SSLKEYLOGFILE Extension for Encrypted Client Hello (ECH)
draft-ietf-tls-ech-keylogfile-01
| Document | Type | Active Internet-Draft (tls WG) | |
|---|---|---|---|
| Authors | Yaroslav Rosomakho , Hannes Tschofenig | ||
| Last updated | 2024-10-21 | ||
| Replaces | draft-rosomakho-tls-ech-keylogfile | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | Informational | ||
| Formats | |||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | WG Document | |
| Document shepherd | (None) | ||
| IESG | IESG state | I-D Exists | |
| Consensus boilerplate | Unknown | ||
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| Send notices to | (None) |
draft-ietf-tls-ech-keylogfile-01
Transport Layer Security Y. Rosomakho
Internet-Draft Zscaler
Intended status: Informational H. Tschofenig
Expires: 24 April 2025 H-BRS
21 October 2024
SSLKEYLOGFILE Extension for Encrypted Client Hello (ECH)
draft-ietf-tls-ech-keylogfile-01
Abstract
This document specifies an extension to the SSLKEYLOGFILE format to
support the logging of information about Encrypted Client Hello (ECH)
related secrets. Two new labels are introduced, namely ECH_SECRET
and ECH_CONFIG, which log the Hybrid Public Key Encryption (HPKE)-
derived shared secret and the ECHConfig used for the ECH,
respectively.
This extension aims to facilitate debugging of TLS connections
employing ECH.
About This Document
This note is to be removed before publishing as an RFC.
The latest revision of this draft can be found at
https://tlswg.github.io/draft-ietf-tls-ech-keylogfile/draft-ietf-tls-
ech-keylogfile.html. Status information for this document may be
found at https://datatracker.ietf.org/doc/draft-ietf-tls-ech-
keylogfile/.
Discussion of this document takes place on the Transport Layer
Security Working Group mailing list (mailto:tls@ietf.org), which is
archived at https://mailarchive.ietf.org/arch/browse/tls/. Subscribe
at https://www.ietf.org/mailman/listinfo/tls/.
Source for this draft and an issue tracker can be found at
https://github.com/tlswg/draft-ietf-tls-ech-keylogfile.
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 24 April 2025.
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Copyright (c) 2024 IETF Trust and the persons identified as the
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 3
3. SSLKEYLOGFILE Labels for ECH . . . . . . . . . . . . . . . . 3
3.1. ECH_SECRET . . . . . . . . . . . . . . . . . . . . . . . 3
3.2. ECH_CONFIG . . . . . . . . . . . . . . . . . . . . . . . 4
4. Client_random for other TLS 1.3 SSLKEYLOGFILE Entries . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . 4
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
7.1. Normative References . . . . . . . . . . . . . . . . . . 6
7.2. Informative References . . . . . . . . . . . . . . . . . 7
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
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1. Introduction
Debugging protocols with TLS can be difficult due to encrypted
communications. Analyzing these messages in diagnostic and debug
tools requires inspecting the encrypted content. Various TLS
implementations have informally adopted a file format to log the
secret values generated by the TLS key schedule, aiding in this
analysis.
In many implementations, the file that the secrets are logged to is
specified in an environment variable named "SSLKEYLOGFILE".
[I-D.ietf-tls-keylogfile] standardizes this format. With the
introduction of [I-D.ietf-tls-esni] additional secrets are derived
during the handshake to encrypt the ClientHello message using Hybrid
Public Key Encryption (HPKE) [RFC9180]. This document extends the
SSLKEYLOGFILE format to also offer support for the ECH extension to
enable debugging of ECH-enabled connections. The proposed extension
can also be used with all protocols that support ECH, including TLS
1.3 [RFC8446], DTLS 1.3 [RFC9147] and QUIC [RFC9000][RFC9001].
2. Conventions and Definitions
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.
