Use of the RSAKEM Algorithm in the Cryptographic Message Syntax (CMS)
draftietflampsrfc5990bis10
Document  Type  Active InternetDraft (lamps WG)  

Authors  Russ Housley , Sean Turner  
Last updated  20240802 (Latest revision 20240730)  
Replaces  drafthousleylampsrfc5990bis  
RFC stream  Internet Engineering Task Force (IETF)  
Intended RFC status  Proposed Standard  
Formats  
Reviews  
Additional resources  Mailing list discussion  
Stream  WG state  Submitted to IESG for Publication  
Document shepherd  Tim Hollebeek  
Shepherd writeup  Show Last changed 20240405  
IESG  IESG state  RFC Ed Queue  
Action Holders 
(None)


Consensus boilerplate  Yes  
Telechat date  (None)  
Responsible AD  Deb Cooley  
Send notices to  tim.hollebeek@digicert.com  
IANA  IANA review state  Version Changed  Review Needed  
IANA action state  RFCEdAck  
IANA expert review state  Expert Reviews OK  
RFC Editor  RFC Editor state  AUTH  
Details 
draftietflampsrfc5990bis10
Limited Additional Mechanisms for PKIX and SMIME R. Housley InternetDraft Vigil Security Obsoletes: 5990 (if approved) S. Turner Intended status: Standards Track sn3rd Expires: 31 January 2025 30 July 2024 Use of the RSAKEM Algorithm in the Cryptographic Message Syntax (CMS) draftietflampsrfc5990bis10 Abstract The RSA Key Encapsulation Mechanism (RSAKEM) Algorithm is a onepass (storeandforward) cryptographic mechanism for an originator to securely send keying material to a recipient using the recipient's RSA public key. The RSAKEM Algorithm is specified in Clause 11.5 of ISO/IEC: 180332:2006. This document specifies the conventions for using the RSAKEM Algorithm as a standalone KEM algorithm and the conventions for using the RSAKEM Algorithm with the Cryptographic Message Syntax (CMS) using KEMRecipientInfo as specified in RFC XXXX. This document obsoletes RFC 5990. RFC EDITOR: Please replace XXXX with the RFC number assigned to draftietflampscmskemri. About This Document This note is to be removed before publishing as an RFC. Status information for this document may be found at https://datatracker.ietf.org/doc/draftietflampsrfc5990bis/. Discussion of this document takes place on the Limited Additional Mechanisms for PKIX and SMIME Working Group mailing list (mailto:spasm@ietf.org), which is archived at https://mailarchive.ietf.org/arch/browse/spasm/. Subscribe at https://www.ietf.org/mailman/listinfo/spasm/. Status of This Memo This InternetDraft is submitted in full conformance with the provisions of BCP 78 and BCP 79. InternetDrafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as InternetDrafts. The list of current Internet Drafts is at https://datatracker.ietf.org/drafts/current/. Housley & Turner Expires 31 January 2025 [Page 1] InternetDraft RSAKEM with CMS KEMRecipientInfo July 2024 InternetDrafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use InternetDrafts as reference material or to cite them other than as "work in progress." This InternetDraft will expire on 31 January 2025. Copyright Notice Copyright (c) 2024 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/ licenseinfo) 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. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. RSAKEM Algorithm Rationale . . . . . . . . . . . . . . . 3 1.2. RSAKEM Algorithm Summary . . . . . . . . . . . . . . . . 4 1.3. CMS KEMRecipientInfo Processing Summary . . . . . . . . . 5 1.4. Conventions and Definitions . . . . . . . . . . . . . . . 6 1.5. ASN.1 . . . . . . . . . . . . . . . . . . . . . . . . . . 6 1.6. Changes Since RFC 5990 . . . . . . . . . . . . . . . . . 6 2. Use of the RSAKEM Algorithm in CMS . . . . . . . . . . . . . 7 2.1. Mandatory To Implement . . . . . . . . . . . . . . . . . 7 2.2. RecipientInfo Conventions . . . . . . . . . . . . . . . . 8 2.3. Certificate Conventions . . . . . . . . . . . . . . . . . 8 2.4. SMIMECapabilities Attribute Conventions . . . . . . . . . 10 3. Security Considerations . . . . . . . . . . . . . . . . . . . 11 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 5. References . . . . . . . . . . . . . . . . . . . . . . . . . 13 5.1. Normative References . . . . . . . . . . . . . . . . . . 13 5.2. Informative References . . . . . . . . . . . . . . . . . 15 Appendix A. RSAKEM Algorithm . . . . . . . . . . . . . . . . . 16 A.1. Originator's Operations: RSAKEM Encapsulate() . . . . . 16 A.2. Recipient's Operations: RSAKEM Decapsulate() . . . . . . 17 Appendix B. ASN.1 Syntax . . . . . . . . . . . . . . . . . . . . 18 B.1. Underlying Components . . . . . . . . . . . . . . . . . . 19 B.2. ASN.1 Module . . . . . . . . . . . . . . . . . . . . . . 20 Appendix C. SMIMECapabilities Examples . . . . . . . . . . . . . 25 Appendix D. RSAKEM CMS EnvelopedData Example . . . . . . . . . 26 Housley & Turner Expires 31 January 2025 [Page 2] InternetDraft RSAKEM with CMS KEMRecipientInfo July 2024 D.1. Originator RSAKEM Encapsulate() Processing . . . . . . . 26 D.2. Originator CMS Processing . . . . . . . . . . . . . . . . 28 D.3. Recipient RSAKEM Decapsulate() Processing . . . . . . . 31 D.4. Recipient CMS Processing . . . . . . . . . . . . . . . . 32 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 33 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 33 1. Introduction The RSA Key Encapsulation Mechanism (RSAKEM) Algorithm is a onepass (storeandforward) cryptographic mechanism for an originator to securely send keying material to a recipient using the recipient's RSA public key. The RSAKEM Algorithm is specified in Clause 11.5 of [ISO180332]. The RSAKEM Algorithm takes a different approach than other RSA key transport mechanisms [RFC8017], with the goal of providing higher security assurance while also satisfying the KEM interface. The RSA KEM Algorithm encrypts a random integer with the recipient's RSA public key, and derives a shared secret from the random integer. The originator and recipient can derive a symmetric key from the shared secret. For example, a keyencryption key can be derived from the shared secret to wrap a contentencryption key. In the Cryptographic Message Syntax (CMS) [RFC5652] using KEMRecipientInfo [ID.ietflampscmskemri], the shared secret value is input to a keyderivation function to compute a keyencryption key, and wrap a symmetric contentencryption key with the key encryption key. In this way, the originator and the recipient end up with the same contentencryption key. For completeness, a specification of the RSAKEM Algorithm is given in Appendix A of this document; ASN.1 syntax is given in Appendix B. 1.1. RSAKEM Algorithm Rationale The RSAKEM Algorithm provides higher security assurance than other variants of the RSA cryptosystem for two reasons. First, the input to the underlying RSA operation is a stringencoded random integer between 0 and n1, where n is the RSA modulus, so it does not have any structure that could be exploited by an adversary. Second, the input is independent of the keying material so the result of the RSA decryption operation is not directly available to an adversary. As a result, the RSAKEM Algorithm enjoys a "tight" security proof in the random oracle model. (In other padding schemes, such as PKCS #1 v1.5 [RFC8017], the input has structure and/or depends on the keying material, and the provable security assurances are not as strong.) Housley & Turner Expires 31 January 2025 [Page 3] InternetDraft RSAKEM with CMS KEMRecipientInfo July 2024 The approach is also architecturally convenient because the public key operations are separate from the symmetric operations on the keying material. Another benefit is that the length of the keying material is determined by the symmetric algorithms, not the size of the RSA modulus. 