draft-ietf-dhc-sedhcpv6-05.txt   draft-ietf-dhc-sedhcpv6-06.txt 
DHC Working Group S. Jiang, Ed. DHC Working Group S. Jiang, Ed.
Internet-Draft Huawei Technologies Co., Ltd Internet-Draft Huawei Technologies Co., Ltd
Intended status: Standards Track S. Shen Intended status: Standards Track S. Shen
Expires: June 11, 2015 CNNIC Expires: August 22, 2015 CNNIC
D. Zhang D. Zhang
Huawei Technologies Co., Ltd Huawei Technologies Co., Ltd
T. Jinmei T. Jinmei
Infoblox Inc. Infoblox Inc.
December 8, 2014 February 18, 2015
Secure DHCPv6 Secure DHCPv6
draft-ietf-dhc-sedhcpv6-05 draft-ietf-dhc-sedhcpv6-06
Abstract Abstract
The Dynamic Host Configuration Protocol for IPv6 (DHCPv6) enables The Dynamic Host Configuration Protocol for IPv6 (DHCPv6) enables
DHCPv6 servers to pass configuration parameters. It offers DHCPv6 servers to pass configuration parameters. It offers
configuration flexibility. If not being secured, DHCPv6 is configuration flexibility. If not being secured, DHCPv6 is
vulnerable to various attacks, particularly spoofing attacks. This vulnerable to various attacks, particularly spoofing attacks. This
document analyzes the security issues of DHCPv6 and specifies a document analyzes the security issues of DHCPv6 and specifies a
Secure DHCPv6 mechanism for communications between DHCPv6 clients and Secure DHCPv6 mechanism for communications between DHCPv6 clients and
DHCPv6 servers. This document provides a DHCPv6 client/server DHCPv6 servers. This document provides a DHCPv6 client/server
authentication mechanism based on server's public/private key pairs authentication mechanism based on sender's public/private key pairs
and client's certificates. The DHCPv6 message exchanges are or certificates with associated private keys. The DHCPv6 message
protected by the signature option and the timestamp option newly exchanges are protected by the signature option and the timestamp
defined in this document. option newly defined in this document.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on June 11, 2015. This Internet-Draft will expire on August 22, 2015.
Copyright Notice Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements Language and Terminology . . . . . . . . . . . . 3 2. Requirements Language and Terminology . . . . . . . . . . . . 3
3. Security Overview of DHCPv6 . . . . . . . . . . . . . . . . . 4 3. Security Overview of DHCPv6 . . . . . . . . . . . . . . . . . 4
4. Overview of Secure DHCPv6 Mechanism with Public Key . . . . . 4 4. Overview of Secure DHCPv6 Mechanism with Public Key . . . . . 4
4.1. New Components . . . . . . . . . . . . . . . . . . . . . 5 4.1. New Components . . . . . . . . . . . . . . . . . . . . . 5
4.2. Support for Algorithm Agility . . . . . . . . . . . . . . 6 4.2. Support for Algorithm Agility . . . . . . . . . . . . . . 6
4.3. Applicability . . . . . . . . . . . . . . . . . . . . . . 6 4.3. Applicability . . . . . . . . . . . . . . . . . . . . . . 7
5. Extensions for Secure DHCPv6 . . . . . . . . . . . . . . . . 7 5. Extensions for Secure DHCPv6 . . . . . . . . . . . . . . . . 7
5.1. Public Key Option . . . . . . . . . . . . . . . . . . . . 7 5.1. Public Key Option . . . . . . . . . . . . . . . . . . . . 7
5.2. Certificate Option . . . . . . . . . . . . . . . . . . . 8 5.2. Certificate Option . . . . . . . . . . . . . . . . . . . 8
5.3. Signature Option . . . . . . . . . . . . . . . . . . . . 9 5.3. Signature Option . . . . . . . . . . . . . . . . . . . . 9
5.4. Timestamp Option . . . . . . . . . . . . . . . . . . . . 10 5.4. Timestamp Option . . . . . . . . . . . . . . . . . . . . 10
5.5. Status Codes . . . . . . . . . . . . . . . . . . . . . . 11 5.5. Status Codes . . . . . . . . . . . . . . . . . . . . . . 11
6. Processing Rules and Behaviors . . . . . . . . . . . . . . . 11 6. Processing Rules and Behaviors . . . . . . . . . . . . . . . 11
6.1. Processing Rules of Sender . . . . . . . . . . . . . . . 11 6.1. Processing Rules of Sender . . . . . . . . . . . . . . . 11
6.2. Processing Rules of Recipient . . . . . . . . . . . . . . 13 6.2. Processing Rules of Recipient . . . . . . . . . . . . . . 13
6.3. Processing Rules of Relay Agent . . . . . . . . . . . . . 15 6.3. Processing Rules of Relay Agent . . . . . . . . . . . . . 15
6.4. Timestamp Check . . . . . . . . . . . . . . . . . . . . . 15 6.4. Timestamp Check . . . . . . . . . . . . . . . . . . . . . 15
7. Deployment Consideration . . . . . . . . . . . . . . . . . . 17 7. Deployment Consideration . . . . . . . . . . . . . . . . . . 17
7.1. Authentication on a client . . . . . . . . . . . . . . . 17 7.1. Authentication on a client . . . . . . . . . . . . . . . 17
7.2. Authentication on a server . . . . . . . . . . . . . . . 17 7.2. Authentication on a server . . . . . . . . . . . . . . . 17
8. Security Considerations . . . . . . . . . . . . . . . . . . . 18 8. Security Considerations . . . . . . . . . . . . . . . . . . . 18
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 20 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 20
11. Change log [RFC Editor: Please remove] . . . . . . . . . . . 21 11. Change log [RFC Editor: Please remove] . . . . . . . . . . . 20
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 21 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 21
12.1. Normative References . . . . . . . . . . . . . . . . . . 22 12.1. Normative References . . . . . . . . . . . . . . . . . . 21
12.2. Informative References . . . . . . . . . . . . . . . . . 23 12.2. Informative References . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23
1. Introduction 1. Introduction
The Dynamic Host Configuration Protocol for IPv6 (DHCPv6, [RFC3315]) The Dynamic Host Configuration Protocol for IPv6 (DHCPv6, [RFC3315])
enables DHCPv6 servers to pass configuration parameters and offers enables DHCPv6 servers to pass configuration parameters and offers
configuration flexibility. If not being secured, DHCPv6 is configuration flexibility. If not being secured, DHCPv6 is
vulnerable to various attacks, particularly spoofing attacks. vulnerable to various attacks, particularly spoofing attacks.
This document analyzes the security issues of DHCPv6 in details. This document analyzes the security issues of DHCPv6 in details.
skipping to change at page 3, line 26 skipping to change at page 3, line 26
o the identity of a DHCPv6 message sender, which can be a DHCPv6 o the identity of a DHCPv6 message sender, which can be a DHCPv6
server or a client, can be verified by a recipient. server or a client, can be verified by a recipient.
o the integrity of DHCPv6 messages can be checked by the recipient o the integrity of DHCPv6 messages can be checked by the recipient
of the message. of the message.
o anti-replay protection based on timestamps. o anti-replay protection based on timestamps.
Note: this secure mechanism in this document does not protect the Note: this secure mechanism in this document does not protect the
relay-relevant options, either added by a relay agent toward a server relay-relevant options, either added by a relay agent toward a server
or added by a server toward a relay agent, are considered less or added by a server toward a relay agent, because they are only
vulnerable, because they are only transported within operator transported within operator networks and considered less vulnerable.
networks. Communication between a server and a relay agent, and Communication between a server and a relay agent, and communications
communications between relay agents, may be secured through the use between relay agents, may be secured through the use of IPsec, as
of IPsec, as described in section 21.1 in [RFC3315]. described in section 21.1 in [RFC3315].
The security mechanisms specified in this document is based on The security mechanisms specified in this document is based on
server's public/private key pairs and client's certificates. The sender's public/private key pairs or certificates with associated
reason for such design and deployment consideration are discussed in private keys. The reason for such design and deployment
Section 7. It also integrates message signatures for the integrity consideration are discussed in Section 7. It also integrates message
and timestamps for anti-replay. The client authentication on server signatures for the integrity and timestamps for anti-replay. The
procedure defined in this document depends on deployed Public Key sender authentication procedure using certificates defined in this
Infrastructure (PKI, [RFC5280]). However, the deployment of PKI is document depends on deployed Public Key Infrastructure (PKI,
out of the scope. [RFC5280]). However, the deployment of PKI is out of the scope.
Secure DHCPv6 is applicable in environments where physical security Secure DHCPv6 is applicable in environments where physical security
on the link is not assured (such as over wireless) and attacks on on the link is not assured (such as over wireless) and attacks on
DHCPv6 are a concern. DHCPv6 are a concern.
2. Requirements Language and Terminology 2. Requirements Language and Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in "OPTIONAL" in this document are to be interpreted as described in
skipping to change at page 4, line 24 skipping to change at page 4, line 24
The basic DHCPv6 specifications can optionally authenticate the The basic DHCPv6 specifications can optionally authenticate the
origin of messages and validate the integrity of messages using an origin of messages and validate the integrity of messages using an
authentication option with a symmetric key pair. [RFC3315] relies on authentication option with a symmetric key pair. [RFC3315] relies on
pre-established secret keys. For any kind of meaningful security, pre-established secret keys. For any kind of meaningful security,
each DHCPv6 client would need to be configured with its own secret each DHCPv6 client would need to be configured with its own secret
key; [RFC3315] provides no mechanism for doing this. key; [RFC3315] provides no mechanism for doing this.
For the keyed hash function, there are two key management mechanisms. For the keyed hash function, there are two key management mechanisms.
The first one is a key management done out of band, usually through The first one is a key management done out of band, usually through
some manual process. The second approach is use Public Key some manual process. The second approach is to use Public Key
Infrastructure (PKI). Infrastructure (PKI).
As an example of the first approach, operators can set up a key As an example of the first approach, operators can set up a key
database for both servers and clients which the client obtains a key database for both servers and clients from which the client obtains a
before running DHCPv6. Manual key distribution runs counter to the key before running DHCPv6. Manual key distribution runs counter to
goal of minimizing the configuration data needed at each host. the goal of minimizing the configuration data needed at each host.
[RFC3315] provides an additional mechanism for preventing off-network [RFC3315] provides an additional mechanism for preventing off-network
timing attacks using the Reconfigure message: the Reconfigure Key timing attacks using the Reconfigure message: the Reconfigure Key
authentication method. However, this method provides little message authentication method. However, this method provides little message
integrity or source integrity check, and it protects only the integrity or source integrity check, and it protects only the
Reconfigure message. This key is transmitted in plaintext. Reconfigure message. This key is transmitted in plaintext.
In comparison, the security mechanism defined in this document allows In comparison, the security mechanism defined in this document allows
the public key database on the client to be populated the public key database on the client or server to be populated
opportunistically or manually, depending on the degree of confidence opportunistically or manually, depending on the degree of confidence
desired in a specific application. PKI security mechanism is simpler desired in a specific application. PKI security mechanism is simpler
in the local key management respect. in the local key management respect.
4. Overview of Secure DHCPv6 Mechanism with Public Key 4. Overview of Secure DHCPv6 Mechanism with Public Key
This document introduces a Secure DHCPv6 mechanism that uses This document introduces a Secure DHCPv6 mechanism that uses
signatures to secure the DHCPv6 protocol. In order to enable DHCPv6 signatures to secure the DHCPv6 protocol. In order to enable DHCPv6
clients and DHCPv6 servers to perform mutual authentication without clients and servers to perform mutual authentication without previous
previous key deployment, this solution provides a DHCPv6 client/ key deployment, this solution provides a DHCPv6 client/server
server authentication mechanism based on server's public/private key authentication mechanism based on public/private key pairs and,
pairs and client's certificates: the server only accept the client optionally, PKI certificates. The purpose of this design is to make
messages that are protected by the client public key certificate that it easier to deploy DHCPv6 authentication and provides protection of
is signed by a trusted CA (Certificate Authority) ; a client can DHCPv6 message within the scope of whatever trust relationship exists
build up trust relationship with a server for subsequent message for the particular key used to authenticate the message.
exchanges based on leap of faith mechanism. This purpose of this
design is to simplify the precondition of deploying DHCPv6
authentication and provides limited protection of DHCPv6 message.
In this document, we introduce a public key option (only sent by In this document, we introduce a public key option, a certificate
servers), a certificate option (only sent by clients), a signature option, a signature option and a timestamp option with corresponding
option and a timestamp with corresponding verification mechanisms. A verification mechanisms. A DHCPv6 message can include a public key
DHCPv6 message from a server is attached with a public key option, option, and carrying a digital signature and a timestamp option. The
and carrying a digital signature and a timestamp option. It can be signature can be verified using the supplied public key. The
verified by the client. The client processes the payload of the recipient processes the payload of the DHCPv6 message only if the
DHCPv6 message only if the validation is successful. Reversely, a validation is successful: the signature validates, and a trust
DHCPv6 message from a client is attached with a certificate option, relationship exists for the key. Alternatively, a DHCPv6 message can
and also carrying a digital signature and a timestamp option. It can include a certificate option, and also carrying a digital signature
be verified by the server. The server processes the payload of the and a timestamp option. The signature can be verified by the
DHCPv6 message only if the validation is successful. The end-to-end recipient. The recipient processes the payload of the DHCPv6 message
security protection is bidirection that covers both from DHCPv6 only if the validation is successful: the certificate validates, and
servers to clients and from clients to DHCPv6 servers. Additionally, a trust relationship exists on the recipient for the provided
the optional timestamp mechanism provides anti-replay protection. certificate. The recipient processes the payload of the DHCPv6
message only if the validation is successful. The end-to-end
security protection can be bidirectional, covering messages from
servers to clients and from clients to servers. Additionally, the
optional timestamp mechanism provides anti-replay protection.
By recording the public key that was used by the DHCPv6 server, when A trust relationship for a public key can be the result either of a
the first time it is seen, the DHCPv6 client can make a leap of faith Trust-on-first-use (TOFU) policy, or a list of trusted keys
that the server is trustworthy. If no evidence to the contrary configured on the recipient.
surfaces, the client can then validate the server as trustworthy when
it subsequently sees the same public key used to sign messages from
the same server. In opposite, once the client has determined that it
is being attacked, it can either forget that server, or remember that
server in a blacklist and drop further packets associated with that
server.
On the server DHCPv6 side, upon receiving the client's public key A trust relationship for a certificate could also be treated either
certificate, the server asserts the validity of the certificate, for as Trust-on-first-use or configured in a list of trusted certificate
example through PKI. authorities, depending on the application. Such applications are out
of scope for this document.
Secure DHCPv6 messages are commonly large. IPv6 fragments [RFC2460] Secure DHCPv6 messages are commonly large. One example is normal
are highly possible. Hence, deployment of Secure DHCPv6 should also DHCPv6 message length plus a 1 KB for a X.509 certificate and
consider the issues of IP fragment, PMTU, etc. Also, if there are signature and 256 Byte for a signature. IPv6 fragments [RFC2460] are
firewalls between secure DHCPv6 clients and secure DHCPv6 servers, it highly possible. In practise, the total length would be various in a
is RECOMMENDED that the firewalls are configured to pass ICMP Packet large range. Hence, deployment of Secure DHCPv6 should also consider
Too Big messages [RFC4443]. 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].
