Internet Engineering Task Force (IETF) V. Cakulev
Request for Comments: 6267 G. Sundaram
Category: Informational Alcatel Lucent
ISSN: 2070-1721 June 2011
MIKEY-IBAKE: Identity-Based Authenticated Key Exchange (IBAKE) Mode of
Key Distribution in Multimedia Internet KEYing (MIKEY)
Abstract
This document describes a key management protocol variant for the
Multimedia Internet KEYing (MIKEY) protocol that relies on a trusted
key management service. In particular, this variant utilizes
Identity-Based Authenticated Key Exchange (IBAKE) framework that
allows the participating clients to perform mutual authentication and
derive a session key in an asymmetric Identity-Based Encryption (IBE)
framework. This protocol, in addition to providing mutual
authentication, eliminates the key escrow problem that is common in
standard IBE and provides perfect forward and backward secrecy.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6267.
Copyright Notice
Copyright (c) 2011 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
Cakulev & Sundaram Informational [Page 1]RFC 6267 MIKEY-IBAKE June 2011
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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
2.2. Definitions and Notation . . . . . . . . . . . . . . . . . 4
2.3. Abbreviations . . . . . . . . . . . . . . . . . . . . . . 5
3. Use Case Scenarios . . . . . . . . . . . . . . . . . . . . . . 6
3.1. Forking . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.2. Retargeting . . . . . . . . . . . . . . . . . . . . . . . 6
3.3. Deferred Delivery . . . . . . . . . . . . . . . . . . . . 7
4. MIKEY-IBAKE Protocol Description . . . . . . . . . . . . . . . 7
4.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 7
4.2. Message Exchanges and Processing . . . . . . . . . . . . . 10
4.2.1. REQUEST_KEY_INIT/REQUEST_KEY_RESP Message Exchange . . 10
4.2.2. I_MESSAGE/R_MESSAGE Message Exchanges . . . . . . . . 12
5. Key Management . . . . . . . . . . . . . . . . . . . . . . . . 16
5.1. Generating Keys from the Session Key . . . . . . . . . . . 17
5.2. Generating Keys for MIKEY Messages . . . . . . . . . . . . 17
5.3. CSB Update . . . . . . . . . . . . . . . . . . . . . . . . 18
5.4. Generating MAC and Verification Message . . . . . . . . . 18
6. Payload Encoding . . . . . . . . . . . . . . . . . . . . . . . 19
6.1. Common Header Payload (HDR) . . . . . . . . . . . . . . . 19
6.1.1. IBAKE Payload . . . . . . . . . . . . . . . . . . . . 20
6.1.2. Encrypted Secret Key (ESK) Payload . . . . . . . . . . 21
6.1.3. Key Data Sub-Payload . . . . . . . . . . . . . . . . . 21
6.1.4. EC Diffie-Hellman Sub-Payload . . . . . . . . . . . . 22
6.1.5. Secret Key Sub-Payload . . . . . . . . . . . . . . . . 23
7. Security Considerations . . . . . . . . . . . . . . . . . . . 24
7.1. General Security Considerations . . . . . . . . . . . . . 24
7.2. IBAKE Protocol Security Considerations . . . . . . . . . . 25
7.3. Forking . . . . . . . . . . . . . . . . . . . . . . . . . 26
7.4. Retargeting . . . . . . . . . . . . . . . . . . . . . . . 26
7.5. Deferred Delivery . . . . . . . . . . . . . . . . . . . . 26
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 28
9.1. Normative References . . . . . . . . . . . . . . . . . . . 28
9.2. Informative References . . . . . . . . . . . . . . . . . . 29
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1. Introduction
The Multimedia Internet Keying (MIKEY) [RFC3830] specification
describes several modes of key distribution solution that address
multimedia scenarios using pre-shared keys, Public Keys, and
optionally a Diffie-Hellman key exchange. Multiple extensions of
MIKEY have been specified, such as HMAC-Authenticated (Hashed Message
Authentication Code) Diffie-Hellman [RFC4650] and MIKEY-RSA-R
[RFC4738].
To address deployment scenarios in which security systems serve a
large number of users, a key management service is often preferred.
With such a service in place, it would be possible for a user to
request credentials for any other user when they are needed. Some
proposed solutions [RFC6043] rely on Key Management Services (KMSs)
in the network that create, distribute, and manage keys in a real
time. Due to this broad functionality, key management services would
have to be online, maintain high availability, and be networked
across operator boundaries.
This document describes a solution in which KMSs are low-availability
servers that communicate with end-user clients periodically (e.g.,
once a month). The online transactions between the end-user clients
(for media plane security) are based on Identity-Based Encryption
(IBE) [BF]. These online transactions between the end-user clients
allow them to perform mutual authentication and derive a session key
not known to any external entity (including KMSs). This protocol, in
addition to providing keys not known to any external entity and
allowing for end-user clients to mutually authenticate each other (at
the media plane layer), provides perfect forward and backward
secrecy. In this protocol, the KMS-to-client exchange is used
sparingly (e.g., once a month); hence, the KMS is no longer required
to be a high-availability server, and in particular different KMSs
don't have to communicate with each other (across operator
boundaries). Moreover, given that an IBE is used, the need for
costly Public Key Infrastructure (PKI) and all the operational costs
of certificate management and revocation are eliminated. This is
achieved by concatenating Public Keys with a date field, thereby
ensuring corresponding Private Keys change with the date and, more
importantly, limiting the damage due to loss of a Private Key to just
that date while not requiring endpoints involved in communication to
be time synchronized. The granularity in the date field is a matter
of security policy and deployment scenario. For instance, an
operator may choose to use one key per day and hence the KMS may
issue Private Keys for a whole subscription cycle at the beginning of
a subscription cycle. Therefore, unlike in the PKI systems, where
issued certificate is typically valid for period of time thereby
requiring revocation procedures to limit their validity, the scheme
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described in this document uses time-bound public identities, which
automatically expire at the end of a time span indicated in the
identity itself. With the self-expiration of the public identities,
the traditional real-time validity verification and revocation is not
required. For example, if the public identity is bound to one day,
then, at the end of the day, the Public/Private Key pair issued to
this peer will simply not be valid anymore. Nevertheless, just like
with Public-Key-based certificate systems, if there is a need to
revoke keys before the designated expiry time, communication with a
third party will be needed.
Additionally, various call scenarios are securely supported -- this
includes secure forking, retargeting, deferred delivery and pre-
encoded content.
MIKEY is widely used in the 3GPP community. This specification is
intended primarily for use with 3GPP media security, but it may also
be applicable in Internet applications.
2. Terminology
2.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2.2. Definitions and Notation
IBE Encryption: Identity-Based Encryption (IBE) is a Public-Key
encryption technology that allows a Public Key to be calculated from
an identity, and the corresponding Private Key to be calculated from
the Public Key. [RFC5091], [RFC5408], and [RFC5409] describe
algorithms required to implement the IBE.
(Media) session: The communication session intended to be secured by
the MIKEY-IBAKE provided key(s).
E(k, x) Encryption of x with the key k
[x]P Point multiplication on an elliptic curve, i.e., adding
a point P to itself total of x times
K_PUBx Public Key of x
[x] x is optional
{x} Zero or more occurrences of x
(x) One or more occurrences of x
|| Concatenation
| OR (selection operator)
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2.3. Abbreviations
EC Elliptic Curve
ESK Encrypted Secret Key
HMAC Hashed Message Authentication Code
IBE Identity-Based Encryption
I Initiator
IBAKE Identity-Based Authenticated Key Exchange
IDRi Initiator's Identity
IDRr Responder's Identity
KMS Key Management Service
K_PR Private Key
K_PUB Public Key
K_SESSION Session Key
MAC Message Authentication Code
MIKEY Multimedia Internet KEYing
MKI Master Key Identifier
MPK MIKEY Protection Key
PKI Public Key Infrastructure
PRF Pseudorandom Function
R Responder
SK Secret Key
SIP Session Initiation Protocol
SPI Security Parameter Index
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SRTP Secure Realtime Transport Protocol
TEK Traffic Encryption Key
TGK TEK Generation Key
3. Use Case Scenarios
This section describes some of the use case scenarios supported by
MIKEY-IBAKE, in addition to regular two-party communication.
3.1. Forking
Forking is the delivery of a request (e.g., SIP INVITE message) to
multiple endpoints. This happens when a single user is registered
more than once. An example of forking is when a user has a desk
phone, PC client, and mobile handset all registered with the same
public identity.
+---+ +-------+ +---+ +---+
| A | | PROXY | | B | | C |
+---+ +-------+ +---+ +---+
Request
-------------------->
Request
-------------------->
Request
------------------------------------->
Figure 1: Forking
3.2. Retargeting
Retargeting is a scenario in which a functional element decides to
redirect the session to a different destination. This decision to
redirect a session may be made for different reasons by a number of
different functional elements and at different points in the
establishment of the session.
There are two basic scenarios of session redirection. In scenario
one, a functional element (e.g., Proxy) decides to redirect the
session by passing the new destination information to the originator.
As a result, the originator initiates a new session to the redirected
destination provided by the Proxy. For the case of MIKEY-IBAKE, this
means that the originator will initiate a new session with the
identity of the redirected destination. This scenario is depicted in
Figure 2 below.
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+---+ +-------+ +---+ +---+
| A | | PROXY | | B | | C |
+---+ +-------+ +---+ +---+
Request
-------------------->
Request
-------------------->
Redirect
<--------------------
Redirect
<-------------------
Request
---------------------------------------------------------->
Figure 2: Retargeting
In the second scenario, a proxy decides to redirect the session
without informing the originator. This is a common scenario
specified in SIP [RFC3261].
3.3. Deferred Delivery
Deferred delivery is a type of service such that the session content
cannot be delivered to the destination at the time that it is being
sent (e.g., the destination user is not currently online).
Nevertheless, the sender expects the network to deliver the message
as soon as the recipient becomes available. A typical example of
deferred delivery is voicemail.
4. MIKEY-IBAKE Protocol Description
4.1. Overview
Most of the previously defined MIKEY modes consist of a single (or
half) roundtrip between two peers. MIKEY-IBAKE consists of up to
three roundtrips. In the first roundtrip, users (Initiator and
Responder) obtain their Private Key(s) (K_PR) from the KMS. This
roundtrip can be performed at anytime and, as explained earlier,
takes place, for example, once a month (or once per subscription
cycle). The second and the third roundtrips are between the
Initiator and the Responder. Observe that the Key Management Service
is only involved in the first roundtrip. In Figure 3, a conceptual
signaling diagram for the MIKEY-IBAKE mode is depicted.
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+---+ +------+ +------+ +---+
| I | | KMS1 | | KMS2 | | R |
+---+ +------+ +------+ +---+
REQUEST_KEY_INIT REQUEST_KEY_INIT
------------------> <----------------------
REQUEST_KEY_RESP REQUEST_KEY_RESP
<------------------ ---------------------->
I_MESSAGE_1
----------------------------------------------------------->
R_MESSAGE_1
<-----------------------------------------------------------
I_MESSAGE_2
----------------------------------------------------------->
R_MESSAGE_2
<-----------------------------------------------------------
Figure 3: Example Message Exchange
The Initiator (I) wants to establish a secure media session with the
Responder (R). The Initiator and the Responder trust a third party,
the Key Management Service (KMS), with which they both have, or can
establish, shared credentials. These pre-established trust relations
are used by a user (i.e., Initiator and Responder) to obtain Private
Keys. Rather than a single KMS, several different KMSs may be
involved, e.g., one for the Initiator and one for the Responder as
shown in Figure 3. The Initiator and the Responder do not share any
credentials; however, the Initiator knows the Responder's public
identity. The assumed trust model is illustrated in Figure 4.
+---+ +------+ +------+ +---+
| I | | KMS1 | | KMS2 | | R |
+---+ +------+ +------+ +---+
Pre-established Pre-established
trust relation trust relation
<-----------------> <--------------------->
Security association based on mutual authentication
performed during MIKEY-IBAKE exchange
<---------------------------------------------------------->
Figure 4: Trust Model
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Below, a description of how Private Keys are obtained using MIKEY
messages is provided. An alternative way for obtaining Private Keys
using HTTP is described in [RFC5408].
The Initiator obtains Private Key(s) from the KMS by sending a
REQUEST_KEY_INIT message. The REQUEST_KEY_INIT message includes
Initiator's public identity(s) (if the Initiator has more than one
public identity, it may request Private Keys for every identity
registered) and is protected via a MAC based on a pre-shared key or
via a signature (similar to the MIKEY-PSK and MIKEY-RSA modes). If
the request is authorized, the KMS generates the requested keys,
encodes them, and returns them in a REQUEST_KEY_RESP message. This
exchange takes place periodically and does not need to be performed
every time an Initiator needs to establish a secure connection with a
Responder.
