| DHC Working Group | S. Jiang, Ed. |
| Internet-Draft | Huawei Technologies Co., Ltd |
| Intended status: Standards Track | S. Shen |
| Expires: September 24, 2015 | CNNIC |
| D. Zhang | |
| Huawei Technologies Co., Ltd | |
| T. Jinmei | |
| Infoblox Inc. | |
| March 23, 2015 |
Secure DHCPv6
draft-ietf-dhc-sedhcpv6-07
The Dynamic Host Configuration Protocol for IPv6 (DHCPv6) enables DHCPv6 servers to pass configuration parameters. It offers configuration flexibility. If not being secured, DHCPv6 is vulnerable to various attacks, particularly spoofing attacks. This document analyzes the security issues of DHCPv6 and specifies a Secure DHCPv6 mechanism for communications between DHCPv6 clients and DHCPv6 servers. This document provides a DHCPv6 client/server authentication mechanism based on sender's public/private key pairs or certificates with associated private keys. The DHCPv6 message exchanges are protected by the signature option and the timestamp option newly defined in this document.
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 Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any 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 24, 2015.
Copyright (c) 2015 IETF Trust and the persons identified as the document authors. All rights reserved.
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 to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.
The Dynamic Host Configuration Protocol for IPv6 (DHCPv6, [RFC3315]) enables DHCPv6 servers to pass configuration parameters and offers configuration flexibility. If not being secured, DHCPv6 is vulnerable to various attacks, particularly spoofing attacks.
This document analyzes the security issues of DHCPv6 in details. This document provides mechanisms for improving the security of DHCPv6 between client and server:
Note: this secure mechanism in this document does not protect the relay-relevant options, either added by a relay agent toward a server or added by a server toward a relay agent, because they are only transported within operator networks and considered less vulnerable. Communication between a server and a relay agent, and communications between relay agents, may be secured through the use of IPsec, as described in section 21.1 in [RFC3315].
The security mechanisms specified in this document is based on sender's public/private key pairs or certificates with associated private keys. It also integrates message signatures for the integrity and timestamps for anti-replay. The sender authentication procedure using certificates defined in this document depends on deployed Public Key Infrastructure (PKI, [RFC5280]). However, the deployment of PKI is out of the scope of this document.
Secure DHCPv6 is applicable in environments where physical security on the link is not assured (such as over wireless) and attacks on DHCPv6 are a concern.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "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.
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. In the basic DHCPv6 specification [RFC3315], security of DHCPv6 messages 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 keyed hash function, there are two key management mechanisms. The first one is a key management done out of band, usually through some manual process. The second approach is to use Public Key Infrastructure (PKI).
As an example of the first approach, operators can set up a key database for both servers and clients from which the client obtains a key before running DHCPv6. Manual key distribution runs counter to the goal of minimizing the configuration data needed at each host.
[RFC3315] provides an additional mechanism for preventing off-network timing attacks using the Reconfigure message: the Reconfigure Key authentication method. However, this method provides little message integrity or source integrity check, and it protects only the Reconfigure message. This key is transmitted in plaintext.
In comparison, the security mechanism defined in this document allows the public key database on the client or server to be populated opportunistically or manually, depending on the degree of confidence desired in a specific application. PKI security mechanism is simpler in the local key management respect.
This document introduces a Secure DHCPv6 mechanism that uses signatures to secure the DHCPv6 protocol. In order to enable DHCPv6 clients and servers to perform mutual authentication without previous key deployment, this solution provides a DHCPv6 client/server authentication mechanism based on public/private key pairs and, optionally, PKI certificates. The purpose of this design is to make it easier to deploy DHCPv6 authentication and provides protection of DHCPv6 message within the scope of whatever trust relationship exists for the particular key used to authenticate the message.
In this document, we introduce a public key option, a certificate option, a signature option and a timestamp option with corresponding verification mechanisms. A DHCPv6 message can include a public key option, and carrying a digital signature and a timestamp option. The signature can be verified using the supplied public key. The recipient processes the payload of the DHCPv6 message only if the validation is successful: the signature validates, and a trust relationship exists for the key. Alternatively, a DHCPv6 message can include a certificate option, and also carrying a digital signature and a timestamp option. The signature can be verified by the recipient. The recipient processes the payload of the DHCPv6 message only if the validation is successful: the certificate validates, and a trust relationship exists on the recipient for the provided 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.
A trust relationship for a public key can be the result either of a Trust-on-first-use (TOFU) policy, or a list of trusted keys configured on the recipient.
