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)
<draft-ietf-smime-bfibecms-00.txt>
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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 recipients identity
are also defined.
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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
recipients 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 users 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].
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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.
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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)
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}
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)
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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].
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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) },
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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)
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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.
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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
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