1.2. RSAKEM Algorithm Summary All KEM algorithms provide three functions: KeyGen(), Encapsulate(), and Decapsulate(). The following summarizes these three functions for RSAKEM: KeyGen() > (pk, sk): Generate the public key (pk) and a private key (sk) as described in Section 3 of [RFC8017]. Encapsulate(pk) > (ct, SS): Given the recipient's public key (pk), produce a ciphertext (ct) to be passed to the recipient and a shared secret (SS) for use by the originator, as follows: 1. Generate a random integer z between 0 and n1. 2. Encrypt the integer z with the recipient's RSA public key to obtain the ciphertext: ct = z^e mod n 3. Derive a shared secret from the integer z using a Key Derivation Function (KDF): SS = KDF(Z, ssLen) 4. The ciphertext and the shared secret are returned by the function. The originator sends the ciphertext to the recipient. Decapsulate(sk, ct) > SS: Given the private key (sk) and the ciphertext (ct), produce the shared secret (SS) for the recipient as follows: 1. Decrypt the ciphertext with the recipient's RSA private key to obtain the random integer z: z = ct^d mod n Housley & Turner Expires 31 January 2025 [Page 4] InternetDraft RSAKEM with CMS KEMRecipientInfo July 2024 2. Derive a shared secret from the integer z: SS = KDF(Z, ssLen) 3. The shared secret is returned by the function. 1.3. CMS KEMRecipientInfo Processing Summary To support the RSAKEM algorithm, the CMS originator MUST implement Encapsulate(). Given a contentencryption key CEK, the RSAKEM Algorithm processing by the originator to produce the values that are carried in the CMS KEMRecipientInfo can be summarized as: 1. Obtain the shared secret using the Encapsulate() function of the RSAKEM algorithm and the recipient's RSA public key: (ct, SS) = Encapsulate(pk) 2. Derive a keyencryption key KEK from the shared secret: KEK = KDF(SS, kekLength, otherInfo) 3. Wrap the CEK with the KEK to obtain wrapped keying material WK: WK = WRAP(KEK, CEK) 4. The originator sends the ciphertext and WK to the recipient in the CMS KEMRecipientInfo structure. To support the RSAKEM algorithm, the CMS recipient MUST implement Decapsulate(). The RSAKEM algorithm recipient processing of the values obtained from the KEMRecipientInfo structure can be summarized as: 1. Obtain the shared secret using the Decapsulate() function of the RSAKEM algorithm and the recipient's RSA private key: SS = Decapsulate(sk, ct) 2. Derive a keyencryption key KEK from the shared secret: KEK = KDF(SS, kekLength, otherInfo) Housley & Turner Expires 31 January 2025 [Page 5] InternetDraft RSAKEM with CMS KEMRecipientInfo July 2024 3. Unwrap the WK with the KEK to obtain contentencryption key CEK: CEK = UNWRAP(KEK, WK) Note that the KDF used to process the KEMRecipientInfo structure MAY be different from the KDF used to derive the shared secret in the RSAKEM algorithm. 1.4. Conventions and Definitions The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. 1.5. ASN.1 CMS values are generated using ASN.1 [X.680], which uses the Basic Encoding Rules (BER) and the Distinguished Encoding Rules (DER) [X.690]. 1.6. Changes Since RFC 5990 RFC 5990 [RFC5990] specified the conventions for using the RSAKEM Algorithm in CMS as a key transport algorithm. That is, it used KeyTransRecipientInfo [RFC5652] for each recipient. Since the publication of RFC 5990, a new KEMRecipientInfo structure [ID.ietflampscmskemri] has been defined to support KEM algorithms. When the idrsakem algorithm identifier appears in the SubjectPublicKeyInfo field of a certificate, the complex parameter structure defined in RFC 5990 can be omitted; however, the parameters are allowed for backward compatibility. Also, to avoid visual confusion with idkemrsa, idrsakemspki is introduced as an alias for idrsakem. RFC 5990 used EK as the EncryptedKey, which is the concatenation of the ciphertext C and the wrapped key WK, EK = (C  WK). The use of EK was necessary to align with the KeyTransRecipientInfo structure. In this document, the ciphertext and the wrapped key are sent in separate fields of the KEMRecipientInfo structure. In particular, the ciphertext is carried in the kemct field, and wrapped key is carried in the encryptedKey field. See Appendix A for details about the computation of the ciphertext. Housley & Turner Expires 31 January 2025 [Page 6] InternetDraft RSAKEM with CMS KEMRecipientInfo July 2024 RFC 5990 included support for Camellia and TripleDES block ciphers; discussion of these block ciphers is removed from this document, but the algorithm identifiers remain in the ASN.1 Module Appendix B.2. RFC 5990 included support for SHA1 hash function; discussion of this hash function is removed from this document, but the algorithm identifier remains in the ASN.1 module Appendix B.2. RFC 5990 required support for the KDF3 keyderivation function [ANSX9.44]; this document continues to require support for the KDF3 keyderivation function, but it requires support for SHA256 [SHS] as the hash function. RFC 5990 recommended support for alternatives to KDF3 and AESWrap 128; this document simply states that other keyderivation functions and other keyencryption algorithms MAY be supported. RFC 5990 supported the future definition of additional KEM algorithms that use RSA; this document supports only one, and it is identified by the idkemrsa object identifier. RFC 5990 included an ASN.1 module; this document provides an alternative ASN.1 module that follows the conventions established in [RFC5911], [RFC5912], and [RFC6268]. The new ASN.1 module Appendix B.2 produces the same bitsonthewire as the one in RFC 5990. 2. Use of the RSAKEM Algorithm in CMS The RSAKEM Algorithm MAY be employed for one or more recipients in the CMS envelopeddata content type [RFC5652], the CMS authenticated data content type [RFC5652], or the CMS authenticatedenvelopeddata content type [RFC5083]. In each case, the KEMRecipientInfo [ID.ietflampscmskemri] is used with the RSAKEM Algorithm to securely transfer the contentencryption key from the originator to the recipient. 2.1. Mandatory To Implement A CMS implementation that supports the RSAKEM Algorithm MUST support at least the following underlying components: * For the keyderivation function, an implementation MUST support KDF3 [ANSX9.44] with SHA256 [SHS]. * For keywrapping, an implementation MUST support the AESWrap128 [RFC3394] keyencryption algorithm. Housley & Turner Expires 31 January 2025 [Page 7] InternetDraft RSAKEM with CMS KEMRecipientInfo July 2024 An implementation MAY also support other keyderivation functions and other keyencryption algorithms as well. 2.2. RecipientInfo Conventions When the RSAKEM Algorithm is employed for a recipient, the RecipientInfo alternative for that recipient MUST be OtherRecipientInfo using the KEMRecipientInfo structure [ID.ietflampscmskemri]. The fields of the KEMRecipientInfo MUST have the following values: version is the syntax version number; it MUST be 0. rid identifies the recipient's certificate or public key. kem identifies the KEM algorithm; it MUST contain idkemrsa. kemct is the ciphertext produced for this recipient; it contains C from steps 1 and 2 of Originator's Operations in Appendix A. kdf identifies the keyderivation function (KDF). Note that the KDF used for CMS RecipientInfo process MAY be different than the KDF used within the RSAKEM Algorithm. kekLength is the size of the keyencryption key in octets. ukm is an optional random input to the keyderivation function. wrap identifies a keyencryption algorithm used to encrypt the keying material. encryptedKey is the result of encrypting the keying material with the keyencryption key. When used with the CMS envelopeddata content type [RFC5652], the keying material is a content encryption key. When used with the CMS authenticateddata content type [RFC5652], the keying material is a messageauthentication key. When used with the CMS authenticatedenvelopeddata content type [RFC5083], the keying material is a contentauthenticated encryption key. NOTE: For backward compatibility, implementations MAY also support RSAKEM Key Transport Algorithm, identified by idrsakemspki, which uses KeyTransRecipientInfo as specified in [RFC5990]. 