Network Working Group R. Housley

Network Working Group R. Housley
Request for Comments: 5008 Vigil Security
Category: Informational J. Solinas
NSA
September 2007

Suite B in Secure/Multipurpose Internet Mail Extensions (S/MIME)

Status of This Memo

This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.

Abstract

This document specifies the conventions for using the United States
National Security Agency's Suite B algorithms in Secure/Multipurpose
Internet Mail Extensions (S/MIME) as specified in RFC 3851.

1. Introduction

This document specifies the conventions for using the United States
National Security Agency's Suite B algorithms [SuiteB] in
Secure/Multipurpose Internet Mail Extensions (S/MIME) [MSG]. S/MIME
makes use of the Cryptographic Message Syntax (CMS) [CMS]. In
particular, the signed-data and the enveloped-data content types are
used.

Since many of the Suite B algorithms enjoy uses in other environments
as well, the majority of the conventions needed for the Suite B
algorithms are already specified in other documents. This document
references the source of these conventions, and the relevant details
are repeated to aid developers that choose to support Suite B. In a
few cases, additional algorithm identifiers are needed, and they are
provided in this document.

1.1. Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [STDWORDS].

Housley & Solinas Informational [Page 1]

RFC 5008 Suite B in S/MIME September 2007

1.2. ASN.1

CMS values are generated using ASN.1 [X.208-88], the Basic Encoding
Rules (BER) [X.209-88], and the Distinguished Encoding Rules (DER)
[X.509-88].

1.3. Suite B Security Levels

Suite B offers two security levels: Level 1 and Level 2. Security
Level 2 offers greater cryptographic strength by using longer keys.

For S/MIME signed messages, Suite B follows the direction set by RFC
3278 [CMSECC], but some additional algorithm identifiers are
assigned. Suite B uses these algorithms:

Security Level 1 Security Level 2
---------------- ----------------
Message Digest: SHA-256 SHA-384
Signature: ECDSA with P-256 ECDSA with P-384

For S/MIME-encrypted messages, Suite B follows the direction set by
RFC 3278 [CMSECC] and follows the conventions set by RFC 3565
[CMSAES]. Again, additional algorithm identifiers are assigned.
Suite B uses these algorithms:

Security Level 1 Security Level 2
---------------- ----------------
Key Agreement: ECDH with P-256 ECDH with P-384
Key Derivation: SHA-256 SHA-384
Key Wrap: AES-128 Key Wrap AES-256 Key Wrap
Content Encryption: AES-128 CBC AES-256 CBC

2. SHA-256 and SHA-256 Message Digest Algorithms

This section specifies the conventions employed by implementations
that support SHA-256 or SHA-384 [SHA2]. In Suite B, Security Level
1, the SHA-256 message digest algorithm MUST be used. In Suite B,
Security Level 2, SHA-384 MUST be used.

Within the CMS signed-data content type, message digest algorithm
identifiers are located in the SignedData digestAlgorithms field and
the SignerInfo digestAlgorithm field. Also, message digest values
are located in the Message Digest authenticated attribute. In
addition, message digest values are input into signature algorithms.

The SHA-256 and SHA-384 message digest algorithms are defined in FIPS
Pub 180-2 [SHA2, EH]. The algorithm identifier for SHA-256 is:

Housley & Solinas Informational [Page 2]

RFC 5008 Suite B in S/MIME September 2007

id-sha256 OBJECT IDENTIFIER ::= { joint-iso-itu-t(2)
country(16) us(840) organization(1) gov(101) csor(3)
nistalgorithm(4) hashalgs(2) 1 }

The algorithm identifier for SHA-384 is:

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

There are two possible encodings for the AlgorithmIdentifier
parameters field. The two alternatives arise from the fact that when
the 1988 syntax for AlgorithmIdentifier was translated into the 1997
syntax, the OPTIONAL associated with the AlgorithmIdentifier
parameters got lost. Later, the OPTIONAL was recovered via a defect
report, but by then many people thought that algorithm parameters
were mandatory. Because of this history some implementations encode
parameters as a NULL element and others omit them entirely. The
correct encoding for the SHA-256 and SHA-384 message digest
algorithms is to omit the parameters field; however, to ensure
compatibility, implementations ought to also handle a SHA-256 and
SHA-384 AlgorithmIdentifier parameters field, which contains a NULL.

