draft-ietf-dhc-forcerenew-nonce-04.txt   draft-ietf-dhc-forcerenew-nonce-05.txt 
dhc D. Miles dhc D. Miles
Internet-Draft Google Internet-Draft Google
Updates: 3203 (if approved) W. Dec Updates: 3203 (if approved) W. Dec
Intended status: Standards Track Cisco Systems Intended status: Standards Track Cisco Systems
Expires: August 17, 2012 J. Bristow Expires: September 10, 2012 J. Bristow
Swisscom Schweiz AG Swisscom Schweiz AG
R. Maglione R. Maglione
Telecom Italia Telecom Italia
February 14, 2012 March 9, 2012
Forcerenew Nonce Authentication Forcerenew Nonce Authentication
draft-ietf-dhc-forcerenew-nonce-04 draft-ietf-dhc-forcerenew-nonce-05
Abstract Abstract
Dynamic Host Configuration Protocol (DHCP) FORCERENEW allows for the Dynamic Host Configuration Protocol (DHCP) FORCERENEW allows for the
reconfiguration of a single host by forcing the DHCP client into a reconfiguration of a single host by forcing the DHCP client into a
Renew state on a trigger from the DHCP server. In Forcerenew Nonce Renew state on a trigger from the DHCP server. In Forcerenew Nonce
Authentication the server sends a nonce to the client on the initial Authentication the server sends a nonce to the client in the initial
DHCP ACK that is used for subsequent validation of a FORCERENEW DHCP ACK that is used for subsequent validation of a FORCERENEW
message. This document updates RFC 3203. message. This document updates RFC 3203.
Status of this Memo Status of this Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
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time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 17, 2012. This Internet-Draft will expire on September 10, 2012.
Copyright Notice Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
skipping to change at page 2, line 16 skipping to change at page 2, line 16
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
3. Message authentication . . . . . . . . . . . . . . . . . . . . 3 3. Message authentication . . . . . . . . . . . . . . . . . . . . 3
3.1. Forcerenew Nonce Authentication . . . . . . . . . . . . . 3 3.1. Forcerenew Nonce Authentication . . . . . . . . . . . . . 4
3.1.1. Forcerenew Nonce Protocol Capability Option . . . . . 4 3.1.1. Forcerenew Nonce Protocol Capability Option . . . . . 4
3.1.2. Forcerenew Nonce Protocol . . . . . . . . . . . . . . 6 3.1.2. Forcerenew Nonce Protocol . . . . . . . . . . . . . . 6
3.1.3. Server considerations for Forcerenew Nonce 3.1.3. Server considerations for Forcerenew Nonce
Authentication . . . . . . . . . . . . . . . . . . . . 8 Authentication . . . . . . . . . . . . . . . . . . . . 8
3.1.4. Client considerations for Forcerenew Nonce 3.1.4. Client considerations for Forcerenew Nonce
Authentication . . . . . . . . . . . . . . . . . . . . 9 Authentication . . . . . . . . . . . . . . . . . . . . 9
4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10 4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
6. Security Considerations . . . . . . . . . . . . . . . . . . . 10 6. Security Considerations . . . . . . . . . . . . . . . . . . . 10
6.1. Protocol vulnerabilities . . . . . . . . . . . . . . . . . 11 6.1. Protocol vulnerabilities . . . . . . . . . . . . . . . . . 11
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11 7. Normative References . . . . . . . . . . . . . . . . . . . . . 11
7.1. Normative References . . . . . . . . . . . . . . . . . . . 11 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
7.2. Informative References . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction 1. Introduction
The DHCP Reconfigure Extension defined in [RFC3203] is a useful The DHCP Reconfigure Extension defined in [RFC3203] is a useful
mechanism allowing dynamic reconfiguration of a single host triggered mechanism allowing dynamic reconfiguration of a single host triggered
by the DHCP server. Its application is currently limited by a by the DHCP server. Its application is currently limited by a
requirement that FORCERENEW message is always authenticated using requirement that FORCERENEW message is always authenticated using
procedures as described in [RFC3118]. Authentication for DHCP procedures as described in [RFC3118]. Authentication for DHCP
[RFC3118] is mandatory for FORCERENEW, however as it is currently [RFC3118] is mandatory for FORCERENEW, however as it is currently
defined [RFC3118] requires distribution of constant token or shared- defined [RFC3118] requires distribution of constant token or shared-
secret out-of-band to DHCP clients. The mandatory authentication was secret out-of-band to DHCP clients.
originally motivated by a legitimate security concern whereby in some
network environments DHCP messages can be spoofed and an attacker The motivation for making authentication mandatory in DHCP FORCERENEW
could more accurately guess the timing of DHCP renewal messages by was to prevent an off-network attacker from taking advantage of DHCP
first sending a FORCERENEW message. However, in some networks native FORCERENEW to accurately predict the timing of a DHCP renewal.
security mechanisms already provide sufficient protection against Without DHCP FORCERENEW, DHCP renewal timing is under the control of
spoofing of DHCP traffic. An example of such network is a Broadband the client, and an off-network attacker has no way of predicting when
Forum TR-101 [TR-101i2] compliant access network. In such it will happen, since it doesn't have access to the exchange between
environments the mandatory coupling between FORCERENEW and DHCP the DHCP client and DHCP server.
Authentication [RFC3118] can be relaxed and a lighter authentication
mechanism can be used for the FORCERENEW message. This document However, the requirement to use the DHCP authentication described in
defines extensions to Authentication for DHCPv4 Messages [RFC3118] to [RFC3118] is more stringent than is required for this use case, and
create a new authentication protocol for DHCPv4 FORCERENEW [RFC3203] has limited adoption of DHCP FORCERENEW. [RFC3315] defines an
messages; this method does not require out-of-band key distribution authentication protocol using a nonce to prevent off-network
to DHCP clients. The Forcerenew Nonce is exchanged between server attackers from successfully causing clients to renew. Since the off-
and client on initial DHCP ACK and is used for verification of any network attacker doesn't have access to the nonce, it can't trick the
subsequent FORCERENEW message. This document updates [RFC3203] client into renewing at a time of its choosing.
This document defines extensions to Authentication for DHCPv4
Messages [RFC3118] to create a new authentication protocol for DHCPv4
FORCERENEW [RFC3203] messages; this method does not require out-of-
band key distribution to DHCP clients. The Forcerenew Nonce is
exchanged between server and client on initial DHCP ACK and is used
for verification of any subsequent FORCERENEW message. This document
updates [RFC3203]
2. Requirements Language 2. Requirements Language
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 this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
3. Message authentication 3. Message authentication
The FORCERENEW message must be authenticated using either [RFC3118] The FORCERENEW message MUST be authenticated using either [RFC3118]
or the proposed Forcerenew Nonce Authentication protocol. or the proposed Forcerenew Nonce Authentication protocol.
3.1. Forcerenew Nonce Authentication 3.1. Forcerenew Nonce Authentication
The Forcerenew nonce authentication protocol provides protection The Forcerenew nonce authentication protocol provides protection
against misconfiguration of a client caused by a FORCERENEW message against misconfiguration of a client caused by a FORCERENEW message
sent by a malicious DHCP server. In this protocol, a DHCP server sent by a malicious DHCP server. In this protocol, a DHCP server
sends a Forcerenew nonce to the client in the initial exchange of sends a Forcerenew nonce to the client in the initial exchange of
DHCP messages. The client records the Forcerenew nonce for use in DHCP messages. The client records the Forcerenew nonce for use in
authenticating subsequent Forcerenew messages from that server. The authenticating subsequent Forcerenew messages from that server. The
skipping to change at page 4, line 25 skipping to change at page 4, line 34
specified in [RFC3118] and the client and server have negotiated to specified in [RFC3118] and the client and server have negotiated to
use the Forcerenew Nonce Authentication protocol. use the Forcerenew Nonce Authentication protocol.
