draft-ietf-msec-mikey-dhhmac-02.txt   draft-ietf-msec-mikey-dhhmac-03.txt 
HMAC-authenticated Diffie-Hellman for MIKEY June 2003 HMAC-authenticated Diffie-Hellman for MIKEY July 2003
Internet Engineering Task Force - MSEC WG Internet Engineering Task Force - MSEC WG
Internet Draft M. Euchner Internet Draft M. Euchner
Intended Category: Proposed Standard Intended Category: Proposed Standard
Expires: December 2003 June 2003 Expires: January 2004 July 2003
HMAC-authenticated Diffie-Hellman for MIKEY HMAC-authenticated Diffie-Hellman for MIKEY
<draft-ietf-msec-mikey-dhhmac-02.txt> <draft-ietf-msec-mikey-dhhmac-03.txt>
Status of this Memo Status of this Memo
This document is an Internet-Draft and is in full conformance with This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026 [1]. all provisions of Section 10 of RFC2026 [1].
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Abstract Abstract
This document describes a point-to-point key management protocol This document describes a point-to-point key management protocol
variant for the multimedia Internet keying (MIKEY). In particular, variant for the multimedia Internet keying (MIKEY). In particular,
the classic Diffie-Hellman key agreement protocol is used for key the classic Diffie-Hellman key agreement protocol is used for key
establishment in conjunction with a keyed hash (HMAC-SHA1) for establishment in conjunction with a keyed hash (HMAC-SHA1) for
HMAC-authenticated Diffie-Hellman for MIKEY June 2003 HMAC-authenticated Diffie-Hellman for MIKEY July 2003
achieving mutual authentication and message integrity of the key achieving mutual authentication and message integrity of the key
management messages exchanged. This MIKEY variant is called the management messages exchanged. This MIKEY variant is called the
HMAC-authenticated Diffie-Hellmann (DHHMAC). It addresses the HMAC-authenticated Diffie-Hellmann (DHHMAC). It addresses the
security and performance constraints of multimedia key management in security and performance constraints of multimedia key management in
MIKEY. MIKEY.
Conventions used in this document Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
this document are to be interpreted as described in RFC-2119 [2]. document are to be interpreted as described in RFC-2119 [2].
Table of Contents Table of Contents
1. Introduction................................................3 1. Introduction................................................3
1.1. Definitions.................................................5 1.1. Definitions.................................................5
1.2. Abbreviations...............................................5 1.2. Abbreviations...............................................6
2. Scenario....................................................6 2. Scenario....................................................7
2.1. Applicability...............................................7 2.1. Applicability...............................................7
3. DHHMAC Security Protocol....................................7 3. DHHMAC Security Protocol....................................8
3.1. TGK re-keying...............................................9 3.1. TGK re-keying...............................................9
4. DHHMAC payload formats.....................................10 4. DHHMAC payload formats.....................................10
4.1. Common header payload (HDR)................................11 4.1. Common header payload (HDR)................................11
4.2. Key data transport payload (KEMAC).........................11 4.2. Key data transport payload (KEMAC).........................12
4.3. ID payload (ID)............................................12 4.3. ID payload (ID)............................................12
5. Security Considerations....................................12 5. Security Considerations....................................13
5.1. Security environment.......................................13 5.1. Security environment.......................................13
5.2. Threat model...............................................13 5.2. Threat model...............................................13
5.3. Security features and properties...........................16 5.3. Security features and properties...........................16
5.4. Assumptions................................................20 5.4. Assumptions................................................20
5.5. Residual risk..............................................21 5.5. Residual risk..............................................21
IANA considerations.............................................22 IANA considerations.............................................22
Intellectual Property Rights....................................22 Intellectual Property Rights....................................22
References......................................................23 References......................................................23
Normative References............................................23 Normative References............................................23
Informative References..........................................23 Informative References..........................................24
Acknowledgments.................................................25 Acknowledgments.................................................25
Conclusions.....................................................25 Conclusions.....................................................25
Full Copyright Statement........................................25 Full Copyright Statement........................................26
Expiration Date.................................................26 Expiration Date.................................................27
Revision History................................................26 Revision History................................................27
HMAC-authenticated Diffie-Hellman for MIKEY June 2003 HMAC-authenticated Diffie-Hellman for MIKEY July 2003
Author's Addresses..............................................27 Author's Addresses..............................................28
1. Introduction 1. Introduction
There is work done in IETF to develop key management schemes. For
example, IKE [14] is a widely accepted unicast scheme for IPsec, and
the MSEC WG is developing other schemes, addressed to group
communication [24], [25]. For reasons discussed below, there is
however a need for a scheme with low latency, suitable for demanding
cases such as real-time data over heterogeneous networks, and small
interactive groups.
As pointed out in MIKEY (see [3]), secure real-time multimedia As pointed out in MIKEY (see [3]), secure real-time multimedia
applications demand a particular adequate key management scheme that applications demand a particular adequate key management scheme that
cares for how to securely and efficiently establish dynamic session cares for how to securely and efficiently establish dynamic session
keys in a conversational multimedia scenario. keys in a conversational multimedia scenario.
In general, MIKEY scenarios cover peer-to-peer, simple-one-to-many In general, MIKEY scenarios cover peer-to-peer, simple-one-to-many
and small-sized groups. MIKEY in particular, describes three key and small-sized groups. MIKEY in particular, describes three key
management schemes for the peer-to-peer case that all finish their management schemes for the peer-to-peer case that all finish their
task within one round trip: task within one round trip:
- a symmetric key distribution protocol based upon pre-shared - a symmetric key distribution protocol based upon pre-shared
master keys; master keys;
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signatures and certificates. signatures and certificates.
All these three key management protocols are designed such that they All these three key management protocols are designed such that they
complete their work within just one round trip. This requires complete their work within just one round trip. This requires
depending on loosely synchronized clocks and deploying timestamps depending on loosely synchronized clocks and deploying timestamps
within the key management protocols. within the key management protocols.
However, it is known [7] that each of the three key management However, it is known [7] that each of the three key management
schemes has its subtle constraints and limitations: schemes has its subtle constraints and limitations:
- The symmetric key distribution protocol is simple to - The symmetric key distribution protocol is simple to
implement but does not nicely scale in any larger HMAC-authenticated Diffie-Hellman for MIKEY July 2003
configuration of potential peer entities due to the need of
mutually pre-assigned shared master secrets. implement but does not nicely scale in any larger configuration
of potential peer entities due to the need of mutually pre-
assigned shared master secrets.
Moreover, the security provided does not achieve the property Moreover, the security provided does not achieve the property
of perfect forward secrecy; i.e. compromise of the shared of perfect forward secrecy; i.e. compromise of the shared
master secret would render past and even future session keys master secret would render past and even future session keys
susceptible to compromise. susceptible to compromise.
HMAC-authenticated Diffie-Hellman for MIKEY June 2003
Further, the generation of the session key happens just at the Further, the generation of the session key happens just at the
initiator. Thus, the responder has to fully trust the initiator. Thus, the responder has to fully trust the
initiator on choosing a good and secure session secret; the initiator on choosing a good and secure session secret; the
responder neither is able to participate in the key generation responder neither is able to participate in the key generation
nor to influence that process. This is considered as a nor to influence that process. This is considered as a
specific limitation in less trusted environments. specific limitation in less trusted environments.
- The public-key encryption scheme depends upon a public-key - The public-key encryption scheme depends upon a public-key
infrastructure that certifies the private-public keys by infrastructure that certifies the private-public keys by
issuing and maintaining digital certificates. While such a issuing and maintaining digital certificates. While such a key
key management scheme provides full scalability in large management scheme provides full scalability in large networked
networked configurations, public-key infrastructures are still configurations, public-key infrastructures are still not widely
not widely available and in general, implementations are available and in general, implementations are significantly
significantly more complex. more complex.
Further additional round trips might be necessary for each Further, additional round trips might be necessary for each
side in order to ascertain verification of the digital side in order to ascertain verification of the digital
certificates. certificates.
Finally, as in the symmetric case, the responder depends Finally, as in the symmetric case, the responder depends
completely upon the initiator choosing good and secure session completely upon the initiator choosing good and secure session
keys. keys.
- The third MIKEY key management protocol deploys the Diffie- - The third MIKEY key management protocol deploys the Diffie-
Hellman key agreement scheme and authenticates the exchange of Hellman key agreement scheme and authenticates the exchange of
the Diffie-Hellman half-keys in each direction by using a the Diffie-Hellman half-keys in each direction by using a
digital signature upon. As in the previous method, this digital signature upon. As in the previous method, this
introduces the dependency upon a public-key infrastructure introduces the dependency upon a public-key infrastructure with
with its strength on scalability but also the limitations on its strength on scalability but also the limitations on
computational costs in performing the asymmetric long-integer computational costs in performing the asymmetric long-integer
operations and the potential need for additional communication operations and the potential need for additional communication
for verification of the digital certificates. for verification of the digital certificates.