For both SHA-256 and SHA-384, the AlgorithmIdentifier parameters
field is OPTIONAL, and if present, the parameters field MUST contain
a NULL. Implementations MUST accept SHA-256 and SHA-384
AlgorithmIdentifiers with absent parameters. Implementations MUST
accept SHA-256 and SHA-384 AlgorithmIdentifiers with NULL parameters.
Implementations SHOULD generate SHA-256 and SHA-384
AlgorithmIdentifiers with absent parameters.

3. ECDSA Signature Algorithm

This section specifies the conventions employed by implementations
that support Elliptic Curve Digital Signature Algorithm (ECDSA). The
direction set by RFC 3278 [CMSECC] is followed, but additional
message digest algorithms and additional elliptic curves are
employed. In Suite B, Security Level 1, ECDSA MUST be used with the
SHA-256 message digest algorithm and the P-256 elliptic curve. In
Suite B, Security Level 2, ECDSA MUST be used with the SHA-384
message digest algorithm and the P-384 elliptic curve. The P-256 and
P-384 elliptic curves are specified in [DSS].

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

Housley & Solinas Informational [Page 3]

RFC 5008 Suite B in S/MIME September 2007

Within the CMS signed-data content type, signature values are located
in the SignerInfo signature field of SignedData. In addition,
signature values are located in the SignerInfo signature field of
countersignature attributes.

As specified in RFC 3279 [PKIX1ALG], ECDSA and Elliptic Curve
Diffie-Hellman (ECDH) use the same algorithm identifier for subject
public keys in certificates, and it is repeated here:

id-ecPublicKey OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) ansi-x9-62(10045) keyType(2) 1 }

This object identifier is used in public key certificates for both
ECDSA signature keys and ECDH encryption keys. The intended
application for the key may be indicated in the key usage field (see
RFC 3280 [PKIX1]). The use of separate keys for signature and
encryption purposes is RECOMMENDED; however, the use of a single key
for both signature and encryption purposes is not forbidden.

As specified in RFC 3279 [PKIX1ALG], ECDSA and ECDH use the same
encoding for subject public keys in certificates, and it is repeated
here:

ECPoint ::= OCTET STRING

The elliptic curve public key (an OCTET STRING) is mapped to a
subject public key (a BIT STRING) as follows: the most significant
bit of the OCTET STRING becomes the most significant bit of the BIT
STRING, and the least significant bit of the OCTET STRING becomes the
least significant bit of the BIT STRING. Note that this octet string
may represent an elliptic curve point in compressed or uncompressed
form. Implementations that support elliptic curves according to this
specification MUST support the uncompressed form and MAY support the
compressed form.

ECDSA and ECDH require use of certain parameters with the public key.
The parameters may be inherited from the certificate issuer,
implicitly included through reference to a named curve, or explicitly
included in the certificate. As specified in RFC 3279 [PKIX1ALG],
the parameter structure is:

EcpkParameters ::= CHOICE {
ecParameters ECParameters,
namedCurve OBJECT IDENTIFIER,
implicitlyCA NULL }

Housley & Solinas Informational [Page 4]

RFC 5008 Suite B in S/MIME September 2007

In Suite B, the namedCurve CHOICE MUST be used. The object
identifier for P-256 is:

ansip256r1 OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) ansi-x9-62(10045) curves(3) prime(1) 7 }

The object identifier for P-384 is:

secp384r1 OBJECT IDENTIFIER ::= { iso(1)
identified-organization(3) certicom(132) curve(0) 34 }

The algorithm identifier used in CMS for ECDSA with SHA-256 signature
values is:

ecdsa-with-SHA256 OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) ansi-X9-62(10045) signatures(4) ecdsa-with-sha2(3) 2 }

The algorithm identifier used in CMS for ECDSA with SHA-384 signature
values is:

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

When either the ecdsa-with-SHA256 or the ecdsa-with-SHA384 algorithm
identifier is used, the AlgorithmIdentifier parameters field MUST be
absent.

When signing, the ECDSA algorithm generates two values, commonly
called r and s. To transfer these two values as one signature, they
MUST be encoded using the Ecdsa-Sig-Value type specified in RFC 3279
[PKIX1ALG]:

Ecdsa-Sig-Value ::= SEQUENCE {
r INTEGER,
s INTEGER }

4. Key Management

CMS accommodates the following general key management techniques: key
agreement, key transport, previously distributed symmetric key-
encryption keys, and passwords. In Suite B, ephemeral-static key
agreement MUST be used as described in Section 4.1.

