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Versions: 01 02

JOSE Working Group                                             M. Miller
Internet-Draft                                       Cisco Systems, Inc.
Intended status: Standards Track                       February 21, 2013
Expires: August 25, 2013


    Using JavaScript Object Notation (JSON) Web Encryption (JWE) for
                 Protecting JSON Web Key (JWK) Objects
                 draft-miller-jose-jwe-protected-jwk-01

Abstract

   This document specifies an approach to protecting a private key
   formatted as a JavaScript Syntax Object Notation (JSON) Web Key (JWK)
   object using JSON Web Encryption (JWE).  This document also specifies
   a set of algorithms for protecting such content using password-based
   cryptography.

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 http://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 August 25, 2013.

Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.












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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://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
   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.  Protecting Keys . . . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Details for Private Keys  . . . . . . . . . . . . . . . .   4
     3.2.  Details for Symmetric Keys  . . . . . . . . . . . . . . .   4
   4.  Private Key Example . . . . . . . . . . . . . . . . . . . . .   5
   5.  Symmetric Key Example . . . . . . . . . . . . . . . . . . . .   8
   6.  Using Password-Based Cryptography . . . . . . . . . . . . . .  10
     6.1.  PBKDF2 Key Type . . . . . . . . . . . . . . . . . . . . .  10
       6.1.1.  's' Parameter . . . . . . . . . . . . . . . . . . . .  10
       6.1.2.  'c' Parameter . . . . . . . . . . . . . . . . . . . .  10
       6.1.3.  'hint' Parameter  . . . . . . . . . . . . . . . . . .  10
     6.2.  PBES2 Key Encryption Algorithms . . . . . . . . . . . . .  10
       6.2.1.  PBES2-HS256+A128KW  . . . . . . . . . . . . . . . . .  11
       6.2.2.  PBES2-HS512+A256KW  . . . . . . . . . . . . . . . . .  11
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
     7.1.  JSON Web Key Types Registration . . . . . . . . . . . . .  11
     7.2.  JSON Web Key Parameters Registration  . . . . . . . . . .  12
     7.3.  JSON Web Encryption Algorithms  . . . . . . . . . . . . .  12
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
     8.1.  Re-using Keying Material  . . . . . . . . . . . . . . . .  13
     8.2.  Password Considerations . . . . . . . . . . . . . . . . .  13
   9.  Internationalization Considerations . . . . . . . . . . . . .  13
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  14
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  14
     10.2.  Informative References . . . . . . . . . . . . . . . . .  15
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .  15
   Appendix B.  Document History . . . . . . . . . . . . . . . . . .  15
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  16

1.  Introduction

   There are times when it is necessary to transport a private key,
   whether the private component to an asymmetric cipher key-pair or a
   symmetric cipher key used for encryption or generating a message
   authentication code (MAC), where the transport mechanism might not



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   provide adequate content protection for the key.  For instance, end-
   to-end scenarios where the key holder and key recipient are linked
   through multiple network hops that might or might not employ
   transport layer security (TLS, [RFC5246]), or the key holder an key
   recipient (often the same human being) might exchange a private key
   using physical media such as a USB drive that itself is not
   encrypted.

   This document specifies an approach that uses JavaScript Object
   Notation (JSON) Web Encryption [JWE] to encrypt a private key that is
   formatted as a JSON Web Key [JWK].  While [JWE] provides protection
   of symmetric keys, this key is itself intended for the protection of
   content, not as the content itself.  Further, [JWE] does not itself
   provide protection of an asymmetric private key.

   Ofttimes the transport of private keys involves direct interaction
   with human beings.  In these scenarios the use of a human-
   understandable password or passphrase to protect the private key is
   desirable.  Therefore, this document also specifies and registers JWK
   formats and JWE algorithms based on [RFC2898] to allow for protecting
   content using a password.

