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Internet Engineering Task Force (IETF)                         S. TurnerRequest for Comments: 6032                                          IECACategory: Standards Track                                     R. HousleyISSN: 2070-1721                                           Vigil Security                                                           December 2010Cryptographic Message Syntax (CMS)Encrypted Key Package Content TypeAbstract   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 is an Internet Standards Track document.   This document is a product of the Internet Engineering Task Force   (IETF).  It represents the consensus of the IETF community.  It has   received public review and has been approved for publication by the   Internet Engineering Steering Group (IESG).  Further information on   Internet Standards is available inSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc6032.Turner & Housley             Standards Track                    [Page 1]

RFC 6032         CMS Encrypted Key Package Content Type    December 2010Copyright Notice   Copyright (c) 2010 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 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.  [RFC6031] and [RFC5958]   define symmetric key package and asymmetric key package content types   that can be signed or encrypted using CMS.  CMS allows the   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 [RFC6010]   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 mayTurner & Housley             Standards Track                    [Page 2]

RFC 6032         CMS Encrypted Key Package Content Type    December 2010   be authenticated and passed to another entity.  In these cases,   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 [RFC6031] or an asymmetric key package   [RFC5958].  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   [RFC6010].  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; then, during   certificate path validation, the recipient determines whether the   originator is authorized to originate the encrypted key package.   In [RFC6010] 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 [RFC6010].      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 [RFC6010].        As specified in [RFC6010], the validator may use the attributes        and public keys returned from the second step as inputs for this        CMS content constraints processing.Turner & Housley             Standards Track                    [Page 3]

RFC 6032         CMS Encrypted Key Package Content Type    December 2010      o Use the symmetric key material.            +--------------------------------------+            | 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.  ThisTurner & Housley             Standards Track                    [Page 4]

RFC 6032         CMS Encrypted Key Package Content Type    December 2010   content type makes use of the CMS EncryptedData content type   [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 ::=        { 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 (seeSection 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             Standards Track                    [Page 5]

RFC 6032         CMS Encrypted Key Package Content Type    December 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 [RFC6031] or a   SignedData that further encapsulates an AsymmetricKeyPackage   [RFC5958].  Implementations that support AuthEnvelopedData to   encapsulate with this content type MUST support an   EncryptedKeyPackage that encapsulates either a SymmetricKeyPackage   [RFC6031] or an AsymmetricKeyPackage [RFC5958].  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 [RFC6031] or a SignedData that further   encapsulates an AsymmetricKeyPackage [RFC5958].  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 innermost 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 [RFC5912].  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             Standards Track                    [Page 6]

RFC 6032         CMS Encrypted Key Package Content Type    December 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], [RFC5911],   [RFC5912], [RFC5958], and [RFC6031] apply.  If the CCC extension is   used as an authorization mechanism, then the security considerations   from [RFC6010] 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             Standards Track                    [Page 7]

RFC 6032         CMS Encrypted Key Package Content Type    December 20105.  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 inAppendix A.  All OIDs are registered in an arc delegated by RSADSI to   the SMIME Working Group.6.  References6.1.  Normative References   [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)", STD               70,RFC 5652, September 2009.   [RFC5911]   Hoffman, P. and J. Schaad, "New ASN.1 Modules for               Cryptographic Message Syntax (CMS) and S/MIME",RFC 5911,               June 2010.   [RFC5912]   Hoffman, P. and J. Schaad, "New ASN.1 Modules for the               Public Key Infrastructure Using X.509 (PKIX)",RFC 5912,               June 2010.   [RFC5958]   Turner, S., "Asymmetric Key Packages",RFC 5958, August               2010.   [RFC6010]   Housley, R., Ashmore, S., and C. Wallace, "Cryptographic               Message Syntax (CMS) Content Constraints Extension",RFC6010, September 2010.   [RFC6031]   Turner, S. and R. Housley, "Cryptographic Message Syntax               (CMS) Symmetric Key Package Content Type",RFC 6031,               December 2010.   [X.680]     ITU-T Recommendation X.680 (2002) | ISO/IEC 8824-1:2002.               Information Technology - Abstract Syntax Notation One.Turner & Housley             Standards Track                    [Page 8]

RFC 6032         CMS Encrypted Key Package Content Type    December 2010   [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.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.Turner & Housley             Standards Track                    [Page 9]

RFC 6032         CMS Encrypted Key Package Content Type    December 2010Appendix 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 [RFC5911]   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 [RFC5911]   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) }   -- From New PKIX ASN.1 [RFC5912]   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 --   }Turner & Housley             Standards Track                   [Page 10]

RFC 6032         CMS Encrypted Key Package Content Type    December 2010   ct-encrypted-key-package CONTENT-TYPE ::=       { 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   ENDAuthors' Addresses   Sean Turner   IECA, Inc.   3057 Nutley Street, Suite 106   Fairfax, VA 22031   USA   EMail: turners@ieca.com   Russell Housley   Vigil Security, LLC   918 Spring Knoll Drive   Herndon, VA 20170   USA   EMail: housley@vigilsec.comTurner & Housley             Standards Track                   [Page 11]