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TLS                                                        N. Cam-Winget
Internet-Draft                                             Cisco Systems
Intended status: Informational                                 J. Visoky
Expires: December 30, 2018                                          ODVA
                                                           June 28, 2018


         TLS 1.3 Authentication and Integrity only Ciphersuites
              draft-camwinget-tls-ts13-macciphersuites-00

Abstract

   There are use cases, specifically in Internet of Things (IoT) and
   constrained environments that do not require confidentiality, though
   mutual authentication during tunnel establishment and message
   integrity is still mandated.  This document defines the use of HMAC
   only as ciphersuites in 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 December 30, 2018.

Copyright Notice

   Copyright (c) 2018 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




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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Applicability Statement . . . . . . . . . . . . . . . . . . .   3
   4.  Using Integrity only Cipher Suites  . . . . . . . . . . . . .   4
   5.  Record Payload Protection for Integrity only Cipher Suites  .   4
   6.  Key Schedule when using Integrity only Cipher Suites  . . . .   5
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   8.  Security and Privacy Considerations . . . . . . . . . . . . .   5
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     10.1.  Normative References . . . . . . . . . . . . . . . . . .   6
     10.2.  Informative Reference  . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   There are several use cases in which communications privacy is not
   strictly needed, although authenticity of the communications
   transport is still very important.  For example, within the
   Industrial Automation space there could be TCP or UDP communications
   which command a robotic arm to move a certain distance at a certain
   speed.  Without authenticity guarantees an attacker could modify the
   packets to change the movement of the robotic arm, potentially
   causing physical damage.  However, the motion control commands are
   not considered to be sensitive information and thus there is no
   requirement to provide confidentiality.  Another IoT example with no
   strong requirement for confidentiality is the reporting of weather
   information; however, message authenticity is required to ensure
   integrity of the message..

   Besides having a strong need for authenticity and a weak need for
   confidentiality, many of these systems also have serious latency
   requirements.  Furthermore, several IoT devices (industrial or
   otherwise) have limited processing capability.  However, these IoT
   systems still gain great benefit from leveraging TLS 1.3 for secure
   communications.  Given the reduced need for confidentiality TLS 1.3
   [I-D.ietf-tls-tls13] cipher suites that maintain data integrity
   without confidentiality are described in this document.








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2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

3.  Applicability Statement

   The ciphersuites defined in this document are intended for a small
   limited set of applications where confidentiality requirements are
   relaxed and the need to minimize the cryptographic algorithms are
   prioritized.  This section describes some of those applicable use
   cases.

   Use cases in the industrial automation industry, while requiring data
   integrity, relax the confidential communications requirement.
   Mainly, information communicated to unmanned machines to execute
   repetitive tasks do not convey private information.  For example,
   there could be a system with a robotic arm that is doing high speed
   pick-and-place of materials.  The position synchronization data and
   motion commands are required to have very low latency, as the process
   needs to be done at high speed on a compute and memory constrained
   device.  However, information such as the position, speed,
   acceleration of the robotic arm or other material in the system is
   not confidential.  That is, while an attacker can determine the
   behavioral aspects and task of the device; no intellectual property
   concerns or data privacy concerns exist for these communications.
   However, data integrity is required as being able to modify this data
   would be a threat that an attacker might seek to exploit with serious
   consequences; the attacker could modify the motion information in
   order to cause physical damage to the equipment.

   Another use case which is closely related is that of fine grained
   time updates.  Motion systems often rely on time synchronization to
   ensure proper execution.  Time updates are essentially public, there
   is no threat from an attacker knowing the time update information.
   This should make intuitive sense to those not familiar with these
   applications; rarely if ever does time information present a serious
   attack surface dealing with privacy.  However the authenticity is
   still quite important.  Modification of the data can at best lead to
   a denial-of-service attack, although a more intelligent threat actor
   might be able to cause actual physical damage.  As these time
   synchronization updates are very fine-grained, it is again important
   for latency to be very low.

   A third use case deals with Alarming data.  Industrial control
   sensing equipment can be configured to send alarm information when it
   meets certain conditions.  Often times this data is used to detect



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   certain out-of-tolerance conditions, allowing an operator or
   automated system to take corrective action.  Once again, in many
   systems the reading of this data doesn't grant the attacker
   information that can be exploited, it is generally just information
   regarding the physical state of the system.  At the same time, being
   able to modify this data would allow an attacker to either trigger
   alarms falsely or to cover up evidence of an attack that might allow
   for detection of their malicious activity.  Furthermore, sensors are
   often low powered devices that might struggle to process encrypted
   and authenticated data.  Sending data that is just authenticated
   significantly eases the burden placed on these devices, yet still
   allows the data to be protected against any tampering threats.

