ETSI TS 103 523-3 V1.3.1 (2019-08)

CYBER; Middlebox Security Protocol; Part 3: Enterprise Transport Security

RTS/CYBER-0027-3v131

General Information

• Status: Published
• Publication Date: 04-Aug-2019
• Technical Committee: CYBER - Cyber Security
• Current Stage: 12 - Completion
• Due Date: 15-Aug-2019
• Completion Date: 05-Aug-2019

Standards Content (Sample)

ETSI TS 103 523-3 V1.3.1 (2019-08)






TECHNICAL SPECIFICATION
CYBER;
Middlebox Security Protocol;
Part 3: Enterprise Transport Security

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2 ETSI TS 103 523-3 V1.3.1 (2019-08)



Reference
RTS/CYBER-0027-3v131
Keywords
cyber security
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3 ETSI TS 103 523-3 V1.3.1 (2019-08)
Contents
Intellectual Property Rights . 4
Foreword . 4
Modal verbs terminology . 4
Executive summary . 4
Introduction . 5
1 Scope . 6
2 References . 6
2.1 Normative references . 6
2.2 Informative references . 7
3 Definition of terms, symbols and abbreviations . 7
3.1 Terms . 7
3.2 Symbols . 8
3.3 Abbreviations . 8
4 Enterprise Transport Security for the MSP framework . 8
4.1 MSP requirements mapping . 8
4.2 Enterprise Transport Security architectures . 8
4.2.1 Enterprise Transport Security with enterprise clients and servers . 8
4.2.2 Enterprise Transport Security with enterprise servers . 9
4.2.3 Enterprise Transport Security with enterprise clients . 10
4.3 The Enterprise Transport Security profile . 10
4.3.1 Normal TLS 1.3 Diffie-Hellman key exchange . 10
4.3.2 Enterprise Transport Security Diffie-Hellman key exchange . 11
4.3.3 Visibility information . 11
4.3.4 Directly installed keys . 12
4.3.5 Centrally managed keys . 12
4.3.6 Asymmetric key package . 13
4.3.7 Protecting the key package . 14
4.3.8 Transferring keys . 14
4.3.8.1 Protocol overview . 14
4.3.8.2 Transfer initiated by the key manager . 14
4.3.8.3 Transfer initiated by the key consumer . 15
5 Security. 16
Annex A (normative): Middlebox visibility information variant . 17
Annex B (normative): Requirements for an Enterprise Transport Security aware client . 18
Annex C (informative): Mapping MSP desired capabilities to the Enterprise Transport
Security profile . 19
History . 21


