Network Working Group S. Turner, IECA
Internet Draft R. Housley, Vigil Security
Intended Status: Standards Track May 7, 2010
Expires: November 7, 2010
Cryptographic Message Syntax (CMS)
Encrypted Key Package Content Type
draft-turner-encryptedkeypackagecontenttype-02.txt
Abstract
This document defines the Cryptographic Message Syntax (CMS)
encrypted key package content type, which can be used to encrypt a
content that includes a key package, such as a symmetric key package
or an asymmetric key package. It is transport independent. CMS can
be used to digitally sign, digest, authenticate, or further encrypt
this content type. It is designed to be used with the CMS Content
Constraints (CCC) extension, which does not constrain the
EncryptedData, EnvelopedData, and AuthEnvelopedData.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
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."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html
This Internet-Draft will expire on November 7, 2010.
Turner & Housley Expires November 7, 2010 [Page 1]
Internet-Draft CMS Encrypted Key Package Content Type May 2010
Copyright Notice
Copyright (c) 2010 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
(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.
1. Introduction
The Cryptographic Message Syntax (CMS) specification [RFC5652]
defines mechanisms to digitally sign, digest, authenticate or encrypt
arbitrary message content. Many specifications define content types
intended for use with CMS. [RFCTBD1] and [RFCTBD2] define symmetric
key package and asymmetric key package content types that can be
signed or encrypted using CMS. CMS allows composition of complex
messages with an arbitrary number of layers. CMS has been augmented
by several specifications ([RFC3274], [RFC4073] and [RFC5083]) that
define additional mechanisms to enable creation of messages of
arbitrary depth and breadth using a variety of authentication,
encryption and compression techniques.
The CMS Content Constraints (CCC) certificate extension [CCC] defines
an authorization mechanism that allows recipients to determine
whether the originator of an authenticated CMS content type is
authorized to produce messages of that type. CCC is used to
authorize CMS-protected content. CCC cannot be used to constrain the
following structures that are used to provide layers of protection:
SignedData, EnvelopedData, EncryptedData, DigestData, CompressedData,
AuthenticatedData, ContentCollection, ContentWithAttributes or
AuthEnvelopedData.
Using the existing CMS mechanisms, producers of authenticated
plaintext key packages can be authorized by including a CCC extension
containing the appropriate content type in the producer's
certificate. However, these mechanisms cannot be used to authorize
the producers of encrypted key material. In some key management
systems, encrypted key packages are exchanged between entities that
cannot decrypt the key package. The encrypted key package itself may
be authenticated and passed to another entity. In these cases,
Turner & Housley Expires November 7, 2010 [Page 2]
Internet-Draft CMS Encrypted Key Package Content Type May 2010
checking the authorization of the producer of the encrypted key
package may be desired at the intermediate points.
This document defines the encrypted key package content type, which
can be used to encrypt a content that includes a key package, such as
a symmetric key package [RFCTBD1] or an asymmetric key package
[RFCTBD2]. It is transport independent. The Cryptographic Message
Syntax (CMS) [RFC5652] can be used to digitally sign, digest,
authenticate, or further encrypt this content type.
The encrypted key package content type is designed for use with
[CCC]. To authorize an originator's public key to originate an
encrypted key package, the object identifier associated with the
encrypted key package content type is included in the originator's
public key certificate CCC certificate extension. For CCC to
function, originators encapsulate the encrypted key package in a
SignedData, EnvelopedData, or AuthEnvelopedData, and then during
certificate path validation the recipient determines whether the
originator is authorized to originate the encrypted key package.
In [CCC] terminology, the encrypted key package is a leaf node.
Additional authorization checks may be required once the key package
is decrypted. For example, the key package shown below consists of a
SignedData layer that encapsulates an encrypted key package that
encapsulates a SignedData layer containing a symmetric key package.
A recipient capable of decrypting the key package would perform the
following steps prior to accepting the encapsulated symmetric key
material:
o Verify the signature on the outer SignedData layer per [RFC5652].
o Build and validate a certification path of the outer signer and
confirm the outer signer is authorized to produce the encrypted
key package per [RFC5280] and [CCC].
o Decrypt the encrypted key package
o Verify the signature on the inner SignedData layer per [RFC5652].
o Build and validate a certification path to the signer of the
inner SignedData and confirm the inner signer is authorized to
produce the symmetric key package per [RFC5280] and [CCC].
As specified in [CCC], the validator may use the attributes and
public keys returned from the second step as inputs for this CMS
content constraints processing.
o Use the symmetric key material.
