draft-ietf-smime-cms-rsaes-oaep-00.txt   draft-ietf-smime-cms-rsaes-oaep-01.txt 
S/MIME Working Group R. Housley S/MIME Working Group R. Housley
Internet Draft SPYRUS Internet Draft SPYRUS
expires in six months February 2000 expires in six months June 2000
CMS RSAES-OAEP Conventions Use of the RSAES-OAEP Key Transport Algorithm in CMS
<draft-ietf-smime-cms-rsaes-oaep-00.txt> <draft-ietf-smime-cms-rsaes-oaep-01.txt>
Status of this Memo Status of this Memo
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Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2000). All Rights Reserved. Copyright (C) The Internet Society (2000). All Rights Reserved.
Abstract Abstract
This document describes the use of the RSAES-OAEP key transport This document describes the use of the RSAES-OAEP key transport
method of key management within the Cryptographic Message Syntax method of key management within the Cryptographic Message Syntax
[CMS]. [CMS].
This draft is being discussed on the "ietf-smime" mailing list. To This draft is being discussed on the "ietf-smime" mailing list. To
join the list, send a message to <ietf-smime-request@imc.org> with join the list, send a message to <ietf-smime-request@imc.org> with
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smime/>. smime/>.
1 Introduction 1 Introduction
When the variant of the RSA algorithm specified in PKCS #1 Version When the variant of the RSA key transport algorithm specified in PKCS
1.5 [PKCS#1v1.5] is used for key management, it is vulnerable to #1 Version 1.5 [PKCS#1v1.5] is used for key management, it is
adaptive chosen ciphertext attacks. The use of PKCS #1 Version 1.5 vulnerable to adaptive chosen ciphertext attacks. This attack is
explained in [RSALAB] and [CRYPTO98]. The use of PKCS #1 Version 1.5
key transport in interactive applications is especially vulnerable. key transport in interactive applications is especially vulnerable.
Exploitation of this identified vulnerability, revealing the result Exploitation of this identified vulnerability, revealing the result
of a particular RSA decryption, requires access to an oracle which of a particular RSA decryption, requires access to an oracle which
will respond to hundreds of thousands of ciphertexts, which are will respond to hundreds of thousands of ciphertexts, which are
constructed adaptively in response to previously-received replies constructed adaptively in response to previously-received replies
providing information on the successes or failures of attempted providing information on the successes or failures of attempted
decryption operations. As a result, the attack appears significantly decryption operations.
less feasible in store-and-forward environments, such as S/MIME.
When PKCS #1 Version 1.5 key transport is applied as an intermediate The attack appears significantly less feasible in store-and-forward
encryption layer within an interactive request-response environments, such as S/MIME. When PKCS #1 Version 1.5 key transport
communications environment, exploitation could be more feasible. is applied as an intermediate encryption layer within an interactive
request-response communications environment, exploitation could be
more feasible. However, Secure Sockets Layer (SSL) [SSL] and
Transport Layer Security (TLS) [TLS] protocol implementations could
include countermeasures that detect and prevent Bleichenbacher's and
other chosen-ciphertext attacks, without changing the way the RSA key
transport algorithm is used. These countermeasures are performed
within the protocol level. In the interest of long-term security
assurance, it is prudent to adopt an improved cryptographic technique
rather than embedding countermeasures within protocols.
An updated version of PKCS #1 has been published, PKCS #1 Version 2.0 An updated version of PKCS #1 has been published, PKCS #1 Version 2.0
[PKCS#1v2.0]. This new document supersedes RFC 2313. PKCS #1 [PKCS#1v2.0]. This new document supersedes RFC 2313. PKCS #1
Version 2.0 preserves support for the encryption padding format Version 2.0 preserves support for the encryption padding format
defined in PKCS #1 Version 1.5 [PKCS#1v1.5], and it also defines a defined in PKCS #1 Version 1.5 [PKCS#1v1.5], and it also defines a
new alternative. To resolve the adaptive chosen ciphertext new alternative. To resolve the adaptive chosen ciphertext
vulnerability, the PKCS #1 Version 2.0 specifies and recommends use vulnerability, the PKCS #1 Version 2.0 specifies and recommends use
of Optimal Asymmetric Encryption Padding (OAEP) when RSA encryption of Optimal Asymmetric Encryption Padding (OAEP) when RSA encryption
is used to provide confidentiality. is used to provide confidentiality, such as key transport.