However, the Diffie-Hellman key agreement protocol is known HMAC-authenticated Diffie-Hellman for MIKEY July 2003
for its subtle security strengths in that it is able to
provide full perfect secrecy and further have both parties However, the Diffie-Hellman key agreement protocol is known for
actively involved in session key generation. its subtle security strengths in that it is able to provide
full perfect secrecy and further have both parties actively
involved in session key generation.
This document describes a fourth key management scheme for MIKEY that This document describes a fourth key management scheme for MIKEY that
could somehow be seen as a synergetic optimization between the pre- could somehow be seen as a synergetic optimization between the pre-
shared key distribution scheme and the Diffie-Hellman key agreement. shared key distribution scheme and the Diffie-Hellman key agreement.
HMAC-authenticated Diffie-Hellman for MIKEY June 2003
The idea of that protocol is to apply the Diffie-Hellman key The idea of that protocol is to apply the Diffie-Hellman key
agreement but instead of deploying a digital signature for agreement but instead of deploying a digital signature for
authenticity of the exchanged keying material rather uses a keyed- authenticity of the exchanged keying material rather uses a keyed-
hash upon using symmetrically pre-assigned shared secrets. This hash upon using symmetrically pre-assigned shared secrets. This
combination of security mechanisms is called the HMAC-authenticated combination of security mechanisms is called the HMAC-authenticated
Diffie-Hellman (DH) key agreement for MIKEY (DHHMAC). Diffie-Hellman (DH) key agreement for MIKEY (DHHMAC).
The DHHMAC variant closely follows the design and philosophy of MIKEY The DHHMAC variant closely follows the design and philosophy of MIKEY
and reuses MIKEY protocol payload components and MIKEY mechanisms to and reuses MIKEY protocol payload components and MIKEY mechanisms to
its maximum benefit and for best compatibility. its maximum benefit and for best compatibility.
Like the MIKEY Diffie-Hellman protocol, DHHMAC does not scale beyond Like the MIKEY Diffie-Hellman protocol, DHHMAC does not scale beyond
a point-to-point constellation; thus, both MIKEY Diffie-Hellman a point-to-point constellation; thus, both MIKEY Diffie-Hellman
protocols do not support group-based keying for any group size larger protocols do not support group-based keying for any group size larger
than two entities. than two entities.
1.1. Definitions 1.1. Definitions
The definitions and notations in this document are aligned with The definitions and notations in this document are aligned with
MIKEY, see [3] and [3] sections 1.2 - 1.3. MIKEY, see [3] and [3] sections 1.3 - 1.4.
All large integer computations in this document should be understood All large integer computations in this document should be understood
as being mod p within some fixed group G for some large prime p; see as being mod p within some fixed group G for some large prime p; see
[3] section 3.3; however, the DHHMAC protocol is applicable in [3] section 3.3; however, the DHHMAC protocol is applicable in
general to other appropriate groups as well. general to other appropriate finite, cyclical groups as well.
It is assumed that a pre-shared key s is known by both entities It is assumed that a pre-shared key s is known by both entities
(initiator and responder). The authentication key auth_key is (initiator and responder). The authentication key auth_key is
derived from the pre-shared secret s using the pseudo-random function derived from the pre-shared secret s using the pseudo-random function
PRF; see [3] sections 4.1.3 and 4.1.5. PRF; see [3] sections 4.1.3 and 4.1.5.
HMAC-authenticated Diffie-Hellman for MIKEY July 2003
In this text, [X] represents an optional piece of information. In this text, [X] represents an optional piece of information.
Generally throughout the text, X SHOULD be present unless certain Generally throughout the text, X SHOULD be present unless certain
circumstance MAY allow X being optional and not be present thereby circumstance MAY allow X being optional and not be present thereby
resulting in weaker security potentially. Likewise [X, Y] represents resulting in weaker security potentially. Likewise [X, Y] represents
an optional compound piece of information where the pieces X and Y an optional compound piece of information where the pieces X and Y
SHOULD be either both present or MAY optionally be both absent. SHOULD be either both present or MAY optionally be both absent.
1.2. Abbreviations 1.2. Abbreviations
HMAC-authenticated Diffie-Hellman for MIKEY June 2003
auth_key pre-shared authentication key, PRF-derived from auth_key pre-shared authentication key, PRF-derived from
pre-shared key s. pre-shared key s.
DH Diffie-Hellman DH Diffie-Hellman
DHi public Diffie-Hellman half key g**(xi) of Initiatior DHi public Diffie-Hellman half key g^(xi) of Initiatior
DHr public Diffie-Hellman half key g**(xr) of Responder DHr public Diffie-Hellman half key g^(xr) of Responder
DHHMAC HMAC-authenticated Diffie-Hellman DHHMAC HMAC-authenticated Diffie-Hellman
DoS Denial-of-service DoS Denial-of-service
G Diffie-Hellman group G Diffie-Hellman group
HDR MIKEY common header payload HDR MIKEY common header payload
HMAC keyed Hash Message Authentication Code HMAC keyed Hash Message Authentication Code
HMAC-SHA1 HMAC using SHA1 as hash function (160-bit result) HMAC-SHA1 HMAC using SHA1 as hash function (160-bit result)
HMAC-SHA1-96 HMAC-SHA1 truncated to 96 bits HMAC-SHA1-96 HMAC-SHA1 truncated to 96 bits
IDi Identity of initiator IDi Identity of initiator
IDr Identity of receiver IDr Identity of receiver
IKE Internet Key Exchange IKE Internet Key Exchange
skipping to change at page 6, line 35 skipping to change at page 6, line 45
RSA Rivest, Shamir and Adleman RSA Rivest, Shamir and Adleman
s pre-shared key s pre-shared key
SDP Session Description Protocol SDP Session Description Protocol
SOI Son-of-IKE, IKEv2 SOI Son-of-IKE, IKEv2
SP MIKEY Security Policy (Parameter) Payload SP MIKEY Security Policy (Parameter) Payload
T timestamp T timestamp
TEK Traffic Encryption Key TEK Traffic Encryption Key
TGK MIKEY TEK Generation Key as the common Diffie- TGK MIKEY TEK Generation Key as the common Diffie-
Hellman shared secret Hellman shared secret
TLS Transport Layer Security TLS Transport Layer Security
xi secret, random Diffie-Hellman key of Initiator xi secret, (pseudo) random Diffie-Hellman key of Initiator
xr secret, random Diffie-Hellman key of Responder xr secret, (pseudo) random Diffie-Hellman key of Responder
HMAC-authenticated Diffie-Hellman for MIKEY July 2003
2. Scenario 2. Scenario
The HMAC-authenticated Diffie-Hellman key agreement protocol (DHHMAC) The HMAC-authenticated Diffie-Hellman key agreement protocol (DHHMAC)
for MIKEY addresses the same scenarios and scope as the other three for MIKEY addresses the same scenarios and scope as the other three
key management schemes in MIKEY address. key management schemes in MIKEY address.
DHHMAC is applicable in a peer-to-peer group where no access to a DHHMAC is applicable in a peer-to-peer group where no access to a
public-key infrastructure can be assumed available. Rather, pre- public-key infrastructure can be assumed available. Rather, pre-
HMAC-authenticated Diffie-Hellman for MIKEY June 2003
shared master secrets are assumed available among the entities in shared master secrets are assumed available among the entities in
such an environment. such an environment.
In a pair-wise group, it is assumed that each client will be setting In a pair-wise group, it is assumed that each client will be setting
up a session key for its outgoing links with it's peer using the DH- up a session key for its outgoing links with it's peer using the DH-
MAC key agreement protocol. MAC key agreement protocol.
As is the case for the other three MIKEY key management protocol, As is the case for the other three MIKEY key management protocol,
DHHMAC assumes loosely synchronized clocks among the entities in the DHHMAC assumes loosely synchronized clocks among the entities in the
small group. small group.
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encapsulated and transported in SDP containers of the SDP encapsulated and transported in SDP containers of the SDP
offer/answer handshake, offer/answer handshake,
b) H.323 (see [22]) where the encoded MIKEY messages are transported b) H.323 (see [22]) where the encoded MIKEY messages are transported
in the H.225.0 fast start call signaling handshake. in the H.225.0 fast start call signaling handshake.
MIKEY-DHHMAC is offered as option to the other MIKEY key management MIKEY-DHHMAC is offered as option to the other MIKEY key management
variants (MIKEY-pre-shared, MIKEY-public-key and MIKEY-DH-SIGN) for variants (MIKEY-pre-shared, MIKEY-public-key and MIKEY-DH-SIGN) for
all those cases where DHHMAC has its peculiar strengths (see section all those cases where DHHMAC has its peculiar strengths (see section
5). 5).