2.  Terminology

   This document inherits JSON Web Algorithms (JWA)-related terminology
   from [JWA], JSON Web Encryption (JWE)-related terminology from [JWE],
   JSON Web Key (JWK)-related terminology from [JWK], and password-based
   cryptography-related terminology from [RFC2898].  Security-related
   terms are to be understood in the sense defined in [RFC4949].

   The capitalized 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.  Protecting Keys

   The process for protecting private keys and symmetric keys are
   identical.  The only differences are typically the algorithms used to
   protect the key.

   To protect a private key, the key holder performs the following
   steps:


   1.  Converts the JWK object to a UTF-8 encoded string (K').





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   2.  Performs the message encryption steps from [JWE] to generate the
       JWE header H, JWE Encrypted Key E, JWE Initialization Vector IV,
       JWE Ciphertext C, and JWE Integrity Value I, using the following
       inputs:


       *  The 'alg' property set to the intended key encryption
          algorithm (e.g., "RSA-OAEP", or "PBES2-HS512+A256KW" from
          below).


       *  Keying material appropriate for the selected key encryption
          algorithm (e.g., private key for "RSA-OAEP", or shared
          password, salt, and iteration count for "PBES2-HS512+A256KW").


       *  The 'enc' property set to the intended content encryption
          algorithm (e.g., "A256GCM" or "A256CBC+HS512").


       *  Keying material appropriate for the selected content
          encryption algorithm (e.g., Content Encryption Key and
          Initialization Vector).


       *  K' as the plaintext content to encrypt.

   3.  Serializes to the appropriate format for exchange, such as the
       Compact Serialization documented in [JWE].


3.1.  Details for Private Keys

   Private keys are typically protected using a symmetric key.  This
   symmetric key can be exchanged or determined in various ways, such as
   deriving one from a user-supplied password; the algorithms
   "PBES2-HS256+A128KW" and "PBES2-HS512+A256KW" (defined in
   Section 6.2) enable this.

3.2.  Details for Symmetric Keys

   Symmetric keys are typically protected using public-private key
   pairs.  It is assumed the key holder has the appropriate public
   key(s) for the key recipient(s).

   The process defined herein expects JWK objects.  While more compact
   to simply encrypt the symmetric key directly with a public key, using
   the complete JWE process on complete JWK objects allows additional



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   properties to be protected (e.g., expected lifetime, acceptable uses)
   without exceeding the very restrictive plaintext length limits in
   most public-private key operations (e.g., 234 octects when using the
   "RSA-OAEP" algorithm with a 2048-bit key).

4.  Private Key Example

   NOTE: unless otherwise indicated, all line breaks are included for
   readability.

   The key holder begins with the [JWK] representation of the private
   key (here using a [RFC3447] RSA private key, formatted per [JPSK]):