This document specifies the use of RSAES-OAEP key transport algorithm This document specifies the use of RSAES-OAEP key transport algorithm
in the Cryptographic Message Syntax (CMS) [CMS]. in the Cryptographic Message Syntax (CMS) [CMS]. CMS can be used in
either a store-and-forward or an interactibe request-response
environment.
CMS supports variety of architectures for certificate-based key CMS supports variety of architectures for certificate-based key
management, particularly the one defined by the PKIX working group management, particularly the one defined by the PKIX working group
[PROFILE]. [PROFILE].
CMS values are generated using ASN.1 [X.208-88], using the Basic CMS values are generated using ASN.1 [X.208-88], using the Basic
Encoding Rules (BER) [X.209-88] and the Distinguished Encoding Rules Encoding Rules (BER) [X.209-88] and the Distinguished Encoding Rules
(DER) [X.509-88]. (DER) [X.509-88].
Throughout this document, when the terms MUST, MUST NOT, SHOULD and Throughout this document, when the terms MUST, MUST NOT, SHOULD and
skipping to change at page 3, line 8 skipping to change at page 3, line 17
definitions in [MUSTSHOULD]. [MUSTSHOULD] defines these key words to definitions in [MUSTSHOULD]. [MUSTSHOULD] defines these key words to
help make the intent of standards track documents as clear as help make the intent of standards track documents as clear as
possible. The same key words are used in this document to help possible. The same key words are used in this document to help
implementers achieve interoperability. Implementations that claims implementers achieve interoperability. Implementations that claims
compliance with this document MUST provide the capabilities as compliance with this document MUST provide the capabilities as
indicated by the MUST, MUST NOT, SHOULD and MAY terms. indicated by the MUST, MUST NOT, SHOULD and MAY terms.
2 Enveloped-data Conventions 2 Enveloped-data Conventions
The CMS enveloped-data content type consists of encrypted content and The CMS enveloped-data content type consists of encrypted content and
wrapped content-encryption keys for one or more recipients. The RSAES- wrapped content-encryption keys for one or more recipients. The
OAEP key transport algorithm is used to wrap the content-encryption key RSAES-OAEP key transport algorithm is used to wrap the content-
for one recipient. encryption key for one recipient.
Compliant software MUST meet the requirements for constructing an Compliant software MUST meet the requirements for constructing an
enveloped-data content type stated in [CMS] Section 6, "Enveloped-data enveloped-data content type stated in [CMS] Section 6, "Enveloped-
Content Type". [CMS] Section 6 should be studied before reading this data Content Type". [CMS] Section 6 should be studied before reading
section, because this section does not repeat the [CMS] text. this section, because this section does not repeat the [CMS] text.
A content-encryption key MUST be randomly generated for each instance of A content-encryption key MUST be randomly generated for each instance
an enveloped-data content type. The content-encryption key is used to of an enveloped-data content type. The content-encryption key is
encipher the content. used to encipher the content.
2.1 EnvelopedData Fields 2.1 EnvelopedData Fields
The enveloped-data content type is ASN.1 encoded using the The enveloped-data content type is ASN.1 encoded using the
EnvelopedData syntax. The fields of the EnvelopedData syntax must be EnvelopedData syntax. The fields of the EnvelopedData syntax must be
populated as follows: populated as follows:
The EnvelopedData version MUST be either 0 or 2. The EnvelopedData version MUST be either 0 or 2.
The EnvelopedData originatorInfo field MUST be absent. The EnvelopedData originatorInfo field MUST be absent.
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iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-1(1) 8 } iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-1(1) 8 }
id-pSpecified OBJECT IDENTIFIER ::= { id-pSpecified OBJECT IDENTIFIER ::= {
iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-1(1) 9 } iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-1(1) 9 }
The fields of type RSAES-OAEP-params have the following meanings: The fields of type RSAES-OAEP-params have the following meanings:
hashFunc identifies the one-way hash function. Implementations hashFunc identifies the one-way hash function. Implementations
MUST support SHA-1 [SHA1]. The SHA-1 algorithm identifier is MUST support SHA-1 [SHA1]. The SHA-1 algorithm identifier is
comprised of the id-sha1 object identifier and a parameter of comprised of the id-sha1 object identifier and a parameter of
NULL. NULL. Implementations that perform encryption MUST omit the
hashFunc field when SHA-1 is used, indicating that the default
algorithm was used. Implementations that perform decryption MUST
recognize both the id-sha1 object identifier and an absent
hashFunc field as an indication that SHA-1 was used.
maskGenFunc identifies the mask generation function. maskGenFunc identifies the mask generation function.
