draft-ietf-dhc-auth-suboption-03.txt   draft-ietf-dhc-auth-suboption-04.txt 
DHC Working Group M. Stapp DHC Working Group M. Stapp
Internet-Draft Cisco Systems, Inc. Internet-Draft Cisco Systems, Inc.
Expires: August 5, 2004 T. Lemon Expires: January 6, 2005 T. Lemon
Nominum, Inc. Nominum, Inc.
February 5, 2004 July 8, 2004
The Authentication Suboption for the DHCP Relay Agent Option The Authentication Suboption for the DHCP Relay Agent Option
<draft-ietf-dhc-auth-suboption-03.txt> <draft-ietf-dhc-auth-suboption-04.txt>
Status of this Memo Status of this Memo
This document is an Internet-Draft and is in full conformance with By submitting this Internet-Draft, I certify that any applicable
all provisions of Section 10 of RFC2026. patent or other IPR claims of which I am aware have been disclosed,
and any of which I become aware will be disclosed, in accordance with
RFC 3667.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that other
other groups may also distribute working documents as groups may also distribute working documents as Internet-Drafts.
Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six Internet-Drafts are draft documents valid for a maximum of six months
months and may be updated, replaced, or obsoleted by other documents and may be updated, replaced, or obsoleted by other documents at any
at any 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."
The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at http://
http://www.ietf.org/ietf/1id-abstracts.txt. www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html. http://www.ietf.org/shadow.html.
This Internet-Draft will expire on August 5, 2004. This Internet-Draft will expire on January 6, 2005.
Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved. Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract Abstract
The DHCP Relay Agent Information Option (RFC 3046) conveys The DHCP Relay Agent Information Option (RFC 3046) conveys
information between a DHCP Relay Agent and a DHCP server. This information between a DHCP Relay Agent and a DHCP server. This
specification defines an authentication suboption for that option specification defines an authentication suboption for that option,
which supports source entity authentication and data integrity for containing a keyed hash in its payload. The suboption supports data
relayed DHCP messages. The authentication suboption contains a integrity and replay protection for relayed DHCP messages.
cryptographic signature in its payload.
Table of Contents Table of Contents
1. Requirements Terminology . . . . . . . . . . . . . . . . . . 3 1. Requirements Terminology . . . . . . . . . . . . . . . . . . 3
2. DHCP Terminology . . . . . . . . . . . . . . . . . . . . . . 3 2. DHCP Terminology . . . . . . . . . . . . . . . . . . . . . . 3
3. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Suboption Format . . . . . . . . . . . . . . . . . . . . . . 4 4. Suboption Format . . . . . . . . . . . . . . . . . . . . . . 4
5. Replay Detection . . . . . . . . . . . . . . . . . . . . . . 5 5. Replay Detection . . . . . . . . . . . . . . . . . . . . . . 5
6. The Relay Identifier Field . . . . . . . . . . . . . . . . . 5 6. The Relay Identifier Field . . . . . . . . . . . . . . . . . 5
7. Computing Authentication Information . . . . . . . . . . . . 6 7. Computing Authentication Information . . . . . . . . . . . . 6
7.1 The HMAC-MD5 Algorithm . . . . . . . . . . . . . . . . . . . 6 7.1 The HMAC-MD5 Algorithm . . . . . . . . . . . . . . . . . . . 6
8. Procedures for Sending Messages . . . . . . . . . . . . . . 8 8. Procedures for Sending Messages . . . . . . . . . . . . . . 7
8.1 Replay Detection . . . . . . . . . . . . . . . . . . . . . . 8 8.1 Replay Detection . . . . . . . . . . . . . . . . . . . . . . 7
8.2 Packet Preparation . . . . . . . . . . . . . . . . . . . . . 8 8.2 Packet Preparation . . . . . . . . . . . . . . . . . . . . . 8
8.3 Signature Computation . . . . . . . . . . . . . . . . . . . 8 8.3 Checksum Computation . . . . . . . . . . . . . . . . . . . . 8
8.4 Sending the Message . . . . . . . . . . . . . . . . . . . . 8 8.4 Sending the Message . . . . . . . . . . . . . . . . . . . . 8
9. Procedures for Processing Incoming Messages . . . . . . . . 8 9. Procedures for Processing Incoming Messages . . . . . . . . 8
9.1 Initial Examination . . . . . . . . . . . . . . . . . . . . 8 9.1 Initial Examination . . . . . . . . . . . . . . . . . . . . 8
9.2 Replay Detection Check . . . . . . . . . . . . . . . . . . . 9 9.2 Replay Detection Check . . . . . . . . . . . . . . . . . . . 9
9.3 Signature Check . . . . . . . . . . . . . . . . . . . . . . 9 9.3 Testing the Checksum . . . . . . . . . . . . . . . . . . . . 9
10. Relay Agent Behavior . . . . . . . . . . . . . . . . . . . . 9 10. Relay Agent Behavior . . . . . . . . . . . . . . . . . . . . 9
10.1 Receiving Messages from Other Relay Agents . . . . . . . . . 10 10.1 Receiving Messages from Other Relay Agents . . . . . . . . . 10
10.2 Sending Messages to Servers . . . . . . . . . . . . . . . . 10 10.2 Sending Messages to Servers . . . . . . . . . . . . . . . . 10
10.3 Receiving Messages from Servers . . . . . . . . . . . . . . 10 10.3 Receiving Messages from Servers . . . . . . . . . . . . . . 10
11. DHCP Server Behavior . . . . . . . . . . . . . . . . . . . . 10 11. DHCP Server Behavior . . . . . . . . . . . . . . . . . . . . 10
11.1 Receiving Messages from Relay Agents . . . . . . . . . . . . 11 11.1 Receiving Messages from Relay Agents . . . . . . . . . . . . 10
11.2 Sending Reply Messages to Relay Agents . . . . . . . . . . . 11 11.2 Sending Reply Messages to Relay Agents . . . . . . . . . . . 10
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . 11 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . 11
13. Security Considerations . . . . . . . . . . . . . . . . . . 11 13. Security Considerations . . . . . . . . . . . . . . . . . . 11
13.1 Protocol Vulnerabilities . . . . . . . . . . . . . . . . . . 12 13.1 The Key ID Field . . . . . . . . . . . . . . . . . . . . . . 12
13.2 Protocol Vulnerabilities . . . . . . . . . . . . . . . . . . 12
14. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12 14. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12
References . . . . . . . . . . . . . . . . . . . . . . . . . 12 Normative References . . . . . . . . . . . . . . . . . . . . 13
References . . . . . . . . . . . . . . . . . . . . . . . . . 13 Informative References . . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 13 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 14
Full Copyright Statement . . . . . . . . . . . . . . . . . . 15 Intellectual Property and Copyright Statements . . . . . . . 15
1. Requirements Terminology 1. Requirements Terminology
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 RFC 2119[2]. document are to be interpreted as described in RFC 2119[2].