   {
       "kty":"RSA",
       "kid":"juliet@capulet.lit",
       "n":"ALekPD1kotXZCY_YUz_ITWBZb2nTOw35VvZlnqTiYSeusO58qCtYDz
            ahTEkEcjtduRqfkxJKHYVq9Iro4x1cewXFdJZUuMOQAhoD63AHemXE
            kdPiKqJvkBXDT_Eo4NPOjMKKkFPy2MsJQBmdtVknUvzxEchhYjZ490
            EJTvGJ7OYwrSwkcCxy9D29XxL-OQLkSLlH1XD8kgVmJw8hsb42Bg0j
            PgKlkvcyENmYpYE_hqlJoqYNFzgtAnNtK4C3tspix46R3IgilQG2Of
            i99vpUnmTvjrOlNef2l65PRsPHD1Gl9fyPLCxrkolXbdwvxZ9j2d2f
            Iu-OBTxRhnBtarNls_k",
       "e":"AQAB",
       "d":"GRtbIQmhOZtyszfgKdg4u_N-R_mZGU_9k7JQ_jn1DnfTuMdSNprTea
            STyWfSNkuaAwnOEbIQVy1IQbWVV25NY3ybc_IhUJtfri7bAXYEReWa
            Cl3hdlPKXy9UvqPYGR0kIXTQRqns-dVJ7jahlI7LyckrpTmrM8dWBo
            4_PMaenNnPiQgO0xnuToxutRZJfJvG4Ox4ka3GORQd9CsCZ2vsUDms
            XOfUENOyMqADC6p1M3h33tsurY15k9qMSpG9OX_IJAXmxzAh_tWiZO
            wk2K4yxH9tS3Lq1yX8C1EWmeRDkK2ahecG85-oLKQt5VEpWHKmjOi_
            gJSdSgqcN96X52esAQ",
       "p":"ANq50jleISkjfLEuAoHEBxW7NPF26BQ6irpt7HOIdxkca05kHZdWSv
            bsPjyB30D9BZMV1a8flhPmRG66orx_9ogi1Eu8AJel7wEbdSpCGlMT
            z0mAfcpN9bNEPFCvehN_zqwAwGLQCbPjNycQi3zYKoeehw5xE00IR9
            6wk-U98icL",
       "q":"2a43135aa05479f570676fc36e3d693d0ab21d21e38fdd0be71fcc
            3b3a9800931c2cc66d6d4b702aabd50eaded6c4a3764872885b0ed
            b7a49b7e65b382069ba50c4dc6e069a0e39ffdafc780c5cafe586a
            8a0238cbf92a4b5c18e762308d49f9ae046b27ec98a35878d4a47e
            bf3da9621100798ae1b6d5adc55a8b0915620fa7",
       "dp":"KkMTWqBUefVwZ2_Dbj1pPQqyHSHjj90L5x_MOzqYAJMcLMZtbUtwK
             qvVDq3tbEo3ZIcohbDtt6SbfmWzggabpQxNxuBpoOOf_a_HgMXK_l
             hqigI4y_kqS1wY52IwjUn5rgRrJ-yYo1h41KR-vz2pYhEAeYrhttW
             txVqLCRViD6c",
       "dq":"AvfS0-gRxvn0bwJoMSnFxYcK1WnuEjQFluMGfwGitQBWtfZ1Er7t1
             xDkbN9GQTB9yqpDoYaN06H7CFtrkxhJIBQaj6nkF5KKS3TQtQ5qCz
             kOkmxIe3KRbBymXxkb5qwUpX5ELD5xFc6FeiafWYY63TmmEAu_lRF
             COJ3xDea-ots",



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       "qi":"AJUkIvsPQqclEXjBKz9UbAS5O8DbTr7OREKT6prjL6luezQVHM0nB
             KD8JlKqmm7vVdPj8uHUOe_22qaCkbtUfdG77hZ1Ot0h1hBYJWULyQ
             zHgL5o-LJvhadKGLv53qLYENIc2yOYK8u2o3WMvftpTcf--mgWaDl
             LvRwiflLH0jiP"
   }


   The key holder uses the following [JWE] inputs:


   JWE Header:

   {
     "alg":"PBES2-HS256+A128KW",
     "enc":"A128CBC+HS256",
     "jwk":{
       "kty":"PBKDF2",
       "s":"2WCTcJZ1Rvd_CJuJripQ1w",
       "c":4096
     }
   }



   Password:

   Thus from my lips, by yours, my sin is purged.



   Content Master Key (encoded as base64url per [RFC4648]):

   1ICvnpc3zPRNS7JoJ9bnJ929eX7EnRwmc0CHNOF1zKc



   Initialization Vector (encoded as base64url per [RFC4648]):

   B9BVK3hIsEu9zUOWjKeOSg



   The key holder performs steps 1 and 2 to generate the [JWE] outputs
   (represented using the Compact Serialization):


   eyJhbGciOiJQQkVTMi1IUzI1NitBMTI4S1ciLCJlbmMiOiJBMTI4Q0JDK0hTMjU
   2IiwiandrIjp7Imt0eSI6IlBCS0RGMiIsInNhbHQiOiIyV0NUY0paMVJ2ZF9DSn