Implementations MUST support MFG1 [PKCS#1v2.0]. MFG1 requires a Implementations MUST support MFG1 [PKCS#1v2.0]. MFG1 requires a
one-way hash function, and it is identified in the parameter field one-way hash function, and it is identified in the parameter field
of the algorithm identifier. Implementations MUST support SHA-1 of the algorithm identifier. Implementations MUST support SHA-1
[SHA1]. The MFG1 algorithm identifier is comprised of the id-mgf1 [SHA1]. The MFG1 algorithm identifier is comprised of the id-mgf1
object identifier and a parameter of the SHA-1 algorithm object identifier and a parameter of the SHA-1 algorithm
identifier. Again, the SHA-1 algorithm identifier is comprised of identifier. Again, the SHA-1 algorithm identifier is comprised of
the id-sha1 object identifier and a parameter of NULL. the id-sha1 object identifier and a parameter of NULL.
Implementations that perform encryption MUST omit the maskGenFunc
field when MFG1 with SHA-1 is used, indicating that the default
algorithm was used. Implementations that perform decryption MUST
recognize both the id-mgf1 and id-sha1 object identifiers as well
as an absent maskGenFunc field as an indication that MFG1 with
SHA-1 was used.
pSourceFunc identifies the source (and possibly the value) of the pSourceFunc identifies the source (and possibly the value) of the
encoding parameters, commonly called P. Implementations MUST encoding parameters, commonly called P. Implementations MUST
represent P by an algorithm identifier, id-pSpecified, indicating represent P by an algorithm identifier, id-pSpecified, indicating
that P is explicitly provided as an OCTET STRING in the that P is explicitly provided as an OCTET STRING in the
parameters. The default value for P is an empty string. In this parameters. The default value for P is an empty string. In this
case, pHash in EME-OAEP contains the hash of a zero length string. case, pHash in EME-OAEP contains the hash of a zero length string.
Implementations MUST support a zero length P value.
Implementations that perform encryption MUST omit the pSourceFunc
field when a zero length P value is used, indicating that the
default value was used. Implementations that perform decryption
MUST recognize both the id-pSpecified object identifier and an
absent pSourceFunc field as an indication that a zero length P
value was used.
4 SMIMECapabilities Attribute Conventions 4 SMIMECapabilities Attribute Conventions
RFC 2633, Section 2.5.2 defines the SMIMECapabilities signed RFC 2633, Section 2.5.2 defines the SMIMECapabilities signed
attribute (defined as a SEQUENCE of SMIMECapability SEQUNCEs) to be attribute (defined as a SEQUENCE of SMIMECapability SEQUNCEs) to be
used to specify a partial list of algorithms that the software used to specify a partial list of algorithms that the software
announcing the SMIMECapabilities can support. When constructing a announcing the SMIMECapabilities can support. When constructing a
signedData object, compliant software MAY include the signedData object, compliant software MAY include the
SMIMECapabilities signed attribute announcing that it supports the SMIMECapabilities signed attribute announcing that it supports the
RSAES-OAEP algorithm. RSAES-OAEP algorithm.
The SMIMECapability SEQUENCE representing RSAES-OAEP MUST include the The SMIMECapability SEQUENCE representing RSAES-OAEP MUST include the
id-RSAES-OAEP object identifier in the capabilityID field and MUST id-RSAES-OAEP object identifier in the capabilityID field and MUST
include a RSAES-OAEP-Default-Identifier SEQUENCE in the parameters include the RSAES-OAEP-Default-Identifier SEQUENCE in the parameters
field. field.