4.1. New Components 4.1. New Components
The components of the solution specified in this document are as The components of the solution specified in this document are as
follows: follows:
o The server generates a public/private key pair. A DHCPv6 option o Servers and clients using public keys in their secure DHCPv6
that carries the public key is defined. messages generate a public/private key pair. A DHCPv6 option that
carries the public key is defined.
o The client obtains a public key certificate from a Certificate o Servers and clients that use certifiicates first generate a
Authority that can be used to establish the trustworthiness with public/private key pair and then obtain a public key certificate
the server. Another option is defined to carry the certificate. from a Certificate Authority that signs the public key. Another
option is defined to carry the certificate.
o A signature generated using the private key which is used by the o A signature generated using the private key which is used by the
receiver to verify the integrity of the DHCPv6 messages and then receiver to verify the integrity of the DHCPv6 messages and then
the identity of the sender. the identity of the sender.
o A timestamp, to detect replayed packet. The secure DHCPv6 nodes o A timestamp, to detect replayed packet. The secure DHCPv6 nodes
need to meet some accuracy requirements and be synced to global need to meet some accuracy requirements and be synced to global
time, while the timestamp checking mechanism allows a configurable time, while the timestamp checking mechanism allows a configurable
time value for clock drift. The real time provision is out of time value for clock drift. The real time provision is out of
scope. scope of this document.
4.2. Support for Algorithm Agility 4.2. Support for Algorithm Agility
Hash functions are used to provide message integrity checks. In Hash functions are used to provide message integrity checks. In
order to provide a means of addressing problems that may emerge in order to provide a means of addressing problems that may emerge in
the future with existing hash algorithms, as recommended in the future with existing hash algorithms, as recommended in
[RFC4270], this document provides a mechanism for negotiating the use [RFC4270], this document provides a mechanism for negotiating the use
of more secure hashes in the future. of more secure hashes in the future.
In addition to hash algorithm agility, this document also provides a In addition to hash algorithm agility, this document also provides a
skipping to change at page 6, line 50 skipping to change at page 7, line 7
If the recipient does not support the algorithm used by the sender, If the recipient does not support the algorithm used by the sender,
it cannot authenticate the message. In the client-to-server case, it cannot authenticate the message. In the client-to-server case,
the server SHOULD reply with an AlgorithmNotSupported status code the server SHOULD reply with an AlgorithmNotSupported status code
(defined in Section 5.5). Upon receiving this status code, the (defined in Section 5.5). Upon receiving this status code, the
client MAY resend the message protected with the mandatory algorithm client MAY resend the message protected with the mandatory algorithm
(defined in Section 5.3). (defined in Section 5.3).
4.3. Applicability 4.3. Applicability
By default, a secure DHCPv6 enabled client SHOULD start with secure By default, a secure DHCPv6 enabled client or server SHOULD start
mode by sending secure DHCPv6 messages. If the recipient is secure with secure mode by sending secure DHCPv6 messages. If the recipient
DHCPv6 enabled server, their communication would be in secure mode. is secure DHCPv6 enabled and the key or certificate authority is
trusted by the recipient, then their communication would be in secure
In the scenario where the secure DHCPv6 enabled client and server mode. In the scenario where the secure DHCPv6 enabled client and
fail to build up secure communication between them, the secure DHCPv6 server fail to build up secure communication between them, the secure
enabled client MAY choose to send unsecured DHCPv6 message towards DHCPv6 enabled client MAY choose to send unsecured DHCPv6 message
the server according to its local policies. towards the server according to its local policies.
In the scenario where the recipient is a legacy DHCPv6 server that In the scenario where the recipient is a legacy DHCPv6 server that
does not support secure mechanism, the DHCPv6 server (for all of does not support secure mechanism, the DHCPv6 server (for all of
known DHCPv6 implementations) would just omit or disregard unknown known DHCPv6 implementations) would just omit or disregard unknown
options (secure options defined in this document) and still process options (secure options defined in this document) and still process
the known options. The reply message would be unsecured, of course. the known options. The reply message would be unsecured, of course.
It is up to the local policy of the client whether to accept the It is up to the local policy of the client whether to accept the
messages. If the client accepts the unsecured messages from the messages. If the client accepts the unsecured messages from the
DHCPv6 server, the subsequent exchanges will be in the unsecured DHCPv6 server, the subsequent exchanges will be in the unsecured
mode. mode.
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restricted. restricted.
5. Extensions for Secure DHCPv6 5. Extensions for Secure DHCPv6
This section describes the extensions to DHCPv6. Four new options This section describes the extensions to DHCPv6. Four new options
have been defined. The new options MUST be supported in the Secure have been defined. The new options MUST be supported in the Secure
DHCPv6 message exchange. DHCPv6 message exchange.
5.1. Public Key Option 5.1. Public Key Option
The Public Key option carries the public key of the server. The The Public Key option carries the public key of the sender. The
format of the Public Key option is described as follows: format of the Public Key option is described as follows:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_PUBLIC_KEY | option-len | | OPTION_PUBLIC_KEY | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
. Public Key (variable length) . . Public Key (variable length) .
. . . .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
option-code OPTION_PUBLIC_KEY (TBA1). option-code OPTION_PUBLIC_KEY (TBA1).
option-len Length of public key in octets. option-len Length of public key in octets.
Public Key A variable-length field containing a Public Key A variable-length field containing a
SubjectPublicKeyInfo object specified in [RFC5280]. SubjectPublicKeyInfo object specified in [RFC5280].
The SubjectPublicKeyInfo structure is comprised with The SubjectPublicKeyInfo structure is comprised with
a public key and a AlgorithmIdentifier object a public key and an AlgorithmIdentifier object
which is specified in section 4.1.1.2, [RFC5280]. The which is specified in section 4.1.1.2, [RFC5280]. The
object identifiers for the supported algorithms and object identifiers for the supported algorithms and
the methods for encoding the public key materials the methods for encoding the public key materials
(public key and parameters) are specified in (public key and parameters) are specified in
[RFC3279], [RFC4055], and [RFC4491]. [RFC3279], [RFC4055], and [RFC4491].
5.2. Certificate Option 5.2. Certificate Option
The Certificate option carries the public key certificate of the The Certificate option carries the public key certificate of the
client. The format of the Certificate option is described as client. The format of the Certificate option is described as
skipping to change at page 12, line 5 skipping to change at page 12, line 5
6. Processing Rules and Behaviors 6. Processing Rules and Behaviors
This section only covers the scenario where both DHCPv6 client and This section only covers the scenario where both DHCPv6 client and
DHCPv6 server are secure enabled. DHCPv6 server are secure enabled.
6.1. Processing Rules of Sender 6.1. Processing Rules of Sender
The sender of a Secure DHCPv6 message could be a DHCPv6 server or a The sender of a Secure DHCPv6 message could be a DHCPv6 server or a
DHCPv6 client. DHCPv6 client.
The server must have a public/private key pair in order to create The sender must have a public/private key pair in order to create
Secure DHCPv6 messages. The client must have a public key Secure DHCPv6 messages. The sender may also have a public key
certificate, which is signed by a CA trusted by both server and certificate, which is signed by a CA assumed to be trusted by the
client, and its corresponding private key. recipient, and its corresponding private key.
To support secure DHCPv6, the secure DHCPv6 enabled sender MUST To support Secure DHCPv6, the Secure DHCPv6 enabled sender MUST
construct the DHCPv6 message following the rules defined in construct the DHCPv6 message following the rules defined in
[RFC3315]. [RFC3315].
A Secure DHCPv6 message, except for Relay-forward and Relay-reply A Secure DHCPv6 message sent by a DHCPv6 server or a client, except
messages, MUST contain either a Public Key or a Certificate option, for Relay-reply messages, MUST either contain a Public Key option,
which MUST be constructed as explained in Section 5.1 or Section 5.2. which MUST be constructed as explained in Section 5.1, or a
Certificate option, which MUST be constructed as explained in
Section 5.2.
A Secure DHCPv6 message, except for Relay-forward and Relay-reply A Secure DHCPv6 message, except for Relay-forward and Relay-reply
messages, MUST contain one and only one Signature option, which MUST messages, MUST contain one and only one Signature option, which MUST
be constructed as explained in Section 5.3. It protects the message be constructed as explained in Section 5.3. It protects the message
header and all DHCPv6 options except for the Authentication Option. header and all DHCPv6 options except for the Authentication Option.
A Secure DHCPv6 message, except for Relay-forward and Relay-reply A Secure DHCPv6 message, except for Relay-forward and Relay-reply
messages, SHOULD contain one and only one Timestamp option. The messages, SHOULD contain one and only one Timestamp option, which
Timestamp field SHOULD be set to the current time, according to MUST be constructed as explained in Section 5.4. The Timestamp field
sender's real time clock. SHOULD be set to the current time, according to sender's real time
clock.
A Relay-forward and relay-reply message MUST NOT contain any A Relay-forward and relay-reply message MUST NOT contain any
additional Public Key or Certificate option or Signature Option or additional Public Key or Certificate option or Signature Option or
Timestamp Option, aside from those present in the innermost Timestamp Option, aside from those present in the innermost
encapsulated messages from the client or server. encapsulated messages from the client or server.
If the sender is a DHCPv6 client, in the failure cases, it receives a If the sender is a DHCPv6 client, in the failure cases, it receives a
Reply message with an error status code. The error status code Reply message with an error status code. The error status code
indicates the failure reason on the server side. According to the indicates the failure reason on the server side. According to the
received status code, the client MAY take follow-up action: received status code, the client MAY take follow-up action:
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is not able to build up the secure communication with the is not able to build up the secure communication with the
recipient. The client MAY switch to other public key certificate recipient. The client MAY switch to other public key certificate
if it has another one. But it SHOULD NOT retry with the same if it has another one. But it SHOULD NOT retry with the same
certificate. However, if the client decides to retransmit using certificate. However, if the client decides to retransmit using
the same certificate after receiving AuthenticationFail, it MUST the same certificate after receiving AuthenticationFail, it MUST
NOT retransmit immediately and MUST follow normal retransmission NOT retransmit immediately and MUST follow normal retransmission
routines defined in [RFC3315]. routines defined in [RFC3315].
o Upon receiving a TimestampFail error status code, the client MAY o Upon receiving a TimestampFail error status code, the client MAY
fall back to unsecured mode, or resend the message without a fall back to unsecured mode, or resend the message without a
Timestamp option. However, the DHCP server MAY not accept the Timestamp option. However, the DHCPv6 server MAY not accept the
message without a Timestamp option. message without a Timestamp option.
o Upon receiving a SignatureFail error status code, the client MAY o Upon receiving a SignatureFail error status code, the client MAY
resend the message following normal retransmission routines resend the message following normal retransmission routines
defined in [RFC3315]. defined in [RFC3315].
6.2. Processing Rules of Recipient 6.2. Processing Rules of Recipient
The recipient of a Secure DHCPv6 message could be a DHCPv6 server or The recipient of a Secure DHCPv6 message could be a DHCPv6 server or
a DHCPv6 client. In the failure cases, either DHCPv6 server or a DHCPv6 client. In the failure cases, either DHCPv6 server or
client SHOULD NOT process received message, and the server SHOULD client SHOULD NOT process received message, and the server SHOULD
reply a correspondent error status code, while the client does reply a correspondent error status code, while the client does
nothing. The specific behavior depends on the configured local nothing. The specific behavior depends on the configured local
policy. policy.
When receiving a DHCPv6 message, except for Relay-Forward and Relay- When receiving a DHCPv6 message, except for Relay-Forward and Relay-
Reply messages, a secure DHCPv6 enabled recipient SHOULD discard any Reply messages, a Secure DHCPv6 enabled recipient SHOULD discard any
DHCPv6 messages that meet any of the following conditions: DHCPv6 messages that meet any of the following conditions:
o the Signature option is absent, o the Signature option is absent,
o multiple Signature options are present, o multiple Signature options are present,
o the Public Key option is absent in the server-to-client message, o both the Public Key option and the Certificate option are absent,
o the Certificate option is present in the server-to-client message,
o the Certificate option is absent in the client-to-server message,
o the Public Key option is present in the client-to-server message. o both the Public Key option and the Certificate option are present.
In such failure, if the recipient is a DHCPv6 server, the server In such failure, if the recipient is a DHCPv6 server, the server
SHOULD reply an UnspecFail (value 1, [RFC3315]) error status code. SHOULD reply an UnspecFail (value 1, [RFC3315]) error status code.
If none of the Signature, Public Key or Certificate options is If none of the Signature, Public Key or Certificate options is
present, the sender MAY be a legacy node or in unsecured mode, then, present, the sender MAY be a legacy node or in unsecured mode, then,
the recipient MAY fall back to the unsecured DHCPv6 mode if its local the recipient MAY fall back to the unsecured DHCPv6 mode if its local
policy allows. policy allows.
The recipient SHOULD first check the support of algorithms that The recipient SHOULD first check the support of algorithms that
sender used. If not pass, the message is dropped. In such failure, sender used. If not pass, the message is dropped. In such failure,
if the recipient is a DHCPv6 server, the server SHOULD reply an if the recipient is a DHCPv6 server, the server SHOULD reply an
AlgorithmNotSupported error status code, defined in Section 5.5, back AlgorithmNotSupported error status code, defined in Section 5.5, back
to the client. If both algorithms are supported, the recipient then to the client. If both algorithms are supported, the recipient then
checks the authority of this sender. The recipient SHOULD also use checks the authority of this sender. The recipient SHOULD also use
the same algorithms in the return messages. the same algorithms in the return messages.
The DHCPv6 server SHOULD validate the client's public key certificate If a Certificate option is provided, the recipient SHOULD validate
following the rules defined in [RFC5280]. An implementation may the certificate according to the rules defined in [RFC5280]. An
create a local trust certificate record for verified certificates in implementation may create a local trust certificate record for
order to avoid repeated verification procedure in the future. A verified certificates in order to avoid repeated verification
client certificate that finds a match in the local trust certificate procedure in the future. A certificate that finds a match in the
list is treated as verified. A fast search index may be created for local trust certificate list is treated as verified.
this list.
The DHCPv6 client SHOULD validate it by finding a matching public key If a Public Key option is provided, the recipient SHOULD validate it
from the local trust public key list, which is pre-configured or by finding a matching public key from the local trust public key
recorded from previous communications. A local trust public key list list, which is pre-configured or recorded from previous
is a data table maintained by the recipient. It stores public keys communications (TOFU). A local trust public key list is a data table
from all trustworthy senders. A fast search index may be created for maintained by the recipient. It stores public keys from all
this list. trustworthy senders.
The message that fails authentication check MUST be dropped. In such The message that fails authentication check MUST be dropped. In such
failure, the DHCPv6 server SHOULD reply an AuthenticationFail error failure, the DHCPv6 server SHOULD reply an AuthenticationFail error
status code, defined in Section 5.5, back to the client. status code, defined in Section 5.5, back to the client.
The client MAY choose to further process messages from a server for The recipient MAY choose to further process messages from a sender
which there is no matched public key. By recording the public key, when there is no matched public key. By recording the public key,
when the first time it is seen, the client can make a leap of faith when the first time it is seen, the recipient can make a Trust On
that the server is trustworthy. If no evidence to the contrary First Use that the sender is trustworthy. The circumstances under
surfaces, the client can then validate the server as trustworthy for which this might be done are out of scope for this document.
subsequent message exchanges. In opposite, once the client has
determined that it is being attacked, it can either forget that
public key, or remember that public key in a blacklist and drop
further packets associated with that public key.
