6TiSCH G. Piro
INTERNET-DRAFT (Politecnico di Bari)
Intended Status: Informational G. Boggia
Expires: June 13, 2015 (Politecnico di Bari)
L. A. Grieco
(Politecnico di Bari)
December 10, 2014
Layer-2 security aspects for the IEEE 802.15.4e MAC
draft-piro-6tisch-security-issues-03
Abstract
The aim of this Internet Draft is to define standard compliant
procedures for configuring layer-2 security services in IEEE
802.15.4e-based Low-power and Lossy Networks. In particular, it
provides a review of security aspects presented in both IEEE
802.15.4-2011 and IEEE 802.15.4e-2012 specifications, the
classification of secure network configurations and layer-2 keys, the
description of a set of consecutive steps required to establish a
layer-2 secure link, and a lightweight Key Management Protocol
designed for negotiating a layer-2 one-hop link key. As the final
goal, the document would describe how security MAC attributes can by
initialized and updated in order to offer layer-2 security services
in real networks.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
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Task Force (IETF), its areas, and its working groups. Note that
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http://www.ietf.org/shadow.html
Copyright and License Notice
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Table of Contents
1 Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
3 Security in IEEE 802.15.4-2011 (and IEEE 802.15.4e-2012) . . . 4
5 Definition of layer-2 keys . . . . . . . . . . . . . . . . . . 7
4 Security Configurations . . . . . . . . . . . . . . . . . . . . 8
6 Establishing a secured layer-2 link . . . . . . . . . . . . . . 10
6.1 Setting-up phase . . . . . . . . . . . . . . . . . . . . . 12
6.2 Bootstrap phase . . . . . . . . . . . . . . . . . . . . . . 13
6.2.1 Bootstrap phase for the PAN coordinator . . . . . . . . 13
6.2.2 Bootstrap phase for a "joining node" . . . . . . . . . 16
6.3 Join Phase . . . . . . . . . . . . . . . . . . . . . . . . 19
6.4 Key Negotiation Phase . . . . . . . . . . . . . . . . . . . 19
6.4.1 New Header Information Elements . . . . . . . . . . . . 20
6.4.2 KMP description . . . . . . . . . . . . . . . . . . . . 20
6.4.2 Calculation of the "per-peer L2 key" . . . . . . . . . . 22
7 Security Considerations . . . . . . . . . . . . . . . . . . . . 24
8 IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 24
9 References . . . . . . . . . . . . . . . . . . . . . . . . . . 24
9.1 Normative References . . . . . . . . . . . . . . . . . . . 24
9.2 Informative References . . . . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 26
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1 Acronyms
In addition to the acronyms defined in [I-D.ietf-6tisch-terminology],
the following acronyms are used in this document:
ECDH Elliptic Curve Diffie Hellman
KMP Key Management Protocol
2 Introduction
The IEEE 802.15.4 standard [IEEE802154] is widely recognized as one
of the most successful enabling technologies for short-range low-rate
wireless communications. It covers all the details related to the
Medium Access Control (MAC) and physical layers of the protocol stack
and supports the possibility to protect MAC packets by means of
symmetric-key cryptography techniques with several security options.
However, the IEEE 802.15.4 standard does not explain how handling the
initialization of a secure IEEE 802.15.4 domain, the generation and
the exchange of keys, and the management of joining operations in a
secure 802.15.4 network already configured in the past, thus
delegating the upper layers to orchestrate, enable, configure, and
negotiate security services. The IEEE 802.15.4e [IEEE802154e]
standard introduces some amendments to the IEEE 802.15.4 standard.
Among its key features there is the Time-slotted Channel Hopping
(TSCH), i.e., a novel MAC protocol, which better supports multi-hop
communications in emerging industrial applications. In addition, it
provides very few upgrades to security-related aspects.
Since the IEEE 802.15.4e amendment focuses only on link-layer
aspects, the 6TiSCH WG was created to define open standards in
support of the adoption of IPv6 over the TSCH mode of the
IEEE802.15.4e standard, thus covering all facets related to the
management of network communications in complex (and eventually
distributed) Low-Power and Lossy Networks (LLNs) [I-D.ietf-6tisch-
tsch] [I-D.wang-6tisch-6top].
Security aspects represent an important issue that needs to be
considered in a 6TiSCH network. TSCH defines mechanisms to encrypt
and authenticate MAC frames but it does not define how this keying
material is generated [IEEE802154]. For this reason, the 6TiSCH WG
needs to define (i) security requirements and related architecture,
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(ii) join processes, (iii) the keying material and authentication
mechanism needed by a new mote to join an existing network; (iv) a
mechanism to allow for the secure transfer of application data
between neighbor motes; and (v) define a mechanism to allow for the
secure transfer of signaling data between motes and 6TiSCH.
The description of the security architecture and related
architectural elements are being investigated in [I-D.draft-
richardson-6tisch-security-architecture] and [I-D.draft-struik-
6tisch-security-architecture-elements], respectively.