2.3. Certificate Conventions The conventions specified in this section augment RFC 5280 [RFC5280]. Housley & Turner Expires 31 January 2025 [Page 8] InternetDraft RSAKEM with CMS KEMRecipientInfo July 2024 A recipient who employs the RSAKEM Algorithm MAY identify the public key in a certificate by the same AlgorithmIdentifier as for the PKCS #1 v1.5 algorithm, that is, using the rsaEncryption object identifier [RFC8017]. The fact that the recipient will accept RSAKEM with this public key is not indicated by the use of this object identifier. The willingness to accept the RSAKEM Algorithm MAY be signaled by the use of the SMIMECapabilities Attribute as specified in Section 2.5.2. of [RFC8551] or the SMIMECapabilities certificate extension as specified in [RFC4262]. If the recipient wishes only to employ the RSAKEM Algorithm with a given public key, the recipient MUST identify the public key in the certificate using the idrsakemspki object identifier; see Appendix B. The use of the idrsakemspki object identifier allows certificates that were issued to be compatible with RSAKEM Key Transport to also be used with this specification. When the idrsa kemspki object identifier appears in the SubjectPublicKeyInfo algorithm field of the certificate, the parameters field from AlgorithmIdentifier SHOULD be absent. That is, the AlgorithmIdentifier SHOULD be a SEQUENCE of one component, the id rsakemspki object identifier. With absent parameters, the KDF3 keyderivation function [ANSX9.44] with SHA256 [SHS] are used to derive the shared secret. When the AlgorithmIdentifier parameters are present, the GenericHybridParameters MUST be used. Within the kem element, the algorithm identifier MUST be set to idkemrsa, and RsaKemParameters MUST be included. As described in Section 2.4, the GenericHybridParameters constrain the values that can be used with the RSA public key for the kdf, kekLength, and wrap fields of the KEMRecipientInfo structure. Regardless of the AlgorithmIdentifier used, the RSA public key MUST be carried in the subjectPublicKey BIT STRING within the SubjectPublicKeyInfo field of the certificate using the RSAPublicKey type defined in [RFC8017]. The intended application for the public key MAY be indicated in the key usage certificate extension as specified in Section 4.2.1.3 of [RFC5280]. If the keyUsage extension is present in a certificate that conveys an RSA public key with the idrsakemspki object identifier as discussed above, then the key usage extension MUST contain only the following value: keyEncipherment Housley & Turner Expires 31 January 2025 [Page 9] InternetDraft RSAKEM with CMS KEMRecipientInfo July 2024 Other keyUsage extension values MUST NOT be present. That is, a public key intended to be employed only with the RSAKEM Algorithm MUST NOT also be employed for data encryption or for digital signatures. 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. 2.4. SMIMECapabilities Attribute Conventions Section 2.5.2 of [RFC8551] defines the SMIMECapabilities attribute to announce a partial list of algorithms that an S/MIME implementation can support. When constructing a CMS signeddata content type [RFC5652], a compliant implementation MAY include the SMIMECapabilities attribute that announces support for the RSAKEM Algorithm. The SMIMECapability SEQUENCE representing the RSAKEM Algorithm MUST include the idrsakemspki object identifier in the capabilityID field; see Appendix B for the object identifier value, and see Appendix C for examples. When the idrsakemspki object identifier appears in the capabilityID field and the parameters are present, then the parameters field MUST use the GenericHybridParameters type. GenericHybridParameters ::= SEQUENCE { kem KeyEncapsulationMechanism, dem DataEncapsulationMechanism } The fields of the GenericHybridParameters type have the following meanings: kem is an AlgorithmIdentifer. The algorithm field MUST be set to idkemrsa, and the parameters field MUST be RsaKemParameters, which is a SEQUENCE of an AlgorithmIdentifier that identifies the supported keyderivation function and a positive INTEGER that identifies the length of the keyencryption key in octets. dem is an AlgorithmIdentifier. The algorithm field MUST be present, and it identifies the keyencryption algorithm. The parameters are optional. If the GenericHybridParameters are present, then the provided dem value MUST be used in the wrap field of KEMRecipientInfo. If the GenericHybridParameters are present, then the provided kem value MUST be used as the keyderivation function in the kdf field of KEMRecipientInfo, and the provided key length MUST be used in the kekLength of KEMRecipientInfo. Housley & Turner Expires 31 January 2025 [Page 10] InternetDraft RSAKEM with CMS KEMRecipientInfo July 2024 3. Security Considerations The RSAKEM Algorithm should be considered as a replacement for the key transport portion of the widely implemented PKCS #1 v1.5 [RFC8017] for new applications that use CMS to avoid potential vulnerabilities to chosenciphertext attacks and gain a tighter security proof; however, the RSAKEM Algorithm has the disadvantage of slightly longer encrypted keying material. With PKCS #1 v1.5, the originator encrypts the keyencryption key directly with the recipient's RSA public key. With the RSAKEM, the keyencryption key is encrypted separately. The security of the RSAKEM Algorithm can be shown to be tightly related to the difficulty of either solving the RSA problem, or breaking the underlying symmetric keyencryption algorithm, if the underlying keyderivation function is modeled as a random oracle, and assuming that the symmetric keyencryption algorithm satisfies the properties of a data encapsulation mechanism [SHOUP]. While in practice a randomoracle result does not provide an actual security proof for any particular keyderivation function, the result does provide assurance that the 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 randomoracle model. The RSA key size and the underlying components need to be selected consistent with the desired security level. Several security levels have been identified in the NIST SP 80057 Part 1 [NISTSP80057pt1r5]. For example, one way to achieve 128bit security, the RSA key size would be at least 3072 bits, the key derivation function would be SHA256, and the symmetric key encryption algorithm would be AES Key Wrap with a 128bit key. Implementations MUST protect the RSA private key, the keyencryption key, the contentencryption key, messageauthentication key, and the contentauthenticatedencryption key. Disclosure of the RSA private key could result in the compromise of all messages protected with that