draft-ietf-smime-cms-rsa-kem-00.txt   draft-ietf-smime-cms-rsa-kem-01.txt 
S/MIME Working Group B. Kaliski S/MIME Working Group B. Kaliski
Internet Draft RSA Laboratories Internet Draft RSA Laboratories
Document: draft-ietf-smime-cms-rsa-kem-00.txt May 2003 Document: draft-ietf-smime-cms-rsa-kem-01.txt October 2003
Category: Standards Category: Standards
Use of the RSA-KEM Key Transport Algorithm in CMS Use of the RSA-KEM Key Transport Algorithm in CMS
<draft-ietf-smime-cms-rsa-kem-00.txt> <draft-ietf-smime-cms-rsa-kem-01.txt>
Status of this Memo Status of this Memo
This document is an Internet-Draft and is subject to all provisions This document is an Internet-Draft and is subject to all provisions
of Section 10 of RFC2026. of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that
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Drafts. Drafts.
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Abstract Abstract
The RSA-KEM Key Transport Algorithm is a one-pass (store-and- The RSA-KEM Key Transport Algorithm is a one-pass (store-and-forward)
forward) mechanism for transporting keying data to a recipient using mechanism for transporting keying data to a recipient using the
the recipient's RSA public key. This document specifies the recipient's RSA public key. This document specifies the conventions
conventions for using the RSA-KEM Key Transport Algorithm with the for using the RSA-KEM Key Transport Algorithm with the Cryptographic
Cryptographic Message Syntax (CMS). Message Syntax (CMS). This version (-01) updates the ASN.1 syntax to
align with the latest drafts of ANS X9.44 and ISO/IEC 18033-2, and
adds material on certificate conventions and S/MIME capabilities.
Conventions Used in This Document Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
this document are to be interpreted as described in RFC 2119 this document are to be interpreted as described in RFC 2119
[STDWORDS]. [STDWORDS].
1. Introduction 1. Introduction
The RSA-KEM Key Transport Algorithm is a one-pass (store-and- The RSA-KEM Key Transport Algorithm is a one-pass (store-and-forward)
forward) mechanism for transporting keying data to a recipient using mechanism for transporting keying data to a recipient using the
the recipient's RSA public key. recipient's RSA public key.
Most previous key transport algorithms based on the RSA public-key Most previous key transport algorithms based on the RSA public-key
cryptosystem (e.g., the popular PKCS #1 v1.5 algorithm [PKCS1]) have cryptosystem (e.g., the popular PKCS #1 v1.5 algorithm [PKCS1]) have
the following general form: the following general form:
1. Format or "pad" the keying data to obtain an integer m. 1. Format or "pad" the keying data to obtain an integer m.
2. Encrypt the integer m with the recipient's RSA public key: 2. Encrypt the integer m with the recipient's RSA public key:
c = m^e mod n c = m^e mod n
3. Output c as the encrypted keying data. 3. Output c as the encrypted keying data.
The RSA-KEM Key Transport Algorithm takes a different approach that The RSA-KEM Key Transport Algorithm takes a different approach that
provides higher security assurance, by encrypting a _random_ integer provides higher security assurance, by encrypting a _random_ integer
with the recipient's public key, and using a symmetric key wrapping with the recipient's public key, and using a symmetric key-wrapping
scheme to encrypt the keying data. It has the following form: scheme to encrypt the keying data. It has the following form:
1. Generate a random integer z between 0 and n-1. 1. Generate a random integer z between 0 and n-1.
2. Encrypt the integer z with the recipient's RSA public key: 2. Encrypt the integer z with the recipient's RSA public key:
c = z^e mod n. c = z^e mod n.
3. Derive a key-encrypting key KEK from the integer z. 3. Derive a key-encrypting key KEK from the integer z.
4. Wrap the keying data using KEK to obtain wrapped keying data 4. Wrap the keying data using KEK to obtain wrapped keying data
KD. WK.
5. Output c and KD as the encrypted keying data. 5. Output c and WK as the encrypted keying data.
This different approach provides higher security assurance because This different approach provides higher security assurance because
the input to the underlying RSA operation is random and independent the input to the underlying RSA operation is random and independent
of the message, and the key-encrypting key KEK is derived from it in of the message, and the key-encrypting key KEK is derived from it in
a strong way. As a result, the algorithm enjoys a "tight" security a strong way. As a result, the algorithm enjoys a "tight" security
proof in the random oracle model. It is also architecturally proof in the random oracle model. It is also architecturally
convenient because the public-key operations are separate from the convenient because the public-key operations are separate from the
symmetric operations on the keying data. One benefit is that the symmetric operations on the keying data. One benefit is that the
length of the keying data is bounded only by the symmetric key length of the keying data is bounded only by the symmetric key-
wrapping scheme, not the size of the RSA modulus. wrapping scheme, not the size of the RSA modulus.
The RSA-KEM Key Transport Algorithm in various forms is being The RSA-KEM Key Transport Algorithm in various forms is being adopted
adopted in several draft standards including ANSI X9.44 [ANSI-X9.44] in several draft standards including the draft ANS X9.44 [ANS-X9.44]
and ISO/IEC 18033-2 [ISO-IEC-18033-2]. It has also been recommended and the draft ISO/IEC 18033-2 [ISO-IEC-18033-2]. It has also been
by the NESSIE project [NESSIE]. Although the other standards are recommended by the NESSIE project [NESSIE]. Although the other
still in development, the algorithm is fairly stable across the standards are still in development, the algorithm is stable across
drafts. For completeness, a specification of the algorithm is given the drafts. For completeness, a specification of the algorithm is
in Appendix A of this document; ASN.1 syntax is given in Appendix B. given in Appendix A of this document; ASN.1 syntax is given in
Appendix B.
NOTE: The term KEM stands for "key encapsulation mechanism" and NOTE: The term KEM stands for "key encapsulation mechanism" and
refers to the first three steps of the process above. The refers to the first three steps of the process above. The
formalization of key transport algorithms (or more generally, formalization of key transport algorithms (or more generally,
asymmetric encryption schemes) in terms of key encapsulation asymmetric encryption schemes) in terms of key encapsulation
mechanisms is a result of research by Victor Shoup leading to the mechanisms is described further in research by Victor Shoup leading
development of the ISO/IEC 18033-2 standard [SHOUP]. to the development of the ISO/IEC 18033-2 standard [SHOUP].
2. Use in CMS 2. Use in CMS
The RSA-KEM Key Transport Algorithm MAY be employed for one or more The RSA-KEM Key Transport Algorithm MAY be employed for one or more
recipients in the CMS enveloped-data content type (Section 6 of recipients in the CMS enveloped-data content type (Section 6 of
[CMS]), where the keying data processed by the algorithm is the CMS [CMS]), where the keying data processed by the algorithm is the CMS
content-encryption key. content-encryption key.
The RSA-KEM Key Transport Algorithm SHOULD be considered for new The RSA-KEM Key Transport Algorithm SHOULD be considered for new
CMS-based applications as a replacement for the widely implemented CMS-based applications as a replacement for the widely implemented
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has also been proposed as a replacement (see [PKCS1] and [CMS- has also been proposed as a replacement (see [PKCS1] and [CMS-
OAEP]). RSA-KEM has the advantage over RSAES-OAEP of a tighter OAEP]). RSA-KEM has the advantage over RSAES-OAEP of a tighter
security proof, but the disadvantage of slightly longer encrypted security proof, but the disadvantage of slightly longer encrypted
keying data. keying data.
