Recommendations for Secure Use of Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS)
draft-ietf-uta-rfc7525bis-00
UTA Working Group Y. Sheffer
Internet-Draft Intuit
Obsoletes: 7525 (if approved) R. Holz
Intended status: Best Current Practice University of Twente
Expires: May 3, 2021 P. Saint-Andre
Mozilla
October 30, 2020
Recommendations for Secure Use of Transport Layer Security (TLS) and
Datagram Transport Layer Security (DTLS)
draft-ietf-uta-rfc7525bis-00
Abstract
Transport Layer Security (TLS) and Datagram Transport Layer Security
(DTLS) are widely used to protect data exchanged over application
protocols such as HTTP, SMTP, IMAP, POP, SIP, and XMPP. Over the
last few years, several serious attacks on TLS have emerged,
including attacks on its most commonly used cipher suites and their
modes of operation. This document provides recommendations for
improving the security of deployed services that use TLS and DTLS.
The recommendations are applicable to the majority of use cases.
This document was published as RFC 7525 when the industry was in the
midst of its transition to TLS 1.2. Years later this transition is
largely complete and TLS 1.3 is widely available. Given the new
environment, we believe new guidance is needed.
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 May 3, 2021.
Sheffer, et al. Expires May 3, 2021 [Page 1]
Internet-Draft TLS Recommendations October 2020
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. General Recommendations . . . . . . . . . . . . . . . . . . . 4
3.1. Protocol Versions . . . . . . . . . . . . . . . . . . . . 4
3.1.1. SSL/TLS Protocol Versions . . . . . . . . . . . . . . 4
3.1.2. DTLS Protocol Versions . . . . . . . . . . . . . . . 6
3.1.3. Fallback to Lower Versions . . . . . . . . . . . . . 6
3.2. Strict TLS . . . . . . . . . . . . . . . . . . . . . . . 7
3.3. Compression . . . . . . . . . . . . . . . . . . . . . . . 7
3.4. TLS Session Resumption . . . . . . . . . . . . . . . . . 8
3.5. TLS Renegotiation . . . . . . . . . . . . . . . . . . . . 8
3.6. Server Name Indication . . . . . . . . . . . . . . . . . 9
4. Recommendations: Cipher Suites . . . . . . . . . . . . . . . 9
4.1. General Guidelines . . . . . . . . . . . . . . . . . . . 9
4.2. Recommended Cipher Suites . . . . . . . . . . . . . . . . 11
4.2.1. Implementation Details . . . . . . . . . . . . . . . 11
4.3. Public Key Length . . . . . . . . . . . . . . . . . . . . 12
4.4. Modular Exponential vs. Elliptic Curve DH Cipher Suites . 13
4.5. Truncated HMAC . . . . . . . . . . . . . . . . . . . . . 14
5. Applicability Statement . . . . . . . . . . . . . . . . . . . 14
5.1. Security Services . . . . . . . . . . . . . . . . . . . . 15
5.2. Opportunistic Security . . . . . . . . . . . . . . . . . 16
6. Security Considerations . . . . . . . . . . . . . . . . . . . 16
6.1. AES-GCM . . . . . . . . . . . . . . . . . . . . . . . . . 17
6.2. Forward Secrecy . . . . . . . . . . . . . . . . . . . . . 17
6.3. Diffie-Hellman Exponent Reuse . . . . . . . . . . . . . . 18
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