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   VKcmlwUTF3IiwiaXRycyI6NDA5Nn19.
   dO4VTHV1JJnnPxbc9xswMA6ezNLCQ1Nq0Bnt4l2hjzxyXfbgM3w-cQ.
   B9BVK3hIsEu9zUOWjKeOSg.
   mUt0YpU0Gsfis7tK70aggz5Qb5J6oppjl7aSn_S4DIHJkSF-Gd9KEu4XF0vbMc1
   kvovNOmnahDLoJIq7hoB666zt1yp4umZKuzhOQ5O3jwOwC4rUf1W3hDM5p2nYZq
   LFqDBme-Z8KVwosfBj2TkZSnFWC6cqMy6d7K6egWz7uct39ZH6_FAUrr0JiMMnj
   0jxTEBP6apiLD-GJutxITnWISmGmX0jOWyTKRh-F-I3lJ3pXE0_4vWR8-gXaFGW
   CgItofAOsdKKoxiSJvXPVxK-oqPFPlS0H5OLHw9tkjmPVZ0Ot-RLgoMPQJ0Yi47
   U0DBh_2-IQBcpPvwBnUzl8KcrLFh-NpTSoC_zIn6xos5r4JVXf5v1V79MKGvk3-
   evdQoEKtS9LnimKTP8YmeqAnU1Y3VoUkgeRTZikKhQ_kwpAxakaRuBzfaIOKjqY
   X5J_jSJuuBQU_4fgHPkvrq1zJ3TnUAWZIqFcw27dKGMxXLMlz_sbW2YerZ0BULc
   xbe8bJpbHkE64r7Nc86iZyL6e-8htkUvpGmdQGqno-q723Ry-u2Iz1-exjgjbNu
   z4tbSrf49Y0_VSFEuHLnCRChVQE8cgupCy8GioEpuC7v1hMNE7JZTVbG3Ud3QzZ
   Webr0sAYjWwqa2ySoJ7AaRfIiVgMdTAS2_gBdbYRSYI2pkQTHpyZ8D_lp5RvYFR
   FNsHWoEToXeL1P_csuKaGsikKbzgXdevrjmCJTOpByGYO5cb2O8xFyYy1VX_pM6
   bxqj5ai8-jyiCoDKvF_40wT_9F6H79UIZtuc3L7r7OxKrmY32LLvfofVRsfdIcK
   AhMvnvOCpzRN3sHiR7iAx1bvaIaz40Mshf8z-__70GEqr5oWxRwyv2uhCiPHtV6
   lBIhCqki6th317-n_lR58LHw894ja0xbOOxUJfZziaG14O9tqjetTSB0JGKXC4S
   ry6zzeyqDwsSpY439Uqn7va_V5ELLfJf9S7fh0AtZS3ogpw4oT-6LbywFPf0jH9
   LgNmatORG_J2wgu8R8QpKogo_WTQK7izHVtEMe1vQQElAy8P2SUjOJiOU6wAW4o
   neU7HUUwD3cvFSn-ykze48FurI5f6DXyPNTVtzaEjBnVVP517bGb_3V_-1SCBdZ
   1f_sYWJ0S8r2u5ccy28CP_7MhZOY8r4oJJn2NmT_jDOllCNtJLKVdKon0QslEER
   GXa8r6Jtp3UbfLVjZQbnFl2mBygH4PoWbyGVxUNDE66mZVKM4Y-6ng5L84PrDt5
   aAQ0HREqjvX4bsQgWyXKq-HRe5DXO2qdoPAIoPGhqOlZz70iYHO5lkX_Oso3eBv
   DCDVbkD7Gr-LZJusrVtA6Hf82YpUUldjyPsD985T2hdcSQMoxol8aWNDL52T4Eo
   FTTLFNG0Xy3qvS79ScgMOSIOE8k_DgzyBrcGJibeeaVKGdbqUQRADaeWO2QM3Rq
   9TOyizLNyyjkJBgecWtIfLAWSTPx7n39zuBhGb5oChAFlR1HqrV76KO22rj08ra
   J_zi8YQpp4qTTXmYwY5sjftE8IDDcLxk6ovvDM7262onZ5CP3GKp09s9dTJZi2L
   tmZ8NAHlJ5Q9v9XMHi0tvLKKlahdcvgnG3sC_gL46osnNE3gBipLe_IQNl0X0zU
   cakwzYtC02JeBbNFQSduY4OBiAAhD2VhyhLMNvGyt9QjntCru1z_gkr1qZR4y5W
   Uec9WtxPqqC-dny-MZOINZd13LdStVY_g0KaAJET0etT4vYZJ6IfqdEXRSKKQKN
   CJpencNhJH99NEumPwY0J8hYGC-KkGb6ZQ0yeQDIpcH2reMS9_DU0JaFtd5BpKm
   pNDAvmekzWv65o6MCzLVN4Wlf4tZ6a7FnLxDg0jQBsPGh3ZKEeGmvxJKSvGK_Or
   5-gXJdMyj1n0bWyex-ZTmtbR3OHKgAlFQUdLuB-47UFS0HtF0Lo1ENPZUoxwFcg
   Uu2Yr30O8vhHLhkRAyAvrFPBHhSqcGr954FeMhMo18dKu3zdykyueIQpLIpU7qN
   btXXSOu1c1rPqBMm3h77iLmNzSByFER32-W7hQwx9-Ikbwy52DaZACpXdyzZOQ2
   PSYEJeuy8CyHap8_Dwucb3CQiqBi-iz25Mmwx8qBjWq3K31W4WeF0heC_rCe6LS
   vOCuHJXpu8Wqa1LeyTbuHyQawH8Aev-MzVLXp0E-WtggfNi-mqcThs25993uveI
   TpmK6lyQu6SX31t6MlQKI_29e46cYRMFhsEZSGM--acnZiryvi39IKsVNtOf33E
   9zlKntRdmMoROenR-q5--9nObKaF81k3Xb-yWNTlQh1ot59rWAeqpPv0uA.
   big8BFT-dXJqoKGScpLk0ssjuyWn7fxDvJc7AN7ONPw