RSAES-OAEP-Default-Identifier ::= AlgorithmIdentifier { RSAES-OAEP-Default-Identifier ::= AlgorithmIdentifier {
id-RSAES-OAEP, { id-RSAES-OAEP, {
sha1Identifier, mgf1SHA1Identifier, pSpecifiedEmptyIdentifier } } sha1Identifier, mgf1SHA1Identifier, pSpecifiedEmptyIdentifier } }
The SMIMECapability SEQUENCE representing RSAES-OAEP MUST be DER- When all of the default settings are selected, the SMIMECapability
encoded as follows: {{{TBD}}}. SEQUENCE representing RSAES-OAEP MUST be DER-encoded as: 30 length
[id-RSAES-OAEP OID encoding] [30 00].
References References
CMS Housley, R. Cryptographic Message Syntax. RFC 2630. CMS Housley, R. Cryptographic Message Syntax. RFC 2630.
June 1999. June 1999.
CRYPTO98 Bleichenbacher, D. "Chosen Ciphertext Attacks Against
Protocols Based on the RSA Encryption Standard PKCS #1,"
in H. Krawczyk (editor), Advances in Cryptology - CRYPTO '98
Proceedings, Lecture Notes in Computer Science 1462 (1998),
Springer-Verlag, pp. 1-12.
MUSTSHOULD Bradner, S. Key Words for Use in RFCs to Indicate MUSTSHOULD Bradner, S. Key Words for Use in RFCs to Indicate
Requirement Levels. BCP 14, RFC 2119. March 1997. Requirement Levels. BCP 14, RFC 2119. March 1997.
PKCS#1v1.5 Kaliski, B. PKCS #1: RSA Encryption, Version 1.5. PKCS#1v1.5 Kaliski, B. PKCS #1: RSA Encryption, Version 1.5.
RFC 2313. March 1998. RFC 2313. March 1998.
PKCS#1v2.0 Kaliski, B. PKCS #1: RSA Encryption, Version 2.0. PKCS#1v2.0 Kaliski, B. PKCS #1: RSA Encryption, Version 2.0.
RFC 2347. October 1998. RFC 2347. October 1998.
PROFILE Housley, R., W. Ford, W. Polk, and D. Solo. Internet PROFILE Housley, R., W. Ford, W. Polk, and D. Solo. Internet
X.509 Public Key Infrastructure: Certificate and CRL X.509 Public Key Infrastructure: Certificate and CRL
Profile. RFC 2459. January 1999. Profile. RFC 2459. January 1999.
RANDOM Eastlake, D., S. Crocker, and J. Schiller. Randomness RANDOM Eastlake, D., S. Crocker, and J. Schiller. Randomness
Recommendations for Security. RFC 1750. December 1994. Recommendations for Security. RFC 1750. December 1994.
RSALABS Daniel Bleichenbacher, D., B. Kaliski, and J. Staddon.
Recent Results on PKCS #1: RSA Encryption Standard. RSA
Laboratories' Bulletin No. 7, June 26, 1998.
[Available at http://www.rsasecurity.com/rsalabs/bulletins]
SHA1 National Institute of Standards and Technology. SHA1 National Institute of Standards and Technology.
FIPS Pub 180-1: Secure Hash Standard. 17 April 1995. FIPS Pub 180-1: Secure Hash Standard. 17 April 1995.
SSL Freier, A., P. Karlton, and P. Kocher. The SSL Protocol,
Version 3.0. Netscape Communications. November 1996.
[Available at http://draft-freier-ssl-version3-02.txt]
TLS Dierks, T. and C. Allen. The TLS Protocol Version 1.0.
RFC 2246. January 1999.
X.208-88 CCITT. Recommendation X.208: Specification of Abstract X.208-88 CCITT. Recommendation X.208: Specification of Abstract
Syntax Notation One (ASN.1). 1988. Syntax Notation One (ASN.1). 1988.
X.209-88 CCITT. Recommendation X.209: Specification of Basic Encoding X.209-88 CCITT. Recommendation X.209: Specification of Basic Encoding
Rules for Abstract Syntax Notation One (ASN.1). 1988. Rules for Abstract Syntax Notation One (ASN.1). 1988.
X.509-88 CCITT. Recommendation X.509: The Directory - Authentication X.509-88 CCITT. Recommendation X.509: The Directory - Authentication
Framework. 1988. Framework. 1988.
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