC and Encrypted Metadata" Context Header is included in a received
NSH packet. The imposer MUST silently discard the packet and MUST
log an error at least once per the SPI if at least one of the
following is observed:
o
* the "MAC and Encrypted Metadata" Context Header is missing,
o
* the enclosed key identifier is unknown or invalid (e.g., the
corresponding key expired),
o or
* the timestamp is invalid (Section 7.4).
If the timestamp check is successfully passed, the SFC data plane
element proceeds with NSH data integrity validation. After storing
the value of the MAC field in the "MAC and Encrypted Metadata"
Context Header, the SFC data plane element fills the MAC field with
zeros. Then, the SFC data plane element generates the message
integrity for the target NSH data (depending on the integrity integrity-
protection scope discussed in Section 5) using the MAC_KEY and HMAC
algorithm. If the value of the newly generated digest is identical
to the stored one, the SFC data plane element is certain that the NSH
data has not been tampered with and validation is therefore
successful. Otherwise, the NSH packet MUST be discarded. The
comparison of the computed HMAC value to the stored value MUST be
done in a constant-
time constant-time manner to thwart timing attacks.
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 a decryption
algorithm for the key identifier in the NSH.
Authenticated
The 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 2.2 of [RFC5116]).
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 that defined in Section 5.
o
* Steer the traffic along the SFPs: This is realized by means of
transport encapsulation.
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 that 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 features 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 tunnel mechanisms such as those discussed in
[I-D.ietf-intarea-tunnels].
[INTERNET-IP-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 which is
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 group key management protocol related protocol-related security
considerations discussed in Section 8 of [RFC4046] needs need to be taken
into consideration.
The interaction between the SFC data plane elements and a key
management system MUST NOT be transmitted in clear unencrypted since this
would completely destroy the security benefits of the integrity 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. Additional guidance for users of AEAD functions
about rekeying can be found in [I-D.irtf-cfrg-aead-limits]. [AEAD-LIMITS].
The security and integrity of the key-distribution mechanism is vital
to the security of the SFC system as a whole.
NSH data are is exposed to several threats:
o A
* An on-path attacker modifying the NSH data.
o Attacker
* An attacker spoofing the NSH data.
o Attacker
* An attacker capturing and replaying the NSH data.
o
* Data carried in Context Headers revealing privacy-sensitive
information to attackers.
o Attacker
* An attacker replacing the packet on which the NSH is imposed with
a modified or bogus packet.
In an SFC-enabled domain where the above attacks are possible, (1)
NSH data MUST be integrity-protected integrity protected and replay-protected, replay protected, and (2)
privacy-sensitive NSH metadata MUST be encrypted for confidentiality
preservation purposes. The Base and Service Path headers 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] [ARCH-SFC-THREATS] are handled owing to based on the
solution specified in this document, except for with the exception of attacks
dropping packets. Such attacks can be detected by 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 that 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- 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.
9.1. MAC#1
An active attacker can potentially modify the Base header Header (e.g.,
decrement the TTL so the next SFF in the SFP discards the NSH
packet). An active attacker can typically also drop NSH packets. As
such, this attack is not considered an attack against the security
mechanism specified in the document.
It is expected that specific devices in the SFC-enabled domain will
be configured such that no device other than the classifiers Classifiers (when
reclassification is enabled), NSH-aware SFs, and SFC proxies will be
able to update the integrity protected integrity-protected NSH data (Section 7.1), and
also such that no
device other than the NSH-aware SFs and SFC proxies will be able to
decrypt and update the Context Headers carrying sensitive metadata
(Section 7.1). In other words, if it is expected that 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 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. Header. Such messages must be discarded with appropriate
logs and alarms generated (see Section 7.1).
Similar to Section 9.1, 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 sensitive metadata.
9.3. Time Synchronization
[RFC8633] describes best current practices to be considered in
deployments where SFC data plane elements use NTP for time 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 has added the following types from to the "NSH IETF-Assigned Optional
Variable-Length Metadata Types" registry (0x0000 IETF Base NSH MD
Class) registry available at:
https://www.iana.org/assignments/nsh/nsh.xhtml#optional-variable-
length-metadata-types.
+-------+-------------------------------+----------------+ at <https://www.iana.org/assignments/nsh>.
