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RFC 8351

The PKCS #8 EncryptedPrivateKeyInfo Media Type

Pages: 7

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Independent Submission                                        S. Leonard
Request for Comments: 8351                                 Penango, Inc.
Category: Informational                                        June 2018
ISSN: 2070-1721

             The PKCS #8 EncryptedPrivateKeyInfo Media Type


This document registers the application/pkcs8-encrypted media type for the EncryptedPrivateKeyInfo type of PKCS #8. An instance of this media type carries a single encrypted private key, BER-encoded as a single EncryptedPrivateKeyInfo value. Status of This Memo This document is not an Internet Standards Track specification; it is published for informational purposes. This is a contribution to the RFC Series, independently of any other RFC stream. The RFC Editor has chosen to publish this document at its discretion and makes no statement about its value for implementation or deployment. Documents approved for publication by the RFC Editor are not candidates for any level of Internet Standard; see Section 2 of RFC 7841. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at 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 ( 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.
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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Registration Application . . . . . . . . . . . . . . . . . . 2 3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 4. Security Considerations . . . . . . . . . . . . . . . . . . . 6 5. Normative References . . . . . . . . . . . . . . . . . . . . 6 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7

1. Introduction

The private key is encrypted with an encryption algorithm, which could be a password-based encryption scheme as that term is used in PKCS #5: Password-Based Cryptography Specification Version 2.1 as published in [RFC2898] and updated by [RFC8018]. This document registers the application/pkcs8-encrypted media type for the EncryptedPrivateKeyInfo type of PKCS #8 (as originally described in [RFC5208], which was obsoleted by [RFC5958]). An instance of this media type carries a single encrypted private key [RFC5958] BER- encoded as a single EncryptedPrivateKeyInfo value.

2. Registration Application

Type name: application Subtype name: pkcs8-encrypted Required parameters: None. Optional parameters: password-mapping: The private key is encrypted with an encryption algorithm, which could be a password-based encryption scheme as that term is used in PKCS #5 ([RFC2898] and [RFC8018]). Such algorithms take a password as input. A "password" is a secret text value (see Section 3 of [RFC2898] and [RFC8018]), but for algorithmic purposes the term "password" refers to an octet string (see Section 2 of [RFC2898] and [RFC8018]). Therefore, there must be some mapping between the text value (which might be user input) and the octet string. Section 3 of [RFC2898] (which was replaced by [RFC8018]) recommends "that applications follow some common text encoding rules"; it then offers, but does not recommend, ASCII and UTF-8.
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        While many modern applications support Unicode and Unicode-based
        encodings such as UTF-8 and UTF-16, interchange is still needed
        with private key artifacts that are encrypted with passwords in
        other encodings.  Therefore, this parameter specifies the
        charset (see Section 1.3 of [RFC2978]) that a recipient should
        attempt first, in "reverse", when mapping from a sequence of
        characters to an octet string.  This parameter is not
        cryptographically protected, so recipients cannot rely on it as
        the exclusive mapping possibility.

        This parameter has similar semantics to the charset parameter
        from text/plain, except that it only applies to the user's input
        (text value) of a password.  There is no default value.

        The following special values, which all begin with "*" to
        distinguish them from registered charsets, are defined:

        *pkcs12      UTF-16LE with U+0000 NULL terminator: PKCS #12
                     style, see [RFC7292].

        *precis      Preparation, Enforcement, and Comparison of
                     Internationalized Strings (PRECIS) password
                     profile, i.e., OpaqueString from Section 4 of
                     [RFC7613], which was obsoleted by [RFC8265]: always
                     UTF-8 in Normalization Form C (NFC).

        *precis-XXX  Any profile from the IANA "PRECIS Profiles"
                     registry where "XXX" is replaced by the profile
                     name as shown in the registry.

        *hex         hexadecimal input: the input is mapped to 0-9, A-F,
                     and then converted directly to octets.  If there
                     are an odd number of hex digits, either the final
                     digit 0 is appended or an error condition is
                     raised.  Compare with Annex M.4 of

        *dtmf        The characters "0"-"9", "A"-"D", "*", and "#",
                     which map to their corresponding ASCII codes.
                     "A"-"D" map to the uppercase range 0x41 - 0x44.
                     (This is to support restricted-input devices, i.e.,
                     telephones and telephone-like equipment.)  User
                     input outside of these values is either ignored or
                     an error condition is raised.
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        Otherwise, the value of this parameter is a charset, from the
        IANA "Character Sets" registry [CHARREG].

        This parameter is case insensitive.

   Encoding considerations: Binary.

   Security considerations:

      Carries a cryptographic private key.  See Section 6 of [RFC5958].

      EncryptedPrivateKeyInfo PKCS #8 data contains exactly one private
      key.  Poor password choices, weak algorithms, or improper
      parameter selections (e.g., insufficient salting rounds) will make
      the confidential payloads much easier to compromise.

   Interoperability considerations:

      PKCS #8 is a widely recognized format for private key information
      on all modern cryptographic stacks.  The contents are exactly one
      private key (with optional key attributes), so there is no
      possibility for hidden "Easter eggs" in the payload such as
      unexpected certificates or miscellaneous secrets.