Turner & Housley Expires November 7, 2010 [Page 3]
Internet-Draft CMS Encrypted Key Package Content Type May 2010
+--------------------------------------+
| ContentInfo |
| |
| +----------------------------------+ |
| | SignedData | |
| | | |
| | +------------------------------+ | |
| | | EncryptedKeyPackage | | |
| | | (encrypted) | | |
| | | | | |
| | | +-------------------------+ | | |
| | | | SignedData | | | |
| | | | | | | |
| | | | +---------------------+ | | | |
| | | | | SymmetricKeyPackage | | | | |
| | | | +---------------------+ | | | |
| | | +-------------------------+ | | |
| | +------------------------------+ | |
| +----------------------------------+ |
+--------------------------------------+
In the example, authorization of the SymmetricKeyPackage originator
need not require an intermediate SignedData layer. For example, if
the AuthEnvelopedData option within an EncryptedKeyPackage were used,
the second authorization check would be performed beginning with the
authEnveloped field.
This document also defines an unprotected attribute, Content
Decryption Key Identifier, for use with EncryptedData.
1.1. Terminology
The 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].
1.2. ASN.1 Syntax Notation
The key package is defined using the ASN.1 [X.680], [X.681], [X.682],
and [X.683].
2. Encrypted Key Package
The encrypted key package content type is used to encrypt a content
that includes a key package. This content type is usually used to
provide encryption of a key package or a signed key package. This
content type makes use of the CMS EncryptedData content type
Turner & Housley Expires November 7, 2010 [Page 4]
Internet-Draft CMS Encrypted Key Package Content Type May 2010
[RFC5652], the CMS EnvelopedData content type [RFC5652], or the CMS
AuthEnvelopedData content type [RFC5083] depending on the fields that
are needed for key management. The difference between the encrypted
key package content type and these three protecting content types is
the object identifier and one tag; otherwise, the encrypted key
package content type is the same as the selected protecting content
type, which is either EncryptedData, EnvelopedData, or
AuthEnvelopedData.
The encrypted key package content type has the following syntax:
ct-encrypted-key-package CONTENT-TYPE ::=
{ EncryptedKeyPackage IDENTIFIED BY id-ct-KP-encryptedKeyPkg }
id-ct-KP-encryptedKeyPkg OBJECT IDENTIFIER ::=
{ joint-iso-itu-t(2) country(16) us(840) organization(1)
gov(101) dod(2) infosec(1) formats(2)
key-package-content-types(78) 2 }
EncryptedKeyPackage ::= CHOICE {
encrypted EncryptedData,
enveloped [0] EnvelopedData,
authEnveloped [1] AuthEnvelopedData }
The EncryptedData structure is used for simple symmetric encryption,
where the sender and the receiver already share the necessary
encryption key. The EncryptedData structure carries an encryption
algorithm identifier, and an unprotected attribute can be used to
carry an encryption key identifier if one is needed (see Section 3).
See [RFC5652] for further discussion of the EncryptedData fields.
The EnvelopedData structure is used for encryption, where transferred
key management information enables decryption by the receiver.
Encryption details depend on the key management algorithm used. In
addition to the key management information, the EnvelopedData
structure carries an encryption algorithm identifier. See [RFC5652]
for further discussion of the EnvelopedData fields.
The AuthEnvelopedData structure is used for authenticated encryption,
and it includes key management information in a manner similar to
EnvelopedData. Encryption details depend on the key management
algorithm used. In addition to the key management information, the
AuthEnvelopedData structure carries a message authentication code
that covers the content as well as authenticated attributes. See
[RFC5083] for further discussion of the AuthEnvelopedData fields.
Turner & Housley Expires November 7, 2010 [Page 5]
Internet-Draft CMS Encrypted Key Package Content Type May 2010
Implementations of this document MUST support the EnvelopedData
choice, SHOULD support the EncryptedData choice, and MAY support the
AuthEnvelopedData.
Implementations that support EnvelopedData and EncryptedData to
encapsulate with this content type MUST support an
EncryptedKeyPackage that encapsulates either a SignedData [RFC5652]
that further encapsulates a SymmetricKeyPackage [RFCTBD1] or a
SignedData that further encapsulates an AsymmetricKeyPackage
[RFCTBD2]. Implementations that support AuthEnvelopedData to
encapsulate with this content type MUST support an
EncryptedKeyPackage that encapsulates either a SymmetricKeyPackage
[RFCTBD1] or an AsymmetricKeyPackage [RFCTBD2]. It is OPTIONAL for
implementations that support AuthEnvelopedData to encapsulate with
this content type to support an EncryptedKeyPackage that encapsulates
either a SignedData [RFC5652] that further encapsulates a
SymmetricKeyPackage [RFCTBD1] or a SignedData that further
encapsulates an AsymmetricKeyPackage [RFCTBD2]. Likewise,
implementations that process this content type to decrypt the
encapsulated data MUST support an EncryptedKeyPackage that
encapsulates either a SignedData that further encapsulates a
SymmetricKeyPackage or a SignedData that further encapsulates an
AsymmetricKeyPackage. An EncryptedKeyPackage content type MUST
contain at least one SymmetricKeyPackage or AsymmetricKeyPackage.
