Minimal Security Framework for 6TiSCH
draft-ietf-6tisch-minimal-security-10
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 9031.
|
|
|---|---|---|---|
| Authors | Mališa Vučinić , Jonathan Simon , Kris Pister , Michael Richardson | ||
| Last updated | 2019-06-12 (Latest revision 2019-04-05) | ||
| Replaces | draft-vucinic-6tisch-minimal-security | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Formats | |||
| Reviews | |||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | WG Consensus: Waiting for Write-Up | |
| Document shepherd | Pascal Thubert | ||
| IESG | IESG state | Became RFC 9031 (Proposed Standard) | |
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | Pascal Thubert <pthubert@cisco.com> |
draft-ietf-6tisch-minimal-security-10
state object. Since the CoAP token is echoed back in the response,
the JP is able to decode the state object and configure the state
needed to forward the response to the pledge. The information that
the JP needs to encode in the state object to operate in a fully
stateless manner with respect to a given pledge is implementation
specific.
It is RECOMMENDED that the JP operates in a stateless manner and
signals the per-pledge state within the CoAP token, for every request
it forwards into the network on behalf of unauthenticated pledges.
When operating in a stateless manner, the security considerations
from [I-D.ietf-core-stateless] apply and the type of the CoAP message
that the JP forwards on behalf of the pledge MUST be non-confirmable
(NON), regardless of the message type received from the pledge. The
use of a non-confirmable message by the JP alleviates the JP from
keeping CoAP message exchange state. The retransmission burden is
then entirely shifted to the pledge. A JP that operates in a
stateless manner still needs to keep congestion control state with
the JRC, see Section 9. Recommended values of CoAP settings for use
during the join process, both by the pledge and the JP, are given in
Section 7.2.
Note that in some networking stack implementations, a fully (per-
pledge) stateless operation of the JP may be challenging from the
implementation's point of view. In those cases, the JP may operate
as a statefull proxy that stores the per-pledge state until the
response is received or timed out, but this comes at a price of a DoS
vector.
7.2. Recommended Settings
This section gives RECOMMENDED values of CoAP settings during the
join process.
+-------------------+-----------------------+-------------------+
| Name | Default Value: Pledge | Default Value: JP |
+-------------------+-----------------------+-------------------+
| ACK_TIMEOUT | 10 seconds | (10 seconds) |
| | | |
| ACK_RANDOM_FACTOR | 1.5 | (1.5) |
| | | |
| MAX_RETRANSMIT | 4 | (4) |
+-------------------+-----------------------+-------------------+
Recommended CoAP settings. Values enclosed in () have no effect when
JP operates in a stateless manner.
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These values may be configured to values specific to the deployment.
The default values have been chosen to accommodate a wide range of
deployments, taking into account dense networks.
The PROBING_RATE value at the JP is controlled by the join rate
parameter, see Section 8.4.2. Following [RFC7252], the average data
rate in sending to the JRC must not exceed PROBING_RATE. For
security reasons, the average data rate SHOULD be measured over a
rather short window, e.g. ACK_TIMEOUT, see Section 9.
7.3. OSCORE
Before the (6LBR) pledge and the JRC start exchanging CoAP messages
protected with OSCORE, they need to derive the OSCORE security
context from the provisioned parameters, as discussed in Section 3.
The OSCORE security context MUST be derived as per Section 3 of
[I-D.ietf-core-object-security].
o the Master Secret MUST be the PSK.
o the Master Salt MUST be the empty byte string.
o the ID Context MUST be set to the pledge identifier.
o the ID of the pledge MUST be set to the empty byte string. This
identifier is used as the OSCORE Sender ID of the pledge in the
security context derivation, since the pledge initially acts as a
CoAP client.
o the ID of the JRC MUST be set to the byte string 0x4a5243 ("JRC"
in ASCII). This identifier is used as the OSCORE Recipient ID of
the pledge in the security context derivation, as the JRC
initially acts as a CoAP server.
o the Algorithm MUST be set to the value from [RFC8152], agreed out-
of-band by the same mechanism used to provision the PSK. The
default is AES-CCM-16-64-128.
o the Key Derivation Function MUST be agreed out-of-band by the same
mechanism used to provision the PSK. Default is HKDF SHA-256
[RFC5869].
Since the pledge's OSCORE Sender ID is the empty byte string, when
constructing the OSCORE option, the pledge sets the k bit in the
OSCORE flag byte, but indicates a 0-length kid. The pledge
transports its pledge identifier within the kid context field of the
OSCORE option. The derivation in [I-D.ietf-core-object-security]
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results in OSCORE keys and a common IV for each side of the
conversation. Nonces are constructed by XOR'ing the common IV with
the current sequence number. For details on nonce and OSCORE option
construction, refer to [I-D.ietf-core-object-security].
Implementations MUST ensure that multiple CoAP requests, including to
different JRCs, are properly incrementing the sequence numbers, so
that the same sequence number is never reused in distinct requests.
The pledge typically sends requests to different JRCs if it is not
provisioned with the network identifier and attempts to join one
network at a time. Failure to comply will break the security
guarantees of the Authenticated Encryption with Associated Data
(AEAD) algorithm because of nonce reuse.
This OSCORE security context is used for initial joining of the
(6LBR) pledge, where the (6LBR) pledge acts as a CoAP client, as well
as for any later parameter updates, where the JRC acts as a CoAP
client and the joined node as a CoAP server, as discussed in
Section 8.2. Note that when the (6LBR) pledge and the JRC change
roles between CoAP client and CoAP server, the same OSCORE security
context as initially derived remains in use and the derived
parameters are unchanged, for example Sender ID when sending and
Recipient ID when receiving (see Section 3.1 of
[I-D.ietf-core-object-security]). A (6LBR) pledge is expected to
have exactly one OSCORE security context with the JRC.
7.3.1. Replay Window and Persistency
Both (6LBR) pledge and the JRC MUST implement a replay protection
mechanism. The use of the default OSCORE replay protection mechanism
specified in Section 3.2.2 of [I-D.ietf-core-object-security] is
RECOMMENDED.
Implementations MUST ensure that mutable OSCORE context parameters
(Sender Sequence Number, Replay Window) are stored in persistent
memory. A technique that prevents reuse of sequence numbers,
detailed in Appendix B.1.1 of [I-D.ietf-core-object-security], MUST
be implemented. Each update of the OSCORE Replay Window MUST be
written to persistent memory.
This is an important security requirement in order to guarantee nonce
uniqueness and resistance to replay attacks across reboots and
rejoins. Traffic between the (6LBR) pledge and the JRC is rare,
making security outweigh the cost of writing to persistent memory.
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7.3.2. OSCORE Error Handling
Errors raised by OSCORE during the join process MUST be silently
dropped, with no error response being signaled. The pledge MUST
silently discard any response not protected with OSCORE, including
error codes.
Such errors may happen for a number of reasons, including failed
lookup of an appropriate security context (e.g. the pledge attempting
to join a wrong network), failed decryption, positive replay window
lookup, formatting errors (possibly due to malicious alterations in
transit). Silently dropping OSCORE messages prevents a DoS attack on
the pledge where the attacker could send bogus error responses,
forcing the pledge to attempt joining one network at a time, until
all networks have been tried.
7.3.3. Mandatory to Implement Algorithms
The mandatory to implement AEAD algorithm for use with OSCORE is AES-
CCM-16-64-128 from [RFC8152]. This is the algorithm used for
securing IEEE Std 802.15.4 frames, and hardware acceleration for it
is present in virtually all compliant radio chips. With this choice,
CoAP messages are protected with an 8-byte CCM authentication tag,
and the algorithm uses 13-byte long nonces.
The mandatory to implement hash algorithm is SHA-256 [RFC4231]. The
mandatory to implement key derivation function is HKDF [RFC5869],
instantiated with a SHA-256 hash. See Appendix B for implementation
guidance when code footprint is important.
8. Constrained Join Protocol (CoJP)
The Constrained Join Protocol (CoJP) is a lightweight protocol over
CoAP [RFC7252] and a secure channel provided by OSCORE
[I-D.ietf-core-object-security]. CoJP allows the (6LBR) pledge to
request admission into a network managed by the JRC, and for the JRC
to configure the pledge with the parameters necessary for joining the
network, or advertising it in the case of 6LBR pledge. The JRC may
update the parameters at any time, by reaching out to the joined node
that formerly acted as a (6LBR) pledge. For example, network-wide
rekeying can be implemented by updating the keying material on each
node.
This section specifies how the CoJP messages are mapped to CoAP and
OSCORE, CBOR data structures carrying different parameters,
transported within CoAP payload, and the parameter semantics and
processing rules.
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CoJP relies on the security properties provided by OSCORE. This
includes end-to-end confidentiality, data authenticity, replay
protection, and a secure binding of responses to requests.
+-----------------------------------+
| Constrained Join Protocol (CoJP) |
+-----------------------------------+
+-----------------------------------+ \
| Requests / Responses | |
|-----------------------------------| |
| OSCORE | | CoAP
|-----------------------------------| |
| Messaging Layer | |
+-----------------------------------+ /
+-----------------------------------+
| UDP |
+-----------------------------------+
Figure 2: Abstract layering of CoJP.
When a (6LBR) pledge requests admission to a given network, it
undergoes the CoJP join exchange that consists of:
o the Join Request message, sent by the (6LBR) pledge to the JRC,
potentially proxied by the JP. The Join Request message and its
mapping to CoAP is specified in Section 8.1.1.
o the Join Response message, sent by the JRC to the (6LBR) pledge,
if the JRC successfully processes the Join Request using OSCORE
and it determines through a mechanism that is out of scope of this
specification that the (6LBR) pledge is authorized to join the
network. The Join Response message is potentially proxied by the
JP. The Join Response message and its mapping to CoAP is
specified in Section 8.1.2.
When the JRC needs to update the parameters of a joined node that
formerly acted as a (6LBR) pledge, it executes the CoJP parameter
update exchange that consists of:
o the Parameter Update message, sent by the JRC to the joined node
that formerly acted as a (6LBR) pledge. The Parameter Update
message and its mapping to CoAP is specified in Section 8.2.1.
o the Parameter Update Response message, sent by the joined node to
the JRC in response to the Parameter Update message to signal
successful reception of the updated parameters. The Parameter
Update Response message and its mapping to CoAP is specified in
Section 8.2.2.
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The payload of CoJP messages is encoded with CBOR [RFC7049]. The
CBOR data structures that may appear as the payload of different CoJP
messages are specified in Section 8.4.
8.1. Join Exchange
This section specifies the messages exchanged when the (6LBR) pledge
requests admission and configuration parameters from the JRC.
8.1.1. Join Request Message
The Join Request message that the (6LBR) pledge sends SHALL be mapped
to a CoAP request:
o The request method is POST.
o The type is Confirmable (CON).
o The Proxy-Scheme option is set to "coap".
o The Uri-Host option is set to "6tisch.arpa". This is an anycast
type of identifier of the JRC that is resolved to its IPv6 address
by the JP or the 6LBR pledge.
o The Uri-Path option is set to "j".
o The OSCORE option SHALL be set according to
[I-D.ietf-core-object-security]. The OSCORE security context used
is the one derived in Section 7.3. The OSCORE kid context allows
the JRC to retrieve the security context for a given pledge.
o The payload is a Join_Request CBOR object, as defined in
Section 8.4.1.
Since the Join Request is a confirmable message, the transmission at
(6LBR) pledge will be controlled by CoAP's retransmission mechanism.
The JP, when operating in a stateless manner, forwards this Join
Request as a non-confirmable (NON) CoAP message, as specified in
Section 7. If the CoAP at (6LBR) pledge declares the message
transmission as failure, the (6LBR) pledge SHOULD attempt to join the
next advertised 6TiSCH network. See Section 7.2 for recommended
values of CoAP settings to use during the join exchange.
If all join attempts to advertised networks have failed, the (6LBR)
pledge SHOULD signal to the user the presence of an error condition,
through some out-of-band mechanism.
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8.1.2. Join Response Message
The Join Response message that the JRC sends SHALL be mapped to a
CoAP response:
o The response Code is 2.04 (Changed).
o The payload is a Configuration CBOR object, as defined in
Section 8.4.2.
8.2. Parameter Update Exchange
During the network lifetime, parameters returned as part of the Join
Response may need to be updated. One typical example is the update
of link-layer keying material for the network, a process known as
rekeying. This section specifies a generic mechanism when this
parameter update is initiated by the JRC.
At the time of the join, the (6LBR) pledge acts as a CoAP client and
requests the network parameters through a representation of the "/j"
resource, exposed by the JRC. In order for the update of these
parameters to happen, the JRC needs to asynchronously contact the
joined node. The use of the CoAP Observe option for this purpose is
not feasible due to the change in the IPv6 address when the pledge
becomes the joined node and obtains a global address.
Instead, once the (6LBR) pledge receives and successfully validates
the Join Response and so becomes a joined node, it becomes a CoAP
server. The joined node exposes the "/j" resource that is used by
the JRC to update the parameters. Consequently, the JRC operates as
a CoAP client when updating the parameters. The request/response
exchange between the JRC and the (6LBR) pledge happens over the
already-established OSCORE secure channel.
8.2.1. Parameter Update Message
The Parameter Update message that the JRC sends to the joined node
SHALL be mapped to a CoAP request:
o The request method is POST.
o The type is Confirmable (CON).
o The Uri-Path option is set to "j".
o The OSCORE option SHALL be set according to
[I-D.ietf-core-object-security]. The OSCORE security context used
is the one derived in Section 7.3. When a joined node receives a
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request with the Sender ID set to 0x4a5243 (ID of the JRC), it is
able to correctly retrieve the security context with the JRC.
o The payload is a Configuration CBOR object, as defined in
Section 8.4.2.
The JRC has implicit knowledge on the global IPv6 address of the
joined node, as it knows the pledge identifier that the joined node
used when it acted as a pledge, and the IPv6 network prefix. The JRC
uses this implicitly derived IPv6 address of the joined node to
directly address CoAP messages to it.
In case the JRC does not receive a response to a Parameter Update
message, it attempts multiple retransmissions, as configured by the
underlying CoAP retransmission mechanism triggered for confirmable
messages. Finally, if the CoAP implementation declares the
transmission as failure, the JRC may consider this as a hint that the
joined node is no longer in the network. How the JRC decides when to
stop attempting to contact a previously joined node is out of scope
of this specification but security considerations on the reuse of
assigned resources apply, as discussed in Section 9.
8.2.2. Parameter Update Response Message
The Parameter Update Response message that the joined node sends to
the JRC SHALL be mapped to a CoAP response:
o The response Code is 2.04 (Changed).
o The payload is empty.
8.3. Error Handling
8.3.1. CoJP CBOR Object Processing
CoJP CBOR objects are transported within both CoAP requests and
responses. This section describes handling in case certain CoJP CBOR
object parameters are not supported by the implementation or their
processing fails. See Section 7.3.2 for the handling of errors that
may be raised by the underlying OSCORE implementation.
When such a parameter is detected in a CoAP request (Join Request
message, Parameter Update message), a Diagnostic Response message
MUST be returned. A Diagnostic Response message maps to a CoAP
response and is specified in Section 8.3.2.
When a parameter that cannot be acted upon is encountered while
processing a CoJP object in a CoAP response (Join Response message),
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a (6LBR) pledge SHOULD reattempt to join. In this case, the (6LBR)
pledge SHOULD include the Unsupported Configuration CBOR object
within the Join Request object in the following Join Request message.
