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2	Internet Engineering Task Force                               M. Jenkins
3	Internet-Draft                                                       NSA
4	Intended status: Informational                            August 6, 2019
5	Expires: February 7, 2020

7	Using Commercial National Security Algorithm Suite Algorithms in Secure/
8	                 Multipurpose Internet Mail Extensions
9	                  draft-jenkins-cnsa-smime-profile-01

11	Abstract

13	   The United States Government has published the NSA Commercial
14	   National Security Algorithm (CNSA) Suite, which defines cryptographic
15	   algorithm policy for national security applications.  This document
16	   specifies the conventions for using the United States National
17	   Security Agency's CNSA Suite algorithms in Secure/Multipurpose
18	   Internet Mail Extensions (S/MIME) as specified in RFC 8551.  It
19	   applies to the capabilities, configuration, and operation of all
20	   components of US National Security Systems that employ S/MIME
21	   messaging.  US National Security Systems are described in NIST
22	   Special Publication 800-59.  It is also appropriate for all other US
23	   Government systems that process high-value information.  It is made
24	   publicly available for use by developers and operators of these and
25	   any other system deployments.

27	Status of This Memo

29	   This Internet-Draft is submitted in full conformance with the
30	   provisions of BCP 78 and BCP 79.

32	   Internet-Drafts are working documents of the Internet Engineering
33	   Task Force (IETF).  Note that other groups may also distribute
34	   working documents as Internet-Drafts.  The list of current Internet-
35	   Drafts is at https://datatracker.ietf.org/drafts/current/.

37	   Internet-Drafts are draft documents valid for a maximum of six months
38	   and may be updated, replaced, or obsoleted by other documents at any
39	   time.  It is inappropriate to use Internet-Drafts as reference
40	   material or to cite them other than as "work in progress."

42	   This Internet-Draft will expire on February 7, 2020.

44	Copyright Notice

46	   Copyright (c) 2019 IETF Trust and the persons identified as the
47	   document authors.  All rights reserved.

49	   This document is subject to BCP 78 and the IETF Trust's Legal
50	   Provisions Relating to IETF Documents
51	   (https://trustee.ietf.org/license-info) in effect on the date of
52	   publication of this document.  Please review these documents
53	   carefully, as they describe your rights and restrictions with respect
54	   to this document.  Code Components extracted from this document must
55	   include Simplified BSD License text as described in Section 4.e of
56	   the Trust Legal Provisions and are provided without warranty as
57	   described in the Simplified BSD License.

59	Table of Contents

61	   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
62	   2.  The Commercial National Security Algorithm Suite  . . . . . .   3
63	   3.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
64	   4.  Requirements and Assumptions  . . . . . . . . . . . . . . . .   4
65	   5.  SHA-384 Message Digest Algorithm  . . . . . . . . . . . . . .   5
66	   6.  Digital Signature . . . . . . . . . . . . . . . . . . . . . .   5
67	     6.1.  ECDSA Signature . . . . . . . . . . . . . . . . . . . . .   5
68	     6.2.  RSA Signature . . . . . . . . . . . . . . . . . . . . . .   6
69	   7.  Key Establishment . . . . . . . . . . . . . . . . . . . . . .   7
70	     7.1.  Elliptic Curve Key Agreement  . . . . . . . . . . . . . .   7
71	     7.2.  RSA Key Transport . . . . . . . . . . . . . . . . . . . .  11
72	   8.  Content Encryption  . . . . . . . . . . . . . . . . . . . . .  13
73	     8.1.  AES-CBC Content Encryption  . . . . . . . . . . . . . . .  13
74	     8.2.  AES-GCM Content Encryption  . . . . . . . . . . . . . . .  13
75	   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  14
76	   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  15
77	   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  15
78	     11.1.  Normative References . . . . . . . . . . . . . . . . . .  15
79	     11.2.  Informative References . . . . . . . . . . . . . . . . .  18
80	   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  18

82	1.  Introduction

84	   This document specifies the conventions for using the United States
85	   National Security Agency's Commercial National Security Algorithm
86	   (CNSA) Suite algorithms [CNSA] in Secure/Multipurpose Internet Mail
87	   Extensions (S/MIME) [RFC8551].  It applies to the capabilities,
88	   configuration, and operation of all components of US National
89	   Security Systems that employ S/MIME messaging.  US National Security
90	   Systems are described in NIST Special Publication 800-59 [SP80059].
91	   It is also appropriate for all other US Government systems that
92	   process high-value information.  It is made publicly available for
93	   use by developers and operators of these and any other system
94	   deployments.

96	   S/MIME makes use of the Cryptographic Message Syntax (CMS) [RFC5652]
97	   [RFC5083].  In particular, the signed-data, enveloped-data, and
98	   authenticated-enveloped-data content types are used.  This document
99	   only addresses CNSA Suite compliance for S/MIME.  Other applications
100	   of CMS are outside the scope of this document.

