Networking Working Group R. Alexander
Internet-Draft T. Tsao
Intended status: Standards Track Cooper Power Systems
Expires: March 16, 2013 September 12, 2012
Adapted Multimedia Internet KEYing (AMIKEY): An extension of Multimedia
Internet KEYing (MIKEY) Methods for Generic LLN Environments
draft-alexander-roll-mikey-lln-key-mgmt-04
Abstract
Multimedia Internet Keying (MIKEY) is a key management protocol used
for real-time applications. As standardized within RFC3830 it
defines four key distribution methods, including pre-shared keys,
public-key encryption, and Diffie-Hellman key exchange, with
allowances for ready protocol extension. A number of additional
methods have been developed and continue to be built from the base
protocol (see for example, RFC4442, RFC4563, RFC4650, RFC4738,
RFC5410, RFC6043 and RFC6267. However, in spite of its extensibility
and more general applicability, MIKEY and its related extensions have
primarily focused on the support of the Secure Real-time Transport
Protocol (SRTP).
This document specifies a simple adaptation of the MIKEY
specification to allow the base protocol and its various key
management mode extensions to be readily applied in more general
environments beyond the multimedia SRTP domain. In particular, the
document defines a repurposing of the MIKEY multimedia crypto
sessions structure and introduces a set of message extensions to the
base specification to allow the MIKEY key management methods to be
applied within Low-power and Lossy Networks (LLNs) and other general
constrained-device networks.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in RFC
2119 [RFC2119].
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on March 16, 2013.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2. MIKEY Key Management Methods Background . . . . . . . . . 6
1.3. Adapting MIKEY to General LLNs . . . . . . . . . . . . . . 7
1.4. Terminology and Definitions . . . . . . . . . . . . . . . 7
1.5. Document Outline . . . . . . . . . . . . . . . . . . . . . 9
1.6. Section Headings Notation . . . . . . . . . . . . . . . . 10
2. AMIKEY Overview . . . . . . . . . . . . . . . . . . . . . . . 10
3. AMIKEY Key Management Signaling . . . . . . . . . . . . . . . 14
3.1. Pre-shared key . . . . . . . . . . . . . . . . . . . . . . 15
3.2. Public-Key Encryption . . . . . . . . . . . . . . . . . . 17
3.3. [RFC3830] Diffie-Hellman Key Exchange . . . . . . . . . . 18
3.4. Example of AMIKEY Applied to RPL . . . . . . . . . . . . . 18
3.4.1. AMIKEY Key Assignment for RPL Join Process . . . . . . 18
3.4.2. AMIKEY Key Update for RPL Authenticated Mode . . . . . 21
4. [RFC3830] Selected Key Management Functions . . . . . . . . . 25
4.1. [RFC3830] Key Calculation . . . . . . . . . . . . . . . . 25
4.1.1. [RFC3830] Assumptions . . . . . . . . . . . . . . . . 25
4.1.2. Default PRF Description . . . . . . . . . . . . . . . 25
4.1.3. [RFC3830] Generating Keys from TGK . . . . . . . . . . 25
4.1.4. [RFC3830] Generating Keys for MIKEY Messages from
an Envelope/Pre-shared Key . . . . . . . . . . . . . . 25
4.2. [RFC3830] Pre-defined Transforms and Timestamp Formats . . 25
4.2.1. Hash Functions . . . . . . . . . . . . . . . . . . . . 25
4.2.2. Pseudo-Random Number Generator . . . . . . . . . . . . 25
4.2.3. [RFC3830] Key Data Transport Encryption . . . . . . . 26
4.2.4. [RFC3830] MAC Verification Message Function . . . . . 26
4.3. [RFC3830] Certificates, Policies and Authorization . . . . 26
4.4. [RFC3830] Retrieving the Data SA . . . . . . . . . . . . . 26
5. [RFC3830] Behavior and Message Handling . . . . . . . . . . . 26
5.1. [RFC3830] General . . . . . . . . . . . . . . . . . . . . 26
5.2. [RFC3830] Creating a message . . . . . . . . . . . . . . . 26
6. [RFC3830] Payload Encoding . . . . . . . . . . . . . . . . . . 26
6.1. [RFC3830] Common Header Payload (HDR) . . . . . . . . . . 27
6.1.1. [RFC3830] SRTP ID . . . . . . . . . . . . . . . . . . 29
6.1.2. The Generic_LLN-ID Map Type . . . . . . . . . . . . . 29
6.2. [RFC3830] Key Data Transport Payload (KEMAC) . . . . . . . 31
6.3. [RFC3830] Envelope Data Payload (PKE) . . . . . . . . . . 32
6.4. [RFC3830] DH Data Payload (DH) . . . . . . . . . . . . . . 32
6.5. [RFC3830] Signature Payload (SIGN) . . . . . . . . . . . . 32
6.6. [RFC3830] Timestamp Payload (T) . . . . . . . . . . . . . 32
6.7. ID Payload (ID) . . . . . . . . . . . . . . . . . . . . . 32
6.8. [RFC3830] Cert Hash Payload (CHASH) . . . . . . . . . . . 33
6.9. [RFC3830] Ver msg payload (V) . . . . . . . . . . . . . . 33
6.10. Security Policy (SP) Payload . . . . . . . . . . . . . . . 33
6.10.1. [RFC3830] SRTP Policy . . . . . . . . . . . . . . . . 34
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6.10.2. AMIKEY Generic_LLN Policy . . . . . . . . . . . . . . 34
6.11. [RFC3830] RAND Payload (RAND) . . . . . . . . . . . . . . 36
6.12. [RFC3830] Error Payload (ERR) . . . . . . . . . . . . . . 36
6.13. [RFC3830] Key Data Sub-Payload . . . . . . . . . . . . . . 36
6.14. [RFC3830] Key Validity Data . . . . . . . . . . . . . . . 36
6.15. [RFC3830] General Extension Payload . . . . . . . . . . . 36
6.16. Key Index Payload . . . . . . . . . . . . . . . . . . . . 36
6.17. Key Source Identifier Payload . . . . . . . . . . . . . . 37
7. [RFC3830] Transport Protocols . . . . . . . . . . . . . . . . 38
8. Security Considerations . . . . . . . . . . . . . . . . . . . 38
9. [RFC3830] Groups . . . . . . . . . . . . . . . . . . . . . . . 38
10. Additional Specification Considerations . . . . . . . . . . . 38
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 38
12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 40
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 40
13.1. Normative References . . . . . . . . . . . . . . . . . . . 40
13.2. Informative References . . . . . . . . . . . . . . . . . . 40
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 42
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1. Introduction
Any sufficiently large scale network offering security services
requires an automated key management mechanism for the exchange of
keys and the update of related security credentials [RFC4107]. Key
management may be needed for individual session exchanges or for the
long-term control and update of security parameters from which
session keys may be derived. In many Low-power and Lossy Networks
(LLN) and other constrained-device environments, key management
emphasis is often on the management of long-term keys. This may
automatically follow network associations based on device pre-
configuration or may be based on specified key lifetimes or
administrative or event-driven need for key credential changes. This
would apply to the case of a network routing protocol like RPL
([RFC6550]) that employs security as well as to other secured
communications layer protocols.
Multimedia Internet Keying (MIKEY) is a key management protocol that
has been used for real-time applications both for peer-to-peer and
group communications. The capabilities of the protocol lend
themselves just as readily to the management of long-term keys as to
per-session or per association key control. MIKEY [RFC3830] defines
four key distribution methods including pre-shared keys, public-key
encryption, and Diffie-Hellman key exchange. Given its design
simplicity, efficiency and flexibility a number of additional modes
and extensions have indeed been developed and continue to be built
from the base protocol (see for example, [RFC4442], [RFC4563],
[RFC4650], [RFC4738], [RFC5410], [RFC6043] and [RFC6267]). MIKEY and
its related RFC extensions have however primarily focused on the
support of the SRTP and related Session Initiation Protocol (SIP)
call scenarios [RFC3711].
This document specifies an adaptation of the MIKEY protocol
specification to allow the base protocol and its various key
management mode extensions to be more generally applied to LLN
environments. In particular, the document defines a repurposing of
the MIKEY multimedia crypto sessions structure to allow optional
support for simultaneous management of multiple protocol or device
interface key. The specification also introduces a set of message
extensions to the base MIKEY protocol to allow its key management
methods to be applied within generic LLN and constrained-device
networks.
1.1. Motivation
Key distribution describes the process of delivering cryptographic
keys to the required communicating parties. The MIKEY protocol has
defined the mechanisms for establishing the security context used by
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SRTP however the mechanisms for security parameter negotiation and
update is just as readily extended to LLN protocols.
The flexibly to employ different key distribution methods according
to available network infrastructure and particular operating
scenarios together with the compact efficiency of its binary
specification makes MIKEY well suited for general LLN use. The wide
range of key management support extending from light-weight, low
latency half round-trip pre-shared key distribution methods to multi-
exchange Diffie-Hellman key agreements protected with digital
signatures or pre-shared keys offers great flexibility to meet the
needs of diverse LLN application environments.
The option to embed the MIKEY key management messages within an
existing network signaling protocol or to be directly transported or
UDP or TCP (using port 2269) also increases the ability to apply the
methods in more general LLN domains.
MIKEY has met its original stated design goals [RFC3830] of end-to-
end security, simplicity, efficiency, tunneling (even beyond
integration with Session Description Protocol (SDP) [RFC4566] or RTCP
[RFC3605]), and independence of underlying transport. In so doing it
offers an excellent base for a generic key management protocol for
LLN application. Key management protocols are also difficult to
design and validate (see [RFC4107] guidelines) providing a further
motivation for reliance on an established protocol like MIKEY that
has had the benefit of wider operational deployment and evaluation.
1.2. MIKEY Key Management Methods Background
As noted in [RFC5197], several key distribution methods have been
described for MIKEY, including:
o Symmetric key distribution as defined in [RFC3830] (MIKEY-PSK)
o Asymmetric key distribution as defined in [RFC3830] (MIKEY-RSA)
o Diffie-Hellman key agreement protected by digital signatures as
defined in [RFC3830] (MIKEY-DHSIGN)
o Diffie-Hellman key agreement protected by symmetric pre-shared
keys as defined in [RFC4650] (MIKEY-DHHMAC)
o Asymmetric key distribution (based on asymmetric encryption) with
in-band certificate provision as defined in [RFC4738]
(MIKEY-RSA-R)
Further extensions to MIKEY comprising algorithm enhancements and new
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payload definitions have since been defined generally motivated by
the specific problems associated with SIP signaling and associated
multimedia use case scenarios (see [RFC5197]for an earlier
assessment). This specification proposes a new extension that is
focused on a new domain of application.
1.3. Adapting MIKEY to General LLNs
This document specifies a set of additional message information
elements to the base MIKEY protocol that provide both algorithm and
message payload extensions. These additions allow the adapted
protocol to be used directly for key transport and security policy
specification between communications generic network entities.
Furthermore, through integration within the base MIKEY specification
it will allow current and future key methods and extensions to be
utilized outside of the current multimedia environment.
The developed protocol adaption includes the specification of
alternative default algorithms (in particular AES-based as widely
available in emerging device hardware) and configurations that are
particular to more constrained communications devices. MIKEY's
general extensibility is also used to define new elements applicable
to the LLN environment.
An important element of the protocol extension is the re-use of the
MIKEY crypto-session structure to apply to individual device
communications protocol layers or interfaces instead of applying to
multimedia streams. By maintaining this base protocol structure and
re-purposing associated message identifiers, the specification
minimizes the protocol changes needed for network adaptation.
As with the original specification the intent is to allow MIKEY
messages to be embedded into existing communications signaling
protocols or to be independently transported between communicating
entities over UDP or TCP transport connections.
Note: While MIKEY and its extensions provide a variety of choices in
terms of modes of operation, implementations for a given LLN
application domain will be able to simplify node behavior by
operating in a single mode. To ensure necessary interoperability
within the LLN environment, mandatory methods within the Adapted
MIKEY protocol (AMIKEY), akin to those of MIKEY, shall be specified.
1.4. Terminology and Definitions
The following definitions have been taken from [RFC3830] with
necessary augmentation for AMIKEY as indicated:
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(Data) Security Protocol
The security protocol used to protect the actual data traffic.
Examples of security protocols are IPsec and SRTP. For generic
LLNs, security protocols may include secure versions of
protocols such as RPL [RFC6550].
Data SA
Data Security Association information for the security
protocol, including a TEK and a set of parameters/policies.
CS Crypto Session, uni- or bidirectional data stream(s) protected
by a single instance of a security protocol. For AMIKEY the
concept of a crypto-session is expanded to allow definition of
a particular protocol layer, logical device interface, or other
communications association for which key management support is
provided.
CSB Crypto Session Bundle, collection of one or more Crypto
Sessions, which can have common TGKs (see below) and security
parameters.
CS ID Crypto Session ID, unique identifier for the CS within a CSB.
For AMIKEY the CS ID is used to identify a specific protocol
layer, logical device interface or other communications
association for which AMIKEY is being used to support key
management (establishment of re-keying update).
CSB ID
Crypto Session Bundle ID, unique identifier for the CSB. For
AMIKEY the CSB ID in conjunction with the Timestamp filed is
used as a unique key management exchange message reference
identifier. This identifier will allow for the acknowledged
key management message exchanges where applicable. The ID plus
timestamp will also support the filtering of repeated or
redundant AMIKEY messages when key management occurs over an
unreliable transport network.
TGK TEK Generation Key, a bit-string agreed upon by two or more
parties, associated with CSB. From the TGK, Traffic-Encrypting
Keys can then be generated without needing further
communication.
TEK Traffic-Encrypting Key, the key used by the security protocol
to protect the CS (this key may be used directly by the
security protocol or may be used to derive further keys
depending on the security protocol). The TEKs are derived from
the CSB's TGK.
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The following definitions have been added to the ones from [RFC3830]
specifically related to supporting AMIKEY:
Key Index
The Key Index (KI) is used as identifier to allow for reference
to the key(s) that are associated with a given CS. Where TEKs
may be updated over time a TGK can be associated with a KI that
is transported as a payload within the AMIKEY message from the
Initiator. Any TEK generated from the AMIKEY TGK shall be
assigned the key index value associated with the TGK. Within
general LLN protocol communications related to a given CS
(device layer protocol or interface), to ensure security
association synchronization reference can be made to the key
index that is being applied for the given protocol security.
Following successfully TGK key establishment communicating
devices can verify security contexts through reference to
maintained KI (see Section 6.16).
Key Source Identifier
The Key Source Identifier (KSI) is used as a logical identifier
to allow for reference to the entity associated with the
origination of a given TGK. Where TEKs are dynamically
generated or updated, each TGK can be associated with a
specific key source. The KSI, when used, is transported as a
payload within the AMIKEY message from the entity responsible
for the TGK origination (see Section 6.17).
1.5. Document Outline
Section 2 provides a brief general system overview of key management
as introduced in MIKEY specification. This section generalizes the
context in which the Adapted MIKEY (AMIKEY) protocol extension is
applied. It also provides a reference to the common key management
operating base of MIKEY and AMIKEY.
Sections 3 to 4 go into further detail by identifying the specific
section and subsection extensions and enhancements needed to support
the MIKEY protocol adaptation. These Sections mirror those of MIKEY
[RFC3830] and are used to show the necessary commonality and make
reference to specific changes would be required for AMIKEY.
Reference is made only to the applicable Sections and Subsections of
[RFC3830] for which special changes are proposed.
Section 6 includes the specific protocol specification elements that
are needed to extend MIKEY for the support of the generic LLN key
management requirements.
The remaining document sections are place-holders for standard RFC
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draft sections.
1.6. Section Headings Notation
This document is written as a delta document to [RFC3830]. For ease
of cross-reference and to maintain consistency with the MIKEY
specification document structure, Section heading and Table and
Figure numbers are maintained consistent with the [RFC3830] usage.
The notation of Section number followed by [RFC3830] "x.x.
[RFC3830]" is used is this document for Sections specifically meant
to align with [RFC3830]. Section numbers followed by [RFC3830] with
additional heading text indicates some new element or clarification
introduced by this specification. Section numbers followed by
[RFC3830] without further heading text implies no change to [RFC3830]
and is used only to align and maintain the current document headings
structure.
The new parameters introduced in this specification are made
consistent with the MIKEY recommendations (see Section 4.2.9
[RFC3830]).
2. AMIKEY Overview
This section provides an overview of AMIKEY. Material from MIKEY
[RFC3830] is also repeated to clearly establish the common context in
which MIKEY can be applied to LLN environments with the simple
extension to the Adapted MIKEY (AMIKEY) specification.
The objective of the AMIKEY extension is exactly the same as that of
MIKEY - "to produce a data security association (SA) for a security
protocol, including a Traffic-Encrypting Key (TEK), which is derived
from a TEK Generation Key (TGK), and used as input for the security
protocol." In the case of AMIKEY the objective is support generic
security protocols and particularly those that may be associated with
LLNs.
AMIKEY uses the specified MIKEY mechanisms and features to "support
the possibility of establishing keys and parameters for more than one
security protocol (or for several instances of the same security
protocol) at the same time." In MIKEY the Crypto Session Bundle
(CSB), which derives from the multimedia (multi-stream) context, is
used to denote this collection of one or more Crypto Sessions that
can have a common TGK and security parameters, but that obtain
distinct TEKs from MIKEY.
In the AMIKEY extension, the concept of CSB is used to provide the
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option of simultaneously establishing multiple SAs on a given device.
The individual Crypto Session (CS) SAs may be associated with
different device layer or device interface security protocols.
AMIKEY further uses the flexibility of the MIKEY specification to
allow separate security policies to be defined in the SA established
for each security protocol. The distribution mechanisms defined by
MIKEY for re-keying and updating of established security associations
is hence also directly applied. The ability to establish and
maintain multiple SAs through a single key management association
provides an important efficiency element in LLN domains.
As specified in [RFC3830], Section 2.3, the procedure of setting up a
CSB and creating a TEK (and Data SA), is done in accordance with
Figure 1:
1. A set of security parameters and TGK(s) are agreed upon for the
Crypto Session Bundle. This is done by one of many alternative
key transport/exchange mechanisms (see [RFC3830], Section 3, as
well as subsequent extension RFCs).
2. The TGK(s) is used to derive (in a cryptographically secure way)
a TEK for each Crypto Session or associated security protocol.
3. The TEK, together with the security protocol parameters,
represent the Data SA, which is used as the input to the security
protocol(s).
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+-----------------+
| CSB |
| Key transport | (see [RFC3830], Section 3)
| /exchange |
+-----------------+
| :
| TGK :
v :
+----------+ :
CS ID ->| TEK | : Security protocol parameters (policies)
|derivation| : (see [RFC3830], Section 4)
+----------+ :
TEK | :
v v
Data SA
|
v
+-------------------+
| Crypto Session |
|(Security Protocol)|
+-------------------+
Figure 1: Overview of MIKEY (and AMIKEY extension) key management
procedure
For generic LLNs that are the focus of this document, the default
algorithms applied in the generation of the TEK for each protocol is
defined within this AMIKEY specification. An additional MIKEY
message extension is also specified to define the security protocol
parameters (policies) for generic LLNs.
Whereas MIKEY CS IDs are associated with multimedia streams and have
no intrinsic designation, in this specification the CS IDs are
assigned values (public or private/vendor-specific) that are used to
identify security protocols associated with specific device protocol
layers or device interfaces.
As considered for the device security model discussed in
[I-D.ietf-roll-security-framework], Section 6.5, Figure 2 provides an
overview of the key management context introduced by the AMIKEY
extension defined in this specification. The multi-protocol key
management capability (through the particular use of the MIKEY CS-
IDs) allows for the efficient, simultaneous management and update of
one or more protocol layer security parameters.
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............................. .............................
: +----------+ : : +----------+ :
: |+--------+| : : |+--------+| :
: || AMIKEY || : AMIKEY : || AMIKEY || :
: || Key |<========================================>| Key || :
: || Mgmt. || Key Exchange (TGK) || Mgmt. || :
: || Entity || : : || Entity || :
: |+--------+| : : |+--------+| :
: | Security | Node i : : Node j | Security | :
: | Services | : : | Services | :
: | Entity | : : | Entity | :
: +----------+ : : +----------+ :
: | : : | :
: | +-----------+: :+-----------+ | :
: | (CSn)+--->| Protocol-n|: :| Protocol-n|<---+(CSn) | :
: | | +-----------+: :+-----------+ | | :
: | | +-----------+ : : +-----------+ | | :
: | (CS7)|->|Application| : : |Application|<-|(CS7) | :
: | | +-----------+ : : +-----------+ | | :
: | | +-----------+ : : +-----------+ | | :
: | (CS4)|->| Transport | : : | Transport |<-|(CS4) | :
: | | +-----------+ : : +-----------+ | | :
: +------| : : |------+ :
: | +-----------+ : : +-----------+ | :
: (CS3)|->| Network | : : | Network |<-|(CS3) :
: | +-----------+ : : +-----------+ | :
: | +-----------+ : : +-----------+ | :
: (CS2)|->| L2 | : : | L2 |<-|(CS2) :
: | +-----------+ : : +-----------+ | :
: | +-----------+ : : +-----------+ | :
: (CS1)+->| L1 | : : | L1 |<-+(CS1) :
: +-----------+ : : +-----------+ :
:...........................: :...........................:
Figure 2: Overview of AMIKEY multi-protocol key management context
As in the base MIKEY specification, the security protocol can either
use the TEK directly, or, if supported, derive further session keys
from the TEK. It is however up to the targeted security protocol and
the associated security policy to define how the TEK is used.
MIKEY can be used to update TEKs and the Crypto Sessions in a current
Crypto Session Bundle (see [RFC3830], Section 4.5). This is done by
executing the transport/exchange phase once again to obtain a new TGK
(and consequently derive new TEKs) or to update some other specific
CS parameters.
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3. AMIKEY Key Management Signaling
The following subsections detail the proposed additions to the MIKEY
specification [RFC3830] to support the AMIKEY extension.
The MIKEY defined key management modes consist of a single (or half)
round trip signaling exchange between network peers. In conjunction
with the peer-to-peer modes, AMIKEY incorporates support for client-
server infrastructures while retaining the maximum single round trip
key signaling exchange.
For AMIKEY, a client device may request a key assignment or update by
sending a request message (Q_MESSAGE) to a key management server
(KMS). The request message is protected by a pre-shared secret or a
public key. The server initiates the key assignment and completes
the exchange by sending a key Initiator message (I_MESSAGE)
correspondingly protected by a pre-shared secret or a public key.
Mutual authentication and key assignment confirmation is achieved at
the requesting device upon receipt of the Initiator message. This
signaling mode is shown in Figure 3.
Key Assignment Key
Initiator ReQuestor
+-----+ +------+
| I | | Q |
+-----+ +------+
Q_MESSAGE
<-----------------------------------------
I_MESSAGE
----------------------------------------->
Figure 3: (Client) requested key assignment
A KMS may also autonomously initiate a key assignment or update by
sending a key Initiator message (I_MESSAGE) to a client, protected by
a pre-shared secret or a public key. As dictated by the KMS, a key
response message (R_MESSAGE) is returned by the key client
(Responder) where mutual authentication and assignment confirmation
is required. This key management signaling mode is shown in
Figure 4.
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Key Assignment Key
Initiator Responder
+-----+ +------+
| I | | R |
+-----+ +------+
I_MESSAGE
----------------------------------------->
[Optional] R_MESSAGE
<-----------------------------------------
Figure 4: (Server) initiated key assignment
As shown, the AMIKEY message flows will typically consist of a
request followed by a response in the form on a Requestor-Initiator
or Initiator-Responder exchange. It is the responsibility of the
Requestor or the Initiator, respectively to ensure reliability of the
key assignment signaling exchange. If a response is not received
within a timeout interval the Requestor/Initiator needs to retransmit
the request or abandon the connection. The timeout interval and the
number of retries before a connection is abandoned shall be
implementation defined according to the particular network
application.
3.1. Pre-shared key
The AMIKEY signaling flow and message information content for the
Pre-shared key (PSK) method is as shown in Figure 5 below, in which
"[]" indicates optional messages or elements:
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Requestor
Q_MESSAGE =
[<---] HDR, T, [IDq], V
Initiator Responder
I_MESSAGE =
HDR, T, RAND, [IDi],[IDr],
{SP}, KEMAC --->
R_MESSAGE =
[<---] HDR, T, [IDr], V
Figure 5: Signaling exchange and message content for the PSK method
The format of the AMIKEY pre-shared key Requestor message (Q_MESSAGE)
will follow that of the standard MIKEY Initiator and Responder
messages (I_MESSAGE and R_MESSAGE, respectively). Beyond the header
(HDR) and Timestamp (T) information elements, the message will
include the Identity of the Requestor IDq and the message
verification, V. The entire message SHALL be authenticated by V and
sent in cleartext. The Requestor IDq MAY be left out only when it
can be expected that the peer already knows the other party's ID
(otherwise it cannot look up the pre-shared key). For example, this
could be the case if the ID can be extracted from the signaling
protocol in which the key management message is embedded.
The Initiator's message securely transports one or more TGKs (carried
in the KEMAC) and a set of security parameters (SPs) to the Responder
using the pre-shared key to protect the message and its sub-payloads.
The Responder message MAY be sent in response to a key assignment
initiated by the Initiator I_MESSAGE. Since the verification message
V from the Responder is optional, the Initiator indicates in the HDR
whether it requires a verification message or not from the Responder.
The verification message, V, is a MAC computed over the Responder's
entire message, the timestamp (the same as the one that was included
in the Initiator's message), and the two parties identities, using
the authentication key. See [RFC3830] Section 5.2 for the exact
definition of the Verification MAC calculation and [RFC3830] Section
6.9 for payload definition.
The Initiator message SHALL indicate that the Responder message is
not required when a Requestor message has been used to initiate the
key exchange. In that case mutual authentication will be provided
through the Initiator message sent in response to the triggering
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Requestor message.
Where the key assignment is triggered by the AMIKEY Requestor
message, the timestamp, T, of the Initiator message shall be the same
as the one that was included in the Requestor's message. The CS ID
map info of the Requestor message HDR will specify the requested
protocol key(s) to be assigned (see Section 6.1).
For AMIKEY the pre-shared key method is mandatory to implement.
3.2. Public-Key Encryption
For the public-key encryption method, the signaling exchange and
message content is similar to that of the PSK case as shown in
Figure 6 below:
Requestor
Q_MESSAGE =
[<---] HDR, T, [IDq|CERTq], SIGNq
Initiator Responder
I_MESSAGE =
HDR, T, RAND, [IDi|CERTi],
[IDr], (SP), KEMAC,
[CHASH], PKE, SIGNi --->
R_MESSAGE =
[<---] HDR, T, [IDr], V
Figure 6: Signaling exchange and message content for the PK method
The AMIKEY public key Requestor message follows the standard MIKEY
format. Beyond the header (HDR) and Timestamp (T) information
elements, the message may include the Identity or Certificate of the
Requestor [IDq|CERTq] and a message Signature, SIGNq. The SIGNq is a
signature covering the entire Requestor's AMIKEY message, Q_MESSAGE,
using the Requestor's (private) signature key (see Section 5.2
[RFC3830] for the exact definition of the Signature calculation).
The message SHALL be sent in cleartext, authenticated by the
signature.
The Requestor IDq and certificate SHOULD be included, but the CERTq
MAY be left out when it can be expected that the peer can obtain the
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certificate in some other manner from the Requestor ID. The ID may
be left out when it can be expected that the peer already knows the
other party's ID.
The Initiator's message securely transports one or more TGKs and a
set of security parameters to the Responder. This is done using an
envelope approach where the TGKs are encrypted (and integrity
protected) with keys derived from a randomly/pseudo-randomly chosen
"envelope key". The envelope key is sent to the Responder encrypted
with the public key of the Responder.
Where the key assignment is triggered by the Requestor message, the
timestamp, T, of the Initiator message shall be the same as the one
that was included in the Requestor's message. As for the PSK method,
the CS ID map info of the Requestor message HDR will specify the
requested protocol key(s) to be assigned (see Section 6.1).
The Responder message MAY be sent in response to a key assignment
initiated by the Initiator I_MESSAGE. The indication of the
requirement to send the Responder verification message V as well as
its calculation shall be the same as in the pre-shared key mode. The
timestamp in a Responder message will be the same as the one that was
included in the Initiator message.
The Initiator message SHALL indicate that the Responder message is
not required when a Requestor message has been used to initiate the
key exchange.
For AMIKEY the public key method is mandatory to implement.
3.3. [RFC3830] Diffie-Hellman Key Exchange
For the Diffie-Hellman key exchange method, the peer-to-peer
association in which both devices contribute equally to the key
generation will be the same as given in [RFC3830] even with a key
client-server network infrastructure.
For AMIKEY this method is optional to implement.
3.4. Example of AMIKEY Applied to RPL
The following sub-sections provide examples of how AMIKEY can be used
to support key management for the RPL routing protocol [RFC6550].
3.4.1. AMIKEY Key Assignment for RPL Join Process
The process of a node joining a secured RPL instance is described in
Section 10.2 of the RPL specification [RFC6550]. Where the DODAG
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operates in "authenticated mode", as indicated by the "A" bit being
set in the DODAG Configuration option of the DIO messages, a joining
node is required to access a key server to obtain the current key for
securing RPL messages. AMIKEY is intended to support the
requirements of the key management protocol that allows RPL nodes to
be able to obtain (and receive) the dynamic DODAG security key (see
Section 3.2.3 of [RFC6550]). For AMIKEY, the security of the key
management protocol exchanges between the nodes and the key server
may be based on a pre-shared key (PSK), public key (PKE) or Diffie-
Hellman (DH) method as described in Section 3.
Figure 7 illustrates how AMIKEY may be employed to obtain the DODAG
security key. The figure depicts how the joining node uses AMIKEY to
request the DODAG key when a pre-shared key is used for securing the
key management exchange with the key server.
Joining Node RPL Router Key Server
| | |
| 1. Secure DIS (KI=0) | |
|----------------------------->| |
| | |
| 2. Secure DIO (KI=0,"A"bit set) |
|<-----------------------------| |
| | |
| |
| 3. AMIKEY: Q_MESSAGE (HDR, T, IDq, V) |
|========================================================>|
| 4. AMIKEY: I_MESSAGE (HDR, T, RAND, IDi, {SP}, KEMAC) |
|<========================================================|
| |
|
| 5. Secure DIS (KI=n) |
|----------------------------->|
| |
| 6. Secure DIO (KI=n) |
|<-----------------------------|
| |
Figure 7: Key Assignment with AMIKEY in the RPL Join Process
1. A joining node broadcasts a RPL Secure DIS message to request DIO
information for joining the DODAG. The DIS message is secured
using the pre-installed key (see [RFC6550], Section 3.2.3). The
secure DIS message security header includes the Key Index, KI=0,
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that references the pre-installed key used to secure the message.
2. An existing DODAG RPL node responds with a secure DIO message
that is similarly secured with the pre-installed key, even where
that key differs from the DODAG RPL security key being used by
nodes that have joined the DODAG (see [RFC6550], Section 10.2).
This initial DIS/DIO exchange allows the joining node to operate
as a leaf node and forward data traffic into the network without
being part of the secure routing exchange.
3. Based on the A-bit being set within the Secure DIO message, the
joining node uses its leaf node network access to initiate the
key request to the key server to request the current DODAG
security key; the joining node does this by sending an AMIKEY key
request (Q_MESSAGE) to the key server (see Section 3). In the
example in Figure 7 the Q_MESSAGE is secured based on the pre-
shared key maintained between the joining node and the key
server. The verification field (V) authenticates the message
sent by the requesting node (see Section 4.2.4).
4. The key server responds to the request by assigning the current
DODAG key within the I_MESSAGE (see Section 3.1). Like the
Q_MESSAGE, the I_MESSAGE is secured based on the pre-shared key
maintained between the joining node and the key server. The T
field included in the I_MESSAGE is the same as that sent by the
key requesting node in the Q_MESSAGE. This field in the form of
a timestamp or counter allows for replay protection (and
timeliness verification if network-wide time is supported in the
DODAG). The KEMAC information element includes the DODAG key
material assigned by the key server encrypted using the pre-
shared key maintained between the joining node and the key
server.
5. The assigned DODAG key (given by Key Index=n in the message
security header) is used to secure the subsequent secure DIS
message.
6. Once the secure DIS message is authenticated by the receiver a
secure DIO message (with KI=n) is returned. That message
provides current DODAG routing information and allows the joining
node to be a full RPL participant of the secure DODAG.
The particular information elements of the AMIKEY Q_MESSAGE include:
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HDR Header (common AMIKEY header)
T Timestamp/counter
IDq ID of the requestor (joining node)
V Message verification
The particular information elements of the AMIKEY I_MESSAGE include:
HDR Header
T Timestamp/counter
RAND A (pseudo-)random bit-string used for generating the DODAG
security key (using AMIKEY, the RPL DODAG key is generated from
the key assigned by the key server)
IDi ID of the assignment initiator (key server)
SP Security Policy that defines the policy information of the
secure RPL protocol for which the key assignment is being made
KEMAC Key data transport payload that includes the assigned key
generating key from which the RPL DODAG security key is derived
Note: In conjunction with RPL, AMIKEY can also be applied to support
proactive key assignment/update by the key server using an I_MESSAGE
and R_MESSAGE exchange as discussed in Section 3.
3.4.2. AMIKEY Key Update for RPL Authenticated Mode
The RPL security key for a DODAG operating in authenticated mode may
be updated one or more times during the lifetime of the DODAG. Such
key updates are initiated by the key server and pushed to individual
RPL nodes using the AMIKEY protocol.
Figure 8 illustrates how AMIKEY is employed for the key update. The
scenario assumes a pre-shared key (PSK) for securing the key
management exchange between the RPL nodes and the key server. Public
key encryption (PKE) or Diffie-Hellman (DH) methods may also be used
as described in Section 3.
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RPL Node i RPL Node j Key Server
| | |
| 1. Secure DIO | |
| (KI=n,"A"bit set) | |
|------------------------->| |
| | |
| 2. Secure DAO (KI=n) | |
|<-------------------------| |
| | |
| 3. Secure DAO ACK (KI=n) | |
|------------------------->| |
~ ~ |
~ ~ |
| |
| 4a. AMIKEY: I_MESSAGE (HDR,T,RAND,IDi,{SP},KEMAC) |
|<===========================================================|
| |
| 5a. AMIKEY: R_MESSAGE (HDR,T,IDr V) |
|===========================================================>|
| |
| | 4b. AMIKEY: I_MESSAGE |
| | (HDR,T,RAND,IDi,{SP},KEMAC) |
| |<================================|
| | 5b. AMIKEY: R_MESSAGE |
| | (HDR,T,IDr V) |
| |================================>|
~ ~
~ ~
| |
| 6. Secure DIO |
| (KI=n+1,"A"bit set) |
|------------------------->|
| |
| 7. Secure DAO (KI=n+1) |
|<-------------------------|
| |
| 8. Secure DAO ACK |
| (KI=n+1) |
|------------------------->|
| |
Figure 8: Key Update during RPL Operation Using AMIKEY
1. An operating RPL node (Node i) transmits a Secure DIO message
providing information on its DODAG routing connectivity. The DIO
message is secured using the current DODAG security key indicated
by the inclusion of the Key Index, KI=n, within the message
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security header.
2. In response to the DIO message the RPL routing peer (Node j)
sends a Secure DAO message to establish/maintain its routing
connectivity. The DAO message is secured with the current DODAG
security key indicated by the inclusion of KI=n within the
message security header.
3. The RPL node receiving the DAO message may acknowledge receipt of
the message by sending a Secure DAO ACK message, also secured by
the current DODAG key.
4. The key server can choose at any time to update the current DODAG
key by making a new key assignment to each network node. The new
key is encrypted within the KEMAC information element of the
I_MESSAGE (see Section 3.1). In this example the I_MESSAGE is
secured based on the pre-shared key maintained between each node
and the key server. The T field included in the I_MESSAGE, in
the form of a timestamp or counter allows for replay protection
(and timeliness verification if network-wide time is supported).
5. The key assignment is acknowledged by the receiving node through
the sending of the R_MESSAGE (see Section 3). The requirement
for the sending of the R_MESSAGE is specified through the setting
of the V-bit flag in the I_MESSAGE Header (HDR). For replay
protection and timeliness verification on the part of the key
server, the T field included in the R_MESSAGE, is copied and
repeated from the I_MESSAGE. The verification field (V)
authenticates the message sent by the responding node using the
node-key server pre-shared secret.
6. The updated DODAG key, indicated by the Key Index=n+1 in the
message security header, is used to secure the subsequent
transmitted Secure DIO messages.
7. Following the key update the Secure DAO messages also use the
newly assigned key (indicated by KI=n+1 in the message security
header).
8. Any Secure DAO ACK messages are similarly protected using the
newly assigned key.
The particular information elements of the AMIKEY I_MESSAGE include:
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HDR Header (common AMIKEY header)
T Timestamp/counter
RAND A (pseudo-)random bit-string used for generating the DODAG
security key (using AMIKEY, the RPL DODAG key is generated from
the key assigned by the key server).
IDi ID of the assignment initiator (key server)
SP Security Policy that defines the policy information of the
secure RPL protocol for which the key assignment is being made
KEMAC Key data transport payload that includes the assigned key
generating key from which the RPL DODAG security key is derived
The particular information elements of the AMIKEY R_MESSAGE include:
HDR Header
T Timestamp/counter
IDr ID of the responder (RPL node)
V Message verification
Note: In an ad hoc network there is the potential for nodes that have
received a DODAG key update to initiate routing exchanges with nodes
that have not yet received the update. This situation will be
detected by the mis-match between the node's maintained DODAG key
index and that of its corresponding peer. Where a received RPL
message is secured by a key different from that maintained by the
recipient node it will not be possible to verify the authenticity or
validity of the message. To avoid potential denial of service
attacks from forged or purported Secure RPL messages, a RPL node
should silently discard such messages if it has not received an
updated key. One consequence is the potential for broken RPL
associations when the key update is not sufficiently synchronized
across the DODAG. A key activation time can be used to limit the
potential for such routing disruptions during the key update. The
Key Activation time in the form of a UTC clock time or future count
can be specified through the AMIKEY Key Validity information element
(see [RFC3830] Key data sub-payload, Section 6.13).
A node recovering from reset and receiving Secure DIO messages with a
Key Index different from the one currently maintained can revert its
status to a non-routing (leaf) node. The node can then initiate an
AMIKEY key request to the key server to obtain the current DODAG key.
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4. [RFC3830] Selected Key Management Functions
For AMIKEY all the key derivation functionality defined in MIKEY
shall be based on a new default Pseudo-Random Function (PRF) given by
the AES-based, AES-CMAC algorithm as specified in [RFC4493].
4.1. [RFC3830] Key Calculation
4.1.1. [RFC3830] Assumptions
For AMIKEY cs_id is defined so that session represents a protocol
layer, logical device interface, or communications association. The
cs-id values shall be as defined in this specification (see
Section 6.1.2) and may be public or private/vendor-specific.
4.1.2. Default PRF Description
For AMIKEY the default pseudo random function shall be AES-CMAC
[RFC4493]. Note: AES-CMAC aligns with HMAC-SHA1 and HMAC-MD5 as
PRFs.
