TLS Encrypted Client Hello
draft-ietf-tls-esni-09
tls E. Rescorla
Internet-Draft RTFM, Inc.
Intended status: Standards Track K. Oku
Expires: 19 June 2021 Fastly
N. Sullivan
C.A. Wood
Cloudflare
16 December 2020
TLS Encrypted Client Hello
draft-ietf-tls-esni-09
Abstract
This document describes a mechanism in Transport Layer Security (TLS)
for encrypting a ClientHello message under a server public key.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 19 June 2021.
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
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Rescorla, et al. Expires 19 June 2021 [Page 1]
Internet-Draft TLS Encrypted Client Hello December 2020
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 4
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Topologies . . . . . . . . . . . . . . . . . . . . . . . 4
3.2. Encrypted ClientHello (ECH) . . . . . . . . . . . . . . . 6
4. Encrypted ClientHello Configuration . . . . . . . . . . . . . 7
4.1. Configuration Extensions . . . . . . . . . . . . . . . . 8
5. The "encrypted_client_hello" Extension . . . . . . . . . . . 9
5.1. Encoding the ClientHelloInner . . . . . . . . . . . . . . 10
5.2. Authenticating the ClientHelloOuter . . . . . . . . . . . 11
6. Client Behavior . . . . . . . . . . . . . . . . . . . . . . . 12
6.1. Offering ECH . . . . . . . . . . . . . . . . . . . . . . 12
6.1.1. ClientHelloInner Indication Extension . . . . . . . . 14
6.1.2. Recommended Padding Scheme . . . . . . . . . . . . . 15
6.1.3. Handling the Server Response . . . . . . . . . . . . 16
6.1.4. Handling HelloRetryRequest . . . . . . . . . . . . . 18
6.2. GREASE ECH . . . . . . . . . . . . . . . . . . . . . . . 19
7. Server Behavior . . . . . . . . . . . . . . . . . . . . . . . 20
7.1. Client-Facing Server . . . . . . . . . . . . . . . . . . 21
7.1.1. Handling HelloRetryRequest . . . . . . . . . . . . . 22
7.2. Backend Server . . . . . . . . . . . . . . . . . . . . . 23
8. Compatibility Issues . . . . . . . . . . . . . . . . . . . . 24
8.1. Misconfiguration and Deployment Concerns . . . . . . . . 24
8.2. Middleboxes . . . . . . . . . . . . . . . . . . . . . . . 25
9. Compliance Requirements . . . . . . . . . . . . . . . . . . . 25
10. Security Considerations . . . . . . . . . . . . . . . . . . . 26
10.1. Security and Privacy Goals . . . . . . . . . . . . . . . 26
10.2. Unauthenticated and Plaintext DNS . . . . . . . . . . . 27
10.3. Client Tracking . . . . . . . . . . . . . . . . . . . . 27
10.4. Optional Configuration Identifiers and Trial
Decryption . . . . . . . . . . . . . . . . . . . . . . 28
10.5. Outer ClientHello . . . . . . . . . . . . . . . . . . . 28
10.6. Related Privacy Leaks . . . . . . . . . . . . . . . . . 29
10.7. Attacks Exploiting Acceptance Confirmation . . . . . . . 30
10.8. Comparison Against Criteria . . . . . . . . . . . . . . 30
10.8.1. Mitigate Cut-and-Paste Attacks . . . . . . . . . . . 30
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