key. Disclosure of the keyencryption key, the content encryption key, or the contentauthenticatedencryption key could result in compromise of the associated encrypted content. Disclosure of the keyencryption key, the messageauthentication key, or the contentauthenticatedencryption key could allow modification of the associated authenticated content. Additional considerations related to key management may be found in [NISTSP80057pt1r5]. Housley & Turner Expires 31 January 2025 [Page 11] InternetDraft RSAKEM with CMS KEMRecipientInfo July 2024 The security of the RSAKEM Algorithm depends on a quality random number generator. For further discussion on random number generation, see [RFC4086]. The RSAKEM Algorithm does not use an explicit padding scheme; instead, an encoded random value (z) between zero and the RSA modulus minus one (n1) is directly encrypted with the recipient's RSA public key. The IntegerToString(z, nLen) encoding produces a string that is the full length of the RSA modulus. In addition, the random value is passed through a keyderivation function (KDF) to reduce possible harm from a poorly implemented random number source or a maliciously chosen random value (z). Implementations MUST NOT use z directly for any purpose. As long as a fresh random integer z is chosen as part of each invocation of the Encapsulate() function, RSAKEM does not degrade as the number of ciphertexts increases. Since RSA encryption provides a bijective map, a collision in the KDF is the only way that RSAKEM can produce more than one ciphertext that encapsulates the same shared secret. The RSAKEM Algorithm provides a fixedlength ciphertext. The recipient MUST check that the received byte string is the expected length and the length corresponds to an integer in the expected range prior to attempting decryption with their RSA private key as described in Steps 1 and 2 of Appendix A.2. Implementations SHOULD NOT reveal information about intermediate values or calculations, whether by timing or other "side channels", otherwise an opponent may be able to determine information about the keying data and/or the recipient's private key. Although not all intermediate information may be useful to an opponent, it is preferable to conceal as much information as is practical, unless analysis specifically indicates that the information would not be useful to an opponent. 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. RSA public keys have often been employed for multiple purposes such as key transport and digital signature without any known bad interactions; however, 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 RSAKEM Algorithm SHOULD NOT also be used for digital signatures. Indeed, the Accredited Standards Committee X9 (ASC X9) requires such a separation between Housley & Turner Expires 31 January 2025 [Page 12] InternetDraft RSAKEM with CMS KEMRecipientInfo July 2024 key pairs used for key establishment and key pairs used for digital signature [ANSX9.44]. Continuing this principle of key separation, a key pair used for the RSAKEM Algorithm SHOULD NOT be used with other key establishment schemes, or for data encryption, or with more than one set of underlying algorithm components. It is acceptable to use the same RSA key pair for RSAKEM Key Transport as specified in [RFC5990] and this specification. This is acceptable because the operations involving the RSA public key and the RSA private key are identical in the two specifications. Parties can gain assurance that implementations are correct through formal implementation validation, such as the NIST Cryptographic Module Validation Program (CMVP) [CMVP]. 4. IANA Considerations For the ASN.1 Module in Appendix B.2, IANA is requested to assign an object identifier (OID) for the module identifier. The OID for the module should be allocated in the "SMI Security for S/MIME Module Identifier" registry (1.2.840.113549.1.9.16.0), and the Description for the new OID should be set to "idmodcmsrsakem2023". IANA is requested to update the idalgrsakem entry in the SMI Security for S/MIME Algorithms (1.2.840.113549.1.9.16.3) repository to refer to this document. In addition, IANA is requested to add the following note to the registry: Value 14, "idalgrsakem," is also referred to as "idrsakemspki." 5. References 5.1. Normative References [ANSX9.44] American National Standards Institute, "Public Key Cryptography for the Financial Services Industry  Key Establishment Using Integer Factorization Cryptography", American National Standard X9.44, 2007. [ID.ietflampscmskemri] Housley, R., Gray, J., and T. Okubo, "Using Key Encapsulation Mechanism (KEM) Algorithms in the Cryptographic Message Syntax (CMS)", Work in Progress, InternetDraft, draftietflampscmskemri08, 6 February 2024, <https://datatracker.ietf.org/doc/html/draftietf lampscmskemri08>. Housley & Turner Expires 31 January 2025 [Page 13] InternetDraft RSAKEM with CMS KEMRecipientInfo July 2024 [ISO180332] ISO/IEC JTC 1/SC 27, "Information technology  Security techniques  Encryption algorithms  Part 2: Asymmetric ciphers", ISO/IEC 180332:2006, 2006, <https://www.iso.org/standard/37971.html>. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, <https://www.rfceditor.org/info/rfc2119>. [RFC3394] Schaad, J. and R. Housley, "Advanced Encryption Standard (AES) Key Wrap Algorithm", RFC 3394, DOI 10.17487/RFC3394, September 2002, <https://www.rfceditor.org/info/rfc3394>. [RFC5083] Housley, R., "Cryptographic Message Syntax (CMS) AuthenticatedEnvelopedData Content Type", RFC 5083, DOI 10.17487/RFC5083, November 2007, <https://www.rfceditor.org/info/rfc5083>. [RFC5280] 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, DOI 10.17487/RFC5280, May 2008, <https://www.rfceditor.org/info/rfc5280>. [RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70, RFC 5652, DOI 10.17487/RFC5652, September 2009, <https://www.rfceditor.org/info/rfc5652>. [RFC5911] Hoffman, P. and J. Schaad, "New ASN.1 Modules for Cryptographic Message Syntax (CMS) and S/MIME", RFC 5911, DOI 10.17487/RFC5911, June 2010, <https://www.rfceditor.org/info/rfc5911>. [RFC5912] Hoffman, P. and J. Schaad, "New ASN.1 Modules for the Public Key Infrastructure Using X.509 (PKIX)", RFC 5912, DOI 10.17487/RFC5912, June 2010, <https://www.rfceditor.org/info/rfc5912>. [RFC6268] Schaad, J. and S. Turner, "Additional New ASN.1 Modules for the Cryptographic Message Syntax (CMS) and the Public Key Infrastructure Using X.509 (PKIX)", RFC 6268, DOI 10.17487/RFC6268, July 2011, <https://www.rfceditor.org/info/rfc6268>. Housley & Turner Expires 31 January 2025 [Page 14] InternetDraft RSAKEM with CMS KEMRecipientInfo July 2024 [RFC8017] Moriarty, K., Ed., Kaliski, B., Jonsson, J., and A. Rusch, "PKCS #1: RSA Cryptography Specifications Version 2.2", RFC 8017, DOI 10.17487/RFC8017, November 2016, <https://www.rfceditor.org/info/rfc8017>. [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, <https://www.rfceditor.org/info/rfc8174>. [RFC8551] Schaad, J., Ramsdell, B., and S. Turner, "Secure/ Multipurpose Internet Mail Extensions (S/MIME) Version 4.0 Message Specification", RFC 8551, DOI 10.17487/RFC8551, April 2019, <https://www.rfceditor.org/info/rfc8551>. [SHS] National Institute of Standards and Technology, "Secure Hash Standard", DOI 10.6028/nist.fips.1804, July 2015, <https://doi.org/10.6028/nist.fips.1804>. [X.680] ITUT, "Information technology  Abstract Syntax Notation One (ASN.1): Specification of basic notation", ITUT Recommendation X.680, ISO/IEC 88241:2021, February 2021, <https://www.itu.int/rec/TRECX.680>. [X.690] ITUT, "Information technology  ASN.1 encoding rules: Specification of Basic Encoding Rules (BER), Canonical Encoding Rules (CER) and Distinguished Encoding Rules (DER)", ITUT Recommendation X.690, ISO/IEC 88251:2021, February 2021, <https://www.itu.int/rec/TRECX.680>. 