2. DHCP Terminology 2. DHCP Terminology
This document uses the terms "DHCP server" (or "server") and "DHCP This document uses the terms "DHCP server" (or "server") and "DHCP
skipping to change at page 3, line 26 skipping to change at page 3, line 26
3. Introduction 3. Introduction
DHCP (RFC 2131[6]) provides IP addresses and configuration DHCP (RFC 2131[6]) provides IP addresses and configuration
information for IPv4 clients. It includes a relay-agent capability information for IPv4 clients. It includes a relay-agent capability
(RFC 951[7], RFC 1542[8]), in which processes within the network (RFC 951[7], RFC 1542[8]), in which processes within the network
infrastructure receive broadcast messages from clients and forward infrastructure receive broadcast messages from clients and forward
them to servers as unicast messages. In network environments like them to servers as unicast messages. In network environments like
DOCSIS data-over-cable and xDSL, for example, it has proven useful DOCSIS data-over-cable and xDSL, for example, it has proven useful
for the relay agent to add information to the DHCP message before for the relay agent to add information to the DHCP message before
forwarding it, using the relay-agent information option (RFC forwarding it, using the relay-agent information option (RFC 3046
3046[1]). The kind of information that relays add is often used in [1]). The kind of information that relays add is often used in the
the server's decision making about the addresses and configuration server's decision making about the addresses and configuration
parameters that the client should receive. The way that the parameters that the client should receive. The way that the
relay-agent data is used in server decision-making tends to make relay-agent data is used in server decision-making tends to make that
that data very important, and highlights the importance of the trust data very important, and highlights the importance of the trust
relationship between the relay agent and the server. relationship between the relay agent and the server.
The existing DHCP Authentication specification (RFC 3118)[9] only The existing DHCP Authentication specification (RFC 3118)[9] only
covers communication between the DHCP client and server. Because covers communication between the DHCP client and server. Because
relay-agent information is added after the client has signed its relay-agent information is added after the client has sent its
message, the DHCP Authentication specification explictly excludes message, the DHCP Authentication specification explictly excludes
relay-agent data from that authentication. relay-agent data from that authentication.
The goal of this specification is to define methods that a relay The goal of this specification is to define methods that a relay
agent can use to: agent can use to:
1. protect the integrity of the data that the relay adds 1. protect the integrity of relayed DHCP messages
2. provide replay protection for that data 2. provide replay protection for those messages
3. leverage existing mechanisms such as DHCP Authentication 3. leverage existing mechanisms such as DHCP Authentication
In order to meet these goals, we specify a new relay-agent In order to meet these goals, we specify a new relay-agent suboption,
suboption, the Authentication suboption. The format of this the Authentication suboption. The format of this suboption is very
suboption is very similar to the format of the DHCP Authentication similar to the format of the DHCP Authentication option, and the
option, and the specification of the cryptographic methods and specification of the cryptographic methods and hash computation for
signature computation for the suboption are also similar to that the suboption are also similar to that specification.
option's specification.
The Authentication suboption is included by relay agents that wish The Authentication suboption is included by relay agents that wish to
to ensure the integrity of the data they include in the Relay Agent ensure the integrity of the data they include in the Relay Agent
option. These relay agents are configured with the parameters option. These relay agents are configured with the parameters
necessary to generate cryptographically strong signatures of the necessary to generate cryptographic checksums of the data in the DHCP
data in the DHCP messages which they forward to DHCP servers. A DHCP messages which they forward to DHCP servers. A DHCP server configured
server configured to process the Authentication suboption uses the to process the Authentication suboption uses the information in the
information in the suboption to validate the signature in the suboption to verify the checksum in the suboption, and continues
suboption, and continues processing the relay agent information processing the relay agent information option only if the checksum is
option only if the signature is valid. If the DHCP server sends a valid. If the DHCP server sends a response, it includes an
response, it includes an Authentication suboption in its response Authentication suboption in its response message. Relay agents test
message, signing the data in its message. Relay agents check the the checksums in DHCP server responses to decide whether to forward
signatures in DHCP server responses and decide whether to forward the responses.
the responses based on the signatures' validity.
4. Suboption Format 4. Suboption Format
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Code | Length | Algorithm | MBZ | RDM | | Code | Length | Algorithm | MBZ | RDM |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Replay Detection (64 bits) | | Replay Detection (64 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 4, line 38 skipping to change at page 4, line 37
| Relay Identifier | | Relay Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
| | | |
| Authentication Information | | Authentication Information |
| | | |
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The code for the suboption is TBD. The length field includes the The code for the suboption is TBD. The length field includes the
lengths of the algorithm, RDM, and all subsequent suboption fields lengths of the algorithm, RDM, and all subsequent suboption fields in
in octets. octets.
The Algorithm field defines the algorithm used to generate the The Algorithm field defines the algorithm used to generate the
authentication information. authentication information.
Four bits are reserved for future use. These bits SHOULD be set to Four bits are reserved for future use. These bits SHOULD be set to
zero, and MUST be not be used when the suboption is processed. zero, and MUST be not be used when the suboption is processed.
The Replay Detection Method (RDM) field defines the method used to The Replay Detection Method (RDM) field defines the method used to
generate the Replay Detection Data. generate the Replay Detection Data.
The Replay Detection field contains a value used to detect replayed The Replay Detection field contains a value used to detect replayed
messages, interpreted according to the RDM. messages, interpreted according to the RDM.
The Relay Identifier field is used by relay agents that do not set The Relay Identifier field is used by relay agents that do not set
giaddr, as described in RFC 3046[1], Section 2.1. giaddr, as described in RFC 3046[1], Section 2.1.
The Authentication Information field contains the data required to The Authentication Information field contains the data required to
communicate algorithm-specific parameters, as well as the signature. communicate algorithm-specific parameters, as well as the checksum.
The signature is usually a digest of the data in the DHCP packet The checksum is usually a digest of the data in the DHCP packet
computed using the method specified by the Algorithm field. computed using the method specified by the Algorithm field.
5. Replay Detection 5. Replay Detection
The replay-detection mechanism is based on the notion that a The replay-detection mechanism is based on the notion that a receiver
receiver can determine whether or not a message has a valid replay can determine whether or not a message has a valid replay token
token value. The default RDM, with value 1, specifies that the value. The default RDM, with value 1, specifies that the Replay
Replay Detection field contains an increasing counter value. The Detection field contains an increasing counter value. The receiver
receiver associates a replay counter with each sender, and rejects associates a replay counter with each sender, and rejects any message
any message containing an authentication suboption with a Replay containing an authentication suboption with a Replay Detection
Detection counter value less than or equal to the last valid value. counter value less than or equal to the last valid value. DHCP
DHCP servers MAY identify relay agents by giaddr value or by other servers MAY identify relay agents by giaddr value or by other data in
data in the message (e.g. data in other relay agent suboptions). the message (e.g. data in other relay agent suboptions). Relay agents
Relay agents identify DHCP servers by source IP address. If the identify DHCP servers by source IP address. If the message's replay
message's replay detection value is valid, and the signature is also detection value is valid, and the checksum is also valid, the
valid, the receiver updates its notion of the last valid replay receiver updates its notion of the last valid replay counter value
counter value associated with the sender. associated with the sender.
All implementations MUST support the default RDM. Additional methods All implementations MUST support the default RDM. Additional methods
may be defined in the future, following the process described in may be defined in the future, following the process described in
Section 12. Section 12.
Receivers SHOULD perform the replay-detection check before Receivers SHOULD perform the replay-detection check before testing
validating the signature. The authentication hash calculation is the checksum. The keyed hash calculation is likely to be much more
likely to be much more expensive than the replay-detection value expensive than the replay-detection value check.
check.
DISCUSSION: DISCUSSION:
This places a burden on the receiver to maintain some run-time This places a burden on the receiver to maintain some run-time
state (the most-recent valid counter value) for each sender, but state (the most-recent valid counter value) for each sender, but
the number of members in a DHCP agent-server system is unlikely the number of members in a DHCP agent-server system is unlikely to
to be unmanageably large. be unmanageably large.
6. The Relay Identifier Field 6. The Relay Identifier Field
The Relay Agent Information Option[1] specification permits a relay The Relay Agent Information Option[1] specification permits a relay
agent to add a relay agent option to relayed messages without agent to add a relay agent option to relayed messages without setting
setting the giaddr field. In this case, the eventual receiver of the the giaddr field. In this case, the eventual receiver of the message
message needs a stable identifier to use in order to associate needs a stable identifier to use in order to associate per-sender
per-sender state such as Key ID and replay-detection counters. state such as Key ID and replay-detection counters.
A relay agent that adds a relay agent information option and sets A relay agent that adds a relay agent information option and sets
giaddr MUST NOT set the Relay ID field. A relay agent that does not giaddr MUST NOT set the Relay ID field. A relay agent that does not
set giaddr MAY be configured to place a value in the Relay ID field. set giaddr MAY be configured to place a value in the Relay ID field.
If the relay agent is configured to use the Relay ID field, it MAY If the relay agent is configured to use the Relay ID field, it MAY be
be configured with a value to use, or it MAY be configured to configured with a value to use, or it MAY be configured to generate a
generate a value based on some other data, such its MAC or IP value based on some other data, such its MAC or IP addresses. If a
addresses. If a relay generates a Relay ID value it SHOULD select a relay generates a Relay ID value it SHOULD select a value that it can
value that it can regenerate reliably, e.g. across reboots. regenerate reliably, e.g. across reboots.
Servers that process an Authentication Suboption SHOULD use the Servers that process an Authentication Suboption SHOULD use the
giaddr value to identify the sender if the giaddr field is set. giaddr value to identify the sender if the giaddr field is set.
Servers MAY be configured to use some other data in the message to Servers MAY be configured to use some other data in the message to
identify the signer. If giaddr is not set, the server SHOULD use the identify the sender. If giaddr is not set, the server SHOULD use the
Relay ID field if it is non-zero. If neither the giaddr nor the Relay ID field if it is non-zero. If neither the giaddr nor the Relay
Relay ID field is set, the server MAY be configured to use some ID field is set, the server MAY be configured to use some other data
other data in the message, or it MAY increment an error counter. in the message, or it MAY increment an error counter.
7. Computing Authentication Information 7. Computing Authentication Information
The Authentication Information field contains a computed signature, The Authentication Information field contains a keyed hash, generated
generated by the sender. All algorithms are defined to process the by the sender. All algorithms are defined to process the data in the
data in the DHCP messages in the same way. The sender and receiver DHCP messages in the same way. The sender and receiver compute a hash
compute the signature across a buffer containing all of the bytes in across a buffer containing all of the bytes in the DHCP message,
the DHCP message, including the fixed DHCP message header, the DHCP including the fixed DHCP message header, the DHCP options, and the
options, and the relay agent suboptions, with the following relay agent suboptions, with the following exceptions. The value of
exceptions. The value of the 'hops' field MUST be set to zero for the 'hops' field MUST be set to zero for the computation, because its
the computation, because its value may be changed in transmission. value may be changed in transmission. The value of the 'giaddr' field
The value of the 'giaddr' field MUST also be set to zero for the MUST also be set to zero for the computation because it may be
computation because it may be modified in networks where one relay modified in networks where one relay agent adds the relay agent
agent adds the relay agent option but another relay agent sets option but another relay agent sets 'giaddr' (see RFC 3046, section
'giaddr' (see RFC 3046, section 2.1). In addition, because the relay 2.1). In addition, because the relay agent option itself is included
agent option itself is included in the computation, the 'signature' in the computation, the 'authentication information' field in the
part of the 'authentication information' field in the Authentication Authentication suboption is set to all zeroes. The relay agent option
suboption is set to all zeroes. The relay agent option length, the length, the Authentication suboption length and other Authentication
Authentication suboption length and other Authentication suboption suboption fields are all included in the computation.
fields are all included in the computation.
All implementations MUST support Algorithm 1, the HMAC-MD5 All implementations MUST support Algorithm 1, the HMAC-MD5 algorithm.
algorithm. Additional algorithms may be defined in the future, Additional algorithms may be defined in the future, following the
following the process described in Section 12. process described in Section 12.
7.1 The HMAC-MD5 Algorithm 7.1 The HMAC-MD5 Algorithm
Algorithm 1 is assigned to the HMAC[3] protocol, using the MD5[4] Algorithm 1 is assigned to the HMAC[3] protocol, using the MD5[4]
hash function. This algorithm requires that a shared secret key be hash function. This algorithm requires that a shared secret key be
configured at the relay agent and the DHCP server. A 32-bit Key configured at the relay agent and the DHCP server. A 32-bit Key
Identifier is associated with each shared key, and this identifier Identifier is associated with each shared key, and this identifier is
is carried in the first 4 bytes of the Authentication Information carried in the first 4 bytes of the Authentication Information field
field of the Authentication suboption. The HMAC-MD5 computation of the Authentication suboption. The HMAC-MD5 computation generates a
generates a 16-byte signature, which is placed in the Authentication 16-byte hash value, which is placed in the Authentication Information
Information field after the Key ID. field after the Key ID.
The format of the Authentication suboption when Algorithm 1 is used The format of the Authentication suboption when Algorithm 1 is used
is: is:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Code | 34 |0 0 0 0 0 0 0 1| MBZ | RDM | | Code | 34 |0 0 0 0 0 0 0 1| MBZ | RDM |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Replay Detection (64 bits) | | Replay Detection (64 bits) |
skipping to change at page 7, line 32 skipping to change at page 7, line 32
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
| HMAC-MD5 (128 bits) | | HMAC-MD5 (128 bits) |
| | | |
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The suboption length is 34. The RDM and Replay Detection fields are The suboption length is 34. The RDM and Replay Detection fields are
as specified in Section 5. The Relay ID field is set as specified in as specified in Section 5. The Relay ID field is set as specified in
Section 6. The Key ID is set by the sender to the ID of the key used Section 6. The Key ID is set by the sender to the ID of the key used
in computing the signature, as an integer value in network in computing the checksum, as an integer value in network byte-order.
byte-order. The HMAC signature follows the Key ID. The HMAC result follows the Key ID.
The Key ID exists only to allow the sender and receiver to specify a The Key ID exists only to allow the sender and receiver to specify a
shared secret in cases where more than one secret is in use among a shared secret in cases where more than one secret is in use among a
network's relays and DHCP servers. The Key ID values are entirely a network's relays and DHCP servers. The Key ID values are entirely a
matter of local configuration; they only need to be locally unique. matter of local configuration; they only need to be locally unique.
This specification does not define any semantics or impose any This specification does not define any semantics or impose any
requirements on this algorithm's Key ID values. requirements on this algorithm's Key ID values.
DISCUSSION:
We specify a four-byte Key ID, following the example of the DHCP
Authentication RFC. Other authentication protocols, like DNS
TSIG[10], use a key name. A key name is more flexible and
potentially more human-readable than a key id. DHCP servers may
well be configured to use key names for DNS updates using TSIG,
so it might simplify DHCP server configuration if some of the
key-management for both protocols could be shared.
On the other hand, it is crucial to minimize the size expansion
caused by the introduction of the relay agent information option.
Named keys would require more physical space, and would entail
more complex suboption encoding and parsing implementations.
These considerations have led us to specify a fixed-length Key ID
instead of a variable-length key name.
8. Procedures for Sending Messages 8. Procedures for Sending Messages
8.1 Replay Detection 8.1 Replay Detection
The sender obtains a replay-detection counter value to use, based on The sender obtains a replay-detection counter value to use, based on
the RDM it is using. If the sender is using RDM 1, the default RDM, the RDM it is using. If the sender is using RDM 1, the default RDM,
the value MUST be greater than any previously-sent value. the value MUST be greater than any previously-sent value.
8.2 Packet Preparation 8.2 Packet Preparation
The sender sets the 'giaddr' field and the 'hops' field to all The sender sets the 'giaddr' field and the 'hops' field to all
zeroes. The sender appends the relay agent information option to the zeroes. The sender appends the relay agent information option to the
client's packet, including the Authentication suboption. The sender client's packet, including the Authentication suboption. The sender
selects an appropriate Replay Detection value. The sender places its selects an appropriate Replay Detection value. The sender places its
identifier into the Relay ID field, if necessary, or sets the field identifier into the Relay ID field, if necessary, or sets the field
to all zeroes. The sender sets the suboption length, places the to all zeroes. The sender sets the suboption length, places the
Replay Detection value into the Replay Detection field of the Replay Detection value into the Replay Detection field of the
suboption, and sets the algorithm to the algorithm number that it is suboption, and sets the algorithm to the algorithm number that it is
using. If the sender is using HMAC-MD5, it sets the Key ID field to using. If the sender is using HMAC-MD5, it sets the Key ID field to
the appropriate value. The sender sets the field which will contain the appropriate value. The sender sets the field which will contain
the signature to all zeroes. Other algorithms may specify additional the checksum to all zeroes. Other algorithms may specify additional
preparation steps. preparation steps.
8.3 Signature Computation 8.3 Checksum Computation
The sender computes the signature across the entire DHCP message, The sender computes the checksum across the entire DHCP message,
using the algorithm it has selected. The sender places the result of using the algorithm it has selected. The sender places the result of
the computation into the signature field of the Authentication the computation into the Authentication Information field of the
suboption. Authentication suboption.
8.4 Sending the Message 8.4 Sending the Message
The sender restores the values of the 'hops' and 'giaddr' fields, The sender restores the values of the 'hops' and 'giaddr' fields, and
and sends the message. sends the message.
9. Procedures for Processing Incoming Messages 9. Procedures for Processing Incoming Messages
9.1 Initial Examination 9.1 Initial Examination
The receiver examines the message, the value of the giaddr field, The receiver examines the message, the value of the giaddr field, and
and determines whether the packet includes the relay agent determines whether the packet includes the relay agent information
information option. The receiver uses its configuration to determine option. The receiver uses its configuration to determine whether it
whether it should expect an Authentication suboption. The receiver should expect an Authentication suboption. The receiver MUST support
MUST support configuration that allows it to drop incoming messages configuration that allows it to drop incoming messages that do not
that do not contain a valid relay agent information option and contain a valid relay agent information option and Authentication
Authentication suboption. suboption.
If the receiver determines that the Authentication suboption is If the receiver determines that the Authentication suboption is
present and that it should process the suboption, it uses the data present and that it should process the suboption, it uses the data in
in the message to determine which algorithm, key, and RDM to use in the message to determine which algorithm, key, and RDM to use in
validating the message. If the receiver cannot determine which validating the message. If the receiver cannot determine which
algorithm, key, and RDM to use, or if it does not support the value algorithm, key, and RDM to use, or if it does not support the value
indicated in the message, it SHOULD drop the message. Because this indicated in the message, it SHOULD drop the message. Because this
situation could indicate a misconfiguration which could deny service situation could indicate a misconfiguration which could deny service
to clients, receivers MAY attempt to notify their administrators or to clients, receivers MAY attempt to notify their administrators or
log an error message. log an error message.
9.2 Replay Detection Check 9.2 Replay Detection Check
The receiver examines the RDM field. Receivers MUST discard The receiver examines the RDM field. Receivers MUST discard messages
messages containing RDM values that they do not support. Because containing RDM values that they do not support. Because this may
this may indicate a misconfiguration at the sender, an attempt indicate a misconfiguration at the sender, an attempt SHOULD be made
SHOULD be made to indicate this condition to the administrator, by to indicate this condition to the administrator, by incrementing an
incrementing an error counter or writing a log message. If the error counter or writing a log message. If the receiver supports the
receiver supports the RDM, it examines the value in the Replay RDM, it examines the value in the Replay Detection field using the
Detection field using the procedures in the RDM and in Section 5. If procedures in the RDM and in Section 5. If the Replay value is not
the Replay value is not valid, the receiver MUST drop the message. valid, the receiver MUST drop the message.
Note that the receiver MUST NOT update its notion of the last valid Note that the receiver MUST NOT update its notion of the last valid
Replay Detection value for the sender at this point. Until the Replay Detection value for the sender at this point. Until the
signature has been checked, the Replay Detection field cannot be checksum has been tested, the Replay Detection field cannot be
trusted. If the receiver trusts the Replay Detection value without trusted. If the receiver trusts the Replay Detection value without
checking the signature, a malicious host could send a replayed testing the checksum, a malicious host could send a replayed message
message with a Replay Detection value that was very high, tricking with a Replay Detection value that was very high, tricking the
the receiver into rejecting legitimate values from the sender. receiver into rejecting legitimate values from the sender.
9.3 Signature Check 9.3 Testing the Checksum
The receiver prepares the packet in order to check the signature. The receiver prepares the packet in order to test the checksum by
The receiver sets the 'giaddr' and 'hops' fields to zero, and sets setting the 'giaddr' and 'hops' fields to zero, and setting the
the signature field of the Authentication suboption to all zeroes. Authentication Information field of the suboption to all zeroes.
Using the algorithm and key associated with the sender, the receiver Using the algorithm and key associated with the sender, the receiver
computes a hash of the message. The receiver compares the result of computes a hash of the message. The receiver compares the result of
its computation with the value sent by the sender. If the signatures its computation with the value sent by the sender. If the checksums
do not match, the receiver MUST drop the message. Otherwise, the do not match, the receiver MUST drop the message. Otherwise, the
receiver updates its notion of the last valid Replay Detection value receiver updates its notion of the last valid Replay Detection value
associated with the sender, and processes the message. associated with the sender, and processes the message.
10. Relay Agent Behavior 10. Relay Agent Behavior
DHCP Relay agents are typically configured with the addresses of one DHCP Relay agents are typically configured with the addresses of one
or more DHCP servers. A relay agent that implements this suboption or more DHCP servers. A relay agent that implements this suboption
requires an algorithm number for each server, as well as appropriate requires an algorithm number for each server, as well as appropriate
credentials (i.e. keys) to use. Relay implementations SHOULD support credentials (i.e. keys) to use. Relay implementations SHOULD support
configuration which indicates that all relayed messages should configuration which indicates that all relayed messages should
include the authentication suboption. Use of the authentication include the authentication suboption. Use of the authentication
suboption SHOULD be disabled by default. Relay agents MAY support suboption SHOULD be disabled by default. Relay agents MAY support
configuration that indicates that certain destination servers configuration that indicates that certain destination servers support
support the authentication suboption, while other servers do not. the authentication suboption, while other servers do not. Relay
Relay agents MAY support configuration of a single algorithm number agents MAY support configuration of a single algorithm number and key
and key to be used with all DHCP servers, or they MAY support to be used with all DHCP servers, or they MAY support configuration
configuration of different algorithms and keys for each server. of different algorithms and keys for each server.
10.1 Receiving Messages from Other Relay Agents 10.1 Receiving Messages from Other Relay Agents
There are network configurations in which one relay agent adds the There are network configurations in which one relay agent adds the
relay agent option, and then forwards the DHCP message to another relay agent option, and then forwards the DHCP message to another
relay agent. For example, a layer-2 switch might be directly relay agent. For example, a layer-2 switch might be directly
connected to a client, and it might forward messages to an connected to a client, and it might forward messages to an
aggregating router, which sets giaddr and then forwards the message aggregating router, which sets giaddr and then forwards the message
to a DHCP server. When a DHCP relay which implements the to a DHCP server. When a DHCP relay which implements the
Authentication suboption receives a message, it MAY use the Authentication suboption receives a message, it MAY use the
skipping to change at page 10, line 38 skipping to change at page 10, line 28
When the relay agent receives a broadcast packet from a client, it When the relay agent receives a broadcast packet from a client, it
determines which DHCP servers (or other relay agents) should receive determines which DHCP servers (or other relay agents) should receive
copies of the message. If the relay agent is configured to include copies of the message. If the relay agent is configured to include
the Authentication suboption, it determines which Algorithm and RDM the Authentication suboption, it determines which Algorithm and RDM
to use, and then it performs the steps in Section 8. to use, and then it performs the steps in Section 8.
10.3 Receiving Messages from Servers 10.3 Receiving Messages from Servers
When the relay agent receives a message, it determines from its When the relay agent receives a message, it determines from its
configuration whether it expects the message to contain a relay configuration whether it expects the message to contain a relay agent
agent information option and an Authentication suboption. The relay information option and an Authentication suboption. The relay agent
agent MAY be configured to drop response messages that do not MAY be configured to drop response messages that do not contain the
contain the Authentication suboption. The relay agent then follows Authentication suboption. The relay agent then follows the procedures
the procedures in Section 9. in Section 9.