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5.  Symmetric Key Example

   NOTE: unless otherwise indicated, all line breaks are included for
   readability.

   The key holder begins with the [JWK] representation of the symmetric
   key (here using a [AES] 128-bit key, formatted as per [JPSK]):

   {
       "kty":"oct",
       "kid": "b8acba65-8af2-4e93-a8e0-d4abd7f25e52",
       "k": "fKrBr19_ne9Cp3akXGpqgA"
   }


   The key holder uses the following [JWE] inputs:

   JWE Header:

   {
     "alg":"RSA-OAEP",
     "enc":"A128CBC+HS256",
     "jwk":{
       "kty":"RSA",
       "n":"ALekPD1kotXZCY_YUz_ITWBZb2nTOw35VvZlnqTiYSeusO58qCtYDz
            ahTEkEcjtduRqfkxJKHYVq9Iro4x1cewXFdJZUuMOQAhoD63AHemXE
            kdPiKqJvkBXDT_Eo4NPOjMKKkFPy2MsJQBmdtVknUvzxEchhYjZ490
            EJTvGJ7OYwrSwkcCxy9D29XxL-OQLkSLlH1XD8kgVmJw8hsb42Bg0j
            PgKlkvcyENmYpYE_hqlJoqYNFzgtAnNtK4C3tspix46R3IgilQG2Of
            i99vpUnmTvjrOlNef2l65PRsPHD1Gl9fyPLCxrkolXbdwvxZ9j2d2f
            Iu-OBTxRhnBtarNls_k",
       "e":"AQAB"
     }
   }



   Content Master Key (encoded as base64url per [RFC4648]):

   ci5IlLIHnFLn-1lhL5CWOS3DdbXGU-BPuFCrLspXAkA



   Initialization Vector (encoded as base64url per [RFC4648]):

