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Network Working Group                                          L. MartinRequest for Comments: 5409                              Voltage SecurityCategory: Informational                                     M. Schertler                                                                   Axway                                                            January 2009Using the Boneh-Franklin and Boneh-Boyen Identity-Based EncryptionAlgorithms with the Cryptographic Message Syntax (CMS)Status of This Memo   This memo provides information for the Internet community.  It does   not specify an Internet standard of any kind.  Distribution of this   memo is unlimited.Copyright Notice   Copyright (c) 2009 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.Abstract   This document describes the conventions for using the Boneh-Franklin   (BF) and Boneh-Boyen (BB1) identity-based encryption algorithms in   the Cryptographic Message Syntax (CMS) to encrypt content-encryption   keys.  Object identifiers and the convention for encoding a   recipient's identity are also defined.Martin & Schertler           Informational                      [Page 1]

RFC 5409                   Using IBE with CMS               January 2009Table of Contents1. Introduction ....................................................21.1. Terminology ................................................31.2. IBE Overview ...............................................32. Using Identity-Based Encryption .................................33. Key Encryption Algorithm Identifiers ............................64. Processing by the Sender ........................................75. Processing by the Receiver ......................................76. ASN.1 Module ....................................................87. Security Considerations .........................................97.1. Attacks outside the Scope of This Document .................97.2. Attacks within the Scope of This Document .................10      7.3. Attacks to Which the Protocols Defined in This Document           Are Susceptible............................................118. References .....................................................128.1. Normative References ......................................128.2. Informative References ....................................121.  Introduction   This document defines the way to use the Boneh-Franklin [IBCS] and   Boneh-Boyen [IBCS] identity-based encryption (IBE) public-key   algorithms in the Cryptographic Message Syntax (CMS) [CMS].  IBE is a   public-key technology for encrypting content-encryption keys (CEKs)   that can be implemented within the framework of the CMS: 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 and BB1 algorithms, which are   described in detail in [IBCS].   IBE algorithms are a type of public-key cryptographic algorithm in   which the public key is calculated directly from a user's identity   instead of being generated randomly.  This requires a different set   of steps for encryption and decryption than would be used with other   public-key algorithms, and these steps are defined in Sections4 and   5 of this document, respectively.   This document also 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 ASN.1 [ASN1].Martin & Schertler           Informational                      [Page 2]

RFC 5409                   Using IBE with CMS               January 20091.1.  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 inRFC 2119 [KEYWORDS].1.2.  IBE Overview   In addition to the client components that are described in this   document, the following additional components are required for a   complete IBE messaging system.      o  A Private-Key Generator (PKG).  The PKG contains the         cryptographic material, known as a master secret, for         generating an individual's IBE private key.  A PKG accepts an         IBE user's private key request and, after successfully         authenticating them in some way, returns their IBE private key.      o  A Public Parameter Server (PPS).  IBE system parameters include         publicly sharable cryptographic material, known as IBE public         parameters, and policy information for the PKG.  A PPS provides         a well-known location for distribution of IBE public parameters         and policy information for the IBE PKG.   The interactions of senders and receivers of IBE-encrypted messages   are described in [IBE].  All communications between users of an IBE   system and the PPS or PKG MUST be protected using TLS [TLS] as   described in [IBE].  This provides confidentiality and integrity of   all information that is delivered to users as well as authentication   of the PPS and PKG.2.  Using Identity-Based Encryption   To use IBE, the ori field in RecipientInfo MUST be used.  The fields   are set as follows: oriType is set to ibeORIType; oriValue is set to   ibeORIValue.   These fields 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 the following:   ibeORIType OBJECT IDENTIFIER ::= {     joint-iso-itu(2) country(16) us(840)     organization(1) identicrypt(114334)     ibcs(1) cms(4) ori-oid(1) version(1)   }Martin & Schertler           Informational                      [Page 3]