Implementations MAY support additional encapsulating layers.
Note that interoperability between an originator and a recipient that
do not support the same inner-most content (e.g., originator supports
AsymmetricKeyPackage while recipient supports SymmetricKeyPackage) is
not a concern as originators should be aware of the recipient's
capabilities; however, the mechanism for the exchange of the
recipient's capabilities is beyond the scope of this document.
3. Content Decryption Key Identifier
The content-decryption-key-identifier attribute can be used to
identify the symmetric keying material that is needed for decryption
of the EncryptedData content if there is any ambiguity. The
ATTRIBUTE definition is taken from [RFCTBD3]. There MUST be only one
instance of the content-decryption-key-identifier attribute and there
MUST be only one value for the content-decryption-key-identifier
attribute.
Turner & Housley Expires November 7, 2010 [Page 6]
Internet-Draft CMS Encrypted Key Package Content Type May 2010
The content-decryption-key-identifier attribute has the following
syntax:
aa-content-decrypt-key-identifier ATTRIBUTE ::= {
TYPE ContentDecryptKeyID
IDENTIFIED BY id-aa-KP-contentDecryptKeyID }
id-aa-KP-contentDecryptKeyID OBJECT IDENTIFIER ::= {
joint-iso-itu-t(2) country(16) us(840) organization(1) gov(101)
dod(2) infosec(1) attributes(5) 66 }
ContentDecryptKeyID ::= OCTET STRING
The content decryption key identifier contains an octet string, and
this syntax does not impose any particular structure on the
identifier value.
Due to multiple layers of encryption, the content-decryption-key-
identifier attribute can appear in more than one location in the
overall key package. When there are multiple occurrences of the
content-decryption-key-identifier attribute, each occurrence is
evaluated independently. Each one is used to identify the needed
keying material for that layer of encryption.
4. Security Considerations
Implementers of this protocol are strongly encouraged to consider
generally accepted principles of secure key management when
integrating this capability within an overall security architecture.
The security considerations from [RFC5083], [RFC5652], [RFCTBD1],
[RFCTBD2], [RFCTBD3], and [RFCTBD4] apply. If the CCC extension is
used as an authorization mechanism, then the security considerations
from [CCC] also apply.
The encrypted key package content type might not provide proof of
origin if the content encryption algorithm does not support
authenticated key exchange. To provide proof of origin for this
content, another security protocol needs to be used. This is the
reason that support for encapsulating the SymmetricKeyPackage and
AsymmetricKeypackage with a SignedData content type from [RFC5652] is
required for the EnvelopedData and EncryptedData choices.
When this content type is used the CMS SignedData [RFC5652]
validation rules MUST be used. The PKCS #7 [RFC2315] validation
rules MUST NOT be used.
Turner & Housley Expires November 7, 2010 [Page 7]
Internet-Draft CMS Encrypted Key Package Content Type May 2010
5. IANA Considerations
This document makes use of object identifiers to identify a CMS
content type, a CMS attribute, and the ASN.1 module; all found in
Appendix A. All OIDs are registered in an arc delegated by IANA to
the SMIME Working Group. No further action by IANA is necessary for
this document or any anticipated updates.
6. References
6.1. Normative References
[CCC] Wallace, C., and R. Housley, "Cryptographic Message
Syntax (CMS) Content Constraints X.509 Certificate
Extension", draft-housley-cms-content-constraints-extn-
05.txt, work-in-progress.
/**
RFC Editor: Please replace [CCC] with [RFCXXXX] where XXXX is the
number of the published RFC. Please do this in both the references
and the text.
**/
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5083] Housley, R., "Cryptographic Message Syntax (CMS)
Authenticated-Enveloped-Data Content Type", RFC 5083,
November 2007.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation
List (CRL) Profile", RFC 5280, May 2008.
[RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", RFC
5652, September 2009.
[RFCTBD1] Housley, R. and S. Turner, "Symmetric Key package Content
Type", draft-ietf-keyprov-symmetrickeyformat-08.txt,
work-in-progress.
Turner & Housley Expires November 7, 2010 [Page 8]
Internet-Draft CMS Encrypted Key Package Content Type May 2010
/**
RFC Editor: Please replace "TBD1" with the number of the published
RFC. Please do this in both the references and the text.
**/
[RFCTBD2] Turner, S., "Asymmetric Key Packages", draft-turner-
asymmetrickeyformat-05.txt, work-in-progress.
/**
RFC Editor: Please replace "TB2" with the number of the published
RFC. Please do this in both the references and the text.