3. SSLKEYLOGFILE Labels for ECH
This document defines two new labels for SSLKEYLOGFILE format:
ECH_SECRET and ECH_CONFIG. The client SHOULD log the labels if it
offered ECH regardless of server acceptance. The server MAY log the
labels only if it successfully decrypted and accepted ECH offered by
the client. The 32-byte random value from the Outer ClientHello
message is used as the client_random value for these log records.
The client MUST NOT log the labels for connections that use the
GREASE ECH extension (see Section 6.2 of [I-D.ietf-tls-esni]).
3.1. ECH_SECRET
This label corresponds to the KEM shared secret derived during the
HPKE key schedule process. Length of the secret is defined by the
KEM negotiated for use with ECH.
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3.2. ECH_CONFIG
This label is used to log the ECHConfig used for construction of the
ECH extension. Note that the value is logged in hexadecimal
representation, similarly to other entries in the SSLKEYLOGFILE.
4. Client_random for other TLS 1.3 SSLKEYLOGFILE Entries
The SSLKEYLOGFILE uses the random value from the ClientHello message
as a "connection identifier". This creates ambiguity since the TLS
handshake with ECH contains two different random values, one in the
Outer ClientHello structure and the second one in the Inner
ClientHello.
The SSLKEYLOGFILE entries corresponding to TLS 1.3 secrets for
connections that successfully negotiated ECH MUST use the random from
the Inner ClientHello structure. In all other cases the random value
from the Outer ClientHello structure MUST be used.
5. Security Considerations
The applicability statement of [I-D.ietf-tls-keylogfile] also applies
to this document: if unauthorized entities gain access to the logged
secrets then the core guarantees that TLS provides are completely
undermined.
This specification extends the SSLKEYLOGFILE specification
[I-D.ietf-tls-keylogfile] and therefore introduces the following
threats:
* Access to the ECH_SECRET record in the SSLKEYLOGFILE allows the
attacker to decrypt the ECH extension and thereby reveal the
content of the ClientHello message, including the payload of the
Server Name Indication (SNI) extension.
* Access to the HPKE-established shared secret introduces a
potential attack surface against the HPKE library since access to
this keying material is normally not available otherwise.
Implementers MUST take measures to prevent unauthorized access to the
SSLKEYLOGFILE text file.
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As per the SSLKEYLOGFILE specification [I-D.ietf-tls-keylogfile],
this extension is intended for use in environments where TLS protects
only test data. While the access it provides to TLS connections can
be valuable for debugging during development, this mechanism MUST NOT
be used in production environments. To minimize the risk of
accidental activation in production, implementers SHOULD incorporate
appropriate compile-time controls.
6. IANA Considerations
IANA is requested to create a new registry "SSLKEYLOGFILE Labels",
within the existing "Transport Layer Security (TLS) Parameters"
registry page. This new registry reserves labels used for
SSLKEYLOGFILE entries. The initial contents of this registry are as
follows.
