DHC Working Group S. Jiang
Internet-Draft Huawei Technologies Co., Ltd
Intended status: Standards Track L. Li
Expires: September 9, 2016 Y. Cui
Tsinghua University
T. Jinmei
Infoblox Inc.
T. Lemon
Nominum, Inc.
D. Zhang
March 8, 2016
Secure DHCPv6
draft-ietf-dhc-sedhcpv6-11
Abstract
The Dynamic Host Configuration Protocol for IPv6 (DHCPv6) enables
DHCPv6 servers to pass configuration parameters. It offers
configuration flexibility. If not secured, DHCPv6 is vulnerable to
various attacks. This document analyzes the security issues of
DHCPv6 and specifies the secure DHCPv6 mechanism for authentication
and encryption of messages between a DHCPv6 client and a DHCPv6
server.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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Internet-Drafts are draft documents valid for a maximum of six months
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time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 9, 2016.
Copyright Notice
Copyright (c) 2016 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
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language and Terminology . . . . . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Security Issues of DHCPv6 . . . . . . . . . . . . . . . . . . 4
5. Secure DHCPv6 Overview . . . . . . . . . . . . . . . . . . . 5
5.1. Solution Overview . . . . . . . . . . . . . . . . . . . . 5
5.2. New Components . . . . . . . . . . . . . . . . . . . . . 6
5.3. Support for Algorithm Agility . . . . . . . . . . . . . . 7
5.4. Applicability . . . . . . . . . . . . . . . . . . . . . . 7
6. DHCPv6 Client Behavior . . . . . . . . . . . . . . . . . . . 8
7. DHCPv6 Server Behavior . . . . . . . . . . . . . . . . . . . 11
8. Relay Agent Behavior . . . . . . . . . . . . . . . . . . . . 12
9. Processing Rules . . . . . . . . . . . . . . . . . . . . . . 12
9.1. Timestamp Check . . . . . . . . . . . . . . . . . . . . . 12
10. Extensions for Secure DHCPv6 . . . . . . . . . . . . . . . . 14
10.1. New DHCPv6 Options . . . . . . . . . . . . . . . . . . . 14
10.1.1. Certificate Option . . . . . . . . . . . . . . . . . 14
10.1.2. Timestamp Option . . . . . . . . . . . . . . . . . . 15
10.1.3. Encrypted-message Option . . . . . . . . . . . . . . 16
10.2. New DHCPv6 Messages . . . . . . . . . . . . . . . . . . 17
10.3. Status Codes . . . . . . . . . . . . . . . . . . . . . . 17
11. Security Considerations . . . . . . . . . . . . . . . . . . . 18
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 19
14. Change log [RFC Editor: Please remove] . . . . . . . . . . . 20
15. Open Issues [RFC Editor: Please remove] . . . . . . . . . . . 21
16. References . . . . . . . . . . . . . . . . . . . . . . . . . 22
16.1. Normative References . . . . . . . . . . . . . . . . . . 22
16.2. Informative References . . . . . . . . . . . . . . . . . 23
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23
1. Introduction
The Dynamic Host Configuration Protocol for IPv6 (DHCPv6, [RFC3315])
enables DHCPv6 servers to pass configuration parameters and offers
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configuration flexibility. If not being secured, DHCPv6 is
vulnerable to various attacks.
This document analyzes the security issues of DHCPv6 and provides the
following mechanisms for improving the security of DHCPv6 between the
DHCPv6 client and the DHCPv6 server:
o the authentication of the DHCPv6 client and the DHCPv6 server to
defend against active attacks, such as spoofing attack.
o the encryption between the DHCPv6 client and the DHCPv6 server in
order to protect the DHCPv6 from passive attacks, such as
pervasive monitoring.
