MIKEY-SAKKE: Sakai-Kasahara Key Encryption in Multimedia Internet KEYing (MIKEY)
draft-groves-mikey-sakke-03
The information below is for an old version of the document that is already published as an RFC.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 6509.
|
|
|---|---|---|---|
| Author | Michael Groves | ||
| Last updated | 2015-10-14 (Latest revision 2011-10-27) | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | Informational | ||
| Formats | |||
| Reviews | |||
| Stream | WG state | (None) | |
| Document shepherd | (None) | ||
| IESG | IESG state | Became RFC 6509 (Informational) | |
| Action Holders |
(None)
|
||
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
| Responsible AD | Sean Turner | ||
| IESG note | |||
| Send notices to | tim.polk@nist.gov |
draft-groves-mikey-sakke-03
Network Working Group Groves
Internet Draft CESG
Intended Status: Informational October 27, 2011
Expires: April 29, 2012
MIKEY-SAKKE: Sakai-Kasahara Key Exchange in Multimedia Internet KEYing
(MIKEY)
draft-groves-mikey-sakke-03
Status of this Memo
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Abstract
This document describes MIKEY-SAKKE, a method of key exchange
designed for use in IP Multimedia Subsystem (IMS) [3GPP.33.328] Media
Plane Security, but with potential for wider applicability. The
MIKEY-SAKKE mode uses Identifier-based Public Key Cryptography
(IDPKC) to establish a shared secret value and certificate-less
signatures to provide source authentication. MIKEY-SAKKE has a
number of desirable features, including simplex transmission,
scalability, low-latency call setup and support for secure deferred
delivery.
Table of Contents
1. Introduction.....................................................2
1.1. Requirements Terminology....................................3
2. A New MIKEY Mode: MIKEY-SAKKE....................................3
2.1. Outline.....................................................3
2.1.1. Parameters.............................................4
2.1.2. Key types..............................................5
2.2. Preparing and processing MIKEY-SAKKE messages...............5
2.2.1. Components of the I_MESSAGE............................5
2.2.2. Processing the I_MESSAGE...............................7
2.3. Forking and Retargeting.....................................7
2.4. Group Communications........................................8
2.5. Deferred Delivery...........................................8
3. Key Management...................................................9
3.1. Generating Keys from the Shared Secret Value................9
3.2. Identifiers.................................................9
3.3. Key Longevity and Update...................................10
3.4. Key Delivery...............................................11
4. Payload Encoding................................................11
4.1. Common Header Payload (HDR)................................11
4.2. SAKKE payload..............................................12
4.3. SIGN payload...............................................13
4.4. IDR payload................................................13
5. Applicability of MIKEY-SAKKE mode...............................13
6. Security Considerations.........................................13
6.1. Forking....................................................14
6.2. Retargeting................................................14
6.3. Group Calls................................................15
6.4. Deferred Delivery..........................................15
7. IANA Considerations.............................................15
8. References......................................................16
8.1. Normative References.......................................16
8.2. Informative References.....................................17
Appendix A. Parameters for use in MIKEY-SAKKE......................18
1. Introduction
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Multimedia Internet Keying (MIKEY) [RFC3830] defines a protocol
framework for key distribution and specifies key distribution methods
using pre-shared keys, RSA and optionally, a Diffie-Hellman Key
Exchange. Since the original specification, several alternative key
distribution methods for MIKEY have been proposed such as [RFC4650],
[RFC4738], [RFC6043] and [RFC6267].
This document defines an Identifier-based cryptography key
distribution method called MIKEY-SAKKE. This scheme makes use of a
Key Management Server (KMS) as a root of trust and distributor of key
material. The KMS provides users with assurance of the authenticity
of the peers with which they communicate. Unlike traditional key
distribution systems, MIKEY-SAKKE does not require the KMS to offer
high availability. Rather it need only distribute new keys to its
users periodically.
MIKEY-SAKKE consists of an IDPKC scheme based on that of Sakai and
Kasahara [S-K], and a source authentication algorithm which is
tailored to use Identifiers instead of certificates. The algorithms
behind this protocol are described in [SAKKE] and [ECCSI].
The primary motivation for the MIKEY protocol design is the
low-latency requirement of real-time communication; hence many of the
defined exchanges finish in one-half to 1 roundtrip. However, some
exchanges, such as [RFC6043] and [RFC6267], have been proposed which
extend the latency of the protocol with the intent of providing
additional security. MIKEY-SAKKE affords similarly enhanced
security, but requires only a single simplex transmission (one half
roundtrip).
