DHC Working Group S. Jiang
Internet-Draft Huawei Technologies Co., Ltd
Intended status: Standards Track L. Li
Expires: June 12, 2016 Y. Cui
Tsinghua University
T. Jinmei
Infoblox Inc.
T. Lemon
Nominum, Inc.
D. Zhang
December 10, 2015
Secure DHCPv6
draft-ietf-dhc-sedhcpv6-10
Abstract
The Dynamic Host Configuration Protocol for IPv6 (DHCPv6) enables
DHCPv6 servers to pass configuration parameters. It offers
configuration flexibility. If not being secured, DHCPv6 is
vulnerable to various attacks. This document analyzes the security
issues of DHCPv6 and specifies a secure DHCPv6 mechanism for the
authentication and encryption between DHCPv6 client and DHCPv6
server.
Status of This Memo
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This Internet-Draft will expire on June 12, 2016.
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements Language and Terminology . . . . . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Security Issues of DHCPv6 . . . . . . . . . . . . . . . . . . 4
5. secure DHCPv6 overview . . . . . . . . . . . . . . . . . . . 5
5.1. Solution Overview . . . . . . . . . . . . . . . . . . . . 5
5.2. New Components . . . . . . . . . . . . . . . . . . . . . 7
5.3. Support for Algorithm Agility . . . . . . . . . . . . . . 7
5.4. Imposed Additional Constraints . . . . . . . . . . . . . 8
5.5. Applicability . . . . . . . . . . . . . . . . . . . . . . 8
6. DHCPv6 Client Behavior . . . . . . . . . . . . . . . . . . . 9
7. DHCPv6 Server Behavior . . . . . . . . . . . . . . . . . . . 11
8. Relay Agent Behavior . . . . . . . . . . . . . . . . . . . . 13
9. Processing Rules . . . . . . . . . . . . . . . . . . . . . . 14
9.1. Timestamp Check . . . . . . . . . . . . . . . . . . . . . 14
10. Extensions for Secure DHCPv6 . . . . . . . . . . . . . . . . 15
10.1. New DHCPv6 Options . . . . . . . . . . . . . . . . . . . 15
10.1.1. Certificate Option . . . . . . . . . . . . . . . . . 15
10.1.2. Signature Option . . . . . . . . . . . . . . . . . . 16
10.1.3. Timestamp Option . . . . . . . . . . . . . . . . . . 17
10.1.4. Encrypted-message Option . . . . . . . . . . . . . . 18
10.2. New DHCPv6 Messages . . . . . . . . . . . . . . . . . . 19
10.2.1. Encrypted-Query Message . . . . . . . . . . . . . . 19
10.2.2. Encrypted-Response Message . . . . . . . . . . . . . 19
10.3. Status Codes . . . . . . . . . . . . . . . . . . . . . . 20
11. Security Considerations . . . . . . . . . . . . . . . . . . . 20
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21
13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 22
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 23
14.1. Normative References . . . . . . . . . . . . . . . . . . 23
14.2. Informative References . . . . . . . . . . . . . . . . . 24
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24
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1. Introduction
The Dynamic Host Configuration Protocol for IPv6 (DHCPv6, [RFC3315])
enables DHCPv6 servers to pass configuration parameters and offers
configuration flexibility. If not being secured, DHCPv6 is
vulnerable to various attacks.
This document analyzes the security issues of DHCPv6 in details and
provides the following mechanisms for improving the security of
DHCPv6 between client and server:
o the authentication of the DHCPv6 client and the DHCPv6 server to
defend against active attack, such as spoofing attack.
o the encryption between the DHCPv6 client and the DHCPv6 server in
order to protect the DHCPv6 from passive attack, such as pervasive
monitoring.
o the integrity check of DHCPv6 messages by the recipient of the
message based on signature.
o anti-replay protection based on timestamps.
Note: this secure mechanism in this document does not protect outer
options in Relay-Forward and Relay-Reply messages, either added by a
relay agent toward a server or added by a server toward a relay
agent, because they are only transported within operator networks and
considered less vulnerable. Communication between a server and a
relay agent, and communications between relay agents, may be secured
through the use of IPsec, as described in section 21.1 in [RFC3315].
The security mechanisms specified in this document achieves the
DHCPv6 authentication and encryption based on the sender's public key
certificate. We introduce two new DHCPv6 messages: Encrypted-Query
message and Encrypted-Response message and four new DHCPv6 options:
certificate option, signature option, timestamp option and encrypted-
message option for the DHCPv6 authentication and encryption. The
certificate option is used for the DHCPv6 authentication. It also
integrates signature option for the integrity check and timestamps
option for anti-replay protection. The Encryption-Query message,
Encryption-Response message, and encrypted-message option are used
for the DHCPv6 encryption.
2. Requirements Language and Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119] when they
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appear in ALL CAPS. When these words are not in ALL CAPS (such as
"should" or "Should"), they have their usual English meanings, and
are not to be interpreted as [RFC2119] key words.
