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. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts 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 Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on September 6, 2012. Copyright Notice Copyright (c) 2012 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 (http://trustee.ietf.org/license-info) 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 Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Burgin & Hennessy Expires September 6, 2012 [Page 1] Internet-Draft Suite B Ciphersuites for BSP March 2012 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 Burgin & Hennessy Expires September 6, 2012 [Page 2] Internet-Draft Suite B Ciphersuites for BSP March 2012 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 Burgin & Hennessy Expires September 6, 2012 [Page 3] Internet-Draft Suite B Ciphersuites for BSP March 2012 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 Burgin & Hennessy Expires September 6, 2012 [Page 4] Internet-Draft Suite B Ciphersuites for BSP March 2012 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 Burgin & Hennessy Expires September 6, 2012 [Page 5] Internet-Draft Suite B Ciphersuites for BSP March 2012 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 Burgin & Hennessy Expires September 6, 2012 [Page 6] Internet-Draft Suite B Ciphersuites for BSP March 2012 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 Burgin & Hennessy Expires September 6, 2012 [Page 7] Internet-Draft Suite B Ciphersuites for BSP March 2012 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. Burgin & Hennessy Expires September 6, 2012 [Page 8] Internet-Draft Suite B Ciphersuites for BSP March 2012 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 Burgin & Hennessy Expires September 6, 2012 [Page 9] Internet-Draft Suite B Ciphersuites for BSP March 2012 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 Burgin & Hennessy Expires September 6, 2012 [Page 10] Internet-Draft Suite B Ciphersuites for BSP March 2012 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. Burgin & Hennessy Expires September 6, 2012 [Page 11] Internet-Draft Suite B Ciphersuites for BSP March 2012 [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 Burgin & Hennessy Expires September 6, 2012 [Page 12]