102	   This document does not define any new cryptographic algorithm suite;
103	   instead, it defines a CNSA compliant profile of S/MIME.  Since many
104	   of the CNSA Suite algorithms enjoy uses in other environments as
105	   well, the majority of the conventions needed for these algorithms are
106	   already specified in other documents.  This document references the
107	   source of these conventions, with some relevant details repeated to
108	   aid developers that choose to support the CNSA Suite.  Where details
109	   have been repeated, the cited documents are authoritative.

111	2.  The Commercial National Security Algorithm Suite

113	   The National Security Agency (NSA) profiles commercial cryptographic
114	   algorithms and protocols as part of its mission to support secure,
115	   interoperable communications for US Government National Security
116	   Systems.  To this end, it publishes guidance both to assist with the
117	   US Government transition to new algorithms, and to provide vendors -
118	   and the Internet community in general - with information concerning
119	   their proper use and configuration.

121	   Recently, cryptographic transition plans have become overshadowed by
122	   the prospect of the development of a cryptographically-relevant
123	   quantum computer.  NSA has established the Commercial National
124	   Security Algorithm (CNSA) Suite to provide vendors and IT users near-
125	   term flexibility in meeting their IA interoperability requirements.
126	   The purpose behind this flexibility is to avoid vendors and customers
127	   making two major transitions in a relatively short timeframe, as we
128	   anticipate a need to shift to quantum-resistant cryptography in the
129	   near future.

131	   NSA is authoring a set of RFCs, including this one, to provide
132	   updated guidance concerning the use of certain commonly available
133	   commercial algorithms in IETF protocols.  These RFCs can be used in
134	   conjunction with other RFCs and cryptographic guidance (e.g., NIST
135	   Special Publications) to properly protect Internet traffic and data-
136	   at-rest for US Government National Security Systems..

138	3.  Terminology

140	   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
141	   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
142	   "OPTIONAL" in this document are to be interpreted as described in BCP
143	   14 [RFC2119] [RFC8174] when, and only when, they appear in all
144	   capitals, as shown here.

146	4.  Requirements and Assumptions

148	   CMS values are generated using ASN.1 [X208], the Basic Encoding Rules
149	   (BER) [X209], and the Distinguished Encoding Rules (DER) [X509].

151	   The elliptic curve used in the CNSA Suite is specified in [FIPS186],
152	   and appears in the literature under two different names.  For the
153	   sake of clarity, we list both names below:

155	         Curve       NIST Name    SECG Name    OID  [FIPS186]
156	         ---------------------------------------------------------
157	         nistp384    P-384        secp384r1    1.3.132.0.34

159	   For CNSA Suite applications, public key certificates used to verify
160	   S/MIME signatures MUST be compliant with the CNSA Suite Certificate
161	   and Certificate Revocation List (CRL) Profile specified in [RFC8603].

163	   Within the CMS signed-data content type, signature algorithm
164	   identifiers are located in the SignerInfo signatureAlgorithm field of
165	   SignedData.  In addition, signature algorithm identifiers are located
166	   in the SignerInfo signatureAlgorithm field of countersignature
167	   attributes.

169	   Elliptic Curve Cryptography (ECC) based implementations also require
170	   specification of schemes for key derivation and key wrap.
171	   Requirements for these schemes are in sections Section 7.1.1 and
172	   Section 7.1.2 repectively.

174	   RSA key pairs (public, private) are identified by the modulus size
175	   expressed in bits; RSA-3072 and RSA-4096 are computed using moduli of
176	   3072 bits and 4096 bits, respectively.

178	   RSA signature key pairs used in CNSA Suite compliant implementations
179	   are either RSA-3072 or RSA-4096.  The RSA exponent e MUST satisfy
180	   2^16<e<2^256 and be odd per [FIPS186].

182	   It is recognized that, while the vast majority of RSA signatures are
183	   currently made using the RSASSA-PKCS1-v1_5 algorithm, the preferred
184	   RSA signature scheme for new applications is RSASSA-PSS.  CNSA Suite
185	   compliant X.509 certificates will be issued in accordance with
186	   [RFC8603], and while those certificates must be signed and validated
187	   using RSASSA-PKCS1-v1_5, the subject's RSA key pair can be used to
188	   generate and validate signatures appropriate for either signing
189	   scheme.  Where use of RSASSA-PSS is indicated in this document, the
190	   parameters in Section 6.2.2 apply.

192	   This document assumes that required trust anchors have been securely
193	   provisioned to the client.

195	   All implementations use SHA-384 for hashing and either AES-CBC or
196	   AES-GCM for encryption, the requirements for which are given in
197	   Section 5 and Section 8, respectively.

199	5.  SHA-384 Message Digest Algorithm

201	   SHA-384 is the sole CNSA Suite message digest algorithm.  [RFC5754]
202	   specifies the conventions for using SHA-384 with the Cryptographic
203	   Message Syntax (CMS).  CNSA Suite compliant S/MIME implementations
204	   MUST follow the conventions in [RFC5754].

206	   Within the CMS signed-data content type, message digest algorithm
207	   identifiers are located in the SignedData digestAlgorithms field and
208	   the SignerInfo digestAlgorithm field.

210	   The SHA-384 message digest algorithm is defined in FIPS Pub 180
211	   [FIPS180].  The algorithm identifier for SHA-384 is defined in
212	   [RFC5754] as follows:

214	         id-sha384  OBJECT IDENTIFIER  ::=  { joint-iso-itu-t(2)
215	             country(16) us(840) organization(1) gov(101) csor(3)
216	             nistalgorithm(4) hashalgs(2) 2 }

218	   For SHA-384, the AlgorithmIdentifier parameters field is OPTIONAL,
219	   and if present, the parameters field MUST contain a NULL.  As
220	   specified in [RFC5754], implementations MUST generate SHA-384
221	   AlgorithmIdentifiers with absent parameters.  Implementations MUST
222	   accept SHA-384 AlgorithmIdentifiers with absent parameters or with
223	   NULL parameters.

225	6.  Digital Signature

227	6.1.  ECDSA Signature

229	   The Elliptic Curve Digital Signature Algorithm (ECDSA) is the CNSA
230	   Suite digital signature algorithm based on ECC.  [RFC5753] specifies
231	   the conventions for using ECDSA with the Cryptographic Message Syntax
232	   (CMS).  CNSA Suite compliant S/MIME implementations MUST follow the
233	   conventions in [RFC5753].

235	   [RFC5480] defines the signature algorithm identifier used in CMS for
236	   ECDSA with SHA-384 as follows:

238	         ecdsa-with-SHA384  OBJECT IDENTIFIER  ::=  { iso(1)
239	            member-body(2) us(840) ansi-X9-62(10045) signatures(4)
240	            ecdsa-with-sha2(3) 3 }

242	   When the ecdsa-with-SHA384 algorithm identifier is used, the
243	   AlgorithmIdentifier parameters field MUST be absent.

245	   When signing, the ECDSA algorithm generates two values, commonly
246	   called r and s.  These two values MUST be encoded using the ECDSA-
247	   Sig-Value type specified in [RFC5480]:

249	         ECDSA-Sig-Value  ::=  SEQUENCE {
250	            r  INTEGER,
251	            s  INTEGER }

253	6.2.  RSA Signature

255	   The RSA signature generation process and the encoding of the result
256	   is either RSASSA-PKCS1-v1_5 or RSA-PSS as described in detail in PKCS
257	   #1 version 2.2 [RFC8017].

259	6.2.1.  RSA-PKCS1-v1_5

261	   [RFC5754] defines the signature algorithm identifier used in CMS for
262	   RSA signature with SHA-384 as follows:

264	         sha384WithRSAEncryption  OBJECT IDENTIFIER  :== { iso(1)
265	           member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-1(1) 12 }

267	   When the sha384WithRSAEncryption algorithm identifier is used, the
268	   parameters MUST be NULL.  Implementations MUST accept the parameters
269	   being absent as well as present.

271	6.2.2.  RSA-PSS

273	   [RFC4056] defines the signature algorithm identifier used in CMS for
274	   RSA-PSS signature as follows:

276	         RSASSA-PSS  OBJECT IDENTIFIER  :== { iso(1)
277	           member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-1(1) 10 }

279	   The parameters field of an AlgorithmIdentifier that identifies
280	   RSASSA-PSS is defined in [RFC4055] as follows:

282	          RSASSA-PSS-params  ::=  SEQUENCE  {
283	             hashAlgorithm      [0] HashAlgorithm DEFAULT
284	                                       sha1Identifier,
285	             maskGenAlgorithm   [1] MaskGenAlgorithm DEFAULT
286	                                       mgf1SHA1Identifier,
287	             saltLength         [2] INTEGER DEFAULT 20,
288	             trailerField       [3] INTEGER DEFAULT 1  }

290	   The AlgorithmIdentifier parameters field MUST contain RSASSA-PSS-
291	   params with the following values:

293	   o  the hash algorithm MUST be id-sha384 as defined in [RFC8017];

295	   o  the mask generation function MUST use the algorithm identifier
296	      mfg1SHA384Identifier as defined in [RFC4055];

298	   o  the salt length MUST be 48 octets; and

300	   o  the trailerField MUST have value 1.

302	7.  Key Establishment

304	7.1.  Elliptic Curve Key Agreement

306	   Elliptic Curve Diffie-Hellman (ECDH) is the CNSA Suite key agreement
307	   algorithm.  Since S/MIME is used in store-and-forward communications,
308	   ephemeral-static ECDH is always employed.  This means that the
309	   message originator possesses an ephemeral ECDH key pair and that the
310	   message recipient possesses a static ECDH key pair whose public key
311	   is provided in an X.509 certificate.  The certificate used to obtain
312	   the recipient's public key MUST be compliant with [RFC8603].

