Network Working Group Y. Ohba, Ed. Internet-Draft Toshiba Intended status: Experimental June 28, 2015 Expires: December 30, 2015 An Extension to Mesh Link Establishment (MLE) for Host Identity Protocol Diet Exchange (HIP DEX) draft-ohba-mle-hip-dex-01 Abstract This document defines an extension of MLE (Mesh Link Establishment) protocol to encapsulate HIP DEX key exchange protocol messages. 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 December 30, 2015. Copyright Notice Copyright (c) 2015 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. Ohba Expires December 30, 2015 [Page 1] Internet-Draft HIP DEX over MLE June 2015 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Requirement Language . . . . . . . . . . . . . . . . . . 3 1.2. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . 3 1.3. Convention . . . . . . . . . . . . . . . . . . . . . . . 3 2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Key Establishment Phase . . . . . . . . . . . . . . . . . . . 4 4. Key Update Phase . . . . . . . . . . . . . . . . . . . . . . 6 5. Key Materials . . . . . . . . . . . . . . . . . . . . . . . . 7 5.1. Pair-wise Key . . . . . . . . . . . . . . . . . . . . . . 7 5.2. Group Keys . . . . . . . . . . . . . . . . . . . . . . . 7 6. MLE Security . . . . . . . . . . . . . . . . . . . . . . . . 8 7. Certificate Revocation . . . . . . . . . . . . . . . . . . . 8 8. Security Considerations . . . . . . . . . . . . . . . . . . . 8 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 9.1. MLE TLV Types . . . . . . . . . . . . . . . . . . . . . . 9 9.2. HIP Parameter . . . . . . . . . . . . . . . . . . . . . . 9 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 10 11.1. Normative References . . . . . . . . . . . . . . . . . . 10 11.2. External Informative References . . . . . . . . . . . . 10 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 10 1. Introduction HIP DEX (Host Identity Protocol Diet EXchange) [I-D.moskowitz-hip-dex] is a light-weight key exchange protocol designed for constrained devices. HIP DEX builds on the HIP Base EXchange (HIP BEX) [I-D.ietf-hip-rfc5201-bis] and inherits the transport-agnostic property of HIP BEX. MLE (Mesh Link Establishment) [I-D.kelsey-intarea-mesh-link-establishment] is defined for establishing and configuring secure links in IEEE 802.15.4 mesh networks. MLE assumes that shared keys to secure link-layer frames and MLE messages exchanged between a pair of nodes are pre-configured between the nodes. Therefore, a key exchange protocol is required in order to dynamically configure the required shared keys. While such a key exchange protocol can be run outside MLE, sequentially running a key exchange protocol and MLE as separate protocols requires more message roundtrips. For example, running a HIP DEX 4-way handshake followed by an MLE 3-way handshake requires 3.5 message roundtrips. In this document, an extension to the MLE protocol for encapsulating HIP DEX messages is defined in order to realize optimized key exchange and link establishment for IEEE 802.15.4 mesh networks. Ohba Expires December 30, 2015 [Page 2] Internet-Draft HIP DEX over MLE June 2015 1.1. Requirement Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. 1.2. Acronyms DEX-I1, DEX-R1, DEX-I2, DEX-R2: HIP DEX I1, R1, I2, R2 messages ECDH: Elliptic Curve Diffie-Hellman EI: HIP DEX Key Establishment Initiator ER: HIP DEX Key Establishment Responder LLFC: Link-Layer Frame Counter MIC: MLE Message Integrity Code MLFC: MLE Frame Counter UI: HIP DEX Key Update Initiator UR: HIP DEX Key Update Responder 1.3. Convention In the figures of this document, MLE messages marked with '*' are those secured by the MLE protocol. In the key material formats in this document, '|' denotes concatenation operator. 2. Overview HIP DEX over MLE consists of two phases, i.e., Key Establishment Phase and Key Update Phase. In Key Establishment Phase, a HIP DEX 4-way handshake using I1, R1, I2 and R2 messages is conducted to establish a secure channel between an EI and an ER based on an ECDH shared secret and exchange session key materials over the secure channel. In Key Update Phase, HIP DEX Update messages encrypting session key materials are exchanged between a UI and each UR using an MLE Update Request and Update exchange, followed by a multicast MLE Update message for triggering each UR to simultaneously activate new key Ohba Expires December 30, 2015 [Page 3] Internet-Draft HIP DEX over MLE June 2015 materials and reset the associated link-layer frame counters. The UI and UR roles for a pair of nodes may be determined independently of the EI and ER roles that