The Unsupported Configuration CBOR object is self-contained and
enables the (6LBR) pledge to signal any parameters that the
implementation of the networking stack may not support. A (6LBR)
pledge MUST NOT attempt more than MAX_RETRANSMIT number of attempts
to join if the processing of the Join Response message fails each
time. If COJP_MAX_JOIN_ATTEMPTS number of attempts is reached
without success, the (6LBR) pledge SHOULD signal to the user the
presence of an error condition, through some out-of-band mechanism.
8.3.2. Diagnostic Response Message
The Diagnostic Response message is returned for any CoJP request when
the processing of the payload failed. The Diagnostic Response
message is protected by OSCORE as any other CoJP protocol message.
The Diagnostic Response message SHALL be mapped to a CoAP response:
o The response Code is 4.00 (Bad Request).
o The payload is an Unsupported Configuration CBOR object, as
defined in Section 8.4.5, containing more information about the
parameter that triggered the sending of this message.
8.3.3. Failure Handling
The Parameter Update exchange may be triggered at any time during the
network lifetime, which may span several years. During this period,
it may occur that a joined node or the JRC experience unexpected
events such as reboots or complete failures.
This document mandates that the mutable parameters in the security
context are written to persistent memory (see Section 7.3.1) by both
the JRC and pledges (joined nodes). As the joined node (pledge) is
typically a constrained device that handles the write operations to
persistent memory in a predictable manner, the retrieval of mutable
security context parameters is feasible across reboots such that
there is no risk of AEAD nonce reuse due to reinitialized Sender
Sequence numbers, or of a replay attack due to the reinitialized
replay window. JRC may be hosted on a generic machine where the
write operation to persistent memory may lead to unpredictable delays
due to caching. In case of a reboot event at JRC occurring before
the cached data is written to persistent memory, the loss of mutable
security context parameters is likely which consequently poses the
risk of AEAD nonce reuse.
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In the event of a complete device failure, where the mutable security
context parameters cannot be retrieved, it is expected that a failed
joined node is replaced with a new physical device, using a new
pledge identifier and a PSK. When such a failure event occurs at the
JRC, it is possible that the static information on provisioned
pledges, like PSKs and pledge identifiers, can be retrieved through
available backups. However, it is likely that the information about
joined nodes, their assigned short identifiers and mutable security
context parameters is lost. If this is the case, during the process
of JRC reinitialization, the network administrator MUST force through
out-of-band means all the networks managed by the failed JRC to
rejoin, through e.g. the reinitialization of the 6LBR nodes and
freshly generated dynamic cryptographic keys and other parameters
that have influence on the security properties of the network.
In order to recover from such a failure event, the reinitialized JRC
can trigger the renegotiation of the OSCORE security context through
the procedure described in Appendix B.2 of
[I-D.ietf-core-object-security]. Aware of the failure event, the
reinitialized JRC responds to the first join request of each pledge
it is managing with a 4.01 Unauthorized error and a random nonce.
The pledge verifies the error response and then initiates the CoJP
join exchange using a new OSCORE security context derived from an ID
Context consisting of the concatenation of two nonces, one that it
received from the JRC and the other that the pledge generates
locally. After verifying the join request with the new ID Context
and the derived OSCORE security context, the JRC should consequently
take action in mapping the new ID Context with the previously used
pledge identifier. How JRC handles this mapping is implementation
specific.
The described procedure is specified in Appendix B.2 of
[I-D.ietf-core-object-security] and is RECOMMENDED in order to handle
the failure events or any other event that may lead to the loss of
mutable security context parameters. The length of nonces exchanged
using this procedure SHOULD be at least 8 bytes.
The procedure does require both the pledge and the JRC to have good
sources of randomness. While this is typically not an issue at the
JRC side, the constrained device hosting the pledge may pose
limitations in this regard. If the procedure outlined in
Appendix B.2 of [I-D.ietf-core-object-security] is not supported by
the pledge, the network administrator MUST take action in
reprovisioning the concerned devices with freshly generated
parameters, through out-of-band means.
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8.4. CoJP Objects
This section specifies the structure of CoJP CBOR objects that may be
carried as the payload of CoJP messages. Some of these objects may
be received both as part of the CoJP join exchange when the device
operates as a (CoJP) pledge, or the parameter update exchange, when
the device operates as a joined (6LBR) node.
8.4.1. Join Request Object
The Join_Request structure is built on a CBOR map object.
The set of parameters that can appear in a Join_Request object is
summarized below. The labels can be found in the "CoJP Parameters"
registry Section 11.1.
o role: The identifier of the role that the pledge requests to play
in the network once it joins, encoded as an unsigned integer.
Possible values are specified in Table 1. This parameter MAY be
included. In case the parameter is omitted, the default value of
0, i.e. the role "6TiSCH Node", MUST be assumed.
o network identifier: The identifier of the network, as discussed in
Section 3, encoded as a CBOR byte string. When present in the
Join_Request, it hints to the JRC the network that the pledge is
requesting to join, enabling the JRC to manage multiple networks.
The pledge obtains the value of the network identifier from the
received EB frames. This parameter MUST be included in a
Join_Request object regardless of the role parameter value.
o unsupported configuration: The identifier of the parameters that
are not supported by the implementation, encoded as an
Unsupported_Configuration object described in Section 8.4.5. This
parameter MAY be included. If a (6LBR) pledge previously
attempted to join and received a valid Join Response message over
OSCORE, but failed to act on its payload (Configuration object),
it SHOULD include this parameter to facilitate the recovery and
debugging.
The CDDL fragment that represents the text above for the Join_Request
follows.
Join_Request = {
? 1 : uint, ; role
? 5 : bstr, ; network identifier
? 8 : Unsupported_Configuration ; unsupported configuration
}
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+--------+-------+-------------------------------------+------------+
| Name | Value | Description | Reference |
+--------+-------+-------------------------------------+------------+
| 6TiSCH | 0 | The pledge requests to play the | [[this |
| Node | | role of a regular 6TiSCH node, i.e. | document]] |
| | | non-6LBR node. | |
| | | | |
| 6LBR | 1 | The pledge requests to play the | [[this |
| | | role of 6LoWPAN Border Router | document]] |
| | | (6LBR). | |
+--------+-------+-------------------------------------+------------+
Table 1: Role values.
8.4.2. Configuration Object
The Configuration structure is built on a CBOR map object. The set
of parameters that can appear in a Configuration object is summarized
below. The labels can be found in "CoJP Parameters" registry
Section 11.1.
o link-layer key set: An array encompassing a set of cryptographic
keys and their identifiers that are currently in use in the
network, or that are scheduled to be used in the future. The
encoding of individual keys is described in Section 8.4.3. The
link-layer key set parameter MAY be included in a Configuration
object. When present, the link-layer key set parameter MUST
contain at least one key. When a pledge is joining for the first
time and receives this parameter, before sending the first
outgoing frame secured with a received key, the pledge needs to
successfully complete the security processing of an incoming
frame. To do so, the pledge can wait to receive a new frame, or
it can store an EB frame that it used to find the JP and use it
for immediate security processing upon reception of the key set.
This parameter is also used to implement rekeying in the network.
How the keys are installed and used differs for the 6LBR and other
(regular) nodes, and this is explained in Section 8.4.3.1 and
Section 8.4.3.2.
o short identifier: a compact identifier assigned to the pledge.