5.2. Informative References [CMVP] National Institute of Standards and Technology, "Cryptographic Module Validation Program", 2016, <https://csrc.nist.gov/projects/cryptographicmodule validationprogram>. [NISTSP80057pt1r5] National Institute of Standards and Technology, "Recommendation for Key Management:Part 1  General", DOI 10.6028/nist.sp.80057pt1r5, May 2020, <https://doi.org/10.6028/nist.sp.80057pt1r5>. [RFC4086] Eastlake 3rd, D., Schiller, J., and S. Crocker, "Randomness Requirements for Security", BCP 106, RFC 4086, DOI 10.17487/RFC4086, June 2005, <https://www.rfceditor.org/info/rfc4086>. Housley & Turner Expires 31 January 2025 [Page 15] InternetDraft RSAKEM with CMS KEMRecipientInfo July 2024 [RFC4262] Santesson, S., "X.509 Certificate Extension for Secure/ Multipurpose Internet Mail Extensions (S/MIME) Capabilities", RFC 4262, DOI 10.17487/RFC4262, December 2005, <https://www.rfceditor.org/info/rfc4262>. [RFC5990] Randall, J., Kaliski, B., Brainard, J., and S. Turner, "Use of the RSAKEM Key Transport Algorithm in the Cryptographic Message Syntax (CMS)", RFC 5990, DOI 10.17487/RFC5990, September 2010, <https://www.rfceditor.org/info/rfc5990>. [RFC6194] Polk, T., Chen, L., Turner, S., and P. Hoffman, "Security Considerations for the SHA0 and SHA1 MessageDigest Algorithms", RFC 6194, DOI 10.17487/RFC6194, March 2011, <https://www.rfceditor.org/info/rfc6194>. [SHOUP] Shoup, V., "A Proposal for an ISO Standard for Public Key Encryption", Cryptology ePrint Archive Paper 2001/112, 2001, <https://eprint.iacr.org/2001/112>. Appendix A. RSAKEM Algorithm The RSAKEM Algorithm is a onepass (storeandforward) cryptographic mechanism for an originator to securely send keying material to a recipient using the recipient's RSA public key. With the RSAKEM Algorithm, an originator encrypts a random integer (z) with the recipient's RSA public key to produce a ciphertext (ct), and the originator derives a shared secret (SS) from the random integer (z). The originator then sends the ciphertext (ct) to the recipient. The recipient decrypts the ciphertext (ct) using their private key to recover the random integer (z), and the recipient derives a shared secret (SS) from the random integer(z). In this way, originator and recipient obtain the same shared secret (SS). The RSAKEM Algorithm depends on a keyderivation function (KDF), which is used to derive the shared secret (SS). Many keyderivation functions support the inclusion of other information in addition to the shared secret (SS) in the input to the function; however, no other information is included as an input to the KDF by the RSAKEM Algorithm. A.1. Originator's Operations: RSAKEM Encapsulate() Let (n,e) be the recipient's RSA public key; see [RFC8017] for details. Housley & Turner Expires 31 January 2025 [Page 16] InternetDraft RSAKEM with CMS KEMRecipientInfo July 2024 Let nLen denote the length in bytes of the modulus n, i.e., the least integer such that 2^(8*nLen) > n. The originator performs the following operations: 1. Generate a random integer z between 0 and n1 (see note), and convert z to a byte string Z of length nLen, most significant byte first: z = RandomInteger (0, n1) Z = IntegerToString (z, nLen) 2. Encrypt the random integer z using the recipient's RSA public key (n,e), and convert the resulting integer c to a ciphertext C, a byte string of length nLen: c = z^e mod n ct = IntegerToString (c, nLen) 3. Derive a symmetric shared secret SS of length ssLen bytes (which MUST be the length of the keyencryption key) from the byte string Z using the underlying keyderivation function: SS = KDF (Z, ssLen) 4. Output the shared secret SS and the ciphertext ct. Send the ciphertext ct to the recipient. NOTE: The random integer z MUST be generated independently at random for different encryption operations, whether for the same or different recipients. A.2. Recipient's Operations: RSAKEM Decapsulate() Let (n,d) be the recipient's RSA private key; see [RFC8017] for details, but other private key formats are allowed. Let ct be the ciphertext received from the originator. Let nLen denote the length in bytes of the modulus n. The recipient performs the following operations: 1. If the length of the encrypted keying material is less than nLen bytes, output "decryption error", and stop. Housley & Turner Expires 31 January 2025 [Page 17] InternetDraft RSAKEM with CMS KEMRecipientInfo July 2024 2. Convert the ciphertext ct to an integer c, most significant byte first (see NOTE below): c = StringToInteger (ct) If the integer c is not between 0 and n1, output "decryption error", and stop. 3. Decrypt the integer c using the recipient's private key (n,d) to recover an integer z (see NOTE below): z = c^d mod n 4. Convert the integer z to a byte string Z of length nLen, most significant byte first (see NOTE below): Z = IntegerToString (z, nLen) 5. Derive a shared secret SS of length ssLen bytes from the byte string Z using the keyderivation function (see NOTE below): SS = KDF (Z, ssLen) 6. Output the shared secret SS. NOTE: Implementations SHOULD NOT reveal information about the integer z, the string Z, or about the calculation of the exponentiation in Step 2, the conversion in Step 3, or the key derivation in Step 4, whether by timing or other "side channels". The observable behavior of the implementation SHOULD be the same at these steps for all ciphertexts C that are in range. For example, IntegerToString conversion should take the same amount of time regardless of the actual value of the integer z. The integer z, the string Z, and other intermediate results MUST be securely deleted when they are no longer needed. Appendix B. ASN.1 Syntax The ASN.1 syntax for identifying the RSAKEM Algorithm is an extension of the syntax for the "generic hybrid cipher" in ANS X9.44 [ANSX9.44]. The ASN.1 Module is unchanged from RFC 5990. The idrsakemspki object identifier is used in a backward compatible manner in certificates [RFC5280] and SMIMECapabilities [RFC8551]. Of course, the use of the idkemrsa object identifier in the new KEMRecipientInfo structure [ID.ietflampscmskemri] was not yet defined at the time that RFC 5990 was written. Housley & Turner Expires 31 January 2025 [Page 18] InternetDraft RSAKEM with CMS KEMRecipientInfo July 2024 B.1. Underlying Components Implementations that conform to this specification MUST support the KDF3 [ANSX9.44] keyderivation function using SHA256 [SHS]. KDF2 [ANSX9.44] and KDF3 are both keyderivation functions based on a hash function. The only difference between KDF2 and KDF3 is the order of the components to be hashed. KDF2 calculates T as: T = T  Hash (Z  D  otherInfo) KDF3 calculates T as: T = T  Hash (D  Z  otherInfo) The object identifier for KDF3 is: idkdfkdf3 OBJECT IDENTIFIER ::= { x944components kdf3(2) } The KDF3 parameters identify the underlying hash function. For alignment with the ANS X9.44, the hash function MUST be an ASC X9approved hash function. While the SHA1 hash algorithm is included in the ASN.1 definitions, SHA1 MUST NOT be used. SHA1 is considered to be obsolete; see [RFC6194]. SHA1 remains in the ASN.1 module for compatibility with RFC 5990. In addition, other hash functions MAY be used with CMS. kdakdf3 