Internet DRAFT - draft-hennessy-bsp-suiteb-ciphersuites
draft-hennessy-bsp-suiteb-ciphersuites
Network Working Group K. Burgin
Internet-Draft A. Hennessy
Intended status: Informational National Security Agency
Expires: September 6, 2012 March 5, 2012
Suite B Ciphersuites for the Bundle Security Protocol
draft-hennessy-bsp-suiteb-ciphersuites-00
Abstract
This document proposes eight ciphersuites for the Bundle Security
Protocol (BSP), similar to the four suites specified in RFC 6257.
The eight new ciphersuites provide compatibility with the United
States National Security Agency's Suite B specifications.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on September 6, 2012.
Copyright Notice
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document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
3. Suite B Ciphersuites . . . . . . . . . . . . . . . . . . . . . 3
3.1. Suites BAB-HMAC256 and BAB-HMAC384 . . . . . . . . . . . . 3
3.2. Suites PIB-ECDSA-SHA256 and PIB-ECDSA-SHA384 . . . . . . . 4
3.3. Suites PCB-ECDH-SHA256-AES128 and
PCB-ECDH-SHA384-AES256 . . . . . . . . . . . . . . . . . . 5
3.4. Suites ESB-ECDH-SHA256-AES128 and
ESB-ECDH-SHA384-AES256 . . . . . . . . . . . . . . . . . . 8
4. Security Considerations . . . . . . . . . . . . . . . . . . . 10
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
6. Normative References . . . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
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1. Introduction
This document extends RFC 6257 and specifies eight ciphersuites for
the Bundle Security Protocol. The new suites provide compatibility
with the United States National Security Agency's Suite B
specifications.
2. Requirements Language
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 [RFC2119].
3. Suite B Ciphersuites
This section defines eight new ciphersuites for use with the security
block types BAB, PIB, PCB, and ESB. The PIB ciphersuites are based
on digital signatures using ECDSA. The PCB and ESB ciphersuites use
ECDH for key agreement, AES in Galois/Counter Mode (GCM) for content
encryption, and AES Key Wrap for key encryption. All proposed
ciphersuites use SHA-256 or SHA-384 as the hash algorithm.
The ciphersuites use the mechanisms defined in Cryptographic Message
Syntax (CMS) [RFC5652] for packaging the keys, signatures, etc., for
transport in the appropriate security block. Additionally, the
ciphersuites follow the guidance and requirements of RFC 6318
[RFC6318] which specifies the conventions for using Suite B
algorithms in Secure/Multipurpose Internet Mail Extensions (S/MIME).
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].
3.1. Suites BAB-HMAC256 and BAB-HMAC384
The BAB-HMAC256 ciphersuite has ciphersuite ID value 0x05, and the
BAB-HMAC384 ciphersuite has ciphersuite ID value 0x09.
RFC 3370 [RFC3370] specifies the conventions for using HMAC with CMS
and RFC 5754 [RFC5754] defines the algorithm identifiers for SHA-256
and SHA-384. MAC algorithm identifiers are located in the
AuthenticatedData macAlgorithm field. MAC values are located in the
AuthenticatedData mac field.
BAB-HMAC256 and BAB-HMAC384 use the strict canonicalization algorithm
as described in [RFC6257], Section 3.4.1. Strict canonicalization
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supports digesting a fragment-bundle. It does not permit the
digesting of only a subset of the payload, but only the complete
contents of the payload of the current bundle, which might be a
fragment. The fragment-range item for security-parameters is not
used to indicate a fragment, as this information is digested within
the primary block.
These ciphersuites require the use of two related instances of the
BAB. It involves placing the first BAB instance just after the
primary block. The second (correlated) instance of the BAB MUST be
placed after all other blocks (except possibly other BAB blocks) in
the bundle. Both required BAB instances MUST be included in the
bundle before canonicalization.
The security-result field is the output of the HMAC calculation with
the input being the result of running the entire bundle through the
strict canonicalization algorithm. The security-parameters field is
OPTIONAL, but if used, then the only field that can be present is
key-information.