2.1 Underlying Components 2.1 Underlying Components
A CMS implementation that supports the RSA-KEM Key Transport A CMS implementation that supports the RSA-KEM Key Transport
Algorithm MUST support at least the following underlying components: Algorithm MUST support at least the following underlying components:
* For the key derivation function, KDF2 (see [ANSI-X9.44][IEEE- * For the key derivation function, KDF2 (see [ANS-X9.44][IEEE-
P1363a]) based on SHA-1 (see [NIST-SHA2]) (this function is P1363a]) based on SHA-1 (see [FIPS-180-2]) (this function is
also specified as the key derivation function in [ANSI-X9.63]) also specified as the key derivation function in [ANS-X9.63])
* For the key wrapping scheme, AES-Wrap-128, i.e., the AES Key * For the key-wrapping scheme, AES-Wrap-128, i.e., the AES Key
Wrap with a 128-bit key encrypting key (see [AES-WRAP]) Wrap with a 128-bit key encrypting key (see [AES-WRAP])
An implementation SHOULD also support KDF2 based on SHA-256 (see An implementation SHOULD also support KDF2 based on SHA-256 (see
[NIST-SHA2]), and the Triple-DES Key Wrap (see [3DES-WRAP]). It MAY [FIPS-180-2]), and the Triple-DES Key Wrap (see [3DES-WRAP]). It MAY
support other underlying components. support other underlying components.
2.2 RecipientInfo Conventions 2.2 RecipientInfo Conventions
When the RSA-KEM Key Transport Algorithm is employed for a When the RSA-KEM Key Transport Algorithm is employed for a recipient,
recipient, the RecipientInfo alternative for that recipient MUST be recipient, the RecipientInfo alternative for that recipient MUST be
KeyTransRecipientInfo. The algorithm-specific fields of the KeyTransRecipientInfo. The algorithm-specific fields of the
KeyTransRecipientInfo value MUST have the following values: KeyTransRecipientInfo value MUST have the following values:
* keyEncryptionAlgorithm.algorithm MUST be id-kts2-basic (see * keyEncryptionAlgorithm.algorithm MUST be id-ac-generic-hybrid
Appendix B) (see Appendix B)
* keyEncryptionAlgorithm.parameters MUST be a value of type * keyEncryptionAlgorithm.parameters MUST be a value of type
KTS2-Parms (see Appendix B) GenericHybridParameters, identifying the RSA-KEM key
encapsulation mechanism (see Appendix B)
* encryptedKey MUST be the encrypted keying data output by the * encryptedKey MUST be the encrypted keying data output by the
algorithm (see Appendix A) algorithm (see Appendix A)
2.3 Certificate Conventions 2.3 Certificate Conventions
The conventions specified in this section augment RFC 3280 [PROFILE].
A recipient who employs the RSA-KEM Key Transport Algorithm MAY A recipient who employs the RSA-KEM Key Transport Algorithm MAY
identify the public key in a certificate by the same identify the public key in a certificate by the same
AlgorithmIdentifier as for the PKCS #1 v1.5 algorithm, i.e., using AlgorithmIdentifier as for the PKCS #1 v1.5 algorithm, i.e., using
the rsaEncryption object identifier [PKCS1]. the rsaEncryption object identifier [PKCS1].
If the recipient wishes only to employ the RSA-KEM Key Transport If the recipient wishes only to employ the RSA-KEM Key Transport
Algorithm with a given public key, the recipient MUST identify the Algorithm with a given public key, the recipient MUST identify the
public key in the certificate using the id-kts2-basic object public key in the certificate using the id-ac-generic-hybrid object
identifier (see Appendix B) where the KTS2-Params value indicates identifier (see Appendix B) where the associated
the underlying components with which the algorithm is to be GenericHybridParameters value indicates the underlying components
employed. with which the algorithm is to be employed. The certificate user MUST
perform the RSA-KEM Key Transport algorithm using only those
components.
[[matching rules to be added]] Regardless of the AlgorithmIdentifier used, the RSA public key is
encoded in the same manner in the subject public key information.
The RSA public key MUST be encoded using the type RSAPublicKey type:
RSAPublicKey ::= SEQUENCE {
modulus INTEGER, -- n
publicExponent INTEGER -- e
}
Here, the modulus is the modulus n, and publicExponent is the public
exponent e. The DER encoded RSAPublicKey is carried in the
subjectPublicKey BIT STRING within the subject public key
information.
The intended application for the key MAY be indicated in the key
usage certificate extension (see [PROFILE], Section 4.2.1.3). If the
keyUsage extension is present in a certificate that conveys an RSA
public key with the id-ac-generic-hybrid object identifier as
discussed above, then the key usage extension MUST contain the
following value:
keyEncipherment.
dataEncipherment SHOULD NOT be present. That is, a key intended to be
employed only with the RSA-KEM Key Transport Algorithm SHOULD NOT
also be employed for data encryption.
2.4 SMIMECapabilities Attribute Conventions 2.4 SMIMECapabilities Attribute Conventions
[[to be added]] RFC 2633 [MSG], Section 2.5.2 defines the SMIMECapabilities signed
attribute (defined as a SEQUENCE of SMIMECapability SEQUENCEs) to be
used to specify a partial list of algorithms that the software
announcing the SMIMECapabilities can support. When constructing a
signedData object, compliant software MAY include the
SMIMECapabilities signed attribute announcing that it supports the
RSA-KEM Key Transport algorithm.
The SMIMECapability SEQUENCE representing the RSA-KEM Key Transport
Algorithm MUST include the id-ac-generic-hybrid object identifier
(see Appendix B) in the capabilityID field and MUST include a
GenericHybridParameters value in the parameters field identifying the
components with which the algorithm is to be employed.
The DER encoding of a SMIMECapability SEQUENCE is the same as the DER
encoding of an AlgorithmIdentifier. Example DER encodings for typical
sets of components are given in Appendix B.4.
3. Security Considerations 3. Security Considerations
The security of the RSA-KEM Key Transport Algorithm described in The security of the RSA-KEM Key Transport Algorithm described in
this document has been shown to be tightly related to the difficulty this document can be shown to be tightly related to the difficulty
of either solving the RSA problem or breaking the underlying of either solving the RSA problem or breaking the underlying
symmetric key wrapping scheme, if the underlying key derivation symmetric key-wrapping scheme, if the underlying key derivation
function is modeled as a random oracle [SHOUP]. While in practice a function is modeled as a random oracle, and assuming that the
random-oracle result does not provide an actual security proof for symmetric key-wrapping scheme satisfies the properties of a data
any particular key derivation function, the result does provide encapsulation mechanism [SHOUP]. While in practice a random-oracle
assurance that the general construction is reasonable; a key result does not provide an actual security proof for any particular
derivation function would need to be particularly weak to lead to an key derivation function, the result does provide assurance that the
attack that is not possible in the random oracle model. general construction is reasonable; a key derivation function would
need to be particularly weak to lead to an attack that is not
possible in the random oracle model.