have been taken by the nodes. All MLE messages used for the extension defined in this document SHOULD NOT be protected by link-layer so that a key exchange can be done regardless of the security state of the link-layer. A node that implements this specification MUST allow sending and receiving MLE messages not secured by the link-layer. Secured 802.15.4 MAC frames and MLE messages that use keys established via HIP DEX MUST use a 5-octet Frame Counter so that the Frame Counter does not reach its maximum value throughout the lifetime of a node. An MLE Frame Counter is always carried in the Frame Counter field in the Aux Header of any secured MLE frame. Other than the rules described in this document, the rules defined in [I-D.kelsey-intarea-mesh-link-establishment] are preserved. 3. Key Establishment Phase A message exchange diagram for Key Establishment Phase is shown in Figure 1. (EI) (ER) --> Advertisement [HIP{DEX-I1}, Link Quality] <-- Advertisement [HIP{DEX-R1}, Link Quality] --> Link Request [HIP{DEX-I2}, Source Address, Mode, Timeout, Challenge]* <-- Link Accept and Request [HIP{DEX-R2}, LLFC, MLFC, Source Address, Mode, Timeout, Response, Challenge]* --> Link Accept [LLFC, MLFC, Response]* Figure 1: Key Establishment Phase An EI sends an MLE Advertisement message containing a HIP TLV and a Link Quality TLV to an ER. The HIP TLV carries a DEX-I1 packet. How an EI discovers an ER is outside the scope of this document. The ER receives the MLE Advertisement message containing a DEX-I1 packet from the EI and sends an MLE Advertisement message containing a HIP TLV and a Link Quality TLV to the EI. The HIP TLV carries a DEX-R1 packet. The DEX-R1 packet MUST contain mandatory R1 Ohba Expires December 30, 2015 [Page 4] Internet-Draft HIP DEX over MLE June 2015 parameters specified in [I-D.moskowitz-hip-dex]. The DEX-R1 packet MAY contain optional R1 parameters specified in [I-D.moskowitz-hip-dex] and a CERT parameter defined in [RFC6253]. The EI receives the MLE Advertisement message from the ER and sends a secured MLE Link Request message containing HIP, Source Address, Mode, Timeout and Challenge TLVs to the ER. The HIP TLV carries a DEX-I2 packet. The DEX-I2 packet MUST contain mandatory I2 parameters specified in [I-D.moskowitz-hip-dex] including an ENCRYPTED_KEY parameter wrapping a session key material of the EI. The DEX-I2 packet MUST also contain an ENCRYPTED parameter wrapping group key materials of the EI. The DEX-I2 packet MAY contain optional I2 parameters specified in [I-D.moskowitz-hip-dex] and a CERT parameter defined in [RFC6253]. The MLE Link Request message is protected by the EI's group MLE key (see section Section 5.2) derived from the EI's group key materials. The ER receives the MLE Link Request message from the EI and extracts the EI's session key material wrapped in the ENCRYPTED_KEY parameter and the EI's group key materials wrapped in the ENCRYPTED parameter. Then the ER sends a secured MLE Link Accept and Request message containing HIP, LLFC, MLFC, Source Address, Mode Timeout, Response and Challenge TLVs to the EI. The HIP TLV carries a DEX-R2 packet. The DEX-R2 packet MUST contain R2 parameters specified in [I-D.moskowitz-hip-dex] including an ENCRYPTED_KEY parameter wrapping a session key material of the ER. The DEX-R2 packet MUST also contain an ENCRYPTED parameter wrapping group key materials of the ER. The DEX-R2 packet MAY contain optional R2 parameters specified in [I-D.moskowitz-hip-dex]. Note that the MIC field of the MLE Link Request message is verified after the ER successfully extracts the EI's group key materials. The EI receives the MLE Link Accept and Request message from the ER and extracts the ER's session key material wrapped in the ENCRYPTED_KEY parameter and the ER's group key materials wrapped in the ENCRYPTED parameter. Then the EI sends a secured MLE Link Accept message containing LLFC TLV, MLFC and Response TLVs to the ER. If a pair-wise key is used by the link-layer, the EI also creates a Pair- wise Key SA with the session key generated by the pair of session key materials of the EI and ER as specified in [I-D.moskowitz-hip-dex]. Note that the MIC field of the MLE Link Accept and Request message is verified after the EI successfully extracts the ER's group key materials. The ER receives the MLE Link Accept message from the EI. If a pair- wise key is used by the link-layer, the EI creates a Pair-wise Key SA with the session key generated by the pair of session key materials of the EI and ER as specified in [I-D.moskowitz-hip-dex]. Ohba Expires December 30, 2015 [Page 5] Internet-Draft HIP DEX over MLE June 2015 4. Key Update Phase In Key Update Phase, group key materials are updated. Since the 5-octet Frame Counter space is large enough considering the maximum bandwidth of 250Kbps in 802.15.4 [IEEE802154] to make an assumption that a Frame Counter does not reach its maximum value throughout the lifetime of a node, a mechanism for updating a pair- wise key is not defined in this document. Both link-layer Frame Counters and MLE Frame Counters are not reset in the Key Update Phase. Updating a group key may happen when a node that shares the group key is revoked. A message exchange diagram for group key update is shown in Figure 2. (UI) (UR1)..