11. DHCP Server Behavior 11. DHCP Server Behavior
DHCP servers may interact with multiple relay agents. Server DHCP servers may interact with multiple relay agents. Server
implementations MAY support configuration that associates the same implementations MAY support configuration that associates the same
algorithm and key with all relay agents. Servers MAY support algorithm and key with all relay agents. Servers MAY support
configuration which specifies the algorithm and key to use with each configuration which specifies the algorithm and key to use with each
relay agent individually. relay agent individually.
11.1 Receiving Messages from Relay Agents 11.1 Receiving Messages from Relay Agents
skipping to change at page 11, line 20 skipping to change at page 11, line 8
11.2 Sending Reply Messages to Relay Agents 11.2 Sending Reply Messages to Relay Agents
When the server has prepared a reply message, it uses the incoming When the server has prepared a reply message, it uses the incoming
request message and its configuration to determine whether it should request message and its configuration to determine whether it should
include a relay agent information option and an Authentication include a relay agent information option and an Authentication
suboption. If the server is configured to include the Authentication suboption. If the server is configured to include the Authentication
suboption, it determines which Algorithm and RDM to use, and then suboption, it determines which Algorithm and RDM to use, and then
performs the steps in Section 8. performs the steps in Section 8.
DISCUSSION: DISCUSSION:
This server behavior represents a slight variance from RFC This server behavior represents a slight variance from RFC 3046
3046[1], Section 2.2. The Authentication suboption is not echoed [1], Section 2.2. The Authentication suboption is not echoed back
back from the server to the relay: the server generates its own from the server to the relay: the server generates its own
suboption. suboption.
12. IANA Considerations 12. IANA Considerations
Section 4 defines a new suboption for the DHCP relay agent option, Section 4 defines a new suboption for the DHCP relay agent option,
called the Authentication Suboption. IANA is requested to allocate a called the Authentication Suboption. IANA is requested to allocate a
new suboption code from the relay agent option suboption number new suboption code from the relay agent option suboption number
space. space.
This specification introduces two new number-spaces for the This specification introduces two new number-spaces for the
Authentication suboption's 'Algorithm' and 'Replay Detection Method' Authentication suboption's 'Algorithm' and 'Replay Detection Method'
fields. These number spaces are to be created and maintained by IANA. fields. These number spaces are to be created and maintained by IANA.
The Algorithm identifier is a one-byte value. Algorithm value 0 is The Algorithm identifier is a one-byte value. Algorithm value 0 is
reserved. Algorithm value 1 is assigned to the HMAC-MD5 signature as reserved. Algorithm value 1 is assigned to the HMAC-MD5 keyed hash as
defined in Section 7.1. Additional algorithm values will be defined in Section 7.1. Additional algorithm values will be allocated
allocated and assigned through IETF consensus, as defined in RFC and assigned through IETF consensus, as defined in RFC 2434 [5].
2434[5].
The RDM identifier is a four-bit value. RDM value 0 is reserved. RDM The RDM identifier is a four-bit value. RDM value 0 is reserved. RDM
value 1 is assigned to the use of a monotonically increasing counter value 1 is assigned to the use of a monotonically increasing counter
value as defined in Section 5. Additional RDM values will be value as defined in Section 5. Additional RDM values will be
allocated and assigned through IETF consensus, as defined in RFC allocated and assigned through IETF consensus, as defined in RFC 2434
2434[5]. [5].
13. Security Considerations 13. Security Considerations
This specification describes a protocol to add source authentication This specification describes a protocol to add source authentication
and message integrity protection to the messages between DHCP relay and message integrity protection to the messages between DHCP relay
agents and DHCP servers. agents and DHCP servers.
The use of this protocol imposes a new computational burden on relay The use of this protocol imposes a new computational burden on relay
agents and servers, because they must perform cryptographic hash agents and servers, because they must perform cryptographic hash
calculations when they send and receive messages. This burden may calculations when they send and receive messages. This burden may add
add latency to DHCP message exchanges. Because relay agents are latency to DHCP message exchanges. Because relay agents are involved
involved when clients reboot, periods of very high reboot activity when clients reboot, periods of very high reboot activity will result
will result in the largest number of messages which have to be in the largest number of messages which have to be processed. During
signed and verified. During a cable MSO head-end reboot event, for a cable MSO head-end reboot event, for example, the time required for
example, the time required for all clients to be served may increase. all clients to be served may increase.
13.1 Protocol Vulnerabilities 13.1 The Key ID Field
The Authentication suboption contains a four-byte Key ID, following
the example of the DHCP Authentication RFC. Other authentication
protocols, like DNS TSIG [10], use a key name. A key name is more
flexible and potentially more human-readable than a key id. DHCP
servers may well be configured to use key names for DNS updates using
TSIG, so it might simplify DHCP server configuration if some of the
key-management for both protocols could be shared.
On the other hand, it is crucial to minimize the size expansion
caused by the introduction of the relay agent information option.
Named keys would require more physical space, and would entail more
complex suboption encoding and parsing implementations. These
considerations have led us to specify a fixed-length Key ID instead
of a variable-length key name.