3.1.1. Forcerenew Nonce Protocol Capability Option 3.1.1. Forcerenew Nonce Protocol Capability Option
A DHCP client indicates DHCP Forcerenew Nonce Protocol capability by A DHCP client indicates DHCP Forcerenew Nonce Protocol capability by
including a FORCERENEW_NONCE_CAPABLE(<TBD>) option in DHCP Discover including a FORCERENEW_NONCE_CAPABLE(<TBD>) option in DHCP Discover
and Request messages sent to the server. and Request messages sent to the server.
A DHCP server that does not support Forcerenew Nonce Protocol A DHCP server that does not support Forcerenew Nonce Protocol
authentication should ignore the FORCERENEW_NONCE_CAPABLE(<TBD>) authentication SHOULD ignore the FORCERENEW_NONCE_CAPABLE(<TBD>)
option. A DHCP server indicates DHCP Forcerenew Nonce Protocol option. A DHCP server indicates DHCP Forcerenew Nonce Protocol
preference by including a FORCERENEW_NONCE_CAPABLE(<TBD>) option in preference by including a FORCERENEW_NONCE_CAPABLE(<TBD>) option in
any DHCP Offer messages sent to the client. any DHCP Offer messages sent to the client.
A DHCP client MUST NOT send DHCP messages with authentication options A DHCP client MUST NOT send DHCP messages with authentication options
where the protocol value is Forcerenew Nonce Authentication(<TBD>). where the protocol value is Forcerenew Nonce Authentication(<TBD>).
The FORCERENEW_NONCE_CAPABLE option is a zero length option with code The FORCERENEW_NONCE_CAPABLE option is a zero length option with code
of <TDB> and format as follows: of <TDB> and format as follows:
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If a capable server receives a DISCOVER or REQUEST (any type) that If a capable server receives a DISCOVER or REQUEST (any type) that
indicates the client is capable, and the server has no previous nonce indicates the client is capable, and the server has no previous nonce
recorded, it MUST generate a nonce and include it in the ACK. recorded, it MUST generate a nonce and include it in the ACK.
The server selects a Forcerenew nonce for a client only during The server selects a Forcerenew nonce for a client only during
Request/Ack message exchange. The server records the Forcerenew Request/Ack message exchange. The server records the Forcerenew
nonce and transmits that nonce to the client in an Authentication nonce and transmits that nonce to the client in an Authentication
option in the DHCP Ack message. option in the DHCP Ack message.
The server SHOULD NOT include the nonce in an ACK when responding to The server SHOULD NOT include the nonce in an ACK when responding to
a renew unless a nonce was generated. This minimizes the number of a renew unless a new nonce was generated. This minimizes the number
times the nonce is sent over the wire. of times the nonce is sent over the wire.
If the server to which the DHCP Request message was sent at time T1 If the server to which the DHCP Request message was sent at time T1
has not responded, the client enters the REBINDING state and attempts has not responded, the client enters the REBINDING state and attempts
to contact any server. The new Server receiving the DHCP message to contact any server. The new Server receiving the DHCP message
MUST generate a new nonce. MUST generate a new nonce.
The Forcerenew nonce is 128 bits long, and MUST be a The Forcerenew nonce is 128 bits long, and MUST be a
cryptographically strong random or pseudo-random number that cannot cryptographically strong random or pseudo-random number that cannot
easily be predicted. The nonce is embedded as a 128-bit value of the easily be predicted. The nonce is embedded as a 128-bit value of the
Authentication information where type is set to 1 (Forcerenew nonce Authentication information where type is set to 1 (Forcerenew nonce
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Data lenght: 1 Data lenght: 1
Description: Forcerenew Nonce Capable Description: Forcerenew Nonce Capable
Reference: this document Reference: this document
6. Security Considerations 6. Security Considerations
As in some network environments FORCERENEW can be used to snoop and As in some network environments FORCERENEW can be used to snoop and
spoof traffic, the FORCERENEW message MUST be authenticated using the spoof traffic, the FORCERENEW message MUST be authenticated using the
procedures as described in [RFC3118] or this proposal. procedures as described in [RFC3118] or the mechanism described in
this document.