The short identifier structure is described in Section 8.4.4. The
short identifier parameter MAY be included in a Configuration
object.
o JRC address: the IPv6 address of the JRC, encoded as a byte
string, with the length of 16 bytes. If the length of the byte
string is different from 16, the parameter MUST be discarded. If
the JRC is not co-located with the 6LBR and has a different IPv6
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address than the 6LBR, this parameter MUST be included. In the
special case where the JRC is co-located with the 6LBR and has the
same IPv6 address as the 6LBR, this parameter MAY be included. If
the JRC address parameter is not present in the Configuration
object, this indicates that the JRC has the same IPv6 address as
the 6LBR. The joined node can then discover the IPv6 address of
the JRC through network control traffic. See Section 6.
o blacklist: An array encompassing a list of pledge identifiers that
are blacklisted by the JRC, with each pledge identifier encoded as
a byte string. The blacklist parameter MAY be included in a
Configuration object. When present, the array MUST contain zero
or more byte strings encoding pledge identifiers. The joined node
MUST silently drop any link-layer frames originating from the
pledge identifiers enclosed in the blacklist parameter. When this
parameter is received, its value MUST overwrite any previously set
values. This parameter allows the JRC to configure the node
acting as a JP to filter out traffic from misconfigured or
malicious pledges before their traffic is forwarded into the
network. If the JRC decides to remove a given pledge identifier
from a blacklist, it omits the pledge identifier in the blacklist
parameter value it sends next.
o join rate: Average data rate of join traffic forwarded into the
network that should not be exceeded when a joined node operates as
a JP, encoded as an unsigned integer in bytes per second. The
join rate parameter MAY be included in a Configuration object.
This parameter allows the JRC to configure different nodes in the
network to operate as JP, and act in case of an attack by
throttling the rate at which JP forwards unauthenticated traffic
into the network. When this parameter is present in a
Configuration object, the value MUST be used to set the
PROBING_RATE of CoAP at the joined node for communication with the
JRC. In case this parameter is set to zero, a joined node MUST
silently drop any join traffic coming from unauthenticated
pledges. In case this parameter is omitted, the value of positive
infinity SHOULD be assumed. Node operating as a JP MAY use
another mechanism that is out of scope of this specification to
configure PROBING_RATE of CoAP in the absence of join rate
parameter from the Configuration object.
The CDDL fragment that represents the text above for the
Configuration follows. Structures Link_Layer_Key and
Short_Identifier are specified in Section 8.4.3 and Section 8.4.4.
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Configuration = {
? 2 : [ +Link_Layer_Key ], ; link-layer key set
? 3 : Short_Identifier, ; short identifier
? 4 : bstr, ; JRC address
? 6 : [ *bstr ], ; blacklist
? 7 : uint ; join rate
}
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+---------------+-------+----------+-------------------+------------+
| Name | Label | CBOR | Description | Reference |
| | | type | | |
+---------------+-------+----------+-------------------+------------+
| role | 1 | unsigned | Identifies the | [[this |
| | | integer | role parameter | document]] |
| | | | | |
| link-layer | 2 | array | Identifies the | [[this |
| key set | | | array carrying | document]] |
| | | | one or more link- | |
| | | | level | |
| | | | cryptographic | |
| | | | keys | |
| | | | | |
| short | 3 | array | Identifies the | [[this |
| identifier | | | assigned short | document]] |
| | | | identifier | |
| | | | | |
| JRC address | 4 | byte | Identifies the | [[this |
| | | string | IPv6 address of | document]] |
| | | | the JRC | |
| | | | | |
| network | 5 | byte | Identifies the | [[this |
| identifier | | string | network | document]] |
| | | | identifier | |
| | | | parameter | |
| | | | | |
| blacklist | 6 | array | Identifies the | [[this |
| | | | blacklist | document]] |
| | | | parameter | |
| | | | | |
| join rate | 7 | unsigned | Identifier the | [[this |
| | | integer | join rate | document]] |
| | | | parameter | |
| | | | | |
| unsupported | 8 | array | Identifies the | [[this |
| configuration | | | unsupported | document]] |
| | | | configuration | |
| | | | parameter | |
+---------------+-------+----------+-------------------+------------+
Table 2: CoJP parameters map labels.
8.4.3. Link-Layer Key
The Link_Layer_Key structure encompasses the parameters needed to
configure the link-layer security module: the key identifier; the
value of the cryptographic key; the link-layer algorithm identifier
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and the security level and the frame types that it should be used
with, both for outgoing and incoming security operations; and any
additional information that may be needed to configure the key.
For encoding compactness, the Link_Layer_Key object is not enclosed
in a top-level CBOR object. Rather, it is transported as a sequence
of CBOR elements, some being optional.
The set of parameters that can appear in a Link_Layer_Key object is
summarized below, in order:
o key_id: The identifier of the key, encoded as a CBOR unsigned
integer. This parameter MUST be included. If the decoded CBOR
unsigned integer value is larger than the maximum link-layer key
identifier, the key is considered invalid. In case the key is
considered invalid, the key MUST be discarded and the
implementation MUST signal the error as specified in
Section 8.3.1.
o key_usage: The identifier of the link-layer algorithm, security
level and link-layer frame types that can be used with the key,
encoded as an integer. This parameter MAY be included. Possible
values and the corresponding link-layer settings are specified in
IANA "CoJP Key Usage" registry (Section 11.2). In case the
parameter is omitted, the default value of 0 from Table 3 MUST be
assumed.
o key_value: The value of the cryptographic key, encoded as a byte
string. This parameter MUST be included. If the length of the
byte string is different than the corresponding key length for a
given algorithm specified by the key_usage parameter, the key MUST
be discarded and the implementation MUST signal the error as
specified in Section 8.3.1.
o key_addinfo: Additional information needed to configure the link-
layer key, encoded as a byte string. This parameter MAY be
included. The processing of this parameter is dependent on the
link-layer technology in use and a particular keying mode.
To be able to decode the keys that are present in the link-layer key
set, and to identify individual parameters of a single Link_Layer_Key
object, the CBOR decoder needs to differentiate between elements
based on the CBOR type. For example, a uint that follows a byte
string signals to the decoder that a new Link_Layer_Key object is
being processed.
The CDDL fragment that represents the text above for the
Link_Layer_Key follows.
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Link_Layer_Key = (
key_id : uint,
? key_usage : int,
key_value : bstr,
? key_addinfo : bstr,
)
+-----------------+-----+------------------+-------------+----------+
| Name | Val | Algorithm | Description | Referenc |
| | ue | | | e |
+-----------------+-----+------------------+-------------+----------+
| 6TiSCH-K1K2 | 0 | IEEE802154-AES- | Use MIC-32 | [[this d |
| -ENC-MIC32 | | CCM-128 | for EBs, | ocument] |
| | | | ENC-MIC-32 | ] |
| | | | for DATA | |
| | | | and ACKNOWL | |
| | | | EDGMENT. | |
| | | | | |
| 6TiSCH-K1K2 | 1 | IEEE802154-AES- | Use MIC-64 | [[this d |
| -ENC-MIC64 | | CCM-128 | for EBs, | ocument] |
| | | | ENC-MIC-64 | ] |
| | | | for DATA | |
| | | | and ACKNOWL | |
| | | | EDGMENT. | |
| | | | | |
| 6TiSCH-K1K2 | 2 | IEEE802154-AES- | Use MIC-128 | [[this d |
| -ENC-MIC128 | | CCM-128 | for EBs, | ocument] |
| | | | ENC-MIC-128 | ] |
| | | | for DATA | |
| | | | and ACKNOWL | |
| | | | EDGMENT. | |
| | | | | |
| 6TiSCH- | 3 | IEEE802154-AES- | Use MIC-32 | [[this d |
| K1K2-MIC32 | | CCM-128 | for EBs, | ocument] |
| | | | DATA and AC | ] |
| | | | KNOWLEDGMEN | |
| | | | T. | |
| | | | | |
| 6TiSCH- | 4 | IEEE802154-AES- | Use MIC-64 | [[this d |
| K1K2-MIC64 | | CCM-128 | for EBs, | ocument] |
| | | | DATA and AC | ] |
| | | | KNOWLEDGMEN | |
| | | | T. | |
| | | | | |
| 6TiSCH- | 5 | IEEE802154-AES- | Use MIC-128 | [[this d |
| K1K2-MIC128 | | CCM-128 | for EBs, | ocument] |
| | | | DATA and AC | ] |
| | | | KNOWLEDGMEN | |
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| | | | T. | |
| | | | | |
| 6TiSCH-K1-MIC32 | 6 | IEEE802154-AES- | Use MIC-32 | [[this d |
| | | CCM-128 | for EBs. | ocument] |
| | | | | ] |
| | | | | |
| 6TiSCH-K1-MIC64 | 7 | IEEE802154-AES- | Use MIC-64 | [[this d |
| | | CCM-128 | for EBs. | ocument] |
| | | | | ] |
| | | | | |
| 6TiSCH-K1-MIC12 | 8 | IEEE802154-AES- | Use MIC-128 | [[this d |
| 8 | | CCM-128 | for EBs. | ocument] |
| | | | | ] |
| | | | | |
| 6TiSCH-K2-MIC32 | 9 | IEEE802154-AES- | Use MIC-32 | [[this d |
| | | CCM-128 | for DATA | ocument] |
| | | | and ACKNOWL | ] |
| | | | EDGMENT. | |
| | | | | |
| 6TiSCH-K2-MIC64 | 10 | IEEE802154-AES- | Use MIC-64 | [[this d |
| | | CCM-128 | for DATA | ocument] |
| | | | and ACKNOWL | ] |
| | | | EDGMENT. | |
| | | | | |
| 6TiSCH-K2-MIC12 | 11 | IEEE802154-AES- | Use MIC-128 | [[this d |
| 8 | | CCM-128 | for DATA | ocument] |
| | | | and ACKNOWL | ] |
| | | | EDGMENT. | |
| | | | | |
| 6TiSCH-K2-ENC- | 12 | IEEE802154-AES- | Use ENC- | [[this d |
| MIC32 | | CCM-128 | MIC-32 for | ocument] |
| | | | DATA and AC | ] |
| | | | KNOWLEDGMEN | |
| | | | T. | |
| | | | | |
| 6TiSCH-K2-ENC- | 13 | IEEE802154-AES- | Use ENC- | [[this d |
| MIC64 | | CCM-128 | MIC-64 for | ocument] |
| | | | DATA and AC | ] |
| | | | KNOWLEDGMEN | |
| | | | T. | |
| | | | | |
| 6TiSCH-K2-ENC- | 14 | IEEE802154-AES- | Use ENC- | [[this d |
| MIC128 | | CCM-128 | MIC-128 for | ocument] |
| | | | DATA and AC | ] |
| | | | KNOWLEDGMEN | |
| | | | T. | |
+-----------------+-----+------------------+-------------+----------+
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Table 3: Key Usage values.