**/
[RFCTBD3] Schaad, J., and P. Hoffman, "New ASN.1 Modules for PKIX",
draft-ietf-pkix-new-asn1-08.txt, work-in-progress.
/**
RFC Editor: Please replace "TBD3" with the number of the published
RFC. Please do this in both the references and the text.
**/
[RFCTBD4] Schaad, J., and P. Hoffman, "New ASN.1 Modules for
SMIME", draft-ietf-smime-new-asn1-07.txt, work-in-
progress.
/**
RFC Editor: Please replace "TBD4" with the number of the published
RFC. Please do this in both the references and the text.
**/
[X.680] ITU-T Recommendation X.680 (2002) | ISO/IEC 8824-1:2002.
Information Technology - Abstract Syntax Notation One.
[X.681] ITU-T Recommendation X.681 (2002) | ISO/IEC 8824-2:2002.
Information Technology - Abstract Syntax Notation One:
Information Object Specification.
[X.682] ITU-T Recommendation X.682 (2002) | ISO/IEC 8824-3:2002.
Information Technology - Abstract Syntax Notation One:
Constraint Specification.
[X.683] ITU-T Recommendation X.683 (2002) | ISO/IEC 8824-4:2002.
Information Technology - Abstract Syntax Notation One:
Parameterization of ASN.1 Specifications.
Turner & Housley Expires November 7, 2010 [Page 9]
Internet-Draft CMS Encrypted Key Package Content Type May 2010
6.2. Informative References
[RFC2315] Kaliski, B., "PKCS #7: Cryptographic Message Syntax
Version 1.5", RFC 2315, March 1998.
[RFC3274] Gutmann, P., "Compressed Data Content Type for
Cryptographic Message Syntax (CMS)", RFC 3274, June 2002.
[RFC4073] Housley, R., "Protecting Multiple Contents with the
Cryptographic Message Syntax (CMS)", RFC 4073, May 2005.
Appendix A. ASN.1 Module
This appendix provides the normative ASN.1 [X.680] definitions for
the structures described in this specification using ASN.1 as defined
in [X.680] through [X.683].
EncryptedKeyPackageModuleV1
{ iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) modules(0) id-mod-encryptedKeyPkgV1(51) }
DEFINITIONS IMPLICIT TAGS ::=
BEGIN
-- EXPORTS ALL --
IMPORTS
-- From New SMIME ASN.1 [RFCTBD4]
EncryptedData, EnvelopedData, CONTENT-TYPE
FROM CryptographicMessageSyntax-2009
{ iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) modules(0) cms-2004-02(41) }
-- From New SMIME ASN.1 [RFCTBD4]
AuthEnvelopedData
FROM CMS-AuthEnvelopedData-2009
{ iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1)
pkcs-9(9) smime(16) modules(0) cms-authEnvelopedData-02(43) }
Turner & Housley Expires November 7, 2010 [Page 10]
Internet-Draft CMS Encrypted Key Package Content Type May 2010
-- From New PKIX ASN.1 [RFCTBD3]
ATTRIBUTE
FROM PKIX-CommonTypes-2009
{ iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-pkixCommon-02(57) }
;
ContentSet CONTENT-TYPE ::= {
ct-encrypted-key-package,
... -- Expect additional content types --
}
ct-encrypted-key-package CONTENT-TYPE ::=
{ EncryptedKeyPackage IDENTIFIED BY id-ct-KP-encryptedKeyPkg }
id-ct-KP-encryptedKeyPkg OBJECT IDENTIFIER ::=
{ joint-iso-itu-t(2) country(16) us(840) organization(1) gov(101)
dod(2) infosec(1) formats(2) key-package-content-types(78) 2 }
EncryptedKeyPackage ::= CHOICE {
encrypted EncryptedData,
enveloped [0] EnvelopedData,
authEnveloped [1] AuthEnvelopedData }
aa-content-decrypt-key-identifier ATTRIBUTE ::= {
TYPE ContentDecryptKeyID
IDENTIFIED BY id-aa-KP-contentDecryptKeyID }
id-aa-KP-contentDecryptKeyID OBJECT IDENTIFIER ::= {
joint-iso-itu-t(2) country(16) us(840) organization(1) gov(101)
dod(2) infosec(1) attributes(5) 66 }
ContentDecryptKeyID ::= OCTET STRING
END
Turner & Housley Expires November 7, 2010 [Page 11]
Internet-Draft CMS Encrypted Key Package Content Type May 2010
Authors' Addresses
Sean Turner
IECA, Inc.
3057 Nutley Street, Suite 106
Fairfax, VA 22031
USA
EMail: turners@ieca.com
Russ Housley
Vigil Security, LLC
918 Spring Knoll Drive
Herndon, VA 20170
USA
EMail: housley@vigilsec.com
Turner & Housley Expires November 7, 2010 [Page 12]