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. 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 mechanism specified in this document achieves DHCPv6
authentication and encryption based on the sender's certificate. We
introduce two new DHCPv6 messages: Encrypted-Query message and
Encrypted-Response message and three new DHCPv6 options: Certificate
option, Timestamp option and Encrypted-message option for DHCPv6
authentication and encryption. The Certificate option is used for
DHCPv6 authentication. The Encryption-Query message, Encryption-
Response message and Encrypted-message option are used for DHCPv6
encryption. The timestamp option is used to defend against replay
attack.
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
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
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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 some flaws and can be improved.
The basic DHCPv6 specifications can optionally authenticate the
origin of messages 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 protects only the
Reconfigure message. The key is transmitted in plaintext to the
client in earlier exchanges and so this method is vulnerable to
active attacks.
In addition, the current DHCPv6 messages are still transmitted in
cleartext and the privacy information within the DHCPv6 message is
not protected from passive attack, such as pervasive monitoring. The
IETF has expressed strong agreement that pervasive monitoring is an
attack that needs to be mitigated where possible in [RFC7258].
In comparison, the security mechanisms defined in this document
provides for authentication and encryption based on the public key
certificates of the client and server. The DHCPv6 authentication can
protect DHCPv6 from active attacks, such as spoofing attack. And the
DHCPv6 encryption defends against passive attacks, such as pervasive
monitoring attack.
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5. Secure DHCPv6 Overview
5.1. Solution Overview
This solution provides authentication and encryption mechanisms based
on the 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. After the mutual authentication between the DHCPv6 client
and server, the following DHCPv6 configuration process is encrypted
to avoid the privacy information disclosure. We introduce two new
DHCPv6 messages: Encrypted-Query message, Encrypted-Response message
and three new DHCPv6 options: Encrypted-message option, Certificate
option, Timestamp option. Based on the new defined messages and
options, the corresponding authentication and encryption mechanisms
are achieved.
The following figure illustrates 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 the servers' certificates
information, without going through any address, prefix or non-
security option assignment process. The Information-request is sent
without any client's private information, such as Client Identifier
option or the Certificate option, to minimize client's privacy
information leakage. When receiving the Information-request message,
the server sends the Reply message that contains the server's
Certificate option and Server Identifier option. Upon the receipt of
the Reply message, the DHCPv6 client verifies the server's identity
according to the contained certificate in the 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 should retry a
number of times. In this way, it is difficult for a rogue server to
beat out a busy "real" server. And then the client takes some other
alternative action depending on its local policy.
After the server's authentication, the first DHCPv6 message sent from
the client to the server, such as Solicit message, contains the
client's Certificate information for client authentication. The
DHCPv6 client sends the Encrypted-Query message to server, which
carries the Encrypted-message option and the Server Identifier
option. The Encrypted-message option contains the encrypted DHCPv6
message sent from the client to the server. 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
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Certificate option, the DHCPv6 server verifies the client's identity
according to the contained client certificate 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. If the message fails client authentication,
then the server sends the corresponding error status code to the
client. During the encrypted DHCPv6 configuration process, the
timestamp option can be contained in the encrypted DHCPv6 messages to
defend against replay attacks.
+-------------+ +-------------+
|DHCPv6 Client| |DHCPv6 Server|
+-------------+ +-------------+
| Information-request |
|----------------------------------------->|
| Option Request option |
| |
| Reply |
|<-----------------------------------------|
| Certificate option |
| Server Identifier option |
| |
| Encryption-Query |
|----------------------------------------->|
| Encrypted-message option |
| Server Identifier option |
| |
| Encryption-Response |
|<-----------------------------------------|
| Encrypted-message option |
| |
Secure DHCPv6 Procedure
5.2. New Components
The new components of the mechanism 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 certificate that signs the
public key. The Certificate option is defined to carry the
certificate of the sender.
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o A timestamp that can be used to detect replayed packet. The
Timestamp option is defined to carry the current time of the
client/server. 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.
o The Encrypted-message option that contains the encrypted DHCPv6
message.
o The Encrypted-Query message that is sent from the secure DHCPv6
client to the secure DHCPv6 server. The Encrypted-Query message
contains the Encrypted-message option and Server Identifier
option.
o The Encrypted-Response message that is sent from the secure DHCPv6
server to the secure DHCPv6 client. The Encrypted-Response
message contains the Encrypted-message option.