MIKEY-SAKKE additionally offers support for scenarios such as
forking, retargeting, deferred delivery and pre-encoded content.
1.1. Requirements Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
[RFC2119].
2. A New MIKEY Mode: MIKEY-SAKKE
2.1. Outline
The proposed MIKEY mode requires a single simplex transmission. The
Initiator sends a MIKEY I_MESSAGE containing SAKKE Encapsulated Data
and a signature to the intended recipient. The Responder MUST
validate the signature. Following signature validation, the
Responder processes the Encapsulated Data according to the operations
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defined in [SAKKE] to derive a Shared Secret Value (SSV). This SSV
is used as the TGK (the TEK Generation Key defined in [RFC3830]).
A verification message from the Responder (as in Pre-shared key mode,
for example) is not needed as the parties are mutually authenticated
following processing of the single I_MESSAGE. The notation used for
MIKEY messages and their payloads in Figure 1, and in the rest of
this document, is defined in [RFC3830].
Initiator Responder
I_MESSAGE =
HDR, T, RAND, [IDRi], [IDRr], [IDRkmsi], [IDRkmsr],
[CERT], {SP}, SAKKE, SIGN --->
Figure 1: MIKEY-SAKKE Unicast Mode
The Initiator wants to establish a secure media session with the
Responder. The Initiator and the Responder trust a third party, the
KMS, which provisions them with key material by a secure mechanism.
In addition to the public and secret keys corresponding to their
Identifier, the KMS MUST provision devices with its KMS Public Key
and, where [ECCSI] is used, its KMS Public Authentication Key. A
description of all key material used in MIKEY-SAKKE can be found in
Section 2.1.2. The Initiator and the Responder do not share any
credentials, instead the Initiator is able to derive the Responder's
public Identifier.
Implementations MAY provide support for multiple KMSs. In this case,
rather than a single KMS, several different KMSs could be involved,
e.g. one for the Initiator and one for the Responder. To allow
this, each interoperating KMS MUST provide its users with the KMS
public keys for every KMS subscriber domain with which its users
communicate. It is not anticipated that large mutually communicating
groups of KMSs will be needed as each KMS only needs to provide its
domain of devices with key material once per key period (see Section
3.3) rather than to be active in each call.
As MIKEY-SAKKE is based on [RFC3830], the same terminology,
processing and considerations still apply unless otherwise stated.
Following [RFC3830], messages are integrity protected and encryption
is not applied to entire messages.
2.1.1. Parameters
[SAKKE] requires each application to define the set of public
parameters to be used by implementations. The parameters in Appendix
A SHOULD be used in MIKEY-SAKKE; alternative parameters MAY be
subsequently defined, see Section 4.2.
[ECCSI] requires each application to define the Hash function and
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various other parameters to be used (see Section 4.1 of [ECCSI]).
For MIKEY-SAKKE, the P256 elliptic curve and base-point [FIPS186-3]
and SHA-256 [FIPS180-3] MUST be used.
2.1.2. Key types
Users require keys for [SAKKE] and to sign messages. These keys MUST
be provided by the users' KMS. It is RECOMMENDED that
implementations support the [ECCSI] scheme for signatures.
Alternatively, RSA signing as defined in [RFC3830] MAY be used.
SAKKE keys SAKKE requires each user to have a Receiver Secret Key,
created by the KMS, and the KMS Public Key. For
systems that support multiple KMSs, each user also
requires the KMS Public Key of every KMS subscriber
domain with which communication is authorised.
ECCSI keys If ECCSI signatures are used, each user requires a
Secret Signing Key and Public Validation Token, created
by the KMS, and the KMS Public Authentication Key. For
systems that support multiple KMSs, each user also
requires the KMS Public Authentication Key of every KMS
subscriber domain with which communication is
authorised.
If instead RSA signatures are to be used, certificates and
corresponding private keys MUST be supplied.
2.2. Preparing and processing MIKEY-SAKKE messages
Preparation and parsing of MIKEY messages are as described in
Sections 5.2 and 5.3 of [RFC3830]. Error handling is described in
Section 5.1.2 and replay protection guidelines are in Section 5.4 of
[RFC3830]. In the following, we describe the components of
MIKEY-SAKKE messages and specify message processing and parsing rules
in addition to those in [RFC3830].
2.2.1. Components of the I_MESSAGE
MIKEY-SAKKE requires a single simplex transmission (a half roundtrip)
to establish a shared TGK. The I_MESSAGE MUST contain the MIKEY HDR
and timestamp payload in order to provide replay protection. The HDR
field contains a CSB_ID (Crypto Session Bundle ID) randomly selected
by the Initiator. The V bit in the HDR payload MUST be set to '0'
and ignored by the Responder as a response is not expected in this
mode. The timestamp payload MUST use TS type NTP-UTC (TS type 0) or
NTP (TS type 1) as defined in Section 6.6 of [RFC3830] so that the
Responder can determine the Identifiers used by the Initiator (see
Section 3.2). It is RECOMMENDED that the time always be specified in
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UTC.
The I_MESSAGE MUST be signed by the Initiator following either the
procedure to sign MIKEY messages specified in [RFC3830], or using
[ECCSI] as specified in this document. The SIGN payload contains
this signature. Thus the I_MESSAGE is integrity and replay
protected. The ECCSI signature scheme [ECCSI] SHOULD be used. If
this signature scheme is used, then the Initiator MUST NOT include a
CERT payload. To form this signature type, the Initiator requires a
Secret Signing Key which is provided by the KMS.
Other signature types defined for use with MIKEY MAY be used. If
signature types 0 or 1 (RSA) are used, then the Initiator SHOULD
include a CERT payload; in this case the CERT payload MAY be left out
if it is expected that the Responder is able to obtain the
certificate in some other manner. If a CERT payload is included, it
MUST correspond to the private key used to sign the I_MESSAGE.
The Initiator MUST include a RAND payload in the I_MESSAGE as this is
used to derive session keys.
The I_MESSAGE MAY contain IDRi, IDRr, IDRkmsi and IDRkmsr
respectively the identities of the Initiator, Responder, the
Initiator's KMS (root of trust for authentication of the Initiator)
and the Responder's KMS (root of trust for authentication of the
Responder). The IDR payload is defined in [RFC6043] and modified in
Section 4.4. When used, this payload provides the Identifier for any
of the Initiator, the Responder and their respective KMSs.
The ID role MUST be Initiator (value 1) for the IDRi payload and
Responder (value 2) for the IDRr payload. The Initiator's ID is used
to validate [ECCSI] signatures. If included, the IDRi payload MUST
contain the URI of the Initiator incorporated in the Identifier used
to sign the I_MESSAGE (see Section 3.2). If included, the IDRr
payload MUST contain the URI of the Responder incorporated in the
Identifier which the Initiator used in SAKKE (see Section 3.2). If
included, the ID role MUST be Initiator's KMS (value TBD4) for the
IDRkmsi payload and Responder's KMS (value TBD5) for the IDRkmsr
payload and MUST correspond to the KMS used as root of trust for the
signature (for the IDRkmsi payload) and the KMS used as the root of
trust for the SAKKE key exchange (for the IDRkmsr payload).
It is OPTIONAL to include any IDR payloads, as in some user groups
Identifiers could be inferred by other means, e.g. through the
signalling used to establish a call. Furthermore, a closed user
group could rely on only one KMS, whose identity will be understood
and need not be included in the signalling.
The I_MESSAGE MUST contain a SAKKE payload constructed as defined in
Section 4.2.
The Initiator MAY also send security policy (SP) payload(s)
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containing all the security policies that it supports. If the
Responder does not support any of the policies included, it SHOULD
reply with an Error message of type "Invalid SPpar" (Error no. 10).
The Responder has the option not to send the Error message in MIKEY
if a generic session establishment failure indication is deemed
appropriate and communicated via other means (see Section 4.1.2 of
[RFC4567] for additional guidance).
2.2.2. Processing the I_MESSAGE
The Responder MUST process the I_MESSAGE according to the rules
specified in Section 5.3 of [RFC3830]. The following additional
processing MUST also be applied.
* If the Responder does not support the MIKEY-SAKKE mode of
operation, or otherwise cannot correctly parse the received
MIKEY message then it SHOULD send an Error message "Message type
not supported (Error no 13). Error no 13 is not defined in
[RFC3830], and so [RFC3830] compliant implementations MAY return
"an unspecified error occurred" (Error no 12).
* The Responder MAY compare the IDi payload against his local
policy to determine whether he wishes to establish secure
communications from the Initiator. If the Responder's policy
does not allow this communication, then the Responder MAY
respond with an Authentication Error (Error no 0).
* If the Responder supports MIKEY-SAKKE and has determined that it
wishes to establish secure communications with the initiator,
then it MUST verify the signature according to the method
described in Section 5.2.2 of [ECCSI] if it is of type TBD3, or
according to the certificate used if a signature of type 0 or 1
is used. If the verification of the signature fails then an
Authentication Error (Error no 0) MAY be sent to the Initiator.