RFC 5409                   Using IBE with CMS               January 2009   ibeORIValue defines the identity that was used in the IBE algorithm   to encrypt the CEK.  This is an IBERecipientInfo type, which is   defined as follows:   IBERecipientInfo ::= SEQUENCE {     cmsVersion         INTEGER { v3(3) },     keyFetchMethod     OBJECT IDENTIFIER,     recipientIdentity  IBEIdentityInfo,     serverInfo         SEQUENCE SIZE (1..MAX) OF       OIDValuePairs OPTIONAL,     encryptedKey       EncryptedKey   }   The fields of IBERecipientInfo MUST be set as follows.   The cmsVersion MUST be set to 3.   The keyFetchMethod is the OID that defines the method of retrieving   the private key that the recipient MUST use.  This SHOULD be set to   uriPPSOID [IBE], which is defined to be the following:   uriPPSOID OBJECT IDENTIFIER ::= {     joint-iso-itu-t(2) country(16) us(840)     organization(1) identicrypt(114334)     pps-schemas(3) ic-schemas(1) pps-uri(1) version(1)   }   The recipientIdentity is the data that the sender used to calculate   the IBE public key that the sender used to encrypt the content-   encryption key.  This recipientIdentity is used to calculate IBE   public and private keys as described in [IBCS].  This MUST be a DER-   encoded [DER] IBEIdentityInfo type [IBE], which is defined as   follows:   IBEIdentityInfo ::= SEQUENCE {     district        IA5String,     serial          INTEGER,     identityType    OBJECT IDENTIFIER,     identityData    OCTET STRING   }   The identityType defines the format that is used to encode the   information that defines the identity of the recipient.  This MUST be   set to cmsIdentityOID to indicate that identityData contains an   EmailIdentityData type.  The value of cmsIdentityOID is the   following:Martin & Schertler           Informational                      [Page 4]

RFC 5409                   Using IBE with CMS               January 2009   cmsIdentityOID OBJECT IDENTIFIER ::= {     joint-iso-itu-t(2) country(16) us(840)     organization(1) identicrypt(114334)     keyschemas(2) icschemas(1) email(1) version(1)   }   The identityData MUST be an EmailIdentityData type, which is defined   as follows:   EmailIdentityData ::= SEQUENCE {     rfc822Name   IA5String,     time         GeneralizedTime   }   The rfc822Name field is the email address of the recipient in the   format defined in Section 4.2.1.6 of [PKIX] for the rfc822Name   subjectAltName variant.  Rules for encoding Internet mail addresses   that include internationalized domain names are specified inSection7.5 of [PKIX].   The value of the time field is the UTC time after 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.  The value of   "time" MUST be expressed in Greenwich Mean Time (Zulu), MUST include   seconds (i.e., times are always YYYYMMDDHHMMSSZ), even where the   number of seconds is equal to zero, and MUST be expressed to the   nearest second.   The sender of an IBE-encrypted message may want to express this time   rounded to a time interval to create a key lifetime.  A key lifetime   reduces the number of IBE private keys that a recipient needs to   retrieve, but still forces the IBE user to periodically re-   authenticate.  Based on the time interval chosen a recipient would   only have to retrieve a new IBE key once during the interval.  To do   this, follow the steps below.  Let "time-interval" be the number of   seconds in this larger time interval.      1. Find the GeneralizedTime for the not-before value.      2. Convert this GeneralizedTime 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 GeneralizedTime to get the not-before         "time" value.   An example of this algorithm for computing a one-week time interval   is as follows.Martin & Schertler           Informational                      [Page 5]