314	   When a key agreement algorithm is used, the following steps are
315	   performed:

317	   1.  A content-encryption key (CEK) for a particular content-
318	       encryption algorithm is generated at random.

320	   2.  The recipient's public key and sender's private key are used with
321	       a key agreement scheme to generate a shared secret (Z).

323	   3.  The shared secret is used with a key derivation function (KDF) to
324	       produce a key-encryption key (KEK).

326	   4.  The KEK is used with a key wrap algorithm to encrypt the CEK.

328	   Key derivation is discussed in Section 7.1.1.  Key wrapping is
329	   discussed in Section 7.1.2.

331	   Section 3.1 of [RFC5753] specifies the conventions for using ECDH
332	   with the CMS.  CNSA Suite compliant S/MIME implementations MUST
333	   follow these conventions.

335	   Within the CMS enveloped-data and authenticated-enveloped-data
336	   content types, key agreement algorithm identifiers are located in the
337	   EnvelopedData RecipientInfos KeyAgreeRecipientInfo
338	   keyEncryptionAlgorithm field.

340	   The keyEncryptionAlgorithm field comprises two fields, an algorithm
341	   field and a parameter field.  The algorithm field MUST identify
342	   dhSinglePass-stdDH-sha384kdf-scheme.  The algorithm identifier for
343	   the dhSinglePass-stdDH-sha384kdf-scheme, repeated from Section 7.1.4
344	   of [RFC5753], is:

346	         dhSinglePass-stdDH-sha384kdf-scheme  OBJECT IDENTIFIER  ::=
347	             { iso(1) identified-organization(3) certicom(132)
348	               schemes(1) 11 2 }

350	   The keyEncryptionAlgorithm parameter field MUST be constructed as
351	   described in Section 7.1.2.

353	7.1.1.  Key Derivation Functions

355	   KDFs based on SHA-384 are used to derive a pairwise key-encryption
356	   key from the shared secret produced by ephemeral-static ECDH.
357	   Sections 7.1.8 and 7.2 of [RFC5753] specify the CMS conventions for
358	   using a KDF with the shared secret generated during ephemeral-static
359	   ECDH.  CNSA Suite compliant S/MIME implementations MUST follow these
360	   conventions.

362	   The KDF based on SHA-384 MUST be used.

364	   As specified in Section 7.2 of [RFC5753], when using ECDH with the
365	   CMS enveloped-data or authenticated-enveloped-data content type, the
366	   derivation of key-encryption keys makes use of the ECC-CMS-SharedInfo
367	   type:

369	         ECC-CMS-SharedInfo  ::=  SEQUENCE {
370	            keyInfo      AlgorithmIdentifier,
371	            entityUInfo  [0] EXPLICIT OCTET STRING OPTIONAL,
372	            suppPubInfo  [2] EXPLICIT OCTET STRING }

374	   In CNSA Suite for S/MIME, the fields of ECC-CMS-SharedInfo are used
375	   as follows:

377	      keyInfo contains the object identifier of the key-encryption
378	      algorithm used to wrap the content-encryption key.  If AES-256 Key
379	      Wrap is used, then the keyInfo will contain id-aes256-wrap-pad,
380	      and the parameters will be absent.

382	      entityUInfo optionally contains a random value provided by the
383	      message originator.  If user keying material (ukm) is included in
384	      the KeyAgreeRecipientInfo, then the entityUInfo MUST be present,
385	      and it MUST contain the ukm value.  If the ukm is not present,
386	      then the entityUInfo MUST be absent.

388	      suppPubInfo contains the length of the generated key-encryption
389	      key, in bits, represented as a 32-bit unsigned number, as
390	      described in [RFC2631].  When a 256-bit AES key is used, the
391	      length MUST be 0x00000100.

393	   ECC-CMS-SharedInfo is DER encoded and used as input to the key
394	   derivation function, as specified in Section 3.6.1 of [SEC1].  Note
395	   that ECC-CMS-SharedInfo differs from the OtherInfo specified in
396	   [RFC2631].  Here, a counter value is not included in the keyInfo
397	   field because the KDF specified in [SEC1] ensures that sufficient
398	   keying data is provided.

400	   The KDF specified in Section 3.6.1 of [SEC1] describes how to
401	   generate an essentially arbitrary amount of keying material from a
402	   shared secret, Z, produced by ephemeral-static ECDH.  To generate an
403	   L-bit key-encryption key (KEK), KM is computed:

405	         KM(Counter) = Hash ( Z || Counter || ECC-CMS-SharedInfo )

407	   incrementing Counter appropriately, until enough material has been
408	   generated.  The KM blocks are concatenated left to right, as they are
409	   generated, and the first (leftmost) L bits are used as the KEK:

411	         KEK = the leftmost L bits of
412	                  [KM ( counter=1 ) || KM ( counter=2 ) ...]

414	   In CNSA Suite for S/MIME, the elements of the KDF are defined as
415	   follows:

417	      Hash is a one-way hash function.  The SHA-384 hash MUST be used.

419	      Z is the shared secret value generated during ephemeral-static
420	      ECDH.  Z MUST be exactly 384 bits, i.e., leading zero bits MUST be
421	      preserved.