When a key agreement algorithm is used, a key-encryption algorithm is
also needed. In Suite B, the Advanced Encryption Standard (AES) Key
Wrap, as specified in RFC 3394 [AESWRAP, SH], MUST be used as the
key-encryption algorithm. AES Key Wrap is discussed further in
Section 4.2. The key-encryption key used with the AES Key Wrap

Housley & Solinas Informational [Page 5]

RFC 5008 Suite B in S/MIME September 2007

algorithm is obtained from a key derivation function (KDF). In Suite
B, there are two KDFs, one based on SHA-256 and one based on SHA-384.
These KDFs are discussed further in Section 4.3.

4.1. ECDH Key Agreement Algorithm

This section specifies the conventions employed by implementations
that support ECDH. The direction set by RFC 3278 [CMSECC] is
followed, but additional key derivation functions and key wrap
algorithms are employed. S/MIME is used in store-and-forward
communications, which means that ephemeral-static ECDH is always
employed. This means that the message originator uses an ephemeral
ECDH key and that the message recipient uses a static ECDH key, which
is obtained from an X.509 certificate. In Suite B, Security Level 1,
ephemeral-static ECDH MUST be used with the SHA-256 KDF, AES-128 Key
Wrap, and the P-256 elliptic curve. In Suite B, Security Level 2,
ephemeral-static ECDH MUST be used with the SHA-384 KDF, AES-256 Key
Wrap, and the P-384 elliptic curve.

Within the CMS enveloped-data content type, key agreement algorithm
identifiers are located in the EnvelopedData RecipientInfos
KeyAgreeRecipientInfo keyEncryptionAlgorithm field.

As specified in RFC 3279 [PKIX1ALG], ECDSA and ECDH use the same
conventions for carrying a subject public key in a certificate.
These conventions are discussed in Section 3.

Ephemeral-static ECDH key agreement is defined in [SEC1] and
[IEEE1363]. When using ephemeral-static ECDH, the EnvelopedData
RecipientInfos keyAgreeRecipientInfo field is used as follows:

version MUST be 3.

originator MUST be the originatorKey alternative. The
originatorKey algorithm field MUST contain the id-ecPublicKey
object identifier (see Section 3) with NULL parameters. The
originatorKey publicKey field MUST contain the message
originator's ephemeral public key, which is a DER-encoded ECPoint
(see Section 3). The ECPoint SHOULD be represented in
uncompressed form.

ukm can be present or absent. However, message originators SHOULD
include the ukm. As specified in RFC 3852 [CMS], implementations
MUST support ukm message recipient processing, so interoperability
is not a concern if the ukm is present or absent. When present,
the ukm is used to ensure that a different key-encryption key is
generated, even when the ephemeral private key is improperly used

Housley & Solinas Informational [Page 6]

RFC 5008 Suite B in S/MIME September 2007

more than once. See [RANDOM] for guidance on generation of random
values.

keyEncryptionAlgorithm MUST be one of the two algorithm
identifiers listed below, and the algorithm identifier parameter
field MUST be present and identify the key wrap algorithm. The
key wrap algorithm denotes the symmetric encryption algorithm used
to encrypt the content-encryption key with the pairwise key-
encryption key generated using the ephemeral-static ECDH key
agreement algorithm (see Section 4.3). In Suite B, Security Level
1, the keyEncryptionAlgorithm MUST be dhSinglePass-stdDH-
sha256kdf-scheme, and the keyEncryptionAlgorithm parameter MUST be
a KeyWrapAlgorithm containing id-aes128-wrap (see Section 4.2).
In Suite B, Security Level 2, the keyEncryptionAlgorithm MUST be
dhSinglePass-stdDH-sha384kdf-scheme, and the
keyEncryptionAlgorithm parameter MUST be a KeyWrapAlgorithm
containing id-aes256-wrap (see Section 4.2). The algorithm
identifier for dhSinglePass-stdDH-sha256kdf-scheme and
dhSinglePass-stdDH-sha384kdf-scheme are:

dhSinglePass-stdDH-sha256kdf-scheme OBJECT IDENTIFIER ::=
{ iso(1) identified-organization(3) certicom(132)
schemes(1) 11 1 }