      The encrypted variation in this registration,
      EncryptedPrivateKeyInfo (Section 3, "Encrypted Private Key Info",
      of [RFC5958], and Section 6 of PKCS #8 as originally described in
      [RFC5208], which was obsoleted by [RFC5958]), is less widely used
      for exchange than PKCS #12, but it is much simpler to implement.
      Actually, PKCS #12 incorporates the PKCS #8 types, so a PKCS #12
      processor ought to be able to process PKCS #8 data by embedding
      the PKCS #8 data in PKCS #12 "scaffolding".

      The password-mapping parameter aids in interoperability when the
      creator (who encrypted the keying material) and the user (who is
      attempting to decrypt the keying material) are not operating in
      the same character-encoding environment.  An anticipated scenario
      is that the creator may have created the keying material with a
      password in a Shift-JIS environment a long time ago, while the
      user is in a UTF-8 environment.  There are potentially many
      Unicode sequences that code for the same abstract character, such
      as precomposed and decomposed forms; yet, such an abstract
      character (however coded in Unicode) will tend to map to one
      coding in the legacy charset, if it can be represented at all.
      Therefore, the password-mapping parameter will almost never be
      ambiguous when mapping to legacy encodings.  When mapping from one
      Unicode form to another (such as an internal Unicode
      representation to *pkcs12), code sequences are either preserved or
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      folded deterministically to common Unicode code points or
      sequences, producing the same holistic result as mapping to legacy

      It is possible that an abstract character might map to multiple
      legacy encodings under the same charset.  However, the possibility
      is sufficiently remote as to be ignored in this media type
      registration.  One possible workaround is to set the user's
      (decrypting party's) local operating environment to the password-
      mapping legacy encoding parameter for the purpose of generating
      the password octet string from user input.  Another possibility is
      to generate all possible legacy encoding combinations from the
      abstract text (i.e., Unicode text), attempting decryption with
      them.  Customized behavior can be defined by updating this media
      type registration with a new password-mapping special value,
      prefixed with *.

   Published specification:

      RSA Laboratories PKCS #8 v1.2 RSA Encryption Standard, November
      1993 (republished as [RFC5208], May 2008, and updated as
      [RFC5958], August 2010); RFC 5958, August 2010

   Applications that use this media type:

      Machines, applications, browsers, Internet kiosks, and so on, that
      support this standard allow a user to import, export, and exercise
      a single private key.

   Fragment identifier considerations: None.

   Additional information:

      Deprecated alias names for this type: N/A
      Magic number(s): None.
      File extension(s): .p8e
      Macintosh file type code(s): None.  A uniform type identifier
      (UTI) of "com.rsa.pkcs-8-encrypted" is recommended.

   Object Identifiers: 1.2.840.113549. (when in PKCS #12)

   Person & email address to contact for further information:

     Sean Leonard <>

   Intended usage: COMMON

   Restrictions on usage: None.
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   Author/Change controller: Sean Leonard <>

   Provisional registration?  No

3. IANA Considerations

IANA has registered the media type application/pkcs8-encrypted in the Standards tree using the information provided in Section 2 of this document.

4. Security Considerations

See the registration template.

5. Normative References

[CHARREG] IANA, "Character Sets", December 2013, <>. [IEEE.802.11-2012] IEEE, "IEEE Standard for Information technology-- Telecommunications and information exchange between systems Local and metropolitan area networks--Specific requirements Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications", IEEE 802.11-2012, DOI 10.1109/ieeestd.2012.6178212, <>. [RFC2898] Kaliski, B., "PKCS #5: Password-Based Cryptography Specification Version 2.0", RFC 2898, DOI 10.17487/RFC2898, September 2000, <>. [RFC2978] Freed, N. and J. Postel, "IANA Charset Registration Procedures", BCP 19, RFC 2978, DOI 10.17487/RFC2978, October 2000, <>. [RFC5208] Kaliski, B., "Public-Key Cryptography Standards (PKCS) #8: Private-Key Information Syntax Specification Version 1.2", RFC 5208, DOI 10.17487/RFC5208, May 2008, <>. [RFC5958] Turner, S., "Asymmetric Key Packages", RFC 5958, DOI 10.17487/RFC5958, August 2010, <>.
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   [RFC7292]  Moriarty, K., Ed., Nystrom, M., Parkinson, S., Rusch, A.,
              and M. Scott, "PKCS #12: Personal Information Exchange
              Syntax v1.1", RFC 7292, DOI 10.17487/RFC7292, July 2014,

   [RFC7613]  Saint-Andre, P. and A. Melnikov, "Preparation,
              Enforcement, and Comparison of Internationalized Strings
              Representing Usernames and Passwords", RFC 7613,
              DOI 10.17487/RFC7613, August 2015,

   [RFC8018]  Moriarty, K., Ed., Kaliski, B., and A. Rusch, "PKCS #5:
              Password-Based Cryptography Specification Version 2.1",
              RFC 8018, DOI 10.17487/RFC8018, January 2017,

   [RFC8265] Saint-Andre, P. and A. Melnikov, "Preparation, Enforcement,
              and Comparison of Internationalized Strings Representing
              Usernames and Passwords", RFC 8265, DOI 10.17487/RFC8265,
              October 2017, <>.

Author's Address

Sean Leonard Penango, Inc. 5900 Wilshire Blvd Ste 2600 Los Angeles, CA 90036 United States of America Email: URI: