Internet DRAFT - draft-ietf-6lo-mle-hip-dex
draft-ietf-6lo-mle-hip-dex
Network Working Group Y. Ohba, Ed.
Internet-Draft Toshiba
Intended status: Experimental April 19, 2016
Expires: October 21, 2016
An Extension to Mesh Link Establishment (MLE) for Host Identity Protocol
Diet Exchange (HIP DEX)
draft-ietf-6lo-mle-hip-dex-01
Abstract
HIP DEX (Host Identity Protocol Diet EXchange) is a light-weight key
exchange protocol designed for constrained devices. MLE (Mesh Link
Establishment) is defined for establishing and configuring secure
links in IEEE 802.15.4 mesh networks. This document defines an
extension of MLE protocol to encapsulate HIP DEX key exchange
protocol messages.
Status of This Memo
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This Internet-Draft will expire on October 21, 2016.
Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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 . . . . . . . . . . . . . . . . . . . 9
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
9.1. MLE TLV Types . . . . . . . . . . . . . . . . . . . . . . 10
9.2. HIP Parameter . . . . . . . . . . . . . . . . . . . . . . 10
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
11.1. Normative References . . . . . . . . . . . . . . . . . . 10
11.2. External Informative References . . . . . . . . . . . . 11
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
HIP DEX (Host Identity Protocol Diet EXchange) [I-D.ietf-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.ietf-6lo-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.
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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.
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.
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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
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. An MLE
Frame Counter is always carried in the Frame Counter field in the Aux
Header of any secured MLE frame. Note that [IEEE802154e] supports
5-octet MAC Frame Counter for CSMA (Carrier Sense Multiple Access)
and uses 5-octet ASN (Absolute Slot Number) as MAC Frame Counter for
TSCH (Time-Slotted Channel Hopping) MAC.
Other than the rules described in this document, the rules defined in
[I-D.ietf-6lo-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
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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
parameters specified in [I-D.ietf-hip-dex]. The DEX-R1 packet MAY
contain optional R1 parameters specified in [I-D.ietf-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.ietf-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.ietf-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.ietf-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.ietf-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.ietf-hip-dex]. Note
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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.ietf-hip-dex].
In addition to initial key establishment time, Key Establishment
Phase is also entered when an outgoing MAC Frame Counter or an
outgoing MLE Frame Counter of a node reaches its maximum value (this
is almost unlikely to happen with 5-octet Frame Counter, though). In
this case, the node MUST first update its HIP-DEX certificate before
re-entering Key Establishment Phase. How a HIP-DEX certificate is
updated is out of the scope of this document.
4. Key Update Phase
In Key Update Phase, group key materials are updated.
A Key Update Phase is invoked when a peer node that shares the group
key is revoked. Both link-layer Frame Counters and MLE Frame
Counters are not reset in the Key Update Phase. A message exchange
diagram for group key update is shown in Figure 2.
(UI) (UR1)..(URn)
// Update 1st peer
----> Update Request [HIP{UPDATE}, MLFC, Source Address]*
<---- Update [HIP{UPDATE}, MLFC, Source Address]*
.. ..
// Update n-th peer
-----------> Update Request [HIP{UPDATE}, MLFC, Source Address]*
<----------- Update [HIP{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 HIP
UPDATE packet containing SEQ, HIP_MAC and ENCRYPTED parameters.
The ENCRYPTED parameter wraps new group key materials of the UI.
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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 HIP UPDATE packet
containing ACK and HIP_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.
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.ietf-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
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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).
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.ietf-6lo-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 complete CRL or a delta
CRL is contained in a CRL TLV. 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.
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When a CRL TLV is carried in a multicast Update message and forwarded
multiple hops, MPL [RFC7731] MAY be used. In this case, the
multicast Update message MUST be secured at the link layer and MUST
NOT be secured by MLE as specified in
[I-D.ietf-6lo-mesh-link-establishment]. Detailed MPL parameters for
the multicast-based CRL distribution are out of the scope of this
document.
In order to reduce the size of a CRL, there are several guidelines.
A delta CRL should be used whenever applicable. Expired certificates
should be excluded from a CRL. A short lived (e.g., one month)
certificate may be used (at the cost of increased frequency of
certificate updates). Hierarchically formed CAs may be used where
each CA is expected to sign only a small number of certificates.
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.ietf-hip-dex].
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.
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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.ietf-6lo-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, Robert Cragie and Subir Das.
11. References
11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[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, DOI 10.17487/RFC5280, May 2008,
<http://www.rfc-editor.org/info/rfc5280>.
[RFC6253] Heer, T. and S. Varjonen, "Host Identity Protocol
Certificates", RFC 6253, DOI 10.17487/RFC6253, May 2011,
<http://www.rfc-editor.org/info/rfc6253>.
[RFC7731] Hui, J. and R. Kelsey, "Multicast Protocol for Low-Power
and Lossy Networks (MPL)", RFC 7731, DOI 10.17487/RFC7731,
February 2016, <http://www.rfc-editor.org/info/rfc7731>.
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[I-D.ietf-hip-dex]
Moskowitz, R. and R. Hummen, "HIP Diet EXchange (DEX)",
draft-ietf-hip-dex-02 (work in progress), March 2016.
[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.ietf-6lo-mesh-link-establishment]
Kelsey, R., "Mesh Link Establishment", draft-ietf-6lo-
mesh-link-establishment-00 (work in progress), December
2015.
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.
[IEEE802154e]
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 - Amendment 1: MAC
sublayer (Amendment to IEEE Std 802.15.4-2011)", April
2012.
Author's Address
Yoshihiro Ohba (editor)
Toshiba Electronics Asia
20 Pasir Panjang Road, #12-25/28, Mapletree Business City
117439
Singapore
Phone: +65 6278 5252
Email: yoshihiro.ohba@toshiba.co.jp
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