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The PKCS #8 EncryptedPrivateKeyInfo Media Type

The information below is for an old version of the document that is already published as an RFC.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 8351.
Author Sean Leonard
Last updated 2018-06-26 (Latest revision 2017-11-13)
RFC stream Independent Submission
Intended RFC status Informational
IETF conflict review conflict-review-seantek-pkcs8-encrypted
Stream ISE state Published RFC
Consensus boilerplate Unknown
Document shepherd Eliot Lear
Shepherd write-up Show Last changed 2017-11-14
IESG IESG state Became RFC 8351 (Informational)
Telechat date (None)
Responsible AD (None)
Send notices to Nevil Brownlee <>
IANA IANA review state IANA OK - Actions Needed
IANA action state RFC-Ed-Ack
Network Working Group                                         S. Leonard
Internet-Draft                                             Penango, Inc.
Intended Status: Informational                         November 14, 2017
Expires: May 18, 2018                                                   

             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 Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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1. Definitions

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

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]. Such algorithms take a
     password as input. A "password" is a secret text value (Section 3
     of PKCS #5), but for algorithmic purposes the term "password"
     refers to an octet string (Section 2 of PKCS #5). Therefore, there
     must be some mapping between the text value (which might be user
     input) and the octet string. Section 3 of PKCS #5 recommends "that
     applications follow some common text encoding rules"; it then
     offers, but does not recommend, ASCII and UTF-8.

     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 SHOULD NOT rely on it as the exclusive mapping

     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     = PRECIS password profile, i.e., OpaqueString from
                   Section 4 of [RFC7613]: always UTF-8 in Normalization
                   Form C (NFC)
     *precis-XXX = PRECIS profile as named XXX in the IANA PRECIS

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                   Profiles 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 IEEE 802.11-2012.
     *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.

     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), 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

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     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 folded deterministically to
     common Unicode code points or sequences, producing the same
     holistic result as mapping to legacy encodings.

     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:

     PKCS #8 v1.2, November 1993 (republished as RFC 5208, May 2008);
     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):

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       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 <>

   Restrictions on usage: None.

   Author/Change controller: Sean Leonard <>

   Intended usage: COMMON

   Provisional registration? No

3.  IANA Considerations

   IANA is asked to register the media type application/pkcs8-encrypted
   in the Standards tree using the applications provided in Section 1 of
   this document.

4. Security Considerations

   See the registration template.

5. Normative References

   [CHARREG]  IANA, "Character Sets",
              <>, December

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

   [RFC2898]  Kaliski, B., "PKCS #5: Password-Based Cryptography
              Specification Version 2.0", RFC 2898, September 2000.

   [RFC2978]  Freed, N. and J. Postel, "IANA Charset Registration
              Procedures", BCP 19, RFC 2978, October 2000.

   [RFC5208]  Kaliski, B., "Public-Key Cryptography Standards (PKCS) #8:
              Private-Key Information Syntax Specification Version 1.2",
              RFC 5208, May 2008.

   [RFC5958]  Turner, S., "Asymmetric Key Packages", RFC 5958, August

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   [RFC7292]  Moriarty, K., Nystrom, S., Parkinson, S., Rusch, A., and
              M. Scott, "PKCS #12: Personal Information Exchange Syntax
              v1.1", RFC 7292, July 2014.

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

Author's Address

   Sean Leonard
   Penango, Inc.
   5900 Wilshire Blvd
   Ste 2600
   Los Angeles, CA  90036


Appendix A.  Changes from -02 to -03

   Updated the document based on discussions. Added much more
   explanatory text about the password-mapping parameter.

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