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4 ETSI TS 103 523-3 V1.3.1 (2019-08)
Intellectual Property Rights
Essential patents
IPRs essential or potentially essential to normative deliverables may have been declared to ETSI. The information
pertaining to these essential IPRs, if any, is publicly available for ETSI members and non-members, and can be found
in ETSI SR 000 314: "Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to ETSI in
respect of ETSI standards", which is available from the ETSI Secretariat. Latest updates are available on the ETSI Web
server (https://ipr.etsi.org/).
Pursuant to the ETSI IPR Policy, no investigation, including IPR searches, has been carried out by ETSI. No guarantee
can be given as to the existence of other IPRs not referenced in ETSI SR 000 314 (or the updates on the ETSI Web
server) which are, or may be, or may become, essential to the present document.
Trademarks
The present document may include trademarks and/or tradenames which are asserted and/or registered by their owners.
ETSI claims no ownership of these except for any which are indicated as being the property of ETSI, and conveys no
right to use or reproduce any trademark and/or tradename. Mention of those trademarks in the present document does
not constitute an endorsement by ETSI of products, services or organizations associated with those trademarks.
Foreword
This Technical Specification (TS) has been produced by ETSI Technical Committee Cyber Security (CYBER).
The present document is part 3 of a multi-part deliverable. Full details of the entire series can be found in part 1 [i.1].
Modal verbs terminology
In the present document "shall", "shall not", "should", "should not", "may", "need not", "will", "will not", "can" and
"cannot" are to be interpreted as described in clause 3.2 of the ETSI Drafting Rules (Verbal forms for the expression of
provisions).
"must" and "must not" are NOT allowed in ETSI deliverables except when used in direct citation.
Executive summary
Requirements - such as legal mandates and service agreements - exist for enterprise network and data centre operators
and service providers, organizations, and small businesses to be able to observe and audit the content and metadata of
encrypted sessions transported across their infrastructures [i.2]. The original TLS protocol standards adopted in the
1986-1995 period in multiple bodies and IETF versions up to and including TLS 1.2, provided for these capabilities
[i.3] and [1]. The latest version of the protocol, TLS 1.3, does not provide for these capabilities [2]. Where these
capabilities do not exist, this new encryption protocol could be blocked altogether at the enterprise gateway, forcing
users to revert to older, less secure TLS protocols.
The present document is one of a series of MSP implementation profiles that support these capabilities, while allowing
enterprise operators and users to stay in control of access to their data. It sets forth an MSP profile, "Enterprise
Transport Security", for use in enterprise networks and data centres that meets mandatory capabilities for the Middlebox
Security Protocol (MSP) [i.1].
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5 ETSI TS 103 523-3 V1.3.1 (2019-08)
Introduction
The present document specifies an MSP profile for enterprise network and data centre domains: Enterprise Transport
Security. This is an implementation variant of Transport Layer Security (TLS) protocol version 1.3 [2].
TLS 1.3 is a recent version in a series of TLS protocol standards [i.6] and [i.3]. TLS 1.3 [2] introduces several
significant changes compared with TLS 1.2 [1]. One of these changes is the removal of support for RSA key exchange
and static Diffie-Hellman key exchange. The primary key exchange mechanism in TLS 1.3 is ephemeral
Diffie-Hellman. Ephemeral Diffie-Hellman prevents passive decryption of TLS 1.3 sessions at any scale. However,
there are operational circumstances where passive decryption of TLS sessions by authorized entities is a requirement.
The decryption may need to be performed in real-time, or the packets may need to be stored and decrypted post-capture.
Situations requiring passive decryption of TLS sessions generally occur in environments where both the client and
server, and by inference the data being exchanged over the TLS session, are under the control of the same entity. TLS
encryption is often stipulated by internal or external security policies, but access to the unencrypted packet data is
required for operational reasons, including:
• Application health monitoring and troubleshooting.
• Intrusion detection.
• Detection of malware activity, e.g. lateral movement, command and control, and data exfiltration traffic.
• Detection of advanced Distributed Denial Of Service (DDOS) attacks.
• Compliance audits.
One possible approach to passively decrypting TLS 1.3 sessions is to export the ephemeral keys generated for each TLS
session to middleboxes. However, this approach has several significant limitations. Firstly, it is very difficult to ensure
that the exported ephemeral keys will arrive at the middlebox in sufficient time to allow decryption in real-time.
Secondly, the keys need to be correlated with every stored packet session in anticipation of post-capture decryption. For
these reasons, this approach does not scale to the needs of a data centre.
The Enterprise Transport Security profile therefore uses longer-lived static Diffie-Hellman keys that are re-used across
multiple sessions; enterprises could implement automated key rotation in order to reduce the rotation cycle time. This
ensures that the keys can be distributed to real-time decryption middleboxes in advance, and it greatly reduces the
number of keys to be stored and correlated with packet storage systems.
The Enterprise Transport Security profile also requires the server to report visibility information in its certificate, to
indicate to the client that Transport Layer Security is in use with a particular static Diffie-Hellman public key, and to
describe the set of entities or roles or domains, or any combination of these, for which the policy of the party signing the
certificate allows sharing of the corresponding private key.
There are circumstances in which visibility information is not suitable and in which the client operator has been
informed by other means that connections can be inspected; in such circumstances, annex A can be used. annex A,
which is optional, specifies a variant of the Enterprise Transport Security profile where the visibility information is not
sent.
EXAMPLE: Annex A can be used when the client and server are wholly within a private enterprise network
and the client operator has already been notified by alternative means, such as a condition of
access to the network, that connections can be inspected.
The Enterprise Transport Security profile is compatible with any TLS 1.3 compliant client. Annex B, which is optional,
defines the concept of an "Enterprise Transport Security aware client" whereby a TLS 1.3 client provides additional
capabilities in relation to Enterprise Transport Security visibility.