5.3. Support for Algorithm Agility
Encryption algorithm is used for DHCPv6 encryption to defend against
passive attack. In order to provide a means of addressing problems
that may emerge in the future with existing encryption algorithms,
this document provides a mechanism for negotiating the use of more
encryption algorithms in the future.
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 a 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 server does not support the algorithm used by the client, the
server SHOULD reply with an AlgorithmNotSupported status code
(defined in Section 10.3) to the client. Upon receiving this status
code, the client MAY resend the message protected with the mandatory
algorithm (defined in Section 10.1.1).
5.4. Applicability
In principle, Secure DHCPv6 is applicable in any environment where
physical security on the link is not assured and attacks on DHCPv6
are a concern. In practice, however, it will rely on some
operational assumptions mainly regarding public key distribution and
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management, until more lessons are learned and more experiences are
achieved.
One feasible environment in an early deployment stage would be
enterprise networks. In such networks the security policy tends to
be strict and it will be easier to manage client hosts. One trivial
deployment scenario is therefore to manually pre-configure client
with the trusted servers' public key and manually register clients'
public keys for the server. It may also be possible to deploy an
internal PKI to make this less reliant on manual operations, although
it is currently subject to future study specifically how to integrate
such a PKI into the DHCPv6 service for the network.
Note that this deployment scenario based on manual operation is not
different very much from the existing, shared-secret based
authentication mechanisms defined in [RFC3315] in terms of
operational costs. However, Secure DHCPv6 is still securer than the
shared-secret mechanism in that even if clients' keys stored for the
server are stolen that does not mean an immediate threat as these are
public keys. In addition, if some kind of PKI is used with Secure
DHCPv6, even if the initial installation of the certificates is done
manually, it will help reduce operational costs of revocation in case
a private key (especially that of the server) is compromised.
It is believed that Secure DHCPv6 could be more widely applicable
with integration of generic PKI so that it will be more easily
deployed. But such a deployment requires more general issues with
PKI deployment be addressed, and it is currently unknown whether we
can find practical deployment scenarios. It is subject to future
study and experiments, and out of scope of this document.
6. DHCPv6 Client Behavior
For the secure DHCPv6 client, a certificate is needed for client
authentication. The client is pre-configured with a certificate and
its corresponding private key. If the client is pre-configured with
public key not certificate, it can generate the self-signed
certificate for client authentication.
The secure 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 or the Certificate
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 the Certificate option.
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When receiving the Reply messages from DHCPv6 servers, a secure
DHCPv6 client SHOULD discard any DHCPv6 messages when the Certificate
option or Server Identifier option is missing. And then the client
SHOULD first check the support of the encryption algorithm that the
server used. If the check fails, the Reply message SHOULD be
dropped. If the encryption algorithm is 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. The message transaction-id is used as the identifier of
the authenticated server's public key for encryption. At this point,
the client has either recognized the certificate of the server, or
decided to drop the message.
If there are multiple authenticated DHCPv6 servers, the client
selects one DHCPv6 server for the following network parameters
configuration. The client can also choose other implementation
method depending on the client's local policy if the defined protocol
can also run normally. For example, the client can try multiple
transactions (each with different server) at the "same" time. If
there are no authenticated DHCPv6 servers or existing servers failed
authentication, the client should retry a number of times. In this
way, it is difficult for the rogue server to beat out a busy "real"
server. And then the client takes some alternative action depending
on its local policy, such as attempting to use an unsecured DHCPv6
server. The client conducts the server discovery process as per
section 18.1.5 of [RFC3315] 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 contains the Encrypted-message option, which MUST be
constructed as explained in Section 10.1.3, 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 decryption cost by
those unselected servers.