   _dYbckd_xuJUBUNsxkT9yw





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   The key holder performs steps 1 and 2 to generate the [JWE] outputs
   (represented using the Compact Serialization):


   eyJhbGciOiJSU0EtT0FFUCIsImVuYyI6IkExMjhDQkMrSFMyNTYiLCJqd2siOns
   ia3R5IjoiUlNBIiwibiI6IkFMZWtQRDFrb3RYWkNZX1lVel9JVFdCWmIyblRPdz
   M1VnZabG5xVGlZU2V1c081OHFDdFlEemFoVEVrRWNqdGR1UnFma3hKS0hZVnE5S
   XJvNHgxY2V3WEZkSlpVdU1PUUFob0Q2M0FIZW1YRWtkUGlLcUp2a0JYRFRfRW80
   TlBPak1LS2tGUHkyTXNKUUJtZHRWa25Vdnp4RWNoaFlqWjQ5MEVKVHZHSjdPWXd
   yU3drY0N4eTlEMjlYeEwtT1FMa1NMbEgxWEQ4a2dWbUp3OGhzYjQyQmcwalBnS2
   xrdmN5RU5tWXBZRV9ocWxKb3FZTkZ6Z3RBbk50SzRDM3RzcGl4NDZSM0lnaWxRR
   zJPZmk5OXZwVW5tVHZqck9sTmVmMmw2NVBSc1BIRDFHbDlmeVBMQ3hya29sWGJk
   d3Z4WjlqMmQyZkl1LU9CVHhSaG5CdGFyTmxzX2siLCJlIjoiQVFBQiJ9fQ.
   UW26BTjbDGjgQ288JXJpGGpbZVV3WyZYJdm1Fvux8wM_t7bh6UbjbOdYXjL3rzD
   phZteaD-DXiKrdGaVndTMLUmjg78H0R9K2WHxWNhTWiq8iMDGtw6BYnHW_r5DSf
   vhojcDhCCBKWyO-QLXvTO1mfgo6UQwYY32Lvz-IrbxphrfBePsEXVYm75PLIIft
   PnRwN3fWDMkKLCq2AesvWDuRWtKVjsh7uu_AX2ky6dvov2Lw_xMiDshsNz62RES
   bNUW-ylMqNNn_VAYWKHK83k5CZppPlBb_8MDEUBPyGe_NDCa3118eo20tJGMn8v
   XRg8k7D0nJ051hGlzAkMQ0S_x9g.
   _dYbckd_xuJUBUNsxkT9yw.
   QHkwptAlO0Gdo5BrbkaGPSek6wASr-twP8ZQ3YYHOkbRMedtsM0QwpvdnfUXoJL
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6.  Using Password-Based Cryptography

   There are often times when a key is exchanged through immediate human
   interaction.  To help facilitate such exchanges, a number of
   password-based cryptography schemes utilizing [RFC2898] are defined
   to supplement the key format and encryption algorithms from [JWA].

6.1.  PBKDF2 Key Type

   The "PBKDF2" key type is used to contain the parameters necessary to
   derive a cipher key from a password using the PBKDF2 algorithm from
   [RFC2898].  The following parameters are defined:

6.1.1.  's' Parameter

   The REQUIRED "s" parameter contains the PBKDF2 salt value (S), as a
   base64url encoded string (per [RFC4648]).  This value MUST NOT be the
   empty string "".

   The salt expands the possible keys that can be derived from a given
   password.  [RFC2898] originally recommended a minimum salt length of
   8 octets (since there is no concern here of a derived key being re-
   used for different purposes).  The salt MUST be generated randomly;
   see [RFC4086] for considerations on generating random values.

6.1.2.  'c' Parameter

   The REQUIRED "c" parameter contains the PBKDF2 iteration count (c),
   as an integer.  This value MUST NOT be less than 1, as per [RFC2898].

   The iteration count adds computational expense, ideally compounded by
   the possible range of keys introduced by the salt.  [RFC2898]
   originally recommended a minimum iteration count of 1000.