KEYDERIVATION ::= { IDENTIFIER idkdfkdf3 PARAMS TYPE KDF3HashFunction ARE required  No S/MIME caps defined  } KDF3HashFunction ::= AlgorithmIdentifier { DIGESTALGORITHM, {KDF3HashFunctions} } KDF3HashFunctions DIGESTALGORITHM ::= { X9HashFunctions, ... } X9HashFunctions DIGESTALGORITHM ::= { mdasha1  mdasha224  mdasha256  mdasha384  mdasha512, ... } Implementations that conform to this specification MUST support the AES Key Wrap [RFC3394] keyencryption algorithm with a 128bit key. There are three object identifiers for the AES Key Wrap, one for each permitted size of the keyencryption key. There are three object identifiers imported from [RFC5912], and none of these algorithm identifiers have associated parameters: Housley & Turner Expires 31 January 2025 [Page 19] InternetDraft RSAKEM with CMS KEMRecipientInfo July 2024 kwaaes128wrap KEYWRAP ::= { IDENTIFIER idaes128wrap PARAMS ARE absent SMIMECAPS { IDENTIFIED BY idaes128wrap } } kwaaes192wrap KEYWRAP ::= { IDENTIFIER idaes192wrap PARAMS ARE absent SMIMECAPS { IDENTIFIED BY idaes192wrap } } kwaaes256wrap KEYWRAP ::= { IDENTIFIER idaes256wrap PARAMS ARE absent SMIMECAPS { IDENTIFIED BY idaes256wrap } } B.2. ASN.1 Module RFC EDITOR: Please replace TBD2 with the value assigned by IANA during the publication of [ID.ietflampscmskemri]. <CODE BEGINS> CMSRSAKEM2023 { iso(1) memberbody(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9) smime(16) modules(0) idmodcmsrsakem2023(TBD1) } DEFINITIONS EXPLICIT TAGS ::= BEGIN  EXPORTS ALL IMPORTS KEMALGORITHM FROM KEMAlgorithmInformation2023  [ID.ietflampscmskemri] { iso(1) identifiedorganization(3) dod(6) internet(1) security(5) mechanisms(5) pkix(7) idmod(0) idmodkemAlgorithmInformation2023(TBD2) } AlgorithmIdentifier{}, PUBLICKEY, DIGESTALGORITHM, KEYDERIVATION, KEYWRAP, SMIMECAPS FROM AlgorithmInformation2009  [RFC5912] { iso(1) identifiedorganization(3) dod(6) internet(1) security(5) mechanisms(5) pkix(7) idmod(0) idmodalgorithmInformation02(58) } kwaaes128wrap, kwaaes192wrap, kwaaes256wrap FROM CMSAesRsaesOaep2009  [RFC5911] { iso(1) memberbody(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9) smime(16) modules(0) Housley & Turner Expires 31 January 2025 [Page 20] InternetDraft RSAKEM with CMS KEMRecipientInfo July 2024 idmodcmsaes02(38) } kwa3DESWrap FROM CryptographicMessageSyntaxAlgorithms2009  [RFC5911] { iso(1) memberbody(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9) smime(16) modules(0) idmodcmsalg200102(37) } idcamellia128wrap, idcamellia192wrap, idcamellia256wrap FROM CamelliaEncryptionAlgorithmInCMS  [RFC3657] { iso(1) memberbody(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9) smime(16) modules(0) idmodcmscamellia(23) } mdasha1, pkrsa, RSAPublicKey FROM PKIXAlgs2009  [RFC5912] { iso(1) identifiedorganization(3) dod(6) internet(1) security(5) mechanisms(5) pkix(7) idmod(0) idmodpkix1algorithms200802(56) } mdasha224, mdasha256, mdasha384, mdasha512 FROM PKIX1PSSOAEPAlgorithms2009  [RFC5912] { iso(1) identifiedorganization(3) dod(6) internet(1) security(5) mechanisms(5) pkix(7) idmod(0) idmodpkix1rsapkalgs02(54) } ;  Useful types and definitions OID ::= OBJECT IDENTIFIER  alias NullParms ::= NULL  ISO/IEC 180332 arc is180332 OID ::= { iso(1) standard(0) is18033(18033) part2(2) }  NIST algorithm arc nistAlgorithm OID ::= { jointisoitut(2) country(16) us(840) organization(1) gov(101) csor(3) nistAlgorithm(4) }  PKCS #1 arc pkcs1 OID ::= { iso(1) memberbody(2) us(840) rsadsi(113549) pkcs(1) pkcs1(1) }  X9.44 arc Housley & Turner Expires 31 January 2025 [Page 21] InternetDraft RSAKEM with CMS KEMRecipientInfo July 2024 x944 OID ::= { iso(1) identifiedorganization(3) tc68(133) country(16) x9(840) x9Standards(9) x944(44) } x944components OID ::= { x944 components(1) }  RSAKEM Algorithm idrsakem OID ::= { iso(1) memberbody(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9) smime(16) alg(3) 14 } idrsakemspki OID ::= idrsakem GenericHybridParameters ::= SEQUENCE { kem KeyEncapsulationMechanism, dem DataEncapsulationMechanism } KeyEncapsulationMechanism ::= AlgorithmIdentifier { KEMALGORITHM, {KEMAlgorithms} } KEMAlgorithms KEMALGORITHM ::= { kemakemrsa  kemarsakem, ... } kemarsakem KEMALGORITHM ::= { IDENTIFIER idrsakemspki PARAMS TYPE GenericHybridParameters ARE optional PUBLICKEYS { pkrsa  pkrsakem } UKM ARE optional SMIMECAPS { TYPE GenericHybridParameters IDENTIFIED BY idrsakemspki } } kemakemrsa KEMALGORITHM ::= { IDENTIFIER idkemrsa PARAMS TYPE RsaKemParameters ARE optional PUBLICKEYS { pkrsa  pkrsakem } UKM ARE optional SMIMECAPS { TYPE GenericHybridParameters IDENTIFIED BY idrsakemspki } } idkemrsa OID ::= { is180332 keyencapsulationmechanism(2) rsa(4) } RsaKemParameters ::= SEQUENCE { keyDerivationFunction KeyDerivationFunction, keyLength KeyLength } pkrsakem PUBLICKEY ::= { IDENTIFIER idrsakemspki KEY RSAPublicKey PARAMS TYPE GenericHybridParameters ARE preferredAbsent Housley & Turner Expires 31 January 2025 [Page 22] InternetDraft RSAKEM with CMS KEMRecipientInfo July 2024  Private key format is not specified here  CERTKEYUSAGE {keyEncipherment} } KeyDerivationFunction ::= AlgorithmIdentifier { KEYDERIVATION, {KDFAlgorithms} } KDFAlgorithms KEYDERIVATION ::= { kdakdf2  kdakdf3, ... } KeyLength ::= INTEGER (1..MAX) DataEncapsulationMechanism ::= AlgorithmIdentifier { KEYWRAP, {DEMAlgorithms} } DEMAlgorithms KEYWRAP ::= { X9SymmetricKeyWrappingSchemes  CamelliaKeyWrappingSchemes, ... } X9SymmetricKeyWrappingSchemes KEYWRAP ::= { kwaaes128wrap  kwaaes192wrap  kwaaes256wrap  kwa3DESWrap, ... } X9SymmetricKeyWrappingScheme ::= AlgorithmIdentifier { KEYWRAP, {X9SymmetricKeyWrappingSchemes} } CamelliaKeyWrappingSchemes KEYWRAP ::= { kwacamellia128wrap  kwacamellia192wrap  kwacamellia256wrap, ... } CamelliaKeyWrappingScheme ::= AlgorithmIdentifier { KEYWRAP, {CamelliaKeyWrappingSchemes} } kwacamellia128wrap KEYWRAP ::= { IDENTIFIER idcamellia128wrap PARAMS ARE absent SMIMECAPS { IDENTIFIED BY idcamellia128wrap } } kwacamellia192wrap KEYWRAP ::= { IDENTIFIER idcamellia192wrap PARAMS ARE absent SMIMECAPS { IDENTIFIED BY idcamellia192wrap } } kwacamellia256wrap KEYWRAP ::= { IDENTIFIER idcamellia256wrap PARAMS ARE absent SMIMECAPS { IDENTIFIED BY idcamellia256wrap } }  Key Derivation Functions Housley & Turner Expires 31 January 2025 [Page 23] InternetDraft RSAKEM with CMS KEMRecipientInfo July 2024 idkdfkdf2 OID ::= { x944components kdf2(1) } kdakdf2 KEYDERIVATION ::= { IDENTIFIER idkdfkdf2 PARAMS TYPE KDF2HashFunction ARE required  No S/MIME caps defined  } KDF2HashFunction ::= AlgorithmIdentifier { DIGESTALGORITHM, {KDF2HashFunctions} } KDF2HashFunctions DIGESTALGORITHM ::= { X9HashFunctions, ... } idkdfkdf3 OID ::= { x944components kdf3(2) } kdakdf3 KEYDERIVATION ::= { IDENTIFIER idkdfkdf3 PARAMS TYPE KDF3HashFunction ARE required  No S/MIME caps defined  } KDF3HashFunction ::= AlgorithmIdentifier { DIGESTALGORITHM, {KDF3HashFunctions} } KDF3HashFunctions DIGESTALGORITHM ::= { X9HashFunctions, ... }  Hash Functions X9HashFunctions DIGESTALGORITHM ::= { mdasha1  mdasha224  mdasha256  mdasha384  mdasha512, ... }  Updates for the SMIMECAPS Set from RFC 5911 SMimeCapsSet SMIMECAPS ::= { kemakemrsa.&smimeCaps  kwaaes128wrap  kwaaes192wrap  kwaaes256wrap  kwacamellia128wrap.&smimeCaps  kwacamellia192wrap.&smimeCaps  kwacamellia256wrap.