HMAC-authenticated Diffie-Hellman for MIKEY July 2003
3. DHHMAC Security Protocol 3. DHHMAC Security Protocol
The following figure defines the security protocol for DHHMAC: The following figure defines the security protocol for DHHMAC:
Initiator Responder Initiator Responder
I_message = HDR, T, RAND, [IDi], I_message = HDR, T, RAND, [IDi],
{SP}, DHi, KEMAC {SP}, DHi, KEMAC
HMAC-authenticated Diffie-Hellman for MIKEY June 2003
I_message I_message
-----------------------> R_message = HDR, T, -----------------------> R_message = HDR, T,
[IDr], IDi, DHr, [IDr], IDi, DHr,
DHi, KEMAC DHi, KEMAC
R_message R_message
<---------------------- <----------------------
TGK = g**(xi * yi) TGK = g**(xi * yi) TGK = g^(xi * yi) TGK = g^(xi * yi)
Figure 1: HMAC-authenticated Diffie-Hellman key based exchange, Figure 1: HMAC-authenticated Diffie-Hellman key based exchange,
where xi and xr are randomly chosen respectively where xi and xr are (pseudo) randomly chosen respectively
by the initiator and the responder. by the initiator and the responder.
The DHHMAC key exchange SHALL be done according to Figure 1. The The DHHMAC key exchange SHALL be done according to Figure 1. The
initiator chooses a random value xi, and sends an HMACed message initiator chooses a (pseudo) random value xi, and sends an HMACed
including g**xi and a timestamp to the responder. It is message including g^(xi) and a timestamp to the responder. It is
recommended that the initiator SHOULD always include the identity recommended that the initiator SHOULD always include the identity
payload IDi within the I_message; unless the receiver can defer payload IDi within the I_message; unless the receiver can defer the
the initiator's identity by some other means and IDi MAY initiator's identity by some other means, then IDi MAY optionally
optionally be left out. be left out.
The group parameters (e.g., the group G) are a set of parameters The group parameters (e.g., the group G) are a set of parameters
chosen by the initiator. The responder chooses a random positive chosen by the initiator. The responder chooses a (pseudo) random
integer xr, and sends an HMACed message including g**xr and the positive integer xr, and sends an HMACed message including g^(xr)
timestamp to the initiator. The responder SHALL always include the and the timestamp to the initiator. The responder SHALL always
initiator's identity IDi regardless of whether the I_message include the initiator's identity IDi regardless of whether the
conveyed any IDi. It is recommended that the responder SHOULD I_message conveyed any IDi. It is recommended that the responder
always include the identity payload IDr within the R_message; SHOULD always include the identity payload IDr within the
unless the initiator can defer the reponder's identity by some R_message; unless the initiator can defer the reponder's identity
other means and IDr MAY optionally be left out. by some other means, then IDr MAY optionally be left out.
Both parties then calculate the TGK, g**(xi * xr). HMAC-authenticated Diffie-Hellman for MIKEY July 2003
Both parties then calculate the TGK, g^(xi * xr).
The HMAC authentication is due to provide authentication of the DH The HMAC authentication is due to provide authentication of the DH
half-keys, and is necessary to avoid man-in-the-middle attacks. half-keys, and is necessary to avoid man-in-the-middle attacks.
This approach is less expensive than digitally signed Diffie- This approach is less expensive than digitally signed Diffie-
Hellman. It requires first of all, that both sides compute one Hellman. It requires first of all, that both sides compute one
exponentiation and one HMAC, then one HMAC verification and exponentiation and one HMAC, then one HMAC verification and finally
finally another Diffie-Hellman exponentiation. another Diffie-Hellman exponentiation.
HMAC-authenticated Diffie-Hellman for MIKEY June 2003
With off-line pre-computation, the initial Diffie-Hellman half-key With off-line pre-computation, the initial Diffie-Hellman half-key
MAY be computed before the key management transaction and thereby MAY be computed before the key management transaction and thereby
MAY further reduce the overall round trip delay as well as reduce MAY further reduce the overall round trip delay as well as reduce
the risk of denial-of-service attacks. the risk of denial-of-service attacks.
Processing of the TGK SHALL be accomplished as described in MIKEY Processing of the TGK SHALL be accomplished as described in MIKEY
[3] chapter 4. [3] chapter 4.
The computed HMAC result SHALL be conveyed in the KEMAC payload The computed HMAC result SHALL be conveyed in the KEMAC payload
field where the MAC fields holds the HMAC result. The HMAC shall field where the MAC fields holds the HMAC result. The HMAC shall
be computed over the entire message using auth_key, see also be computed over the entire message excluding the MAC field using
section 4.2. auth_key, see also section 4.2.
3.1. TGK re-keying 3.1. TGK re-keying
TGK re-keying for DHHMAC generally proceeds as described in [3] TGK re-keying for DHHMAC generally proceeds as described in [3]
section 4.5. Specifically, figure 2 provides the message fields section 4.5. Specifically, figure 2 provides the message fields
for DHHMAC update message. for DHHMAC update message.
Initiator Responder Initiator Responder
I_message = HDR, T, [IDi], I_message = HDR, T, [IDi],
{SP}, [DHi], KEMAC {SP}, [DHi], KEMAC
I_message I_message
-----------------------> R_message = HDR, T, -----------------------> R_message = HDR, T,
[IDr], IDi, [IDr], IDi,
[DHr, DHi], KEMAC [DHr, DHi], KEMAC
HMAC-authenticated Diffie-Hellman for MIKEY July 2003
R_message R_message
<---------------------- <----------------------
[TGK = g**(xi * yi)] [TGK = g**(xi * yi)] [TGK = g^(xi * yi)] [TGK = g^(xi * yi)]
Figure 2: DHHMAC update message Figure 2: DHHMAC update message
TGK re-keying supports two procedures: TGK re-keying supports two procedures:
HMAC-authenticated Diffie-Hellman for MIKEY June 2003
a) True re-keying by exchanging new and fresh Diffie-Hellman half- a) True re-keying by exchanging new and fresh Diffie-Hellman half-
keys. For this, the initiator SHALL provide a new, fresh DHi keys. For this, the initiator SHALL provide a new, fresh DHi
and the responder SHALL respond with a new, fresh DHr and the and the responder SHALL respond with a new, fresh DHr and the
received DHi. received DHi.
b) Non-key related information update without any Diffie-Hellman b) Non-key related information update without any Diffie-Hellman
half-keys included in the exchange. Such transaction does not half-keys included in the exchange. Such transaction does not
change the actual TGK but updates other information like change the actual TGK but updates other information like
security policy parameters for example. To only update the security policy parameters for example. To only update the
non-key related information, [DHi] and [DHr, DHi] SHALL be left non-key related information, [DHi] and [DHr, DHi] SHALL be left
skipping to change at page 10, line 39 skipping to change at page 11, line 4
* SRTP ID sub-payload, see [3] section 6.1.1, * SRTP ID sub-payload, see [3] section 6.1.1,
* Key data transport payload (KEMAC), see section 4.2 and [3] section * Key data transport payload (KEMAC), see section 4.2 and [3] section
6.2 6.2
* DH data payload, see [3] section 6.4 * DH data payload, see [3] section 6.4
* Timestamp payload, [3] section 6.6 * Timestamp payload, [3] section 6.6
* ID payload, [3] section 6.7 * ID payload, [3] section 6.7
HMAC-authenticated Diffie-Hellman for MIKEY July 2003
* Security Policy payload (SP), [3] section 6.10 * Security Policy payload (SP), [3] section 6.10
* RAND payload (RAND), [3] section 6.11 * RAND payload (RAND), [3] section 6.11
* Error payload (ERR), [3] section 6.12 * Error payload (ERR), [3] section 6.12
* General Extension Payload, [3] section 6.15 * General Extension Payload, [3] section 6.15
HMAC-authenticated Diffie-Hellman for MIKEY June 2003
4.1. Common header payload (HDR) 4.1. Common header payload (HDR)
Referring to [3] section 6.1, for DHHMAC the following data types Referring to [3] section 6.1, for DHHMAC the following data types
SHALL be used: SHALL be used:
Data type | Value | Comment Data type | Value | Comment
------------------------------------------------------------- -------------------------------------------------------------
DHHMAC init | 7 | Initiator's DHHMAC exchange message DHHMAC init | 7 | Initiator's DHHMAC exchange message
DHHMAC resp | 8 | Responder's DHHMAC exchange message DHHMAC resp | 8 | Responder's DHHMAC exchange message
skipping to change at page 11, line 33 skipping to change at page 12, line 5
T | 5 | [3] section 6.6 T | 5 | [3] section 6.6
ID | 6 | [3] section 6.7 ID | 6 | [3] section 6.7
SP | 10 | [3] section 6.10 SP | 10 | [3] section 6.10
RAND | 11 | [3] section 6.11 RAND | 11 | [3] section 6.11
ERR | 12 | [3] section 6.12 ERR | 12 | [3] section 6.12
General Ext.| 21 | [3] section 6.15 General Ext.| 21 | [3] section 6.15
Other defined next payload values defined in [3] SHALL not be Other defined next payload values defined in [3] SHALL not be
applied to DHHMAC. applied to DHHMAC.