423	      Counter is a 32-bit unsigned number, represented in network byte
424	      order.  Its initial value MUST be 0x00000001 for any key
425	      derivation operation.

427	      ECC-CMS-SharedInfo is composed as described above.  It MUST be DER
428	      encoded.

430	   In CNSA Suite for S/MIME, exactly one iteration is needed; the
431	   Counter is not incremented.  The key-encryption key (KEK) MUST be the
432	   first (leftmost) 256 bits of the SHA-384 output value:

434	         KEK = the leftmost 256 bits of
435	                  SHA-384 ( Z || 0x00000001 || ECC-CMS-SharedInfo )

437	   In CNSA Suite for S/MIME, the key-encryption key MUST be the most
438	   significant 256 bits of the SHA-384 output value.

440	   Note that the only source of secret entropy in this computation is Z.

442	7.1.2.  AES Key Wrap

444	   The AES Key Wrap with Padding key-encryption algorithm, as specified
445	   in [RFC5649] and [SP80038F], is used to encrypt the content-
446	   encryption key with a pairwise key-encryption key that is generated
447	   using ephemeral-static ECDH.  Section 8 of [RFC5753] specifies the
448	   CMS conventions for using AES Key Wrap with a pairwise key generated
449	   through ephemeral-static ECDH.  CNSA Suite compliant S/MIME
450	   implementations MUST follow these conventions.

452	   Within the CMS enveloped-data content type, key wrap algorithm
453	   identifiers are located in the KeyWrapAlgorithm parameters within the
454	   EnvelopedData RecipientInfos KeyAgreeRecipientInfo
455	   keyEncryptionAlgorithm field.

457	   The KeyWrapAlgorithm MUST be id-aes256-wrap-pad.  The required
458	   algorithm identifier, specified in [RFC5649], is:

460	         id-aes256-wrap-pad  OBJECT IDENTIFIER ::=  { joint-iso-itu-t(2)
461	            country(16) us(840) organization(1) gov(101) csor(3)
462	            nistAlgorithm(4) aes(1) 48 }

464	7.2.  RSA Key Transport

466	   RSA encryption (RSA) is the CNSA Suite key transport algorithm.  The
467	   RSA key transport algorithm is the RSA encryption scheme defined in
468	   [RFC8017], where the message to be encrypted is the content-
469	   encryption key.

471	   The recipient of an S/MIME message possesses an RSA key pair whose
472	   public key is represented by an X.509 certificate.  The certificate
473	   used to obtain the recipient's public key MUST be compliant with
474	   [RFC8603].  These certificates are suitable for use with either
475	   RSAES-OAEP or RSAES-PKCS1-v1_5.

477	7.2.1.  RSAES-PKCS1-v1_5

479	   Section 4.2 of [RFC3370] specifies the conventions for using RSAES-
480	   PKCS1-v1_5 with the CMS.  S/MIME implementations employing this form
481	   of key transport MUST follow these conventions.

483	   Within the CMS enveloped-data and authenticated-enveloped-data
484	   content types, key transport algorithm identifiers are located in the
485	   EnvelopedData RecipientInfos KeyTransRecipientInfo
486	   keyEncryptionAlgorithm field.

488	   The algorithm identifier for RSA (PKCS #1 v1.5) is:

490	         rsaEncryption OBJECT IDENTIFIER ::= { iso(1) member-body(2)
491	             us(840) rsadsi(113549) pkcs(1) pkcs-1(1) 1 }

493	   The AlgorithmIdentifier parameters field MUST be present, and the
494	   parameters field MUST contain NULL.

496	7.2.2.  RSAES-OAEP

498	   [RFC3560] specifies the conventions for using RSAES-OAEP with the
499	   CMS.  CNSA Suite compliant S/MIME implementations employing this form
500	   of key transport MUST follow these conventions.

502	   Within the CMS enveloped-data and authenticated-enveloped-data
503	   content types, key transport algorithm identifiers are located in the
504	   EnvelopedData RecipientInfos KeyTransRecipientInfo
505	   keyEncryptionAlgorithm field.