3. Terminology
This section defines terminology specific to secure DHCPv6 used in
this document.
secure DHCPv6 client: A node that initiates the DHCPv6 request on a
link to obtain the DHCPv6 configuration parameters
from one or more DHCPv6 servers. The configuration
process is authenticated and encrypted using the
defined mechanisms in this document.
secure DHCPv6 server: A node that responds to requests from clients
using the authentication and encryption mechanism
defined in this document.
4. Security Issues of DHCPv6
DHCPv6 is a client/server protocol that provides managed
configuration of devices. It enables a DHCPv6 server to
automatically configure relevant network parameters on clients. The
basic DHCPv6 specification [RFC3315] defines security mechanisms, but
they have significant flaws and can be improved
The basic DHCPv6 specifications can optionally authenticate the
origin of message and validate the integrity of messages using an
authentication option with a symmetric key pair. [RFC3315] relies on
pre-established secret keys. For any kind of meaningful security,
each DHCPv6 client would need to be configured with its own secret
key; [RFC3315] provides no mechanism for doing this.
For the out of band approach, operators can set up a key database for
both servers and clients from which the client obtains a key before
running DHCPv6. Manual key distribution runs counter to the goal of
minimizing the configuration data needed at each host.
[RFC3315] provides an additional mechanism for preventing off-network
timing attacks using the Reconfigure message: the Reconfigure Key
authentication method. However, this method provides little message
integrity or source integrity check, and it protects only the
Reconfigure message. This key is transmitted in plaintext.
In addition, the current DHCPv6 messages are still transmitted in
clear text and the privacy information within the DHCPv6 message is
not protected from passive attack, such as pervasive monitoring. The
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IETF has expressed strong agreement that PM is an attack that needs
to be mitigated where possible in [RFC7258].
In comparison, the security mechanism defined in this document
provides the authentication and encryption mechanism based on the
public key certificates on the client or server. The DHCPv6
authentication can protect DHCPv6 from active attack, such as
spoofing attack. And the DHCPv6 encryption defends against passive
attack, such as pervasive monitoring attack.
5. secure DHCPv6 overview
5.1. Solution Overview
This solution provides the authentication and encryption mechanisms
based on the public certificates of the DHCPv6 client and server.
Before the standard DHCPv6 configuration process, the Information-
request and Reply messages are exchanged to select one authenticated
DHCPv6 server. The following DHCPv6 configuration process is
encrypted to avoid the privacy disclosure. We introduce two new
DHCPv6 messages: Encrypted-Query message, Encrypted-Response message
and four new DHCPv6 options: encrypted-message option, certificate
option, signature option, timestamp option. Based on the new defined
messages and options, the corresponding authentication and encryption
mechanisms are proposed.
The following figure illustrates the secure DHCPv6 procedure. The
DHCPv6 client first sends an Information-request message to the
standard multicast address to all DHCPv6 servers. The Information-
request message is used to request the servers for server
authentication information, without going through any address, prefix
or non-security option assignment process. The information-request
is sent without client's privacy information, such as client
identifier option to minimize information leak and increase client's
privacy. When receiving the Information-request message, the server
sends the Reply message that contains the server's certificate
option, signature option, timestamp option, and server identifier
option. Upon the receipt of the Reply message, the DHCPv6 client
verifies the server's identity according to the contained server
authentication information in Reply message. If there are multiple
authenticated DHCPv6 servers, the client selects one authenticated
DHCPv6 server for the following DHCPv6 configuration process. If
there are no authenticated DHCPv6 servers or existing servers failed
authentication, the client behavior is policy specific. Depending on
its policy, it can choose to connect repeat the server discovery
process after certain delay or attempt to connect to a different
network.
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After the server's authentication, the first DHCPv6 message sent from
client to server, such as Solicit message, contains the client's
certificate option, signature option and timestamp option for client
authentication. The DHCPv6 message sent from client to server is
encrypted with the server's public key and encapsulated into the
encrypted-message option. The DHCPv6 client sends the Encrypted-
Query message to server, which carries the server identifier option
and the encrypted-message option. When the DHCPv6 server receives
the Encrypted-Query message, it decrypts the message using its
private key. If the decrypted message contains the client's
certificate option, signature option, timestamp option, the DHCPv6
server verifies the client's identity according to the contained
client authentication information. After the client's
authentication, the server sends the Encrypted-Response message to
the client, which contains the encrypted-message option. The
encrypted-message option contains the encrypted DHCPv6 message sent
from server to client, which is encrypted using the client's public
key. The message that fails client authentication, MUST be dropped.
And the server sends the corresponding error status code to client.
+-------------+ +-------------+
|DHCPv6 Client| |DHCPv6 Server|
+-------------+ +-------------+
| Information-request |
|----------------------------------------->|
| Option Request option |
| |
| Reply |
|<-----------------------------------------|
| certificate option |
| signature option |
| timestamp option |
| server identifier option |
| |
| Encryption-Query |
|----------------------------------------->|
| encrypted-message option |
| server identifier option |
| |
| Encryption-Response |
|<-----------------------------------------|
| encrypted-message option |
| |
Secure DHCPv6 Procedure
It is worth noticing that the signature on a Secure DHCPv6 message
can be expected to significantly increase the size of the message.
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One example is normal DHCPv6 message length plus a 1 KB for a X.509
certificate and signature and 256 Byte for a signature. IPv6
fragments [RFC2460] are highly possible. In practise, the total
length would be various in a large range. Hence, deployment of
Secure DHCPv6 should also consider the issues of IP fragment, PMTU,
etc. Also, if there are firewalls between secure DHCPv6 clients and
secure DHCPv6 servers, it is RECOMMENDED that the firewalls are
configured to pass ICMP Packet Too Big messages [RFC4443].
5.2. New Components
The new components of the solution specified in this document are as
follows:
o Servers and clients that use certificates first generate a public/
private key pair and then obtain a public key certificate from a
Certificate Authority that signs the public key. One option is
defined to carry the certificate.
o A signature generated using the private key which is used by the
receiver to verify the integrity of the DHCPv6 messages and then
the authentication of the client/server. Another option is
defined to carry the signature.
o A timestamp that can be used to detect replayed packet. The
secure DHCPv6 client/server need to meet some accuracy
requirements and be synced to global time, while the timestamp
checking mechanism allows a configurable time value for clock
drift. The real time provision is out of scope of this document.
Another option is defined to carry the current time of the client/
server.
o An encrypted-message option that contains the encrypted DHCPv6
message.
o An Encrypted-Query message that sent from client to server. The
Encrypted-Query message contains the encrypted-message option and
server identifier option.
o An Encrypted-Response message that sent from server to client.
The Encrypted-Response message contains the encrypted-message
option.
5.3. Support for Algorithm Agility
Hash functions are used to provide message integrity checks. In
order to provide a means of addressing problems that may emerge in
the future with existing hash algorithms, as recommended in
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[RFC4270], this document provides a mechanism for negotiating the use
of more secure hashes in the future.
In addition to hash algorithm agility, this document also provides a
mechanism for signature algorithm agility.
The support for algorithm agility in this document is mainly a
unilateral notification mechanism from sender to recipient. A
recipient MAY support various algorithms simultaneously among
different senders, and the different senders in the same
administrative domain may be allowed to use various algorithms
simultaneously. It is NOT RECOMMENDED that the same sender and
recipient use various algorithms in a single communication session.
If the recipient does not support the algorithm used by the sender,
it cannot authenticate the message. In the client-to-server case,
the server SHOULD reply with an AlgorithmNotSupported status code
(defined in Section 10.3). Upon receiving this status code, the
client MAY resend the message protected with the mandatory algorithm
(defined in Section 10.1.2).
5.4. Imposed Additional Constraints
The client/server that supports the identity verification MAY impose
additional constraints for the verification. For example, it may
impose limits on minimum and maximum key lengths.
Minbits The minimum acceptable key length for public keys. An upper
limit MAY also be set for the amount of computation needed when
verifying packets that use these security associations. The
appropriate lengths SHOULD be set according to the signature
algorithm and also following prudent cryptographic practice. For
example, minimum length 1024 and upper limit 2048 may be used for
RSA [RSA].
5.5. Applicability
Secure DHCPv6 is applicable in environments where physical security
on the link is not assured and attacks on DHCPv6 are a concern, such
as enterprise network. In enterprise network, the security policy is
strict and the clients are stable terminals. The PKI model is used
for the secure DHCPv6 deployment. The deployment of PKI is out of
the scope of this document. The server is always considered to have
connectivity to authorized CA and verify the clients' certificates.
The client performs the server authentication locally. The trusted
servers' certificates or trusted CAs' certificates, which form a
certification path [RFC5280], is deployed in the client to achieve
the server authentication. The DHCPv6 client obtains the trusted
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certificates through the pre-configuration method or out of band,
such as QR code. After the mutual authentication, the DHCPv6 message
is encrypted with the recipient's public key, which is contained in
the certificate.
6. DHCPv6 Client Behavior
For the security DHCPv6 client, it must have a public certificate.
The client may be pre-configured with a public key certificate, which
is signed by a CA trusted by the server, and its corresponding
private key.
The DHCPv6 client multicasts the Information-request message to the
DHCPv6 servers. The Information-request message MUST NOT include any
option which may reveal the private information of the client, such
as the client identifier option. The information-request message is
used by the DHCPv6 client to request the server's identity
verification information without having addresses, prefixes or any
non-security options assigned to it. The Option Request option in
the Information-request message MUST contain the option code of
certificate option, signature option, timestamp option, and server
identifier option.
When receiving the Reply messages from DHCPv6 servers, a secure
DHCPv6 client SHOULD discard any DHCPv6 messages that meet any of the
following conditions:
o the signature option is missing,
o multiple signature options are present,
o the certificate option is missing.
And then the client SHOULD first check the support of the hash and
signature algorithms that the server used. If the check fails, the
Reply message SHOULD be dropped. If both hash and signature
algorithms are supported, the client then checks the authority of
this server. The client SHOULD also use the same algorithms in the
return messages.
The client SHOULD validate the certificate according to the rules
defined in [RFC5280]. An implementation may create a local trust
certificate record for verified certificates in order to avoid
repeated verification procedure in the future. A certificate that
finds a match in the local trust certificate list is treated as
verified. At this point, the client has either recognized the
authentication of the server, or decided to drop the message.
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The client MUST now authenticate the server by verifying the
signature and checking timestamp (see details in Section 9.1), if
there is a timestamp option. The order of two procedures is left as
an implementation decision. It is RECOMMENDED to check timestamp
first, because signature verification is much more computationally
expensive.
The signature field verification MUST show that the signature has
been calculated as specified in Section 10.1.2. Only the messages
that get through both the signature verification and timestamp check
(if there is a timestamp option) are accepted. Reply message that
does not pass the above tests MUST be discarded.
If there are multiple authenticated DHCPv6 servers, the client
selects one DHCPv6 server for the following network parameters
configuration. If there are no authenticated DHCPv6 servers or
existing servers failed authentication, the client behavior is policy
specific. Depending on its policy, it can choose to connect using
plain, unencrypted DHCPv6, repeat the server discovery process after
certain delay or attempt to connect to a different network. The
client MUST NOT conduct the server discovery process immediately to
avoid the packet storm.
Once the server has been authenticated, the DHCPv6 client sends the
Encrypted-Query message to the DHCPv6 server. The Encrypted-Query
message is constructed with the encrypted-message option, which MUST
be constructed as explained in Section 10.1.4, and server identifier
option. The encrypted-message option contains the DHCPv6 message
that is encrypted using the selected server's public key. The server
identifier option is externally visible to avoid extra of decryption
cost by those unselected servers.
The information for client authentication is contained in the
Solicit/Information-request message, which is encrypted and then
encapsulated into the Encrypted-Query message to avoid client privacy
disclosure. The Solicit/Information-request message MUST contain the
certificate option, which MUST be constructed as explained in
Section 10.1.1. In addition, one and only one signature option MUST
be contained, which MUST be constructed as explained in
Section 10.1.2. It protects the message header and all DHCPv6
options except for the Authentication Option. One and only one
Timestamp option, which MUST be constructed as explained in
Section 10.1.3. The Timestamp field SHOULD be set to the current
time, according to sender's real time clock.
For the received Encrypted-Response message, the client extracts the
encrypted-message option and decrypts it using its private key to
obtain the original DHCPv6 message. Then it handles the message as
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per [RFC3315]. If the client fails to get the proper parameters from
the chosen server, it sends the Encrypted-Query message to another
authenticated server for parameters configuration until the client
obtains the proper parameters.
When the client receives a Reply message with an error status code,
the error status code indicates the failure reason on the server
side. According to the received status code, the client MAY take
follow-up action:
o Upon receiving an AlgorithmNotSupported error status code, the
client SHOULD resend the message protected with one of the
mandatory algorithms.
o Upon receiving an AuthenticationFail error status code, the client
is not able to build up the secure communication with the
recipient. However, there may be other DHCPv6 servers available
that successfully complete authentication. The client MAY use the
AuthenticationFail as a hint and switch to other public key
certificate if it has another one; but otherwise treat the message
containing the status code as if it had not been received. But it
SHOULD NOT retry with the same certificate. However, if the
client decides to retransmit using the same certificate after
receiving AuthenticationFail, it MUST NOT retransmit immediately
and MUST follow normal retransmission routines defined in
[RFC3315].
o Upon receiving a TimestampFail error status code, the client MAY
resend the message with an adjusted timestamp according to the
returned clock from the DHCPv6 server. The client SHOULD NOT
change its own clock, but only compute an offset for the
communication session.
o Upon receiving a SignatureFail error status code, the client MAY
resend the message following normal retransmission routines
defined in [RFC3315].
7. DHCPv6 Server Behavior
For the secure DHCPv6 server, it also MUST have a public certificate.
The server may be pre-configured a public key certificate, which is
signed by a CA trusted by the server, and its corresponding private
key.
When the DHCPv6 server receives the Information-request message and
the contained Option Request option informs the request for the
server authentication information, it replies the Reply message to
the client. The reply message MUST contain the requested certificate
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option, which MUST be constructed as explained in Section 10.1.1. In
addition, the Reply message MUST contain one and only one Signature
option, which MUST be constructed as explained in Section 10.1.2. It
protects the message header and all DHCPv6 options except for the
Authentication Option. Besides, the Reply message SHOULD contain one
and only one Timestamp option, which MUST be constructed as explained
in Section 10.1.3. The Timestamp field SHOULD be set to the current
time, according to server's real time clock.
Upon the receipt of Encrypted-Query message, the server checks the
server identifier option. It decrypts the encrypted-message option
using its private key if it is the target server. The DHCPv6 server
drops the message that is not for it, thus not paying cost to decrypt
the message.
If the decrypted message is Solicit/Information-request message, the
secure DHCPv6 server SHOULD discard the received message that meet
any of the following conditions:
o the signature option is missing,
o multiple signature options are present,
o the certificate option is missing.
In such failure, the server SHOULD reply an UnspecFail (value 1,
[RFC3315]) error status code.
The server SHOULD first check the support of the hash and signature
algorithms that the client used. If the check fails, the server
SHOULD reply with an AlgorithmNotSupported error status code, defined
in Section 10.3, back to the client. If both hash and signature
algorithms are supported, the server then checks the authority of
this client.
If a certificate option is provided, the server SHOULD validate the
certificate according to the rules defined in [RFC5280]. An
implementation may create a local trust certificate record for
verified certificates in order to avoid repeated verification
procedure in the future. A certificate that finds a match in the
local trust certificate list is treated as verified.
The message that fails certificate validation, MUST be dropped. In
such failure, the DHCPv6 server SHOULD reply an AuthenticationFail
error status code, defined in Section 10.3, back to the client. At
this point, the server has either recognized the authentication of
the client, or decided to drop the message.
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If the server does not send the timestamp option, the client ignores
the timestamp check and verifies the signature. If there is a
timestamp option, the server MUST now authenticate the client by
verifying the signature and checking timestamp (see details in
Section 9.1). The order of two procedures is left as an
implementation decision. It is RECOMMENDED to check timestamp first,
because signature verification is much more computationally
expensive. Depending on server's local policy, the message without a
Timestamp option MAY be acceptable or rejected. If the server
rejects such a message, a TimestampFail error status code, defined in
Section 10.3, should be sent back to the client. The reply message
that carries the TimestampFail error status code SHOULD carry a
timestamp option, which indicates the server's clock for the client
to use.
The signature field verification MUST show that the signature has
been calculated as specified in Section 10.1.2. Only the clients
that get through both the signature verification and timestamp check
(if there is a Timestamp option) are accepted as authenticated
clients and continue to be handled their message as defined in
[RFC3315]. Clients that do not pass the above tests MUST be treated
as unauthenticated clients. The DHCPv6 server SHOULD reply a
SignatureFail error status code, defined in Section 10.3, for the
signature verification failure; or a TimestampFail error status code,
defined in Section 10.3, for the timestamp check failure, back to the
client.
Once the client has been authenticated, the DHCPv6 server sends the
Encrypted-response message to the DHCPv6 client. The Encrypted-
response message contains the encrypted-message option, which MUST be
constructed as explained in Section 10.1.4. The encrypted-message
option contains the encrypted DHCPv6 message that is encrypted using
the authenticated client's public key.
8. Relay Agent Behavior
When a DHCPv6 relay agent receives an Encrypted-query or Encrypted-
response message, it may not recognize this message. The unknown
messages MUST be forwarded as describes in [RFC7283].
When a DHCPv6 relay agent recognizes the Encrypted-query and
Encrypted-response messages, it forwards the message according to
section 20 of [RFC3315]. There is nothing more the relay agents have
to do, it neither needs to verify the messages from client or server,
nor add any secure DHCPv6 options. Actually, by definition in this
document, relay agents SHOULD NOT add any secure DHCPv6 options.
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Relay-forward and Relay-reply messages MUST NOT contain any
additional certificate option or signature Option or timestamp
Option, aside from those present in the innermost encapsulated
messages from the client or server.
9. Processing Rules
9.1. Timestamp Check
In order to check the Timestamp option, defined in Section 10.1.3,
recipients SHOULD be configured with an allowed timestamp Delta
value, a "fuzz factor" for comparisons, and an allowed clock drift
parameter. The recommended default value for the allowed Delta is
300 seconds (5 minutes); for fuzz factor 1 second; and for clock
drift, 0.01 second.
Note: the Timestamp mechanism is based on the assumption that
communication peers have roughly synchronized clocks, with certain
allowed clock drift. So, accurate clock is not necessary. If one
has a clock too far from the current time, the timestamp mechanism
would not work.
To facilitate timestamp checking, each recipient SHOULD store the
following information for each sender, from which at least one
accepted secure DHCPv6 message is successfully verified (for both
timestamp check and signature verification):
o The receive time of the last received and accepted DHCPv6 message.
This is called RDlast.
o The timestamp in the last received and accepted DHCPv6 message.
This is called TSlast.
A verified (for both timestamp check and signature verification)
secure DHCPv6 message initiates the update of the above variables in
the recipient's record.
Recipients MUST check the Timestamp field as follows:
o When a message is received from a new peer (i.e., one that is not
stored in the cache), the received timestamp, TSnew, is checked,
and the message is accepted if the timestamp is recent enough to
the reception time of the packet, RDnew:
-Delta < (RDnew - TSnew) < +Delta
After the signature verification also succeeds, the RDnew and
TSnew values SHOULD be stored in the cache as RDlast and TSlast.
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o When a message is received from a known peer (i.e., one that
already has an entry in the cache), the timestamp is checked
against the previously received Secure DHCPv6 message:
TSnew + fuzz > TSlast + (RDnew - RDlast) x (1 - drift) - fuzz
If this inequality does not hold or RDnew < RDlast, the recipient
SHOULD silently discard the message. If, on the other hand, the
inequality holds, the recipient SHOULD process the message.
Moreover, if the above inequality holds and TSnew > TSlast, the
recipient SHOULD update RDlast and TSlast after the signature
verification also successes. Otherwise, the recipient MUST NOT
update RDlast or TSlast.
An implementation MAY use some mechanism such as a timestamp cache to
strengthen resistance to replay attacks. When there is a very large
number of nodes on the same link, or when a cache filling attack is
in progress, it is possible that the cache holding the most recent
timestamp per sender will become full. In this case, the node MUST
remove some entries from the cache or refuse some new requested
entries. The specific policy as to which entries are preferred over
others is left as an implementation decision.
An implementation MAY statefully record the latest timestamps from
senders. In such implementation, the timestamps MUST be strictly
monotonously increasing. This is reasonable given that DHCPv6
messages are rarely misordered.
10. Extensions for Secure DHCPv6
This section describes the extensions to DHCPv6. Five new DHCPv6
options, two new DHCPv6 messages and five status codes are defined.
10.1. New DHCPv6 Options
10.1.1. Certificate Option
The certificate option carries the public key certificate of the
client/server. The format of the certificate option is described as
follows:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_CERTIFICATE | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. Certificate (variable length) .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
option-code OPTION_CERTIFICATE (TBA1).
option-len Length of certificate in octets.
Certificate A variable-length field containing certificate. The
encoding of certificate and certificate data MUST
be in format as defined in Section 3.6, [RFC7296].
The support of X.509 certificate - Signature (4)
is mandatory.
10.1.2. Signature Option
The signature option allows a signature that is signed by the private
key to be attached to a DHCPv6 message. The signature option could
be any place within the DHCPv6 message while it is logically created
after the entire DHCPv6 header and options, except for the
Authentication Option. It protects the entire DHCPv6 header and
options, including itself, except for the Authentication Option. The
format of the Signature option is described as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_SIGNATURE | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| HA-id | SA-id | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| |
. Signature (variable length) .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
option-code OPTION_SIGNATURE (TBA2).
option-len 2 + Length of Signature field in octets.
HA-id Hash Algorithm id. The hash algorithm is used for
computing the signature result. This design is
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adopted in order to provide hash algorithm agility.
The value is from the Hash Algorithm for Secure
DHCPv6 registry in IANA. The support of SHA-256 is
mandatory. A registry of the initial assigned values
is defined in Section 8.
SA-id Signature Algorithm id. The signature algorithm is
used for computing the signature result. This
design is adopted in order to provide signature
algorithm agility. The value is from the Signature
Algorithm for Secure DHCPv6 registry in IANA. The
support of RSASSA-PKCS1-v1_5 is mandatory. A
registry of the initial assigned values is defined
in Section 8.
Signature A variable-length field containing a digital
signature. The signature value is computed with
the hash algorithm and the signature algorithm,
as described in HA-id and SA-id. The signature
constructed by using the sender's private key
protects the following sequence of octets:
1. The DHCPv6 message header.
2. All DHCPv6 options including the Signature
option (fill the signature field with zeroes)
except for the Authentication Option.
The signature field MUST be padded, with all 0, to
the next octet boundary if its size is not a
multiple of 8 bits. The padding length depends on
the signature algorithm, which is indicated in the
SA-id field.
Note: if both signature and authentication option are present,
signature option does not protect the Authentication Option. It
allows the Authentication Option be created after signature has been
calculated and filled with the valid signature. It is because both
options need to apply hash algorithm to whole message, so there must
be a clear order and there could be only one last-created option.
changing auth option, the authors chose not include authentication
option in the signature.
10.1.3. Timestamp Option
The Timestamp option carries the current time on the sender. It adds
the anti-replay protection to the DHCPv6 messages. It is optional.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_TIMESTAMP | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Timestamp (64-bit) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
option-code OPTION_TIMESTAMP (TBA3).
option-len 8, in octets.
Timestamp The current time of day (SeND-format timestamp
in UTC (Coordinated Universal Time). It can reduce
the danger of replay attacks.
10.1.4. Encrypted-message Option
The encrypted-message option carries the encrypted DHCPv6 message
with the recipient's public key.
The format of the encrypted-message option is:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| option-code | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. encrypted DHCPv6 message .
. (variable) .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: encrypted-message Option Format
option-code OPTION_ENCRYPTED_MSG (TBA4).
option-len Length of the encrypted DHCPv6 message.
encrypted DHCPv6 message A variable length field containing the
encrypted DHCPv6 message sent by the client or the server. In
Encrypted-Query message, it contains encrypted DHCPv6 message sent
by a client. In Encrypted-response message, it contains encrypted
DHCPv6 message sent by a server.
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10.2. New DHCPv6 Messages
10.2.1. Encrypted-Query Message
The Encrypted-Query message is sent from DHCPv6 client to DHCPv6
server, which contains the server identifier option and encrypted-
message option.
The format of the Encrypted-Query message is:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| msg-type | transaction-id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. DUID .
| (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. encrypted-message option .
. (variable) .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: The format of Encrypted-Query Message
msg-type ENCRYPTED-QUERY (TBA5)
transaction-id The transaction ID for this message exchange.
DUID The DUID for the server.
encrypted-message option The encrypted DHCPv6 message.
10.2.2. Encrypted-Response Message
The Encrypted-Response message is sent from DHCPv6 server to DHCPv6
client, which contains the encrypted-message option.
The format of the Encrypted-Response message is:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| msg-type | transaction-id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. encrypted-message option .
. (variable) .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: The format of Encrypted-Response Message
msg-type ENCRYPTED-RESPONSE (TBA6).
transaction-id The transaction ID for this message exchange.
encrypted-message option The encrypted DHCPv6 message.
10.3. Status Codes
The following new status codes, see Section 5.4 of [RFC3315] are
defined.
o AlgorithmNotSupported (TBD7): indicates that the DHCPv6 server
does not support algorithms that sender used.
o AuthenticationFail (TBD8): indicates that the DHCPv6 client fails
authentication check.
o TimestampFail (TBD9): indicates the message from DHCPv6 client
fails the timestamp check.
o SignatureFail (TBD10): indicates the message from DHCPv6 client
fails the signature check.
11. Security Considerations
This document provides the authentication and encryption mechanisms
for DHCPv6.
[RFC6273] has analyzed possible threats to the hash algorithms used
in SEND. Since the Secure DHCPv6 defined in this document uses the
same hash algorithms in similar way to SEND, analysis results could
be applied as well: current attacks on hash functions do not
constitute any practical threat to the digital signatures used in the
signature algorithm in the Secure DHCPv6.
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A server, whose local policy accepts messages without a Timestamp
option, may have to face the risk of replay attacks.
A window of vulnerability for replay attacks exists until the
timestamp expires. Secure DHCPv6 nodes are protected against replay
attacks as long as they cache the state created by the message
containing the timestamp. The cached state allows the node to
protect itself against replayed messages. However, once the node
flushes the state for whatever reason, an attacker can re-create the
state by replaying an old message while the timestamp is still valid.
In addition, the effectiveness of timestamps is largely dependent
upon the accuracy of synchronization between communicating nodes.
However, how the two communicating nodes can be synchronized is out
of scope of this work.
Attacks against time synchronization protocols such as NTP [RFC5905]
may cause Secure DHCPv6 nodes to have an incorrect timestamp value.
This can be used to launch replay attacks, even outside the normal
window of vulnerability. To protect against these attacks, it is
recommended that Secure DHCPv6 nodes keep independently maintained
clocks or apply suitable security measures for the time
synchronization protocols.
12. IANA Considerations
This document defines five new DHCPv6 [RFC3315] options. The IANA is
requested to assign values for these five options from the DHCPv6
Option Codes table of the DHCPv6 Parameters registry maintained in
http://www.iana.org/assignments/dhcpv6-parameters. The five options
are:
The Certificate Option (TBA1), described in Section 10.1.1.
The Signature Option (TBA2), described in Section 10.1.2.
The Timestamp Option (TBA3),described in Section 10.1.3.
The Encrypted-message Option (TBA4), described in Section 10.1.4.
The IANA is also requested to assign value for these two messages
from the DHCPv6 Message Types table of the DHCPv6 Parameters registry
maintained in http://www.iana.org/assignments/dhcpv6-parameters. The
two messages are:
The Encrypted-Query Message (TBA5), described in Section 10.2.1.
The Encrypted-Response Message (TBA6), described in
Section 10.2.2.
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The IANA is also requested to add two new registry tables to the
DHCPv6 Parameters registry maintained in
http://www.iana.org/assignments/dhcpv6-parameters. The two tables
are the Hash Algorithm for Secure DHCPv6 table and the Signature
Algorithm for Secure DHCPv6 table.
Initial values for these registries are given below. Future
assignments are to be made through Standards Action [RFC5226].
Assignments for each registry consist of a name, a value and a RFC
number where the registry is defined.
Hash Algorithm for Secure DHCPv6. The values in this table are 8-bit
unsigned integers. The following initial values are assigned for
Hash Algorithm for Secure DHCPv6 in this document:
Name | Value | RFCs
-------------------+---------+--------------
SHA-256 | 0x01 | this document
SHA-512 | 0x02 | this document
Signature Algorithm for Secure DHCPv6. The values in this table are
8-bit unsigned integers. The following initial values are assigned
for Signature Algorithm for Secure DHCPv6 in this document:
Name | Value | RFCs
-------------------+---------+--------------
RSASSA-PKCS1-v1_5 | 0x01 | this document
IANA is requested to assign the following new DHCPv6 Status Codes,
defined in Section 10.3, in the DHCPv6 Parameters registry maintained
in http://www.iana.org/assignments/dhcpv6-parameters:
Code | Name | Reference
---------+-----------------------+--------------
TBD7 | AlgorithmNotSupported | this document
TBD8 | AuthenticationFail | this document
TBD9 | TimestampFail | this document
TBD10 | SignatureFail | this document
13. Acknowledgements
The authors would like to thank Tomek Mrugalski, Bernie Volz, Randy
Bush, Yiu Lee, Jianping Wu, Sean Shen, Ralph Droms, Jari Arkko, Sean
Turner, Stephen Farrell, Christian Huitema, Stephen Kent, Thomas
Huth, David Schumacher, Francis Dupont, Gang Chen, Suresh Krishnan,
Fred Templin, Robert Elz, Nico Williams, Erik Kline, Alan DeKok,
Bernard Aboba, Sam Hartman, Qi Sun, Zilong Liu, and other members of
the IETF DHC working group for their valuable comments.
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This document was produced using the xml2rfc tool [RFC2629].
14. References
14.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
December 1998, <http://www.rfc-editor.org/info/rfc2460>.
[RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins,
C., and M. Carney, "Dynamic Host Configuration Protocol
for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July
2003, <http://www.rfc-editor.org/info/rfc3315>.
[RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet
Control Message Protocol (ICMPv6) for the Internet
Protocol Version 6 (IPv6) Specification", RFC 4443,
DOI 10.17487/RFC4443, March 2006,
<http://www.rfc-editor.org/info/rfc4443>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<http://www.rfc-editor.org/info/rfc5280>.
[RFC5905] Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch,
"Network Time Protocol Version 4: Protocol and Algorithms
Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010,
<http://www.rfc-editor.org/info/rfc5905>.
[RFC7283] Cui, Y., Sun, Q., and T. Lemon, "Handling Unknown DHCPv6
Messages", RFC 7283, DOI 10.17487/RFC7283, July 2014,
<http://www.rfc-editor.org/info/rfc7283>.
[RFC7296] Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.
Kivinen, "Internet Key Exchange Protocol Version 2
(IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October
2014, <http://www.rfc-editor.org/info/rfc7296>.
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14.2. Informative References
[RFC2629] Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629,
DOI 10.17487/RFC2629, June 1999,
<http://www.rfc-editor.org/info/rfc2629>.
[RFC4270] Hoffman, P. and B. Schneier, "Attacks on Cryptographic
Hashes in Internet Protocols", RFC 4270,
DOI 10.17487/RFC4270, November 2005,
<http://www.rfc-editor.org/info/rfc4270>.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
DOI 10.17487/RFC5226, May 2008,
<http://www.rfc-editor.org/info/rfc5226>.
[RFC6273] Kukec, A., Krishnan, S., and S. Jiang, "The Secure
Neighbor Discovery (SEND) Hash Threat Analysis", RFC 6273,
DOI 10.17487/RFC6273, June 2011,
<http://www.rfc-editor.org/info/rfc6273>.
[RFC7258] Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an
Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May
2014, <http://www.rfc-editor.org/info/rfc7258>.
[RSA] RSA Laboratories, "RSA Encryption Standard, Version 2.1,
PKCS 1", November 2002.
Authors' Addresses
Sheng Jiang
Huawei Technologies Co., Ltd
Q14, Huawei Campus, No.156 Beiqing Road
Hai-Dian District, Beijing, 100095
CN
Email: jiangsheng@huawei.com
Lishan Li
Tsinghua University
Beijing 100084
P.R.China
Phone: +86-15201441862
Email: lilishan9248@126.com
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Yong Cui
Tsinghua University
Beijing 100084
P.R.China
Phone: +86-10-6260-3059
Email: yong@csnet1.cs.tsinghua.edu.cn
Tatuya Jinmei
Infoblox Inc.
3111 Coronado Drive
Santa Clara, CA
US
Email: jinmei@wide.ad.jp
Ted Lemon
Nominum, Inc.
2000 Seaport Blvd
Redwood City, CA 94063
USA
Phone: +1-650-381-6000
Email: Ted.Lemon@nominum.com
Dacheng Zhang
Beijing
CN
Email: dacheng.zhang@gmail.com
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