RFC 5409                   Using IBE with CMS               January 2009      1. Suppose that the GeneralizedTime is 20020401000000Z.      2. Then the total-time is 1017612000.      3. A time-interval of 1 week is 604800 seconds.         So the reduced-time = (floor (1017612000 / 604800)) * 604800 =         1017273600.      4. This gives the GeneralizedTime form of the reduced-time of         20020328000000Z.   When issuing IBE private keys, a PKG SHOULD NOT issue them too far   into the future.  This restriction is to prevent an adversary who   obtains an IBE user's authentication credentials from requesting   private keys far into the future and therefore negating the periodic   IBE user re-authentication that key lifetime provides.  For example,   if a one-week period is chosen for the key lifetime, then IBE private   keys should not be issued more than one week in advance.  Otherwise,   once an adversary gains access to the PKG via the stolen IBE user   credentials, they can request all future keys and negate the IBE user   authentication restraints in place.   The serverInfo is an optional sequence of OID-value pairs that are   defined to be the following:   OIDValuePairs ::= SEQUENCE {     fieldID     OBJECT IDENTIFIER,     fieldData   OCTET STRING   }   These can be used to convey any other information that might be used   by a PKG.  Examples of such information could include the user   interface that the recipient will experience.  Differences in the   user interface could include localization information or commercial   branding information.  A client MUST ignore any part of serverInfo   that it is unable to process.   The encryptedKey is the result of encrypting the CEK with an IBE   algorithm using recipientIdentity as the IBE public key.3.  Key Encryption Algorithm Identifiers   The BF and BB1 algorithms as defined in [IBCS] have the following   object identifiers.  These object identifiers are also defined in the   ASN.1 module in [IBCS].   bf OBJECT IDENTIFIER ::= {     joint-iso-itu-t(2) country(16) us(840)     organization(1) identicrypt(114334)     ibcs(1) ibcs1(1) ibe-algorithms(2) bf(1)   }Martin & Schertler           Informational                      [Page 6]

RFC 5409                   Using IBE with CMS               January 2009   This is the object identifier that MUST be inserted in the   keyEncryptionAlgorithm field in the CMS when the BF algorithm is used   to encrypt the CEK.   bb1 OBJECT IDENTIFIER ::= {     joint-iso-itu-t(2) country(16) us(840)     organization(1) identicrypt(114334)     ibcs(1) ibcs1(1) ibe-algorithms(2) bb1(2)   }   This is the object identifier that MUST be inserted in the   keyEncryptionAlgorithm field in the CMS when the BB1   algorithm is used to encrypt the CEK.4.  Processing by the Sender   The sender of a message that uses 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         [IBE].  This information MUST be encoded in the         IBEIdentityInfo as described inSection 2.      2. Sets the fields of an OtherRecipientInfo object to         their appropriate values as described inSection 2.      3. Calculates an IBE public key as defined in [IBCS]         using this IBEIdentityInfo as the identity information.      4. This 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 IBE-encrypted CEK.      6. Within the CMS, keyEncryptionAlgorithm MUST then be         set to the appropriate OID for the IBE algorithm that was         used (seeSection 3).5.  Processing by the Receiver   Upon receiving a message that has a CEK encrypted with IBE,   the recipient performs the following steps to decrypt the   CEK:Martin & Schertler           Informational                      [Page 7]

RFC 5409                   Using IBE with CMS               January 2009      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 IBE encryption of the CEK.      3. Determines the location of the IBE public parameters         and the IBE Private Key Generator as described in         [IBE].      4. Obtains the IBE public parameters from the location         determined in Step 3 using the process defined in         [IBE].      5. Obtains the IBE private key needed to decrypt the         encrypted CEK using the process defined in [IBE].      6. Decrypts the CEK using the IBE private key obtained in         Step 4 using the algorithms described in [IBCS].6.  ASN.1 Module   The following ASN.1 module summarizes the ASN.1 definitions   defined by this document.   IBECMS-module {     joint-iso-itu-t(2) country(16) us(840)     organization(1) identicrypt(114334)     ibcs(1) cms(4) module(5) version(1)   }   DEFINITIONS IMPLICIT TAGS ::= BEGIN   IMPORTS IBEIdentityInfo, uriPPSOID FROM      IBEARCH-module { joint-iso-itu-t(2) country(16)        us(840) organization(1) identicrypt(114334) ibcs(1)        ibearch(5) module(5) version(1)      };   IBEOtherRecipientInfo ::= SEQUENCE {     oriType   OBJECT IDENTIFIER,     oriValue  IBERecipientInfo   }Martin & Schertler           Informational                      [Page 8]