13.2 Protocol Vulnerabilities
Because DHCP is a UDP protocol, messages between relays and servers Because DHCP is a UDP protocol, messages between relays and servers
may be delivered in a different order than the order in which they may be delivered in a different order than the order in which they
were generated. The replay-detection mechanism will cause receivers were generated. The replay-detection mechanism will cause receivers
to drop packets which are delivered 'late', leading to client to drop packets which are delivered 'late', leading to client
retries. The retry mechanisms which most clients implement should retries. The retry mechanisms which most clients implement should not
not cause this to be an enormous issue, but it will cause senders to cause this to be an enormous issue, but it will cause senders to do
do computational work which will be wasted if their messages are computational work which will be wasted if their messages are
re-ordered. re-ordered.
The DHC WG has developed two documents describing authentication of The DHC WG has developed two documents describing authentication of
DHCP relay agent options to accommodate the requirements of DHCP relay agent options to accommodate the requirements of different
different deployment scenarios: this document and Authentication of deployment scenarios: this document and Authentication of Relay Agent
Relay Agent Options Using IPSEC[11]. In deployments where IPsec is Options Using IPsec [11]. As we note in Section 11, the
Authentication suboption can be used without pairwise keys between
each relay and each DHCP server. In deployments where IPsec is
readily available and pairwise keys can be managed efficiently, the readily available and pairwise keys can be managed efficiently, the
use of IPsec as described in that document may be appropriate. If use of IPsec as described in that document may be appropriate. If
IPsec is not available or there are multiple relay agents for which IPsec is not available or there are multiple relay agents for which
multiple keys must be managed, the protocol described in this multiple keys must be managed, the protocol described in this
document may be appropriate. As is the case whenever two document may be appropriate. As is the case whenever two
alternatives are available, local network administration can choose alternatives are available, local network administration can choose
whichever is more appropriate. Because the relay agents and the DHCP whichever is more appropriate. Because the relay agents and the DHCP
server are all in the same administrative domain, the appropriate server are all in the same administrative domain, the appropriate
mechanism can be configured on all interoperating DHCP server mechanism can be configured on all interoperating DHCP server
elements. elements.
skipping to change at page 13, line 32 skipping to change at page 13, line 43
[8] Wimer, W., "Clarifications and Extensions for the Bootstrap [8] Wimer, W., "Clarifications and Extensions for the Bootstrap
Protocol", RFC 1542, October 1993. Protocol", RFC 1542, October 1993.
[9] Droms, R. and W. Arbaugh, "Authentication for DHCP Messages", [9] Droms, R. and W. Arbaugh, "Authentication for DHCP Messages",
RFC 3118, June 2001. RFC 3118, June 2001.
[10] Vixie, P., Gudmundsson, O., Eastlake, D. and B. Wellington, [10] Vixie, P., Gudmundsson, O., Eastlake, D. and B. Wellington,
"Secret Key Transaction Authentication for DNS (TSIG)", RFC "Secret Key Transaction Authentication for DNS (TSIG)", RFC
2845, May 2000. 2845, May 2000.
[11] Droms, R., "Authentication of Relay Agent Options Using IPSEC [11] Droms, R., "Authentication of Relay Agent Options Using IPsec
(draft-ietf-dhc-relay-agent-ipsec-*.txt)", February 2004. (draft-ietf-dhc-relay-agent-ipsec-*.txt)", February 2004.
Authors' Addresses Authors' Addresses
Mark Stapp Mark Stapp
Cisco Systems, Inc. Cisco Systems, Inc.
1414 Massachusetts Ave. 1414 Massachusetts Ave.
Boxborough, MA 01719 Boxborough, MA 01719
USA USA
skipping to change at page 14, line 4 skipping to change at page 14, line 15
Authors' Addresses Authors' Addresses
Mark Stapp Mark Stapp
Cisco Systems, Inc. Cisco Systems, Inc.
1414 Massachusetts Ave. 1414 Massachusetts Ave.
Boxborough, MA 01719 Boxborough, MA 01719
USA USA
Phone: 978.936.0000 Phone: 978.936.0000
EMail: mjs@cisco.com EMail: mjs@cisco.com
Ted Lemon Ted Lemon
Nominum, Inc. Nominum, Inc.
950 Charter St. 950 Charter St.
Redwood City, CA 94063 Redwood City, CA 94063
USA USA
EMail: Ted.Lemon@nominum.com EMail: Ted.Lemon@nominum.com
Full Copyright Statement Intellectual Property Statement
Copyright (C) The Internet Society (2004). All Rights Reserved. The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the IETF's procedures with respect to rights in IETF Documents can
be found in BCP 78 and BCP 79.
This document and translations of it may be copied and furnished to Copies of IPR disclosures made to the IETF Secretariat and any
others, and derivative works that comment on or otherwise explain it assurances of licenses to be made available, or the result of an
or assist in its implementation may be prepared, copied, published attempt made to obtain a general license or permission for the use of
and distributed, in whole or in part, without restriction of any such proprietary rights by implementers or users of this
kind, provided that the above copyright notice and this paragraph specification can be obtained from the IETF on-line IPR repository at
are included on all such copies and derivative works. However, this http://www.ietf.org/ipr.
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be The IETF invites any interested party to bring to its attention any
revoked by the Internet Society or its successors or assigns. copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
This document and the information contained herein is provided on an Disclaimer of Validity
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Acknowledgement This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Funding for the RFC editor function is currently provided by the Copyright Statement
Copyright (C) The Internet Society (2004). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society. Internet Society.
 End of changes. 

This html diff was produced by rfcdiff 1.23, available from http://www.levkowetz.com/ietf/tools/rfcdiff/