8.4.3.1. Rekeying of (6LoWPAN) Border Routers (6LBR)
When the 6LoWPAN Border Router (6LBR) receives the Configuration
object containing a link-layer key set, it MUST immediately install
and start using the new keys for all outgoing traffic, and remove any
old keys it has installed from the previous key set after a delay of
COJP_REKEYING_GUARD_TIME has passed. This mechanism is used by the
JRC to force the 6LBR to start sending traffic with the new key. The
decision is taken by the JRC when it has determined that the new key
has been made available to all (or some overwhelming majority) of
nodes. Any node that the JRC has not yet reached at that point is
either non-functional or in extended sleep such that it will not be
reached. To get the key update, such node needs to go through the
join process anew.
8.4.3.2. Rekeying of regular (6LoWPAN) Nodes (6LN)
When a regular 6LN node receives the Configuration object with a
link-layer key set, it MUST install the new keys. The 6LN will use
both the old and the new keys to decrypt and authenticate any
incoming traffic that arrives based upon the key identifier in the
packet. It MUST continue to use the old keys for all outgoing
traffic until it has detected that the network has switched to the
new key set.
The detection of network switch is based upon the receipt of traffic
secured with the new keys. Upon reception and successful security
processing of a link-layer frame secured with a key from the new key
set, a 6LN node MUST then switch to sending outgoing traffic using
the keys from the new set for all outgoing traffic. The 6LN node
MUST remove any old keys it has installed from the previous key set
after a delay of COJP_REKEYING_GUARD_TIME has passed after it starts
using the new key set.
Sending of traffic with the new keys signals to other downstream
nodes to switch to their new key, and the affect is that there is a
ripple of key updates in outward concentric circles around each 6LBR.
8.4.3.3. Use in IEEE Std 802.15.4
When Link_Layer_Key is used in the context of [IEEE802.15.4], the
following considerations apply.
Signaling of different keying modes of [IEEE802.15.4] is done based
on the parameter values present in a Link_Layer_Key object.
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o Key ID Mode 0x00 (Implicit, pairwise): key_id parameter MUST be
set to 0. key_addinfo parameter MUST be present. key_addinfo
parameter MUST be set to the link-layer address(es) of a single
peer with whom the key should be used. Depending on the
configuration of the network, key_addinfo may carry the peer's
long link-layer address (i.e. pledge identifier), short link-layer
address, or their concatenation with the long address being
encoded first. Which address is carried is determined from the
length of the byte string.
o Key ID Mode 0x01 (Key Index): key_id parameter MUST be set to a
value different than 0. key_addinfo parameter MUST NOT be
present.
o Key ID Mode 0x02 (4-byte Explicit Key Source): key_id parameter
MUST be set to a value different than 0. key_addinfo parameter
MUST be present. key_addinfo parameter MUST be set to a byte
string, exactly 4 bytes long. key_addinfo parameter carries the
Key Source parameter used to configure [IEEE802.15.4].
o Key ID Mode 0x03 (8-byte Explicit Key Source): key_id parameter
MUST be set to a value different than 0. key_addinfo parameter
MUST be present. key_addinfo parameter MUST be set to a byte
string, exactly 8 bytes long. key_addinfo parameter carries the
Key Source parameter used to configure [IEEE802.15.4].
In all cases, key_usage parameter determines how a particular key
should be used in respect to incoming and outgoing security policies.
For Key ID Modes 0x01 - 0x03, parameter key_id sets the "secKeyIndex"
parameter of {{IEEE802.15.4} that is signaled in all outgoing frames
secured with a given key. The maximum value key_id can have is 254.
The value of 255 is reserved in {{IEEE802.15.4} and is therefore
considered invalid.
Key ID Mode 0x00 (Implicit, pairwise) enables the JRC to act as a
trusted third party and assign pairwise keys between nodes in the
network. How JRC learns about the network topology is out of scope
of this specification, but could be done through 6LBR - JRC signaling
for example. Pairwise keys could also be derived through a key
agreement protocol executed between the peers directly, where the
authentication is based on the symmetric cryptographic material
provided to both peers by the JRC. Such a protocol is out of scope
of this specification.
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8.4.4. Short Identifier
The Short_Identifier object represents an identifier assigned to the
pledge. It is encoded as a CBOR array object, containing, in order:
o identifier: The short identifier assigned to the pledge, encoded
as a byte string. This parameter MUST be included. The
identifier MUST be unique in the set of all identifiers assigned
in a network that is managed by a JRC. In case the identifier is
invalid, the decoder MUST silently ignore the Short_Identifier
object.
o lease_time: The validity of the identifier in hours after the
reception of the CBOR object, encoded as a CBOR unsigned integer.
This parameter MAY be included. The node MUST stop using the
assigned short identifier after the expiry of the lease_time
interval. It is up to the JRC to renew the lease before the
expiry of the previous interval. The JRC updates the lease by
executing the Parameter Update exchange with the node and
including the Short_Identifier in the Configuration object, as
described in Section 8.2. In case the lease expires, the node
SHOULD initiate a new join exchange, as described in Section 8.1.
In case this parameter is omitted, the value of positive infinity
MUST be assumed, meaning that the identifier is valid for as long
as the node participates in the network.
The CDDL fragment that represents the text above for the
Short_Identifier follows.
Short_Identifier = [
identifier : bstr,
? lease_time : uint
]
8.4.4.1. Use in IEEE Std 802.15.4
When Short_Identifier is used in the context of [IEEE802.15.4], the
following considerations apply.