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1 Scope
The present document specifies the "Enterprise Transport Security" profile to enable secure communication sessions
between network endpoints whilst enabling network operations. The Enterprise Transport Security (ETS) profile
enables use of Transport Layer Security (TLS) version 1.3 [2] in, for example, compliance constrained environments.
The present document describes three Enterprise Transport Security architectures:
• In the first architecture, both the TLS 1.3 client and the Enterprise Transport Security server are located inside
the enterprise.
• In the second architecture, the server is an Enterprise Transport Security server inside the enterprise and the
TLS 1.3 client is external to the enterprise. TLS 1.3 is terminated at the enterprise edge such that Enterprise
Transport Security is used only inside the enterprise.
• In the third architecture, the TLS 1.3 server is external to the enterprise and the TLS 1.3 client is internal to the
enterprise. TLS 1.3 is again terminated at the network edge such that Enterprise Transport Security is used
only inside the enterprise.
The Diffie-Hellman key exchange and visibility information for indicating the Enterprise Transport Security profile
setup is specified.
The actions of the client on receiving the visibility information and structure of the policy included in the visibility
information are not normatively defined; however, capabilities for an "Enterprise Transport Security aware client" are
defined in annex B, which is optional. The means by which the Enterprise Transport Security endpoints share the
Diffie-Hellman key with key consumers is specified, and examples are provided.
The present document describes a variant of the Enterprise Transport Security profile in annex A for circumstances in
which visibility information is not suitable and in which the client operator has been informed by other means that
connections can be inspected. The means by which the client operator is informed is out of scope.
The present document also includes the security assurances made by the Enterprise Transport Security profile, based on
the security assurances of TLS 1.3. Annex C gives details of the MSP profile capabilities that are applicable to the
Enterprise Transport Security profile, taken from the draft specification of ETSI TS 103 523-1 [i.1], such that this MSP
Part may be a standalone document. A final mapping of MSP profile capabilities to the Enterprise Transport Security
profile is left to a future version of the present document.
2 References
2.1 Normative references
References are either specific (identified by date of publication and/or edition number or version number) or
non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the
referenced document (including any amendments) applies.
Referenced documents which are not found to be publicly available in the expected location might be found at
https://docbox.etsi.org/Reference/.
NOTE: While any hyperlinks included in this clause were valid at the time of publication, ETSI cannot guarantee
their long term validity.
The following referenced documents are necessary for the application of the present document.
[1] IETF RFC 5246: "The Transport Layer Security (TLS) Protocol Version 1.2".
[2] IETF RFC 8446: "The Transport Layer Security (TLS) Protocol Version 1.3".
[3] IETF RFC 5958: "Asymmetric Key Packages".
[4] IETF RFC 7906: "NSA's Cryptographic Message Syntax (CMS) Key Management Attributes".
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[5] IETF RFC 3279: "Algorithms and Identifiers for the Internet X.509 Public Key Infrastructure
Certificate and Certificate Revocation List (CRL) Profile".
[6] IETF RFC 5480: "Elliptic Curve Cryptography Subject Public Key Information".
[7] IETF RFC 5915: "Elliptic Curve Private Key Structure".
[8] IETF RFC 5280: "Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation
List (CRL) Profile".
[9] Recommendation ITU-T X.509 (10/2016) | ISO/IEC 9594-8: "Information technology - Open
Systems Interconnection - The Directory: Public-key and attribute certificate frameworks".
[10] IETF RFC 2818: "HTTP Over TLS".
[11] FIPS 180-4: "Secure Hash Standard (SHS)".
[12] IETF RFC 7231: "Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content".
[13] IETF RFC 8551: "Secure/Multipurpose Internet Mail Extensions (S/MIME) Version 4.0 Message
Specification".
2.2 Informative references
References are either specific (identified by date of publication and/or edition number or version number) or
non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the