The Initiator next chooses a random x and computes [x]P, where P is a
point on elliptic curve E known to all users. The Initiator uses the
Responder's public identity to generate the Responder's Public Key
(e.g., K_PUBr=H1(IDRr||date)), where Hi is hash function known to all
users, and the granularity in date is a matter of security policy and
known publicly. Then the Initiator uses this generated Public Key to
encrypt [x]P, IDRi and IDRr and includes this encrypted information
in an I_MESSAGE_1 message, which is sent to the Responder. The
encryption is Identity-Based Encryption (IBE) as specified in
[RFC5091] and [RFC5408]. In turn, the Responder IBE-decrypts the
received message using its Private Key for that date, chooses random
y and computes [y]P. Next, the Responder uses Initiator's identity
obtained from I_MESSAGE_1 to generate Initiator's Public Key (e.g.,
K_PUBi=H1(IDRi||date)) and IBE-encrypts (IDRi, IDRr, [x]P, [y]P)
using K_PUBi, and includes it in R_MESSAGE_1 message sent to the
Initiator. At this point, the Responder is able to generate the
session key as [x][y]P. This session key is then used to generate
TGK as specified in Section 5.1.
Upon receiving and IBE-decrypting an R_MESSAGE_1 message, the
Initiator verifies the received [x]P. At this point, the Initiator
is able to generate the same session key as [x][y]P. Upon successful
verification, the Initiator sends I_MESSAGE_2 message to the
Responder, including IBE-encrypted IDRi, IDRr and previously received
[y]P. The Responder sends a R_MESSAGE_2 message to the Initiator as
verification.
The above described is the most typical use case; in Section 3, some
alternative use cases are discussed.
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MIKEY-IBAKE is based on [RFC3830]; therefore, the same terminology,
processing, and considerations still apply unless otherwise stated.
Payloads containing EC Diffie-Hellman values and keys exchanged in
I_MESSAGE/R_MESSAGE are IBE encrypted as specified in [RFC5091] and
[RFC5408], while the keys exchanged in KEY_REQUES_INIT/
KEY_REQUEST_RESPONSE are encrypted as specified in [RFC3830]. In all
exchanges, encryption is only applied to the payloads containing keys
and EC Diffie-Hellman values and not to the entire messages.
4.2. Message Exchanges and Processing
4.2.1. REQUEST_KEY_INIT/REQUEST_KEY_RESP Message Exchange
This exchange is used by a user (e.g., Initiator or Responder) to
request Private Keys from a trusted Key Management Service, with
which the user has pre-shared credentials. A full roundtrip is
required for a user to receive keys. As this message must ensure the
identity of the user to the KMS, it is protected via a MAC based on a
pre-shared key or via a signature. The initiation message
REQUEST_KEY_INIT comes in two variants corresponding to the pre-
shared key (PSK) and Public-Key encryption (PKE) methods of
[RFC3830]. The response message REQUEST_KEY_RESP is the same for the
two variants and SHALL be protected by using the pre-shared/envelope
key indicated in the REQUEST_KEY_INIT message.
Initiator/Responder KMS
REQUEST_KEY_INIT_PSK = ---->
HDR, T, RAND, (IDRi/r),
IDRkms, [IDRpsk], [KEMAC], V <---- REQUEST_KEY_RESP =
HDR, T, [IDRi/r], [IDRkms],
KEMAC, V
REQUEST_KEY_INIT_PKE = ---->
HDR, T, RAND, (IDRi/r),
{CERTi/r}, IDRkms, <---- REQUEST_KEY_RESP =
[KEMAC], [CHASH], HDR, T, [IDRi/r], [IDRkms],
PKE, SIGNi/r KEMAC, V
4.2.1.1. Components of the REQUEST_KEY_INIT Message
The main objective of the REQUEST_KEY_INIT message is for a user to
request one or more Private Keys (K_PR) from the KMS. The user may
request a K_PR for each public identity it possesses, as well as for
multiple dates.
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The REQUEST_KEY_INIT message MUST always include the Header (HDR),
Timestamp (T), and RAND payloads. The CSB ID (Crypto Session Bundle
ID) SHALL be assigned as in [RFC3830]. The user SHALL include it in
the CSB ID field of the Header. The user SHALL set the #CS field to
'0' since CS (Crypto Session(s)) SHALL NOT be handled. The CS ID map
type SHALL be the "Empty map" as defined in [RFC4563].
IDRi/r contains the identity of the user. Since the user may have
multiple identities, multiple IDRi/r fields may appear in the
message.
IDRkms SHALL be included.
The KEMAC payload SHALL be used only when the user needs to use
specific keys. Otherwise, this payload SHALL NOT be used.
4.2.1.1.1. Components of the REQUEST_KEY_INIT_PSK Message
The IDRpsk payload MAY be used to indicate the pre-shared key used.
The last payload SHALL be a Verification (V) payload where the
authentication key (auth_key) is derived from the pre-shared key (see
Section 4.1.4 of [RFC3830] for key derivation specification).
4.2.1.1.2. Components of the REQUEST_KEY_INIT_PKE Message
The certificate (CERT) payload SHOULD be included. If a certificate
chain is to be provided, each certificate in the chain MUST be
included in a separate CERT payload.
The PKE payload contains the encrypted envelope key: PKE = E(PKkms,
env_key). It is encrypted using the KMS's Public Key (PKkms). If
the KMS possesses several Public Keys, the user can indicate the key
used in the CHASH payload.
SIGNi/r is a signature covering the entire MIKEY message, using the
Initiator's signature key.
4.2.1.2. Processing of the REQUEST_KEY_INIT Message
If the KMS can verify the integrity of the received message and the
message can be correctly parsed, the KMS MUST check the Initiator's
authorization. If the Initiator is authorized to receive the
requested Private Key(s), the KMS MUST send a REQUEST_KEY_RESP
message. Unexpected payloads in the REQUEST_KEY_INIT message SHOULD
be ignored. Errors are handled as described in [RFC3830].
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4.2.1.3. Components of the REQUEST_KEY_RESP Message
The version, PRF func and CSB ID, #CS, and CS ID map type fields in
the HDR payload SHALL be identical to the corresponding fields in the
REQUEST_KEY_INIT message. The KMS SHALL set the V flag to 0 and the
user receiving it SHALL ignore it as it has no meaning in this
context.
The Timestamp type and value SHALL be identical to the one used in
the REQUEST_KEY_INIT message.
KEMAC = E(encr_key, (ID || K_PR))
The KEMAC payload SHOULD use the NULL authentication algorithm, as a
MAC is included in the V payload. Depending on the type of
REQUEST_KEY_INIT message, either the pre-shared key or the envelope
key SHALL be used to derive the encr_key.
The last payload SHALL be a Verification (V) payload. Depending on
the type of REQUEST_KEY_INIT message, either the pre-shared key or
the envelope key SHALL be used to derive the auth_key.