6.1.3.  'hint' Parameter

   The OPTIONAL "hint" parameter contains a description clue to the
   password, as a string.  If present, this value SHOULD NOT be the
   empty string "".

   The hint is typically displayed to the user as a reminder or mnemonic
   for the actual password used.  This parameter MUST NOT contain the
   actual password, and implementations MAY use various heuristic
   algorithms to prohibit hints that are alternate forms of the actual
   password.

6.2.  PBES2 Key Encryption Algorithms




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   The "PBES2-HS256+A128KW" and "PBES2-HS512+A256KW" algorithms defined
   below are used to encrypt a JWE Content Master Key using a user-
   supplied password to derive the key encryption key.  With these
   algorithms, the derived key is used to encrypt the JWE Content Master
   Key.  These algorithms combine a key derivation function with an
   encryption scheme to encrypt the JWE Content Master Key according to
   PBES2 from section 6.2 of [RFC2898].

6.2.1.  PBES2-HS256+A128KW

   The "PBES2-HS256+A128KW" algorithm uses "HMAC-SHA256" as the PRF and
   "AES128-WRAP" as defined in [RFC3394] for the encryption scheme.  The
   salt (S) and iteration count (c) MUST be specified by the "s" and "c"
   parameters (respectively) in the applicable "PBKDF2" JWK object.  The
   derived-key length (dkLen) is 16 octets.

6.2.2.  PBES2-HS512+A256KW

   The "PBES2-HS512+A256KW" algorithm uses "HMAC-SHA512" as the PRF "and
   "AES256-WRAP" as defined in [RFC3394] for the encryption scheme.  The
   salt (S) and iteration count (c) MUST be specified by the "s" and "c"
   parameters (respectively) in the applicable "PBKDF2" JWK object.  The
   derived-key length (dkLen) is 32 octets.

7.  IANA Considerations

7.1.  JSON Web Key Types Registration

   This document registers the following to the JSON Web Key Types
   registry:

   o  "kty" Paramater value: "PBKDF2"


   o  Implementation Requirements: OPTIONAL


   o  Change Controller: IETF


   o  Specification Document(s): Section 6.1 of [[ this document ]]










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7.2.  JSON Web Key Parameters Registration

   This document registers the following to the JSON Web Key Parameters
   registry:

   o  Parameter Name: "s"


   o  Change Controller: IETF


   o  Specification Document(s): Section 6.1.1 of [[ this document ]]


   o  Parameter Name: "c"


   o  Change Controller: IETF


   o  Specification Document(s): Section 6.1.2 of [[ this document ]]


   o  Parameter Name: "hint"


   o  Change Controller: IETF


   o  Specification Document(s): Section 6.1.3 of [[ this document ]]


7.3.  JSON Web Encryption Algorithms

   This document registers the following to the JSON Web Encryption
   Algorithms registry:

   o  Algorithm Name: "PBES2-HS256+A128KW"


   o  Algorithm Usage Location(s): "alg"

   o  Implementation Requirements: OPTIONAL


   o  Change Controller: IETF





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   o  Specification Document(s): Section 6.2.1 of [[ this document ]]


   o  Algorithm Name: "PBES2-HS512+A256KW"


   o  Algorithm Usage Location(s): "alg"

   o  Implementation Requirements: OPTIONAL


   o  Change Controller: IETF


   o  Specification Document(s): Section 6.2.2 of [[ this document ]]


8.  Security Considerations

8.1.  Re-using Keying Material

   It is NOT RECOMMENDED to re-use the same keying material (Key
   Encryption Key, Content Master Key, Initialization Vector, etc) to
   protect multiple JWK objects, or to protect the same JWK object
   multiple times.  One suggestion for preventing re-use is to always
   generate a new set keying material for each protection operation,
   based on the considerations noted in this document as well as from
   [RFC4086].

8.2.  Password Considerations

   While convenient for end users, passwords have many drawbacks.  To
   help mitigate these limitations, this document applies principles
   from [RFC2898] to derive cryptographic keys from user-supplied
   passwords.