The RSA key size and the underlying components should be selected The RSA key size and the underlying components should be selected
consistent with the desired symmetric security level for an consistent with the desired symmetric security level for an
application. Several security levels have been identified in [NIST- application. Several security levels have been identified in [NIST-
GUIDELINES]. For brevity, the first three levels are mentioned here: GUIDELINE]. For brevity, the first three levels are mentioned here:
* 80-bit security. The RSA key size SHOULD be at least 1024 * 80-bit security. The RSA key size SHOULD be at least 1024 bits,
bits, the hash function underlying KDF2 SHOULD be SHA-1 or the hash function underlying KDF2 SHOULD be SHA-1 or above, and
above, and the symmetric key-wrapping scheme SHOULD be AES Key the symmetric key-wrapping scheme SHOULD be AES Key Wrap or
Wrap or Triple-DES Key Wrap. Triple-DES Key Wrap.
* 112-bit security. The RSA key size SHOULD be at least 2048 * 112-bit security. The RSA key size SHOULD be at least 2048
bits, the hash function underlying KDF2 SHOULD be SHA-224 or bits, the hash function underlying KDF2 SHOULD be SHA-224 or
above, and the symmetric key-wrapping scheme SHOULD be AES Key above, and the symmetric key-wrapping scheme SHOULD be AES Key
Wrap or Triple-DES Key Wrap. Wrap or Triple-DES Key Wrap.
* 128-bit security. The RSA key size SHOULD be at least 3072 * 128-bit security. The RSA key size SHOULD be at least 3072
bits, the hash function underlying KDF2 SHOULD be SHA-256 or bits, the hash function underlying KDF2 SHOULD be SHA-256 or
above, and the symmetric key-wrapping scheme SHOULD be AES Key above, and the symmetric key-wrapping scheme SHOULD be AES Key
Wrap. Wrap.
Note that the AES Key Wrap MAY be used at all three of these levels; Note that the AES Key Wrap MAY be used at all three of these levels;
the use of AES does not require a 128-bit security level for other the use of AES does not require a 128-bit security level for other
components. components.
Implementations MUST protect the RSA private key and the content-
encryption key. Compromise of the RSA private key may result in the
disclosure of all messages protected with that key. Compromise of the
content-encryption key may result in disclosure of the associated
encrypted content.
Additional considerations related to key management may be found in
[NIST-GUIDELINE].
The security of the algorithm also depends on the strength of the The security of the algorithm also depends on the strength of the
random number generator, which SHOULD have a comparable security random number generator, which SHOULD have a comparable security
level. For further discussion on random number generation, please level. For further discussion on random number generation, please
see [RANDOM]. see [RANDOM].
Implementations SHOULD NOT reveal information about intermediate Implementations SHOULD NOT reveal information about intermediate
values or calculations, whether by timing or other "side channels", values or calculations, whether by timing or other "side channels",
or otherwise an opponent may be able to determine information about or otherwise an opponent may be able to determine information about
the keying data and/or the recipient's private key. Although not all the keying data and/or the recipient's private key. Although not all
intermediate information may be useful to an opponent, it is intermediate information may be useful to an opponent, it is
preferable to conceal as much information as is it practical to, preferable to conceal as much information as is practical, unless
unless analysis specifically indicates that the information would analysis specifically indicates that the information would not be
not be useful. useful.
Generally, good cryptographic practice employs a given RSA key pair
in only one scheme. This practice avoids the risk that vulnerability
in one scheme may compromise the security of the other, and may be
essential to maintain provable security. While RSA public keys have
often been employed for multiple purposes such as key transport and
digital signature without any known bad interactions, for increased
security assurance, such combined use of an RSA key pair is NOT
RECOMMENDED in the future (unless the different schemes are
specifically designed to be used together).
Accordingly, an RSA key pair used for the RSA-KEM Key Transport
Algorithm SHOULD NOT also be used for digital signatures. (Indeed,
ASC X9 requires such a separation between key establishment key pairs
and digital signature key pairs.) Continuing this principle of key
separation, a key pair used for the RSA-KEM Key Transport Algorithm
SHOULD NOT be used with other key establishment schemes, or for data
encryption, or with more than one set of underlying algorithm
components.
Parties MAY wish to formalize the assurance that one another's Parties MAY wish to formalize the assurance that one another's
implementations are correct through implementation validation, e.g. implementations are correct through implementation validation, e.g.
NIST's Cryptographic Module Validation Program (CMVP). NIST's Cryptographic Module Validation Program (CMVP).
4. References 4. References
4.1 Normative References 4.1 Normative References
3DES-WRAP Housley, R. Triple-DES and RC2 Key Wrapping. RFC 3DES-WRAP Housley, R. Triple-DES and RC2 Key Wrapping. RFC
3217. December 2001. 3217. December 2001.
AES-WRAP Schaad, J. and R. Housley. Advanced Encryption AES-WRAP Schaad, J. and R. Housley. Advanced Encryption
Standard (AES) Key Wrap Algorithm. RFC 3394. Standard (AES) Key Wrap Algorithm. RFC 3394.
September 2002. September 2002.
ANSI-X9.63 American National Standard X9.63-2002: Public Key ANS-X9.63 American National Standard X9.63-2002: Public Key
Cryptography for the Financial Services Industry: Cryptography for the Financial Services Industry:
Key Agreement and Key Transport Using Elliptic Key Agreement and Key Transport Using Elliptic
Curve Cryptography. Curve Cryptography.
CMS Housley, R. Cryptographic Message Syntax. RFC CMS Housley, R. Cryptographic Message Syntax. RFC
3369. August 2002. 3369. August 2002.
CMSALGS Housley, R. Cryptographic Message Syntax (CMS) CMSALGS Housley, R. Cryptographic Message Syntax (CMS)
Algorithms. RFC 3370. August 2002. Algorithms. RFC 3370. August 2002.
NIST-SHA2 National Institute of Standards and Technology FIPS-180-2 National Institute of Standards and Technology
(NIST). FIPS 180-2: Secure Hash Standard. August (NIST). FIPS 180-2: Secure Hash Standard. August
2002. 2002.
MSG Ramsdell, B. S/MIME Version 3 Message
Specification. RFC 2633. June 1999.
PROFILE Housley, R., Polk, W., Ford, W. and D. Solo.
Internet X.509 Public Key Infrastructure:
Certificate and Certificate Revocation List (CRL)
Profile. RFC 3280. April 2002.
STDWORDS Bradner, S. Key Words for Use in RFCs to Indicate STDWORDS Bradner, S. Key Words for Use in RFCs to Indicate
Requirement Levels. RFC 2119. March 1997. Requirement Levels. RFC 2119. March 1997.
4.2 Informative References 4.2 Informative References
ANSI-X9.44 ANSI X9F1 Working Group. ANSI X9.44: Public Key ANS-X9.44 ASC X9F1 Working Group. Draft American National
Cryptography for the Financial Services Industry - Standard X9.44: Public Key Cryptography for the
- Key Establishment Using Integer Factorization Financial Services Industry -- Key Establishment
Cryptography. Draft D4.1, April 1, 2003. Using Integer Factorization Cryptography. Draft D6,
October 15, 2003.
CMS-OAEP Housley, R. Use of the RSAES-OAEP Key Transport CMS-OAEP Housley, R. Use of the RSAES-OAEP Key Transport
Algorithm in CMS. Internet Draft <draft-ietf- Algorithm in the Cryptographic Message Syntax
smime-cms-rsaes-oaep-07.txt>. December 2002. (CMS). RFC 3560. July 2003.