* If the authentication is successful then the Responder SHALL
process the SAKKE payload and derive the SSV according to the
method described in [SAKKE].
2.3. Forking and Retargeting
Where forking is to be supported, Receiver Secret Keys can be held by
multiple devices. To facilitate this, the Responder needs to load
his Receiver Secret Key into each of his devices that he wishes to
receive MIKEY-SAKKE communications. If forking occurs, each of these
devices can then process the SAKKE payload, and each can verify the
Identifier of the Initiator as they hold the KMS Public
Authentication Key. The traffic keys could therefore be derived by
any of these devices. However, this is the case for any scheme
employing simplex transmission, and it is considered that the
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advantages of this type of scheme are significant for many users.
Furthermore, it is for the owner of the Identifier to determine on
which devices to allow his Receiver Secret Key to be loaded. Thus it
is anticipated that he would have control over all devices that hold
his Receiver Secret Key. This argument also applies to applications
such as call centres, in which the security relationship is typically
between the call centre and the individual calling the centre, rather
than the particular operative who receives the call.
Devices holding the same Receiver Secret Key ought to each hold a
different Secret Signing Key corresponding to the same Identifier.
This is possible because the ECCSI scheme allows multiple keys to be
generated by KMS for the same Identifier.
Secure retargeted calls can only be established in the situation
where the Initiator is aware of the Identifier of the device to whom
the call is being retargeted; in this case the Initiator ought to
initiate a new MIKEY-SAKKE session with the device to whom it has
been retargeted (if willing to do so). Retargeting an Initiator's
call to another device (with a different Identifier) is to be viewed
as insecure when the Initiator is unaware that this has occurred as
this prevents authentication of the Responder.
2.4. Group Communications
SAKKE supports key establishment for group communications. The
Initiator needs to form an I_MESSAGE for each member in the group,
each using the same SSV. Alternatively, a bridge can be used. In
this case the bridge forms an I_MESSAGE for each member of the
group. Any member of the group can invite new members directly by
forming an I_MESSAGE using the group SSV.
2.5. Deferred Delivery
Deferred delivery/secure voicemail is fully supported by
MIKEY-SAKKE. A deferred delivery server that supports MIKEY-SAKKE
needs to store the MIKEY-SAKKE I_MESSAGE along with the encrypted
data. When the recipient of the voicemail requests his data, the
server needs to initiate MIKEY-SAKKE using the stored I_MESSAGE.
Thus the data can be received and decrypted only by a legitimate
recipient, who can also verify the Identifier of the sender. This
requires no additional support from the KMS, and the deferred
delivery server need not be trusted as it is unable to read or tamper
with the messages it receives. Note that the deferred delivery
server does not need to fully implement MIKEY-SAKKE, merely to store
and forward the I_MESSAGE.
The deferred delivery message needs to be collected by its recipient
before the key period in which it was sent expires (see Section 3.3
for a discussion of key periods). Alternatively, if greater
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longevity of deferred delivery payloads is to be supported, the
Initiator needs to include an I_MESSAGE for each key period during
the lifetime of the deferred delivery message, each using the same
SSV. In this case, the deferred delivery server needs to forward the
I_MESSAGE corresponding to the current key period to the recipient.
3. Key Management
3.1. Generating Keys from the Shared Secret Value
Once a MIKEY-SAKKE I_MESSAGE has been successfully processed by the
Responder, he will share an authenticated Shared Secret Value (SSV)
with the Initiator. This SSV is used as the TGK. The keys used to
protect application traffic are derived as specified in [RFC3830].
3.2. Identifiers
One of the primary features and advantages of Identifier-Based
Encryption is that the public keys of users are their Identifiers,
which can be constructed by their peers. This removes the need for
Public Key or Certificate servers, so that all data transmission per
session can take place directly between the peers and high
availability security infrastructure is not needed. In order for the
Identifiers to be constructable, they need to be unambiguously
defined. This section defines the format of Identifiers for use in
MIKEY-SAKKE.
If keys are updated regularly, a KMS is able to revoke devices. To
this end, every Identifier for use in MIKEY-SAKKE MUST contain a
timestamp value indicating the key period for which the Identifier is
valid (see Section 3.3). This document uses a year and month format
to enforce monthly changes of key material. Further Identifier
schemes MAY be defined for communities that require different key
longevity.
An Identifier for use in MIKEY-SAKKE MUST take the form of a
timestamp formatted as a US-ASCII string [ASCII] and terminated by a
NULL byte, followed by identifying data which relates to the identity
of the device or user, also represented by a US-ASCII string and
terminated by a NULL byte.
For the purposes of this document, the timestamp MUST take the form
of a year and month value, formatted according to [ISO8601], with the
format "YYYY-MM", indicating a four digit year, followed by a hyphen
"-", followed by a two digit month.
For the Identifier scheme defined in this document, the identifying
data MUST take the form of a constrained "tel" URI. If an
alternative URI scheme is to be used to form SAKKE Identifiers, a
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subsequent RFC MUST define constraints to ensure that the URI can be
formed unambiguously. The normalization procedures described in
Section 6 of [RFC3986] MUST be used as part of the constraining rules
for the URI format. It would also be possible to define Identifier
types that used identifying data other than a URI.
The restrictions for the "tel" URI scheme [RFC3966] for use in
MIKEY-SAKKE Identifiers are as follows:
* the "tel" URI for use in MIKEY-SAKKE MUST be formed in global
notation,
* visual separators MUST NOT be included,
* the "tel" URI MUST NOT include additional parameters,
* the "tel" URI MUST NOT include phone-context parameters.
These constraints on format are necessary so that all parties can
unambiguously form the "tel" URI.
For example, suppose a user's telephone number is +447700900123 and
the month is 2011-02. Then the user's Identifier is defined as the
ASCII string
2011-02\0tel:+447700900123\0,
where '\0' denotes the null 8-bit ASCII character 0x00.
If included in I_MESSAGE, the IDRi and IDRr payloads MUST contain the
URI used to form the Identifier. The value of the month used to form
the Identifiers MUST be equal to the month as specified by the data
in the timestamp payload.
3.3. Key Longevity and Update
Identifiers for use in MIKEY-SAKKE change regularly in order to force
users to regularly update their key material; we term the interval
for which a key is valid a "key period". This means that if a device
is compromised (and this is reported procedurally), it can continue
to communicate with other users for at most one key period. Key
periods SHOULD be indicated by the granularity of the format of the
timestamp used in the Identifier. In particular, the Identifier
scheme in this document uses monthly key periods. Implementations
MUST allow devices to hold two periods' keys simultaneously to allow
for differences in system time between Initiator and Responder.
Where a monthly key period applies, it is RECOMMENDED that
implementations receive the new key material before the
second-to-last day of the old month, commence allowing receipt of
calls with the new key material on the second-to-last day of the old
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month, and continue to allow receipt calls with the old key material
on the first and second days of the new month. Devices SHOULD cease
to receive calls with key material corresponding to the previous
month on the third day of the month; this is to allow compromised
devices to be keyed out of the communicating user group.
KMSs MAY update their KMS Master Secret Keys and KMS Master Secret
Authentication Keys. If such an update is not deemed necessary, then
the corresponding KMS Public Keys and KMS Public Authentication Keys
will be fixed. If KMS keys are to be updated, then this update MUST
occur at the change of a key period, and new KMS Public Key(s) and
KMS Public Authentication Key(s) MUST be provided to all users with
their user key material.
It is NOT RECOMMENDED for KMSs to distribute multiple key periods'
keys simultaneously, as this prevents the periodic change of keys
from excluding compromised devices.
3.4. Key Delivery
This document does not seek to restrict the mechanisms by which the
necessary key material might be obtained from the KMS. The
mechanisms of [RFC5408] are not suitable for this application as the
MIKEY-SAKKE protocol does not require public parameters to be
obtained from a server: these are fixed for all users in order to
facilitate interoperability and simplify implementation.
The delivery mechanism used MUST provide confidentiality to all
secret keys, integrity protection to all keys and mutual
authentication of the device and the KMS.
4. Payload Encoding
This section describes the new SAKKE payload and also the payloads
for which changes have been made compared to [RFC3830]. A detailed
description of MIKEY payloads is provided in [RFC3830].
4.1. Common Header Payload (HDR)
An additional value is added to the data type and next payload
fields.
* Data type (8 bits): describes the type of message
Data type | Value | Comment
-----------------------------------------------
SAKKE msg | TBD1 | Initiator's SAKKE message
Table 1: Data type (additions)
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* Next payload (8 bits): identifies the payload that is added
after this payload.
Next Payload | Value | Section
-------------------------------
SAKKE | TBD2 | 4.2
Table 2: Next payload (additions)
* V (1 bit): flag to indicate whether a response message is
expected ('1') or not ('0'). It MUST be set to '0' and ignored
by the Responder in a SAKKE message.
4.2. SAKKE payload
The SAKKE payload contains the SAKKE Encapsulated Data as defined in
[SAKKE].