A trust relationship for a certificate could also be treated either as TOFU or configured in a list of trusted certificate authorities, depending on the application.
TOFU can be used by a client to authenticate a server and its messages. It can be deployed without establishing a trust relationship between the client and the server. Unlike the Reconfigure Key Authentication Protocol defined in [RFC3315], it can also be used for other DHCPv6 messages than Reconfigure, and the same single key can be used for all clients since the server does not send a secret in plain text on the wire. Overall this will provide a reasonable balance of easy deployment and moderate level of security, as long as the risk of the attack window on the first use is acceptable.
TOFU can also be used by a server to protect an existing DHCPv6 session with a particular client by preventing a malicious client from hijacking the session. In this case the server does not even have to store the client's public key or certificate after the session; it only has to remember the public key during that particular session and check if it can verify received messages with that key. This type of authentication can be deployed without a pre-established trust relationship.
If authentication has to be provided from the initial use, the Secure DHCPv6 mechanism needs some infrastructure such as PKI so the recipient of a public key or certificate can verify it securely. It is currently a subject of further study how such an infrastructure can be integrated to DHCPv6 in a way it makes the deployment easier.
Secure DHCPv6 messages are commonly large. One example is normal DHCPv6 message length plus a 1 KB for a X.509 certificate and signature and 256 Byte for a signature. IPv6 fragments [RFC2460] are highly possible. In practise, the total length would be various in a large range. Hence, deployment of Secure DHCPv6 should also consider the issues of IP fragment, PMTU, etc. Also, if there are firewalls between secure DHCPv6 clients and secure DHCPv6 servers, it is RECOMMENDED that the firewalls are configured to pass ICMP Packet Too Big messages [RFC4443].
The components of the solution specified in this document are as follows:
Hash functions are used to provide message integrity checks. In order to provide a means of addressing problems that may emerge in the future with existing hash algorithms, as recommended in [RFC4270], this document provides a mechanism for negotiating the use of more secure hashes in the future.
In addition to hash algorithm agility, this document also provides a mechanism for signature algorithm agility.
The support for algorithm agility in this document is mainly a unilateral notification mechanism from sender to recipient. A recipient MAY support various algorithms simultaneously among different senders, and the different senders in 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 recipient does not support the algorithm used by the sender, it cannot authenticate the message. In the client-to-server case, the server SHOULD reply with an AlgorithmNotSupported status code (defined in Section 5.5). Upon receiving this status code, the client MAY resend the message protected with the mandatory algorithm (defined in Section 5.3).
By default, a secure DHCPv6 enabled client or server SHOULD start with secure mode by sending secure DHCPv6 messages. If the recipient is secure DHCPv6 enabled and the key or certificate authority is trusted by the recipient, then their communication would be in secure mode. In the scenario where the secure DHCPv6 enabled client and server fail to build up secure communication between them, the secure DHCPv6 enabled client MAY choose to send unsecured DHCPv6 message towards the server according to its local policies.
In the scenario where the recipient is a legacy DHCPv6 server that does not support secure mechanism, the DHCPv6 server (for all of known DHCPv6 implementations) would just omit or disregard unknown options (secure options defined in this document) and still process 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 messages. If the client accepts the unsecured messages from the DHCPv6 server, the subsequent exchanges will be in the unsecured mode.
In the scenario where a legacy client sends an unsecured message to a secure DHCPv6 enabled server, there are two possibilities depending on the server policy. If the server's policy requires the authentication, an UnspecFail (value 1, [RFC3315]) error status code, SHOULD be returned. In such case, the client cannot build up the connection with the server. If the server has been configured to support unsecured clients, the server MAY fall back to the unsecured DHCPv6 mode, and reply unsecured messages toward the client; depending on the local policy, the server MAY continue to send the secured reply messages with the consumption of computing resource. The resources allocated for unsecured clients SHOULD be separated and restricted.
This section describes the extensions to DHCPv6. Four new options have been defined. The new options MUST be supported in the Secure DHCPv6 message exchange.
The Public Key option carries the public key of the sender. The format of the Public Key option is described as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_PUBLIC_KEY | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. Public Key (variable length) .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
option-code OPTION_PUBLIC_KEY (TBA1).
option-len Length of public key in octets.
Public Key A variable-length field containing a
SubjectPublicKeyInfo object specified in [RFC5280].
The SubjectPublicKeyInfo structure is comprised with
a public key and an AlgorithmIdentifier object
which is specified in section 4.1.1.2, [RFC5280]. The
object identifiers for the supported algorithms and
the methods for encoding the public key materials
(public key and parameters) are specified in
[RFC3279], [RFC4055], and [RFC4491].