IEEE-P1363a IEEE P1363 Working Group. IEEE P1363a: Standard IEEE-P1363a IEEE P1363 Working Group. IEEE P1363a: Standard
Specifications for Public Key Cryptography: Specifications for Public Key Cryptography:
Additional Techniques. Draft D12, May 12, 2003. Additional Techniques. Draft D12, May 12, 2003.
Available via http://grouper.ieee.org/groups/1363. Available via http://grouper.ieee.org/groups/1363.
ISO-IEC-18033-2 ISO/IEC 18033-2: Information technology -- ISO-IEC-18033-2 ISO/IEC 18033-2: Information technology -- Security
Security techniques -- Encryption algorithms -- techniques -- Encryption algorithms Part 2:
Part 2: Asymmetric Ciphers. Committee Draft, Asymmetric Ciphers. 2nd Committee Draft, July 10,
December 18, 2002. 2003.
NESSIE NESSIE Consortium. Portfolio of Recommended NESSIE NESSIE Consortium. Portfolio of Recommended
Cryptographic Primitives. February 27, 2003. Cryptographic Primitives. February 27, 2003.
Available via http://www.cryptonessie.org/. Available via http://www.cryptonessie.org/.
NIST-GUIDELINES National Institute of Standards and Technology. NIST-GUIDELINE National Institute of Standards and Technology.
Special Publication 800-57: Recommendation for Key Special Publication 800-57: Recommendation for Key
Management. Part 1: General Guideline. Draft, Management. Part 1: General Guideline. Draft,
January 2003. Available via January 2003. Available via
http://csrc.nist.gov/CryptoToolkit/tkkeymgmt.html. http://csrc.nist.gov/CryptoToolkit/tkkeymgmt.html.
NIST-SCHEMES National Institute of Standards and Technology.
Special Publication 800-56: Recommendation on Key
Establishment Schemes. Draft 2.0, January 2003.
Available via
http://csrc.nist.gov/CryptoToolkit/tkkeymgmt.html.
PKCS1 Jonsson, J. and B. Kaliski. PKCS #1: RSA PKCS1 Jonsson, J. and B. Kaliski. PKCS #1: RSA
Cryptography Specifications Version 2.1. RFC 3447. Cryptography Specifications Version 2.1. RFC 3447.
February 2003. February 2003.
RANDOM Eastlake, D., S. Crocker, and J. Schiller. RANDOM Eastlake, D., S. Crocker, and J. Schiller.
Randomness Recommendations for Security. RFC 1750. Randomness Recommendations for Security. RFC 1750.
December 1994. December 1994.
SHOUP Shoup, V. A Proposal for an ISO Standard for SHOUP Shoup, V. A Proposal for an ISO Standard for
Public Key Encryption. Version 2.1, December 20, Public Key Encryption. Version 2.1, December 20,
2001. Available via http://www.shoup.net/papers/. 2001. Available via http://www.shoup.net/papers/.
5. IANA Considerations 5. IANA Considerations
Within the CMS, algorithms are identified by object identifiers Within the CMS, algorithms are identified by object identifiers
(OIDs). All of the OIDs used in this document were assigned in (OIDs). With one exception, all of the OIDs used in this document
Public-Key Cryptography Standards (PKCS) documents, Accredited were assigned in other IETF documents, in ISO/IEC standards
Standards Committee (ASC) X9 documents, or by the National Institute documents, by the National Institute of Standards and Technology
of Standards and Technology (NIST). No further action by the IANA is (NIST), and in Public-Key Cryptography Standards (PKCS) documents.
The one exception is that the ASN.1 module's identifier (see Appendix
B.3) is assigned in this document. No further action by the IANA is
necessary for this document or any anticipated updates. necessary for this document or any anticipated updates.
6. Acknowledgments 6. Acknowledgments
This document is one part of a strategy to align algorithm standards This document is one part of a strategy to align algorithm standards
produced by ASC X9, ISO/IEC JTC1 SC27, NIST, and the IETF. I would produced by ASC X9, ISO/IEC JTC1 SC27, NIST, and the IETF. I would
like to thank the members of the ANSI X9F1 working group for their like to thank the members of the ASC X9F1 working group for their
contributions to drafts of ANSI X9.44 which led to this contributions to drafts of ANS X9.44 which led to this specification.
specification. My thanks as well to Russ Housley as well for his My thanks as well to Russ Housley as well for his guidance and
guidance and encouragement. encouragement. I also appreciate the helpful direction I've received
from Blake Ramsdell and Jim Schaad in bringing this document to
fruition.
7. Author Address 7. Author's Address
Burt Kaliski Burt Kaliski
RSA Laboratories RSA Laboratories
174 Middlesex Turnpike 174 Middlesex Turnpike
Bedford, MA 01730 Bedford, MA 01730
USA USA
bkaliski@rsasecurity.com bkaliski@rsasecurity.com
Appendix A. RSA-KEM Key Transport Algorithm Appendix A. RSA-KEM Key Transport Algorithm
The RSA-KEM Key Transport Algorithm is a one-pass (store-and- The RSA-KEM Key Transport Algorithm is a one-pass (store-and-forward)
forward) mechanism for transporting keying data to a recipient using mechanism for transporting keying data to a recipient using the
the recipient's RSA public key. recipient's RSA public key.
With this type of algorithm, a sender encrypts the keying data using With this type of algorithm, a sender encrypts the keying data using
the recipient's public key to obtain encrypted keying data. The the recipient's public key to obtain encrypted keying data. The
recipient decrypts the encrypted keying data using the recipient's recipient decrypts the encrypted keying data using the recipient's
private key to recover the keying data. private key to recover the keying data.
A.1 Underlying Components A.1 Underlying Components
The algorithm has the following underlying components: The algorithm has the following underlying components:
* KDF, a key derivation function, which derives keying data of a * KDF, a key derivation function, which derives keying data of a
specified length from a shared secret value specified length from a shared secret value
* Wrap, a symmetric key wrapping scheme, which encrypts keying * Wrap, a symmetric key-wrapping scheme, which encrypts keying
data using a key-encrypting key data using a key-encrypting key
In the following, kekLen denotes the length in bytes of the key- In the following, kekLen denotes the length in bytes of the key-
encrypting key for the underlying symmetric key-wrapping scheme. encrypting key for the underlying symmetric key-wrapping scheme.
In this scheme, the length of the keying data to be transported MUST In this scheme, the length of the keying data to be transported MUST
be among the lengths supported by the underlying symmetric key be among the lengths supported by the underlying symmetric key-
wrapping scheme. (The AES Key Wrap, for instance, requires the wrapping scheme. (The AES Key Wrap, for instance, requires the length
length of the keying data to be a multiple of 8 bytes, and at least of the keying data to be a multiple of 8 bytes, and at least 16
16 bytes.) Usage and formatting of the keying data (e.g., parity bytes.) Usage and formatting of the keying data (e.g., parity
adjustment for Triple-DES keys) is outside the scope of this adjustment for Triple-DES keys) is outside the scope of this
algorithm. algorithm.
With some key derivation functions, it is possible to include other With some key derivation functions, it is possible to include other
information besides the shared secret value in the input to the information besides the shared secret value in the input to the
function. Also, with some symmetric key wrapping schemes, it is function. Also, with some symmetric key-wrapping schemes, it is
possible to associate a label with the keying data. Such uses are possible to associate a label with the keying data. Such uses are
outside the scope of this document, as they are not directly outside the scope of this document, as they are not directly
supported by CMS. supported by CMS.