3.2. Suites PIB-ECDSA-SHA256 and PIB-ECDSA-SHA384
The PIB-ECDSA-SHA256 ciphersuite has ciphersuite ID value 0x06, and
the PIB-ECDSA-SHA-384 ciphersuite has ciphersuite ID value 0x0A.
In PIB-ECDSA-SHA256, ECDSA MUST be used with the SHA-256 message
digest algorithm and the P-256 elliptic curve, as specified in
[RFC6318]. In PIB-ECDSA-SHA384, ECDSA MUST be used with the SHA-384
message digest algorithm and the P-384 elliptic curve, as specified
in [RFC6318]. The P-256 and P-384 elliptic curves are specified in
[DSS].
The SHA-256 and SHA-384 message digest algorithms are defined in FIPS
Pub 180-3 [RFC5754]. The algorithm identifiers for SHA-256 and SHA-
384 are defined in [RFC5754]. RFC 5754 [RFC5754] specifies the
conventions for using SHA-256 and SHA-384 with CMS. Within the CMS
signed-data content type, message digest algorithm identifiers are
located in the SignedData digestAlgorithms field and the SignerInfo
digestAlgorithm field.
RFC 5753 [RFC5753] specifies the conventions for using ECDSA with
CMS. RFC 5480 [RFC5480] defines the signature algorithm identifiers
used in CMS for ECDSA with SHA-256 and ECDSA with SHA-384. Relevant
details are repeated here.
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
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in the SignerInfo signatureAlgorithm field of countersignature
attributes. When either signature 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 5480
[RFC5480].
These ciphersuites use a slightly modified form of the mutable
canonicalization algorithm described in RFC 6257 [RFC6257], Section
3.4.2, with the security-result data field for only the "current"
block being excluded from the canonical form. Additionally, the
security-result length field for the "current" block is excluded from
the mutable canonical form. The resulting canonical form of the
bundle is the input to the signing process. These ciphersuites
require the use of a single instance of the PIB. The data to be
signed is the output of the mutable canonicalization process.
Because the signature field in SignedData SignatureValue is a
security-result field, the entire key-information item MUST be placed
in the block's security-result field, rather than security-
parameters.
If the bundle being signed has been fragmented before signing, then
we have to specify which bytes were signed in case the signed bundle
is subsequently fragmented for a second time. If the bundle is a
fragment, then the ciphersuite-parameters MUST include a fragment-
range field, as described in [RFC6257], Section 2.6, specifying the
offset and length of the signed fragment. If the entire bundle is
signed, then these numbers MUST be omitted.
3.3. Suites PCB-ECDH-SHA256-AES128 and PCB-ECDH-SHA384-AES256
The PCB-ECDH-SHA256-AES128 ciphersuite has ciphersuite ID value 0x07,
and the PCB-ECDH-SHA384-AES256 ciphersuite has ciphersuite ID value
0x0B.
These schemes encrypt PIBs, PCBs, and the payload. Both ciphersuites
use ephemeral-static ECDH, which means that the security source
possesses an ephemeral ECDH key pair and the security destination
possesses a static ECDH key pair.
When a key agreement algorithm is used in CMS, a key-encryption
algorithm is also needed to encrypt the content encryption key (CEK).
These ciphersuites use Advanced Encryption Standard (AES) Key Wrap,
as specified in RFC 3394 [RFC3394] and [AESWRAP], as the key-
encryption algorithm. The key-encryption key used with the AES Key
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Wrap algorithm is obtained from a key derivation function (KDF).
These ciphersuites use a KDF based on SHA-256 and SHA-384.
In PCB-ECDH-SHA256-AES128, ephemeral-static ECDH MUST be used with
the SHA-256 KDF, AES-128 Key Wrap, and the P-256 elliptic curve, as
specified in [RFC6318]. In PCB-ECDH-SHA384-AES256, ephemeral-static
ECDH MUST be used with the SHA-384 KDF, AES-256 Key Wrap, and the
P-384 elliptic curve, as specified in [RFC6318]. The P-256 and P-384
elliptic curves are specified in [DSS].