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

Both of these algorithm identifiers use KeyWrapAlgorithm as the
type for their parameter:

KeyWrapAlgorithm ::= AlgorithmIdentifier

recipientEncryptedKeys contains an identifier and an encrypted key
for each recipient. The RecipientEncryptedKey
KeyAgreeRecipientIdentifier MUST contain either the
issuerAndSerialNumber identifying the recipient's certificate or
the RecipientKeyIdentifier containing the subject key identifier
from the recipient's certificate. In both cases, the recipient's
certificate contains the recipient's static ECDH public key.
RecipientEncryptedKey EncryptedKey MUST contain the content-
encryption key encrypted with the ephemeral-static, ECDH-generated
pairwise key-encryption key using the algorithm specified by the
KeyWrapAlgorithm (see Section 4.3).

Housley & Solinas Informational [Page 7]

RFC 5008 Suite B in S/MIME September 2007

4.2. AES Key Wrap

CMS offers support for symmetric key-encryption key management;
however, it is not used in Suite B. Rather, the AES Key Wrap key-
encryption algorithm, as specified in RFC 3394 [AESWRAP, SH], is used
to encrypt the content-encryption key with a pairwise key-encryption
key that is generated using ephemeral-static ECDH. In Suite B,
Security Level 1, AES-128 Key Wrap MUST be used as the key-encryption
algorithm. In Suite B, Security Level 2, AES-256 Key Wrap MUST be
used as the key-encryption algorithm.

Within the CMS enveloped-data content type, wrapped content-
encryption keys are located in the EnvelopedData RecipientInfos
KeyAgreeRecipientInfo RecipientEncryptedKeys encryptedKey field, and
key wrap algorithm identifiers are located in the KeyWrapAlgorithm
parameters within the EnvelopedData RecipientInfos
KeyAgreeRecipientInfo keyEncryptionAlgorithm field.

The algorithm identifiers for AES Key Wrap are specified in RFC 3394
[SH], and the ones needed for Suite B are repeated here:

id-aes128-wrap OBJECT IDENTIFIER ::= { joint-iso-itu-t(2)
country(16) us(840) organization(1) gov(101) csor(3)
nistAlgorithm(4) aes(1) 5 }

id-aes256-wrap OBJECT IDENTIFIER ::= { joint-iso-itu-t(2)
country(16) us(840) organization(1) gov(101) csor(3)
nistAlgorithm(4) aes(1) 45 }

4.3. Key Derivation Functions

CMS offers support for deriving symmetric key-encryption keys from
passwords; however, password-based key management is not used in
Suite B. Rather, KDFs based on SHA-256 and SHA-384 are used to
derive a pairwise key-encryption key from the shared secret produced
by ephemeral-static ECDH. In Suite B, Security Level 1, the KDF
based on SHA-256 MUST be used. In Suite B, Security Level 2, KDF
based on SHA-384 MUST be used.

As specified in Section 8.2 of RFC 3278 [CMSECC], using ECDH with the
CMS enveloped-data content type, the derivation of key-encryption
keys makes use of the ECC-CMS-SharedInfo type, which is repeated
here:

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

Housley & Solinas Informational [Page 8]

RFC 5008 Suite B in S/MIME September 2007

In Suite B, the fields of ECC-CMS-SharedInfo are used as follows:

keyInfo contains the object identifier of the key-encryption
algorithm that will be used to wrap the content-encryption key and
NULL parameters. In Suite B, Security Level 1, AES-128 Key Wrap
MUST be used, resulting in {id-aes128-wrap, NULL}. In Suite B,
Security Level 2, AES-256 Key Wrap MUST be used, resulting in
{id-aes256-wrap, NULL}.

entityUInfo optionally contains a random value provided by the
message originator. If the ukm is present, then the entityUInfo
MUST be present, and it MUST contain the ukm value. If the ukm is
not present, then the entityUInfo MUST be absent.

suppPubInfo contains the length of the generated key-encryption
key, in bits, represented as a 32-bit unsigned number, as
described in RFC 2631 [CMSDH]. In Suite B, Security Level 1, a
128-bit AES key MUST be used, resulting in 0x00000080. In Suite
B, Security Level 2, a 256-bit AES key MUST be used, resulting in
0x00000100.