A.2 Sender's Operations A.2 Sender's Operations
Let (n,e) be the recipient's RSA public key (see [PKCS1] for Let (n,e) be the recipient's RSA public key (see [PKCS1] for details)
details) and let K be the keying data to be transported. and let K be the keying data to be transported.
Let nLen denote the length in bytes of the modulus n, i.e., the Let nLen denote the length in bytes of the modulus n, i.e., the least
least integer such that 2^{8*nLen} > n. integer such that 2^{8*nLen} > n.
The sender performs the following operations: The sender performs the following operations:
1. Generate a random integer z between 0 and n-1 (see Note), and 1. Generate a random integer z between 0 and n-1 (see Note), and
convert z to a byte string Z of length nLen, most significant convert z to a byte string Z of length nLen, most significant
byte first: byte first:
z = RandomInteger (0, n-1) z = RandomInteger (0, n-1)
Z = IntegerToString (z, nLen) Z = IntegerToString (z, nLen)
2. Encrypt the random integer z using the recipient's public key 2. Encrypt the random integer z using the recipient's public key
(n,e) and convert the resulting integer c to a ciphertext C, a (n,e) and convert the resulting integer c to a ciphertext C, a
byte string of length nLen: byte string of length nLen:
c = z^e mod n c = z^e mod n
C = IntegerToString (c, nLen) C = IntegerToString (c, nLen)
3. Derive a key-encrypting key KEK of length kekLen bytes from 3. Derive a key-encrypting key KEK of length kekLen bytes from the
the byte string Z using the underlying key derivation byte string Z using the underlying key derivation function:
function:
KEK = KDF (Z, kekLen) KEK = KDF (Z, kekLen)
4. Wrap the keying data K using the underlying key wrapping 4. Wrap the keying data K with the key-encrypting key KEK using
scheme with the key-encrypting key KEK to obtain wrapped the underlying key-wrapping scheme to obtain wrapped keying
keying data WK: data WK:
WK = Wrap (KEK, K) WK = Wrap (KEK, K)
5. Concatenate the ciphertext C and the wrapped keying data WK to 5. Concatenate the ciphertext C and the wrapped keying data WK to
obtain the encrypted keying data EK: obtain the encrypted keying data EK:
EK = C || WK EK = C || WK
6. Output the encrypted keying data EK. 6. Output the encrypted keying data EK.
NOTE: The random integer z MUST be generated independently at random NOTE: The random integer z MUST be generated independently at random
for different encryption operations, whether for the same or for different encryption operations, whether for the same or
different recipients. different recipients.
A.3 Recipient's Operations A.3 Recipient's Operations
Let (n,d) be the recipient's RSA private key (see [PKCS1]; other Let (n,d) be the recipient's RSA private key (see [PKCS1]; other
private key formats are allowed) and let EK be the encrypted keying private key formats are allowed) and let EK be the encrypted keying
skipping to change at page 9, line 49 skipping to change at page 11, line 31
significant byte first (see Note): significant byte first (see Note):
Z = IntegerToString (z, nLen) Z = IntegerToString (z, nLen)
4. Derive a key-encrypting key KEK of length kekLen bytes from 4. Derive a key-encrypting key KEK of length kekLen bytes from
the byte string Z using the underlying key derivation function the byte string Z using the underlying key derivation function
(see Note): (see Note):
KEK = KDF (Z, kekLen) KEK = KDF (Z, kekLen)
5. Unwrap the wrapped keying data WK using the underlying key 5. Unwrap the wrapped keying data WK with the key-encrypting key
wrapping scheme with the key-encrypting key KEK to recover the KEK using the underlying key-wrapping scheme to recover the
keying data K: keying data K:
K = Unwrap (KEK, WK) K = Unwrap (KEK, WK)
If the unwrapping operation outputs an error, output If the unwrapping operation outputs an error, output
"decryption error" and stop. "decryption error" and stop.
6. Output the keying data K. 6. Output the keying data K.
NOTE: Implementations SHOULD NOT reveal information about the NOTE: Implementations SHOULD NOT reveal information about the integer
integer z and the string Z, nor about the calculation of the z and the string Z, nor about the calculation of the exponentiation
exponentiation in Step 2, the conversion in Step 3, or the key in Step 2, the conversion in Step 3, or the key derivation in Step 4,
derivation in Step 4, whether by timing or other "side channels". whether by timing or other "side channels". The observable behavior
The observable behavior of the implementation SHOULD be the same at of the implementation SHOULD be the same at these steps for all
these steps for all ciphertexts C that are in range. (For example, ciphertexts C that are in range. (For example, IntegerToString
IntegerToString conversion should take the same amount of time conversion should take the same amount of time regardless of the
regardless of the actual value of the integer z.) The integer z, the actual value of the integer z.) The integer z, the string Z and other
string Z and other intemediate results MUST be securely deleted when intermediate results MUST be securely deleted when they are no longer
they are no longer needed. needed.
Appendix B. ASN.1 Syntax Appendix B. ASN.1 Syntax
The ASN.1 syntax for identifying the RSA-KEM Key Transport Algorithm The ASN.1 syntax for identifying the RSA-KEM Key Transport Algorithm
is a special case of the syntax for Key Transport Scheme 2 (KTS2) in is an extension of the syntax for the "generic hybrid cipher" in the
the draft ANSI X9.44 [ANSI-X9.44]. The syntax for the scheme is draft ISO/IEC 18033-2 [ISO-IEC-18033-2], and is the same as employed
in the draft ANS X9.44 [ANS-X9.44]. The syntax for the scheme is
given in Section B.1. The syntax for selected underlying components given in Section B.1. The syntax for selected underlying components
including those mentioned above is given in B.2. including those mentioned above is given in B.2.
The following object identifier prefixes are used in the definitions The following object identifier prefixes are used in the definitions
below: below:
x9-44 OID ::= { is18033-2 OID ::= { iso(1) standard(0) is18033(18033) part2(2) }
iso(1) identified-organization(3) tc68(133) country(16)
x9(840) x9Standards(9) x9-44(44) nistAlgorithm OID ::= {
joint-iso-itu-t(2) country(16) us(840) organization(1)
gov(101) csor(3) nistAlgorithm(4)
} }
pkcs-1 OID ::= { pkcs-1 OID ::= {
iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-1(1) iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-1(1)
} }
nistAlgorithm OID ::= { NullParms is a more descriptive synonym for NULL when an algorithm
joint-iso-itu-t(2) country(16) us(840) organization(1) identifier has null parameters:
gov(101) csor(3) nistAlgorithm(4)
} NullParms ::= NULL
The material in this Appendix is based on a draft standard and is The material in this Appendix is based on a draft standard and is
SUBJECT TO CHANGE as that standard is developed. SUBJECT TO CHANGE as that standard is developed.