4.2.1.4. Processing of the REQUEST_KEY_RESP Message
If the Initiator/Responder can correctly parse the received message,
the received session information SHOULD be stored. Otherwise, the
Initiator/Responder SHOULD silently discard the message and abort the
protocol.
4.2.2. I_MESSAGE/R_MESSAGE Message Exchanges
This exchange is used for Initiator and Responder to mutually
authenticate each other and to exchange EC Diffie-Hellman values used
to generate TGK. These exchanges are modeled after the pre-shared
key mode, with the exception that the Elliptic Curve Diffie-Hellman
values and Secret Keys (SKs) are encoded in IBAKE and ESK payloads
instead of a KEMAC payload. Two full roundtrips are required for
this exchange to successfully complete. The messages are preferably
included in the session setup signaling (e.g., SIP INVITE).
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Initiator Responder
I_MESSAGE_1 = ---->
HDR, T, RAND, IDRi, IDRr,
IBAKE, [ESK] <---- R_MESSAGE_1 =
HDR, T, IDRi,
IDRr, IBAKE
I_MESSAGE_2 = ---->
HDR, T, RAND, IDRi, IDRr,
IBAKE, [ESK] <---- R_MESSAGE_2 =
HDR, T, [IDRi], [IDRr],
[IBAKE], V
4.2.2.1. Components of the I_MESSAGE_1 Message
The I_MESSAGE_1 message MUST always include the Header (HDR),
Timestamp (T), and RAND payloads. The CSB ID (Crypto Session Bundle
ID) SHALL be randomly selected by the Initiator. As the R_MESSAGE_1
message is mandatory, the Initiator indicates with the V flag that a
verification message is expected.
The IDRi and IDRr payloads SHALL be included.
The IBAKE payload contains Initiator's Identity and EC Diffie-Hellman
values (ECCPTi), and Responder's Identity all encrypted using
Responder's Public Key (i.e., encr_key = K_PUBr) as follows:
IBAKE = E(encr_key, IDRi || ECCPTi || IDRr)
Optionally, Encrypted Secret Key (ESK) payload MAY be included. If
included, ESK contains an identity and a Secret Key (SK) encrypted
using intended Responder's Public Key (i.e., encr_key = K_PUBr).
ESK = E(encr_key, ID || SK)
4.2.2.2. Processing of the I_MESSAGE_1 Message
The parsing of I_MESSAGE_1 message SHALL be done as in [RFC3830]. If
the received message is correctly parsed, the Responder SHALL use the
Private Key (K_PRr) corresponding to the received IDRr to decrypt the
IBAKE payload. If the message contains ESK payload, the Responder
SHALL decrypt the SK and use it to decrypt the received IBAKE
payload. Otherwise, if the Responder is not able to decrypt the
Cakulev & Sundaram Informational [Page 13]RFC 6267 MIKEY-IBAKE June 2011
IBAKE payload, the Responder SHALL indicate it to the Initiator by
including only its own EC Diffie-Hellman value (ECCPTr) in the next
message (i.e., R_MESSAGE_1) it sends to the Initiator.
If the received message cannot be correctly parsed, the Responder
SHOULD silently discard the message and abort the protocol.
4.2.2.3. Components of the R_MESSAGE_1 Message
The version, PRF func, CSB ID, #CS, and CS ID map type fields in the
HDR payload SHALL be identical to the corresponding fields in the
I_MESSAGE_1 message. The V flag SHALL be set to 1 as I_MESSAGE_2
message is mandatory.
The Timestamp type and value SHALL be identical to the one used in
the I_MESSAGE_1 message.
The IDRi and IDRr payloads SHALL be included. The IDRi payload SHALL
be as received in the I_MESSAGE_1. In the IDRr payload, the
Responder SHALL include its own identity. Note that this identity
might be different from the identity contained in the IDRr payload
received in I_MESSAGE_1 message. The IDRr payloads of I_MESSAGE_1
and R_MESSAGE_1 will be different in the case of forking,
retargeting, and deferred delivery.
The Responder's IBAKE payload contains the Initiator's EC Diffie-
Hellman value (ECCPTi) received in I_MESSAGE_1 (if successfully
decrypted), and the Initiator's EC Diffie-Hellman value generated by
the Responder (ECCPTr), as well as corresponding Initiator and
Responder's identities. If the Responder is unable to decrypt the
IBAKE payload received in I_MESSAGE_1 (e.g., the message is received
by the intended Responder's mailbox), the Responder SHALL include
only its own EC Diffie-Hellman value (ECCPTr). The IBAKE payload in
R_MESSAGE_1 is encrypted using Initiator's Public Key (i.e., encr_key
= P_PUBi) as follows:
IBAKE = E(encr_key, IDRi || {ECCPTi} || IDRr || ECCPTr)
4.2.2.4. Processing of the R_MESSAGE_1 Message
The parsing of R_MESSAGE_1 message SHALL be done as in [RFC3830]. If
the received message is correctly parsed, the Initiator shall use the
Private Key corresponding to the received IDRi to decrypt the IBAKE
payload. If the ECCPTi sent in I_MESSAGE_1 is not present in the
received IBAKE payload (e.g., the Responder is currently offline and
the R_MESSAGE_1 is received from Responder's mailbox), the Initiator
Cakulev & Sundaram Informational [Page 14]RFC 6267 MIKEY-IBAKE June 2011
SHALL include ECCPTi again in the next message, I_MESSAGE_2. In this
case, I_MESSAGE_2 SHALL also contain an ESK payload encrypted using
the intended recipient's K_PUB.
If the received message cannot be correctly parsed, the Initiator
SHOULD silently discard the message and abort the protocol.
4.2.2.5. Components of the I_MESSAGE_2 Message
The I_MESSAGE_2 message MUST always include the Header (HDR),
Timestamp (T), and RAND payloads. The version, PRF func, CSB ID,
#CS, and CS ID map type fields in the HDR payload SHALL be identical
to the corresponding fields in the R_MESSAGE_2 message. As the
R_MESSAGE_2 message is mandatory, the Initiator indicates with the V
flag that a verification message is expected.
The IDRi and IDRr payloads SHALL be included. The IDRr payload SHALL
be the same as the IDRr payload received in the R_MESSAGE_1.