The Certificate option carries the public key certificate of the client. The format of the Certificate option is described as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_CERTIFICATE | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. Certificate (variable length) .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
option-code OPTION_CERTIFICATE (TBA2).
option-len Length of certificate in octets.
Certificate A variable-length field containing certificate. The
encoding of certificate and certificate data MUST
be in format as defined in Section 3.6, [RFC7296].
The support of X.509 certificate - Signature (4)
is mandatory.
The Signature option allows a signature that is signed by the private key to be attached to a DHCPv6 message. The Signature option could be any place within the DHCPv6 message while it is logically created after the entire DHCPv6 header and options, except for the Authentication Option. It protects the entire DHCPv6 header and options, including itself, except for the Authentication Option. The format of the Signature option is described as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_SIGNATURE | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| HA-id | SA-id | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| |
. Signature (variable length) .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
option-code OPTION_SIGNATURE (TBA3).
option-len 2 + Length of Signature field in octets.
HA-id Hash Algorithm id. The hash algorithm is used for
computing the signature result. This design is
adopted in order to provide hash algorithm agility.
The value is from the Hash Algorithm for Secure
DHCPv6 registry in IANA. The support of SHA-256 is
mandatory. A registry of the initial assigned values
is defined in Section 8.
SA-id Signature Algorithm id. The signature algorithm is
used for computing the signature result. This
design is adopted in order to provide signature
algorithm agility. The value is from the Signature
Algorithm for Secure DHCPv6 registry in IANA. The
support of RSASSA-PKCS1-v1_5 is mandatory. A
registry of the initial assigned values is defined
in Section 8.
Signature A variable-length field containing a digital
signature. The signature value is computed with
the hash algorithm and the signature algorithm,
as described in HA-id and SA-id. The signature
constructed by using the sender's private key
protects the following sequence of octets:
1. The DHCPv6 message header.
2. All DHCPv6 options including the Signature
option (fill the signature field with zeroes)
except for the Authentication Option.
The signature field MUST be padded, with all 0, to
the next octet boundary if its size is not a
multiple of 8 bits. The padding length depends on
the signature algorithm, which is indicated in the
SA-id field.
[RFC3315] because of changing auth option, the authors chose not include authentication option in the signature.
The Timestamp option carries the current time on the sender. It adds the anti-replay protection to the DHCPv6 messages. It is optional.
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 (TBA4).
option-len 8, in octets.
Timestamp The current time of day (NTP-format timestamp
[RFC5905] in UTC (Coordinated Universal Time), a
64-bit unsigned fixed-point number, in seconds
relative to 0h on 1 January 1900.). It can reduce
the danger of replay attacks.
The following new status codes, see Section 5.4 of [RFC3315] are defined.
This section only covers the scenario where both DHCPv6 client and DHCPv6 server are secure enabled.
The sender of a Secure DHCPv6 message could be a DHCPv6 server or a DHCPv6 client.
The sender must have a public/private key pair in order to create Secure DHCPv6 messages. The sender may also have a public key certificate, which is signed by a CA assumed to be trusted by the recipient, and its corresponding private key.
To support Secure DHCPv6, the Secure DHCPv6 enabled sender MUST construct the DHCPv6 message following the rules defined in [RFC3315].
A Secure DHCPv6 message sent by a DHCPv6 server or a client, except for Relay-reply messages, MUST either contain a Public Key option, 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 messages, MUST contain one and only one Signature option, which MUST be constructed as explained in Section 5.3. It protects the message header and all DHCPv6 options except for the Authentication Option.
A Secure DHCPv6 message, except for Relay-forward and Relay-reply messages, SHOULD contain one and only one Timestamp option, which MUST be constructed as explained in Section 5.4. The Timestamp field 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 additional Public Key or Certificate option or Signature Option or Timestamp Option, aside from those present in the innermost encapsulated messages from the client or server.
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 indicates the failure reason on the server side. According to the received status code, the client MAY take follow-up action:
The recipient of a Secure DHCPv6 message could be a DHCPv6 server or a DHCPv6 client. In the failure cases, either DHCPv6 server or client SHOULD NOT process received message, and the server SHOULD reply a correspondent error status code, while the client does nothing. The specific behavior depends on the configured local policy.