RFC 5409                   Using IBE with CMS               January 2009   ibeORIType OBJECT IDENTIFIER ::= {     joint-iso-itu-t(2) country(16) us(840)     organization(1) identicrypt(114334)     ibcs(1) cms(4) ori-oid(1) version(1)   }   IBERecipientInfo ::= SEQUENCE {     cmsVersion         INTEGER { v3(3) },     keyFetchMethod     OBJECT IDENTIFIER,     recipientIdentity  IBEIdentityInfo,     serverInfo         SEQUENCE SIZE (1..MAX) OF       OIDValuePairs OPTIONAL,     encryptedKey       EncryptedKey   }   OIDValuePairs ::= SEQUENCE {     fieldID     OBJECT IDENTIFIER,     fieldData   OCTET STRING   }   EncryptedKey ::= OCTET STRING   EmailIdentityData ::= SEQUENCE {     rfc822Name   IA5String,     time         GeneralizedTime   }   cmsIdentityOID OBJECT IDENTIFIER ::= {     joint-iso-itu-t(2) country(16) us(840)     organization(1) identicrypt(114334)     keyschemas(2) icschemas(1) email(1) version(1)   }   END7.  Security Considerations   This document is based on [CMS], [IBCS], and [IBE], and the relevant   security considerations of those documents apply.7.1.  Attacks outside the Scope of This Document   Attacks on the cryptographic algorithms that are used to implement   IBE are outside the scope of this document.  Such attacks are   detailed in [IBCS], which defines parameters that give 80-bit,Martin & Schertler           Informational                      [Page 9]

RFC 5409                   Using IBE with CMS               January 2009   112-bit, 128-bit, and 256-bit encryption strength.  We assume that   capable administrators of an IBE system will select parameters that   provide a sufficient resistance to cryptanalytic attacks by   adversaries.   Attacks that give an adversary the ability to access or change the   information on a PPS or PKG, especially the cryptographic material   (referred to in this document as the master secret), will defeat the   security of an IBE system.  In particular, if the cryptographic   material is compromised, the adversary will have the ability to   recreate any user's private key and therefore decrypt all messages   protected with the corresponding public key.  To address this   concern, it is highly RECOMMENDED that best practices for physical   and operational security for PPS and PKG servers be followed and that   these servers be configured (sometimes known as hardened) in   accordance with best current practices [NIST].  An IBE system SHOULD   be operated in an environment where illicit access to the PKG or the   ability to modify the information distributed by the PPS is   infeasible for attackers to obtain.   Attacks that require administrative access or IBE-user-equivalent   access to machines used by either the client or the server components   defined in this document are also outside the scope of this document.   We also assume that all administrators of a system implementing the   protocols that are defined in this document are trustworthy and will   not abuse their authority to bypass the security provided by an IBE   system.  This is of particular importance with an IBE system, for an   administrator of a PKG could potentially abuse his authority and   configure the PKG to grant him any IBE private key that the PKG is   capable of calculating.  To minimize the possibility of   administrators doing this, a system implementing IBE SHOULD implement   n-out-of-m control for critical administrative functions and SHOULD   maintain auditable logs of all security-critical events that occur in   an operating IBE system.   Similarly, we assume that users of an IBE system will behave   responsibly, not sharing their authentication credentials with   others.  Thus, attacks that require such assumptions are outside the   scope of this document.7.2.  Attacks within the Scope of This Document   Attacks within the scope of this document are those that allow an   adversary to:      o  passively monitor information transmitted between users of an         IBE system and the PPS and PKGMartin & Schertler           Informational                     [Page 10]