At this point, the recipient has either recognized the authentication At this point, the recipient has either recognized the authentication
of the sender, or decided to drop the message. The recipient MUST of the sender, or decided to drop the message. The recipient MUST
now authenticate the sender by verifying the signature and checking now authenticate the sender by verifying the signature and checking
timestamp (see details in Section 6.4), if there is a Timestamp timestamp (see details in Section 6.4), if there is a Timestamp
option. The order of two procedures is left as an implementation option. The order of two procedures is left as an implementation
decision. It is RECOMMENDED to check timestamp first, because decision. It is RECOMMENDED to check timestamp first, because
signature verification is much more computationally expensive. signature verification is much more computationally expensive.
Depending on server's local policy, the message without a Timestamp Depending on server's local policy, the message without a Timestamp
option MAY be acceptable or rejected. If the server rejects such a option MAY be acceptable or rejected. If the server rejects such a
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An implementation MAY use some mechanism such as a timestamp cache to An implementation MAY use some mechanism such as a timestamp cache to
strengthen resistance to replay attacks. When there is a very large 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 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 in progress, it is possible that the cache holding the most recent
timestamp per sender will become full. In this case, the node MUST timestamp per sender will become full. In this case, the node MUST
remove some entries from the cache or refuse some new requested remove some entries from the cache or refuse some new requested
entries. The specific policy as to which entries are preferred over entries. The specific policy as to which entries are preferred over
others is left as an implementation decision. others is left as an implementation decision.
An implementation MAY statefully record the latest timestamps from An implementation MAY statefully record the latest timestamps from
clients. In such implementation, the timestamps MUST be strictly senders. In such implementation, the timestamps MUST be strictly
monotonously increasing. This is reasonable given that DHCPv6 monotonously increasing. This is reasonable given that DHCPv6
messages are rarely misordered. messages are rarely misordered.
7. Deployment Consideration 7. Deployment Consideration
This document defines two directions of authentication: This document defines two directions of authentication:
authentication based on client's public key certificate and authentication based on client's public key certificate and
authentication based on leap of faith to server's public key. authentication based on leap of faith to server's public key.
7.1. Authentication on a client 7.1. Authentication on a client
For clients, DHCPv6 authentication generally means verifying whether For clients, DHCPv6 authentication generally means verifying whether
the sender of DHCP messages is a legal DHCPv6 server and verifying the sender of DHCPv6 messages is a legal DHCPv6 server and verifying
whether the message has been modified during transmission. Because whether the message has been modified during transmission. Because
the client may have to validate the authentication in the condition the client may have to validate the authentication in the condition
of without connectivity wider than link-local, authentication with of without connectivity wider than link-local, authentication with
certificates may not always be feasible. So, this document only certificates may not always be feasible. So, this document only
sticks on Leaf of Faith model, to make sure the client talks to the sticks on Leaf of Faith mode, to make sure the client talks to the
same previous server. same previous server.
Message integrity is provided. But there is a chance for the client Message integrity is provided. But there is a chance for the client
to incorrectly trust a malicious server at the beginning of the first to incorrectly trust a malicious server at the beginning of the first
session with the server (and therefore keep trusting it thereafter). session with the server (and therefore keep trusting it thereafter).
But the leap of faith mechanim guarantees the subsequent messages are But the leap of faith mechanim guarantees the subsequent messages are
sent by the same previous server, and therefore narrows the attack sent by the same previous server, and therefore narrows the attack
scope. This may make sense if the network can be reasonably scope. This may make sense if the network can be reasonably
considered secure and requesting pre-configuration is deemed to be considered secure and requesting pre-configuration is deemed to be
infeasible. A small home network would be an example of such cases. infeasible. A small home network would be an example of such cases.
For environments that are neither controlled nor really trustworthy, For environments that are neither controlled nor really trustworthy,
such as a network in a cafeteria, while the leap of faith model, such as a network in a cafeteria, while the leap of faith mode, i.e.,
i.e., silently trusting the server at the first time, would be too silently trusting the server at the first time, would be too
insecure. But some middle ground might be justified, such as insecure. But some middle ground might be justified, such as
requiring human intervention at the point of the leap of faith. requiring human intervention at the point of the leap of faith.
7.2. Authentication on a server 7.2. Authentication on a server
As for authentication on a server, there are several different As for authentication on a server, there are several different
scenarios to consider, each of which has different applicability scenarios to consider, each of which has different applicability
issues. If the server allows the leap of faith model, any malicious issues. If the server allows the leap of faith mode, any malicious
user can pretend to be a new legitimate client. While the server can user can pretend to be a new legitimate client. While the server can
always be considered to have connectivity to validate certificate, it always be considered to have connectivity to validate certificate, it
is feasible to check client certificates. is feasible to check client certificates.
Network administrators may wish to constrain the allocation of Network administrators may wish to constrain the allocation of
addresses to authorized hosts to avoid denial of service attacks in addresses to authorized hosts to avoid denial of service attacks in
"hostile" environments where the network medium is not physically "hostile" environments where the network medium is not physically
secured, such as wireless networks or college residence halls. A secured, such as wireless networks or college residence halls. A
server may have to selectively serve a specific client or deny server may have to selectively serve a specific client or deny
specific clients depending on the identity of the client in a specific clients depending on the identity of the client in a
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8. Security Considerations 8. Security Considerations
This document provides new security features to the DHCPv6 protocol. This document provides new security features to the DHCPv6 protocol.
