Network Working Group S. Turner, IECA Internet Draft R. Housley, Vigil Security Intended Status: Standard Track September 08, 2009 Expires: March 08, 2010 Encrypted Key Package Content Type draft-turner-encryptedkeypackagecontenttype-00.txt 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 March 08, 2010. Copyright Notice Copyright (c) 2009 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 (http://trustee.ietf.org/license-info). Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Turner & Housley Expires March 08, 2010 [Page 1] Internet-Draft Encrypted Key Package Content Type September 2009 Abstract 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 or an asymmetric key package. It is transport independent. The Cryptographic Message Syntax (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 extension, which does not constrain the EncryptedData, EnvelopedData, and AuthEnvelopedData. 1. Introduction The Cryptographic Message Syntax (CMS) specification [RFC3852] defines means 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 the innermost content type within a CMS-protected message. 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, checking the authorization of the producer of the encrypted key package may be desired at the intermediate points. Turner & Housley Expires March 08, 2010 [Page 2] Internet-Draft Encrypted Key Package Content Type September 2009 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) [RFC3852] 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 SignedData layer per [RFC3852] o Build and validate a certification path to the signer and confirm the 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 SignedData layer per [RFC3852] o Build and validate a certification path to the signer and confirm the signer is authorized to produce the symmetric key package per [RFC5280] and [CCC] o Use the symmetric key material Turner & Housley Expires March 08, 2010 [Page 3] Internet-Draft Encrypted Key Package Content Type September 2009 +--------------------------------------+ | 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 for use with one of the key management options supported by the encrypted key package content type. 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]. 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 March 08, 2010 [Page 4] Internet-Draft Encrypted Key Package Content Type September 2009 [RFC3852], the CMS EnvelopedData content type [RFC3852], 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: encrypted-key-package PKCS7-CONTENT-TYPE ::= { EncryptedKeyPackage IDENTIFIED BY id-ct-KP-encryptedKeyPkg } PKCS7-CONTENT-TYPE ::= TYPE-IDENTIFIER 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 [RFC3852] 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 [RFC3852] 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 March 08, 2010 [Page 5] Internet-Draft Encrypted Key Package Content Type September 2009 Implementations of this document MUST support the EnvelopedData choice, SHOULD support the EncryptedData choice, and MAY support the AuthEnvelopedData. Implementations that encrypt data to encapsulate with this content type MUST support an EncryptedKeyPackage that encapsulates either a SignedData [RFC3852] 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]. The content-decryption-key-identifier attribute has the following syntax: content-decrypt-key-identifier ATTRIBUTE ::= { WITH SYNTAX ContentDecryptKeyID ID 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. Turner & Housley Expires March 08, 2010 [Page 6] Internet-Draft Encrypted Key Package Content Type September 2009 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 The security considerations from [RFC3852], [RFC4073], [RFC5083], [RFCTBD1], [RFCTBD2], and [CCC] 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 EncryptedKeyPackage with a SignedData content type from [RFC3852] is required. 5. IANA Considerations None. Please remove this section prior to publication as an RFC. 6. References 6.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3852] Housley, R., "Cryptographic Message Syntax (CMS)", RFC 3852, July 2004. [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. [RFCTBD1] Housley, R. and S. Turner, "Symmetric Key package Content Type", draft-ietf-keyprov-symmetrickeyformat-05.txt, work-in-progress. Turner & Housley Expires March 08, 2010 [Page 7] Internet-Draft Encrypted Key Package Content Type September 2009 [RFCTBD2] Turner, S., "Asymmetric Key Packages", draft-turner- asymmetrickeyformat-01.txt, work-in-progress. [RFCTBD3] Schaad, J., and P. Hoffman, "New ASN.1 Modules for PKIX", draft-ietf-pkix-new-asn1-07.txt, work-in-progress. [X.680] ITU-T Recommendation X.680 (2002) | ISO/IEC 8824-1:2002. Information Technology - Abstract Syntax Notation One. 6.2. Informative References [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. [CCC] Wallace, C., and R. Housley, "Cryptographic Message Syntax (CMS) Content Constraints X.509 Certificate Extension", draft-housley-cms-content-constraints-extn- 01.txt, work-in-progress. Appendix A. ASN.1 Module This appendix provides the normative ASN.1 definitions for the structures described in this specification using ASN.1 as defined in X.680. EncryptedKeyPackage { id-TBSL } DEFINITIONS EXPLICIT TAGS ::= BEGIN -- EXPORTS ALL -- IMPORTS -- IMPORTS from CMS [RFC3852] EncryptedData, EnvelopedData FROM CryptographicMessageSyntax { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) modules(0) cms-2004(24) } -- IMPORTS from CMS AuthEnvelopedData [RFC5083] Turner & Housley Expires March 08, 2010 [Page 8] Internet-Draft Encrypted Key Package Content Type September 2009 AuthEnvelopedData FROM CMS-AuthEnvelopedData-2007 { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) smime(16) modules(0) cms-authEnvelopedData(31) } -- IMPORTS from 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) } ; PKCS7-CONTENT-TYPE ::= TYPE-IDENTIFIER KeyPackageContentTypes PKCS7-CONTENT-TYPE ::= { encrypted-key-package, ... -- Expect additional content types -- } encrypted-key-package PKCS7-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 } content-decrypt-key-identifier ATTRIBUTE ::= { WITH SYNTAX ContentDecryptKeyID ID 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 March 08, 2010 [Page 9] Internet-Draft Encrypted Key Package Content Type September 2009 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 March 08, 2010 [Page 10]