RFC 5409                   Using IBE with CMS               January 2009      o  masquerade as a PPS or PKG      o  perform a denial-of-service (DoS) attack on a PPS or PKG      o  easily guess an IBE user's authentication credential7.3.  Attacks to Which the Protocols Defined in This Document      Are Susceptible   All communications between users of an IBE system and the PPS or PKG   are protected using TLS [TLS].  The IBE system defined in this   document provides no additional security for the communications   between IBE users and the PPS or PKG.  Therefore, the described IBE   system is completely dependent on the TLS security mechanisms for   authentication of the PKG or PPS server and for confidentiality and   integrity of the communications.  Should there be a compromise of the   TLS security mechanisms, the integrity of all communications between   an IBE user and the PPS or PKG will be suspect.   The protocols defined in this document do not explicitly defend   against an attacker masquerading as a legitimate IBE PPS or PKG.  The   protocols rely on the server authentication mechanism of TLS [TLS].   In addition to the TLS server authentication mechanism, IBE client   software can provide protection against this possibility by providing   user interface capabilities that allows users to visually determine   that a connection to PPS and PKG servers is legitimate.  This   additional capability can help ensure that users cannot easily be   tricked into providing valid authorization credentials to an   attacker.   The protocols defined in this document are also vulnerable to attacks   against an IBE PPS or PKG.  Denial-of-service attacks against either   component can result in users unable to encrypt or decrypt using IBE,   and users of an IBE system SHOULD take the appropriate   countermeasures [DOS,BGPDOS] that their use of IBE requires.   The IBE user authentication method used by an IBE PKG SHOULD be of   sufficient strength to prevent attackers from easily guessing the IBE   user's authentication credentials through trial and error.Martin & Schertler           Informational                     [Page 11]

RFC 5409                   Using IBE with CMS               January 20098.  References8.1.  Normative References   [ASN1]     ITU-T Recommendation X.680: Information Technology -              "Abstract Syntax Notation One (ASN.1): Specification of              Basic Notation", July 2002.   [CMS]      Housley, R., "Cryptographic Message Syntax (CMS)",RFC3852, July 2004.   [DER]      ITU-T Recommendation X.690: OSI Networking and System              Aspects: Abstract Syntax Notation One (ASN.1), July 2002.   [DOS]      Ferguson, P. and D. Senie, "Network Ingress Filtering:              Defeating Denial of Service Attacks which employ IP Source              Address Spoofing",BCP 38,RFC 2827, May 2000.   [IBCS]     Boyen, X. and L. Martin, "Identity-Based Cryptography              Standard (IBCS) #1: Supersingular Curve Implementations of              the BF and BB1 Cryptosystems",RFC 5091, December 2007.   [IBE]      Appenzeller, G., Martin, L., and M. Schertler, "Identity-              Based Encryption Architecture and Supporting Data              Structures",RFC 5408, January 2009.   [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels",BCP 14,RFC 2119, March 1997.   [PKIX]     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.   [TLS]      Dierks, T. and E. Rescorla, "The Transport Layer Security              (TLS) Protocol Version 1.2",RFC 5246, August 2008.8.2.  Informative References   [BGPDOS]   Turk, D., "Configuring BGP to Block Denial-of-Service              Attacks",RFC 3882, September 2004.   [NIST]     M. Souppaya, J. Wack and K. Kent, "Security Configuration              Checklist Program for IT Products - Guidance for Checklist              Users and Developers", NIST Special Publication SP 800-70,              May 2005.Martin & Schertler           Informational                     [Page 12]

RFC 5409                   Using IBE with CMS               January 2009Authors' Addresses   Luther Martin   Voltage Security   1070 Arastradero Rd, Suite 100   Palo Alto, CA 94304   USA   Phone: +1 650 543 1280   EMail: martin@voltage.com   Mark Schertler   Axway   1600 Seaport Blvd, Suite 400   Redwood City, CA 94063   USA   Phone: +1 650 216 2039   EMail: mschertler@us.axway.comMartin & Schertler           Informational                     [Page 13]