507	   The algorithm identifier for RSA (OAEP) is:

509	         id-RSAES-OAEP  OBJECT IDENTIFIER  ::=  { iso(1) member-body(2)
510	             us(840) rsadsi(113549) pkcs(1) pkcs-1(1) 7 }

512	   The parameters field of an AlgorithmIdentifier that identifies RSAES-
513	   OAEP is defined in [RFC4055] as follows:

515	          RSAES-OAEP-params  ::=  SEQUENCE  {
516	             hashFunc          [0] AlgorithmIdentifier DEFAULT
517	                                      sha1Identifier,
518	             maskGenFunc       [1] AlgorithmIdentifier DEFAULT
519	                                      mgf1SHA1Identifier,
520	             pSourceFunc       [2] AlgorithmIdentifier DEFAULT
521	                                      pSpecifiedEmptyIdentifier  }

523	          pSpecifiedEmptyIdentifier  AlgorithmIdentifier  ::=
524	                               { id-pSpecified, nullOctetString }

526	          nullOctetString  OCTET STRING (SIZE (0))  ::=  { ''H }

528	   The AlgorithmIdentifier parameters field MUST be present, and the
529	   parameters field MUST contain RSAES-OAEP-params with values as
530	   follows:

532	   o  the hashFunc algorithm must be id-sha384 as defined in [RFC8017];

534	   o  the mask generation function must use the algorithm identifier
535	      mfg1SHA384Identifier as defined in [RFC4055];

537	   o  the pSourceFunc field must be absent.

539	   The SMIMECapabilities signed attribute is used to specify a partial
540	   list of algorithms that the software announcing the SMIMECapabilities
541	   can support.  If the SMIMECapabilities signed attribute is included
542	   to announce support for the RSAES-OAEP algorithm, it MUST be
543	   constructed as defined in Section 5 of [RFC3560], with the sequence
544	   representing the rSAES-OAEP-SHA384-Identifier.

546	8.  Content Encryption

548	8.1.  AES-CBC Content Encryption

550	   CNSA Suite compliant S/MIME implementations MUST use AES-256
551	   [FIPS197] in Cipher Block Chaining (CBC) mode [SP80038A] as the
552	   content encryption algorithm when using the enveloped-data content
553	   type, and MUST follow the conventions for using AES with the CMS
554	   defined in [RFC3565].

556	   Within the CMS enveloped-data content type, content-encryption
557	   algorithm identifiers are located in the EnvelopedData
558	   EncryptedContentInfo contentEncryptionAlgorithm field.  The content-
559	   encryption algorithm is used to encipher the content located in the
560	   EnvelopedData EncryptedContentInfo encryptedContent field.

562	   The AES CBC content-encryption algorithm is described in [FIPS197]
563	   and [SP80038A].  The algorithm identifier for AES-256 in CBC mode is:

565	         id-aes256-CBC  OBJECT IDENTIFIER  ::=  { joint-iso-itu-t(2)
566	            country(16) us(840) organization(1) gov(101) csor(3)
567	            nistAlgorithm(4) aes(1) 42 }

569	   The AlgorithmIdentifier parameters field MUST be present, and the
570	   parameters field must contain AES-IV:

572	         AES-IV  ::=  OCTET STRING (SIZE(16))

574	   The 16-octet initialization vector is generated at random by the
575	   originator.  See [RFC4086] for guidance on generation of random
576	   values.

578	8.2.  AES-GCM Content Encryption

580	   CNSA Suite compliant S/MIME implementations MUST use AES [FIPS197] in
581	   Galois Counter Mode (GCM) [SP80038D] as the content-authenticated
582	   encryption algorithm when using the authenticated-enveloped-data
583	   content type [RFC5083], and MUST follow the conventions for using
584	   AES-GCM with the CMS defined in [RFC5084].

586	   In CNSA Suite for S/MIME AES-256 in GCM mode MUST be used.

588	   Within the CMS authenticated-enveloped-data content type, content-
589	   authenticated encryption algorithm identifiers are located in the
590	   AuthEnvelopedData EncryptedContentInfo contentEncryptionAlgorithm
591	   field.  The content-authenticated encryption algorithm is used to
592	   encipher the content located in the AuthEnvelopedData
593	   EncryptedContentInfo encryptedContent field.

595	   The AES-GCM content-authenticated encryption algorithm is described
596	   in [FIPS197] and [SP80038D].  The algorithm identifier for AES-256 in
597	   GCM mode is:

599	            id-aes256-GCM  OBJECT IDENTIFIER  ::=  { joint-iso-itu-t(2)
600	               country(16) us(840) organization(1) gov(101) csor(3)
601	               nistAlgorithm(4) aes(1) 46 }

603	   The AlgorithmIdentifier parameters field MUST be present, and the
604	   parameters field must contain GCMParameters:

606	         GCMParameters ::= SEQUENCE {
607	           aes-nonce        OCTET STRING,
608	           aes-ICVlen       AES-GCM-IVClen DEFAULT 12 }

610	   The authentication tag length (aes-ICVlen) SHALL be 16 (indicating a
611	   tag length of 128 bits).

613	   The initialization vector (aes-nonce) MUST be generated in accordance
614	   with [SP80038D].  AES-GCM loses security catastrophically if a nonce
615	   is reused with a given key on more than one distinct set of input
616	   data.  Therefore, a fresh content-authenticated encryption key MUST
617	   be generated for each message.