   An ideal password is one that is as large (or larger) than the
   derived key length but less than the PRF's block size.  Passwords
   larger than the PRF's block size are first hashed, which reduces an
   attacker's effective search space to the length of the hash algorithm
   (32 octects for HMAC-SHA-256; 64 octets for HMAC-SHA-512).  For
   "PBES2-HS256+A128KW", it is RECOMMENDED that the password be no
   longer than 64 octets long; for "PBES2-HS512+A256KW", it is
   RECOMMENDED that the password be no longer than 128 octets long.

9.  Internationalization Considerations





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   Passwords obtained from users are likely to require preparation and
   normalization to account for differences of octet sequences generated
   by different input devices, locales, etc.  It is RECOMMENDED for
   applications to perform the steps outlined in [SASLPREP] to prepare a
   password supplied directly by a user before performing key derivation
   and encryption.

10.  References

10.1.  Normative References

   [JWA]      Jones, M., "JSON Web Algorithms (JWA)", draft-ietf-jose-
              json-web-algorithms-08 (work in progress), December 2012.

   [JWE]      Jones, M., Rescola, E., and J. Hildebrand, "JSON Web
              Encryption (JWE)", draft-ietf-jose-json-web-encryption-08
              (work in progress), December 2012.

   [JWK]      Jones, M., "JSON Web Key (JWK)", draft-ietf-jose-json-web-
              key-08 (work in progress), December 2012.

   [JPSK]     Jones, M., "JSON Private and Symmetric Key", draft-jones-
              jose-json-private-and-symmetric-key-00 (work in progress),
              December 2012.

   [SASLPREP]
              Saint-Andre, P., "Preparation and Comparison of
              Internationalized Strings Representing Simple User Names
              and Passwords", draft-melnikov-precis-saslprepbis-04 (work
              in progress), September 2012.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2898]  Kaliski, B., "Password-Based Cryptography Specification",
              RFC 2898, September 2000.

   [RFC3394]  Schaad, J. and R. Housley, "Advanced Encryption Standard
              (AES) Key Wrap Algorithm", RFC 3394, September 2002.

   [RFC4086]  Eastlake, D., Schiller, J., and S. Crocker, "Randomness
              Requirements for Security", RFC 4086, June 2005.

   [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 4648, October 2006.

   [RFC4949]  Shirey, R., "Internet Security Glossary, Version 2", RFC
              4949, August 2007.



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10.2.  Informative References

   [AES]      National Institute of Standards and Technology (NIST),
              "Advanced Encryption Standard (AES)", FIPS PUB 197,
              November 2001.

   [RFC3447]  Jonsson, J. and B. Kaliski, "Public-Key Cryptography
              Standards (PKCS) #1: RSA Cryptography Specifications
              Version 2.1", RFC 2898, February 2003.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246, August 2008.

Appendix A.  Acknowledgements

Appendix B.  Document History

   -01  Incorporated changes suggested by Jim Schaad:


      *  Expanded the acronym "JSON" on first use.

      *  Expanded the introduction to explain how this document's
         protection of symmetric keys differs from [JWE].

      *  Expanded the introduction to better explain why password-based
         encryption algorithms are needed.

      *  Moved information on PBKDF2 salt from the security
         considerations to the "s" JWK parameter definition.

      *  Moved information on PBKDF2 iteration count from security
         considerations to the "c" JWK parameter definition.

      *  Added the "hint" JWK parameter.

      *  Explicitly noted what registries are updated by the IANA
         considerations.

      *  Relaxed language around re-use of keying material.

      *  Removed section discussing protected key lifetimes.

      *  Improved recommendations around password lengths.

   -00  Initial revision





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Author's Address

   Matthew Miller
   Cisco Systems, Inc.
   1899 Wynkoop Street, Suite 600
   Denver, CO  80202
   USA

   Phone: +1-303-308-3204
   Email: mamille2@cisco.com








































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