(URn) // Update 1st peer ----> Update Request [HIP{DEX-UPDATE}, MLFC, Source Address]* <---- Update [HIP{DEX-UPDATE}, MLFC, Source Address]* .. .. // Update n-th peer -----------> Update Request [HIP{DEX-UPDATE}, MLFC, Source Address]* <----------- Update [HIP{DEX-UPDATE}, MLFC, Source Address]* // Key switch notification (multicast) ----> .. --> Update [LLFC, MLFC]* Figure 2: Group Key Update First, a UI performs the following exchange for each UR: o The UI sends an MLE Update Request message containing HIP, MLFC, Source Address and MIC TLVs to a UR. The HIP TLV carries a DEX- UPDATE packet containing SEC, MAC and ENCRYPTED parameters. The ENCRYPTED parameter wraps new group key materials of the UI. o The UR receives the MLE Update Request message from the UI, extracts UI's new group key materials from the ENCRYPTED parameter, activates the UI's new group key materials for incoming frames, and sends an MLE Update message containing HIP, MLFC and Source Address TLVs, where the HIP TLV carries a DEX-UPDATE packet containing ACK and MAC parameters. Note that the MIC field of the MLE Update message is verified after the UR successfully extracts the UI's new group key materials. Ohba Expires December 30, 2015 [Page 6] Internet-Draft HIP DEX over MLE June 2015 Once MLE Update Request and Update exchange is completed for all URs, the UI activates the UI's new group key materials for outgoing frames by multicasting an MLE Update message containing LLFC and MLFC TLVs. The MLE Update message is protected by the UI's group MLE key (see section Section 5.2) derived from the UI's new group key materials. When a UR receives the multicast MLE Update message, If the received message is valid, the UR deactivates the UI's old group key materials for incoming frames. A UR that did not receive the multicast MLE Update message may deactivate the UI's old group key materials for incoming frames when it receives a valid MAC frame protected by the link-layer key derived from the UI's new group key materials. 5. Key Materials 5.1. Pair-wise Key The first 16 octets of the session key corresponding to the HIP DEX Pair-wise SA [I-D.moskowitz-hip-dex] is used as the pairwise link- layer key used for securing unicast link-layer frames with Key Identifier Mode 0x00. An encrypted session key material is contained in an ENCRYPTED_KEY parameter of HIP when the session key is distributed during Key Establishment Phase. 5.2. Group Keys Group key materials are created by a node and distributed to peer nodes. The group key materials consist of a 1-octet key identifier (KeyId) and a 16-octet group master key (GroupMasterKey), and encoded as follows: Group Key Materials = KeyId | GroupMasterKey A 16-octet group link-layer key (GroupL2Key), and a 16-octet group MLE key (GroupMLEKey) are derived from GroupMasterKey as follows: GroupL2Key = The first 16-octet of HMAC_SHA256(GroupMasterKey, KeyId). GroupMLEKey = The last 16-octet of HMAC_SHA256(GroupMasterKey, KeyId). Ohba Expires December 30, 2015 [Page 7] Internet-Draft HIP DEX over MLE June 2015 A GroupL2Key is used for securing link-layer frames with Key Identifier Mode 0x03 sent by the node that created the group key material. GroupL2Key MUST be used for securing broadcast link-layer frames and MAY also be used for securing unicast link-layer frames. A GroupMLEKey MUST be used for securing MLE messages with Key Identifier Mode 0x03 sent by the node that created the group key material. The group key materials are contained in an GROUP_KEY_MATERIALS parameter of HIP, where the GROUP_KEY_MATERIALS parameter MUST be encrypted in an ENCRYPTED parameter of HIP. 6. MLE Security As described in [I-D.kelsey-intarea-mesh-link-establishment], MLE security reuses that of IEEE 802.15.4, i.e., AES-CCM* [IEEE802154]. Since some of the MLE messages (i.e., MLE Link Accept and Request and MLE Accept messages carrying DEX-I2 and DEX-R2 packets, respectively, and unicast MLE Update Request and Update messages carrying a DEX- UPDATE packet) require to be sent unencrypted and only authentication is needed, MIC-64 (Security Level 2) or MIC-128 (Security Level 3) is used to secure MLE messages. MIC-64 is the default security level for securing MLE messages used in this document. GroupMLEKey (see section Section 5.2) with Key Identifier Mode 0x03 and a 5-octet Frame Counter MUST be used for any secured MLE message. 