The Initiator's IBAKE payload SHALL contain the Initiator's EC
Diffie-Hellman value (ECCPTi) if the ECCPTi was not received in
R_MESSAGE_1. Otherwise, ECCPTi SHALL NOT be included. The IBAKE
payload in I_MESSAGE_2 SHALL contain the Initiator's and Responder's
identities as well as Responder's EC Diffie-Hellman value received in
message R_MESSAGE_1. IBAKE payload SHALL be encrypted using
Responder's Public Key (i.e., encr_key = K_PUBr) as follows:
IBAKE = E(encr_key, IDRi || {ECCPTi} || IDRr || ECCPTr)
Optionally, Encrypted Secret Key (ESK) payload can be included. ESK
SHALL be included in case R_MESSAGE_1 did not contain Initiator's EC
Diffie-Hellman value (ECCPTi) (e.g., in the case of deferred
delivery). If included, it contains an Initiator's identity and
Initiator-generated Secret Key (SK) encrypted using intended
recipient Public Key (i.e., encr_key = K_PUB) as follows:
ESK = E(encr_key, ID || SK)
4.2.2.6. Processing of the I_MESSAGE_2 Message
The parsing of the I_MESSAGE_2 message SHALL be done as in [RFC3830].
If the received message is correctly parsed, the Responder shall use
the K_PRr corresponding to the received IDRr to decrypt the IBAKE
payload. If an ESK is received, the Responder SHALL store it for
future use (e.g., the Responder is a mailbox and will forward the key
to the user once the user is online).
Cakulev & Sundaram Informational [Page 15]RFC 6267 MIKEY-IBAKE June 2011
If the received message cannot be correctly parsed, the Responder
SHOULD silently discard the message and abort the protocol.
4.2.2.7. Components of the R_MESSAGE_2 Message
The version, PRF func, CSB ID, #CS, and CS ID map type fields in the
HDR payload SHALL be identical to the corresponding fields in the
I_MESSAGE_2 message. The V flag SHALL be set to 0 by the Responder
and ignored by the Initiator.
The Timestamp type and value SHALL be identical to the one used in
the I_MESSAGE_2 message.
The IDRi and IDRr payloads SHOULD be included.
If Initiator's EC Diffie-Hellman value (ECCPTi) was received in
I_MESSAGE_2, the Responder SHALL also include the IBAKE payload. If
included, the IBAKE payload SHALL contain Initiator's EC Diffie-
Hellman value (ECCPTi), and the Initiator's identity previously
received in I_MESSAGE_2, encrypted using Initiator's Public Key
(i.e., encr_key = K_PUBi) as follows:
IBAKE = E(encr_key, IDRi || ECCPTi)
The last payload SHALL be a Verification (V) payload where the
authentication key (auth_key) is derived as specified in Section 5.2.
4.2.2.8. Processing of the R_MESSAGE_2 Message
The parsing of R_MESSAGE_2 message SHALL be done as in [RFC3830]. If
the received message is correctly parsed, and if it contains the
IBAKE payload, the Initiator SHALL use the K_PRi corresponding to the
received IDRi to decrypt the IBAKE payload.
If the received message cannot be correctly parsed, the Initiator
SHOULD silently discard the message and abort the protocol.
5. Key Management
The keys used in REQUEST_KEY_INIT/REQUEST_KEY_RESP exchange are
derived from the pre-shared key or the envelope key as specified in
[RFC3830]. As crypto sessions are not handled in this exchange,
further keying material (i.e., TEKs) for this message exchange SHALL
NOT be derived.
Cakulev & Sundaram Informational [Page 16]RFC 6267 MIKEY-IBAKE June 2011
5.1. Generating Keys from the Session Key
As stated above, the session key [x][y]P is generated using exchanged
EC Diffie-Hellman values, where x and y are randomly chosen by the
Initiator and Responder. The session key, as a point on an elliptic
curve, is then converted into octet string as specified in [SEC1].
This octet string K_SESSION is then used to generate MPK and TGK.
Finally, the traffic encryption keys (e.g., TEK) are generated from
TGK as specified in [RFC3830].
The MPK and TGK are generated from K_SESSION as follows.
inkey : K_SESSION
inkey_len : bit length of the MPK
label : constant || 0xFF || 0xFFFFFFFF || RAND
outkey_len : desired bit length of the output key (MPK or TGK)
The constant depends on the derived key type as summarized below.
+-------------+------------+
| Derived Key | Constant |
+-------------+------------+
| MPK | 0x220E99A2 |
| TGK | 0x1F4D675B |
+-------------+------------+
Table 1: Constants for Key Derivation
The constants are taken from the decimal digits of e as described in
[RFC3830].
5.2. Generating Keys for MIKEY Messages
The keys for MIKEY messages are used to protect the MIKEY messages
exchanged between the Initiator and Responder (i.e., I_MESSAGE and
R_MESSAGE). In the REQUEST_KEY_INIT/REQUEST_KEY_RESP exchange, the
key derivation SHALL be done exactly as in [RFC3830].
MIKEY Protection Key (MPK) for I_MESSAGE/R_MESSAGE exchange is
generated as described in Section 5.1. This MPK is then used to
derive keys to protect R_MESSAGE_2 message.
inkey : MPK
inkey_len : bit length of the MPK
label : constant || 0xFF || csb_id || RAND
outkey_len : desired bit length of the output key
where the constants are as defined in [RFC3830].
Cakulev & Sundaram Informational [Page 17]RFC 6267 MIKEY-IBAKE June 2011
5.3. CSB Update
Similar to [RFC3830], MIKEY-IBAKE provides means for updating the CSB
(Crypto Session Bundle), e.g., transporting new EC Diffe-Hellman
values or adding new crypto sessions. The CSB updating is done by
executing the exchange of I_MESSAGE_1/R_MESSAGE_1. The CSB updating
MAY be started by either the Initiator or the Responder.
Initiator Responder
I_MESSAGE_1 = ---->
HDR, T, [IDRi], [IDRr],
[IBAKE] <---- R_MESSAGE_1 =
HDR, T, [IDRi], [IDRr],
[IBAKE], V
Responder Initiator
I_MESSAGE_1 = ---->
HDR, T, [IDRr], [IDRi],
[IBAKE] <---- R_MESSAGE_1 =
HDR, T, [IDRi], [IDRr],
[IBAKE], V
The new message exchange MUST use the same CSB ID as the initial
exchange, but MUST use a new Timestamp. Other payloads that were
provided in the initial exchange SHOULD NOT be included. New RANDs
MUST NOT be included in the message exchange (the RANDs will only
have effect in the initial exchange).
IBAKE payload with new EC Diffie-Hellman values SHOULD be included.
If new EC Diffie-Hellman values are being exchanged during CSB
updating, messages SHALL be protected with keys derived from EC
Diffie-Hellman values exchanged as specified in Section 5.2.
Otherwise, if new EC Diffie-Hellman values are not being exchanged
during CSB update exchange, messages SHALL be protected with the keys
that protected the I_MESSAGE/R_MESSAGE messages in the initial
exchange.
