| DHC Working Group | S. Jiang |
| Internet-Draft | Huawei Technologies Co., Ltd |
| Intended status: Standards Track | L. Li |
| Expires: July 6, 2017 | Y. Cui |
| Tsinghua University | |
| T. Jinmei | |
| Infoblox Inc. | |
| T. Lemon | |
| Nominum, Inc. | |
| D. Zhang | |
| January 2, 2017 |
Secure DHCPv6
draft-ietf-dhc-sedhcpv6-19
DHCPv6 includes no deployable security mechanism that can protect end-to-end communication between DHCP clients and servers. This document describes a mechanism for using public key cryptography to provide such security. The mechanism provides encryption in all cases, and can be used for authentication based on pre-sharing of authorized certificates.
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 July 6, 2017.
Copyright (c) 2017 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]) allows DHCPv6 servers to flexibly provide addressing and other configuration information relating to local network infrastructure to DHCP clients. The protocol provides no deployable security mechanism, and consequently is vulnerable to various attacks.
This document provides a brief summary of the security vulnerabilities of the DHCPv6 protocol and then describes a new extension to the protocol that provides two additional types of security:
The extension specified in this document applies only to end-to-end communication between DHCP servers and clients. Options added by relay agents in Relay-Forward messages, and options other than the client message in Relay-Reply messages sent by DHCP servers, are not protected. Such communications are already protected using the mechanism described in section 21.1 in [RFC3315].
This extension introduces two new DHCPv6 messages: the Encrypted- Query and the Encrypted-Response messages. It defines six new DHCPv6 options: the Algorithm, Certificate, Signature, Increasing-number, Encryption-Key-Tag option and Encrypted-message options. The Algorithm, Certificate, Signature, and Increasing-number options are used for authentication. The Encryption-Query message, Encryption-Response message, Encrypted-message option and Encryption-Key-Tag option are used for encryption.
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.
This section defines terminology specific to secure DHCPv6 used in this document.
[RFC3315] defines an authentication mechanism with integrity protection. This mechanism uses a symmetric key that is shared by the client and server for authentication. It does not provide any key distribution mechanism.
For this approach, operators can set up a key database for both servers and clients from which the client obtains a key before running DHCPv6. However, manual key distribution runs counter to the goal of minimizing the configuration data needed at each host. Consequently, there are no known deployments of this security mechanism.
[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 on-path active attacks.
Anonymity Profile for DHCP Clients [RFC7844] explains how to generate DHCPv4 or DHCPv6 requests that minimize the disclosure of identifying information. However, the anonymity profile limits the use of the certain options. It also cannot anticipate new options that may contain private information. In addition, the anonymity profile does not work in cases where the client wants to maintain anonymity from eavesdroppers but must identify itself to the DHCP server with which it intends to communicate.
Privacy consideration for DHCPv6 [RFC7824] presents an analysis of the privacy issues associated with the use of DHCPv6 by Internet users. No solutions are presented.
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 [RFC7258]. The privacy information of the IPv6 host, such as DUID, may be gleaned to find location information, previous visited networks and so on. [RFC7258] claims that pervasive monitoring should be mitigated in the design of IETF protocol, where possible.
To better address the problem of passive monitoring and to achieve authentication without requiring a symmetric key distribution solution for DHCP, this document defines an asymmetric key authentication and encryption mechanism. This protects against both active attacks, such as spoofing, and passive attacks, such as pervasive monitoring.
The following figure illustrates the secure DHCPv6 procedure. Briefly, this extension establishes the server's identity with an anonymous Information-Request exchange. Once the server's identity has been established, the client may either choose to communicate with the server or not. Not communicating with an unknown server avoids revealing private information, but if there is no known server on a particular link, the client will be unable to communicate with a DHCP server.
If the client chooses to communicate with the selected server(s), it uses the Encrypted-Query message to encapsulate its communications to the DHCP server. The server responds with Encrypted-Response messages. Normal DHCP messages are encapsulated in these two new messages using the new defined Encrypted-message option. Besides the Encrypted-message option, the Signature option is defined to verify the integrity of the DHCPv6 messages and then authentication of the client and the server. The Increasing number option is defined to detect a replay attack.