When receiving a DHCPv6 message, except for Relay-Forward and Relay-Reply messages, a Secure DHCPv6 enabled recipient SHOULD discard any DHCPv6 messages that meet any of the following conditions:
In such failure, if the recipient is a DHCPv6 server, the server SHOULD reply an UnspecFail (value 1, [RFC3315]) error status code. If none of the Signature, Public Key or Certificate options is 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 policy allows.
The recipient SHOULD first check the support of algorithms that sender used. If not pass, the message is dropped. In such failure, if the recipient is a DHCPv6 server, the server SHOULD reply an AlgorithmNotSupported error status code, defined in Section 5.5, back to the client. If both algorithms are supported, the recipient then checks the authority of this sender. The recipient SHOULD also use the same algorithms in the return messages.
If a Certificate option is provided, the recipient 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.
If a Public Key option is provided, the recipient SHOULD validate it by finding a matching public key from the local trust public key list, which is pre-configured or recorded from previous communications (TOFU). A local trust public key list is a data table maintained by the recipient. It stores public keys from all trustworthy senders.
When the local policy of the recipient allows the use of TOFU, if a Public Key option is provided but it is not found in the local trust public key list, the recipient MAY accept the public key. The recipient will normally store the key in the local list for subsequent DHCPv6 sessions, but it may not necessarily have to do so depending on the purpose of the authentication (see the case of authenticating a client with TOFU described in Section 4).
The message that fails authentication check MUST be dropped. In such failure, the DHCPv6 server SHOULD reply an AuthenticationFail error status code, defined in Section 5.5, back to the client.
The recipient MAY choose to further process messages from a sender when there is no matched public key. By recording the public key, when the first time it is seen, the recipient can make a Trust On First Use that the sender is trustworthy. The circumstances under which this might be done are out of scope for this document.
At this point, the recipient has either recognized the authentication of the sender, or decided to drop the message. The recipient MUST now authenticate the sender by verifying the signature and checking timestamp (see details in Section 6.4), if there is a Timestamp option. The order of two procedures is left as an implementation decision. It is RECOMMENDED to check timestamp first, because signature verification is much more computationally expensive. Depending on server's local policy, the message without a Timestamp option MAY be acceptable or rejected. If the server rejects such a message, a TimestampFail error status code, defined in Section 5.5, should be sent back to the client. The reply message that carries the TimestampFail error status code SHOULD NOT carry a timestamp option.
The signature field verification MUST show that the signature has been calculated as specified in Section 5.3. Only the messages that get through both the signature verifications and timestamp check (if there is a Timestamp option) are accepted as secured DHCPv6 messages and continue to be handled for their contained DHCPv6 options as defined in [RFC3315]. Messages that do not pass the above tests MUST be discarded or treated as unsecured messages. In the case the recipient is DHCPv6 server, the DHCPv6 server SHOULD reply a SignatureFail error status code, defined in Section 5.5, for the signature verification failure; or a TimestampFail error status code, defined in Section 5.5, for the timestamp check failure, back to the client.
Furthermore, the node that supports the verification of the Secure DHCPv6 messages MAY impose additional constraints for the verification. For example, it may impose limits on minimum and maximum key lengths.
A Relay-forward or Relay-reply message with any Public Key, Certificate or the Signature option is invalid. The message MUST be discarded silently.
To support Secure DHCPv6, relay agents just need to follow the same processing rules defined in [RFC3315]. There is nothing more the relay agents have to do, either verify the messages from client or server, or add any secure DHCPv6 options. Actually, by definition in this document, relay agents SHOULD NOT add any secure DHCPv6 options.
In order to check the Timestamp option, defined in Section 5.4, recipients SHOULD be configured with an allowed timestamp Delta value, a "fuzz factor" for comparisons, and an allowed clock drift parameter. The recommended default value for the allowed Delta is 300 seconds (5 minutes); for fuzz factor 1 second; and for clock drift, 0.01 second.
Note: the Timestamp mechanism is based on the assumption that communication peers have roughly synchronized clocks, with certain allowed clock drift. So, accurate clock is not necessary. If one has a clock too far from the current time, the timestamp mechanism would not work.
To facilitate timestamp checking, each recipient SHOULD store the following information for each sender, from which at least one accepted secure DHCPv6 message is successfully verified (for both timestamp check and signature verification):
A verified (for both timestamp check and signature verification) secure DHCPv6 message initiates the update of the above variables in the recipient's record.
Recipients MUST check the Timestamp field as follows:
An implementation MAY use some mechanism such as a timestamp cache to strengthen resistance to replay attacks. When there is a very large number of nodes on the same link, or when a cache filling attack is in progress, it is possible that the cache holding the most recent timestamp per sender will become full. In this case, the node MUST remove some entries from the cache or refuse some new requested entries. The specific policy as to which entries are preferred over others is left as an implementation decision.