This Internet Draft focuses on layer-2 security aspects and describes
standard compliant procedures for configuring layer-2 security
services in IEEE 802.15.4e-based Low-power and Lossy Networks. In
particular, main features covered by this document are:
- a review of security aspects presented in both IEEE 802.15.4 and
IEEE 802.15.4e specifications, with particular attention to the
set of parameters that need to be set for enabling security
services at the MAC layer;
- the definition of types and properties of layer-2 keys;
- the classification of possible secure network configurations,
which include Fully Secure, Unsecure, Partial Secure, and Hybrid
Secure networks;
- the description of a set of consecutive steps (i.e., Setting-up,
Bootstrap, Join, and Key Negotiation phases) that are required to
establish a layer-2 secure link among a couple of nodes;
- the design of a lightweight Key Management Protocol useful for
negotiating a per-peer layer-2 key.
3 Security in IEEE 802.15.4-2011 (and IEEE 802.15.4e-2012)
This section summarizes security features defined within IEEE 802.15.4
and IEEE 802.15.4e specifications [IEEE802154] [IEEE802154e].
The standard defines eight security levels to protect MAC frames, as
summarized in Fig. 1 and imposes the adoption of the CCM* algorithm to
perform encryption and description procedures (which requires a key of
128 bit).
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+----------+-------------+-----------+----------------+
| Security | Security | Data | Data |
| level | attribute | Integrity | Confidentiality|
+----------+-------------+-----------+----------------+
| 0 | None | No | No |
+----------+-------------+-----------+----------------+
| 1 | MIC-32 | Yes | No |
+----------+-------------+-----------+----------------+
| 2 | MIC-64 | Yes | No |
+----------+-------------+-----------+----------------+
| 3 | MIC-128 | Yes | No |
+----------+-------------+-----------+----------------+
| 4 | ENC | No | Yes |
+----------+-------------+-----------+----------------+
| 5 | ENC-MIC-32 | Yes | Yes |
+----------+-------------+-----------+----------------+
| 6 | ENC-MIC-64 | Yes | Yes |
+----------+-------------+-----------+----------------+
| 7 | ENC-MIC-128 | Yes | Yes |
+----------+-------------+-----------+----------------+
Figure 1. Security levels available for a IEEE 802.15.4 network.
At the MAC layer, encryption and decryption operations are implemented
within the "outgoing frame security" and the "incoming frame security"
procedures, respectively. They use a number of security attributes,
summarized in what follows:
- macKeyTable: it is composed by a set of KeyDescriptor elements.
A specific KeyDescriptor element is created for each key, composed
by (see Tab. 61 of the IEEE 802.15.4 standard for more details
[IEEE802154]):
- The KeyIdLookupList, which is a list of
KeyIdLookupDescriptor entries. A KeyIdLookupDescriptor is
composed by a set of parameters (see Tab. 65 of the IEEE
802.15.4 standard for more details [IEEE802154]), i.e.,
KeyIdMode, KeySource, KeyIndex, DeviceAddMode, DevicePANId,
and DeviceAddress, that are used to identify the key within
the macKeyTable.
- The DeviceDescriptorHandleList, which contains pointers to
DeviceDescriptor elements stored within the macDeviceTable.
It is used to identify which devices may use the key.
- The KeyUsageList, which is a list of KeyUsageDescriptor
elements. A KeyUsageDescriptor is composed by the FrameType
and the CommandFrameIdentifies fields that indicate the
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frame type with which the considered key may be used (see
Tab. 62 of the IEEE 802.15.4 standard for more details
[IEEE802154]).
- The Key.
- macDeviceTable: it is composed by a set of DeviceDescriptor
elements, providing some information about remote devices which
the node can establish secure communication with. A dedicated
DeviceDescriptor element is associated to each remote device. It
is composed by a number of fields, i.e., PANId, ShortAddress,
ExtAddress, FrameCounter, and Extemp, which collect information
related to a specific remote device (see Tab. 64 of the IEEE
802.15.4 standard for more details [IEEE802154]).
- macSecurityLevelTable: it is made by a set of
SecurityLevelDescriptor elements, which store details about the
security level required for each MAC frame type and subtype.
Fields belonging to the SecurityLevelDescriptor data structure
are: FrameType, ComamndFrameIdentifier, SecurityMinimum,
DeviceOverrideSecurityMinimum, and AllowedSecurityLevels (see Tab.
63 of the IEEE 802.15.4 standard for more details [IEEE802154]).
- macFrameCounter: it is an integer value storing the outgoing
frame counter for the considered device. Its length depends from
the configured macFrameCounterMode (in TSCH-enabled networks it
represents the ASN [IEEE802154e]).
- macAutoRequestSecurityLevel: it is an integer value providing
the security level used for automatic data requests.
- macAutoRequestKeyIdMode: it is an integer value indicating the
key identifier mode used for automatic data requests. It is not
valid if the macAutoRequestSecurityLevel attribute is set to 0x00.
- macAutoRequestKeySource: it represents a short or extended IEEE
802.15.4 MAC address, indicating the originator of the key used
for automatic data requests. This attribute is not valid if the
macAutoRequestKeyIdMode element is not valid or set to 0x00.
- macAutoRequestKeyIndex: it is an integer value storing the index
of the key used for automatic data requests. It is not valid if
the macAutoRequestKeyIdMode attribute is not valid or set to
0x00.
- macDefaultKeySource: it is the extended IEEE 802.15.4 MAC
address of the originator of the default key used for key
identifier mode 0x01.
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- macPANCoordExtendedAddress: it represents the extended address
of the PAN coordinator.
- macPANCoordShortAddress: it represents the short address
assigned to the PAN coordinator.
-macFrameCounterMode: it is an integer value describing the size
of the frame counter (i.e., 0x04 corresponds to a frame size of 4
octets; 0x04 corresponds to a frame size of 5 octets).
During the outgoing security procedure, the high layer uses the
KeyIdMode parameter to select a specific key in the macKeyTable to be
used for protecting the MAC frame.
The KeyIdMode is set to 00, 01, 10, and 11 in the case the key can be
implicitly derived by both sender and the receiver and it is not
specified in the message, the key is explicitly determined by the
KeyIndex parameter stored into the MAC header and the
macDefaultKeySource, the key can be derived by considering KeyIndex and
KeySource fields stored into the MAC header (with KeySource representing
the short address of the device that has generated the key), and the key
can be derived by considering KeyIndex and KeySource fields stored into
the MAC header (with KeySource representing the IEEE extended address of
the device that has generated the key), respectively.
Both IEEE 802.15.4 and IEEE 802.15.4e standards do not provide any
guideline to create (and or negotiate) keys, as well as to configure the
aforementioned security MAC attributes. They just delegate upper layers
to orchestrate such aspects.
5 Definition of layer-2 keys
In line with [I-D.draft-richardson-6tisch-security-architecture], a
"production network" may use two different layer-2 keys, that are
"production network key" and "per-peer L2 key".
The "production network key" is a secret shared by all the authorized
nodes. It can be obtained only if the node is able to correctly complete
the join procedure, which offers authorization and authentication
services.
The "per-peer L2 key" is, instead, negotiated only between a couple of
nodes through a KMP strategy.
In addition, a new layer-2 key, namely "master L2 key", is defined. It
represents an initial secret, which is shared among all the motes and
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configured by the manufacturer or by the network administrator before
the network deployment. Note that a mote can be subjected to any kind of
tamper attacks. Without any further shrewdness, an attacker that may
physically access to the mote could extract the "master L2 key", thus
compromising the security of the whole 6TiSCH network. Hence, it is very
important to ensure the protection to that tampering attacks by using
specific software-based and/or hardware-based mechanisms
[Walters07][Becher2006].
Each layer-2 key is used to protect a specific set of messages. In
particular, the "master L2 key" is used for protecting enhanced beacon
messages and data frames carrying messages exchanged during the join
procedure; the "production network key" is used for protecting broadcast
messages and MAC frames exchanged during the Key Negotiation Phase; the
"per-peer L2 key" is used for encrypting and authenticating messages
exchanged between two nodes at the MAC layer.
"master L2 key" and "production network key" should be identified within
the network by setting KeyIdMode to 0x01 (for both of keys) and the
KeyIndex to 1 and 2, respectively. Differently, the "per-peer L2 key"
should be explicitly identified within the network. Hence, its KeyIdMode
should be set to 0x03 and KeySource and KeyIndex parameters should be
set according to the couple of nodes that negotiated the key (more
details can be found in Sec. 6).
As it will better described in the following sections, the master L2
key" is stored within the device during the Setting-Up Phase and
configured as one of security MAC attribute at the end of the Bootstrap
Phase. The "production network key" is obtained and configured as one of
security MAC attribute during the Join Phase. Finally, the "per-peer L2
key" is negotiated and configured at the MAC layer during the Key
Negotiation Phase.
4 Security Configurations
Based on the status and the configuration of security services, a
"production network" may fall within one of the following security
configurations:
- Fully Secured network: all the devices forming the network are
configured to fully support security services and they have
already obtained (or negotiated) all the keys defined in the
previous section. It represents the most secured configuration:
all packets are encrypted and authenticated by using specific
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keys, which depend from the message they carry. Nodes that do not
support security capabilities (or that are not in posses of all
the information to joining the network, such as key materials and
encryption and decryption algorithms) are not allowed to join the
network.
- Unsecured network: security services are not supported. Even if
in possession of security capabilities, any pair of nodes is not
allowed to establish a secured communication. Differently for the
Fully Secured scheme, this is the lowest security level. Since the
data encryption, the message integrity, and the peer
authentication are not implemented, all the MAC frames are
exchanged in clear. Hence, the setup and the maintaining of the
network are described by the standard and no further upgrades are
required.
- Partial Secured network: only the integrity of message is
supported.
- Hybrid Secured network: a network falls in this configuration
when there still are a group of devices that have not yet
authenticated by the network (because they have not yet correctly
completed the join procedure).
The standard imposes to specify, for each kind of MAC packet, minimum
security levels that should be guaranteed. These restrictions must be
detailed for each remote device. To this end, SecurityMinimum,
DeviceOverrideSecurityMinimum, and AllowedSecurityLevels parameters are
stored into the DeviceDescriptor element (see Sec. 3) to define the
minimum security level (i.e., one of those reported in Fig.1), the
possibility to override the minimum security level (i.e.,
DeviceOverrideSecurityMinimum is just a boolean flag), and the list of
allowed security levels in the case the minimum one could be overridden,
respectively.
Focusing the attention on "production network" that is not in a hybrid
(i.e., dynamic) configuration, these parameters must be set as reported
in Fig. 2.
+----------------------------------------------------+
| Attribute | Secured Network Configurations |
| |Unsecured | Fully | Partial |
+----------------+-----------+-----------+-----------+
| SecurityMinimum|0 | from 5 | from 1 |
| | | to 7 | to 4 |
+----------------+-----------+-----------+-----------+
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| DeviceOverride-| FALSE | FALSE | FALSE |
| SecurityMinimum| | | |
+----------------+-----------+-----------+-----------+
| AllowedSecuri- | 0 | from 5 | from 1 |
| tyLevelsvels | | to 7 | to 4 |
+----------------+-----------+-----------+-----------+
Figure 2. Setting of security attributes of the DeviceDescriptor element
in each defined secure network configuration.
The Unsecured network configuration does not support any security
features. Hence, both minimum and allowable security levels are set to 0
for all the MAC frames and the possibility to override such constraints
is disabled for all devices.
If the Fully Secured configuration is enabled, the minimum security
level must be chosen in the range [5,7], thus allowing the possibility
to support the encryption and the authentication of messages. The
manufacturer must set the default value to 7; it can be updated by the
network administrator. The minimum security level must not be overridden
by any devices and, as a consequence, the field AllowedSecurityLevels
should contain only one value, equal to the minimum security level.
If the Partial Secured configuration is enabled, the minimum security
level must be chosen in the range [1,4], thus allowing the possibility
to support the authentication of messages. The manufacturer must set the
default value to 4; it can be updated by the network administrator. The
minimum security level must not be overridden by any devices and, as a
consequence, the field AllowedSecurityLevels should contain only one
value, equal to the minimum security level.
6 Establishing a secured layer-2 link
A layer-2 secure link can be established through the execution of four
consecutive phases: Setting-up, Bootstrapping, Join, and Key Negotiation
(see Fig. 3).
The Setting-up Phase is used to store into the device all the secrets
required to initialize a secured domain. The Bootstrap Phase, whose
implementation is different for both PAN coordinator and the "join
node", is used for initializing security MAC attributes. The Join Phase
is handled by upper layers for offering authorization and authentication
services and allows the device to receive at the end the NetworkKey.
Finally, the Key Negotiation Phase handles the Key Management Protocol
(KMP) and it is used to negotiate a layer-2 key between a couple of
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nodes that are directly connected at the MAC layer.
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+-----------------------+
| | Installation of
| Setting-up Phase | --> initial secretes
| | in each device
+-----------------------+
|
V
+-----------------------+
| | Initialization of
| Bootstrap Phase | --> security MAC attributes
| |
+-----------------------+
|
V
+-----------------------+
| | Implementation of the
| Join Phase | --> join procedure
| |
+-----------------------+
|
V
+-----------------------+
| | Negotiation of the
| Key Negotiation Phase | --> "per-peer L2 key"
| | between a couple of nodes
+-----------------------+
Figure 3. Summary of the proposed framework.
6.1 Setting-up phase
The setting-up phase is used to properly configure the device that will
join to a "production network". It consists in storing, within the
device, parameters and initial secrets, which will be used by secure
algorithms and procedure to setup the secure domain. They include the
"master L2 key", (ii) the GlobalSecurityLevelsTable, (iii) the private
key of the node, (iv) the public key of the node stored within a
certificate, and (iv) the certificate of the certification authority.
This operation may be performed by the manufacturer or by the network
administrator.
Note that the GlobalSecurityLevelsTable, that has been reported in Fig.
4, is used to store the minimum security level and the list of allowed
security levels that must be adopted for each kind of MAC frame and for
each security configuration defined in Sec. 5. Both the minimum security
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level and the list of allowed security levels must be chosen by the
manufacturer or by the network administrator, according to restrictions
reported in Fig. 2.
+-------------+------------+-----------------------------+
| Attribute | Frame Type |Secured Configurations |
| | |Unsecured| Fully | Partial |
+-------------+------------+---------+---------+---------+
| Security | Beacon | | | |
| Minimum | | | | |
+-------------+------------+---------+---------+---------+
| Security | Data | | | |
| Minimum | | | | |
+-------------+------------+---------+---------+---------+
| Security | Command MAC| | | |
| Minimum | | | | |
+-------------+------------+---------+---------+---------+
| Security | ACK | | | |
| Minimum | | | | |
+-------------+------------+---------+---------+---------+
| AllowedSe- | Beacon | | | |
| curityLevels| | | | |
+-------------+------------+---------+---------+---------+
| AllowedSe- | Data | | | |
| curityLevels| | | | |
+-------------+------------+---------+---------+---------+
| AllowedSe- | Command MAC| | | |
| curityLevels| | | | |
+-------------+------------+---------+---------+---------+
| AllowedSe- | ACK | | | |
| curityLevels| | | | |
+-------------+------------+---------+---------+---------+
Figure 4. Structure of the GlobalSecurityLevelsTable.