619	9.  Security Considerations

621	   This document specifies the conventions for using the NSA's CNSA
622	   Suite algorithms in S/MIME.  All of the algorithms and algorithm
623	   identifiers have been specified in previous documents.

625	   See [RFC4086] for guidance on generation of random values.

627	   The security considerations in [RFC5652] discuss the CMS as a method
628	   for digitally signing data and encrypting data.

630	   The security considerations in [RFC3370] discuss cryptographic
631	   algorithm implementation concerns in the context of the CMS.

633	   The security considerations in [RFC5753] discuss the use of elliptic
634	   curve cryptography (ECC) in the CMS.

636	   The security considerations in [RFC3565] discuss the use of AES in
637	   the CMS.

639	   The security considerations in [RFC8551] apply to this profile, in
640	   particular the recommendation to use authenticated encryption modes
641	   (i.e. use authenticated-enveloped-data with AES-GCM rather than
642	   enveloped-data with AES-CBC).

644	10.  IANA Considerations

646	   This document has no IANA actions.

648	11.  References

650	11.1.  Normative References

652	   [CNSA]     Committee for National Security Systems, "Use of Public
653	              Standards for Secure Information Sharing", CNSSP 15,
654	              October 2016,
655	              <https://www.cnss.gov/CNSS/Issuances/Policies.htm>.

657	   [FIPS180]  National Institute of Standards and Technology, "Secure
658	              Hash Standard (SHS)", Federal Information Processing
659	              Standard 180-4, August 2015,
660	              <https://csrc.nist.gov/publications/detail/fips/180/4/
661	              final>.

663	   [FIPS186]  National Institute of Standards and Technology, "Digital
664	              Signature Standard", Federal Information Processing
665	              Standard 186-4, July 2013,
666	              <https://csrc.nist.gov/publications/detail/fips/186/4/
667	              final>.

669	   [FIPS197]  National Institute of Standards and Technology, "Advanced
670	              Encryption Standard (AES)", Federal Information Processing
671	              Standard 197, November 2001,
672	              <https://csrc.nist.gov/publications/detail/fips/197/
673	              final>.

675	   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
676	              Requirement Levels", BCP 14, RFC 2119,
677	              DOI 10.17487/RFC2119, March 1997,
678	              <https://www.rfc-editor.org/info/rfc2119>.

680	   [RFC2631]  Rescorla, E., "Diffie-Hellman Key Agreement Method",
681	              RFC 2631, DOI 10.17487/RFC2631, June 1999,
682	              <https://www.rfc-editor.org/info/rfc2631>.

684	   [RFC3370]  Housley, R., "Cryptographic Message Syntax (CMS)
685	              Algorithms", RFC 3370, DOI 10.17487/RFC3370, August 2002,
686	              <https://www.rfc-editor.org/info/rfc3370>.

688	   [RFC3560]  Housley, R., "Use of the RSAES-OAEP Key Transport
689	              Algorithm in Cryptographic Message Syntax (CMS)",
690	              RFC 3560, DOI 10.17487/RFC3560, July 2003,
691	              <https://www.rfc-editor.org/info/rfc3560>.

693	   [RFC3565]  Schaad, J., "Use of the Advanced Encryption Standard (AES)
694	              Encryption Algorithm in Cryptographic Message Syntax
695	              (CMS)", RFC 3565, DOI 10.17487/RFC3565, July 2003,
696	              <https://www.rfc-editor.org/info/rfc3565>.

698	   [RFC4055]  Schaad, J., Kaliski, B., and R. Housley, "Additional
699	              Algorithms and Identifiers for RSA Cryptography for use in
700	              the Internet X.509 Public Key Infrastructure Certificate
701	              and Certificate Revocation List (CRL) Profile", RFC 4055,
702	              DOI 10.17487/RFC4055, June 2005,
703	              <https://www.rfc-editor.org/info/rfc4055>.

705	   [RFC4056]  Schaad, J., "Use of the RSASSA-PSS Signature Algorithm in
706	              Cryptographic Message Syntax (CMS)", RFC 4056,
707	              DOI 10.17487/RFC4056, June 2005,
708	              <https://www.rfc-editor.org/info/rfc4056>.

710	   [RFC5083]  Housley, R., "Cryptographic Message Syntax (CMS)
711	              Authenticated-Enveloped-Data Content Type", RFC 5083,
712	              DOI 10.17487/RFC5083, November 2007,
713	              <https://www.rfc-editor.org/info/rfc5083>.

715	   [RFC5084]  Housley, R., "Using AES-CCM and AES-GCM Authenticated
716	              Encryption in the Cryptographic Message Syntax (CMS)",
717	              RFC 5084, DOI 10.17487/RFC5084, November 2007,
718	              <https://www.rfc-editor.org/info/rfc5084>.

