Encrypted Server Name Indication for TLS 1.3
draft-ietf-tls-esni-03
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2019-03-11
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draft-rescorla-tls-esni
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tls E. Rescorla
Internet-Draft RTFM, Inc.
Intended status: Experimental K. Oku
Expires: September 12, 2019 Fastly
N. Sullivan
Cloudflare
C. Wood
Apple, Inc.
March 11, 2019
Encrypted Server Name Indication for TLS 1.3
draft-ietf-tls-esni-03
Abstract
This document defines a simple mechanism for encrypting the Server
Name Indication for TLS 1.3.
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 September 12, 2019.
Copyright Notice
Copyright (c) 2019 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 and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
Rescorla, et al. Expires September 12, 2019 [Page 1]
Internet-Draft TLS 1.3 SNI Encryption March 2019
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 4
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Topologies . . . . . . . . . . . . . . . . . . . . . . . 4
3.2. SNI Encryption . . . . . . . . . . . . . . . . . . . . . 5
4. Publishing the SNI Encryption Key in the DNS . . . . . . . . 5
4.1. Encrypted SNI Record . . . . . . . . . . . . . . . . . . 6
4.2. Encrypted SNI DNS Resolution . . . . . . . . . . . . . . 8
4.2.1. Address Set Extension . . . . . . . . . . . . . . . . 8
4.2.2. Resolution Algorithm . . . . . . . . . . . . . . . . 9
5. The "encrypted_server_name" extension . . . . . . . . . . . . 10
5.1. Client Behavior . . . . . . . . . . . . . . . . . . . . . 11
5.1.1. Sending an encrypted SNI . . . . . . . . . . . . . . 11
5.1.2. Handling the server response . . . . . . . . . . . . 13
5.1.3. Verifying against the public name . . . . . . . . . . 15
5.2. Client-Facing Server Behavior . . . . . . . . . . . . . . 16
5.3. Shared Mode Server Behavior . . . . . . . . . . . . . . . 17
5.4. Split Mode Server Behavior . . . . . . . . . . . . . . . 17
6. Compatibility Issues . . . . . . . . . . . . . . . . . . . . 18
6.1. Misconfiguration and Deployment Concerns . . . . . . . . 18
6.2. Middleboxes . . . . . . . . . . . . . . . . . . . . . . . 19
7. Security Considerations . . . . . . . . . . . . . . . . . . . 19
7.1. Why is cleartext DNS OK? . . . . . . . . . . . . . . . . 19
7.2. Comparison Against Criteria . . . . . . . . . . . . . . . 20
7.2.1. Mitigate against replay attacks . . . . . . . . . . . 20
7.2.2. Avoid widely-deployed shared secrets . . . . . . . . 20
7.2.3. Prevent SNI-based DoS attacks . . . . . . . . . . . . 20
7.2.4. Do not stick out . . . . . . . . . . . . . . . . . . 20
7.2.5. Forward secrecy . . . . . . . . . . . . . . . . . . . 20
7.2.6. Proper security context . . . . . . . . . . . . . . . 21
7.2.7. Split server spoofing . . . . . . . . . . . . . . . . 21
7.2.8. Supporting multiple protocols . . . . . . . . . . . . 21
7.3. Misrouting . . . . . . . . . . . . . . . . . . . . . . . 21
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21
8.1. Update of the TLS ExtensionType Registry . . . . . . . . 21
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