L. Martin S/MIME Working Group M. Schertler Internet Draft Voltage Security Expires: December 2006 June 2006 Using the Boneh-Franklin identity-based encryption algorithm with the Cryptographic Message Syntax (CMS) Status of this Document By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of 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 Abstract This document describes the conventions for using the Boneh-Franklin identity-based encryption (BF-IBE) algorithm in the Cryptographic Message Syntax (CMS). The BF-IBE algorithm supports the transport of symmetric keys to encrypt content encryption keys. Object identifiers and the convention for encoding a recipient’s identity are also defined. Martin, Schertler Expires December 2006 [Page 1] Internet-Draft Using BF-IBE with CMS June 2006 Table of Contents 1. Introduction...................................................2 1.1. Terminology...............................................2 2. Using identity-based encryption................................3 3. Algorithm object identifier....................................5 4. Processing by the sender.......................................6 5. Processing by the receiver.....................................6 6. ASN.1 Module...................................................7 7. Security Considerations........................................9 8. IANA Considerations............................................9 9. References....................................................10 9.1. Normative References.....................................10 Author's Addresses...............................................10 Intellectual Property Statement..................................10 Disclaimer of Validity...........................................11 Copyright Statement..............................................11 Acknowledgment...................................................11 1. Introduction This document defines the steps needed to use the Boneh-Franklin identity-based encryption (BF-IBE) public-key algorithm [BF] in the Cryptographic Message Syntax (CMS) [CMS]. BF-IBE is a public key technology for encrypting content-encryption keys (CEKs). The recipient’s identity is incorporated into the EnvelopedData CMS content type using the OtherRecipientInfo CHOICE in the RecipientInfo field as defined in section 6.2.5 of [CMS]. This document does not describe the implementation of the BF-IBE algorithm, which is described in detail in [IBCS]. The BF-IBE algorithm is a public-key algorithm in which the public key is calculated directly from a user’s identity instead of being generated randomly. This document defines the object identifiers and syntax of the object that is used to define the identity of a message recipient. CMS values and identity objects are defined using ANS.1 [ASN1]. 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 RFC-2119 [KEYWORDS]. Martin, Schertler Expires December 2006 [Page 2] Internet-Draft Using BF-IBE with CMS June 2006 2. Using identity-based encryption To use IBE, the OtherRecipientInfo field MUST be set to an IBEOtherRecipient type. IBEOtherRecipientInfo ::= SEQUENCE { ibeORIType OBJECT IDENTIFIER, ibeORIValue IBERecipientInfo } The fields of IBEOtherRecipientInfo have the following meanings: ibeORIType defines the object identifier (OID) that indicates that the subsequent ibeORIValue is the information necessary to decrypt the message using IBE. This field MUST be set to ibeORIType OBJECT IDENTIFIER ::= { joint-iso-itu(2) country(16) us(840) organization(1) identicrypt(114334) ibcs(1) cms(4) ori-oid(1) } ibeORIValue defines the identity that was used in the BF-IBE algorithm to encrypt the CEK. This is an IBERecipientInfo type. IBERecipientInfo ::= SEQUENCE { cmsVersion INTEGER { v0(0) }, keyFetchMethod OBJECT IDENTIFIER, recipientIdentity IBEIdentityInfo, serverInfo SEQUENCE OF OIDValuePairs OPTIONAL, encryptedKey EncryptedKey } The fields of IBERecipientInfo have the following meanings: cmsVersion MUST be set to 0. Martin, Schertler Expires December 2006 [Page 3] Internet-Draft Using BF-IBE with CMS June 2006 keyFetchMethod is the OID that defines the method