6.2 Bootstrap phase
6.2.1 Bootstrap phase for the PAN coordinator
As soon a node becomes the PAN coordinator, it should configure initial
security MAC attributes, including those related to the "master L2 key".
To this end, specific primitives of the 6top adaptation layer are used
[I-D.wang-6tisch-6top].
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The following operations are executed:
a) A CONFIGURE.security command is generated by the 6top layer and
sent to the MAC entity to initialize security attributes. The set
of parameters handled by this command are set as in the sequel:
a.1) enable = true;
a.2) macAutoRequestSecurityLevel = security level expected
for the beacon message and stored within the
GlobalSecurityLevelsTable;
a.3) macAutoRequestKeyIdMode = 0x03;
a.4) macAutoRequestKeySource = MAC address of the device;
a.5) macAutoRequestKeyIndex = 1;
a.6) macDefaultKeySource = MAC address of the device;
b) CONFIGURE.security.macSecurityLevelTable command is generated
by the 6top layer and sent to the MAC entity to initialize
macSecurityLevelTable. Parameters stored into this command are
taken from the GlobalSecurityLevelsTable.
c) A new KeyIdLookupList data structure is created. A
KeyIdLookupDescriptor is generated and stored into the
KeyIdLookupList data structure. The KeyIdMode, the KeyIndex, and
the key variables of this KeyIdLookupDescriptor are set to 0x01
and 1, respectively. Instead, KeySource, DeviceAddrMode,
DevicePANId, and DeviceAddress are not set due to the selected
KeyIdMode (see Tab. 65 of the IEEE 802.15.4 standard for more
details [IEEE802154]).
d) A KeyUsageList data structure is created. One
KeyUsageDescriptor for each kind of broadcast messages is create
and stored into the KeyUsageList data structure.
e) An empty DeviceDescriptorHandleList is created. No data are
stored within this list because the PAN coordinator does not yet
know the list of devices that may use this key.
f) Then, the 6top layer deliver the "master L2 key", the
KeyIdLookupList, the KeyUsageList, and the
DeviceDescriptorHandleList to the MAC layer by using the
CONFIGURE.security.macKeyTable primitive. Triggered by the
CONFIGURE.security.macKeyTable command, the MAC layer will create
a KeyDescriptor associated to the "master L2 key", where storing
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all the parameters received by the 6top layer, and store it within
the macKeyTable.
The Bootstrap phase for the PAN coordinator has been summarized in Fig.
5.
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6top MAC
| |
| CONFIGURE.security |
|-----------------------------------------> |
| initialize
| security MAC
| attributes
| |
| CONFIGURE.security.macSecurityLevelTable |
|-----------------------------------------> |
| initialize
| minimum security
| levels
| |
| CONFIGURE.security.macKeyTable |
|-----------------------------------------> |
| create the KeyDescriptor
| associated to the
| "master L2 key"
| |
V V
Figure 5. Bootstrap Phase for the PAN coordinator.
6.2.2 Bootstrap phase for a "joining node"
Before executing the Join Phase, a "joining node" should initialize
security MAC attributes, including information related to the "master L2
key", through specific 6top adaptation layer primitives. To this end,
after the reception of the enhanced beacon message, the following
operations are executed:
a) From the received beacon message, the mote extracts the PAN_ID,
the MAC address of the node that sent the beacon, and the
FrameCounter.
b) A CONFIGURE.security primitive is generated by the 6top layer
and sent to the MAC entity to initialize security attributes. The
set of parameters handled by this primitive are set as in the
sequel:
b.1) enable = true;
b.2) macAutoRequestSecurityLevel = security level expected
for the beacon message and stored within the
GlobalSecurityLevelsTable;
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b.3) macAutoRequestKeyIdMode = 0x03;
b.4) macAutoRequestKeySource = MAC address of the device;
b.5) macAutoRequestKeyIndex = 1;
b.6) macDefaultKeySource = MAC address of the device;
c) CONFIGURE.security.macSecurityLevelTable primitive is generated
by the 6top layer and sent to the MAC entity to initialize
macSecurityLevelTable. Parameters stored into this command are
taken from the GlobalSecurityLevelsTable.
d) A new KeyIdLookupList data structure is created. A
KeyIdLookupDescriptor is generated and stored into the
KeyIdLookupList data structure. The KeyIdMode and the KeyIndex
variables of this KeyIdLookupDescriptor are set to 0x00, the MAC
address of the node that sent the beacon message and 1,
respectively. Instead, KeySource, DeviceAddrMode, DevicePANId, and
DeviceAddress are not set due to the selected KeyIdMode (see Tab.