HMAC-authenticated Diffie-Hellman for MIKEY July 2003
The responder in case of a decoding error or of a failed HMAC The responder in case of a decoding error or of a failed HMAC
authentication verification SHALL apply the Error payload data authentication verification SHALL apply the Error payload data
type. type.
4.2. Key data transport payload (KEMAC) 4.2. Key data transport payload (KEMAC)
DHHMAC SHALL apply this payload for conveying the HMAC result DHHMAC SHALL apply this payload for conveying the HMAC result along
along with the indicated authentication algorithm. KEMAC when used with the indicated authentication algorithm. KEMAC when used in
in conjunction with DHHMAC SHALL not convey any encrypted data; conjunction with DHHMAC SHALL not convey any encrypted data; thus
thus Encr alg SHALL be set to 2 (NULL), Encr data len shall be set Encr alg SHALL be set to 2 (NULL), Encr data len shall be set to 0
to 0 and Encr data SHALL be left empty. and Encr data SHALL be left empty. The AES key wrap method (see
[23]) SHALL not be applied for DHHMAC.
HMAC-authenticated Diffie-Hellman for MIKEY June 2003
For DHHMAC, this key data transport payload SHALL be the last For DHHMAC, this key data transport payload SHALL be the last
payload in the message. Note that the Next payload field SHALL be payload in the message. Note that the Next payload field SHALL be
set to Last payload. The HMAC is then calculated over the entire set to Last payload. The HMAC is then calculated over the entire
MIKEY message using auth_key as described in [3] section 5.2 and MIKEY message excluding the MAC field using auth_key as described
then stored within MAC field. in [3] section 5.2 and then stored within MAC field.
MAC alg | Value | Comments MAC alg | Value | Comments
------------------------------------------------------------------ ------------------------------------------------------------------
HMAC-SHA-1 | 0 | Mandatory, Default (see [4]) HMAC-SHA-1 | 0 | Mandatory, Default (see [4])
NULL | 1 | Very restricted use, see NULL | 1 | Very restricted use, see
| [3] section 4.2.4 | [3] section 4.2.4
HMAC-SHA-1-96 | 5 | Optional, HMAC-SHA1 truncated to the 96 HMAC-SHA-1-96 | 5 | Optional, HMAC-SHA1 truncated to the 96
| leftmost bits of the HMAC-SHA-1 result | leftmost bits of the HMAC-SHA-1 result
| when represented in network byte order. | when represented in network byte order.
HMAC-SHA-1 is the default hash function that MUST be implemented HMAC-SHA-1 is the default hash function that MUST be implemented as
as part of the DHHMAC. The length of the HMAC-SHA-1 result is 160 part of the DHHMAC. The length of the HMAC-SHA-1 result is 160
bits. bits.
HMAC-SHA-1-96 produces a slightly shorter HMAC result where the HMAC-SHA-1-96 produces a slightly shorter HMAC result where the
HMAC-SHA-1 result SHALL be truncated to the 96 leftmost bits when HMAC-SHA-1 result SHALL be truncated to the 96 leftmost bits when
represented in network byte order. This saves some bandwidth. represented in network byte order. This saves some bandwidth.
4.3. ID payload (ID) 4.3. ID payload (ID)
For DHHMAC, this payload SHALL only hold a non-certificate based For DHHMAC, this payload SHALL only hold a non-certificate based
identity. identity.
HMAC-authenticated Diffie-Hellman for MIKEY July 2003
5. Security Considerations 5. Security Considerations
This document addresses key management security issues throughout. This document addresses key management security issues throughout.
For a comprehensive explanation of MIKEY security considerations, For a comprehensive explanation of MIKEY security considerations,
please refer to MIKEY [3] section 9. please refer to MIKEY [3] section 9.
In addition to that, this document addresses security issues In addition to that, this document addresses security issues
according to [8] where the following security considerations apply in according to [8] where the following security considerations apply in
particular to this document: particular to this document:
HMAC-authenticated Diffie-Hellman for MIKEY June 2003
5.1. Security environment 5.1. Security environment
Generally, the DHHMAC security protocol described in this document Generally, the DHHMAC security protocol described in this document
focuses primarily on communication security; i.e. the security issues focuses primarily on communication security; i.e. the security issues
concerned with the MIKEY DHHMAC protocol. Nevertheless, some system concerned with the MIKEY DHHMAC protocol. Nevertheless, some system
security issues are of interest as well that are not explicitly security issues are of interest as well that are not explicitly
defined by the DHHMAC protocol, but should be provided locally in defined by the DHHMAC protocol, but should be provided locally in
practice. practice.
The system where the DHHMAC protocol entity runs upon shall provide The system where the DHHMAC protocol entity runs upon shall provide
the capability to generate random numbers as input to the Diffie- the capability to generate (pseudo) random numbers as input to the
Hellman operation (see [9], [15]). Further, the system shall be Diffie-Hellman operation (see [9], [15]). Further, the system shall
capable of storing the generated random data, secret data, keys and be capable of storing the generated (pseudo) random data, secret
other secret security parameters securely (i.e. confidential and safe data, keys and other secret security parameters securely (i.e.
from unauthorized tampering). confidential and safe from unauthorized tampering).
5.2. Threat model 5.2. Threat model
The threat model that this document adheres to cover the issues of The threat model that this document adheres to cover the issues of
end-to-end security in the Internet generally; without ruling out the end-to-end security in the Internet generally; without ruling out the
possibility that MIKEY DHHMAC be deployed in a corporate, closed IP possibility that MIKEY DHHMAC be deployed in a corporate, closed IP
environment. This also includes the possibility that MIKEY DHHMAC be environment. This also includes the possibility that MIKEY DHHMAC be
deployed on a hop-by-hop basis with some intermediate trusted "MIKEY deployed on a hop-by-hop basis with some intermediate trusted "MIKEY
DHHMAC proxies" involved. DHHMAC proxies" involved.
Since DHHMAC is a key management protocol, the following security Since DHHMAC is a key management protocol, the following security
threats are of concern: threats are of concern:
* Unauthorized interception of plain TGKs. * Unauthorized interception of plain TGKs.
HMAC-authenticated Diffie-Hellman for MIKEY July 2003
This threat shall not occur. Nevertheless, for DHHMAC this threat This threat shall not occur. Nevertheless, for DHHMAC this threat
does not occur since the TGK is not actually transmitted on the does not occur since the TGK is not actually transmitted on the
wire (not even in encrypted fashion). wire (not even in encrypted fashion).
* Eavesdropping of other, transmitted keying information: * Eavesdropping of other, transmitted keying information:
DHHMAC protocol does not explicitly transmit the TGK at all. DHHMAC protocol does not explicitly transmit the TGK at all.
Rather, by the Diffie-Hellman "encryption" operation, that conceals Rather, by the Diffie-Hellman "encryption" operation, that conceals
the secret random values, only partial information (i.e. the DH- the secret (pseudo) random values, only partial information (i.e.
half key) for construction of the TGK is transmitted. It is the DH- half key) for construction of the TGK is transmitted. It
fundamentally assumed that availability of such Diffie-Hellman is fundamentally assumed that availability of such Diffie-Hellman
half-keys to an eavesdropper does not result in any substantial half-keys to an eavesdropper does not result in any substantial
security risk; see 5.4. Further, the DHHMAC carries other data security risk; see 5.4. Further, the DHHMAC carries other data
such as timestamps, random values, identification information or such as timestamps, (pseudo) random values, identification
HMAC-authenticated Diffie-Hellman for MIKEY June 2003 information or security policy parameters; eavesdropping of any
such data is considered not to yield any significant security risk.
security policy parameters; eavesdropping of any such data is
considered not to yield any significant security risk.
* Masquerade of either entity: * Masquerade of either entity:
This security threat must be avoided and if a masquerade attack This security threat must be avoided and if a masquerade attack
would be attempted, appropriate detection means must be in place. would be attempted, appropriate detection means must be in place.
DHHMAC addresses this threat by providing mutual peer entity DHHMAC addresses this threat by providing mutual peer entity
authentication. authentication.
* Man-in-the-middle attacks: * Man-in-the-middle attacks:
Such attacks threaten the security of exchanged, non-authenticated Such attacks threaten the security of exchanged, non-authenticated
messages. Man-in-the-middle attacks usually come with masquerade messages. Man-in-the-middle attacks usually come with masquerade
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This security threat relates to unauthorized replay, deletion, This security threat relates to unauthorized replay, deletion,
insertion and manipulation of messages. While any such attacks insertion and manipulation of messages. While any such attacks
cannot be avoided they must be detected at least. DHHMAC addresses cannot be avoided they must be detected at least. DHHMAC addresses
this threat by providing message integrity. this threat by providing message integrity.