of retrieving the private key that the recipient MUST use. How to retrieve an IBE private key using the steps defined in [IBEPPS] is defined by the keyFetchMethod OID. The method for retrieving private keys that is specified in [IBEPPS] is defined by cmsPPSOID. cmsPPSOID OBJECT IDENTIFIER ::= { joint-iso-itu(2) country(16) us(840) organization(1) identicrypt(114334) pps-schemas(3) ic-schemas(1) pps-uri(1) } recipientIdentity is the data that was used to calculate the public key that was used to encrypt the CEK. This MUST be an IBEIdentityInfo type. This recipientIdentity is used to calculate IBE public and private keys as described in [IBCS]. IBEIdentityInfo ::= SEQUENCE { district UTF8STRING, serial INTEGER, identitySchema OBJECT IDENTIFIER, identityData OCTET STRING } The fields of IBEIdentityInfo have the following meanings. district and serial are unique identifiers that are used to construct the URI for the location of where the IBE public parameters are located. The construction and use of this URI is defined in [IBEPPS]. identitySchema defines the format that is used to encode the information that defines the identity of the recipient. This MUST be set to cmsIdentityOID. cmsIdentityOID OBJECT IDENTIFIER ::= { joint-iso-itu(2) country(16) us(840) organization(1) identicrypt(114334) keyschemas(2) icschemas(1) rfc822email(1) Martin, Schertler Expires December 2006 [Page 4] Internet-Draft Using BF-IBE with CMS June 2006 } identityData is the data that defines the identity of the recipient. This MUST be an EmailIdentitySchema type which is DER encoded. EmailIdentitySchema ::= SEQUENCE { rfc822Email UTF8STRING, time UTCTime } rfc822Email is the DER-encoded e-mail address of the recipient in the format defined by [RFC822]. time is the DER-encoded UTC time at which the sender wants to let the recipient decrypt the message, so it may be called the “not-before” time. This is usually set to the time when the message is encrypted, but MAY be set to a future time. UTC time values are expressed to the nearest second, but the sender of an IBE-encrypted message may want to express this time rounded to a larger time interval to reduce the number of IBE private keys that a recipient needs to retrieve. To do this, follow the following steps. Let “time-interval” be the number of seconds in this larger time interval. 1. Find the UTC time for the not-before value. 2. Convert this UTC time into the number of seconds since January 1, 1970. Call this “total-time.” 3. Calculate reduced-time = ( floor( total-time / time-interval ) ) * time-interval. 4. Convert reduced-time to a UTC time to get the not-before value. 3. Algorithm object identifier The BF-IBE algorithm as defined in [IBCS] has the following object identifier: bf-ibe OBJECT IDENTIFIER ::= { joint-iso-itu(2) country(16) us(840) organization(1) identicrypt(114334) ibcs(1) ibcs1(1) Martin, Schertler Expires December 2006 [Page 5] Internet-Draft Using BF-IBE with CMS June 2006 ibe-algorithms(2) bf(1) } This is the object identifier that MUST be inserted in the keyEncryptionAlgorithm field in the CMS when the BF-IBE algorithm is used to encrypt the CEK. 4. Processing by the sender The sender of a message that uses BF-IBE to encrypt content encryption keys performs the following steps: 1. Selects a set of IBE public parameters to use in the subsequent steps in accordance with his local security policy. He then determines the URI where the public parameters can be obtained using the process described in [IBEPPS]. This information MUST be encoded in the IBEIdentityInfo as described in [IBEPPS]. 2. Sets the fields of an OtherRecipientInfo object to their appropriate values as described in Section 2. 3. Calculates a BF-IBE public key as defined in [IBCS] using this IBEIdentityInfo as the identity information. 4. This BF-IBE public key is then used to encrypt the content encryption key (CEK), using the algorithms that are defined in [IBCS]. 5. Sets encryptedKey to the BF-IBE-encrypted CEK. 6. Within the CMS, keyEncryptionAlgorithm MUST then be set to bf- ibe (see Section 3). 