720	   [RFC5480]  Turner, S., Brown, D., Yiu, K., Housley, R., and T. Polk,
721	              "Elliptic Curve Cryptography Subject Public Key
722	              Information", RFC 5480, DOI 10.17487/RFC5480, March 2009,
723	              <https://www.rfc-editor.org/info/rfc5480>.

725	   [RFC5649]  Housley, R. and M. Dworkin, "Advanced Encryption Standard
726	              (AES) Key Wrap with Padding Algorithm", RFC 5649,
727	              DOI 10.17487/RFC5649, September 2009,
728	              <https://www.rfc-editor.org/info/rfc5649>.

730	   [RFC5652]  Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
731	              RFC 5652, DOI 10.17487/RFC5652, September 2009,
732	              <https://www.rfc-editor.org/info/rfc5652>.

734	   [RFC5753]  Turner, S. and D. Brown, "Use of Elliptic Curve
735	              Cryptography (ECC) Algorithms in Cryptographic Message
736	              Syntax (CMS)", RFC 5753, DOI 10.17487/RFC5753, January
737	              2010, <https://www.rfc-editor.org/info/rfc5753>.

739	   [RFC5754]  Turner, S., "Using SHA2 Algorithms with Cryptographic
740	              Message Syntax", RFC 5754, DOI 10.17487/RFC5754, January
741	              2010, <https://www.rfc-editor.org/info/rfc5754>.

743	   [RFC8017]  Moriarty, K., Ed., Kaliski, B., Jonsson, J., and A. Rusch,
744	              "PKCS #1: RSA Cryptography Specifications Version 2.2",
745	              RFC 8017, DOI 10.17487/RFC8017, November 2016,
746	              <https://www.rfc-editor.org/info/rfc8017>.

748	   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
749	              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
750	              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

752	   [RFC8551]  Schaad, J., Ramsdell, B., and S. Turner, "Secure/
753	              Multipurpose Internet Mail Extensions (S/MIME) Version 4.0
754	              Message Specification", RFC 8551, DOI 10.17487/RFC8551,
755	              April 2019, <https://www.rfc-editor.org/info/rfc8551>.

757	   [RFC8603]  Jenkins, M. and L. Zieglar, "Commercial National Security
758	              Algorithm (CNSA) Suite Certificate and Certificate
759	              Revocation List (CRL) Profile", RFC 8603,
760	              DOI 10.17487/RFC8603, May 2019,
761	              <https://www.rfc-editor.org/info/rfc8603>.

763	   [SEC1]     Standards for Efficient Cryptography Group, "SEC1:
764	              Elliptic Curve Cryptography", May 2009,
765	              <https://www.secg.org/sec1-v2.pdf>.

767	   [SP80038A]
768	              National Institute of Standards and Technology,
769	              "Recommendation for Block Cipher Modes of Operation:
770	              Methods and Techniques", Special Publication 800-38A,
771	              December 2001, <https://csrc.nist.gov/publications/detail/
772	              sp/800-38a/final>.

774	   [SP80038D]
775	              National Institute of Standards and Technology,
776	              "Recommendation for Block Cipher Modes of Operation:
777	              Galois/Counter Mode (GCM) and GMAC", Special
778	              Publication 800-38D, November 2007,
779	              <https://csrc.nist.gov/publications/detail/sp/800-38d/
780	              final>.

782	   [SP80038F]
783	              National Institute of Standards and Technology,
784	              "Recommendation for Block Cipher Modes of Operation:
785	              Methods for Key Wrapping", Special Publication 800-38F,
786	              December 2012, <https://csrc.nist.gov/publications/detail/
787	              sp/800-38f/final>.

789	   [X208]     CCITT, "Recommendation X.208: Specification of Abstract
790	              Syntax Notation One (ASN.1)", 1988,
791	              <https://www.itu.int/rec/T-REC-X.208-198811-W/en>.

793	   [X209]     CCITT, "Recommendation X.209: Specification of Basic
794	              Encoding Rules for Abstract Syntax Notation One (ASN.1)",
795	              1988, <https://www.itu.int/rec/T-REC-X.209-198811-W/en>.

797	   [X509]     CCITT, "Recommendation X.509: The Directory -
798	              Authentication Framework", 1988,
799	              <https://www.itu.int/rec/T-REC-X.509-198811-S>.

801	11.2.  Informative References

803	   [RFC4086]  Eastlake 3rd, D., Schiller, J., and S. Crocker,
804	              "Randomness Requirements for Security", BCP 106, RFC 4086,
805	              DOI 10.17487/RFC4086, June 2005,
806	              <https://www.rfc-editor.org/info/rfc4086>.

808	   [SP80059]  National Institute of Standards and Technology, "Guideline
809	              for Identifying an Information System as a National
810	              Security System", Special Publication 800-59 , August
811	              2003, <https://csrc.nist.gov/publications/detail/sp/800-
812	              59/final>.

814	Author's Address

816	   Michael Jenkins
817	   National Security Agency

819	   Email: mjjenki@nsa.gov