+=======+===============================+===========+
| Value | Description | Reference |
+=======+===============================+================+
+=======+===============================+===========+
| TBD1 0x02 | MAC and Encrypted Metadata #1 | [ThisDocument] RFC 9145 |
+-------+-------------------------------+-----------+
| TBD2 0x03 | MAC and Encrypted Metadata #2 | [ThisDocument] RFC 9145 |
+-------+-------------------------------+----------------+
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 secdir review and Juergen
Schoenwaelder for the opsdir review.
Thanks
+-------+-------------------------------+-----------+
Table 4: Additions to Greg Mirsky for the Shepherd review.
Thanks to Alvaro Retana, Lars Eggert, Martin Duke, Erik Kline,
Zaheduzzaman Sarker, Eric Vyncke, Roman Danyliw, Murray Kucherawy,
John Scudder, and Benjamin Kaduk for the IESG review.
12. NSH IETF-Assigned
Optional Variable-Length Metadata Types Registry
11. References
12.1.
11.1. Normative References
[GCM] Dworkin, M., "Recommendation for Block Cipher Modes of
Operation: Galois/Counter Mode (GCM) and GMAC",
NIST Special Publication 800-38D,
DOI 10.6028/NIST.SP.800-38D, November 2007. 2007,
<https://doi.org/10.6028/NIST.SP.800-38D>.
[RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
Hashing for Message Authentication", RFC 2104,
DOI 10.17487/RFC2104, February 1997,
<https://www.rfc-editor.org/info/rfc2104>.
[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>.
[RFC5116] McGrew, D., "An Interface and Algorithms for Authenticated
Encryption", RFC 5116, DOI 10.17487/RFC5116, January 2008,
<https://www.rfc-editor.org/info/rfc5116>.
[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>.
12.2.
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-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.irtf-cfrg-aead-limits]
Guenther,
[AEAD-LIMITS]
Günther, F., Thomson, M., and C. A. Wood, "Usage Limits on
AEAD Algorithms", draft-irtf-cfrg-aead-limits-03 (work Work in progress), Progress, Internet-Draft, draft-
irtf-cfrg-aead-limits-03, 12 July 2021.
[I-D.nguyen-sfc-security-architecture] 2021,
<https://datatracker.ietf.org/doc/html/draft-irtf-cfrg-
aead-limits-03>.
[ARCH-SFC-THREATS]
THANG, N. C. and M. Park, "A Security Architecture Against
Service Function Chaining Threats", draft-nguyen-sfc-
security-architecture-00 (work Work in progress), Progress,
Internet-Draft, draft-nguyen-sfc-security-architecture-00,
24 November
2019. 2019, <https://datatracker.ietf.org/doc/html/
draft-nguyen-sfc-security-architecture-00>.
[INTERNET-IP-TUNNELS]
Touch, J. and M. Townsley, "IP Tunnels in the Internet
Architecture", Work in Progress, Internet-Draft, draft-
ietf-intarea-tunnels-10, 12 September 2019,
<https://datatracker.ietf.org/doc/html/draft-ietf-intarea-
tunnels-10>.
[INTERNET-THREAT-MODEL]
Arkko, J. and S. Farrell, "Challenges and Changes in the
Internet Threat Model", Work in Progress, Internet-Draft,
draft-arkko-farrell-arch-model-t-04, 13 July 2020,
<https://datatracker.ietf.org/doc/html/draft-arkko-
farrell-arch-model-t-04>.
[RFC4046] Baugher, M., Canetti, R., Dondeti, L., and F. Lindholm,
"Multicast Security (MSEC) Group Key Management
Architecture", RFC 4046, DOI 10.17487/RFC4046, April 2005,
<https://www.rfc-editor.org/info/rfc4046>.
[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>.
[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>.
Acknowledgements
This document was created 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 secdir review and Juergen
Schoenwaelder for the opsdir review.
Thanks to Greg Mirsky for the Shepherd review.
Thanks to Alvaro Retana, Lars Eggert, Martin Duke, Erik Kline,
Zaheduzzaman Sarker, Éric Vyncke, Roman Danyliw, Murray Kucherawy,
John Scudder, and Benjamin Kaduk for the IESG review.
Authors' Addresses
Mohamed Boucadair
Orange
Rennes
35000 Rennes
France
Email: mohamed.boucadair@orange.com
Tirumaleswar Reddy Reddy.K
Akamai
Embassy Golf Link Business Park
Bangalore, Karnataka
Bangalore 560071
Karnataka
India
Email: kondtir@gmail.com
Dan Wing
Citrix Systems, Inc.
USA
United States of America
Email: dwing-ietf@fuggles.com