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 ! SAKKE params ! ID scheme ! SAKKE data ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ length (cont) ! SAKKE data ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Table 3: SAKKE payload
* Next payload (8 bits): identifies the payload that is added
after this payload.
* SAKKE params (8 bits): indicates the SAKKE parameter set to be
used.
SAKKE params | Value
------------------------------------------
Parameter Set 1 (See Appendix A) | 1
Table 4: SAKKE params
* ID scheme (8 bits): indicates the SAKKE identifier scheme to be
used.
ID scheme | Value
----------------------------------------------------
tel URI with monthly keys (See Section 3.2) | 1
Table 5: ID scheme
* SAKKE data length (16 bits): length of SAKKE data (in bytes).
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* SAKKE data (variable): the SAKKE Encapsulated Data formatted as
defined in Section 4 of [SAKKE].
4.3. SIGN payload
To enable use of the ECCSI signature algorithm which has efficiency
benefits for use with Identifier-Based Encryption, we define an
additional signature type.
* S type (4 bits): indicates the signature algorithm applied by
the signer.
S type | Value | Comments
-----------------------------------------
ECCSI | TBD3 | ECCSI signature [ECCSI]
Table 6: S type (additions)
4.4. IDR payload
The IDR payload was defined in [RFC6043], but its definition only
provided the facility to identify one KMS per exchange. Since it is
possible that different KMSs could be used by the Initiator and
Responder, this payload is extended to define an ID role for the KMS
of the Initiator and the KMS of the Responder.
* ID Role (8 bits): specifies the sort of identity.
ID Role | Value
---------------------------------
Initiator's KMS (IDRkmsi) | TBD4
Responder's KMS (IDRkmsr) | TBD5
Table 7: ID Role (additions)
5. Applicability of MIKEY-SAKKE mode
MIKEY-SAKKE is suitable for use in a range of applications in which
secure communications under a clear trust model are needed. In
particular, the KMS need not provide high availability as it is only
necessary to provide periodic refresh of key material. Devices are
provided with a high level of authentication as the KMS acts as a
root of trust for both key exchange and signatures.
6. Security Considerations
Unless explicitly stated, the security properties of the MIKEY
protocol as described in [RFC3830] apply to MIKEY-SAKKE as well. In
addition, MIKEY-SAKKE inherits some properties of Identifier-Based
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Cryptography. For instance, by concatenating the "date" with the URI
to form the Identifier, the need for any key revocation mechanisms is
virtually eliminated. It is NOT RECOMMENDED for KMSs to distribute
multiple months' keys simultaneously in an IBE system, as this
prevents the monthly change of keys from excluding compromised
devices.
The solution proposed provides protection suitable for high security
user groups, but is scalable enough that it could be used for large
numbers of users. Traffic keys cannot be derived by any
infrastructure component other than the KMS.
The effective security of the public parameters defined in this
document is 112 bits, as this is the security offered by p of size
1024 bits used in SAKKE (see Section 7 of [SAKKE]). For similar
parameter sizes, MIKEY-SAKKE provides equivalent levels of effective
security to other schemes of this type (such as [RFC6267]). For
reasons of efficiency and security, it is RECOMMENDED to use a mode
of AES-128 [AES] in the traffic application to which MIKEY-SAKKE
supplies key material, but users SHOULD be aware that 112 bits of
security are offered by the defined public parameters. Following
[SP800-57], this choice of security strength is appropriate for use
to protect data until 2030.
User identities cannot be spoofed, since the Public Authentication
Token is tied to the Identifier of the sender by the KMS. In
particular, the Initiator is provided with assurance that nobody
other than a holder of the legitimate Receiver Secret Key can process
the SAKKE Encapsulated Data, and the signature binds the holder of
the Initiator's Secret Signing Key to the I_MESSAGE. Since these
keys are provided via a secure channel by the KMS, mutual
authentication is provided. This mechanism protects against both
passive and active attacks.
If there were a requirement that a caller remain anonymous from any
called parties, then it would be possible to remove the signature
from the protocol. A called user could then decide, according to
local policy, whether to accept such a secure session.
6.1. Forking
Where forking is used, the view is taken that it is not necessary for
each device to have a separate Receiver Secret Key. Rather, where a
user wishes his calls to be forked between his devices, he loads the
same Receiver Secret Key onto each of them. This does not compromise
his security as he controls each of the devices, and is consistent
with the Initiator's expectation that he is authenticated to the
owner of the Identifier he selected when initiating the call.
6.2. Retargeting
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Since the Initiator is made aware by the forwarding server of the
change to the Identifier of the Responder, he creates an I_MESSAGE
that can only be processed by this legitimate Responder. The
Initiator MAY also choose to discontinue the session after checking
his local policy.