65 of the IEEE 802.15.4 standard for more details [IEEE802154]).
e) A KeyUsageList data structure is created. One
KeyUsageDescriptor for each kind of messages is create and stored
into the KeyUsageList data structure.
f) A new DeviceDescriptor element, associated to the node that
sent the enhanced beacon message is created and stored into the
macDeviceTable. It is built considering these specifications (see
Tab. 64 of the IEEE 802.15.4 standard [IEEE802154] for more
details):
f.1) The PANId variable is associated to the PAN_ID value
extracted from the Beacon message.
f.2) The ShortAddress is set to the MAC address of node that
sent the beacon message whenever the short addressing mode
is used. This parameter is set to 0xfffe if only the
extended addressing mode is used. If its value is unknown,
the ShortAddress parameter is set to 0xfff.
f.3) The ExtAddress is set to the IEEE MAC address of node
that sent the beacon message.
f.4) The FrameCounter parameter is set to the FrameCounter
value extracted from the enhanced beacon message (it
represents the ASN in the case the network works in TSCH-
mode [IEEE802154e]).
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f.5) The Exempt boolean flag is set to the allowed value of
the DeviceOverriddeSecurityMinimum variable described in
Fig. 2.
g) The DeviceDescriptorHandleList is created and populated with
the DeviceDescriptor created at the previous step.
h) A KeyUsageList data structure is created and stored within the
KeyDescriptor element. One KeyUsageDescriptor for each broadcast
message is create and stored into the KeyUsageList data
structure.
i) The 6top layer deliver the "master L2 key", the
KeyIdLookupList, the KeyUsageList, and the
DeviceDescriptorHandleList to the MAC layer by using the
CONFIGURE.security.macKeyTable primitive. Triggered by the
CONFIGURE.security.macKeyTable primitive, the MAC layer will
create a KeyDescriptor associated to the "master L2 key", in which
storing all the parameters received by the 6top layer, and will
store it within the macKeyTable.
The Bootstrap Phase for a "joining node" has been summarized in Fig. 6.
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"joining node" "joining node" device that sends
6top MAC the beacon message
| | |
| | Enhanced Beacon |
| | <-----------------|
| | |
| extract PAN_ID |
| and macShortAddress |
| | |
| CONFIGURE.security | |
|----------------------------> | |
| initialize |
| security MAC |
| attributes |
| | |
| CONFIGURE.security. | |
| macSecurityLevelTable | |
|----------------------------> | |
| initialize |
| minimum security |
| levels |
| | |
| CONFIGURE.security. | |
| macKeyTable | |
|----------------------------> | |
| create the KeyDescriptor |
| associated to the |
| "master L2 key" |
| | |
V V V
Figure 6. Bootstrap Phase for the "joining node".
6.3 Join Phase
During the Join Phase, the join procedure is implemented by upper layers
for offering authorization and authentication features. This aspect is
carefully investigated in both [I-D.draft-richardson-6tisch-security-
architecture] and [I-D.draft-struik-6tisch-security-architecture-
elements], thus being out of scope of this Internet Draft.
At the end of the join procedure, the "joining node" obtains the
"production network key" and updates security MAC attributes as
described for the "master L2 key", with the only difference that the
KeyIndex is set to 2.
6.4 Key Negotiation Phase
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Since resource-constrained devices are unable to perform complex
algorithms and protocols [Altolini2013][Riaz2009], a simple key
agreement protocol, based on both ECDH algorithm and Station-To-Station
protocol [StsProtocol], is adopted during the execution of the key
negotiation phase.
As described in Sec. 6.1, it is supposed that each node stores the
certificate of the authority and the couple of its public and private
key (generated through the adoption of elliptic curves). Obviously, the
public key is stored within a certificate, signed by the authority.
In this section is described the KMP implemented between a couple of
nodes, i.e., node A and node B, which want to negotiate a on-hop layer-2
key. Let PBK_A, PVK_A, PBK_B, and PVK_B be A's public key, A's private
key, B's public key, and B's private key, respectively. Moreover, to
handle the Key Negotiation phase, a number of high-level commands have
been defined. In line with IEEE 802.15.4e specifications, they are
mapped into specific Header Information Elements, each one identified by
an unique element ID.
6.4.1 New Header Information Elements
The set of Header Information Elements introduced for handling the KMP
are:
- Crypto Information Element (element ID set to 0x18). It is used
to deliver the certificate storing the ECDH public key. Since the
certificate length is generally higher than the IEEE 802.15.4e MAC
payload, it is necessary to fragment the certificate, thus sending
it through multiple consecutive MAC frames. To this end, the first
byte of the introduced Information Element is used to indicate the
fragment ID to which the current packet refers to. The second byte
of the first fragment stores the RAND parameter, which is a random
value adopted to finalize the mutual authentication.
- Authentication Information Element (element ID set to 0x19),
which stored the AuthField used to execute the mutual
authentication.