referenced document (including any amendments) applies.
NOTE: While any hyperlinks included in this clause were valid at the time of publication, ETSI cannot guarantee
their long term validity.
The following referenced documents are not necessary for the application of the present document but they assist the
user with regard to a particular subject area.
[i.1] ETSI TS 103 523-1: "CYBER; Middlebox Security Protocol; Part 1: Capability Requirements".
[i.2] S. Fenter: "Why Enterprises Need Out-of-Band TLS Decryption", IETF, 2018.
[i.3] Recommendation ITU-T X.274 (1994) | ISO/IEC 10736:1995: "Transport Layer Security
Protocol".
[i.4] IETF RFC 5652: "Cryptographic Message Syntax (CMS)".
[i.5] IETF RFC 5083: "Cryptographic Message Syntax (CMS) Authenticated-Enveloped-Data Content
Type".
[i.6] Nelson & Heimann: "SDNS Architecture and End-to-End Encryption", CRYPTO' 89 Proceedings,
pp 356-366; Ruth Nelson, SDNS Services and Architecture, Proceedings of the 10th National
Computer Security Conference, Sept. 1987, pp 153-157.
3 Definition of terms, symbols and abbreviations
3.1 Terms
For the purposes of the present document, the following terms apply:
1-sided: middlebox traffic observability enabled unilaterally by one endpoint such that the other endpoint is not able to
reject or negotiate the traffic observability, other than by ceasing the communication
Enterprise Transport Security (ETS): MSP profile described in the present document that instantiates an Enterprise
Transport Security session
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single-context: access is granted, or not granted, only to the entire data stream, not to portions of the data stream
3.2 Symbols
Void.
3.3 Abbreviations
For the purposes of the present document, the following abbreviations apply:
ASN Abstract Syntax Notation
CMS Cryptographic Message Syntax
DDOS Distributed Denial Of Service
DER Distinguished Encoding Rules
ETS Enterprise Transport Security
FIPS Federal Information Processing Standards
HSM Hardware Security Module
HTTP HyperText Transfer Protocol
HTTPS Hypertext Transfer Protocol Secure
MSP Middlebox Security Protocol
RSA Rivest-Shamir-Adleman
TLS Transport Layer Security
4 Enterprise Transport Security for the MSP framework
4.1 MSP requirements mapping
MSP Part 1 [i.1] defines several Capability Requirements that are demanded of a profile wishing to comply with the
MSP framework. The full and complete mapping of MSP Part 1 [i.1] requirements to the Enterprise Transport Security
profile described in the current document is left to a future revision of the present document when MSP Part 1 [i.1] is
finalized. However, desired capabilities of MSP profiles are mapped to relevant properties of the Enterprise Transport
Security profile in annex C.
For any mapping, an MSP profile needs categorizing as a 1-sided or 2-sided profile with single or fine-grained context,
as defined in the planned MSP Part 1 [i.1]. This categorization determines the mandatory and optional requirements that
the MSP profile needs to satisfy.
Enterprise Transport Security is a 1-sided MSP profile, as only one endpoint will be using a static Diffie-Hellman key,
and so that endpoint unilaterally enables traffic observability. The Enterprise Transport Security profile is also
single-context, as access is granted, or not granted, only to the entire data stream.
4.2 Enterprise Transport Security architectures
4.2.1 Enterprise Transport Security with enterprise clients and servers
Figure 4.1 depicts the Enterprise Transport Security implementation architecture when both the TLS 1.3 [2] client and
the Enterprise Transport Security server are located in the Enterprise.
Middlebox A is authorized to inspect the traffic flowing between the firewall and the web server. It therefore receives a
passive copy of these packets along with a copy of the static Diffie-Hellman public/private key pair (A) used by the web
server.
EXAMPLE 1: Middlebox A decrypts the traffic in real-time to perform intrusion detection.
The web server acts as a TLS client in its connection to the application server. In this case, Middlebox B is authorized
to inspect the traffic flowing between the two servers, and it decrypts the TLS sessions using the application server's
static Diffie-Hellman public/private key pair (B).
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EXAMPLE 2: Middlebox B decrypts the traffic in real-time to provide application health monitoring, but also
stores the encrypted packets so they can be decrypted at a later date for compliance and auditing
purposes.