6.3. Group Calls
Any device that possesses an SSV can potentially provide it securely
to any other device using SAKKE. Thus group calls can either be
established by an Initiator, or can be extended to further Responders
by any party to whom the original Initiator has sent an I_MESSAGE.
The Initiator in this context MAY be a conference bridge. If a mode
of operation in which a bridge has no knowledge of the SSV is needed,
the role of MIKEY-SAKKE Initiator MUST be carried out by one or more
of the communicating parties, not by the bridge.
Where multi-way communications (rather than broadcast) are needed,
the application using the supplied key material MUST ensure that a
suitable IV scheme is used in order to prevent cryptovariable
re-use.
6.4. Deferred Delivery
Secure deferred delivery is supported in a manner such that no trust
is placed on the deferred delivery server. This is a significant
advantage, as it removes the need for secure infrastructure
components beyond the KMS.
7. IANA Considerations
This document defines new values for the namespaces Data Type, Next
Payload, and S type defined in [RFC3830], and for the ID Role
namespace defined in [RFC6043]. The following IANA assignments were
added to the MIKEY Payload registry [to be removed upon publication:
http://www.iana.org/assignments/mikey-payloads] (in bracket is a
reference to the table containing the registered values):
* Data Type (see Table 1)
* Next Payload (see Table 2)
* S type (see Table 6)
* ID Role (see Table 7)
The SAKKE payload defined in Section 4.2 defines two fields for which
IANA is requested to create and maintain name spaces in the MIKEY
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Payload registry. These two fields are the 8-bit SAKKE params field,
and the 8-bit ID scheme field. IANA is requested to record the
pre-defined values defined in Section 4.2 for each of the two name
spaces. Values in the range 1-239 SHOULD be approved by the process
of Specification Required, values in the range 240-254 are for
Private Use, and the values 0 and 255 are Reserved according to
[RFC5226].
Initial values for the SAKKE params registry are given below.
Assignments consist of a SAKKE parameters name and its associated
value.
Value SAKKE params Definition
----- ------------ ----------
0 Reserved
1 Parameter Set 1 See Appendix A
2-239 Unassigned
240-254 Private Use
255 Reserved
Initial values for the ID scheme registry are given below.
Assignments consist of a name of an identifier scheme name and its
associated value.
Value ID Scheme Definition
----- ------------ ----------
0 Reserved
1 tel URI with monthly keys See Section 3.2
2-239 Unassigned
240-254 Private Use
255 Reserved
8. References
8.1. Normative References
[AES] NIST, "Advanced Encryption Standard (AES)", FIPS
PUB 197, http://www.nist.gov/aes/
[ASCII] American National Standards Institute, "Coded
Character Set -- 7-bit American Standard Code for
Information Interchange", ANSI X3.4, 1986.
[ECCSI] Groves, M., Elliptic Curve-based Certificate-less
Signatures for Identifier Based Encryption
(ECCSI), draft-groves-eccsi-01 [work in progress],
February 2011.
[FIPS180-3] Federal Information Processing Standards
Publication (FIPS PUB) 180-3, Secure Hash Standard
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(SHS), October 2008.
[FIPS186-3] Federal Information Processing Standards
Publication (FIPS PUB) 186-3, Digital Signature
Standard (DSS), June 2009.
[ISO8601] "Data elements and interchange formats --
Information interchange -- Representation of dates
and times", ISO 8601:1988(E), International
Organization for Standardization, June, 1988.
[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.
[RFC3966] Schulzrinne, H., "The tel URI for Telephone
Numbers", RFC 3966, December 2004.
[RFC3986] Berners-Lee, T., Fielding, R. and L. Masinter,
"Uniform Resource Identifier (URI): Generic
Syntax", RFC 3986, January 2005.
[RFC6043] Mattsson, J. and T. Tian, "MIKEY-TICKET: An
Additional Mode of Key Distribution in Multimedia
Internet KEYing (MIKEY)", RFC 6043, March 2011.
[SAKKE] Groves M., "Sakai-Kasahara Key Establishment
(SAKKE)", draft-groves-sakke-03 [work in
progress], October 2011.
[SP800-57] E. Barker, W. Barker, W. Burr, W. Polk and M.
Smid, "Recommendation for Key Management - Part 1:
General (Revised)," NIST Special Publication
800-57, March 2007.
8.2. Informative References
[3GPP.33.328] 3GPP, "IP Multimedia Subsystem (IMS) media plane
security", 3GPP TS 33.328 9.3.0, December 2010.