4.1.3. [RFC3830] Generating Keys from TGK
For AMIKEY the cs-id values shall be as defined in this specification
(see Section 6.1.2).
4.1.4. [RFC3830] Generating Keys for MIKEY Messages from an Envelope/
Pre-shared Key
Change from default PRF to the default AMIKEY PRF given in
Section 4.1.2 of this specification.
Note: For AMIKEY, the Authentication key constant SHALL be used for
generating the single TEK in the case of authenticated encryption
algorithms (such as AES-CCM).
4.2. [RFC3830] Pre-defined Transforms and Timestamp Formats
4.2.1. Hash Functions
For AMIKEY the default hash function shall be AES-CMAC [RFC4493].
4.2.2. Pseudo-Random Number Generator
For AMIKEY it shall be MANDATORY to implement the new default AES-
CMAC PRF specified in [RFC4493] (See Section 4.1.2 of this
specification).
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4.2.3. [RFC3830] Key Data Transport Encryption
As in MIKEY the default and mandatory-to-implement key transport
encryption shall be AES in Counter mode using a 128-bit key (derived
as defined in Section 4.1.4 above). The applied Counter shall be the
IV defined in [RFC3830], Section 4.2.3.
4.2.4. [RFC3830] MAC Verification Message Function
For AMIKEY AES-CCM-64 shall be the defined default for key message
authentication. The Counter used shall be the IV defined in
[RFC3830], Section 4.2.3.
4.3. [RFC3830] Certificates, Policies and Authorization
4.4. [RFC3830] Retrieving the Data SA
For AMIKEY the retrieval of a Data SA will depend on the security
protocol. The support for different security protocols shall be
explicitly identified through the use of public CS ID values (see
Section 6.1.2 of this specification).
5. [RFC3830] Behavior and Message Handling
5.1. [RFC3830] General
5.2. [RFC3830] Creating a message
For AMIKEY where the key exchange is triggered by a Requestor, the
messages from the Requestor MUST use a unique timestamp. The
Initiator does not create a new timestamp but uses the timestamp used
by the Requestor.
When the key exchange is not triggered by a Requestor, the messages
from the Initiator MUST use a unique timestamp. The Responder does
not create a new timestamp, but uses the timestamp used by the
Initiator.
6. [RFC3830] Payload Encoding
The generic LLN security protocol parameters may be transported
between peers as part of a key establishment or re-keying exchange.
Based on IANA registration, MIKEY currently only defines two payloads
for transporting the security policy information (see Section 6.10 of
[RFC3830] and [RFC4442]). This section describes the extension of
MIKEY to allow the transport of Generic LLN security policy
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information and associated key(s) as well as applicable PRF used for
key derivation.
This section describes, in detail, the payload for support of the
Generic LLN security protocol(s) specified by the Adapted MIKEY
protocol. As in RFC3830, for all encoding, network byte order is
always used, and the sign ~ indicates a variable length field.
6.1. [RFC3830] Common Header Payload (HDR)
The Common Header payload MUST always be present as the first payload
in each message. The Common Header includes a general description of
the exchange message.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! version ! data type ! next payload !V! PRF func !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! CSB ID !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! #CS ! CS ID map type! CS ID map info ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9: Common Header [RFC3830]
o version (8 bits): the version number of MIKEY.
o version = 0x01 refers to MIKEY as defined and maintained in
[RFC3830].
o version = 0x03 (to be assigned by IANA) shall be used to refer to
AMIKEY as defined and maintained in this document.
o data type (8 bits): describes the type of message (e.g., public-
key transport message, verification message, error message). See
latest IANA registered values. For AMIKEY new data type values
are used to specify the additional PSK and PK method Requestor
messages (to be assigned by IANA).
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+-------------+-------+---------------------------------------------+
| Data Type | Value | Comment |
+-------------+-------+---------------------------------------------+
| PSK Request | i | Requestor's pre-shared key message (AMIKEY) |
| PK Request | j | Requestor's public key message (AMIKEY) |
+-------------+-------+---------------------------------------------+
Table 6.1.a
o next payload (8 bits): identifies the payload that is added after
this payload. See latest IANA registered values.
For AMIKEY a new next payload value is assigned to carry the Key
Index parameter (see also Section 6.16).
+----------+-------+------------------------------------------------+
| Next | Value | Section |
| Payload | | |
+----------+-------+------------------------------------------------+
| Last | 0 | - |
| payload | | |
| ... | | |
| Key | n | Section 6.16 as given by the AMIKEY |
| Index | | specification (value to be assigned by IANA). |
| Key | m | Section 6.17 as given by the AMIKEY |
| Source | | specification (value to be assigned by IANA) |
| ID | | |
+----------+-------+------------------------------------------------+
Table 6.1.b
o V (1 bit): flag to indicate whether a verification message is
expected or not (this only has meaning when it is set by the
Initiator).
o PRF func (7 bits): indicates the PRF function that has been/will
be used for key derivation; for AMIKEY a new value, 2, has been
specified to indicate the PRF that must be supported for LLNs.
+-----------+-------+-----------------------------------------------+
| PRF | Value | Comments |
| Function | | |
+-----------+-------+-----------------------------------------------+
| AES-CMAC | 2 | As specified in [RFC4493] and that shall be |
| | | mandatory for AMIKEY |
+-----------+-------+-----------------------------------------------+
Table 6.1.c
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(AMIKEY value to be assigned by IANA)
o CSB ID (32 bits): identifies the CSB (generated as specified in
[RFC3830]); for AMIKEY this field is used as a message reference
identifier to allow for duplicate detection where message
exchanges occur over an unreliable transport network.
o #CS (8 bits): indicates the number of Crypto Sessions that will be
handled within the CBS; for AMIKEY this field indicates the number
of protocol layers, logical device interfaces, or other
communications associations that are being configured or managed
within the current key management message exchange.
o CS ID map type (8 bits): specifies the method of uniquely mapping.
Crypto Sessions to the security protocol sessions; for AMIKEY a
new value, 3, has been specified to indicate the Generic-LLN map
type that must be supported for LLNs.
+----------------+-------+------------------------------------------+
| CS ID Map Type | Value | Comments |
+----------------+-------+------------------------------------------+
| Generic_LLN-ID | 3 | As specified in this document and as |
| | | mandatory for AMIKEY |
+----------------+-------+------------------------------------------+
Table 6.1.d
(AMIKEY value to be assigned by IANA)
o CS ID map info (variable length): identifies the crypto session(s)
for which the SA should be created. For AMIKEY the GENERIC_LLN
map type (defined in Section 6.1.2 below) is used to specify the
security association for the individual protocol layers, logical
device interfaces, or other communications associations for which
key management is being provided.
6.1.1. [RFC3830] SRTP ID
6.1.2. The Generic_LLN-ID Map Type
For the Generic_LLN map type, the CS ID map info consists of #CS (see
Section 6.1) number of blocks or segments, where each segment maps
policies (and a key) to a specific protocol layer, logical device
interface or other communications association security protocol.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! CS ID ! #P ! Ps (OPTIONAL) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10: Generic_LLN-ID Map Type
o CS ID (8 bits): specifies the CS ID used to identify a given
security protocol; for AMIKEY, when used in conjunction with the
Generic-LLN map type, values 0-127 shall be reserved for
assignment (by IANA) to specific protocol layer, logical device
interface, or other communications association security protocols
while values 128-255 shall be Reserved for Private Use.
Note: A combination of public and private CS IDs can be specified
within a given CSB when combined key management is being applied.
The following values are currently specified in this document (for
example, with values to be assigned by IANA):
+---------------------------+---------+--------------------------+
| CS ID | Value | Comments |
+---------------------------+---------+--------------------------+
| Reserved | 0 | |
| Generic PHY Layer | 1 | |
| Generic Link Layer | 2 | |
| Generic Network Layer | 3 | |
| Generic Transport Layer | 4 | |
| Generic Application Layer | 7 | |
| RPL Protocol | 20 | |
| ... | | |
| Reserved values | 128-255 | Reserved for private use |
+---------------------------+---------+--------------------------+
Table 6.1.e
o #P (8 bits): indicates the number of security policies provided
for the crypto session (given by the CS ID) for which key
management is being provided. In response messages, #P SHALL
always be exactly 1. So if #P = 0 in an initial message, a
security profile MUST be provided in the response message. If #P
> 0, one of the suggested policies SHOULD be chosen in the
response message. If needed, the suggested policies MAY be
changed.