Section 3.1 of RFC 5753 [RFC5753] specifies the conventions for using
ECDH with CMS. Here the bundle encryption key (BEK), used to encrypt
the BSP payload, is the data to be carried in a CMS enveloped-data
content type. CMS encrypts the BEK with a freshly generated content
encryption key (CEK) and the result is placed in the encryptedContent
field of an EnvelopedData EncryptedContentInfo structure. The CEK is
encrypted with the ECDH-generated pairwise key-encryption key (KEK)
using the AES Key Wrap algorithm. The result is placed in the
EnvelopedData RecipientInfos KeyAgreeRecipientInfo
RecipientEncryptedKey EncryptedKey field.
Algorithm identifiers needed when using ECDH with CMS are provided in
RFC 6318 [RFC6318] section 4. Within the CMS enveloped-data content
type, the key agreement algorithm identifier is placed in the
EnvelopedData RecipientInfos KeyAgreeRecipientInfo
keyEncryptionAlgorithm field. The key wrap algorithm identifier is
placed in the KeyWrapAlgorithm parameters within the EnvelopedData
RecipientInfos KeyAgreeRecipientInfo keyEncryptionAlgorithm field.
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. Section 4.3 of RFC 6318 [RFC6318] specify the conventions for
using the KDF with the shared secret generated with ephemeral-static
ECDH with the CMS.
BSP Payload encryption is done using the AES algorithm in Galois/
Counter Mode (GCM) as described in [RFC5084]. For consistency with
the description in [RFC5084], we refer to the GCM IV as a nonce. The
same key and nonce combination MUST NOT be used more than once. The
nonce has the same format as in RFC 6257 [RFC6257], where a salt
field and iniialization vector field are concatenated to form the
nonce.
The salt field is a four-octet value, usually chosen at random. It
MUST be the same for all PCBs that have the same correlator value.
The salt need not be kept secret.
The initialization vector (IV) is an eight-octet value, usually
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chosen at random. It MUST be different for all PCBs that have the
same correlator value. The value need not be kept secret.
The BEK is a 16-octet (128 bits) value in PCB-ECDH-SHA256-AES128, and
is a 32-octet value (256 bits) in PCB-ECDH-SHA384-AES256. The BEK
SHOULD be chosen randomly and MUST be kept secret.
The Integrity Check Value (ICV) from the AES-GCM content encryption
is a 16-octet value used to verify that the protected data has not
been altered. Normally, the ICV is concatenated with the ciphertext
to produce the output of AES-GCM encryption. However, to avoid
expansion of the payload, the ICV value is placed in the security-
result field of the first PCB. The value need not be kept secret.
These ciphersuites require the use of a single PCB instance to deal
with payload confidentiality, as specified in [RFC6257], Section 4.3.
For payload confidentiality, the first PCB MUST contain security-
parameters and security-result fields. The security-parameters field
includes the salt, IV, and key-information items where the key-
information item contains the encrypted BEK encoded in a CMS
EnvelopedData structure. The security-results-field contains the
ICV.
Subsequent PCBs MUST contain a correlator value to link them to the
first PCB and MUST contain security-parameters and security-result
fields. The security-parameters field contains the IV for the
specific block and the security-result field contains the
encapsulated block. For the payload, only the bytes of the bundle
payload field are affected, being replaced by ciphertext. The salt,
IV, and key values specified in the first PCB are used to encrypt the
payload, and the resultant authentication tag (ICV) is placed in an
ICV item in the security-result field of that first PCB. The other
bytes of the payload block, such as type, flags, and length, are not
modified.
If the bundle being encrypted is a fragment-bundle, we have to
specify which bytes are encrypted in case the bundle is subsequently
fragmented again. If the bundle is a fragment, the ciphersuite-
parameters MUST include a fragment-range field.
For each PIB or PCB to be protected, the entire original block is
encapsulated in a "replacing" PCB. This replacing PCB is placed in
the outgoing bundle in the same position as the original block, PIB
or PCB.
The encryption process uses AES-GCM with the salt and key values from
the first PCB, and an IV unique to this PCB. The process creates
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ciphertext for the entire original block and an authentication tag
for validation at the security-destination. For this encapsulation
process, unlike the processing of the bundle payload, the
authentication tag is appended to the ciphertext for the block, and
the combination is stored into the encapsulated block item in the
security-result.