+-------------+ +-------------+
|DHCPv6 Client| |DHCPv6 Server|
+-------------+ +-------------+
| Information-request |
|----------------------------------------->|
| Algorithm option |
| Option Request option |
| |
| Reply |
|<-----------------------------------------|
| Certificate option |
| Signature option |
| Increasing-number option |
| Server Identifier option |
| |
| Encryption-Query |
|----------------------------------------->|
| Encrypted-message option |
| Server Identifier option |
| Encryption-Key-Tag option |
| |
| Encryption-Response |
|<-----------------------------------------|
| Encrypted-message option |
| |
Figure 1: Secure DHCPv6 Procedure
The new components of the mechanism specified in this document are as follows:
In order to provide a means of addressing problems that may emerge with existing hash algorithms, signature algorithm and encryption algorithms in the future, this document provides a mechanism to support algorithm agility. The support for algorithm agility in this document is mainly a algorithm notification mechanism between the client and the server. The same client and server SHOULD use the same algorithm in a single communication session. The sender can offer a set of algorithms, and then the receiver selects one algorithm for the future communication.
For secure DHCPv6, the Solicit and Rebind messages can be sent only to the selected server(s) which share one common certificate. If the client doesn't like the received Advertise(s) it could restart the whole process and selects another certificate, but it will be more expensive, and there's no guarantee that other servers can provide better Advertise(s).
[RFC3315] provides an additional mechanism for preventing off-network timing attacks using the Reconfigure message: the Reconfigure Key authentication method. Secure DHCPv6 can protect the Reconfigure message using the encryption method. So the Reconfigure Key authentication method SHOULD NOT be used if Secure DHCPv6 is applied.
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, authenticated and encrypted DHCPv6 configuration will rely on some operational assumptions mainly regarding public key distribution and management. In order to achieve the wider use of secure DHCPv6, opportunistic security [RFC7435] can be applied to secure DHCPv6 deployment, which allows DHCPv6 encryption in environments where support for authentication or a key distribution mechanism is not available.
Secure DHCPv6 can achieve authentication and encryption based on pre-sharing of authorized certificates. The One feasible environment in an early deployment stage would be enterprise networks. In enterprise networks, the client is manually pre-configured with the trusted servers' public key and the server is also manually pre-configured with the trusted clients' public keys. In some scenario, such as coffee shop where the certificate cannot be validated and one wants access to the Internet, then the DHCPv6 configuration process can be encrypted without authentication.
Note that this deployment scenario based on manual operation is not much different 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 Public Key Infrastructure (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.
The secure DHCPv6 client is pre-configured with a certificate and its corresponding private key for client authentication. If the client does not obtain a certificate from Certificate Authority (CA), it can generate the self-signed certificate.
The secure DHCPv6 client sends an Information-request message as per [RFC3315]. The Information-request message is used by the DHCPv6 client to request the server's certificate information without having addresses, prefixes or any non-security options assigned to it. The contained Option Request option MUST carry the option code of the Certificate option. In addition, the contained Algorithm option MUST be constructed as explained in Section 10.1.1. The Information-request message MUST NOT include any other DHCPv6 options except the above options to minimize the client's privacy information leakage.
When receiving the Reply messages from the DHCPv6 servers, a secure DHCPv6 client discards any DHCPv6 message that meets any of the following conditions:
And then the client first checks acknowledged hash, signature and encryption algorithms that the server supports. If the hash algorithm field is zero, then it indicates that the hash algorithm is fixed according to the corresponding signature algorithm. The client also uses the acknowledged algorithms in the return messages.
Then the client checks the authority of the server. In some scenario where non-authenticated encryption can be accepted, such as coffee shop, then authentication is optional and can be skipped. For the certificate check method, the client validates the certificates through the pre-configured local trusted certificates list or other methods. A certificate that finds a match in the local trust certificates list is treated as verified. If the certificate check fails, the Reply message is dropped.