6.4.2 KMP description
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The KMP consists of six consecutive steps:
- Step 1: node A sends to node B its certificate through a number
of consecutive MAC frames containing the Crypto Information
Element. Let RAND_A be the random number stored within the second
byte of the Crypto Information Element belonging to the first MAC
frame. All of these packets are protected by using the "production
network key" received at the end of the Join Phase.
- Step 2: node B verifies the authenticity of the received
certificate. In affirmative case, it sends to node A its
certificate through a number of consecutive MAC frames containing
the Crypto Information Element. Let RAND_B be the random number
stored within the second byte of the Crypto Information Element
belonging to the first MAC frame. All of these packets are
protected by using the NetworkKey received at the end of the Join
Phase.
- Step 3: node A and node B computes the PreLinkKey, P_k, by using
the ECDH algorithm.
- Step 4: node A computes the authentication parameter as expected
for the Station-To-Station protocol:
AuthField_A = E(P_k, sign),
where
sign = S(PVK_A, H_128 {P_k || RAND_B || RAND_A})
Then, it creates a Authentication Information Element containing
the aforecomputed AuthField and sends it to node B. Note that
H_128 {.}, E(.), and S(.) operators refer to a 128-bit hash
function, the encryption, and the digital sign algorithm,
respectively.
- Step 5: node B computes the authentication parameter through the
128-bit hash function, as in the sequel:
AuthField_B = E(P_k, sign),
where
sign = S(PVK_B, H_128 {P_k || RAND_A || RAND_B}).
Then, it creates a Authentication Information Element containing
the aforecomputed AuthField and sends it to node A.
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- Step 6: nodes A and B verifies the authenticity of received
AuthField parameters (according to the Station-To-Station)
protocol and computes the "per-peer L2 key".
6.4.2 Calculation of the "per-peer L2 key"
The standard imposes to use the CCM* algorithm and a 128-bit key to
protect MAC frames. At the same time, the CCM* algorithm assumes that
each key must be used for a specific number of block ciphers
[IEEE802154].
For each i-th group of block ciphers, the "per-peer L2 key", L_k, is
computed as in the following:
L_k = H_128 (i | PAN_ID | P_k).
Node A and node B compute the "per-peer L2 key" and updates mac security
attributes accordingly. To this end, the following steps are executed:
a) If i=1, a new DeviceDescriptor element, associated to the
remote mote with which it has negotiated the "per-peer L2 key", is
created. It is composed of:
a.1) the PANId, which is set to the PAN_ID value.
a.2) The ShortAddress, which is set to the MAC address of
the remote node whenever the short addressing mode is used.
This parameter is set to 0xfffe if only the extended
addressing mode is used. In the case its value is unknown,
this parameter is set to 0xfff.
a.3) The ExtAddress, which is set to the IEEE MAC address of
the remote node.
a.4) The FrameCounter, which is set to the FrameCounter
value extracted from the latest packet received by the
remote node.
a.5) The Exempt boolean flag, which is set to the allowed
value of the DeviceOverriddeSecurityMinimum variable
described in Fig. 2.
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b) A new KeyIdLookupList data structure is created. A
KeyIdLookupDescriptor is generated and stored into the
KeyIdLookupList data structure. The KeyIdMode, the KeySource, and
the KeyIndex variables of this KeyIdLookupDescriptor are set to
0x03, the MAC address of the remote mote, and 1, respectively.
DeviceAddrMode, DevicePANId, and DeviceAddress are not set because
of the selected KeyIdMode (see Tab. 65 of the IEEE 802.15.4
standard for more details [IEEE802154]).
c) A KeyUsageList data structure is created and stored within the
KeyDescriptor element. One KeyUsageDescriptor associated to data
MAC frames is created and stored into the KeyUsageList data
structure.
d) A DeviceDescriptorHandleList is created and populated with the
pointer to the DeviceDescriptor created at the point a).
e) The 6top layer delivers the "per-peer L2 key", the
KeyIdLookupList, the KeyUsageList, and the
DeviceDescriptorHandleList to the MAC layer by using the
CONFIGURE.security.macKeyTable command. Triggered by the
CONFIGURE.security.macKeyTable command, the MAC layer will create
a KeyDescriptor associated to the "per-peer L2 key", L_k, in which
storing all the parameters received by the 6top layer, and will
store it within the macKeyTable.
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7 Security Considerations
There are no security considerations for this document.
8 IANA Considerations
There is no IANA action required for this document.
9 References
9.1 Normative 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.
802.15.4e, Part. 15.4: Low-Rate Wireless Personal Area
Networks (LR-WPANs) Amendament 1: MAC sublayer", April
2012.
[I-D.ietf-6tisch-tsch] Watteyne, T., MR. Palattella, and LA. Grieco,
"Using IEEE802.15.4e TSCH in an LLN context: Overview,
Problem Statement and Goals", Internet-Draft draft-ietf-
6tisch-tsch-03, October 2014.
[I-D.wang-6tisch-6top] Wang, Q., Vilajosana, X. and T. Watteyne,
"6TiSCH Operation Sublayer (6top)", Internet-Draft draft-
wang-6tisch-6top-sublayer-01, July 2014.