The mechanism in [RFC3315] for DHCPv6, which this document mirrors The mechanism in [RFC3315] for DHCPv6, which this document mirrors
for DHCPv4, uses a nonce to prevent an off-link attacker from for DHCPv4, uses a nonce to prevent an off-link attacker from
successfully triggering a renewal on a client by sending successfully triggering a renewal on a client by sending
DHCPFORCERENEW; since the attacker is off-link, it doesn't have the DHCPFORCERENEW; since the attacker is off-link, it doesn't have the
nonce, and can't force a renewal. nonce, and can't force a renewal.
An on-link attacker can always simply watch the DHCP renewal message An on-link attacker can always simply watch the DHCP renewal message
go out and respond to it, so this mechanism is useless for preventing go out and respond to it, so this mechanism is useless for preventing
on-link attacks, and hence the security of the nonce in the case of on-link attacks, and hence the security of the nonce in the case of
on-link attacks isn't relevant. Any party able to intercept the on-link attacks isn't relevant. Therefore HMAC-MD5 is by definition
nonce exchange could impersonate a server and thus offers no adequate for the purpose, and there is no need for an extensible HMAC
protection from man-in-the- middle attacks. FORCERENEW messages mechanism. FORCERENEW messages failing the authentication should be
failing the authentication should be silently discarded by the silently discarded by the client.
client.
6.1. Protocol vulnerabilities 6.1. Protocol vulnerabilities
The mechanism described in this document is vulnerable to a denial of The mechanism described in this document is vulnerable to a denial of
service attack through flooding a client with bogus FORCERENEW service attack through flooding a client with bogus FORCERENEW
messages. The calculations involved in authenticating the bogus messages. The calculations involved in authenticating the bogus
FORECERENEW messages may overwhelm the device on which the client is FORECERENEW messages may overwhelm the device on which the client is
running. running.
The mechanism described provides protection against the use of a The mechanism described provides protection against the use of a
FORCERENEW message by a malicious DHCP server to mount a denial of FORCERENEW message by a malicious DHCP server to mount a denial of
service or man-in-the-middle attack on a client. This protocol can service or man-in-the-middle attack on a client. This protocol can
be compromised by an attacker that can intercept the initial message be compromised by an attacker that can intercept the initial message
in which the DHCP server sends the nonce to the client. in which the DHCP server sends the nonce to the client.
7. References 7. Normative References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] 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.
[RFC3118] Droms, R. and W. Arbaugh, "Authentication for DHCP [RFC3118] Droms, R. and W. Arbaugh, "Authentication for DHCP
Messages", RFC 3118, June 2001. Messages", RFC 3118, June 2001.
[RFC3203] T'Joens, Y., Hublet, C., and P. De Schrijver, "DHCP [RFC3203] T'Joens, Y., Hublet, C., and P. De Schrijver, "DHCP
reconfigure extension", RFC 3203, December 2001. reconfigure extension", RFC 3203, December 2001.
[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., [RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
and M. Carney, "Dynamic Host Configuration Protocol for and M. Carney, "Dynamic Host Configuration Protocol for
IPv6 (DHCPv6)", RFC 3315, July 2003. IPv6 (DHCPv6)", RFC 3315, July 2003.
7.2. Informative References
[TR-101i2]
Anschutz, T., "Migration to Ethernet-Based Broadband
Aggregation Broadband Forum TR-101 Issue 2", July 2011.
Authors' Addresses Authors' Addresses
David Miles David Miles
Google Google
Phone: Phone:
Fax: Fax:
Email: Email:
URI: URI:
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