5. Processing by the receiver Upon receiving a message that has a CEK encrypted with BF-IBE, the recipient performs the following steps to decrypt the CEK: 1. Determines that the CEK is IBE-encrypted by noting that the oriType of the OtherRecipientInfo type is set to ibeORIType. 2. Determines that the recipientIdentity was used as the identity in BF encryption of the CEK. 3. Determines the location of the IBE public parameters and the IBE Private Key Generator as described in [IBEPPS]. Martin, Schertler Expires December 2006 [Page 6] Internet-Draft Using BF-IBE with CMS June 2006 4. Obtains the IBE public parameters from the location determined in Step 3 using the process defined in [IBEPPS]. 5. Obtains the IBE private key needed to decrypt the encrypted CEK using the process defined in [IBE3]. 6. Decrypts the CEK using the IBE private key obtained in Step 4 using the algorithms described in [IBCS]. 6. ASN.1 Module BFCMS-module { joint-iso-itu(2) country(16) us(840) organization(1) identicrypt(114334) ibcs(1) cms(4) module(5) version(1) } DEFINITIONS IMPLICIT TAGS ::= BEGIN IBEOtherRecipientInfo ::= SEQUENCE { oriType OBJECT IDENTIFIER, oriValue IBERecipientInfo } ibeORIType OBJECT IDENTIFIER ::= { joint-iso-itu(2) country(16) us(840) organization(1) identicrypt(114334) ibcs(1) cms(4) ori-oid(1) } IBERecipientInfo ::= SEQUENCE { cmsVersion INTEGER { v0(0) }, Martin, Schertler Expires December 2006 [Page 7] Internet-Draft Using BF-IBE with CMS June 2006 keyFetchMethod OBJECT IDENTIFIER, recipientIdentity IBEIdentityInfo, serverInfo SEQUENCE OF OIDValuePairs OPTIONAL, encryptedKey EncryptedKey } IBEIdentityInfo ::= SEQUENCE { district UTF8STRING, serial INTEGER, identitySchema OBJECT IDENTIFIER, identityData OCTET STRING } OIDValuePairs ::= SEQUENCE { fieldID OBJECT IDENTIFIER, fieldData OCTET STRING } EmailIdentitySchema ::= SEQUENCE { rfc822Email UTF8STRING, time UTCTime } cmsIdentityOID OBJECT IDENTIFIER ::= { joint-iso-itu(2) country(16) Martin, Schertler Expires December 2006 [Page 8] Internet-Draft Using BF-IBE with CMS June 2006 us(840) organization(1) identicrypt(114334) keyschemas(2) icschemas(1) rfc822email(1) } cmsPPSOID OBJECT IDENTIFIER ::= { joint-iso-itu(2) country(16) us(840) organization(1) identicrypt(114334) pps-schemas(3) ic-schemas(1) pps-uri(1) } END 7. Security Considerations This document is based on [CMS] and [IBCS1], and the relevant security considerations of those documents apply. 8. IANA Considerations All of the object identifiers used in this document were assigned by the National Institute of Standards and Technology (NIST), so no further action by the IANA is necessary for this document. Martin, Schertler Expires December 2006 [Page 9] Internet-Draft Using BF-IBE with CMS June 2006 9. References 9.1. Normative References [ASN1] CCITT, Recommendation X.209: Specification of Basic Encoding Rules for Abstract Syntax Notation One (ASN.1). 1998. [CMS] R. Housley, “Cryptographic Message Syntax,” RFC 3369, August 2002. [IBCS] X. Boyen, L. Martin, “Identity-based cryptography standard (IBCS) #1: supersingular curve implementations of the BF and BB1 cryptosystems,” draft-ieft-smime-ibcs-00.txt. [IBEPPS] G. Appenzeller, “Parameter and Policy Lookup for Identity- based Encryption,” draft-ietf-ibepps-00.txt. [KEYWORDS] S. Brander, “Key Words for Use in RFCs to Indicate Requirement Levels,” BCP 14, RFC 2119, March 1997. [RFC822] D. Crocker, “Standard for the format of ARPA internet text messages,” RFC 822, August 1982. Authors’ Addresses Luther Martin Voltage Security 1070 Arastradero Rd Suite 100 Palo Alto CA 94304 Phone: +1 650 543 1280 Email: martin@voltage.com Mark Schertler Voltage Security 1070 Arastradero Rd Suite 100 Palo Alto CA 94304 Phone: +1 650 543 1280 Email: mark@voltage.com Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in Martin, Schertler Expires December 2006 [Page 10] Internet-Draft Using BF-IBE with CMS June 2006 this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Disclaimer of Validity This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Copyright Statement Copyright (C) The Internet Society (2006). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Martin, Schertler Expires December 2006 [Page 11]