The identifier MUST be used to set the short address of IEEE Std
802.15.4 module. When operating in TSCH mode, the identifier MUST be
unique in the set of all identifiers assigned in multiple networks
that share link-layer key(s). If the length of the byte string
corresponding to the identifier parameter is different than 2, the
identifier is considered invalid. The values 0xfffe and 0xffff are
reserved by [IEEE802.15.4] and their use is considered invalid.
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The security properties offered by the [IEEE802.15.4] link-layer in
TSCH mode are conditioned on the uniqueness requirement of the short
identifier (i.e. short address). The short address is one of the
inputs in the construction of the nonce, which is used to protect
link-layer frames. If a misconfiguration occurs, and the same short
address is assigned twice under the same link-layer key, the loss of
security properties is eminent. For this reason, practices where the
pledge generates the short identifier locally are not safe and are
likely to result in the loss of link-layer security properties.
The JRC MUST ensure that at any given time there are never two same
short identifiers being used under the same link-layer key. If the
lease_time parameter of a given Short_Identifier object is set to
positive infinity, care needs to be taken that the corresponding
identifier is not assigned to another node until the JRC is certain
that it is no longer in use, potentially through out-of-band
signaling. If the lease_time parameter expires for any reason, the
JRC should take into consideration potential ongoing transmissions by
the joined node, which may be hanging in the queues, before assigning
the same identifier to another node.
8.4.5. Unsupported Configuration Object
The Unsupported_Configuration object is encoded as a CBOR array,
containing at least one Unsupported_Parameter object. Each
Unsupported_Parameter object is a sequence of CBOR elements without
an enclosing top-level CBOR object for compactness. The set of
parameters that appear in an Unsupported_Parameter object is
summarized below, in order:
o code: Indicates the capability of acting on the parameter signaled
by parameter_label, encoded as an integer. This parameter MUST be
included. Possible values of this parameter are specified in the
IANA "CoJP Unsupported Configuration Code Registry"
(Section 11.3).
o parameter_label: Indicates the parameter. This parameter MUST be
included. Possible values of this parameter are specified in the
label column of the IANA "CoJP Parameters" registry
(Section 11.1).
o parameter_addinfo: Additional information about the parameter that
cannot be acted upon. This parameter MUST be included. In case
the code is set to "Unsupported", parameter_addinfo gives
additional information to the JRC. If the parameter indicated by
parameter_label cannot be acted upon regardless of its value,
parameter_addinfo MUST be set to null, signaling to the JRC that
it SHOULD NOT attempt to configure the parameter again. If the
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pledge can act on the parameter, but cannot configure the setting
indicated by the parameter value, the pledge can hint this to the
JRC. In this case, parameter_addinfo MUST be set to the value of
the parameter that cannot be acted upon following the normative
parameter structure specified in this document. For example, it
is possible to include only a subset of the link-layer key set
object, signaling the keys that cannot be acted upon, or the
entire key set that was received. In case the code is set to
"Malformed", parameter_addinfo MUST be set to null, signaling to
the JRC that it SHOULD NOT attempt to configure the parameter
again.
The CDDL fragment that represents the text above for
Unsupported_Configuration and Unsupported_Parameter objects follows.
Unsupported_Configuration = [
+ parameter : Unsupported_Parameter
]
Unsupported_Parameter = (
code : int,
parameter_label : int,
parameter_addinfo : nil / any
)
+-------------+-------+--------------------------------+------------+
| Name | Value | Description | Reference |
+-------------+-------+--------------------------------+------------+
| Unsupported | 0 | The indicated setting is not | [[this |
| | | supported by the networking | document]] |
| | | stack implementation. | |
| | | | |
| Malformed | 1 | The indicated parameter value | [[this |
| | | is malformed. | document]] |
+-------------+-------+--------------------------------+------------+
Table 4: Unsupported Configuration code values.
8.5. Recommended Settings
This section gives RECOMMENDED values of CoJP settings.
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+--------------------------+---------------+
| Name | Default Value |
+--------------------------+---------------+
| COJP_MAX_JOIN_ATTEMPTS | 4 |
| | |
| COJP_REKEYING_GUARD_TIME | 12 seconds |
+--------------------------+---------------+
Recommended CoJP settings.
The COJP_REKEYING_GUARD_TIME value SHOULD take into account possible
retransmissions at the link layer due to imperfect wireless links.
9. Security Considerations
Since this document uses the pledge identifier to set the ID Context
parameter of OSCORE, an important security requirement is that the
pledge identifier is unique in the set of all pledge identifiers
managed by a JRC. The uniqueness of the pledge identifier ensures
unique (key, nonce) pairs for AEAD algorithm used by OSCORE. It also
allows the JRC to retrieve the correct security context, upon the
reception of a Join Request message. The management of pledge
identifiers is simplified if the globally unique EUI-64 is used, but
this comes with privacy risks, as discussed in Section 10.
This document further mandates that the (6LBR) pledge and the JRC are
provisioned with unique PSKs. The PSK is used to set the OSCORE
Master Secret during security context derivation. This derivation
process results in OSCORE keys that are important for mutual
authentication of the (6LBR) pledge and the JRC. Should an attacker
come to know the PSK, then a man-in-the-middle attack is possible.
Many vendors are known to use unsafe practices when generating and
provisioning PSKs. The use of a single PSK shared among a group of
devices is a common pitfall that results in poor security. In this
case, the compromise of a single device is likely to lead to a
compromise of the entire batch, with the attacker having the ability
to impersonate a legitimate device and join the network, generate
bogus data and disturb the network operation. As a reminder, recall
the well-known problem with Bluetooth headsets with a "0000" pin.
Additionally, some vendors use methods such as scrambling or hashing
of device serial numbers or their EUI-64 to generate "unique" PSKs.
Without any secret information involved, the effort that the attacker
needs to invest into breaking these unsafe derivation methods is
quite low, resulting in the possible impersonation of any device from
the batch, without even needing to compromise a single device. The
use of cryptographically secure random number generators to generate
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the PSK is RECOMMENDED, see [NIST800-90A] for different mechanisms
using deterministic methods.
The JP forwards the unauthenticated join traffic into the network. A
data cap on the JP prevents it from forwarding more traffic than the
network can handle. The data cap can be configured by the JRC by
including a join rate parameter in the Join Response and it is
implemented through the CoAP's PROBING_RATE setting. The use of a
data cap at a JP forces attackers to use more than one JP if they
wish to overwhelm the network. Marking the join traffic packets with
a non-zero DSCP allows the network to carry the traffic if it has
capacity, but encourages the network to drop the extra traffic rather
than add bandwidth due to that traffic.
The shared nature of the "minimal" cell used for the join traffic
makes the network prone to a DoS attack by congesting the JP with
bogus traffic. Such an attacker is limited by its maximum transmit
power. The redundancy in the number of deployed JPs alleviates the
issue and also gives the pledge a possibility to use the best
available link for joining. How a network node decides to become a
JP is out of scope of this specification.
At the beginning of the join process, the pledge has no means of
verifying the content in the EB, and has to accept it at "face
value". In case the pledge tries to join an attacker's network, the
Join Response message will either fail the security check or time
out. The pledge may implement a temporary blacklist in order to
filter out undesired EBs and try to join using the next seemingly
valid EB. This blacklist alleviates the issue, but is effectively
limited by the node's available memory. Note that this temporary
blacklist is different from the one communicated as part of the CoJP
Configuration object as it helps pledge fight a DoS attack. These
bogus beacons prolong the join time of the pledge, and so the time
spent in "minimal" [RFC8180] duty cycle mode. The blacklist
communicated as part of the CoJP Configuration object helps JP fight
a DoS attack by a malicious pledge.
10. Privacy Considerations
The join solution specified in this document relies on the uniqueness
of the pledge identifier in the set of all pledge identifiers managed
by a JRC. This identifier is transferred in clear as an OSCORE kid
context. The use of the globally unique EUI-64 as pledge identifier
simplifies the management but comes with certain privacy risks. The
implications are thoroughly discussed in [RFC7721] and comprise
correlation of activities over time, location tracking, address
scanning and device-specific vulnerability exploitation. Since the
join process occurs rarely compared to the network lifetime, long-
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term threats that arise from using EUI-64 as the pledge identifier
are minimal. In addition, the Join Response message contains a short
address which is assigned by the JRC to the (6LBR) pledge. The
assigned short address SHOULD be uncorrelated with the long-term
pledge identifier. The short address is encrypted in the response.