B.1 RSA-KEM Key Transport Algorithm B.1 RSA-KEM Key Transport Algorithm
The object identifier for the RSA-KEM Key Transport Algorithm is the The object identifier for the RSA-KEM Key Transport Algorithm is the
same as for the basic KTS2 scheme in the draft ANSI X9.44, id-kts2- same as for the "generic hybrid cipher" in the draft ANS ISO/IEC
basic, which is defined in the draft as 18033-2, id-ac-generic-hybrid, which is defined in the draft as
id-kts2-basic OID ::= { x9-44 schemes(2) kts2-basic(7) }
The associated parameters for id-kts2-basic have type KTS2-Parms:
KTS2-Parms ::= SEQUENCE { id-ac-generic-hybrid OID ::= {
kas [0] KTS2-KeyAgreementScheme, is18033-2 asymmetric-cipher(1) generic-hybrid(2)
kws [1] KTS2-SymmetricKeyWrappingScheme,
labelMethod [2] KTS2-LabelMethod
} }
The fields of type KTS2-Parms have the following meanings: The associated parameters for id-ac-generic-hybrid have type
GenericHybridParameters:
* kas identifies the underlying key agreement scheme. For the
RSA-KEM Key Transport Algorithm, the scheme is the basic Key
Agreement Scheme 1 (KAS1) from the draft ANSI X9.44.
The object identifier for the basic KAS1 is id-kas1-basic,
which is defined in the draft ANSI X9.44 as
id-kas1-basic OID ::= { x9-44 schemes(2) kas1-basic(1) }
The associated parameters for id-kas1-basic have type KAS1-
Parms:
KAS1-Parms ::= SEQUENCE { GenericHybridParameters ::= {
sves [0] KAS1-SecretValueEncapsulationScheme, kem KeyEncapsulationMechanism,
kdf [1] KAS1-KeyDerivationFunction, dem DataEncapsulationMechanism
otherInfoMethod [2] KAS1-OtherInfoMethod
} }
The fields of type KAS1-Parms have the following meanings: The fields of type GenericHybridParameters have the following
meanings:
* sves identifies the underlying secret-value * kem identifies the underlying key encapsulation mechanism. For
encapsulation mechanism. (In the draft ANSI X9.44, the the RSA-KEM Key Transport Algorithm, the scheme is RSA-KEM from
term "Secret Value Encapsulation Scheme" refers to the the draft ISO/IEC 18033-2.
first _two_ steps of the RSA-KEM Key Transport
Algorithm, which are separated from the key derivation
function for architectural reasons.) For the RSA-KEM Key
Transport Algorithm, the mechanism is RSASVES1 from the
draft ANSI X9.44.
The object identifier for RSASVES1 is id-rsasves1, which The object identifier for RSA-KEM (as a key encapsulation
is defined in the draft ANSI X9.44 as mechanism) is id-kem-rsa, which is defined in the draft ISO/IEC
18033-2 as
id-rsasves1 OID ::= { id-kem-rsa OID ::= {
x9-44 components(1) rsasves1(2) is18033-2 key-encapsulation-mechanism(2) rsa(4)
} }
This object identifier has no associated parameters. The associated parameters for id-kem-rsa have type
RsaKemParameters:
* kdf identifies the underlying key derivation function.
For alignment with the draft ANSI X9.44, it MUST be
KDF2. However, other key derivation functions MAY be
used with CMS. Please see B.2.1 for the syntax for KDF2.
KAS1-KeyDerivationFunction ::= AlgorithmIdentifier
* otherInfoMethod specifies the method for formatting RsaKemParameters ::= {
other information to be included in the input to the key keyDerivationFunction KeyDerivationFunction,
derivation function. For this version of the document, keyLength KeyLength
the method MUST be the "specified other information" }
method.
KAS1-OtherInfoMethod ::= AlgorithmIdentifier The fields of type RsaKemParameters have the following
meanings:
The object identifier for the "specified other * keyDerivationFunction identifies the underlying key
information" method is id-specifiedOtherInfo: derivation function. For alignment with the draft ANS
X9.44, it MUST be KDF2. However, other key derivation
functions MAY be used with CMS. Please see B.2.1 for the
syntax for KDF2.
id-specifiedOtherInfo OID ::= [[to be defined]] KeyDerivationFunction ::=
AlgorithmIdentifier {{KDFAlgorithms}}
The associated parameters for id-specifiedOtherInfo have KDFAlgorithms ALGORITHMS ::= {
type SpecifiedOtherInfo: kdf2,
... -- implementations may define other methods
}
SpecifiedOtherInfo ::= OCTET STRING SIZE((0..MAX)) * keyLength is the length in bytes of the key-encrypting
key, which depends on the underlying symmetric key-
wrapping scheme.
For this version of the document, the value of the other KeyLength ::= INTEGER (1..MAX)
information MUST be the empty string.
* kws identifies the underlying symmetric key-wrapping scheme. * dem identifies the underlying data encapsulation mechanism.
For alignment with the draft ANSI X9.44, it MUST be an X9- For alignment with the draft ANS X9.44, it MUST be an X9-
approved symmetric key-wrapping scheme. (See Note.) However, approved symmetric key-wrapping scheme. (See Note.) However,
other schemes MAY be used with CMS. Please see B.2.2 for the other symmetric key-wrapping schemes MAY be used with CMS.
syntax for the AES and Triple-DES Key Wraps. Please see B.2.2 for the syntax for the AES and Triple-DES Key
Wraps.
KTS2-SymmetricKeyWrappingScheme ::= AlgorithmIdentifier
* labelMethod specifies the method for formatting a label to be
associated with the keying data. For this version of the
document, the method MUST be the "specified label" method.
KTS2-LabelMethod ::= AlgorithmIdentifier
The object identifier for the "specified label" method is id-
specifiedLabel, which is defined in the draft ANSI X9.44 as
id-specifiedLabel OID ::= { pkcs-1 specifiedLabel(9) }
The associated parameters for id-specifiedLabel have type
SpecifiedLabel:
SpecifiedLabel ::= OCTET STRING SIZE((0..MAX))
For this version of the document, the value of the label MUST DataEncapsulationMechanism ::=
be the empty string. AlgorithmIdentifier {{DEMAlgorithms}}
NOTE: As of this writing, the AES Key Wrap and the Triple-DES Key DEMAlgorithms ALGORITHM ::= {
Wrap are in the process of being approved by X9. X9-SymmetricKeyWrappingSchemes,
... -- implementations may define other methods
}
X9-SymmetricKeyWrappingSchemes ALGORITHM ::= {
aes128-Wrap | aes192-Wrap | aes256-Wrap | tdes-Wrap,
... -- allows for future expansion
}
DISCUSSION TOPIC: In NIST's key establishment schemes recommendation NOTE: The generic hybrid cipher in the draft ISO/IEC 18033-2 can
[NIST-SCHEMES], the parties' names are included in the "other encrypt arbitrary data, hence the term "data encapsulation
information" for key derivation. Should they be included here as mechanism". The symmetric key-wrapping schemes take the role of data
well? encapsulation mechanisms in the RSA-KEM Key Transport Algorithm. The
draft ISO/IEC 18033-2 currently allows only three particular data
encapsulation mechanisms, not including any of these symmetric key-
wrapping schemes. However, the ASN.1 syntax in that document expects
that additional algorithms will be allowed.