[I-D.ietf-6tisch-terminology] Palattella, MR., Ed., Thubert, P.,
Watteyne, T., and Q. Wang, "Terminology in IPv6 over Time
Slotted Channel Hopping". Internet Draft draft-ietf-
6tisch-terminology-02, July 2014.
[I-D.draft-richardson-6tisch-security-architecture] M. Richardson,
"security architecture for 6top: requirements and
structure". Internet Draft draft-richardson-6tisch-
security-architecture-02 April 2014.
[I-D.draft-struik-6tisch-security-architecture-elements] R. Struik,
Y. Ohba, and S. Das, "6TiSCH Security Architectural
Elements, Desired Protocol Properties, and Framework".
Internet Draft draft-struik-6tisch-security-architecture-
elements-01 October 2014.
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[DH] W. Diffie and M. Hellman, "New directions in cryptography," IEEE
Trans. Inf. Theor. 22, 6 Sep., 2006.
[StsProtocol] Whitfield Diffie, Paul C. van Oorschot and Michael J,
"Wiener, Authentication and authenticated key exchange",
Designs, Codes, and Cryptography, 1987.
9.2 Informative References
[ZIGBEEIP] ZigBee Public Document 15-002r00, "ZigBee IP
Specification", 2013.
[Camtepe2005] Seyit A. Camtepe and Bulent Yener, "Key Distribution
Mechanisms for Wireless Sensor Networks: a Survey",
Technical Report 2005.
[Walters07] John Paul Walters, Zhengqiang Liang, Weisong Shi, and
Vipin Chaudhary, "Wireless sensor network security: A
survey," in book chapter of Security", Proc. of
Distributed, Grid, and Pervasive Computing, CRC Press,
2007.
[Wang2006] Yong Wang, Garhan Attebury, and Byrav Ramamurthy, "A
survey of security issues in wireless sensor networks",
IEEE Communications Surveys & Tutorials, 2006
[Cayirci2007] Security in Wireless Ad Hoc and Sensor Networks. John
Wiley & Sons, 2007.
[RFC5191] Forsberg, D., Ohba, Y., Patil, B., Tschofenig, H., and A.
Yegin, "Protocol for Carrying Authentication for Network
Access (PANA)", RFC 5191, May 2008.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, January 2012.
[HIPDEX] Moskowitz, R., "HIP Diet EXchange (DEX)", draft-
moskowitzhip-rg-dex-06 (work in progress), May 2012.
[PalattellaSurvey] Maria Rita Palattella, Nicola Accettura, Xavier
Vilajosana, Thomas Watteyne, Luigi Alfredo Grieco, Gennaro
Boggia, and Mischa Dohler," Standardized Protocol Stack
For The Internet Of (Important) Things", IEEE
Communications Surveys & Tutorials, December, 2012
[StallingsSecurityBooks] William Stallings: Cryptography and network
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security - principles and practice. Prentice Hall 2010.
[Becher2006] Alexander Becher, Zinaida Benenson, and Maximillian
Dornseif, "Tampering with motes: real-world physical
attacks on wireless sensor networks", In Proc. of conf.
on Security in Pervasive Computing (SPC), Berlin, 2006
[TELOSB] "Crossbow Technology, TelosB Datasheet." [Online].
Available: http://www.willow.co.uk/TelosB_Datasheet.pdf
[Riaz2009] Riaz, R.; Ki-Hyung Kim; Ahmed, H.F., "Security analysis
survey and framework design for IP connected LoWPANs,"
Autonomous Decentralized Systems, 2009. ISADS '09.
International Symposium on , vol., no., pp.1,6, 23-25
March 2009
[Altolini2013] Altolini, D.; Lakkundi, V.; Bui, N.; Tapparello, C.;
Rossi, M., "Low power link layer security for IoT:
Implementation and performance analysis," Wireless
Communications and Mobile Computing Conference (IWCMC),
2013 9th International , vol., no., pp.919,925, 1-5 July
2013
[Watteyne2012] Thomas Watteyne, Xavier Vilajosana, Branko Kerkez,
Fabien Chraim, Kevin Weekly, Qin Wang, Steven D. Glaser,
Kris Pister: OpenWSN: a standards-based low-power wireless
development environment. Trans. Emerging
Telecommunications Technologies 23(5): 480-493 (2012)
Authors' Addresses
Giuseppe Piro
DEI, Dep. of Electrical and Information Engineering
Politecnico di Bari
Via Orabona 4, 70125, Bari, ITALY
Phone: +39 0805963301
Email: giuseppe.piro@poliba.it
Gennaro Boggia
DEI, Dep. of Electrical and Information Engineering
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Politecnico di Bari
Via Orabona 4, 70125, Bari, ITALY
Phone: +39 0805963913
Email: gennaro.boggia@poliba.it
Luigi Alfredo Grieco
DEI, Dep. of Electrical and Information Engineering
Politecnico di Bari
Via Orabona 4, 70125, Bari, ITALY
Phone: +39 0805963911
Email: alfredo.grieco@poliba.it
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