Key encoding for manual typing operations.
draft-haase-psk-encoding-00

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Network Working Group                                           B. Haase
Internet-Draft                          Endress + Hauser Liquid Analysis
Intended status: Informational                             March 9, 2020
Expires: September 10, 2020

               Key encoding for manual typing operations.
                      draft-haase-psk-encoding-00

Abstract

   This document specifies a string encoding of external pre-shared keys
   (PSK) for applications where the key has to be entered manually by
   use of an alphanumeric or numeric keyboard.

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
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   This Internet-Draft will expire on September 10, 2020.

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   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Notation . . . . . . . . . . . . . . . . . . . .   3
   3.  Considered requirement set  . . . . . . . . . . . . . . . . .   3
   4.  Encoding structure  . . . . . . . . . . . . . . . . . . . . .   3
     4.1.  Alphanumeric encoding . . . . . . . . . . . . . . . . . .   4
     4.2.  Numeric encoding  . . . . . . . . . . . . . . . . . . . .   5
   5.  Reference implementation for encoding . . . . . . . . . . . .   5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   7.  Status of this draft  . . . . . . . . . . . . . . . . . . . .   9
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   9.  Normative References  . . . . . . . . . . . . . . . . . . . .  10
   Appendix A.  Test vectors for numeric and alphanumeric encodings   10
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   In some applications pre-shared keys (PSK) are used as primary means
   of authentication, specifically in settings where a public key
   infrastructure is not available.  When PSK are used as root of trust,
   a sufficient entropy of the keying material is crucial because
   otherwise attacks such as offline dictionary attacks could be
   mounted.  Unfortunately, not all users might be aware of the
   corresponding pitfalls and might be tempted to use low entropy
   password strings as PSK.

   The situation is particularly difficult, if no trusted binary machine
   communication interface is available for initially configuring the
   PSK in a device, as might be the case for several classes of wireless
   devices.  In some environments, key material needs to be entered
   manually by use of keyboards or touch screens with limited
   functionality.  On some devices, such as small touch screens, only a
   numerical keypad might be available.

   Manually tying keys should be considered error prone.  Users might
   also not be able to distinguish between authentication failures due
   to unmatching keys and unmatching keys that just result from typing
   errors.  Without guidance and a user-friendly encoding, users might
   be tempted to use short low entropy passwords.  Note that use of low-
   entropy passwords is suitable only for protocols such as password-
   authenticated key exchange (PAKE) but not for the typical protocols
   using pre-shared keys, such as TLS-PSK.  This crucial difference,
   might not be transparent for some end-users.

   This specification aims at addressing this issue by specifying a
   format for PSK key encoding specifically designed for convenient
   manual typing.  Moreover it is assumed that the encoding specified

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