B.2 Selected Underlying Components B.2 Selected Underlying Components
B.2.1 Key Derivation Functions B.2.1 Key Derivation Functions
The object identifier for KDF2 (see [ANSI-X9.44]) is The object identifier for KDF2 (see [ISO-IEC-18033-2]) is
id-kdf2 OID ::= { x9-44 components(1) kdf2(1) } id-kdf-kdf2 OID ::= {
is18033-2 key-derivation-functions(5) kdf2(2)
}
The associated parameters identify the underlying hash function. For The associated parameters identify the underlying hash function. For
alignment with the draft ANSI X9.44, the hash function MUST be an alignment with the draft ANS X9.44, the hash function MUST be an ASC
X9-approved hash function. (See Note.) However, other hash functions X9-approved hash function. (See Note.) However, other hash functions
MAY be used with CMS. MAY be used with CMS.
KDF2-Parms ::= AlgorithmIdentifier kdf2 ALGORITHM ::= {{ OID id-kdf-kdf2 PARMS KDF2-HashFunction }}
KDF2-HashFunction ::= AlgorithmIdentifier {{KDF2-HashFunctions}}
KDF2-HashFunctions ALGORITHM ::= {
X9-HashFunctions,
... -- implementations may define other methods
}
X9-HashFunctions ALGORITHM ::= {
sha1 | sha224 | sha256 | sha384 | sha512,
... -- allows for future expansion
}
The object identifier for SHA-1 is The object identifier for SHA-1 is
id-sha1 OID ::= { id-sha1 OID ::= {
iso(1) identified-organization(3) oiw(14) secsig(3) iso(1) identified-organization(3) oiw(14) secsig(3)
algorithms(2) sha1(26) algorithms(2) sha1(26)
} }
The object identifiers for SHA-256, SHA-384 and SHA-512 are The object identifiers for SHA-256, SHA-384 and SHA-512 are
id-sha256 OID ::= { nistAlgorithm hashAlgs(2) sha256(1) } id-sha256 OID ::= { nistAlgorithm hashAlgs(2) sha256(1) }
id-sha384 OID ::= { nistAlgorithm hashAlgs(2) sha384(2) } id-sha384 OID ::= { nistAlgorithm hashAlgs(2) sha384(2) }
id-sha512 OID ::= { nistAlgorithm hashAlgs(2) sha512(3) } id-sha512 OID ::= { nistAlgorithm hashAlgs(2) sha512(3) }
There has been some confusion over whether the various SHA object There has been some confusion over whether the various SHA object
identifiers have a NULL parameter, or no associated parameters. As identifiers have a NULL parameter, or no associated parameters. As
also discussed in [PKCS1], implementations SHOULD generate algorithm also discussed in [PKCS1], implementations SHOULD generate algorithm
identifiers without parameters, and MUST accept algorithm identifiers without parameters, and MUST accept algorithm identifiers
identifiers either without parameters, or with NULL parameters. either without parameters, or with NULL parameters.
NOTE: As of this writing, only SHA-1 is an X9-approved hash sha1 ALGORITHM ::= {{ OID id-sha1 }} -- NULLParms MUST be
function; SHA-224 and above are in the process of being approved. sha224 ALGORITHM ::= {{ OID id-sha224 }} -- accepted for these
The object identifier for SHA-224 has not yet been assigned. sha256 ALGORITHM ::= {{ OID id-sha256 }} -- OIDs
sha384 ALGORITHM ::= {{ OID id-sha384 }} - ""
sha512 ALGORITHM ::= {{ OID id-sha512 }} - ""
B.2.2 Symmetric Key Wrapping Schemes NOTE: As of this writing, only SHA-1 is an ASC X9-approved hash
function; SHA-224 and above are in the process of being approved. The
object identifier for SHA-224 has not yet been assigned.
The object identifier for the AES Key Wrap depends on the size of B.2.2 Symmetric Key-Wrapping Schemes
The object identifiers for the AES Key Wrap depends on the size of
the key encrypting key. There are three object identifiers (see the key encrypting key. There are three object identifiers (see
[AES-WRAP]): [AES-WRAP]):
id-aes128-Wrap OID ::= { nistAlgorithm aes(1) aes128-Wrap(5) } id-aes128-Wrap OID ::= { nistAlgorithm aes(1) aes128-Wrap(5) }
id-aes192-Wrap OID ::= { nistAlgorithm aes(1) aes192-Wrap(25) } id-aes192-Wrap OID ::= { nistAlgorithm aes(1) aes192-Wrap(25) }
id-aes256-Wrap OID ::= { nistAlgorithm aes(1) aes256-Wrap(45) } id-aes256-Wrap OID ::= { nistAlgorithm aes(1) aes256-Wrap(45) }
These object identifiers have no associated parameters. These object identifiers have no associated parameters.
aes128-Wrap ALGORITHM ::= {{ OID id-aes128-wrap }}
aes192-Wrap ALGORITHM ::= {{ OID id-aes192-wrap }}
aes256-Wrap ALGORITHM ::= {{ OID id-aes256-wrap }}
The object identifier for the Triple-DES Key Wrap (see [3DES-WRAP]) The object identifier for the Triple-DES Key Wrap (see [3DES-WRAP])
is is
id-alg-CMS3DESwrap OBJECT IDENTIFIER ::= { id-alg-CMS3DESwrap OBJECT IDENTIFIER ::= {
iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9) iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) alg(3) 6 smime(16) alg(3) 6
} }
This object identifier has a NULL parameter. This object identifier has a NULL parameter.
B.3 Example tdes-Wrap ALGORITHM ::=
{{ OID id-alg-CMS3DESwrap PARMS NullParms }}
As an example, if the key derivation function is KDF2 based on SHA-1 NOTE: As of this writing, the AES Key Wrap and the Triple-DES Key
and the symmetric key wrapping scheme is the AES Key Wrap with a Wrap are in the process of being approved by ASC X9.
128-bit KEK, the AlgorithmIdentifier for the RSA-KEM Key Transport
Algorithm will have the following value:
SEQUENCE { B.3 ASN.1 module
id-kts2-basic, -- basic KTS2
SEQUENCE { -- KTS2-Parms CMS-RSA-KEM
[0] SEQUENCE { -- key agreement scheme { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1)
id-kas1-basic, -- basic KAS1 pkcs-9(9) smime(16) modules(0) cms-rsa-kem(21) } [[check]]
SEQUENCE { -- KAS1-Parms
[0] SEQUENCE { -- secret value encapsulation scheme BEGIN
id-rsasves1 -- RSASVES1; no parameters
}, -- EXPORTS ALL
[1] SEQUENCE { -- key derivation function
id-kdf2, -- KDF2 -- IMPORTS None
SEQUENCE { -- KDF2-Parms
id-sha1 -- no parameters (preferred) -- Useful types and definitions
OID ::= OBJECT IDENTIFIER -- alias
-- Unless otherwise stated, if an object identifier has associated
-- parameters (i.e., the PARMS element is specified), the parameters
-- field shall be included in algorithm identifier values. The
-- parameters field shall be omitted if and only if the object
-- identifier does not have associated parameters (i.e., the PARMS
-- element is omitted), unless otherwise stated.