For the encrypted DHCPv6 message sent from the DHCPv6 client to the
DHCPv6 server, the first DHCPv6 message, such as Solicit message,
MUST contain the Certificate option for client authentication. The
Certificate option MUST be constructed as explained in
Section 10.1.1. If the client have multiple certificate with
different public/private key pairs, the message transaction-id is
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used as the identifier of the client's private key for decryption.
In addition, the encrypted DHCPv6 message can contain the timestamp
option to defend against replay attacks. The timestamp option MUST
be constructed as explained in Section 10.1.2.
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
per [RFC3315]. If the decrypted DHCPv6 message contains the
timestamp option, the DHCPv6 client checks the timestamp according to
the rule defined in Section 9.1. The DHCPv6 message, which fails the
timestamp check, MUST be discarded. 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 server.
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 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 DecryptionFail error status code, the client MAY
resend the message following 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.
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7. DHCPv6 Server Behavior
For the secure DHCPv6 server, a certificate is need for server
authentication. The server is pre-configured with a certificate and
its corresponding private key. If the server is pre-configured with
public key not certificate, it can generate the self-signed
certificate for server authentication.
When the DHCPv6 server receives the Information-request message and
the contained Option Request option identifies the request is for the
server certificate information, it replies with a Reply message to
the client. The Reply message MUST contain the requested Certificate
option, which MUST be constructed as explained in Section 10.1.1, and
Server Identifier option.
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
messages not for it.
If the decrypted message is a Solicit/Information-request message,
the secure DHCPv6 server SHOULD discard the received message if the
Certificate option is missing. In such failure, the server SHOULD
reply with an UnspecFail (value 1, [RFC3315]) error status code.
If a Certificate option is provided, the server SHOULD first check
the support of the encryption algorithm 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
the encryption algorithm is supported, the server then checks the
authority of this client.
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 with 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.
If the decrypted message contains the timestamp option, the server
checks the timestamp according to the rule defined in Section 9.1.
If the timestamp check fails, a TimestampFail error status code,
defined in Section 10.3, should be sent back to the client.
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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 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.
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 10.1.3. The Encrypted-message
option contains the encrypted DHCPv6 message that is encrypted using
the authenticated client's public key. To provide the replay
protection, the timestamp option can be contained in the encrypted
DHCPv6 message.
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 described 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 MUST NOT add any secure DHCPv6 options.
Relay-forward and Relay-reply messages MUST NOT contain any
additional Certificate 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 10.1.2,
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, within certain
allowed clock drift. So, an accurate clock is not necessary. If one
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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
timestamp check):
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 timestamp check) 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.
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
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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. Three new DHCPv6
options, two new DHCPv6 messages and four status codes are defined.
10.1. New DHCPv6 Options
10.1.1. Certificate Option
The Certificate option carries the 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| EA-id | |
+-+-+-+-+-+-+-+-+ .
. Certificate (variable length) .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
option-code OPTION_CERTIFICATE (TBA1).
option-len 1 + Length of certificate in octets.
EA-id Encryption Algorithm id. The encryption algorithm
is used for the encrypted DHCPv6 configuration
process. This design is adopted in order to provide
encryption algorithm agility. The value is from the
Encryption Algorithm for Secure DHCPv6 registry in
IANA. A registry of the initial assigned values
is defined in Section 12.
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 is mandatory.
10.1.2. 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 (TBA2).
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. The timestamp data MUST
be in format as defined in Section 5.3.1, [RFC3971].
10.1.3. 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 (TBA3).
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
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by a client. In Encrypted-response message, it contains encrypted
DHCPv6 message sent by a server.
10.2. New DHCPv6 Messages
Two new DHCPv6 messages are defined to achieve the DHCPv6 encryption:
Encrypted-Query and Encrypted-Response. Both the DHCPv6 messages
defined in this document share the following format:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. options .