An implementation MAY statefully record the latest timestamps from senders. In such implementation, the timestamps MUST be strictly monotonously increasing. This is reasonable given that DHCPv6 messages are rarely misordered.
This document provides new security features to the DHCPv6 protocol.
Using public key based security mechanism and its verification mechanism in DHCPv6 message exchanging provides the authentication and data integrity protection. Timestamp mechanism provides anti-replay function.
The Secure DHCPv6 mechanism is based on the pre-condition that the recipient knows the public key of the sender or the sender's public key certificate can be verified through a trust CA. Clients may discard the DHCPv6 messages from unknown/unverified servers, which may be fake servers; or may prefer DHCPv6 messages from known/verified servers over unsigned messages or messages from unknown/unverified servers. The pre-configuration operation also needs to be protected, which is out of scope. The deployment of PKI is also out of scope.
When a recipient first encounters a new public key, it may also store the key using a Trust On First Use policy. If the sender that used that public key is in fact legitimate, then all future communication with that sender can be protected by storing the public key. This does not provide complete security, but it limits the opportunity to mount an attack on a specific recipient to the first time it communicates with a new sender.
Downgrade attacks cannot be avoided if nodes are configured to accept both secured and unsecured messages. A future specification may provide a mechanism on how to treat unsecured DHCPv6 messages.
[RFC6273] has analyzed possible threats to the hash algorithms used in SEND. Since the Secure DHCPv6 defined in this document uses the same hash algorithms in similar way to SEND, analysis results could be applied as well: current attacks on hash functions do not constitute any practical threat to the digital signatures used in the signature algorithm in the Secure DHCPv6.
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.
One more consideration is that this protocol does reveal additional client information in their certificate. It means less privacy. In current practice, the client privacy and the client authentication are mutually exclusive.
This document defines four new DHCPv6 [RFC3315] options. The IANA is requested to assign values for these four options from the DHCPv6 Option Codes table of the DHCPv6 Parameters registry maintained in http://www.iana.org/assignments/dhcpv6-parameters. The four options are:
The IANA is also requested to add two new registry tables to the DHCPv6 Parameters registry maintained in http://www.iana.org/assignments/dhcpv6-parameters. The two tables are the Hash Algorithm for Secure DHCPv6 table and the Signature Algorithm for Secure DHCPv6 table.
Initial values for these registries are given below. Future assignments are to be made through Standards Action [RFC5226]. Assignments for each registry consist of a name, a value and a RFC number where the registry is defined.
Hash Algorithm for Secure DHCPv6. The values in this table are 8-bit unsigned integers. The following initial values are assigned for Hash Algorithm for Secure DHCPv6 in this document:
Name | Value | RFCs
-------------------+---------+--------------
SHA-256 | 0x01 | this document
SHA-512 | 0x02 | this document
Name | Value | RFCs
-------------------+---------+--------------
RSASSA-PKCS1-v1_5 | 0x01 | this document
Section 5.5, in the DHCPv6 Parameters registry maintained in http://www.iana.org/assignments/dhcpv6-parameters:
Code | Name | Reference
---------+-----------------------+--------------
TBD5 | AlgorithmNotSupported | this document
TBD6 | AuthenticationFail | this document
TBD7 | TimestampFail | this document
TBD8 | SignatureFail | this document
The authors would like to thank Bernie Volz, Ted Lemon, Ralph Droms, Jari Arkko, Sean Turner, Stephen Kent, Thomas Huth, David Schumacher, Francis Dupont, Tomek Mrugalski, Gang Chen, Qi Sun, Suresh Krishnan, Fred Templin, Robert Elz and other members of the IETF DHC working group for their valuable comments.
This document was produced using the xml2rfc tool [RFC2629].
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.
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 responsed to the second WGLC.
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.
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.
| [RFC2629] | Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629, June 1999. |
| [RFC4270] | Hoffman, P. and B. Schneier, "Attacks on Cryptographic Hashes in Internet Protocols", RFC 4270, November 2005. |
| [RFC5226] | Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 5226, May 2008. |
| [RFC6273] | Kukec, A., Krishnan, S. and S. Jiang, "The Secure Neighbor Discovery (SEND) Hash Threat Analysis", RFC 6273, June 2011. |
| [RSA] | RSA Laboratories, "RSA Encryption Standard, Version 2.1, PKCS 1", November 2002. |