7. Certificate Revocation Any MLE message used in this document MAY also contain a CRL (Certificate Revocation List) TLV in which CertificateList defined in [RFC5280] is encoded in the Value field. A node that receives a valid MLE message containing a CRL TLV revokes certificates specified in the TLV and deletes all pair-wise and group keys associated with the revoked certificates. A node MUST reject a CERT parameter for a revoked certificate in Key Establishment Phase. How a CRL is propagated in a network depends on the network topology and is out of the scope of this document. 8. Security Considerations The MLE extension defined in this document uses HIP DEX for key management of computation or memory constrained sensor/actuator devices, and thus it inherits all security considerations made for HIP DEX [I-D.moskowitz-hip-dex]. Ohba Expires December 30, 2015 [Page 8] Internet-Draft HIP DEX over MLE June 2015 In order to mitigate security weakness caused by lack of Perfect Forward Secrecy (PFS) in HIP DEX, it is RECOMMENDED to use this MLE extension in conjunction with an additional mechanism to update public/private key pairs and renew HIP DEX SAs using new public/ private key pairs whenever necessary. In both Key Establishment Phase and Key Update Phase, MLE messages are secured using a group key instead of a pairwise key in order to optimize message roundtrips since a group key establishment requires only a half roundtrip. As a result, a Denial of Service (DoS) attack from an insider sharing the group key is possible over MLE TLVs. Due to integration of HIP DEX into MLE, secured MLE messages are authenticated but not encrypted because decryption can be done only after establishing a key. As a result, Source Address, Mode, Timeout, Challenge, Response LLFC and MLFC TLVs are sent in clear, and the cleartext information may be used by attackers for the DoS attack described above. Note that authentication of the MLE message carrying a DEX-I2, DEX-R2 or DEX-UPDATE packet is possible by validating MIC of the MLE message after extracting the authentication key (i.e., GroupMLEKey) from the HIP DEX packet. 9. IANA Considerations 9.1. MLE TLV Types The following MLE TLV types are to be assigned by IANA based on the policy described in [I-D.kelsey-intarea-mesh-link-establishment]: o HIP-DEX (Value: 9, Length: Variable, Meaning: HIP DEX packet, Reference: this document). o CRL (Value: 10, Length: Variable, Meaning: Certificate Revocation List, Reference: this document). 9.2. HIP Parameter The following HIP Parameter is assigned based on the policy described in [I-D.ietf-hip-rfc5201-bis]: o GROUP_KEY_MATERIALS, (Value: 65530, Length: 33, Meaning: Group key materials for MLE and link-layer, Reference: this document). 10. Acknowledgments The author would like to acknowledge the helpful comments of Randy Turner and Robert Cragie. Ohba Expires December 30, 2015 [Page 9] Internet-Draft HIP DEX over MLE June 2015 11. References 11.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., Housley, R., and W. Polk, "Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile", RFC 5280, May 2008. [RFC6253] Heer, T. and S. Varjonen, "Host Identity Protocol Certificates", RFC 6253, May 2011. [I-D.moskowitz-hip-dex] Moskowitz, R. and R. Hummen, "HIP Diet EXchange (DEX)", draft-moskowitz-hip-dex-03 (work in progress), June 2015. [I-D.ietf-hip-rfc5201-bis] Moskowitz, R., Heer, T., Jokela, P., and T. Henderson, "Host Identity Protocol Version 2 (HIPv2)", draft-ietf- hip-rfc5201-bis-20 (work in progress), October 2014. [I-D.kelsey-intarea-mesh-link-establishment] Kelsey, R., "Mesh Link Establishment", draft-kelsey- intarea-mesh-link-establishment-06 (work in progress), May 2014. 11.2. External Informative References [IEEE802154] IEEE standard for Information Technology, "IEEE std. 802.15.4, Part. 15.4: Wireless Medium Access Control (MAC) and Physical Layer (PHY) Specifications for Low-Rate Wireless Personal Area Networks", June 2011. Author's Address Yoshihiro Ohba (editor) Toshiba Corporate Research and Development Center 1 Komukai-Toshiba-cho Saiwai-ku, Kawasaki, Kanagawa 212-8582 Japan Phone: +81 44 549 2127 Email: yoshihiro.ohba@toshiba.co.jp Ohba Expires December 30, 2015 [Page 10]