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.
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
[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
<http://www.iana.org/assignments/character-sets>.
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
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:
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: 1.2.840.113549.1.12.10.1.2 (when in PKCS #12)
Person & email address to contact for further information:
Sean Leonard <dev+ietf&seantek.com>
Intended usage: COMMON
Restrictions on usage: None.
Author/Change controller: Sean Leonard <dev+ietf&seantek.com>
Provisional registration? No