The replacing block has the same correlator value as the first PCB
with which it is associated. It also contains the block-specific IV
in security-parameters, and the combination of original-block-
ciphertext and authentication tag, stored as an encapsulated block
item in the security-result.
3.4. Suites ESB-ECDH-SHA256-AES128 and ESB-ECDH-SHA384-AES256
The ESB-ECDH-SHA256-AES128 ciphersuite has ciphersuite ID value 0x08,
and the ESB-ECDH-SHA384-AES256 ciphersuite has ciphersuite ID value
0x0C.
These schemes encrypt non-payload-related blocks. They MUST NOT be
used to encrypt PIBs, PCBs, or primary or payload blocks. Both
ciphersuites use ephemeral-static ECDH, which means that the security
source uses an ephemeral ECDH key pair and the security destination
uses a static ECDH key pair.
When a key agreement algorithm is used in CMS, a key-encryption
algorithm is also needed to encrypt the content encryption key (CEK).
These ciphersuites use Advanced Encryption Standard (AES) Key Wrap,
as specified in RFC 3394 [RFC3394] and [AESWRAP], as the key-
encryption algorithm. The key-encryption key used with the AES Key
Wrap algorithm is obtained from a key derivation function (KDF).
These ciphersuites use a KDF based on SHA-256 and SHA-384.
In ESB-ECDH-SHA256-AES128, ephemeral-static ECDH MUST be used with
the SHA-256 KDF, AES-128 Key Wrap, and the P-256 elliptic curve, as
specified in [RFC6318]. In ESB-ECDH-SHA384-AES256, ephemeral-static
ECDH MUST be used with the SHA-384 KDF, AES-256 Key Wrap, and the
P-384 elliptic curve, as specified in [RFC6318]. The P-256 and P-384
elliptic curves are specified in [DSS].
Section 3.1 of RFC 5753 [RFC5753] specifies the conventions for using
ECDH with CMS. Within the CMS enveloped-data content type, key
agreement algorithm identifiers are located in the EnvelopedData
RecipientInfos KeyAgreeRecipientInfo keyEncryptionAlgorithm field.
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.
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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. Sections 7.1.8 and 7.2 of RFC 5753 [RFC5753] specify the
conventions for using the KDF with the shared secret generated with
ephemeral-static ECDH with CMS.
Block encryption is done using the AES algorithm in Galois/Counter
Mode (GCM) as described in [RFC5084]. For consistency with the
description in [RFC5084], we refer to the GCM IV as a nonce. The
same key and nonce combination MUST NOT be used more than once. The
nonce has the same format as in RFC 6257 [RFC6257], where a salt
field and iniialization vector field are concatenated to form the
nonce.
The salt field is a four-octet value, usually chosen at random. It
MUST be the same for all ESBs that have the same correlator value.
The salt need not be kept secret.
The initialization vector (IV) is an eight-octet value, usually
chosen at random. It MUST be different for all ESBs that have the
same correlator value. The value need not be kept secret.
The content encryption key, CEK (also called the bundle encryption
key, BEK) is a 16-octet (128 bits) value in ESB-ECDH-SHA256-AES128,
and is a 32-octet value (256 bits) in ESB-ECDH-SHA384-AES256. The
BEK SHOULD be chosen randomly and MUST be kept secret.
The Integrity Check Value from the AES-GCM encryption of the payload
is a 16-octet value used to verify that the protected data has not
been altered. The value need not be kept secret and is appended to
the ciphertext for the block, and the combination is stored into the
encapsulated block item in the security-result field.
These ciphersuites replace each BP extension block to be protected
with a "replacing" ESB, and each can be individually specified, as
described in [RFC6257], Section 4.4.
For each block to be protected, the entire original block is
encapsulated in a "replacing" ESB. This replacing ESB is placed in
the outgoing bundle in the same position as the original block.
The first ESB MUST contain security-parameters and security-result
fields. The security-parameters field contains the salt, IV, and
key-information. The security result field contains the encapsulated
block.
Subsequent ESBs MUST contain a correlator value to link them to the
first ESB. They MUST contain security-parameters that contain the IV
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for the specific block and security-result field that contains the
encapsulated block.