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o Ps (variable length): lists the policies for the crypto session
for which key management is being provided. It SHALL contain
exactly #P policies, each having the specified Prot type (see
Section 6.10.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Policy_no_i ! Policy_no_n ! ... ! Policy_no_#P !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 11: Policies
o Policy_no_i (8 bits): a policy_no that corresponds to the
policy_no of a SP payload. In response messages, the policy_no
may refer to a SP payload in the initial message. The policy
numbers should be listed in increasing order.
6.2. [RFC3830] Key Data Transport Payload (KEMAC)
This section shall apply entirely as specified for MIKEY in [RFC3830]
with the addition of the specific message authentication code
algorithms given below for AMIKEY.
o MAC alg (8 bits): specifies the authentication algorithm used.
+------------------+-------+----------------------------+-----------+
| MAC alg | Value | Comments | Length |
| | | | (bits) |
+------------------+-------+----------------------------+-----------+
| NULL | 0 | restricted usage | 0 |
| | | [RFC3830], Section 4.2.4 | |
| HMAC-SHA-1-160 | 1 | Mandatory, [RFC3830], | 160 |
| | | Section 4.2.4 | |
| HMAC-SHA-256-256 | 2 | Mandatory, [RFC3830], | 256 |
| | | Section 4.2.4 | |
| AES-CBC-MAC-32 | 3 | Mandatory for AMIKEY, see | 32 |
| | | Section 4.2.4 | |
| AES-CBC-MAC-64 | 4 | Mandatory for AMIKEY, see | 64 |
| | | Section 4.2.4 | |
| AES-CBC-MAC-128 | 5 | Mandatory for AMIKEY, see | 128 |
| | | Section 4.2.4 | |
+------------------+-------+----------------------------+-----------+
Table 6.2.b
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(Values for AMIKEY to be assigned by IANA)
o MAC (variable length): the message authentication code of the
entire message.
For AMIKEY the use of AES-CBC-MAC-n may be applied in conjunction
with the AES-CM encryption as given by the Encr alg field. This
authenticated encryption shall be applied using an AES-CCM-n
implementation.
6.3. [RFC3830] Envelope Data Payload (PKE)
6.4. [RFC3830] DH Data Payload (DH)
6.5. [RFC3830] Signature Payload (SIGN)
6.6. [RFC3830] Timestamp Payload (T)
6.7. ID Payload (ID)
For AMIKEY the range of ID types shall be extended to allow for an
expanded array of communications protocol entities that may be key
management participants. The IDs are carried within the key
management message ID payload field with the TLV format as specified
in [RFC3830], Section 6.7.
+--------------------+-------+-------------------------+
| ID Type | Value | Comments |
+--------------------+-------+-------------------------+
| IPv6 Address | 4 | As specified for AMIKEY |
| Device MAC Address | 5 | As specified for AMIKEY |
| Other (TBD) | n | As specified for AMIKEY |
+--------------------+-------+-------------------------+
Table 6.7.a
The IPv6 Address ID type is used to allow an IPv6 Address to be
referenced as the unique entity identifier of the key management
correspondents. To directly reference the IPv6 Address of the
exchanged packets, the ID len value will be set to zero and no ID
data included in the value field (see [RFC3830]).
The Device MAC Address is used to allow an IEEE 48-bit MAC address to
be referenced as the unique entity identifier for correspondents in a
key management exchange. To directly reference the MAC Address of
the exchanged packets, where the IPv6 address has been derived from
the device MAC address in conformance with [RFC4291] the ID len value
will be set to zero and no ID data included in the value field (see
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[RFC3830]).
Note: The ID payload may be used by a supported security protocol as
implicit Key Source Identifier (see Section 6.17) for referencing key
origination.
6.8. [RFC3830] Cert Hash Payload (CHASH)
6.9. [RFC3830] Ver msg payload (V)
6.10. Security Policy (SP) Payload
The Security Policy payload defines a set of policies that apply to a
specific security protocol.
For AMIKEY the definition is based on the same security policy
payload definition in [RFC3830], Section 6.10, with a new security
protocol (Generic-LLN) as defined below.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Next payload ! Policy no ! Prot type ! Policy param ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ length (cont) ! Policy param ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
o Next payload (8 bits): Identifies the payload that is added after
this payload. See Section 6.1 of [RFC3830] for more details.
o Policy no (8 bits): Each security policy payload must be given a
distinct number for the current MIKEY session by the local peer.
This number is used to map a cryptographic session to a specific
policy (see also Section 6.1.1 of [RFC3830]).
o Prot type (8 bits): This value defines the security protocol; For
AMIKEY an additional value shall be assigned as given below.
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+-------------+-------+-------------------------+
| Prot Type | Value | Comments |
+-------------+-------+-------------------------+
| Generic_LLN | 3 | As specified for AMIKEY |
+-------------+-------+-------------------------+
Table 6.10
o Policy param length (16 bits): This field defines the total length
of the policy parameters for the selected security protocol.
o Policy param (variable length): This field defines the policy for
the specific security protocol. The Policy param part is built up
by a set of Type/Length/Value (TLV) payloads. For each security
protocol, a set of possible type/value pairs can be negotiated as
defined.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Type ! Length ! Value ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 12: Policy Parameter
o Type (8 bits): Specifies the type of the parameter.
o Length (8 bits): Specifies the length of the Value field (in
bytes).
o Value (variable length): Specifies the value of the parameter.
6.10.1. [RFC3830] SRTP Policy
6.10.2. AMIKEY Generic_LLN Policy
This policy specifies the parameters for the Generic_LLN (G_LLN)
protocol for which key management is being provided. The types/
values that can be negotiated are defined by the following table for
the known, assigned CS ID values. For Vendor-specific, private CS ID
values the applicable policy specification for a given crypto session
will be left to the communicating parties.
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+------+---------------------------+------------------------+
| Type | Meaning | Possible Values |
+------+---------------------------+------------------------+
| 0 | Encryption algorithm | See below |
| 1 | Encryption key length | Depends on cipher used |
| 2 | Authentication algorithm | See below |
| 3 | Authentication key length | Depends on MAC used |
| 4 | Generic LLN PRF | See below |
| 5 | Encryption off/on | 0 if off, 1 if on |
+------+---------------------------+------------------------+
Table 6.10.2.a
For the Encryption algorithm, a one byte length is sufficient. For
AMIKEY the currently defined possible Values are:
+----------------+-------+
| G_LLN encr alg | Value |
+----------------+-------+
| NULL | 0 |
| AES-CM-128 | 1 |
+----------------+-------+
Table 6.10.2.b
For the Authentication algorithm, a one byte length is sufficient.
For AMIKEY the currently defined possible Values are:
+-----------------+-------+-------------------------------------+
| G_LLN auth alg | Value | Comments |
+-----------------+-------+-------------------------------------+
| NULL | 0 | Not recommended for operational use |
| AES-CBC-MAC-32 | 1 | |
| AES-CBC-MAC-64 | 2 | |
| AES-CBC-MAC-128 | 3 | |
| RSA-SHA-256 Sig | 4 | |
+-----------------+-------+-------------------------------------+
Table 6.10.2.c
Note: Since authentication is mandatory for operational protocol
security, where Encryption is set "on" by the Generic_LLN policy,
authenticated encryption, AES-CCM-n, with the MAC size given by the
selected authentication algorithm, or AES-CM with authentication
given by the identified Signature algorithm, shall be applied.