* Bidding-down attacks: * Bidding-down attacks:
When multiple key management protocols each of a distinct security When multiple key management protocols each of a distinct security
level are offered (e.g., such as is possible by SDP [5]), avoiding level are offered (e.g., such as is possible by SDP [5]), avoiding
bidding-down attacks is of concern. DHHMAC addresses this threat bidding-down attacks is of concern. DHHMAC addresses this threat
by reusing the MIKEY mechanism as described in [3] section 7.1, by reusing the MIKEY mechanism as described in [3] section 7.1,
where all key management protocol identifiers must be listed where all key management protocol identifiers must be listed within
within the MIKEY General Extension Payload. The protocol the MIKEY General Extension Payload. The protocol identifier for
identifier for DHHMAC shall be "mikeydhhmac". The General HMAC-authenticated Diffie-Hellman for MIKEY July 2003
Extension Payload must be integrity-protected with the HMAC using
the shared secret. DHHMAC shall be "mikeydhhmac". The General Extension Payload must
be integrity-protected with the HMAC using the shared secret.
Some potential threats are not within the scope of this threat model: Some potential threats are not within the scope of this threat model:
* Passive and off-line cryptanalysis of the Diffie-Hellman algorithm: * Passive and off-line cryptanalysis of the Diffie-Hellman algorithm:
Under certain reasonable assumptions (see 5.4 below) it is widely Under certain reasonable assumptions (see 5.4 below) it is widely
believed that DHHMAC is sufficiently secure and that such attacks believed that DHHMAC is sufficiently secure and that such attacks
be infeasible although the possibility of a successful attack be infeasible although the possibility of a successful attack
cannot be ruled out completely. cannot be ruled out completely.
HMAC-authenticated Diffie-Hellman for MIKEY June 2003
* Non-repudiation of the receipt or of the origin of the message: * Non-repudiation of the receipt or of the origin of the message:
These are not requirements of this environment and thus related These are not requirements of this environment and thus related
countermeasures are not provided at all. countermeasures are not provided at all.
* Denial-of-service or distributed denial-of-service attacks: * Denial-of-service or distributed denial-of-service attacks:
Some considerations are given on some of those attacks, but DHHMAC Some considerations are given on some of those attacks, but DHHMAC
does not claim to provide full countermeasure against any of those does not claim to provide full countermeasure against any of those
attacks. For example, stressing the availability of the entities attacks. For example, stressing the availability of the entities
are not thwarted by means of the key management protocol; some are not thwarted by means of the key management protocol; some
other local countermeasures should be applied. Further, some DoS other local countermeasures should be applied. Further, some DoS
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protection on its own but may inherit such property from a security protection on its own but may inherit such property from a security
protocol underneath that actually features identity protection. On protocol underneath that actually features identity protection. On
the other hand, it is expected that MIKEY-DHHMAC is typically being the other hand, it is expected that MIKEY-DHHMAC is typically being
deployed within SDP/SIP ([20], [5]); both those protocols do not deployed within SDP/SIP ([20], [5]); both those protocols do not
provide end-to-end identity protection. provide end-to-end identity protection.
The DHHMAC security protocol (see section 3) and the TGK re-keying The DHHMAC security protocol (see section 3) and the TGK re-keying
security protocol (see section 3.1) provide the option not to security protocol (see section 3.1) provide the option not to
supply identity information. This option is only applicable if supply identity information. This option is only applicable if
some other means are available of supplying trustworthy identity some other means are available of supplying trustworthy identity
HMAC-authenticated Diffie-Hellman for MIKEY July 2003
information; e.g., by relying on secured links underneath of MIKEY information; e.g., by relying on secured links underneath of MIKEY
that supply trustworthy identity information otherwise. However, that supply trustworthy identity information otherwise. However,
it is understood that without identity information present, the it is understood that without identity information present, the
MIKEY key management security protocols might be subject to MIKEY key management security protocols might be subject to
security weaknesses such as masquerade, impersonation and security weaknesses such as masquerade, impersonation and
reflection attacks particularly in end-to-end scenarios where no reflection attacks particularly in end-to-end scenarios where no
other secure means of assured identity information is provided. other secure means of assured identity information is provided.
Leaving identity fields optional if possible thus should not be Leaving identity fields optional if possible thus should not be
seen as a privacy method either, but rather as a protocol seen as a privacy method either, but rather as a protocol
optimization feature. optimization feature.
HMAC-authenticated Diffie-Hellman for MIKEY June 2003
5.3. Security features and properties 5.3. Security features and properties
With the security threats in mind, this draft provides the following With the security threats in mind, this draft provides the following
security features and yields the following properties: security features and yields the following properties:
* Secure key agreement with the establishment of a TGK at both peers: * Secure key agreement with the establishment of a TGK at both peers:
This is achieved using an authenticated Diffie-Hellman key This is achieved using an authenticated Diffie-Hellman key
management protocol. management protocol.
* Peer-entity authentication (mutual): * Peer-entity authentication (mutual):
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avoid man-in-the-middle attacks on the exchanged messages in avoid man-in-the-middle attacks on the exchanged messages in
transit and in particular, on the otherwise non-authenticated transit and in particular, on the otherwise non-authenticated
exchanged Diffie-Hellman half keys. exchanged Diffie-Hellman half keys.
Note: This document does not address issues regarding Note: This document does not address issues regarding
authorization; this feature is not provided explicitly. However, authorization; this feature is not provided explicitly. However,
DHHMAC authentication means support and facilitate realization of DHHMAC authentication means support and facilitate realization of
authorization means (local issue). authorization means (local issue).
* Cryptographic integrity check: * Cryptographic integrity check:
HMAC-authenticated Diffie-Hellman for MIKEY July 2003
The cryptographic integrity check is achieved using a message The cryptographic integrity check is achieved using a message
digest (keyed HMAC). It includes the exchanged Diffie-Hellman digest (keyed HMAC). It includes the exchanged Diffie-Hellman
half-keys but covers the other parts of the exchanged message as half-keys but covers the other parts of the exchanged message as
well. Both mutual peer entity authentication and message integrity well. Both mutual peer entity authentication and message integrity
provide effective countermeasure against man-in-the-middle attacks. provide effective countermeasure against man-in-the-middle attacks.
The initiator may deploy a local timer that fires when the awaited The initiator may deploy a local timer that fires when the awaited
response message did not arrive timely. This is to detect deletion response message did not arrive timely. This is to detect deletion
of entire messages. of entire messages.
* Replay protection of the messages is achieved using embedded * Replay protection of the messages is achieved using embedded
timestamps. timestamps.
HMAC-authenticated Diffie-Hellman for MIKEY June 2003
* Limited DoS protection: * Limited DoS protection:
Rapid checking of the message digest allows verifying the Rapid checking of the message digest allows verifying the
authenticity and integrity of a message before launching CPU authenticity and integrity of a message before launching CPU
intensive Diffie-Hellman operations or starting other resource intensive Diffie-Hellman operations or starting other resource
consuming tasks. This protects against some denial-of-service consuming tasks. This protects against some denial-of-service
attacks: malicious modification of messages and spam attacks with attacks: malicious modification of messages and spam attacks with
(replayed or masqueraded) messages. DHHMAC probably does not (replayed or masqueraded) messages. DHHMAC probably does not
explicitly counter sophisticated distributed, large-scale denial- explicitly counter sophisticated distributed, large-scale denial-
of-service attacks that compromise system availability for example. of-service attacks that compromise system availability for example.
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forward secrecy. Thus, none of the other MIKEY protocols is able forward secrecy. Thus, none of the other MIKEY protocols is able
to substitute the Diffie-Hellman PFS property. to substitute the Diffie-Hellman PFS property.
As such, DHHMAC but also digitally signed DH provides a far As such, DHHMAC but also digitally signed DH provides a far
superior security level over the pre-shared or public-key based key superior security level over the pre-shared or public-key based key
distribution protocol in that respect. distribution protocol in that respect.
* Fair, mutual key contribution: * Fair, mutual key contribution:
The Diffie-Hellman key management protocol is not a strict key The Diffie-Hellman key management protocol is not a strict key
distribution protocol per se with the initiator distributing a key distribution protocol per se with the initiator distributing a key
HMAC-authenticated Diffie-Hellman for MIKEY July 2003
to its peers. Actually, both parties involved in the protocol to its peers. Actually, both parties involved in the protocol
exchange are able to equally contribute to the common Diffie- exchange are able to equally contribute to the common Diffie-
Hellman TEK traffic generating key. This reduces the risk of Hellman TEK traffic generating key. This reduces the risk of
either party cheating or unintentionally generating a weak session either party cheating or unintentionally generating a weak session
key. This makes the DHHMAC a fair key agreement protocol. One may key. This makes the DHHMAC a fair key agreement protocol. One may
view this property as an additional distributed security measure view this property as an additional distributed security measure
that is increasing security robustness over the case where all the that is increasing security robustness over the case where all the
security depends just on the proper implementation of a single security depends just on the proper implementation of a single
entity. entity.
In order for Diffie-Hellman key agreement to be secure, each party In order for Diffie-Hellman key agreement to be secure, each party
shall generate its xi or xr values using a strong, unpredictable shall generate its xi or xr values using a strong, unpredictable
pseudo-random generator. Further, these values xi or xr shall be pseudo-random generator if a source of true randomness is not
HMAC-authenticated Diffie-Hellman for MIKEY June 2003 available. Further, these values xi or xr shall be kept private.
It is recommended that these secret values be destroyed once the
kept private. It is recommended that these secret values be common Diffie-Hellman shared secret key has been established.
destroyed once the common Diffie-Hellman shared secret key has been
established.
* Efficiency and performance: * Efficiency and performance:
Like the MIKEY-public key protocol, the MIKEY DHHMAC key agreement Like the MIKEY-public key protocol, the MIKEY DHHMAC key agreement
protocol securely establishes a TGK within just one roundtrip. protocol securely establishes a TGK within just one roundtrip.
Other existing key management techniques like IPSEC-IKE [14], Other existing key management techniques like IPSEC-IKE [14],
IPSEC-IKEv2 [21] and TLS [13] and other schemes are not deemed IPSEC-IKEv2 [21] and TLS [13] and other schemes are not deemed
adequate in addressing sufficiently those real-time and security adequate in addressing sufficiently those real-time and security
requirements; they all use more than a single roundtrip. All the requirements; they all use more than a single roundtrip. All the
MIKEY key management protocols are able to complete their task of MIKEY key management protocols are able to complete their task of
security policy parameter negotiation including key-agreement or security policy parameter negotiation including key-agreement or
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public-key operations. This yields a particular performance public-key operations. This yields a particular performance
benefit of DHHMAC over signed DH or the public-key encryption benefit of DHHMAC over signed DH or the public-key encryption
protocol. protocol.
DHHMAC optionally features a variant where the HMAC-SHA-1 result is DHHMAC optionally features a variant where the HMAC-SHA-1 result is
truncated to 96-bit instead of 160 bits. It is believed that truncated to 96-bit instead of 160 bits. It is believed that
although the truncated HMAC appears significantly shorter, the although the truncated HMAC appears significantly shorter, the
security provided would not suffer; it appears even reasonable that security provided would not suffer; it appears even reasonable that
the shorter HMAC could provide increased security against known- the shorter HMAC could provide increased security against known-
plaintext crypt-analysis, see RFC 2104 [6] for more details. In plaintext crypt-analysis, see RFC 2104 [6] for more details. In
HMAC-authenticated Diffie-Hellman for MIKEY July 2003
any way, truncated DHHMAC is able to reduce the bandwidth during any way, truncated DHHMAC is able to reduce the bandwidth during
Diffie-Hellman key agreement and yield better round trip delay on Diffie-Hellman key agreement and yield better round trip delay on
low-bandwidth links. If a very high security level is desired for low-bandwidth links. If a very high security level is desired for
long-term secrecy of the negotiated Diffie-Hellman shared secret, long-term secrecy of the negotiated Diffie-Hellman shared secret,
longer hash values may be deployed such as SHA256, SHA384 or SHA512 longer hash values may be deployed such as SHA256, SHA384 or SHA512
provide, possibly in conjunction with stronger Diffie-Hellman provide, possibly in conjunction with stronger Diffie-Hellman
groups. This is left as for further study. groups. This is left as for further study.
For the sake of improved performance and reduced round trip delay For the sake of improved performance and reduced round trip delay
either party may off-line pre-compute its public Diffie-Hellman either party may off-line pre-compute its public Diffie-Hellman
half-key. half-key.
HMAC-authenticated Diffie-Hellman for MIKEY June 2003
On the other side and under reasonable conditions, DHHMAC consumes On the other side and under reasonable conditions, DHHMAC consumes
more CPU cycles than the MIKEY pre-shared key distribution more CPU cycles than the MIKEY pre-shared key distribution
protocol. The same might hold true quite likely for the MIKEY protocol. The same might hold true quite likely for the MIKEY
public-key distribution protocol (depending on choice of the public-key distribution protocol (depending on choice of the
private and public key lengths). private and public key lengths).
As such, it can be said that DHHMAC provides sound performance when As such, it can be said that DHHMAC provides sound performance when
compared with the other MIKEY protocol variants. compared with the other MIKEY protocol variants.
The use of optional identity information (with the constraints The use of optional identity information (with the constraints
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in MIKEY. Public-key infrastructures may not always be available in MIKEY. Public-key infrastructures may not always be available
in certain environments nor may they be deemed adequate for real- in certain environments nor may they be deemed adequate for real-
time multimedia applications when taking additional steps for time multimedia applications when taking additional steps for
certificate validation and certificate revocation methods with certificate validation and certificate revocation methods with
additional round-trips into account. additional round-trips into account.
DHHMAC does not depend on PKI nor do implementations require PKI DHHMAC does not depend on PKI nor do implementations require PKI
standards and thus is believed to be much simpler than the more standards and thus is believed to be much simpler than the more
complex PKI facilities. complex PKI facilities.
HMAC-authenticated Diffie-Hellman for MIKEY July 2003
DHHMAC is particularly attractive in those environments where DHHMAC is particularly attractive in those environments where
provisioning of a pre-shared key has already been accomplished. provisioning of a pre-shared key has already been accomplished.
* NAT/Firewall-friendliness: * NAT/Firewall-friendliness:
DHHMAC is able to operate smoothly through firewall/NAT devices as DHHMAC is able to operate smoothly through firewall/NAT devices as
long as the protected identity information of the end entity is not long as the protected identity information of the end entity is not
an IP /transport address. Of course, DHHMAC does not necessarily an IP /transport address. Of course, DHHMAC does not necessarily
require a firewall/NAT to operate. require a firewall/NAT to operate.
* Scalability: * Scalability:
Like the MIKEY signed Diffie-Hellman protocol, DHHMAC does not Like the MIKEY signed Diffie-Hellman protocol, DHHMAC does not
scale to any larger configurations beyond peer-to-peer groups. scale to any larger configurations beyond peer-to-peer groups.
HMAC-authenticated Diffie-Hellman for MIKEY June 2003
5.4. Assumptions 5.4. Assumptions
This document states a couple of assumptions upon which the security This document states a couple of assumptions upon which the security
of DHHMAC significantly depends. It is assumed, that of DHHMAC significantly depends. It is assumed, that
* the parameters xi, xr, s and auth_key are to be kept secret. * the parameters xi, xr, s and auth_key are to be kept secret.
* the pre-shared key s has sufficient entropy and cannot be * the pre-shared key s has sufficient entropy and cannot be
effectively guessed. effectively guessed.
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called the discrete logarithm assumption. Please see [7], [11] or called the discrete logarithm assumption. Please see [7], [11] or
[12] for more background information regarding the Diffie-Hellman [12] for more background information regarding the Diffie-Hellman
problem and its computational complexity assumptions. problem and its computational complexity assumptions.
* the hash function (SHA1) is secure; i.e. that it is computationally * the hash function (SHA1) is secure; i.e. that it is computationally
infeasible to find a message which corresponds to a given message infeasible to find a message which corresponds to a given message
digest, or to find two different messages that produce the same digest, or to find two different messages that produce the same
message digest. message digest.
* the HMAC algorithm is secure and does not leak the auth_key. In * the HMAC algorithm is secure and does not leak the auth_key. In
HMAC-authenticated Diffie-Hellman for MIKEY July 2003
particular, the security depends on the message authentication particular, the security depends on the message authentication
property of the compression function of the hash function H when property of the compression function of the hash function H when
applied to single blocks (see [6]). applied to single blocks (see [6]).
* A source capable of producing sufficiently many bits of randomness * A source capable of producing sufficiently many bits of (pseudo)
is available. randomness is available.
* The systems upon which DHHMAC runs are sufficiently secure. * The systems upon which DHHMAC runs are sufficiently secure.
The assumptions MUST be met as far as they can be enforced. The assumptions MUST be met as far as they can be enforced.
HMAC-authenticated Diffie-Hellman for MIKEY June 2003
5.5. Residual risk 5.5. Residual risk
Although these detailed assumptions are non-negligible, security Although these detailed assumptions are non-negligible, security
experts generally believe that all these assumptions are reasonable experts generally believe that all these assumptions are reasonable
and that the assumptions made can be fulfilled in practice with and that the assumptions made can be fulfilled in practice with
little or no expenses. little or no expenses.
The mathematical and cryptographic assumptions upon the properties of The mathematical and cryptographic assumptions upon the properties of
the PRF, the Diffie-Hellman algorithm (discrete log-assumption), the the PRF, the Diffie-Hellman algorithm (discrete log-assumption), the
HMAC and SHA1 algorithms have not been proved yet nor have they been HMAC and SHA1 algorithms have not been proved yet nor have they been
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* the HMAC method be broken (leaking the auth_key), * the HMAC method be broken (leaking the auth_key),
* systematic brute force attacks are effective by which an attacker * systematic brute force attacks are effective by which an attacker
attempts to discover the shared secret. It is assumed that the attempts to discover the shared secret. It is assumed that the
shared secret yields sufficient entropy to make such attacks shared secret yields sufficient entropy to make such attacks
infeasible, infeasible,
* or some other yet unknown attacking technique will be discovered. * or some other yet unknown attacking technique will be discovered.
HMAC-authenticated Diffie-Hellman for MIKEY July 2003
The Diffie-Hellman mechanism is a generic security technique that is The Diffie-Hellman mechanism is a generic security technique that is
not only applicable to groups of prime order or of characteristic not only applicable to groups of prime order or of characteristic
two. This is because of the fundamental mathematical assumption that two. This is because of the fundamental mathematical assumption that
the discrete logarithm problem is also a very hard one in general the discrete logarithm problem is also a very hard one in general
groups. This enables Diffie-Hellman to be deployed also for GF(p)*, groups. This enables Diffie-Hellman to be deployed also for GF(p)*,
for sub-groups of sufficient size and for groups upon elliptic for sub-groups of sufficient size and for groups upon elliptic
curves. RSA does not allow such generalization, as the core curves. RSA does not allow such generalization, as the core
mathematical problem is a different one (large integer mathematical problem is a different one (large integer
factorization). factorization).
RSA asymmetric keys tend to become increasingly lengthy (1536 bits RSA asymmetric keys tend to become increasingly lengthy (1536 bits
and more) and thus very computational intensive. Neverthess, and more) and thus very computational intensive. Neverthess,
elliptic curve Diffie-Hellman (ECDH) allows to cut-down key lengths elliptic curve Diffie-Hellman (ECDH) allows to cut-down key lengths
HMAC-authenticated Diffie-Hellman for MIKEY June 2003
substantially (say 170 bits or more) while maintaining at least the substantially (say 170 bits or more) while maintaining at least the
security level and providing even significant performance benefits in security level and providing even significant performance benefits in
practice. Moreover, it is believed that elliptic curve techniques practice. Moreover, it is believed that elliptic curve techniques
provide much better protection against side channel attacks due to provide much better protection against side channel attacks due to
the inherent redundancy in the projective coordinates. For all these the inherent redundancy in the projective coordinates. For all these
reasons, one may view elliptic-curve-based Diffie-Hellman as being reasons, one may view elliptic-curve-based Diffie-Hellman as being
more "future-proof" and robust against potential threats than RSA. more "future-proof" and robust against potential threats than RSA.
Note, that an elliptic-curve Diffie-Hellman variant of MIKEY remains Note, that an elliptic-curve Diffie-Hellman variant of MIKEY remains
for further study. for further study.
It is not recommended to deploy DHHMAC for any other usage than It is not recommended to deploy DHHMAC for any other usage than
depicted in section 2. Otherwise any such misapplication might lead depicted in section 2. Otherwise any such misapplication might lead
to unknown, undefined properties. to unknown, undefined properties.
IANA considerations IANA considerations
This document does not define its own new name spaces for DHHMAC, This document does not define its own new name spaces for DHHMAC,
rather additional values for DHHMAC are defined as part of the MIKEY rather additional values for DHHMAC are defined as part of the MIKEY
fields. Thus, close alignment between DHHMAC values and MIKEY fields. Thus, close alignment between DHHMAC values and MIKEY values
values shall be maintained; see also [3] section 10. shall be maintained; see also [3] section 10.
Intellectual Property Rights Intellectual Property Rights
This proposal is in full conformity with [RFC-2026]. This proposal is in full conformity with [RFC-2026].
The author is aware of related intellectual property rights The author is aware of related intellectual property rights
currently being held by Infineon. Pursuant to the provisions of currently being held by Infineon. Pursuant to the provisions of
[RFC-2026], the author represents that he has disclosed the [RFC-2026], the author represents that he has disclosed the
existence of any proprietary or intellectual property rights in existence of any proprietary or intellectual property rights in the
the contribution that are reasonably and personally known to the HMAC-authenticated Diffie-Hellman for MIKEY July 2003
contribution that are reasonably and personally known to the
author. The author does not represent that he personally knows of author. The author does not represent that he personally knows of
all potentially pertinent proprietary and intellectual property all potentially pertinent proprietary and intellectual property
rights owned or claimed by the organizations he represents or rights owned or claimed by the organizations he represents or third
third parties. parties.
The IETF takes no position regarding the validity or scope of any The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to intellectual property or other rights that might be claimed to
pertain to the implementation or use of the technology described pertain to the implementation or use of the technology described in
in this document or the extent to which any license under such this document or the extent to which any license under such rights
rights might or might not be available; neither does it represent might or might not be available; neither does it represent that it
that it has made any effort to identify any such rights. has made any effort to identify any such rights. Information on the
Information on the IETF's procedures with respect to rights in IETF's procedures with respect to rights in standards-track and
HMAC-authenticated Diffie-Hellman for MIKEY June 2003 standards-related documentation can be found in BCP-11. Copies of
claims of rights made available for publication and any assurances
standards-track and standards-related documentation can be found of licenses to be made available, or the result of an attempt made
in BCP-11. Copies of claims of rights made available for to obtain a general license or permission for the use of such
publication and any assurances of licenses to be made available, proprietary rights by implementors or users of this specification
or the result of an attempt made to obtain a general license or can be obtained from the IETF Secretariat.
permission for the use of such proprietary rights by implementors
or users of this specification can be obtained from the IETF
Secretariat.
References References
Normative References Normative References
[1] Bradner, S., "The Internet Standards Process -- Revision 3", [1] Bradner, S., "The Internet Standards Process -- Revision 3",
BCP 9, RFC 2026, October 1996. BCP 9, RFC 2026, October 1996.
[2] Bradner, S., "Key words for use in RFCs to Indicate [2] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[3] J. Arkko, E. Carrara, F. Lindholm, M. Naslund, K. Norrman; [3] J. Arkko, E. Carrara, F. Lindholm, M. Naslund, K. Norrman;
"MIKEY: Multimedia Internet KEYing", Internet Draft <draft-ietf- "MIKEY: Multimedia Internet KEYing", Internet Draft <draft-ietf-
msec-mikey-06.txt>, Work in Progress (MSEC WG), IETF, February msec-mikey-07.txt>, Work in Progress (MSEC WG), IETF, June 2003.
2003.
[4] NIST, FIBS-PUB 180-1, "Secure Hash Standard", April 1995, [4] NIST, FIBS-PUB 180-1, "Secure Hash Standard", April 1995,
http://csrc.nist.gov/fips/fip180-1.ps. http://csrc.nist.gov/fips/fip180-1.ps.
[5] J. Arkko, E. Carrara et al: "Key Management Extensions for SDP [5] J. Arkko, E. Carrara et al: "Key Management Extensions for SDP
and RTSP", Internet Draft <draft-ietf-mmusic-kmgmt-ext-07.txt>, and RTSP", Internet Draft <draft-ietf-mmusic-kmgmt-ext-07.txt>,
Work in Progress (MMUSIC WG), IETF, February 2003. Work in Progress (MMUSIC WG), IETF, February 2003.
[6] H. Krawczyk, M. Bellare, R. Canetti; "HMAC: Keyed-Hashing for [6] H. Krawczyk, M. Bellare, R. Canetti: "HMAC: Keyed-Hashing for
Message Authentication", RFC 2104, February 1997. Message Authentication", RFC 2104, February 1997.
HMAC-authenticated Diffie-Hellman for MIKEY July 2003
Informative References Informative References
[7] A.J. Menezes, P. van Oorschot, S. A. Vanstone: "Handbook of [7] A.J. Menezes, P. van Oorschot, S. A. Vanstone: "Handbook of
Applied Cryptography", CRC Press 1996. Applied Cryptography", CRC Press 1996.
[8] E. Rescorla, B. Korver: " Guidelines for Writing RFC Text on [8] E. Rescorla, B. Korver: " Guidelines for Writing RFC Text on
Security Considerations", Work in Progress <draft-iab-sec-cons- Security Considerations", Work in Progress <draft-iab-sec-cons-
03.txt>, IETF, January 2003. 03.txt>, IETF, January 2003.
[9] D. Eastlake, S. Crocker: "Randomness Recommendations for [9] D. Eastlake, S. Crocker: "Randomness Recommendations for
HMAC-authenticated Diffie-Hellman for MIKEY June 2003
Security", RFC 1750, IETF, December 1994. Security", RFC 1750, IETF, December 1994.
[10] S.M. Bellovin, C. Kaufman, J. I. Schiller: "Security [10] S.M. Bellovin, C. Kaufman, J. I. Schiller: "Security
Mechanisms for the Internet", Work in Progress <draft-iab- Mechanisms for the Internet", Work in Progress <draft-iab-
secmech-02.txt>, IETF, January 2003. secmech-02.txt>, IETF, January 2003.