The client MUST now authenticate the server by verifying the signature and checking increasing number, if there is a Increasing-number option. The order of two procedures is left as an implementation decision. It is RECOMMENDED to check increasing number first, because signature verification is much more computationally expensive. The client checks the Increasing-number option according to the rule defined in Section 9.1. For the message without an Increasing-number option, according to the client's local policy, it MAY be acceptable or rejected. The Signature field verification MUST show that the signature has been calculated as specified in Section 10.1.3. Only the messages that get through both the signature verification and increasing number check (if there is a Increasing-number option) are accepted. Reply message that does not pass the above tests MUST be discarded.
If there are multiple authenticated DHCPv6 certs, the client selects one DHCPv6 cert for the following communication. The selected certificate may correspond to multiple DHCPv6 servers. If there are no authenticated DHCPv6 certs or existing servers fail authentication, the client should retry a number of times. The client conducts the server discovery process as per section 18.1.5 of [RFC3315] to avoid a packet storm. In this way, it is difficult for a 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.
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 10.1.6. The Encrypted-message option contains the encrypted DHCPv6 message using the public key contained in the selected cert. In addition, the Server Identifier option MUST be included if it is in the original message (i.e. Request, Renew, Decline, Release) to avoid the need for other servers receiving the message to attempt to decrypt it. The Encrypted-Query message MUST include the Encryption-Key-Tag option to identify the used public/private key pair, which is constructed as explained in Section 10.1.5. The Encrypted-Query message MUST NOT contain any other DHCPv6 option except the Server Identifier option, Encryption-Key-Tag option, Encrypted-Message option.
The first DHCPv6 message sent from the client to the server, such as Solicit message, MUST contain the Certificate option, Signature option and Increasing-number option for client authentication. The encryption text SHOULD be formatted as explain in [RFC5652]. The Certificate option MUST be constructed as explained in Section 10.1.2. In addition, one and only one Signature option MUST be contained, which MUST be constructed as explained in Section 10.1.3. One and only one Increasing-number option SHOULD be contained, which MUST be constructed as explained in Section 10.1.4. In addition, the subsequent encrypted DHCPv6 message sent from the client can also contain the Increasing-number option to defend against replay attack.
For the received Encrypted-Response message, the client MUST drop the Encrypted-Response message if other DHCPv6 option except Encrypted-message option is contained. Then, the client extracts the Encrypted-message option and decrypts it using its private key to obtain the original DHCPv6 message. In this document, it is assumed that the client uses only one certificate for the encrypted DHCPv6 configuration. So, the corresponding private key is used for decryption. After the decryption, it handles the message as per [RFC3315]. If the decrypted DHCPv6 message contains the Increasing-number option, the DHCPv6 client checks it according to the rule defined in Section 9.1.
If the client fails to get the proper parameters from the chosen server(s), it can select another authenticated certificate and send the Encrypted-Query message to another authenticated server(s) for parameters configuration until the client obtains the proper parameters.
When the decrypted message is 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 secure DHCPv6 server is pre-configured with a certificate and its corresponding private key for server authentication. If the server does not obtain the certificate from Certificate Authority (CA), it can generate the self-signed certificate.
When the DHCPv6 server receives the Information-request message and the contained Option Request option identifies the request is for the server's certificate information, it SHOULD first check the hash, signature, encryption algorithms sets that the client supports. The server selects one hash, signature, encryption algorithm from the acknowledged algorithms sets for the future communication. And then, the server 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 10.1.2, and Server Identifier option. In addition, the Reply message MUST contain one and only one Signature option, which MUST be constructed as explained in Section 10.1.3. Besides, the Reply message SHOULD contain one and only one Increasing-number option, which MUST be constructed as explained in Section 10.1.4.
Upon the receipt of Encrypted-Query message, the server MUST drop the message if the other DHCPv6 option is contained except Server Identifier option, Encryption-Key-Tag option, Encrypted-message option. Then, the server checks the Server Identifier option. The DHCPv6 server drops the message that is not for it, thus not paying cost to decrypt messages. If it is the target server, according to the Encryption-Key-Tag option, the server identifies the used public/private key pair and decrypts the Encrypted-message option using the corresponding private key. If the decryption fails, the server discards the received message.