For the Generic_LLN pseudo-random function, a one byte length is also
sufficient. For AMIKEY the currently defined possible Values are:
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+-----------------+-------+
| Generic_LLN PRF | Value |
+-----------------+-------+
| AES-CMAC | 0 |
+-----------------+-------+
Table 6.10.2.d
6.11. [RFC3830] RAND Payload (RAND)
6.12. [RFC3830] Error Payload (ERR)
6.13. [RFC3830] Key Data Sub-Payload
For AMIKEY, the key validity (KV) period for a TGK/TEK shall be
specified using the KV Interval type indicating a potential key start
and expiration time (see Section 6.14).
6.14. [RFC3830] Key Validity Data
For AMIKEY the Key Validity Data element shall be used to specify the
activation time and validity period of an assigned TGK.
For AMIKEY, the key validity (KV) period for a TGK/TEK shall be
specified using the KV Interval type (see [RFC3830] Section 6.13).
The corresponding Valid From (VF) and Valid To (VT) information
elements that define the applicable key lifetime may be specified
using the Timestamp Counter type to specify time in seconds from the
time given by included key message timestamp (T). A VF Length of
zero (indicating Counter value of 0) specifies an immediate key
activation time. A VT Counter value of all 1s indicates infinite key
validity or no expiration time.
6.15. [RFC3830] General Extension Payload
6.16. Key Index Payload
For AMIKEY the Key Index (KI) payload is used to specify the value of
the key index associated with a given TGK.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Next Payload ! KI len ! KI value (variable) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 13: Key Index
o Next payload (8 bits): identifies the payload that is added after
this payload. See Section 6.1 [RFC3830] for values.
o KI len (8 bits): indicates the length of the key source identifier
field.
o KI value (variable length): indicates the value of the key index
to be assigned to any CS TEK generated from the transported TGK.
6.17. Key Source Identifier Payload
For AMIKEY, where an explicit reference is required, the Key Source
Identifier payload is used to provide a logical reference to the
entity associated with the origination of a given TGK. The
specification of the Key Source Identifier (KSI) shall be given by
the supported security protocol (for example, the secured RPL routing
protocol [RFC6550] specifies the use of an 8-byte KSI).
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Next Payload ! KSI len ! KSI value (variable) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 14: Key Source Identifier
o Next payload (8 bits): identifies the payload that is added after
this payload. See Section 6.1 [RFC3830] for values.
o KSI len (8 bits): indicates the length of the key source
identifier field.
o KSI value (variable length): specifies the logical identifier
assigned to the Source or Originator of a given TGK.
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7. [RFC3830] Transport Protocols
As in [RFC3830], AMIKEY may be integrated within session
establishment or other system signaling protocols or may be directly
transported over UDP or TCP. Where AMIKEY messages are integrated
into other LLN-related signaling protocols its transport shall be
defined as part of those protocols.
8. Security Considerations
A primary motivation for this RFC is the security that comes from a
re-use of the key management methods and framework developed for
MIKEY. The extensive deployment and on-going development provides
the benefit of much wider vetting and validation essential to
assuring greater security.
9. [RFC3830] Groups
10. Additional Specification Considerations
Work had been previously initiated in developing support for an ECC-
based asymmetric key management method ([I-D.ietf-msec-mikey-ecc],
expired). In the context of LLNs application and subject to IPR
considerations, related AMIKEY requirements may be developed.
11. IANA Considerations
This document defines several new name spaces associated with the
AMIKEY payloads. This section summarizes the name spaces for which
IANA is requested to manage the allocation of values. IANA is
requested to record the pre-defined values defined in the given
sections for each name space. IANA is also requested to manage the
definition of additional values in the future. Unless explicitly
stated otherwise, values in the range 0-240 for each name space
SHOULD be approved by the process of IETF consensus and values in the
range 241-255 are reserved for Private Use, according to [RFC5226].
The name spaces for the new fields identified in this document are
requested to be managed by IANA (in bracket is the reference to the
table with the initially registered values):
o Common Header payload (6.1.)
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* Version
o Data type (6.1.a)
* AMIKEY PSK Request msg
* AMIKEY PK Request msg
o Next payload (6.1.b)
* Key index
* Key source identifier
o Prf func (6.1.c)
* AES-CMAC
o CS ID map type (6.1.d)
* Generic_LLN-ID
o MAC alg (6.2.b)
* AES-CBC-MAC-32
* AES-CBC-MAC-64
* AES-CBC-MAC-128
o ID payload (6.7.a)
* IPv6 Address
* Device MAC Address
o Proto type (6.10)
* Generic_LLN
o Generic_LLN policy (6.10.2)
* Policy parameters (6.10.2.a)
* G_LLN encr alg (6.10.2.b)
* G_LLN auth alg (6.10.2.c)
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* G_LLN prf (6.10.2.d)
12. Acknowledgments
The authors would like to acknowledge the review and comments from
Rene Struik and Stephen Farrell.
13. References
13.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3830] Arkko, J., Carrara, E., Lindholm, F., Naslund, M., and K.
Norrman, "MIKEY: Multimedia Internet KEYing", RFC 3830,
August 2004.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[RFC6550] Winter, T., Thubert, P., 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, March 2012.
13.2. Informative References
[I-D.ietf-msec-mikey-ecc]
Milne, A., "ECC Algorithms for MIKEY",
draft-ietf-msec-mikey-ecc-03 (work in progress),
June 2007.
[I-D.ietf-roll-security-framework]
Tsao, T., Alexander, R., Dohler, M., Daza, V., and A.
Lozano, "A Security Framework for Routing over Low Power
and Lossy Networks", draft-ietf-roll-security-framework-07
(work in progress), January 2012.
[RFC3605] Huitema, C., "Real Time Control Protocol (RTCP) attribute
in Session Description Protocol (SDP)", RFC 3605,
October 2003.
[RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
Norrman, "The Secure Real-time Transport Protocol (SRTP)",
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RFC 3711, March 2004.
[RFC4107] Bellovin, S. and R. Housley, "Guidelines for Cryptographic
Key Management", BCP 107, RFC 4107, June 2005.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006.
[RFC4442] Fries, S. and H. Tschofenig, "Bootstrapping Timed
Efficient Stream Loss-Tolerant Authentication (TESLA)",
RFC 4442, March 2006.
[RFC4493] Song, JH., Poovendran, R., Lee, J., and T. Iwata, "The
AES-CMAC Algorithm", RFC 4493, June 2006.
[RFC4563] Carrara, E., Lehtovirta, V., and K. Norrman, "The Key ID
Information Type for the General Extension Payload in
Multimedia Internet KEYing (MIKEY)", RFC 4563, June 2006.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, July 2006.
[RFC4650] Euchner, M., "HMAC-Authenticated Diffie-Hellman for
Multimedia Internet KEYing (MIKEY)", RFC 4650,
September 2006.
[RFC4738] Ignjatic, D., Dondeti, L., Audet, F., and P. Lin, "MIKEY-
RSA-R: An Additional Mode of Key Distribution in
Multimedia Internet KEYing (MIKEY)", RFC 4738,
November 2006.
[RFC5197] Fries, S. and D. Ignjatic, "On the Applicability of
Various Multimedia Internet KEYing (MIKEY) Modes and
Extensions", RFC 5197, June 2008.
[RFC5410] Jerichow, A. and L. Piron, "Multimedia Internet KEYing
(MIKEY) General Extension Payload for Open Mobile Alliance
BCAST 1.0", RFC 5410, January 2009.
[RFC6043] Mattsson, J. and T. Tian, "MIKEY-TICKET: Ticket-Based
Modes of Key Distribution in Multimedia Internet KEYing
(MIKEY)", RFC 6043, March 2011.
[RFC6267] Cakulev, V. and G. Sundaram, "MIKEY-IBAKE: Identity-Based
Authenticated Key Exchange (IBAKE) Mode of Key
Distribution in Multimedia Internet KEYing (MIKEY)",
RFC 6267, June 2011.
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Authors' Addresses
Roger K. Alexander
Cooper Power Systems
20201 Century Blvd. Suite 250
Germantown, Maryland 20874
USA
Email: roger.alexander@cooperindustries.com
Tzeta Tsao
Cooper Power Systems
20201 Century Blvd. Suite 250
Germantown, Maryland 20874
USA
Email: tzeta.tsao@cooperindustries.com
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