&smimeCaps, ... } END <CODE ENDS> Housley & Turner Expires 31 January 2025 [Page 24] InternetDraft RSAKEM with CMS KEMRecipientInfo July 2024 Appendix C. SMIMECapabilities Examples To indicate support for the RSAKEM algorithm coupled with the KDF3 keyderivation function with SHA256 and the AES Key Wrap symmetric keyencryption algorithm 128bit keyencryption key, the SMIMECapabilities will include the following entry: SEQUENCE { idrsakemspki,  RSAKEM Algorithm SEQUENCE {  GenericHybridParameters SEQUENCE {  key encapsulation mechanism idkemrsa,  RSAKEM SEQUENCE {  RsaKemParameters SEQUENCE {  key derivation function idkdfkdf3,  KDF3 SEQUENCE {  KDF3HashFunction idsha256  SHA256; no parameters (preferred) }, 16  KEK length in bytes }, SEQUENCE {  data encapsulation mechanism idaes128Wrap  AES128 Wrap; no parameters } } } This SMIMECapability value has the following DER encoding (in hexadecimal): 30 47 06 0b 2a 86 48 86 f7 0d 01 09 10 03 0e  idrsakemspki 30 38 30 29 06 07 28 81 8c 71 02 02 04  idkemrsa 30 1e 30 19 06 0a 2b 81 05 10 86 48 09 2c 01 02  idkdfkdf3 30 0b 06 09 60 86 48 01 65 03 04 02 01  idsha256 02 01 10  16 bytes 30 0b 06 09 60 86 48 01 65 03 04 01 05  idaes128Wrap To indicate support for the RSAKEM algorithm coupled with the KDF3 keyderivation function with SHA384 and the AES Key Wrap symmetric keyencryption algorithm 192bit keyencryption key, the SMIMECapabilities will include the following SMIMECapability value (in hexadecimal): Housley & Turner Expires 31 January 2025 [Page 25] InternetDraft RSAKEM with CMS KEMRecipientInfo July 2024 30 47 06 0b 2a 86 48 86 f7 0d 01 09 10 03 0e 30 38 30 29 06 07 28 81 8c 71 02 02 04 30 1e 30 19 06 0a 2b 81 05 10 86 48 09 2c 01 02 30 0b 06 09 60 86 48 01 65 03 04 02 02 02 01 18 30 0b 06 09 60 86 48 01 65 03 04 01 19 To indicate support for the RSAKEM algorithm coupled with the KDF3 keyderivation function with SHA512 and the AES Key Wrap symmetric keyencryption algorithm 256bit keyencryption key, the SMIMECapabilities will include the following SMIMECapability value (in hexadecimal): 30 47 06 0b 2a 86 48 86 f7 0d 01 09 10 03 0e 30 38 30 29 06 07 28 81 8c 71 02 02 04 30 1e 30 19 06 0a 2b 81 05 10 86 48 09 2c 01 02 30 0b 06 09 60 86 48 01 65 03 04 02 03 02 01 20 30 0b 06 09 60 86 48 01 65 03 04 01 2d Appendix D. RSAKEM CMS EnvelopedData Example This example shows the establishment of an AES128 contentencryption key using: * RSAKEM with a 3072bit key and KDF3 with SHA256; * KEMRecipientInfo key derivation using KDF3 with SHA256; and * KEMRecipientInfo key wrap using AES128KEYWRAP. In realworld use, the originator would encrypt the content encryption key in a manner that would allow decryption with their own private key as well as the recipient's private key. This is omitted in an attempt to simplify the example. D.1. Originator RSAKEM Encapsulate() Processing Alice obtains Bob's public key: Housley & Turner Expires 31 January 2025 [Page 26] InternetDraft RSAKEM with CMS KEMRecipientInfo July 2024 BEGIN PUBLIC KEY MIIBojANBgkqhkiG9w0BAQEFAAOCAY8AMIIBigKCAYEA3ocW14cxncPJ47fnEjBZ AyfC2lqapL3ET4jvV6C7gGeVrRQxWPDwl+cFYBBR2ej3j3/0ecDmu+XuVi2+s5JH Keeza+itfuhsz3yifgeEpeK8T+SusHhn20/NBLhYKbh3kiAcCgQ56dpDrDvDcLqq vS3jg/VO+OPnZbofoHOOevt8Q/roahJe1PlIyQ4udWB8zZezJ4mLLfbOA9YVaYXx 2AHHZJevo3nmRnlgJXo6mE00E/6qkhjDHKSMdl2WG6mO9TCDZc9qY3cAJDU6Ir0v SH7qUl8/vN13y4UOFkn8hM4kmZ6bJqbZt5NbjHtY4uQ0VMW3RyESzhrO02mrp39a uLNnH3EXdXaV1tk75H3qC7zJaeGWMJyQfOE3YfEGRKn8fxubji716D8UecAxAzFy FL6m1JiOyV5acAiOpxN14qRYZdHnXOM9DqGIGpoeY1UuD4Mo05osOqOUpBJHA9fS whSZG7VNf+vgNWTLNYSYLI04KiMdulnvU6ds+QPz+KKtAgMBAAE= END PUBLIC KEY Bob's RSA public key has the following key identifier: 9eeb67c9b95a74d44d2f16396680e801b5cba49c Alice randomly generates integer z between 0 and n1: 9c126102a5c1c0354672a3c2f19fc9ddea988f815e1da812c7bd4f8eb082bdd1 4f85a7f7c2f1af11d5333e0d6bcb375bf855f208da72ba27e6fb0655f2825aa6 2b93b1f9bbd3491fed58f0380fa0de36430e3a144d569600bd362609be5b9481 0875990b614e406fa6dff500043cbca95968faba61f795096a7fb3687a51078c 4ca2cb663366b0bea0cd9cccac72a25f3f4ed03deb68b4453bba44b943f4367b 67d6cd10c8ace53f545aac50968fc3c6ecc80f3224b64e37038504e2d2c0e2b2 9d45e46c62826d96331360e4c17ea3ef89a9efc5fac99eda830e81450b6534dc 0bdf042b8f3b706649c631fe51fc2445cc8d447203ec2f41f79cdfea16de1ce6 abdfdc1e2ef2e5d5d8a65e645f397240ef5a26f5e4ff715de782e30ecf477293 e89e13171405909a8e04dd31d21d0c57935fc1ceea8e1033e31e1bc8c56da0f3 d79510f3f380ff58e5a61d361f2f18e99fbae5663172e8cd1f21deaddc5bbbea 060d55f1842b93d1a9c888d0bf85d0af9947fe51acf940c7e7577eb79cabecb3 Alice encrypts integer z using the Bob's RSA public key, the result is called ct: c071fc273af8e7bdb152e06bf73310361074154a43abcf3c93c13499d2065344 3eed9ef5d3c0685e4aa76a6854815bb97691ff9f8dac15eea7d74f452bf350a6 46163d68288e978cbf7a73089ee52712f9a4f49e06ace7bbc85ab14d4e336c97 c5728a2654138c7b26e8835c6b0a9fbed26495c4eadf745a2933be283f6a88b1 6695fc06666873cfb6d36718ef3376cefc100c3941f3c494944078325807a559 186b95ccabf3714cfaf79f83bd30537fdd9aed5a4cdcbd8bd0486faed73e9d48 6b3087d6c806546b6e2671575c98461e441f65542bd95de26d0f53a64e7848d7 31d9608d053e8d345546602d86236ffe3704c98ad59144f3089e5e6d527b5497 ba103c79d62e80d0235410b06f71a7d9bd1c38000f910d6312ea2f20a3557535 ad01b3093fb5f7ee507080d0f77d48c9c3b3796f6b7dd3786085fb895123f04c a1f1c1be22c747a8dface32370fb0d570783e27dbb7e74fca94ee39676fde3d8 a9553d878224736e37e191dab953c7e228c07ad5ca3122421c14debd072a9ab6 Alice derives the shared secret (SS) using KDF3 with SHA256: Housley & Turner Expires 31 January 2025 [Page 27] InternetDraft RSAKEM with CMS KEMRecipientInfo July 2024 3cf82ec41b54ed4d37402bbd8f805a52 D.2. Originator CMS Processing Alice encodes the CMSORIforKEMOtherInfo structure with the algorithm identifier for AES128KEYWRAP and a key length of 16 octets. The DER encoding of CMSORIforKEMOtherInfo produces 18 octets: 3010300b0609608648016503040105020110 The CMSORIforKEMOtherInfo structure contains: 0 16: SEQUENCE { 2 11: SEQUENCE { 4 9: OBJECT IDENTIFIER aes128wrap (2 16 840 1 101 3 4 1 5) : } 15 1: INTEGER 16 : } Alice derives the keyencryption key from shared secret produced by RSAKEM Encapsulate() and the CMSORIforKEMOtherInfo structure with KDF3 and SHA256, the KEK is: e6dc9d62ff2b469bef604c617b018718 Alice randomly generates a 128bit contentencryption key: 77f2a84640304be7bd42670a84a1258b Alice uses AES128KEYWRAP to encrypt the 128bit contentencryption key with the derived keyencryption key: 28782e5d3d794a7616b863fbcfc719b78f12de08cf286e09 Alice encrypts the padded content using AES128CBC with the content encryption key. The 16octet IV used is: 480ccafebabefacedbaddecaf8887781 The padded content plaintext is: 48656c6c6f2c20776f726c6421030303 The resulting ciphertext is: c6ca65db7bdd76b0f37e2fab6264b66d Housley & Turner Expires 31 January 2025 [Page 28] InternetDraft RSAKEM with CMS KEMRecipientInfo July 2024 Alice encodes the EnvelopedData (using KEMRecipientInfo) and ContentInfo, and then sends the result to Bob. The Base64encoded result is: MIICXAYJKoZIhvcNAQcDoIICTTCCAkkCAQMxggIEpIICAAYLKoZIhvcNAQkQDQMw ggHvAgEAgBSe62fJuVp01E0vFjlmgOgBtcuknDAJBgcogYxxAgIEBIIBgMBx/Cc6 +Oe9sVLga/czEDYQdBVKQ6vPPJPBNJnSBlNEPu2e9dPAaF5Kp2poVIFbuXaR/5+N rBXup9dPRSvzUKZGFj1oKI6XjL96cwie5ScS+aT0ngas57vIWrFNTjNsl8VyiiZU E4x7JuiDXGsKn77SZJXE6t90Wikzvig/aoixZpX8BmZoc8+202cY7zN2zvwQDDlB 88SUlEB4MlgHpVkYa5XMq/NxTPr3n4O9MFN/3ZrtWkzcvYvQSG+u1z6dSGswh9bI BlRrbiZxV1yYRh5EH2VUK9ld4m0PU6ZOeEjXMdlgjQU+jTRVRmAthiNv/jcEyYrV kUTzCJ5ebVJ7VJe6EDx51i6A0CNUELBvcafZvRw4AA+RDWMS6i8go1V1Na0Bswk/ tffuUHCA0Pd9SMnDs3lva33TeGCF+4lRI/BMofHBviLHR6jfrOMjcPsNVweD4n27 fnT8qU7jlnb949ipVT2HgiRzbjfhkdq5U8fiKMB61coxIkIcFN69ByqatjAbBgor gQUQhkgJLAECMA0GCWCGSAFlAwQCAQUAAgEQMAsGCWCGSAFlAwQBBQQYKHguXT15 SnYWuGP7z8cZt48S3gjPKG4JMDwGCSqGSIb3DQEHATAdBglghkgBZQMEAQIEEEgM