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

The KDF specified in [SEC1] provides an algorithm for generating an
essentially arbitrary amount of keying material from the shared
secret produced by ephemeral-static ECDH, which is called Z for the
remainder of this discussion. The KDF can be summarized as:

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

To generate a key-encryption key, one or more KM blocks are
generated, incrementing Counter appropriately, until enough material
has been generated. The KM blocks are concatenated left to right:

KEK = KM ( counter=1 ) || KM ( counter=2 ) ...

The elements of the KDF are used as follows:

Hash is the one-way hash function, and it is either SHA-256 or
SHA-384 [SHA2]. In Suite B, Security Level 1, the SHA-256 MUST be
used. In Suite B, Security Level 2, SHA-384 MUST be used.

Housley & Solinas Informational [Page 9]

RFC 5008 Suite B in S/MIME September 2007

Z is the shared secret value generated by ephemeral-static ECDH.
Leading zero bits MUST be preserved. In Suite B, Security Level
1, Z MUST be exactly 256 bits. In Suite B, Security Level 2, Z
MUST be exactly 384 bits.

Counter is a 32-bit unsigned number, represented in network byte
order. Its initial value MUST be 0x00000001 for any key
derivation operation. In Suite B, Security Level 1 and Security
Level 2, exactly one iteration is needed; the Counter is not
incremented.

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

To generate a key-encryption key, one KM block is generated, with a
Counter value of 0x00000001:

KEK = KM ( 1 ) = Hash ( Z || Counter=1 || ECC-CMS-SharedInfo )

In Suite B, Security Level 1, the key-encryption key MUST be the most
significant 128 bits of the SHA-256 output value. In Suite B,
Security Level 2, the key-encryption key MUST be the most significant
256 bits of the SHA-384 output value.

Note that the only source of secret entropy in this computation is Z.
The effective key space of the key-encryption key is limited by the
size of Z, in addition to any security level considerations imposed
by the elliptic curve that is used. However, if entityUInfo is
different for each message, a different key-encryption key will be
generated for each message.

5. AES CBC Content Encryption

This section specifies the conventions employed by implementations
that support content encryption using AES [AES] in Cipher Block
Chaining (CBC) mode [MODES]. The conventions in RFC 3565 [CMSAES]
are followed. In Suite B, Security Level 1, the AES-128 in CBC mode
MUST be used for content encryption. In Suite B, Security Level 2,
AES-256 in CBC mode MUST be used.

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

The AES CBC content-encryption algorithm is described in [AES] and
[MODES]. The algorithm identifier for AES-128 in CBC mode is:

Housley & Solinas Informational [Page 10]

RFC 5008 Suite B in S/MIME September 2007

id-aes128-CBC OBJECT IDENTIFIER ::= { joint-iso-itu-t(2)
country(16) us(840) organization(1) gov(101) csor(3)
nistAlgorithm(4) aes(1) 2 }

The algorithm identifier for AES-256 in CBC mode is:

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

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

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

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

6. Security Considerations

This document specifies the conventions for using the NSA's Suite B
algorithms in S/MIME. All of the algorithms have been specified in
previous documents, although a few new algorithm identifiers have
been assigned.

Two levels of security may be achieved using this specification.
Users must consider their risk environment to determine which level
is appropriate for their own use.

For signed and encrypted messages, Suite B provides a consistent
level of security for confidentiality and integrity of the message
content.

The security considerations in RFC 3852 [CMS] discuss the CMS as a
method for digitally signing data and encrypting data.

The security considerations in RFC 3370 [CMSALG] discuss
cryptographic algorithm implementation concerns in the context of the
CMS.

The security considerations in RFC 3278 [CMSECC] discuss the use of
elliptic curve cryptography (ECC) in the CMS.

The security considerations in RFC 3565 [CMSAES] discuss the use of
AES in the CMS.

Housley & Solinas Informational [Page 11]

RFC 5008 Suite B in S/MIME September 2007

7. References

7.1. Normative References

[AES] National Institute of Standards and Technology, "Advanced
Encryption Standard (AES)", FIPS PUB 197, November 2001.