[11] Ueli M. Maurer, S. Wolf: "The Diffie-Hellman Protocol", [11] Ueli M. Maurer, S. Wolf: "The Diffie-Hellman Protocol",
Designs, Codes, and Cryptography, Special Issue Public Key Designs, Codes, and Cryptography, Special Issue Public Key
Cryptography, Kluwer Academic Publishers, vol. 19, pp. 147-171, Cryptography, Kluwer Academic Publishers, vol. 19, pp. 147-171,
2000. ftp://ftp.inf.ethz.ch/pub/crypto/publications/MauWol00c.ps 2000. ftp://ftp.inf.ethz.ch/pub/crypto/publications/MauWol00c.ps
skipping to change at page 24, line 38 skipping to change at page 25, line 5
randomness2-03.txt>; Work in Progress, IETF, July 2002. randomness2-03.txt>; Work in Progress, IETF, July 2002.
[16] J. Schiller: "Strong Security Requirements for Internet [16] J. Schiller: "Strong Security Requirements for Internet
Engineering Task Force Standard Protocols", RFC 3365, IETF, Engineering Task Force Standard Protocols", RFC 3365, IETF,
2002. 2002.
[17] C. Meadows: "Advice on Writing an Internet Draft Amenable to [17] C. Meadows: "Advice on Writing an Internet Draft Amenable to
Security Analysis", Work in Progress <draft-irtf-cfrg-advice- Security Analysis", Work in Progress <draft-irtf-cfrg-advice-
00.txt>, IRTF, October 2002. 00.txt>, IRTF, October 2002.
HMAC-authenticated Diffie-Hellman for MIKEY July 2003
[18] T. Narten: "Guidelines for Writing an IANA Considerations [18] T. Narten: "Guidelines for Writing an IANA Considerations
Section in RFCs", RFC 2434, IETF, October 1998. Section in RFCs", RFC 2434, IETF, October 1998.
[19] J. Reynolds: "Instructions to Request for Comments (RFC) [19] J. Reynolds: "Instructions to Request for Comments (RFC)
Authors", Work in Progress, <draft-rfc-editor-rfc2223bis- Authors", Work in Progress, <draft-rfc-editor-rfc2223bis-
04.txt>, IETF, 24 February 2003. 06.txt>, IETF, June 2003.
[20] J. Rosenberg et all: "SIP: Session Initiation Protocol", RFC [20] J. Rosenberg et all: "SIP: Session Initiation Protocol", RFC
3261, IETF, June 2002. 3261, IETF, June 2002.
[21] Ch. Kaufman: "Internet Key Exchange (IKEv2) Protocol", Work in [21] Ch. Kaufman: "Internet Key Exchange (IKEv2) Protocol", Work in
HMAC-authenticated Diffie-Hellman for MIKEY June 2003
Progress (IPSEC WG), <draft-ietf-ipsec-ikev2-08.txt>, IETF, May Progress (IPSEC WG), <draft-ietf-ipsec-ikev2-08.txt>, IETF, May
2003. 2003.
[22] Draft ITU-T Recommendation H.235 Annex G: "Usage of the Secure [22] Draft ITU-T Recommendation H.235 Annex G: "Usage of the Secure
Real Time Transport Protocol (SRTP) in conjunction with the Real Time Transport Protocol (SRTP) in conjunction with the
MIKEY Key Management Protocol within H.235"; 5/2003. MIKEY Key Management Protocol within H.235"; 5/2003.
[23] Schaad, J., Housley R.: "Advanced Encryption Standard (AES)
Key Wrap Algorithm", IETF, RFC 3394.
[24] Baugher, M., Weis, B., Hardjono, T., Harney, H.: "The Group
Domain of Interpretation", RFC 3547, July 2003.
[25] Harney, H., Colegrove, A., Harder, E., Meth, U., Fleischer, R.:
"Group Secure Association Key Management Protocol", <draft-ietf-
msec-gsakmp-sec-02.txt>, Internet Draft, Work in Progress (MSEC
WG).
Acknowledgments Acknowledgments
This document incorporates kindly review feedback by Steffen Fries This document incorporates kindly review feedback by Steffen Fries
and Fredrick Lindholm and general feedback by the MSEC WG. and Fredrick Lindholm and general feedback by the MSEC WG.
Conclusions Conclusions
Key management for environments and applications with real-time and Key management for environments and applications with real-time and
performance constraints are becoming of interest. Existing key performance constraints are becoming of interest. Existing key
management techniques like IPSEC-IKE [14] and IPSEC-IKEv2 [22], TLS management techniques like IPSEC-IKE [14] and IPSEC-IKEv2 [22], TLS
[13] and other schemes are not deemed adequate in addressing [13] and other schemes are not deemed adequate in addressing
sufficiently those real-time and security requirements. sufficiently those real-time and security requirements.
HMAC-authenticated Diffie-Hellman for MIKEY July 2003
MIKEY defines three key management security protocols addressing MIKEY defines three key management security protocols addressing
real-time constraints. DHHMAC as described in this document defines real-time constraints. DHHMAC as described in this document defines
a fourth MIKEY variant aiming at the same target. a fourth MIKEY variant aiming at the same target.
While each of the four key management protocols has its own merits While each of the four key management protocols has its own merits
there are also certain limitations of each approach. As such there there are also certain limitations of each approach. As such there
is no single ideal solution and none of the variants is able to is no single ideal solution and none of the variants is able to
subsume the other remaining variants. subsume the other remaining variants.
It is concluded that DHHMAC features useful security and performance It is concluded that DHHMAC features useful security and performance
properties that none of the other three MIKEY variants is able to properties that none of the other three MIKEY variants is able to
provide. provide.
Full Copyright Statement Full Copyright Statement
Copyright (C) The Internet Society (2003). All Rights Reserved. Copyright (C) The Internet Society (2003). All Rights Reserved.
This document and translations of it may be copied and furnished to This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published or assist in its implementation may be prepared, copied, published
HMAC-authenticated Diffie-Hellman for MIKEY June 2003
and distributed, in whole or in part, without restriction of any and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than followed, or as required to translate it into languages other than
English. English.
skipping to change at page 26, line 27 skipping to change at page 27, line 5
The limited permissions granted above are perpetual and will not be The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns. revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
HMAC-authenticated Diffie-Hellman for MIKEY July 2003
Expiration Date Expiration Date
This Internet Draft expires on 30 December 2003. This Internet Draft expires on 30 January 2004.
Revision History Revision History
Changes against draft-ietf-msec-mikey-dhhmac-02.txt:
* text allows both random and pseudo-random values.
* exponentiation ** changed to ^.
* Notation aligned with MIKEY-07.
* Clarified that the HMAC is calculated over the entire MIKEY
message excluding the MAC field.
* Section 4.2: The AES key wrap method SHALL not be applied.
* Section 1: Relationship with other, existing work mentioned.
*
Changes against draft-ietf-msec-mikey-dhhmac-01.txt: Changes against draft-ietf-msec-mikey-dhhmac-01.txt:
* bidding-down attacks addressed (see section 5.2). * bidding-down attacks addressed (see section 5.2).
* optional [X], [X, Y] defined and clarified (see section 1.1, * optional [X], [X, Y] defined and clarified (see section 1.1,
5.3). 5.3).
* combination of options defined in key update procedure (see * combination of options defined in key update procedure (see
section 3.1). section 3.1).
* ID payloads clarified (see section 3 and 5.2). * ID payloads clarified (see section 3 and 5.2).
* relationship with MIKEY explained (roundtrip, performance). * relationship with MIKEY explained (roundtrip, performance).
* new section 2.1 on applicability of DHHMAC for SIP/SDP and * new section 2.1 on applicability of DHHMAC for SIP/SDP and
H.323 added. H.323 added.
* more text due to DH resolution incorporated in section 5.3 * more text due to DH resolution incorporated in section 5.3
regarding PFS, security robustness of DH, generalization regarding PFS, security robustness of DH, generalization
capability of DH to general groups in particular EC and capability of DH to general groups in particular EC and
˘future-proofness÷. "future-proofness".
HMAC-authenticated Diffie-Hellman for MIKEY June 2003
* a few editorials and nits. * a few editorials and nits.
* references adjusted and cleaned-up. * references adjusted and cleaned-up.
Changes against draft-ietf-msec-mikey-dhhmac-00.txt: Changes against draft-ietf-msec-mikey-dhhmac-00.txt:
* category set to proposed standard. * category set to proposed standard.
* identity protection clarified. * identity protection clarified.
* aligned with MIKEY-05 DH protocol, notation and with payload * aligned with MIKEY-05 DH protocol, notation and with payload
* some editorials and nits. * some editorials and nits.
HMAC-authenticated Diffie-Hellman for MIKEY July 2003
Changes against draft-euchner-mikey-dhhmac-00.txt: Changes against draft-euchner-mikey-dhhmac-00.txt:
* made a MSEC WG draft * made a MSEC WG draft
* aligned with MIKEY-03 DH protocol, notation and with payload * aligned with MIKEY-03 DH protocol, notation and with payload
formats formats
* clarified that truncated HMAC actually truncates the HMAC result * clarified that truncated HMAC actually truncates the HMAC result
rather than the SHA1 intermediate value. rather than the SHA1 intermediate value.
* improved security considerations section completely rewritten in * improved security considerations section completely rewritten in
the spirit of [8]. the spirit of [8].
 End of changes. 

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