Extension for protecting (D)TLS handshakes against Denial of Service
draft-tiloca-tls-dos-handshake-02

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TLS Working Group                                              M. Tiloca
Internet-Draft                                                  L. Seitz
Intended status: Standards Track                            RISE SICS AB
Expires: September 6, 2018                                      M. Hoeve
                                                                    ENCS
                                                             O. Bergmann
                                                 Universitaet Bremen TZI
                                                          March 05, 2018

  Extension for protecting (D)TLS handshakes against Denial of Service
                   draft-tiloca-tls-dos-handshake-02

Abstract

   This document describes an extension for TLS and DTLS to protect the
   server from Denial of Service attacks against the handshake protocol,
   carried out by an on-path adversary.  The extension includes a nonce
   and a Message Authentication Code (MAC) over that nonce, encoded as a
   Handshake Token that a Trust Anchor entity computes and provides to
   the client.  The server registered at the Trust Anchor verifies the
   MAC to determine whether continuing or aborting the handshake.

Status of This Memo

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   This document is subject to BCP 78 and the IETF Trust's Legal
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   (https://trustee.ietf.org/license-info) in effect on the date of

Tiloca, et al.          Expires September 6, 2018               [Page 1]
Internet-Draft (D)TLS extension against Denial of Service     March 2018

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  DoS Protection Extension  . . . . . . . . . . . . . . . . . .   4
     2.1.  Extension Type  . . . . . . . . . . . . . . . . . . . . .   4
     2.2.  Extension Data  . . . . . . . . . . . . . . . . . . . . .   4
   3.  Protocol overview . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Client to Trust Anchor  . . . . . . . . . . . . . . . . . . .   6
   5.  Client to Server  . . . . . . . . . . . . . . . . . . . . . .   7
   6.  Server Processing . . . . . . . . . . . . . . . . . . . . . .   8
   7.  Replay Protection . . . . . . . . . . . . . . . . . . . . . .   8
   8.  Session Resumption  . . . . . . . . . . . . . . . . . . . . .  10
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
     9.1.  Security Effectiveness  . . . . . . . . . . . . . . . . .  11
     9.2.  Trust Anchor as Target  . . . . . . . . . . . . . . . . .  12
     9.3.  Renewal of Long-Term Key K_M  . . . . . . . . . . . . . .  12
     9.4.  Rate Limit to Nonce Release . . . . . . . . . . . . . . .  13
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13
   11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  13
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  13
     12.2.  Informative References . . . . . . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

   Servers running TLS [RFC5246][I-D.ietf-tls-tls13] and DTLS
   [RFC6347][I-D.ietf-tls-dtls13] are vulnerable to Denial of Service
   (DoS) attacks during the very first step of the handshake protocol.
   That is, an adversary can repeatedly send ClientHello messages to the
   server and induce it to perform computations and execute handshakes,
   before stopping handshake executions and make the server hold state
   open.

   DTLS 1.2 as well as both TLS 1.3 and DTLS 1.3 provide the optional
   Cookie exchange as possible solution to mitigate this DoS attack.
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