[AESWRAP] National Institute of Standards and Technology, "AES Key
Wrap Specification", 17 November 2001. [See
http://csrc.nist.gov/encryption/kms/key-wrap.pdf]

[DSS] National Institute of Standards and Technology, "Digital
Signature Standard (DSS)", FIPS PUB 186-2, January 2000.

[ECDSA] American National Standards Institute, "Public Key
Cryptography For The Financial Services Industry: The
Elliptic Curve Digital Signature Algorithm (ECDSA)", ANSI
X9.62-1998, 1999.

[CMS] Housley, R., "Cryptographic Message Syntax (CMS)", RFC
3852, July 2004.

[CMSAES] Schaad, J., "Use of the Advanced Encryption Standard
(AES) Encryption Algorithm in Cryptographic Message
Syntax (CMS)", RFC 3565, July 2003.

[CMSALG] Housley, R., "Cryptographic Message Syntax (CMS)
Algorithms", RFC 3370, August 2002.

[CMSDH] Rescorla, E., "Diffie-Hellman Key Agreement Method", RFC
2631, June 1999.

[CMSECC] Blake-Wilson, S., Brown, D., and P. Lambert, "Use of
Elliptic Curve Cryptography (ECC) Algorithms in
Cryptographic Message Syntax (CMS)", RFC 3278, April
2002.

[IEEE1363] Institute of Electrical and Electronics Engineers,
"Standard Specifications for Public Key Cryptography",
IEEE Std 1363, 2000.

[MODES] National Institute of Standards and Technology, "DES
Modes of Operation", FIPS Pub 81, 2 December 1980.

[MSG] Ramsdell, B., "Secure/Multipurpose Internet Mail
Extensions (S/MIME) Version 3.1 Message Specification",
RFC 3851, July 2004.

Housley & Solinas Informational [Page 12]

RFC 5008 Suite B in S/MIME September 2007

[PKIX1] Housley, R., Polk, W., Ford, W., and D. Solo, "Internet
X.509 Public Key Infrastructure Certificate and
Certificate Revocation List (CRL) Profile", RFC 3280,
April 2002.

[PKIX1ALG] Bassham, L., Polk, W., and R. Housley, "Algorithms and
Identifiers for the Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation
List (CRL) Profile", RFC 3279, April 2002.

[SEC1] Standards for Efficient Cryptography Group, "Elliptic
Curve Cryptography", 2000. [See http://www.secg.org/
collateral/sec1.pdf.]

[SH] Schaad, J., and R. Housley, "Advanced Encryption Standard
(AES) Key Wrap Algorithm", RFC 3394, September 2002.

[SHA2] National Institute of Standards and Technology, "Secure
Hash Standard", FIPS 180-2, 1 August 2002.

[STDWORDS] S. Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.

[X.208-88] CCITT. Recommendation X.208: Specification of Abstract
Syntax Notation One (ASN.1). 1988.

[X.209-88] CCITT. Recommendation X.209: Specification of Basic
Encoding Rules for Abstract Syntax Notation One (ASN.1).
1988.

[X.509-88] CCITT. Recommendation X.509: The Directory -
Authentication Framework. 1988.

7.2. Informative References

[EH] Eastlake 3rd, D. and T. Hansen, "US Secure Hash
Algorithms (SHA and HMAC-SHA)", RFC 4634, July 2006.

[RANDOM] Eastlake, D., 3rd, Schiller, J., and S. Crocker,
"Randomness Requirements for Security", BCP 106, RFC
4086, June 2005.

[SuiteB] National Security Agency, "Fact Sheet NSA Suite B
Cryptography", July 2005. [See http://www.nsa.gov/ia/
industry/crypto_Suite_b.cfm?MenuID=10.2.7)

Housley & Solinas Informational [Page 13]

RFC 5008 Suite B in S/MIME September 2007

Authors' Addresses

Russell Housley
Vigil Security, LLC
918 Spring Knoll Drive
Herndon, VA 20170
USA

EMail: [email protected]

Jerome A. Solinas
National Information Assurance Laboratory
National Security Agency
9800 Savage Road
Fort George G. Meade, MD 20755
USA

EMail: [email protected]

Housley & Solinas Informational [Page 14]

RFC 5008 Suite B in S/MIME September 2007

Full Copyright Statement

Copyright (C) The IETF Trust (2007).

This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.

This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Intellectual Property

The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.

Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.

The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
[email protected].

Housley & Solinas Informational [Page 15]