5.4. Generating MAC and Verification Message
The authentication tag in all MIKEY-IBAKE messages is generated as
described in [RFC3830]. As described above, the MPK is used to
derive the auth_key. The MAC/Signature in the V/SIGN payloads covers
the entire MIKEY message, except the MAC/Signature field itself and
if there is an ESK payload in the massage it SHALL be omitted from
MAC/Signature calculation. The identities (not whole payloads) of
Cakulev & Sundaram Informational [Page 18]RFC 6267 MIKEY-IBAKE June 2011
the involved parties MUST directly follow the MIKEY message in the
Verification MAC/Signature calculation. Note that in the I_MESSAGE/
R_MESSAGE exchange, IDRr in R_MESSAGE_1 MAY not be the same as that
appearing in I_MESSAGE_1.
6. Payload Encoding
This section does not describe all the payloads that are used in the
new message types. It describes in detail the new IBAKE and ESK
payloads and in less detail the payloads for which changes has been
made compared to [RFC3830]. For a detailed description of the MIKEY
payloads (e.g., Timestamp (T) payload, RAND payload, etc.), see
[RFC3830]. For the description of IDR payload as well as for the
definition of additional PRF functions and encryption algorithms not
defined in [RFC3830], see [RFC6043].
6.1. Common Header Payload (HDR)
For the Common Header Payload, new values are added to the data type
and the next payload namespaces.
o Data type (8 bits): describes the type of message.
+------------------+-------+------------------------------------+
| Data Type | Value | Comment |
+------------------+-------+------------------------------------+
| REQUEST_KEY_PSK | 19 | Request Private Keys message (PSK) |
| REQUEST_KEY_PKE | 20 | Request Private Keys message (PKE) |
| REQUEST_KEY_RESP | 21 | Response Private Keys message |
| I_MESSAGE_1 | 22 | First Initiator's message |
| R_MESSAGE_1 | 23 | First Responder's message |
| I_MESSAGE_2 | 24 | Second Initiator's message |
| R_MESSAGE_2 | 25 | Second Responder's message |
+------------------+-------+------------------------------------+
Table 2: Data Type (Additions)
o Next payload (8 bits): identifies the payload that is added after
this payload.
Cakulev & Sundaram Informational [Page 19]RFC 6267 MIKEY-IBAKE June 2011
+--------------+-------+---------------+
| Next Payload | Value | Section |
+--------------+-------+---------------+
| IBAKE | 22 | Section 6.1.1 |
| ESK | 23 | Section 6.1.2 |
| SK | 24 | Section 6.1.5 |
| ECCPT | 25 | Section 6.1.4 |
+--------------+-------+---------------+
Table 3: Next Payload (Additions)
o V (1 bits): flag to indicate whether or not a response message is
expected (this only has meaning when it is set in an initiation
message). If a response is required, the V flag SHALL always be
set to 1 in the initiation messages and the receiver of the
initiation message (Responder or KMS) SHALL ignore it.
o #CS (8 bits): indicates the number of crypto sessions that will be
handled within the CSB. It SHALL be set to 0 in the Request Key
exchange, as crypto sessions SHALL NOT be handled.
o CS ID map type (8 bits): specifies the method of uniquely mapping
crypto sessions to the security protocol sessions. In the Request
Key exchange, the CS ID map type SHALL be the "Empty map" (defined
in [RFC4563]) as crypto sessions SHALL NOT be handled.
6.1.1. IBAKE Payload
The IBAKE payload contains IBE encrypted (see [RFC5091] and [RFC5408]
for details about IBE) Initiator and Responder's Identities and EC
Diffie-Hellman Sub-Payloads (see Section 6.1.4 for the definition of
EC Diffie-Hellman Sub-Payload). It may contain one or more EC
Diffie-Hellman Sub-Payloads and their associated identities. The
last EC Diffie-Hellman or Identity Sub-Payload has its Next payload
field set to Last payload.
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 ! Encr data len ! Encr data !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Encr data ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
o Next payload (8 bits): identifies the payload that is added after
this payload.
Cakulev & Sundaram Informational [Page 20]RFC 6267 MIKEY-IBAKE June 2011
o Encr data len (16 bits): length of Encr data (in bytes).
o Encr data (variable length): the IBE encrypted EC Diffie-Hellman
Sub-Payloads (see Section 6.1.4) and their associated Identity
payloads.
6.1.2. Encrypted Secret Key (ESK) Payload
The Encrypted Secret Key payload contains IBE encrypted (see
[RFC5091] and [RFC5408] for details about IBE) Secret Key Sub-Payload
and its associated identity (see Section 6.1.5 for the definition of
the Secret Key Sub-Payload).
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 ! Encr data len ! Encr data !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Encr data ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
o Next payload (8 bits): identifies the payload that is added after
this payload.
o Encr data len (16 bits): length of Encr data (in bytes).
o Encr data (variable length): the encrypted secret key Sub-Payloads
(see Section 6.1.5).
6.1.3. Key Data Sub-Payload
For the key data Sub-Payload, a new type of key is defined. The
Private Key (K_PR) is used to decrypt the content encrypted using the
corresponding Public Key (K_PUB). KEMAC in the REQUEST_KEY_RESP
SHALL contain one or more Private Keys.
o Type (4 bits): indicates the type of key included in the payload.
+------+-------+-------------+
| Type | Value | Comments |
+------+-------+-------------+
| K_PR | 7 | Private Key |
+------+-------+-------------+
Table 4: Key Data Type (Additions)
Cakulev & Sundaram Informational [Page 21]RFC 6267 MIKEY-IBAKE June 2011
6.1.4. EC Diffie-Hellman Sub-Payload
The EC Diffie-Hellman (ECCPT) Sub-Payload uses the format defined
below. The EC Diffie-Hellman Sub-Payload in MIKEY-IBAKE is never
included in clear, but as an encrypted part of the IBAKE payload.
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 ! ECC Curve ! ECC Point ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Auth alg ! TGK len ! Reserv! KV !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! KV data (optional) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
o Next payload (8 bits): identifies the payload that is added after
this payload. See Section 6.1 of [RFC3830] for values.
o ECC curve (8 bits): identifies the ECC curve used.
+--------------------------------------+-------+
| ECC Curve | Value |
+--------------------------------------+-------+
| ECPRGF192Random / P-192 / secp192r1 | 1 |
| EC2NGF163Random / B-163 / sect163r2 | 2 |
| EC2NGF163Koblitz / K-163 / sect163k1 | 3 |
| EC2NGF163Random2 / none / sect163r1 | 4 |
| ECPRGF224Random / P-224 / secp224r1 | 5 |
| EC2NGF233Random / B-233 / sect233r1 | 6 |
| EC2NGF233Koblitz / K-233 / sect233k1 | 7 |
| ECPRGF256Random / P-256 / secp256r1 | 8 |
| EC2NGF283Random / B-283 / sect283r1 | 9 |
| EC2NGF283Koblitz / K-283 / sect283k1 | 10 |
| ECPRGF384Random / P-384 / secp384r1 | 11 |
| EC2NGF409Random / B-409 / sect409r1 | 12 |
| EC2NGF409Koblitz / K-409 / sect409k1 | 13 |
| ECPRGF521Random / P-521 / secp521r1 | 14 |
| EC2NGF571Random / B-571 / sect571r1 | 15 |
| EC2NGF571Koblitz / K-571 / sect571k1 | 16 |
+--------------------------------------+-------+
Table 5: Elliptic Curves
o ECC point (variable length): ECC point data, padded to end on a
32-bit boundary, encoded in octet string representation.
Cakulev & Sundaram Informational [Page 22]RFC 6267 MIKEY-IBAKE June 2011
o Auth alg (8 bits): specifies the MAC algorithm used for the
verification message. For MIKEY-IBAKE this field is ignored.
o TGK len (16 bits): the length of the TGK (in bytes). For MIKEY-
IBAKE this field is ignored.
o KV (4 bits): indicates the type of key validity period specified.
This may be done by using an SPI (alternatively an MKI in SRTP) or
by providing an interval in which the key is valid (e.g., in the
latter case, for SRTP this will be the index range where the key
is valid). See Section 6.13 of [RFC3830] for pre-defined values.
o KV data (variable length): This includes either the SPI/MKI or an
interval (see Section 6.14 of [RFC3830]). If KV is NULL, this
field is not included.
6.1.5. Secret Key Sub-Payload
Secret Key payload is included as a Sub-Payload in Encrypted Secret
Key payload. Similar to EC Diffie-Hellman Sub-Payload, it is never
included in clear, but as an encrypted part of the ESK payload.
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 ! Type ! KV ! Key data len !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Key data ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! KV data (optional) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
o Next payload (8 bits): identifies the payload that is added after
this payload.
o Type (4 bits): indicates the type of the key included in the
payload.
+------+-------+
| Type | Value |
+------+-------+
| SK | 1 |
+------+-------+
Table 6: Secret Key Types
Cakulev & Sundaram Informational [Page 23]RFC 6267 MIKEY-IBAKE June 2011
o KV (4 bits): indicates the type of key validity period specified.
This may be done by using an SPI (or MKI in the case of [RFC3711])
or by providing an interval in which the key is valid (e.g., in
the latter case, for SRTP this will be the index range where the
key is valid). KV values are the same as in Section 6.13 of
[RFC3830]
o Key data len (16 bits): the length of the Key data field (in
bytes).
o Key data (variable length): The SK data.
o KV data (variable length): This includes either the SPI or an
interval. If KV is NULL, this field is not included.
7. Security Considerations
Unless explicitly stated, the security properties of the MIKEY
protocol as described in [RFC3830] apply to MIKEY-IBAKE as well. In
addition, MIKEY-IBAKE is based on the basic Identity-Based Encryption
protocol, as specified in [RFC5091], [RFC5408], and [RFC5409], and as
such inherits some properties of that protocol. For instance, by
concatenating the "date" with the identity (to derive the Public
Key), the need for any key revocation mechanisms is virtually
eliminated. Moreover, by allowing the participants to acquire
multiple Private Keys (e.g., for duration of contract) the
availability requirements on the KMS are also reduced without any
reduction in security.
7.1. General Security Considerations
The MIKEY-IBAKE protocol relies on the use of Identity-Based
Encryption. [RFC5091] describes attacks on the cryptographic
algorithms used in Identity-Based Encryption. In addition, [RFC5091]
provides recommendations for security parameters for described IBE
algorithms.
It is assumed that the Key Management Services are secure, not
compromised, trusted, and will not engage in launching active attacks
independently or in a collaborative environment. However, any
malicious insider could potentially launch passive attacks (by
decryption of one or more message exchanges offline). While it is in
the best interest of administrators to prevent such attacks, it is
hard to eliminate this problem. Hence, it is assumed that such
problems will persist, and hence the protocols are designed to
protect participants from passive adversaries.
Cakulev & Sundaram Informational [Page 24]RFC 6267 MIKEY-IBAKE June 2011
7.2. IBAKE Protocol Security Considerations
For the basic IBAKE protocol, from a cryptographic perspective, the
following security considerations apply.
In every step, Identity-Based Encryption (IBE) is used with the
recipient's Public Key. This guarantees that only the intended
recipient of the message can decrypt the message [BF].
Next, the use of identities within the encrypted payload is intended
to eliminate some basic reflection attacks. For instance, suppose
identities were not used as part of the encrypted payload, in the
first step of the IBAKE protocol (i.e., I_MESSAGE_1 of Figure 3 in
Section 4.1). Furthermore, assume an adversary who has access to the
conversation between Initiator and Responder and can actively snoop
into packets and drop/modify them before routing them to the
destination. For instance, assume that the IP source address and
destination address can be modified by the adversary. After the
first message is sent by the Initiator (to the Responder), the
adversary can take over and trap the packet. Next, the adversary can
modify the IP source address to include adversary's IP address,
before routing it onto the Responder. The Responder will assume the
request for an IBAKE session came from the adversary and will execute
step 2 of the IBAKE protocol (i.e., R_MESSAGE_1 of Figure 3 in
Section 4.1) but encrypt it using the adversary's Public Key. The
above message can be decrypted by the adversary (and only by the
adversary). In particular, since the second message includes the
challenge sent by the Initiator to the Responder, the adversary will
now learn the challenge sent by the Initiator. Following this, the
adversary can carry on a conversation with the Initiator "pretending"
to be the Responder. This attack will be eliminated if identities
are used as part of the encrypted payload. In summary, at the end of
the exchange both Initiator and Responder can mutually authenticate
each other and agree on a session key.
Recall that Identity-Based Encryption guarantees that only the
recipient of the message can decrypt the message using the Private
Key. The caveat being, the KMS that generated the Private Key of
recipient of message can decrypt the message as well. However, the
KMS cannot learn the session key [x][y]P given [x]P and [y]P based on
the Elliptic Curve Diffie-Hellman problem. This property of
resistance to passive key escrow from the KMS is not applicable to
the basic IBE protocols proposed in [RFC5091], [RFC5408], and
[RFC5409].