ALGORITHM ::= CLASS {
&id OBJECT IDENTIFIER UNIQUE,
&Type OPTIONAL
} }
}, WITH SYNTAX { OID &id [PARMS &Type] }
[2] SEQUENCE { -- other information method
id-specifiedOtherInfo, -- specified other info. AlgorithmIdentifier { ALGORITHM:IOSet } ::= SEQUENCE {
''H -- empty string algorithm ALGORITHM.&id( {IOSet} ),
parameters ALGORITHM.&Type( {IOSet}{@algorithm} ) OPTIONAL
} }
NullParms ::= NULL
-- ISO/IEC 18033-2 arc
is18033-2 OID ::= { iso(1) standard(0) is18033(18033) part2(2) }
-- NIST algorithm arc
nistAlgorithm OID ::= {
joint-iso-itu-t(2) country(16) us(840) organization(1)
gov(101) csor(3) nistAlgorithm(4)
}
-- PKCS #1 arc
pkcs-1 OID ::= {
iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-1(1)
}
-- RSA-KEM Key Transport Algorithm, based on Generic Hybrid Cipher
id-ac-generic-hybrid OID ::= {
is18033-2 asymmetric-cipher(1) generic-hybrid(2)
}
GenericHybridParameters ::= {
kem KeyEncapsulationMechanism,
dem DataEncapsulationMechanism
}
id-kem-rsa OID ::= {
is18033-2 key-encapsulation-mechanism(2) rsa(4)
}
RsaKemParameters ::= {
keyDerivationFunction KeyDerivationFunction,
keyLength KeyLength
}
KeyDerivationFunction ::= AlgorithmIdentifier {{KDFAlgorithms}}
KDFAlgorithms ALGORITHMS ::= {
kdf2,
... -- implementations may define other methods
}
KeyLength ::= INTEGER (1..MAX)
DataEncapsulationMechanism ::= AlgorithmIdentifier {{DEMAlgorithms}}
DEMAlgorithms ALGORITHM ::= {
X9-SymmetricKeyWrappingSchemes,
... -- implementations may define other methods
}
X9-SymmetricKeyWrappingSchemes ALGORITHM ::= {
aes128-Wrap | aes192-Wrap | aes256-Wrap | tdes-Wrap,
... -- allows for future expansion
}
-- Key Derivation Functions
id-kdf-kdf2 OID ::= { is18033-2 key-derivation-functions(5) kdf2(2) }
kdf2 ALGORITHM ::= {{ OID id-kdf-kdf2 PARMS KDF2-HashFunction }}
KDF2-HashFunction ::= AlgorithmIdentifier {{KDF2-HashFunctions}}
KDF2-HashFunctions ALGORITHM ::= {
X9-HashFunctions,
... -- implementations may define other methods
}
-- Hash Functions
X9-HashFunctions ALGORITHM ::= {
sha1 | sha224 | sha256 | sha384 | sha512,
... -- allows for future expansion
}
id-sha1 OID ::= {
iso(1) identified-organization(3) oiw(14) secsig(3)
algorithms(2) sha1(26)
}
id-sha256 OID ::= { nistAlgorithm hashAlgs(2) sha256(1) }
id-sha384 OID ::= { nistAlgorithm hashAlgs(2) sha384(2) }
id-sha512 OID ::= { nistAlgorithm hashAlgs(2) sha512(3) }
sha1 ALGORITHM ::= {{ OID id-sha1 }} -- NullParms MUST be
sha224 ALGORITHM ::= {{ OID id-sha224 }} -- accepted for these
sha256 ALGORITHM ::= {{ OID id-sha256 }} -- OIDs
sha384 ALGORITHM ::= {{ OID id-sha384 }} - ""
sha512 ALGORITHM ::= {{ OID id-sha512 }} - ""
-- Symmetric Key-Wrapping Schemes
id-aes128-Wrap OID ::= { nistAlgorithm aes(1) aes128-Wrap(5) }
id-aes192-Wrap OID ::= { nistAlgorithm aes(1) aes192-Wrap(25) }
id-aes256-Wrap OID ::= { nistAlgorithm aes(1) aes256-Wrap(45) }
aes128-Wrap ALGORITHM ::= {{ OID id-aes128-wrap }}
aes192-Wrap ALGORITHM ::= {{ OID id-aes192-wrap }}
aes256-Wrap ALGORITHM ::= {{ OID id-aes256-wrap }}
id-alg-CMS3DESwrap OBJECT IDENTIFIER ::= {
iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-9(9)
smime(16) alg(3) 6
} }
tdes-Wrap ALGORITHM ::= {{ OID id-alg-CMS3DESwrap PARMS NullParms }}
B.4 Examples
As an example, if the key derivation function is KDF2 based on
SHA-256 and the symmetric key-wrapping scheme is the AES Key Wrap
with a 128-bit KEK, the AlgorithmIdentifier for the RSA-KEM Key
Transport Algorithm will have the following value:
SEQUENCE {
id-ac-generic-hybrid, -- generic cipher
SEQUENCE { -- GenericHybridParameters
SEQUENCE { -- key encapsulation mechanism
id-kem-rsa, -- RSA-KEM
SEQUENCE { -- RsaKemParameters
SEQUENCE { -- key derivation function
id-kdf-kdf2, -- KDF2
SEQUENCE { -- KDF2-HashFunction
id-sha256 -- SHA-256; no parameters (preferred)
}, },
[1] SEQUENCE { -- symmetric key wrapping scheme 16 -- KEK length in bytes
id-aes128-Wrap -- AES-128 Wrap; no parameters
}, },
[2] SEQUENCE { -- label method SEQUENCE { -- data encapsulation mechanism
id-specifiedLabel, -- specified label id-aes128-Wrap -- AES-128 Wrap; no parameters
''H -- empty string
} }
} }
} }
This AlgorithmIdentifier value has the following DER encoding:
30 4f
06 07 28 81 8c 71 02 01 02 -- id-ac-generic-hybrid
30 44
30 25
06 07 28 81 8c 71 02 02 04 -- id-kem-rsa
30 1a
30 16
06 07 28 81 8c 71 02 05 02 -- id-kdf-kdf2
30 0b
06 09 60 86 48 01 65 03 04 02 01 -- id-sha256
02 10 -- 16 bytes
30 0b
06 09 60 86 48 01 65 03 04 01 05 -- id-aes128-Wrap
The DER encodings for other typical sets of underlying components are
as follows:
* KDF2 based on SHA-384, AES Key Wrap with a 192-bit KEK
30 4f 06 07 28 81 8c 71 02 01 02 30 44 30 25 06
07 28 81 8c 71 02 02 04 30 1a 30 16 06 07 28 81
8c 71 02 05 02 30 0b 06 09 60 86 48 01 65 03 04
02 02 02 18 30 0b 06 09 60 86 48 01 65 03 04 01
19
* KDF2 based on SHA-512, AES Key Wrap with a 256-bit KEK
30 4f 06 07 28 81 8c 71 02 01 02 30 44 30 25 06
07 28 81 8c 71 02 02 04 30 1a 30 16 06 07 28 81
8c 71 02 05 02 30 0b 06 09 60 86 48 01 65 03 04
02 03 02 20 30 0b 06 09 60 86 48 01 65 03 04 01
2d
* KDF2 based on SHA-1, Triple-DES Key Wrap with a 128-bit KEK
(two-key triple-DES)
30 4f 06 07 28 81 8c 71 02 01 02 30 44 30 21 06
07 28 81 8c 71 02 02 04 30 16 30 12 06 07 28 81
8c 71 02 05 02 30 07 06 05 2b 0e 03 02 1a 02 10
30 0f 06 0b 2a 86 48 86 f7 0d 01 09 10 03 06 05
00
* KDF2 based on SHA-224, Triple-DES Key Wrap with a 192-bit
KEK (three-key triple-DES)
[[to be defined, awaiting OID for SHA-224]]
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 End of changes. 

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