Figure 4.1: Enterprise Transport Security architecture with enterprise client and server
4.2.2 Enterprise Transport Security with enterprise servers
Figure 4.2 depicts the Enterprise Transport Security implementation architecture when the TLS 1.3 client is outside the
enterprise and the Enterprise Transport Security server is located in the Enterprise. TLS connections to clients that are
external to an enterprise network or data centre may be made using TLS 1.3 [2], using forward secrecy.
The firewall terminates the Internet TLS 1.3 sessions and uses the Enterprise Transport Security profile between the
firewall and the web server, with the firewall acting as the TLS client. Middlebox A is authorized to inspect the traffic
flowing between the firewall and the web server. It therefore receives a passive copy of these packets along with a copy
of the static Diffie-Hellman public/private key pair (A) used by the web server.

Figure 4.2: Enterprise Transport Security architecture with enterprise servers
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4.2.3 Enterprise Transport Security with enterprise clients
Figure 4.3 depicts the Enterprise Transport Security implementation architecture when enterprise clients are used with a
TLS 1.3 server outside the enterprise. TLS connections to servers that are external to an enterprise network may be
made using TLS 1.3 [2], using forward secrecy.

Figure 4.3: Enterprise Transport Security architecture with enterprise clients
The firewall terminates the enterprise network sessions that are using Enterprise Transport Security, with the firewall
acting as the Enterprise Transport Security server. The firewall then acts as the TLS 1.3 client and uses TLS 1.3 to
communicate to the TLS 1.3 server on the external network. Middlebox A is authorized to inspect the traffic flowing
between the client and the firewall. It therefore receives a passive copy of these packets along with a copy of the static
Diffie-Hellman public/private key pair (A) used by the firewall, in its role as the Enterprise Transport Security server.
NOTE: Although the client is participating in an Enterprise Transport Security connection, it is a TLS 1.3
compliant client.
EXAMPLE: Middlebox A decrypts the traffic in real-time to perform malware detection or data loss
prevention.
4.3 The Enterprise Transport Security profile
4.3.1 Normal TLS 1.3 Diffie-Hellman key exchange
For reference, a description of the normal TLS 1.3 Diffie-Hellman key exchange is included. Unless a pre-shared key is
in use, the TLS 1.3 key exchange mechanism proceeds at the start of a new session as follows [2]:
1) The client generates an ephemeral Diffie-Hellman public and private key. The public key is transmitted to the
server in a "key_share" message with a random client nonce.
2) The server generates an ephemeral Diffie-Hellman public and private key. The public key is transmitted to the
client in a "key_share" message with a random server nonce.
3) The client and server each use a combination of their own private keys and the public key received from the
other side of the connection to generate a shared secret.
4) The client and server then use the shared secret along with the initial handshake messages, which include the
nonce, to generate a set of handshake traffic keys for encryption of the remainder of the handshake.
5) During the remainder of the handshake, the server sends its certificate encrypted using a handshake traffic key.
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6) Upon completion of the handshake, the client and server then use the shared secret along with various elements
of the handshake messages, which again include the nonce, to generate a set of application traffic keys for the
session.
7) The application traffic keys are used to encrypt further data exchanged between the client and server.
4.3.2 Enterprise Transport Security Diffie-Hellman key exchange
The Enterprise Transport Security key exchange shall use exactly the same messages and procedures to establish a set
of session keys as a TLS 1.3 ephemeral Diffie-Hellman key exchange, except for two differences [2]:
1) the server shall use a static public/private key pair at Step 2 in clause 4.3.1; and
2) the server's certificate at Step 5 shall contain visibility information as defined in clause 4.3.3 to indicate to the
client that Enterprise Transport Security is in use.
NOTE: Neither the static public key nor the visibility information affects the operation of a TLS 1.3 compliant
client, so an Enterprise Transport Security server is therefore fully interoperable with TLS 1.3 compliant
clients.
The Enterprise Transport Security server shall be provisioned with a static key pai
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