Observe that the protocol works even if the Initiator and Responder
belong to two different Key Management Services. In particular, the
parameters used for encryption to the Responder and parameters used
Cakulev & Sundaram Informational [Page 25]
RFC 6267 MIKEY-IBAKE June 2011
for encryption to the Initiator can be completely different and
independent of each other. Moreover, the Elliptic Curve used to
generate the session key [x][y]P can be completely different. If
such flexibility is desired, then it would be advantageous to add
optional extra data to the protocol to exchange the algebraic
primitives used in deriving the session key.
In addition to mutual authentication, and resistance to passive
escrow, the Diffie-Hellman property of the session key exchange
guarantees perfect secrecy of keys. In others, accidental leakage of
one session key does not compromise past or future session keys
between the same Initiator and Responder.
7.3. Forking
In the Forking feature, given that there are multiple potential
Responders, it is important to observe that there is one "common
Responder" identity (and corresponding Public and Private Keys) and
each Responder has a unique identity (and corresponding Public and
Private Keys). Observe that, in this framework, if one Responder
responds to the invite from the Initiator, it uses its unique
identity such that the protocol guarantees that no other Responder
learns the session key.
7.4. Retargeting
In the Retargeting feature, the forwarding server does not learn the
Private Key of the intended Responder since it is encrypted using the
retargeted Responder's Public Key. Additionally, the Initiator will
learn that the retargeted Responder answered the phone (and not the
intended Responder) since the retargeted Responder includes its own
identity in the message sent to the Initiator. This will allow the
Initiator to decide whether or not to carry on the conversation.
Finally, the session key cannot be discovered by the intended
Responder since the random number chosen by the retargeted Responder
is not known to the intended Responder.
7.5. Deferred Delivery
In the Deferred Delivery feature, the Initiator and the Responder's
mailbox will mutually authenticate each other thereby preventing
server side "phishing" attacks and conversely guarantees to the
server (and eventually to the Responder) the identity of the
Initiator. Moreover, the key used by Initiator to encrypt the
contents of the message is completely independent from the session
key derived between the Initiator and the server. Finally, the key
Cakulev & Sundaram Informational [Page 26]
RFC 6267 MIKEY-IBAKE June 2011
used to encrypt the message is encrypted using the Responder's Public
Key, which allows the contents of the message to remain unknown to
the mailbox server.
8. IANA Considerations
This document defines several new values for the namespaces Data
Type, Next Payload, and Key Data Type defined in [RFC3830]. The
following IANA assignments have been added to the MIKEY Payload
registry (in bracket is a reference to the table containing the
registered values):
o Data Type (see Table 2)
o Next Payload (see Table 3)
o Key Data Type (see Table 4)
The ECCPT payload defines an 8-bit ECC Curve field for which IANA has
created and will maintain a new namespace in the MIKEY Payload
registry. Assignments consist of an ECC curve and its associated
value. 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]. The initial contents of the registry are as follows:
Value ECC curve
------- ------------------------------------
0 Reserved
1 ECPRGF192Random / P-192 / secp192r1
2 EC2NGF163Random / B-163 / sect163r2
3 EC2NGF163Koblitz / K-163 / sect163k1
4 EC2NGF163Random2 / none / sect163r1
5 ECPRGF224Random / P-224 / secp224r1
6 EC2NGF233Random / B-233 / sect233r1
7 EC2NGF233Koblitz / K-233 / sect233k1
8 ECPRGF256Random / P-256 / secp256r1
9 EC2NGF283Random / B-283 / sect283r1
10 EC2NGF283Koblitz / K-283 / sect283k1
11 ECPRGF384Random / P-384 / secp384r1
12 EC2NGF409Random / B-409 / sect409r1
13 EC2NGF409Koblitz / K-409 / sect409k1
14 ECPRGF521Random / P-521 / secp521r1
15 EC2NGF571Random / B-571 / sect571r1
16 EC2NGF571Koblitz / K-571 / sect571k1
17-239 Unassigned
240-254 Private Use
255 Reserved
Cakulev & Sundaram Informational [Page 27]RFC 6267 MIKEY-IBAKE June 2011
The SK Sub-Payload defines a 4-bit Type field for which IANA has
created and will maintain a new namespace in the MIKEY Payload
registry. Assignments consist of a type of key and its associated
value. Values in the range 2-15 SHOULD be approved by the process of
Specification Required. The initial contents of the registry are as
follows:
Value Type
------- ---------------
0 Reserved
1 Secret Key (SK)
2-15 Unassigned
9. References
9.1. Normative References
[BF] Boneh, D. and M. Franklin, "Identity-Based Encryption from
the Weil Pairing", in SIAM J. of Computing, Vol. 32,
No. 3, pp. 586-615, 2003.
[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.
[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.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[RFC6043] Mattsson, J. and T. Tian, "MIKEY-TICKET: Ticket-Based
Modes of Key Distribution in Multimedia Internet KEYing
(MIKEY)", RFC 6043, March 2011.
[SEC1] Standards for Efficient Cryptography Group, "Elliptic
Curve Cryptography", September 2000.
Cakulev & Sundaram Informational [Page 28]RFC 6267 MIKEY-IBAKE June 2011
9.2. Informative References
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
June 2002.
[RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
Norrman, "The Secure Real-time Transport Protocol (SRTP)",
RFC 3711, March 2004.
[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.
[RFC5091] Boyen, X. and L. Martin, "Identity-Based Cryptography
Standard (IBCS) #1: Supersingular Curve Implementations of
the BF and BB1 Cryptosystems", RFC 5091, December 2007.
[RFC5408] Appenzeller, G., Martin, L., and M. Schertler, "Identity-
Based Encryption Architecture and Supporting Data
Structures", RFC 5408, January 2009.
[RFC5409] Martin, L. and M. Schertler, "Using the Boneh-Franklin and
Boneh-Boyen Identity-Based Encryption Algorithms with the
Cryptographic Message Syntax (CMS)", RFC 5409,
January 2009.
Cakulev & Sundaram Informational [Page 29]RFC 6267 MIKEY-IBAKE June 2011
Authors' Addresses
Violeta Cakulev
Alcatel Lucent
600 Mountain Ave.
3D-517
Murray Hill, NJ 07974
US
Phone: +1 908 582 3207
EMail: violeta.cakulev@alcatel-lucent.com
Ganapathy Sundaram
Alcatel Lucent
600 Mountain Ave.
3D-517
Murray Hill, NJ 07974
US
Phone: +1 908 582 3209
EMail: ganesh.sundaram@alcatel-lucent.com
Cakulev & Sundaram Informational [Page 30]