   The above use cases describe the relaxed requirements to provide
   confidentiality, and as these devices come with a small runtime
   memory footprint, the need to minimize the number of cryptographic
   algorithms used is prioritized.

4.  Using Integrity only Cipher Suites

   This document defines the following cipher suites for use in TLS 1.3:

   TLS_SHA256_SHA256  {0x13, TBD}

   TLS_SHA384_SHA384  {0x13, TBD}

   These cipher suites allow the use of SHA-256 or SHA-384 as the HMACs
   for data integrity protection as well as its use for HKDF.  The
   authentication mechanisms remain unchanged with the intent to only
   update the cipher suites to relax the need for confidentiality.

5.  Record Payload Protection for Integrity only Cipher Suites

   The record payload protection as defined in [I-D.ietf-tls-tls13] can
   be retained when integrity only cipher suites are used.  This section
   describes the mapping of record payload structures when integrity
   only cipher suites are employed.

   As integrity is provided with protection over the full record, the
   encrypted_record in the TLSCiphertext along with the additional_data
   input to AEADEncrypted as defined in Section 5.2 [I-D.ietf-tls-tls13]
   remains the same.  The TLSCiphertext.length for the integrity cipher
   suites will be:

   TLS_SHA256_SHA256:  TLSPlaintext.length + 32

   TLS_SHA384_SHA384:  TLSPlaintext.length + 64




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   The resulting encrypted_record is the concatenation of the
   TLSPlaintext with the resulting HMAC.  With this mapping, the decrypt
   order as defined in Section 5.2 of [I-D.ietf-tls-tls13] remains the
   same.  The encrypt and decrypt operations provide the integrity
   protection using HMAC SHA-256 or SHA-384 as described in [RFC4634].

6.  Key Schedule when using Integrity only Cipher Suites

   The key derivation process for Integrity only Cipher Suites remains
   the same as defined in [I-D.ietf-tls-tls13].  The only difference is
   that the keys used to protect the tunnel applies to the negotiated
   HMAC SHA-256 or HMAC SHA-384 ciphers.

7.  IANA Considerations

   IANA is requested to register the following:

   This document requests a numbers be assigned for each
   TLS_SHA256_SHA256 and TLS_SHA384_SHA384 cipher suites.

8.  Security and Privacy Considerations

   In general, with the exception of confidentiality and privacy, the
   security considerations detailed in [I-D.ietf-tls-tls13] and in
   [RFC5246] apply to this document.  Furthermore, as the cipher suites
   described in this document do not provide any confidentiality, it is
   important that they only be used in cases where there are no
   confidentiality requirements and concerns; and the runtime memory
   requirements can accommodate support for more cryptographic
   constructs.

   With the lack of data encryption specified in this draft, no
   confidentiality or privacy is provided for the data transported in
   the the TLS tunnel.

9.  Acknowledgements

   The authors would like to acknowledge the work done by Industrial
   Communications Standards Groups (such as ODVA) as the motivation for
   this document.  In addition, we are grateful for the advice and
   feedback from Joe Salowey, Blake Anderson and David McGrew.

10.  References








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10.1.  Normative References

   [I-D.ietf-tls-tls13]
              Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", draft-ietf-tls-tls13-28 (work in progress),
              March 2018.

   [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/info/rfc2119>.

   [RFC4634]  Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms
              (SHA and HMAC-SHA)", RFC 4634, DOI 10.17487/RFC4634, July
              2006, <https://www.rfc-editor.org/info/rfc4634>.

10.2.  Informative Reference

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246,
              DOI 10.17487/RFC5246, August 2008,
              <https://www.rfc-editor.org/info/rfc5246>.

Authors' Addresses

   Nancy Cam-Winget
   Cisco Systems
   3550 Cisco Way
   San Jose, CA  95134
   USA

   Email: ncamwing@cisco.com


   Jack Visoky
   ODVA
   1 Allen Bradley Dr
   Mayfield Heights, OH  44124
   USA

   Email: jmvisoky@ra.rockwell.com










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