+===============================+===========+=========================+
|Value |Description|Reference |
+===============================+===========+=========================+
|CLIENT_RANDOM |Master |[I-D.ietf-tls-keylogfile]|
| |secret in | |
| |TLS 1.2 and| |
| |earlier | |
+-------------------------------+-----------+-------------------------+
|CLIENT_EARLY_TRAFFIC_SECRET |Secret for |[I-D.ietf-tls-keylogfile]|
| |client | |
| |early data | |
| |records | |
+-------------------------------+-----------+-------------------------+
|EARLY_EXPORTER_MASTER_SECRET |Early |[I-D.ietf-tls-keylogfile]|
| |exporters | |
| |secret | |
+-------------------------------+-----------+-------------------------+
|CLIENT_HANDSHAKE_TRAFFIC_SECRET|Secret |[I-D.ietf-tls-keylogfile]|
| |protecting | |
| |client | |
| |handshake | |
+-------------------------------+-----------+-------------------------+
|SERVER_HANDSHAKE_TRAFFIC_SECRET|Secret |[I-D.ietf-tls-keylogfile]|
| |protecting | |
| |server | |
| |handshake | |
+-------------------------------+-----------+-------------------------+
|CLIENT_TRAFFIC_SECRET_0 |Secret |[I-D.ietf-tls-keylogfile]|
| |protecting | |
| |client | |
| |records | |
| |post | |
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| |handshake | |
+-------------------------------+-----------+-------------------------+
|SERVER_TRAFFIC_SECRET_0 |Secret |[I-D.ietf-tls-keylogfile]|
| |protecting | |
| |server | |
| |records | |
| |post | |
| |handshake | |
+-------------------------------+-----------+-------------------------+
|EXPORTER_SECRET |Exporter |[I-D.ietf-tls-keylogfile]|
| |secret | |
| |after | |
| |handshake | |
+-------------------------------+-----------+-------------------------+
Table 1
This documents defines two additional labels in Section 3:
* ECH_SECRET, which contains KEM shared secret for the ECH
* ECH_CONFIG, which contains ECHConfig used for construction of the
ECH
New assignments in the "SSLKEYLOGFILE Labels" registry will be
administered by IANA through Expert Review [RFC8126]. Designated
Experts are requested to ensure that defined labels do not overlap in
names or semantics, and have clear definitions.
Registration requests must be sent to the tls@ietf.org mailing list
for review and comment, with an appropriate subject (e.g., "Request
for SSLKEYLOGFILE Label: example").
Within the review period of two weeks, the Designated Experts will
either approve or deny the registration request, communicating this
decision to the review list and IANA. Denials should include an
explanation and, if applicable, suggestions as to how to make the
request successful.
IANA must only accept registry updates from the Designated Experts
and should direct all requests for registration to the TLS mailing
list.
7. References
7.1. Normative References
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[I-D.ietf-tls-esni]
Rescorla, E., Oku, K., Sullivan, N., and C. A. Wood, "TLS
Encrypted Client Hello", Work in Progress, Internet-Draft,
draft-ietf-tls-esni-22, 15 September 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-tls-
esni-22>.
[I-D.ietf-tls-keylogfile]
Thomson, M., "The SSLKEYLOGFILE Format for TLS", Work in
Progress, Internet-Draft, draft-ietf-tls-keylogfile-02, 29
April 2024, <https://datatracker.ietf.org/doc/html/draft-
ietf-tls-keylogfile-02>.
[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/rfc/rfc2119>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/rfc/rfc8126>.
[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/rfc/rfc8174>.
7.2. Informative References
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/rfc/rfc8446>.
[RFC9000] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", RFC 9000,
DOI 10.17487/RFC9000, May 2021,
<https://www.rfc-editor.org/rfc/rfc9000>.
[RFC9001] Thomson, M., Ed. and S. Turner, Ed., "Using TLS to Secure
QUIC", RFC 9001, DOI 10.17487/RFC9001, May 2021,
<https://www.rfc-editor.org/rfc/rfc9001>.
[RFC9147] Rescorla, E., Tschofenig, H., and N. Modadugu, "The
Datagram Transport Layer Security (DTLS) Protocol Version
1.3", RFC 9147, DOI 10.17487/RFC9147, April 2022,
<https://www.rfc-editor.org/rfc/rfc9147>.
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[RFC9180] Barnes, R., Bhargavan, K., Lipp, B., and C. Wood, "Hybrid
Public Key Encryption", RFC 9180, DOI 10.17487/RFC9180,
February 2022, <https://www.rfc-editor.org/rfc/rfc9180>.
Acknowledgments
We would like to thank Stephen Farrell, Rich Salz, Martin Thomson and
Peter Wu for their review comments.
Authors' Addresses
Yaroslav Rosomakho
Zscaler
Email: yrosomakho@zscaler.com
Hannes Tschofenig
University of Applied Sciences Bonn-Rhein-Sieg
Email: Hannes.Tschofenig@gmx.net
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