Once the join process completes, the new node uses the short
addresses for all further layer 2 (and layer-3) operations. This
reduces the aforementioned privacy risks as the short layer-2 address
(visible even when the network is encrypted) is not traceable between
locations and does not disclose the manufacturer, as is the case of
EUI-64. However, an eavesdropper with access to the radio medium
during the join process may be able to correlate the assigned short
address with the extended address based on timing information with a
non-negligible probability. This probability decreases with an
increasing number of pledges joining concurrently.
11. IANA Considerations
Note to RFC Editor: Please replace all occurrences of "[[this
document]]" with the RFC number of this specification.
This document allocates a well-known name under the .arpa name space
according to the rules given in [RFC3172]. The name "6tisch.arpa" is
requested. No subdomains are expected. No A, AAAA or PTR record is
requested.
11.1. CoJP Parameters Registry
This section defines a sub-registries within the "IPv6 over the TSCH
mode of IEEE 802.15.4e (6TiSCH) parameters" registry with the name
"Constrained Join Protocol Parameters Registry".
The columns of the registry are:
Name: This is a descriptive name that enables an easier reference to
the item. It is not used in the encoding.
Label: The value to be used to identify this parameter. The label is
an integer.
CBOR type: This field contains the CBOR type for the field.
Description: This field contains a brief description for the field.
Reference: This field contains a pointer to the public specification
for the field, if one exists.
This registry is to be populated with the values in Table 2.
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The amending formula for this sub-registry is: Different ranges of
values use different registration policies [RFC8126]. Integer values
from -256 to 255 are designated as Standards Action. Integer values
from -65536 to -257 and from 256 to 65535 are designated as
Specification Required. Integer values greater than 65535 are
designated as Expert Review. Integer values less than -65536 are
marked as Private Use.
11.2. CoJP Key Usage Registry
This section defines a sub-registries within the "IPv6 over the TSCH
mode of IEEE 802.15.4e (6TiSCH) parameters" registry with the name
"Constrained Join Protocol Key Usage Registry".
The columns of this registry are:
Name: This is a descriptive name that enables easier reference to the
item. The name MUST be unique. It is not used in the encoding.
Value: This is the value used to identify the key usage setting.
These values MUST be unique. The value is an integer.
Algorithm: This is a descriptive name of the link-layer algorithm in
use and uniquely determines the key length. The name is not used in
the encoding.
Description: This field contains a description of the key usage
setting. The field should describe in enough detail how the key is
to be used with different frame types, specific for the link-layer
technology in question.
Reference: This contains a pointer to the public specification for
the field, if one exists.
This registry is to be populated with the values in Table 3.
The amending formula for this sub-registry is: Different ranges of
values use different registration policies [RFC8126]. Integer values
from -256 to 255 are designated as Standards Action. Integer values
from -65536 to -257 and from 256 to 65535 are designated as
Specification Required. Integer values greater than 65535 are
designated as Expert Review. Integer values less than -65536 are
marked as Private Use.
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11.3. CoJP Unsupported Configuration Code Registry
This section defines a sub-registries within the "IPv6 over the TSCH
mode of IEEE 802.15.4e (6TiSCH) parameters" registry with the name
"Constrained Join Protocol Unsupported Configuration Code Registry".
The columns of this registry are:
Name: This is a descriptive name that enables easier reference to the
item. The name MUST be unique. It is not used in the encoding.
Value: This is the value used to identify the diagnostic code. These
values MUST be unique. The value is an integer.
Description: This is a descriptive human-readable name. The
description MUST be unique. It is not used in the encoding.
Reference: This contains a pointer to the public specification for
the field, if one exists.
This registry is to be populated with the values in Table 4.
The amending formula for this sub-registry is: Different ranges of
values use different registration policies [RFC8126]. Integer values
from -256 to 255 are designated as Standards Action. Integer values
from -65536 to -257 and from 256 to 65535 are designated as
Specification Required. Integer values greater than 65535 are
designated as Expert Review. Integer values less than -65536 are
marked as Private Use.
12. Acknowledgments
The work on this document has been partially supported by the
European Union's H2020 Programme for research, technological
development and demonstration under grant agreements: No 644852,
project ARMOUR; No 687884, project F-Interop and open-call project
SPOTS; No 732638, project Fed4FIRE+ and open-call project SODA.
The following individuals provided input to this document (in
alphabetic order): Christian Amsuss, Tengfei Chang, Klaus Hartke,
Tero Kivinen, Jim Schaad, Goeran Selander, Yasuyuki Tanaka, Pascal
Thubert, William Vignat, Xavier Vilajosana, Thomas Watteyne.
13. References
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13.1. Normative References
[I-D.ietf-core-object-security]
Selander, G., Mattsson, J., Palombini, F., and L. Seitz,
"Object Security for Constrained RESTful Environments
(OSCORE)", draft-ietf-core-object-security-16 (work in
progress), March 2019.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC2597] Heinanen, J., Baker, F., Weiss, W., and J. Wroclawski,
"Assured Forwarding PHB Group", RFC 2597,
DOI 10.17487/RFC2597, June 1999,
<https://www.rfc-editor.org/info/rfc2597>.
[RFC3172] Huston, G., Ed., "Management Guidelines & Operational
Requirements for the Address and Routing Parameter Area
Domain ("arpa")", BCP 52, RFC 3172, DOI 10.17487/RFC3172,
September 2001, <https://www.rfc-editor.org/info/rfc3172>.
[RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049,
October 2013, <https://www.rfc-editor.org/info/rfc7049>.
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014,
<https://www.rfc-editor.org/info/rfc7252>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[RFC8152] Schaad, J., "CBOR Object Signing and Encryption (COSE)",
RFC 8152, DOI 10.17487/RFC8152, July 2017,
<https://www.rfc-editor.org/info/rfc8152>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
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13.2. Informative References
[I-D.ietf-6tisch-architecture]
Thubert, P., "An Architecture for IPv6 over the TSCH mode
of IEEE 802.15.4", draft-ietf-6tisch-architecture-20 (work
in progress), March 2019.
[I-D.ietf-6tisch-terminology]
Palattella, M., Thubert, P., Watteyne, T., and Q. Wang,
"Terms Used in IPv6 over the TSCH mode of IEEE 802.15.4e",
draft-ietf-6tisch-terminology-10 (work in progress), March
2018.
[I-D.ietf-cbor-cddl]
Birkholz, H., Vigano, C., and C. Bormann, "Concise data
definition language (CDDL): a notational convention to
express CBOR and JSON data structures", draft-ietf-cbor-
cddl-08 (work in progress), March 2019.
[I-D.ietf-core-stateless]
Hartke, K., "Extended Tokens and Stateless Clients in the
Constrained Application Protocol (CoAP)", draft-ietf-core-
stateless-01 (work in progress), March 2019.
[IEEE802.15.4]
IEEE standard for Information Technology, ., "IEEE Std
802.15.4 Standard for Low-Rate Wireless Networks", n.d..
[NIST800-90A]
NIST Special Publication 800-90A, Revision 1, ., Barker,
E., and J. Kelsey, "Recommendation for Random Number
Generation Using Deterministic Random Bit Generators",
2015.
[RFC4231] Nystrom, M., "Identifiers and Test Vectors for HMAC-SHA-
224, HMAC-SHA-256, HMAC-SHA-384, and HMAC-SHA-512",
RFC 4231, DOI 10.17487/RFC4231, December 2005,
<https://www.rfc-editor.org/info/rfc4231>.
[RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler,
"Transmission of IPv6 Packets over IEEE 802.15.4
Networks", RFC 4944, DOI 10.17487/RFC4944, September 2007,
<https://www.rfc-editor.org/info/rfc4944>.
[RFC5869] Krawczyk, H. and P. Eronen, "HMAC-based Extract-and-Expand
Key Derivation Function (HKDF)", RFC 5869,
DOI 10.17487/RFC5869, May 2010,
<https://www.rfc-editor.org/info/rfc5869>.
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[RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J.,
Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur,
JP., and R. Alexander, "RPL: IPv6 Routing Protocol for
Low-Power and Lossy Networks", RFC 6550,
DOI 10.17487/RFC6550, March 2012,
<https://www.rfc-editor.org/info/rfc6550>.
[RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C.
Bormann, "Neighbor Discovery Optimization for IPv6 over
Low-Power Wireless Personal Area Networks (6LoWPANs)",
RFC 6775, DOI 10.17487/RFC6775, November 2012,
<https://www.rfc-editor.org/info/rfc6775>.
[RFC7554] Watteyne, T., Ed., Palattella, M., and L. Grieco, "Using
IEEE 802.15.4e Time-Slotted Channel Hopping (TSCH) in the
Internet of Things (IoT): Problem Statement", RFC 7554,
DOI 10.17487/RFC7554, May 2015,
<https://www.rfc-editor.org/info/rfc7554>.
[RFC7721] Cooper, A., Gont, F., and D. Thaler, "Security and Privacy
Considerations for IPv6 Address Generation Mechanisms",
RFC 7721, DOI 10.17487/RFC7721, March 2016,
<https://www.rfc-editor.org/info/rfc7721>.
[RFC8180] Vilajosana, X., Ed., Pister, K., and T. Watteyne, "Minimal
IPv6 over the TSCH Mode of IEEE 802.15.4e (6TiSCH)
Configuration", BCP 210, RFC 8180, DOI 10.17487/RFC8180,
May 2017, <https://www.rfc-editor.org/info/rfc8180>.
[RFC8480] Wang, Q., Ed., Vilajosana, X., and T. Watteyne, "6TiSCH
Operation Sublayer (6top) Protocol (6P)", RFC 8480,
DOI 10.17487/RFC8480, November 2018,
<https://www.rfc-editor.org/info/rfc8480>.
Appendix A. Example
Figure 3 illustrates a successful join protocol exchange. The pledge
instantiates the OSCORE context and derives the OSCORE keys and
nonces from the PSK. It uses the instantiated context to protect the
Join Request addressed with a Proxy-Scheme option, the well-known
host name of the JRC in the Uri-Host option, and its EUI-64 as pledge
identifier and OSCORE kid context. Triggered by the presence of a
Proxy-Scheme option, the JP forwards the request to the JRC and sets
the CoAP token to the internally needed state. The JP has learned
the IPv6 address of the JRC when it acted as a pledge and joined the
network. Once the JRC receives the request, it looks up the correct
context based on the kid context parameter. The OSCORE data
authenticity verification ensures that the request has not been
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modified in transit. In addition, replay protection is ensured
through persistent handling of mutable context parameters.
Once the JP receives the Join Response, it authenticates the state
within the CoAP token before deciding where to forward. The JP sets
its internal state to that found in the token, and forwards the Join
Response to the correct pledge. Note that the JP does not possess
the key to decrypt the CBOR object (configuration) present in the
payload. The Join Response is matched to the Join Request and
verified for replay protection at the pledge using OSCORE processing
rules. In this example, the Join Response does not contain the IPv6
address of the JRC, the pledge hence understands the JRC is co-
located with the 6LBR.
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<---E2E OSCORE-->
Client Proxy Server
Pledge JP JRC
| | |
| Join | | Code: 0.02 (POST)
| Request | | Token: -
+--------->| | Proxy-Scheme: coap
| | | Uri-Host: 6tisch.arpa
| | | OSCORE: kid: -,
| | | kid_context: EUI-64,
| | | Partial IV: 1
| | | Payload: { Code: 0.02 (POST),
| | | Uri-Path: "j",
| | | join_request, <Tag> }
| | |
| | Join | Code: 0.02 (POST)
| | Request | Token: opaque state
| +--------->| OSCORE: kid: -,
| | | kid_context: EUI-64,
| | | Partial IV: 1
| | | Payload: { Code: 0.02 (POST),
| | | Uri-Path: "j",
| | | join_request, <Tag> }
| | |
| | |
| | Join | Code: 2.04 (Changed)
| | Response | Token: opaque state
| |<---------+ OSCORE: -
| | | Payload: { Code: 2.04 (Changed),
| | | configuration, <Tag> }
| | |
| | |
| Join | | Code: 2.04 (Changed)
| Response | | Token: -
|<---------+ | OSCORE: -
| | | Payload: { Code: 2.04 (Changed),
| | | configuration, <Tag> }
| | |
Figure 3: Example of a successful join protocol exchange. { ... }
denotes authenticated encryption, <Tag> denotes the authentication
tag.
Where the join_request object is:
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join_request:
{
5 : h'cafe' / PAN ID of the network pledge is attempting to join /
}
Since the role parameter is not present, the default role of "6TiSCH
Node" is implied.
The join_request object encodes to h'a10542cafe' with a size of 5
bytes.
And the configuration object is:
configuration:
{
2 : [ / link-layer key set /
1, / key_id /
h'e6bf4287c2d7618d6a9687445ffd33e6' / key_value /
],
3 : [ / short identifier /
h'af93' / assigned short address /
]
}
Since the key_usage parameter is not present in the link-layer key
set object, the default value of "6TiSCH-K1K2-ENC-MIC32" is implied.
Since key_addinfo parameter is not present and key_id is different
than 0, Key ID Mode 0x01 (Key Index) is implied. Similarly, since
the lease_time parameter is not present in the short identifier
object, the default value of positive infinity is implied.
The configuration object encodes to
h'a202820150e6bf4287c2d7618d6a9687445ffd33e6038142af93' with a size
of 26 bytes.
Appendix B. Lightweight Implementation Option
In environments where optimizing the implementation footprint is
important, it is possible to implement this specification without
having the implementations of HKDF [RFC5869] and SHA [RFC4231] on
constrained devices. HKDF and SHA are used during the OSCORE
security context derivation phase. This derivation can also be done
by the JRC or a provisioning device, on behalf of the (6LBR) pledge
during the provisioning phase. In that case, the derived OSCORE
security context parameters are written directly into the (6LBR)
pledge, without requiring the PSK be provisioned to the (6LBR)
pledge.
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The use of HKDF to derive OSCORE security context parameters ensures
that the resulting OSCORE keys have good security properties, and are
unique as long as the input for different pledges varies. This
specification ensures the uniqueness by mandating unique pledge
identifiers and a unique PSK for each (6LBR) pledge. From the AEAD
nonce reuse viewpoint, having a unique pledge identifier is a
sufficient condition. However, as discussed in Section 9, the use of
a single PSK shared among many devices is a common security pitfall.
The compromise of this shared PSK on a single device would lead to
the compromise of the entire batch. When using the implementation/
deployment scheme outlined above, the PSK does not need to be written
to individual pledges. As a consequence, even if a shared PSK is
used, the scheme offers the same level of security as in the scenario
where each pledge is provisioned with a unique PSK.
Authors' Addresses
Malisa Vucinic (editor)
Inria
2 Rue Simone Iff
Paris 75012
France
Email: malisa.vucinic@inria.fr
Jonathan Simon
Analog Devices
32990 Alvarado-Niles Road, Suite 910
Union City, CA 94587
USA
Email: jonathan.simon@analog.com
Kris Pister
University of California Berkeley
512 Cory Hall
Berkeley, CA 94720
USA
Email: pister@eecs.berkeley.edu
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Michael Richardson
Sandelman Software Works
470 Dawson Avenue
Ottawa, ON K1Z5V7
Canada
Email: mcr+ietf@sandelman.ca
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