. (variable) .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: The format of Encrypted-Query and Encrypted-Response
Messages
msg-type Identifier of the message type. It can be either
Encrypted-Query (TBA4) or DHCPv6-Response (TBA5).
transaction-id The transaction ID for this message exchange.
options The Encrypted-Query message MUST contain the Server
Identifier option and Encrypted-message option. The
Encrypted-Response message MUST contain the
Encrypted-message option.
10.3. Status Codes
The following new status codes, see Section 5.4 of [RFC3315] are
defined.
o AlgorithmNotSupported (TBD6): indicates that the DHCPv6 server
does not support algorithms that sender used.
o AuthenticationFail (TBD7): indicates that the DHCPv6 client fails
authentication check.
o TimestampFail (TBD8): indicates the message from DHCPv6 client
fails the timestamp check.
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o DecryptionFail (TBD9): indicates the message from DHCPv6 client
fails the DHCPv6 message decryption.
11. Security Considerations
This document provides the authentication and encryption mechanisms
for DHCPv6.
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 three new DHCPv6 [RFC3315] options. The IANA
is requested to assign values for these three options from the DHCPv6
Option Codes table of the DHCPv6 Parameters registry maintained in
http://www.iana.org/assignments/dhcpv6-parameters. The three options
are:
The Certificate option (TBA1), described in Section 10.1.1.
The Timestamp option (TBA2),described in Section 10.1.2.
The Encrypted-message option (TBA3), described in Section 10.1.3.
The IANA is also requested to assign value for these two messages
from the DHCPv6 Message Types table of the DHCPv6 Parameters registry
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maintained in http://www.iana.org/assignments/dhcpv6-parameters. The
two messages are:
The Encrypted-Query message (TBA4), described in Section 10.2.
The Encrypted-Response message (TBA5), described in Section 10.2.
The IANA is also requested to add one new registry tables to the
DHCPv6 Parameters registry maintained in
http://www.iana.org/assignments/dhcpv6-parameters. The table is the
Encryption 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.
Encryption algorithm for Secure DHCPv6. The values in this table are
8-bit unsigned integers. The following initial values are assigned
for encryption algorithm for Secure DHCPv6 in this document:
Name | Value | RFCs
-------------------+---------+--------------
RSA | 0 | 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
---------+-----------------------+--------------
TBD6 | AlgorithmNotSupported | this document
TBD7 | AuthenticationFail | this document
TBD8 | TimestampFail | this document
TBD9 | DecryptionFail | this document
13. Acknowledgements
The authors would like to thank Tomek Mrugalski, Bernie Volz,
Jianping Wu, Randy Bush, Yiu Lee, 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.
This document was produced using the xml2rfc tool [RFC2629].
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14. Change log [RFC Editor: Please remove]
draft-ietf-dhc-sedhcpv6-11: Delete the Signature option, because the
encrypted DHCPv6 message and the Information-request message (only
contain the certificate option) don't need the signature option for
message integrity check; Rewrite the "Applicability" section; Add the
encryption algorithm negotiation process; To support the encryption
algorithm negotiation, the Certificate option contains the EA-
id(encryption algorithm identifier) field; Reserve the timestamp
option to defend against the replay attacks for encrypted DHCPv6
configuration process; Modify the client behavior when there is no
authenticated DHCPv6 server; Add the DecryptionFail error code.
2016-3-9.
draft-ietf-dhc-sedhcpv6-10: merge DHCPv6 authentication and DHCPv6
encryption. The public key option is removed, because the device can
generate the self-signed certificate if it is pre-configured the
public key not the certificate. 2015-12-10.
draft-ietf-dhc-sedhcpv6-09: change some texts about the deployment
part.2015-12-10.
draft-ietf-dhc-sedhcpv6-08: clarified what the client and the server
should do if it receives a message using unsupported algorithm;
refined the error code treatment regarding to AuthenticationFail and
TimestampFail; added consideration on how to reduce the DoS attack
when using TOFU; other general editorial cleanups. 2015-06-10.
draft-ietf-dhc-sedhcpv6-07: removed the deployment consideration
section; instead, described more straightforward use cases with TOFU
in the overview section, and clarified how the public keys would be
stored at the recipient when TOFU is used. The overview section also
clarified the integration of PKI or other similar infrastructure is
an open issue. 2015-03-23.
draft-ietf-dhc-sedhcpv6-06: remove the limitation that only clients
use PKI- certificates and only servers use public keys. The new text
would allow clients use public keys and servers use PKI-certificates.