yv66vvrO263eyviId4GAEMbKZdt73Xaw834vq2Jktm0= This result decodes to: 0 604: SEQUENCE { 4 9: OBJECT IDENTIFIER envelopedData (1 2 840 113549 1 7 3) 15 589: [0] { 19 585: SEQUENCE { 23 1: INTEGER 3 26 516: SET { 30 512: [4] { 34 11: OBJECT IDENTIFIER : KEMRecipientInfo (1 2 840 113549 1 9 16 13 3) 47 495: SEQUENCE { 51 1: INTEGER 0 54 20: [0] : 9E EB 67 C9 B9 5A 74 D4 4D 2F 16 39 66 80 E8 01 : B5 CB A4 9C 76 9: SEQUENCE { 78 7: OBJECT IDENTIFIER kemRSA (1 0 18033 2 2 4) : } 87 384: OCTET STRING : C0 71 FC 27 3A F8 E7 BD B1 52 E0 6B F7 33 10 36 : 10 74 15 4A 43 AB CF 3C 93 C1 34 99 D2 06 53 44 : 3E ED 9E F5 D3 C0 68 5E 4A A7 6A 68 54 81 5B B9 : 76 91 FF 9F 8D AC 15 EE A7 D7 4F 45 2B F3 50 A6 : 46 16 3D 68 28 8E 97 8C BF 7A 73 08 9E E5 27 12 : F9 A4 F4 9E 06 AC E7 BB C8 5A B1 4D 4E 33 6C 97 : C5 72 8A 26 54 13 8C 7B 26 E8 83 5C 6B 0A 9F BE : D2 64 95 C4 EA DF 74 5A 29 33 BE 28 3F 6A 88 B1 : 66 95 FC 06 66 68 73 CF B6 D3 67 18 EF 33 76 CE : FC 10 0C 39 41 F3 C4 94 94 40 78 32 58 07 A5 59 Housley & Turner Expires 31 January 2025 [Page 29] InternetDraft RSAKEM with CMS KEMRecipientInfo July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{ 477 10: OBJECT IDENTIFIER : kdf3 (1 3 133 16 840 9 44 1 2) 489 13: SEQUENCE { 491 9: OBJECT IDENTIFIER : sha256 (2 16 840 1 101 3 4 2 1) 502 0: NULL : } : } 504 1: INTEGER 16 507 11: SEQUENCE { 509 9: OBJECT IDENTIFIER : aes128wrap (2 16 840 1 101 3 4 1 5) : } 520 24: OCTET STRING : 28 78 2E 5D 3D 79 4A 76 16 B8 63 FB CF C7 19 B7 : 8F 12 DE 08 CF 28 6E 09 : } : } : } 546 60: SEQUENCE { 548 9: OBJECT IDENTIFIER data (1 2 840 113549 1 7 1) 559 29: SEQUENCE { 561 9: OBJECT IDENTIFIER : aes128CBC (2 16 840 1 101 3 4 1 2) 572 16: OCTET STRING : 48 0C CA FE BA BE FA CE DB AD DE CA F8 88 77 81 : } 590 16: [0] C6 CA 65 DB 7B DD 76 B0 F3 7E 2F AB 62 64 B6 6D : } : } : } : } Housley & Turner Expires 31 January 2025 [Page 30] InternetDraft RSAKEM with CMS KEMRecipientInfo July 2024 D.3. Recipient RSAKEM Decapsulate() Processing Bob's private key: BEGIN PRIVATE KEY MIIG5AIBAAKCAYEA3ocW14cxncPJ47fnEjBZAyfC2lqapL3ET4jvV6C7gGeVrRQx WPDwl+cFYBBR2ej3j3/0ecDmu+XuVi2+s5JHKeeza+itfuhsz3yifgeEpeK8T+Su sHhn20/NBLhYKbh3kiAcCgQ56dpDrDvDcLqqvS3jg/VO+OPnZbofoHOOevt8Q/ro ahJe1PlIyQ4udWB8zZezJ4mLLfbOA9YVaYXx2AHHZJevo3nmRnlgJXo6mE00E/6q khjDHKSMdl2WG6mO9TCDZc9qY3cAJDU6Ir0vSH7qUl8/vN13y4UOFkn8hM4kmZ6b JqbZt5NbjHtY4uQ0VMW3RyESzhrO02mrp39auLNnH3EXdXaV1tk75H3qC7zJaeGW MJyQfOE3YfEGRKn8fxubji716D8UecAxAzFyFL6m1JiOyV5acAiOpxN14qRYZdHn XOM9DqGIGpoeY1UuD4Mo05osOqOUpBJHA9fSwhSZG7VNf+vgNWTLNYSYLI04KiMd ulnvU6ds+QPz+KKtAgMBAAECggGATFfkSkUjjJCjLvDk4aScpSx6+Rakf2hrdS3x jwqhyUfAXgTTeUQQBs1HVtHCgxQd+qlXYn3/qu8TeZVwG4NPztyi/Z5yB1wOGJEV 3k8N/ytul6pJFFn6p48VM01bUdTrkMJbXERe6g/rr6dBQeeItCaOK7N5SIJH3Oqh 9xYuB5tH4rquCdYLmt17Tx8CaVqU9qPY3vOdQEOwIjjMV8uQUR8rHSO9KkSj8AGs Lq9kcuPpvgJc2oqMRcNePS2WVh8xPFktRLLRazgLP8STHAtjT6SlJ2UzkUqfDHGK q/BoXxBDu6L1VDwdnIS5HXtL54ElcXWsoOyKF8/ilmhRUIUWRZFmlS1ok8IC5IgX UdL9rJVZFTRLyAwmcCEvRM1asbBrhyEyshSOuN5nHJi2WVJ+wSHijeKl1qeLlpMk HrdIYBq4Nz7/zXmiQphpAy+yQeanhP8O4O6C8e7RwKdpxe44su4Z8fEgA5yQx0u7 8yR1EhGKydX5bhBLR5Cm1VM7rT2BAoHBAP/+e5gZLNf/ECtEBZjeiJ0VshszOoUq haUQPA+9Bx9pytsoKm5oQhB7QDaxAvrn8/FUW2aAkaXsaj9F+/q30AYSQtExai9J fdKKook3oimN8/yNRsKmhfjGOj8hd4+GjX0qoMSBCEVdT+bAjjry8wgQrqReuZnu oXU85dmb3jvv0uIczIKvTIeyjXE5afjQIJLmZFXsBm09BG87Ia5EFUKly96BOMJh /QWEzuYYXDqOFfzQtkAefXNFW21Kz4Hw2QKBwQDeiGh4lxCGTjECvG7fauMGlu+q DSdYyMHif6t6mx57eS16EjvOrlXKItYhIyzW8Kw0rf/CSB2j8ig1GkMLTOgrGIJ1 0322o50FOr5oOmZPueeR4pOyAP0fgQ8DD1L3JBpY68/8MhYbsizVrR+Ar4jM0f96 W2bF5Xj3h+fQTDMkx6VrCCQ6miRmBUzH+ZPs5n/lYOzAYrqiKOanaiHy4mjRvlsy mjZ6z5CG8sISqcLQ/k3Qli5pOY/v0rdBjgwAW/UCgcEAqGVYGjKdXCzuDvf9EpV4 mpTWB6yIV2ckaPOn/tZi5BgsmEPwvZYZt0vMbu28Px7sSpkqUuBKbzJ4pcy8uC3I SuYiTAhMiHS4rxIBX3BYXSuDD2RD4vG1+XM0h6jVRHXHh0nOXdVfgnmigPGz3jVJ B8oph/jD8O2YCk4YCTDOXPEi8Rjusxzro+whvRR+kG0gsGGcKSVNCPj1fNISEte4 gJId7O1mUAAzeDjn/VaS/PXQovEMolssPPKn9NocbKbpAoHBAJnFHJunl22W/lrr ppmPnIzjI30YVcYOA5vlqLKyGaAsnfYqP1WUNgfVhq2jRsrHx9cnHQI9Hu442PvI x+c5H30YFJ4ipE3eRRRmAUi4ghY5WgD+1hw8fqyUW7E7l5LbSbGEUVXtrkU5G64T UR91LEyMF8OPATdiV/KD4PWYkgaqRm3tVEuCVACDTQkqNsOOi3YPQcm270w6gxfQ SOEy/kdhCFexJFA8uZvmh6Cp2crczxyBilR/yCxqKOONqlFdOQKBwFbJk5eHPjJz AYueKMQESPGYCrwIqxgZGCxaqeVArHvKsEDx5whI6JWoFYVkFA8F0MyhukoEb/2x 2qB5T88Dg3EbqjTiLg3qxrWJ2OxtUo8pBP2I2wbl2NOwzcbrlYhzEZ8bJyxZu5i1 sYILC8PJ4Qzw6jS4Qpm4y1WHz8e/ElW6VyfmljZYA7f9WMntdfeQVqCVzNTvKn6f hg6GSpJTzp4LV3ougi9nQuWXZF2wInsXkLYpsiMbL6Fz34RwohJtYA== END PRIVATE KEY Bob checks that the length of the ciphertext is less than nLen bytes. Bob checks that the ciphertext is greater than zero and is less than his RSA modulus. Housley & Turner Expires 31 January 2025 [Page 31] InternetDraft RSAKEM with CMS KEMRecipientInfo July 2024 Bob decrypts the ciphertext with his RSA private key to obtain the integer z: 9c126102a5c1c0354672a3c2f19fc9ddea988f815e1da812c7bd4f8eb082bdd1 4f85a7f7c2f1af11d5333e0d6bcb375bf855f208da72ba27e6fb0655f2825aa6 2b93b1f9bbd3491fed58f0380fa0de36430e3a144d569600bd362609be5b9481 0875990b614e406fa6dff500043cbca95968faba61f795096a7fb3687a51078c 4ca2cb663366b0bea0cd9cccac72a25f3f4ed03deb68b4453bba44b943f4367b 67d6cd10c8ace53f545aac50968fc3c6ecc80f3224b64e37038504e2d2c0e2b2 9d45e46c62826d96331360e4c17ea3ef89a9efc5fac99eda830e81450b6534dc 0bdf042b8f3b706649c631fe51fc2445cc8d447203ec2f41f79cdfea16de1ce6 abdfdc1e2ef2e5d5d8a65e645f397240ef5a26f5e4ff715de782e30ecf477293 e89e13171405909a8e04dd31d21d0c57935fc1ceea8e1033e31e1bc8c56da0f3 d79510f3f380ff58e5a61d361f2f18e99fbae5663172e8cd1f21deaddc5bbbea 060d55f1842b93d1a9c888d0bf85d0af9947fe51acf940c7e7577eb79cabecb3 Bob checks that the integer z is greater than zero and is less than his RSA modulus. Bob derives the shared secret (SS) using KDF3 with SHA256: 3cf82ec41b54ed4d37402bbd8f805a52 D.4. Recipient CMS Processing Bob encodes the CMSORIforKEMOtherInfo structure with the algorithm identifier for AES128KEYWRAP and a key length of 16 octets. The DER encoding of CMSORIforKEMOtherInfo is not repeated here. Bob derives the keyencryption key from shared secret and the CMSORIforKEMOtherInfo structure with KDF3 and SHA256, the KEK is: e6dc9d62ff2b469bef604c617b018718 Bob uses AESKEYWRAP to decrypt the contentencryption key with the keyencryption key; the contentencryption key is: 77f2a84640304be7bd42670a84a1258b Bob decrypts the content using AES128CBC with the content encryption key. The 16octet IV used is: 480ccafebabefacedbaddecaf8887781 The received ciphertext content is: c6ca65db7bdd76b0f37e2fab6264b66d Housley & Turner Expires 31 January 2025 [Page 32] InternetDraft RSAKEM with CMS KEMRecipientInfo July 2024 The resulting padded plaintext content is: 48656c6c6f2c20776f726c6421030303 After stripping the AESCBC padding, the plaintext content is: Hello, world! Acknowledgements We thank James Randall, Burt Kaliski, and John Brainard as the original authors of [RFC5990]; this document is based on their work. We thank the members of the ASC X9F1 working group for their contributions to drafts of ANS X9.44, which led to [RFC5990]. We thank Blake Ramsdell, Jim Schaad, Magnus Nystrom, Bob Griffin, and John Linn for helping bring [RFC5990] to fruition. We thank Burt Kaliski, Alex Railean, Joe Mandel, Mike Ounsworth, Peter Campbell, Daniel Van Geest, and David Ireland for careful review and thoughtful comments that greatly improved this document. Authors' Addresses Russ Housley Vigil Security, LLC 516 Dranesville Road Herndon, VA, 20170 United States of America Email: housley@vigilsec.com Sean Turner sn3rd Email: sean@sn3rd.com Housley & Turner Expires 31 January 2025 [Page 33]