The encryption process uses AES-GCM with the salt and key values from
the first ESB and an IV unique to this ESB. The process creates
ciphertext for the entire original block, and an authentication tag
for validation at the security-destination. The authentication tag
is appended to the ciphertext for the block and the combination is
stored into the encapsulated block item in the security-result field.
The replacing block has the same correlator value as the first ESB
with which it is associated. It also contains the block-specific IV
in security-parameters, and the combination of original-block-
ciphertext and authentication tag, stored as an encapsulated block
item in the security-result field.
4. Security Considerations
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.
The security considerations in [RFC6257] discuss the Bundle Security
Protocol and apply here as well.
The security considerations in [RFC5652] discuss the CMS as a method
for digitally signing data and encrypting data.
The security considerations in [RFC3370] discuss cryptographic
algorithm implementation concerns in the context of the CMS.
The security considerations in [RFC5753] discuss the use of elliptic
curve cryptography (ECC) in the CMS.
The security considerations in [RFC3565] discuss the use of AES in
the CMS, and the security considerations in [RFC5084] discuss the
Galois/Counter Mode.
5. IANA Considerations
This protocol has fields that have been registered by IANA.
The BSP has a ciphersuite number field and certain ciphersuites are
defined.
The registration policy for this registry is: Specification Required
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The Value range is: Variable Length
IANA is requested to assign the following values for the ciphersuite
number field.
Ciphersuite Numbers Registry:
+-------+--------------------------------------+----------------+
| Value | Description | Reference |
+-------+--------------------------------------+----------------+
| 5 | BAB-HMAC256 | This document |
| 9 | BAB-HMAC384 | This document |
| 6 | PIB-ECDSA-SHA256 | This document |
| A | PIB-ECDSA-SHA384 | This document |
| 7 | PCB-ECDH-SHA256-AES128 | This document |
| B | PCB-ECDH-SHA384-AES256 | This document |
| 8 | ESB-ECDH-SHA256-AES128 | This document |
| C | ESB-ECDH-SHA256-AES128 | This document |
+-------+--------------------------------------+----------------+
Figure 1
6. Normative References
[AESWRAP] National Institute of Standards and Technology, "AES Key
Wrap Specification", November 2001.
[DSS] National Institute of Standards and Technology, "Digital
Signature Standard (DSS)", FIPS PUB 186-3, June 2009.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3370] Housley, R., "Cryptographic Message Syntax (CMS)
Algorithms", RFC 3370, August 2002.
[RFC3394] Schaad, J. and R. Housley, "Advanced Encryption Standard
(AES) Key Wrap Algorithm", RFC 3394, September 2002.
[RFC3565] Schaad, J., "Use of the Advanced Encryption Standard (AES)
Encryption Algorithm in Cryptographic Message Syntax
(CMS)", RFC 3565, July 2003.
[RFC5084] Housley, R., "Using AES-CCM and AES-GCM Authenticated
Encryption in the Cryptographic Message Syntax (CMS)",
RFC 5084, November 2007.
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[RFC5480] Turner, S., Brown, D., Yiu, K., Housley, R., and T. Polk,
"Elliptic Curve Cryptography Subject Public Key
Information", RFC 5480, March 2009.
[RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
RFC 5652, September 2009.
[RFC5753] Turner, S. and D. Brown, "Use of Elliptic Curve
Cryptography (ECC) Algorithms in Cryptographic Message
Syntax (CMS)", RFC 5753, January 2010.
[RFC5754] Turner, S., "Using SHA2 Algorithms with Cryptographic
Message Syntax", RFC 5754, January 2010.
[RFC6257] Symington, S., Farrell, S., Weiss, H., and P. Lovell,
"Bundle Security Protocol Specification", RFC 6257,
May 2011.
[RFC6318] Housley, R. and J. Solinas, "Suite B in Secure/
Multipurpose Internet Mail Extensions (S/MIME)", RFC 6318,
June 2011.
Authors' Addresses
Kelley Burgin
National Security Agency
Email: kwburgi@tycho.ncsc.mil
Angela Hennessy
National Security Agency
Email: amhenne@nsa.gov
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