Using public key based security mechanism and its verification Using public key based security mechanism and its verification
mechanism in DHCPv6 message exchanging provides the authentication mechanism in DHCPv6 message exchanging provides the authentication
and data integrity protection. Timestamp mechanism provides anti- and data integrity protection. Timestamp mechanism provides anti-
replay function. replay function.
The Secure DHCPv6 mechanism is based on the pre-condition that the The Secure DHCPv6 mechanism is based on the pre-condition that the
client knows the public key of servers or the client's public key recipient knows the public key of the sender or the sender's public
certificate can be verified through a trust CA. It prevents DHCPv6 key certificate can be verified through a trust CA. Clients may
server spoofing. The clients may discard the DHCPv6 messages from discard the DHCPv6 messages from unknown/unverified servers, which
unknown/unverified servers, which may be fake servers; or may prefer may be fake servers; or may prefer DHCPv6 messages from known/
DHCPv6 messages from known/verified servers over unsigned messages or verified servers over unsigned messages or messages from unknown/
messages from unknown/unverified servers. The pre-configuration unverified servers. The pre-configuration operation also needs to be
operation also needs to be protected, which is out of scope. The protected, which is out of scope. The deployment of PKI is also out
deployment of PKI is also out of scope. of scope.
However, when a DHCPv6 client first encounters a new public key, it When a recipient first encounters a new public key, it may also store
can make a leap of faith. If the DHCPv6 server that used that public the key using a Trust On First Use policy. If the sender that used
key is in fact legitimate, then all future communication with that that public key is in fact legitimate, then all future communication
DHCPv6 server can be protected by storing the public key. This does with that sender can be protected by storing the public key. This
not provide complete security, but it limits the opportunity to mount does not provide complete security, but it limits the opportunity to
an attack on a specific DHCPv6 client to the first time it mount an attack on a specific recipient to the first time it
communicates with a new DHCPv6 server. communicates with a new sender.
Downgrade attacks cannot be avoided if nodes are configured to accept Downgrade attacks cannot be avoided if nodes are configured to accept
both secured and unsecured messages. A future specification may both secured and unsecured messages. A future specification may
provide a mechanism on how to treat unsecured DHCPv6 messages. provide a mechanism on how to treat unsecured DHCPv6 messages.
[RFC6273] has analyzed possible threats to the hash algorithms used [RFC6273] has analyzed possible threats to the hash algorithms used
in SEND. Since the Secure DHCPv6 defined in this document uses the in SEND. Since the Secure DHCPv6 defined in this document uses the
same hash algorithms in similar way to SEND, analysis results could same hash algorithms in similar way to SEND, analysis results could
be applied as well: current attacks on hash functions do not be applied as well: current attacks on hash functions do not
constitute any practical threat to the digital signatures used in the constitute any practical threat to the digital signatures used in the
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defined in Section 5.5, in the DHCPv6 Parameters registry maintained defined in Section 5.5, in the DHCPv6 Parameters registry maintained
in http://www.iana.org/assignments/dhcpv6-parameters: in http://www.iana.org/assignments/dhcpv6-parameters:
Code | Name | Reference Code | Name | Reference
---------+-----------------------+-------------- ---------+-----------------------+--------------
TBD5 | AlgorithmNotSupported | this document TBD5 | AlgorithmNotSupported | this document
TBD6 | AuthenticationFail | this document TBD6 | AuthenticationFail | this document
TBD7 | TimestampFail | this document TBD7 | TimestampFail | this document
TBD8 | SignatureFail | this document TBD8 | SignatureFail | this document
10. Acknowledgments 10. Acknowledgements
The authors would like to thank Bernie Volz, Ted Lemon, Ralph Droms, The authors would like to thank Bernie Volz, Ted Lemon, Ralph Droms,
Jari Arkko, Sean Turner, Stephen Kent, Thomas Huth, David Schumacher, Jari Arkko, Sean Turner, Stephen Kent, Thomas Huth, David Schumacher,
Francis Dupont, Tomek Mrugalski, Gang Chen, Qi Sun, Suresh Krishnan, Francis Dupont, Tomek Mrugalski, Gang Chen, Qi Sun, Suresh Krishnan,
Fred Templin and other members of the IETF DHC working group for Fred Templin and other members of the IETF DHC working group for
their valuable comments. their valuable comments.
This document was produced using the xml2rfc tool [RFC2629]. This document was produced using the xml2rfc tool [RFC2629].
11. Change log [RFC Editor: Please remove] 11. Change log [RFC Editor: Please remove]
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
draft-ietf-dhc-sedhcpv6-05: addressed comments from mail list that draft-ietf-dhc-sedhcpv6-05: addressed comments from mail list that
responsed to the second WGLC. responsed to the second WGLC.
draft-ietf-dhc-sedhcpv6-04: addressed comments from mail list. draft-ietf-dhc-sedhcpv6-04: addressed comments from mail list.
Making timestamp an independent and optional option. Reduce the Making timestamp an independent and optional option. Reduce the
serverside authentication to base on only client's certificate. serverside authentication to base on only client's certificate.
Reduce the clientside authentication to only Leaf of Faith base on Reduce the clientside authentication to only Leaf of Faith base on
server's public key. 2014-09-26. server's public key. 2014-09-26.
draft-ietf-dhc-sedhcpv6-03: addressed comments from WGLC. Added a draft-ietf-dhc-sedhcpv6-03: addressed comments from WGLC. Added a
 End of changes. 45 change blocks. 
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