[RFC4567] Arkko, J., Lindholm, F., Naslund, M., Norrman, K.,
and E. Carrara, "Key Management Extensions for
Session Description Protocol (SDP) and Real Time
Streaming Protocol (RTSP)", RFC 4567, July 2006.
[RFC4650] Euchner, M., "HMAC-Authenticated Diffie-Hellman
for Multimedia Internet KEYing (MIKEY)", RFC 4650,
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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.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for
Writing an IANA Considerations Section in RFCs",
BCP 26, RFC 5226, May 2008.
[RFC5408] Appenzeller, G., Martin, L., and M. Schertler,
"Identity- Based Encryption Architecture and
Supporting Data Structures", RFC 5408, January
2009.
[RFC6267] Cakulev, V. and G. Sundaram, "MIKEY-IBAKE:
Identity-Based Mode of Key Distribution in
Multimedia Internet KEYing (MIKEY)", RFC 6267,
June 2011.
[S-K] Sakai, R., Ohgishi, K. and M. Kasahara, "ID
based cryptosystem with pairing on elliptic
curve", Symposium on Cryptography and Information
Security - SCIS, 2003.
Appendix A. Parameters for use in MIKEY-SAKKE
[SAKKE] requires each application to define the set of public
parameters to be used by implementations. Parameter Set 1 is defined
in this appendix. Descriptions of the parameters are provided in
Section 2.1 of [SAKKE].
n = 128
p = 997ABB1F 0A563FDA 65C61198 DAD0657A
416C0CE1 9CB48261 BE9AE358 B3E01A2E
F40AAB27 E2FC0F1B 228730D5 31A59CB0
E791B39F F7C88A19 356D27F4 A666A6D0
E26C6487 326B4CD4 512AC5CD 65681CE1
B6AFF4A8 31852A82 A7CF3C52 1C3C09AA
9F94D6AF 56971F1F FCE3E823 89857DB0
80C5DF10 AC7ACE87 666D807A FEA85FEB
q = 265EAEC7 C2958FF6 99718466 36B4195E
905B0338 672D2098 6FA6B8D6 2CF8068B
BD02AAC9 F8BF03C6 C8A1CC35 4C69672C
39E46CE7 FDF22286 4D5B49FD 2999A9B4
389B1921 CC9AD335 144AB173 595A0738
6DABFD2A 0C614AA0 A9F3CF14 870F026A
A7E535AB D5A5C7C7 FF38FA08 E2615F6C
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203177C4 2B1EB3A1 D99B601E BFAA17FB
Px = 53FC09EE 332C29AD 0A799005 3ED9B52A
2B1A2FD6 0AEC69C6 98B2F204 B6FF7CBF
B5EDB6C0 F6CE2308 AB10DB90 30B09E10
43D5F22C DB9DFA55 718BD9E7 406CE890
9760AF76 5DD5BCCB 337C8654 8B72F2E1
A702C339 7A60DE74 A7C1514D BA66910D
D5CFB4CC 80728D87 EE9163A5 B63F73EC
80EC46C4 967E0979 880DC8AB EAE63895
Py = 0A824906 3F6009F1 F9F1F053 3634A135
D3E82016 02990696 3D778D82 1E141178
F5EA69F4 654EC2B9 E7F7F5E5 F0DE55F6
6B598CCF 9A140B2E 416CFF0C A9E032B9
70DAE117 AD547C6C CAD696B5 B7652FE0
AC6F1E80 164AA989 492D979F C5A4D5F2
13515AD7 E9CB99A9 80BDAD5A D5BB4636
ADB9B570 6A67DCDE 75573FD7 1BEF16D7
g = 66FC2A43 2B6EA392 148F1586 7D623068
C6A87BD1 FB94C41E 27FABE65 8E015A87
371E9474 4C96FEDA 449AE956 3F8BC446
CBFDA85D 5D00EF57 7072DA8F 541721BE
EE0FAED1 828EAB90 B99DFB01 38C78433
55DF0460 B4A9FD74 B4F1A32B CAFA1FFA
D682C033 A7942BCC E3720F20 B9B7B040
3C8CAE87 B7A0042A CDE0FAB3 6461EA46
Hash = SHA-256 (defined in [FIPS180-3]).
Author's Address
Michael Groves
CESG
Hubble Road
Cheltenham
GL51 8HJ
UK
Email: Michael.Groves@cesg.gsi.gov.uk
Acknowledgement
Funding for the RFC Editor function is provided by the IETF
Administrative Support Activity (IASA).
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