2015-02-18.
draft-ietf-dhc-sedhcpv6-05: addressed comments from mail list that
responsed to the second WGLC. 2014-12-08.
draft-ietf-dhc-sedhcpv6-04: addressed comments from mail list.
Making timestamp an independent and optional option. Reduce the
serverside authentication to base on only client's certificate.
Reduce the clientside authentication to only Leaf of Faith base on
server's public key. 2014-09-26.
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draft-ietf-dhc-sedhcpv6-03: addressed comments from WGLC. Added a
new section "Deployment Consideration". Corrected the Public Key
Field in the Public Key Option. Added consideration for large DHCPv6
message transmission. Added TimestampFail error code. Refined the
retransmission rules on clients. 2014-06-18.
draft-ietf-dhc-sedhcpv6-02: addressed comments (applicability
statement, redesign the error codes and their logic) from IETF89 DHC
WG meeting and volunteer reviewers. 2014-04-14.
draft-ietf-dhc-sedhcpv6-01: addressed comments from IETF88 DHC WG
meeting. Moved Dacheng Zhang from acknowledgement to be co-author.
2014-02-14.
draft-ietf-dhc-sedhcpv6-00: adopted by DHC WG. 2013-11-19.
draft-jiang-dhc-sedhcpv6-02: removed protection between relay agent
and server due to complexity, following the comments from Ted Lemon,
Bernie Volz. 2013-10-16.
draft-jiang-dhc-sedhcpv6-01: update according to review comments from
Ted Lemon, Bernie Volz, Ralph Droms. Separated Public Key/
Certificate option into two options. Refined many detailed
processes. 2013-10-08.
draft-jiang-dhc-sedhcpv6-00: original version, this draft is a
replacement of draft-ietf-dhc-secure-dhcpv6, which reached IESG and
dead because of consideration regarding to CGA. The authors followed
the suggestion from IESG making a general public key based mechanism.
2013-06-29.
15. Open Issues [RFC Editor: Please remove]
this protocol changes DHCPv6 message exchanges quite substantially:
previously, the client first sends a Solicit message, gets possibly
multiple Advertise messages, chooses the server (= sender of one of
the Advertises) that would be best for the client, and then sends a
Request to that chosen server. Now the server selection is done at
the key exchange phase (the initial Information-request and Reply
exchange), and the Solicit can be sent only to a single server. If
the client doesn't like the Advertise it could restart the whole
process, but it will be more expensive, and there's no guarantee that
other servers can provide a better Advertise.
One might argue that it's okay as "secure DHCPv6" is an "optional"
extension. But, with keeping in mind that the current IETF trend is
to make everything privacy-aware (often by making everything
encrypted), I'd personally say we should consider it to be the
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standard mode of DHCPv6 operation even if users can still disable it.
From this point of view, I think we should either
o A. make the server selection behavior more compatible with the
pre-encryption protocol, or
o B. accept we give up the previous server selection feature for
privacy (after careful assessment of its effect and with clear wg
consensus), and explicitly note that. we might even have to
reflect that in rfc3315bis.
16. References
16.1. 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>.
[RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander,
"SEcure Neighbor Discovery (SEND)", RFC 3971,
DOI 10.17487/RFC3971, March 2005,
<http://www.rfc-editor.org/info/rfc3971>.
[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>.
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[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>.
16.2. 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
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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: lilishan48@gmail.com
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
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Dacheng Zhang
Beijing
CN
Email: dacheng.zhang@gmail.com
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