If secure DHCPv6 server needs client authentication and decrypted message is a Solicit/Information-request message which contains the information for client authentication, the secure DHCPv6 server discards the received message that meets any of the following conditions:
For the signature failure, the server SHOULD send an encrypted Reply message with an UnspecFail (value 1, [RFC3315]) error status code to the client.
The server validates the client's certificate through the local pre-configured trusted certificates list. A certificate that finds a match in the local trust certificates list is treated as verified. The message that fails authentication validation MUST be dropped. In such failure, the DHCPv6 server replies with an encrypted Reply message 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 Increasing-number option, the server checks it according to the rule defined in Section 9.1. If the check fails, an encrypted Reply message with a ReplayDetected error status code, defined in Section 10.3, should be sent back to the client. In the Reply message, a Increasing-number option is carried to indicate the server's stored number for the client to use. According to the server's local policy, the message without an Increasing-number option MAY be acceptable or rejected.
The Signature field verification MUST show that the signature has been calculated as specified in Section 10.1.3. If the signature check fails, the DHCPv6 server SHOULD send an encrypted Reply message with a SignatureFail error status code. Only the clients that get through both the signature verification and increasing number check (if there is a Increasing-number option) are accepted as authenticated clients and continue to be handled their message as defined in [RFC3315].
Once the client has been authenticated, the DHCPv6 server sends the Encrypted-response message to the DHCPv6 client. The Encrypted-response message MUST only contain the Encrypted-message option, which MUST be constructed as explained in Section 10.1.6. The encryption text SHOULD be formatted as explain in [RFC5652]. 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 Increasing-number option can be contained in the encrypted DHCPv6 message.
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 Increasing-number option, aside from those present in the innermost encapsulated messages from the client or server.
In order to check the Increasing-number option, defined in Section 10.1.4, the client/server has one stable stored number for replay attack detection. The server should keep a record of the increasing number forever. And the client keeps a record of the increasing number during the DHCPv6 configuration process with the DHCPv6 server. And the client can forget the increasing number information after the transaction is finished. The client's initial locally stored increasing number is zero.
It is essential to remember that the increasing number is finite. All arithmetic dealing with sequence numbers must be performed modulo 2^64. This unsigned arithmetic preserves the relationship of sequence numbers as they cycle from 2^64 - 1 to 0 again.
In order to check the Increasing-number option, the following comparison is needed.
NUM.STO = the stored number in the client/server
NUM.REC = the acknowledged number from the received message
The Increasing-number option in the received message passes the increasing number check if NUM.REC is more than NUM.STO. And then, the value of NUM.STO is changed into the value of NUM.REC.
The increasing number check fails if NUM.REC is equal with or less than NUM.STO
It is should be noted that
This section describes the extensions to DHCPv6. Six new DHCPv6 options, two new DHCPv6 messages and six new status codes are defined.
The Algorithm option carries the algorithms sets for algorithm agility, which is contained in the Information-request message.
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_ALGORITHM | option-len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . EA-id List . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . SA-id List . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . HA-id List . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Algorithm Option
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| EA-len | EA-id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. ... .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| EA-id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
EA-len The length of the following EA-ids.
EA-id 2-octets value to indicate the Encryption Algorithm id.
The client enumerates the list of encryption algorithms it
supports to the server. 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. The mandatory encryption
algorithms MUST be included.
Figure 3: EA-id List Field
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SA-len | SA-id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. ... .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SA-id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
SA-len The length of the following SA-ids.
SA-id 2-octets value to indicate the Signature Algorithm id.
The client enumerates the list of signature algorithms it
supports to the server. 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 12. The mandatory
signature algorithms MUST be included.
Figure 4: SA-id List Field
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| HA-len | HA-id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. ... .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| HA-id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
HA-len The length of the following HA-ids.
HA-id 2-octets value to indicate the Hash Algorithm id.
The client enumerates the list of hash algorithms it
supports to the server. 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 12.
The mandatory hash algorithms MUST be included.
Figure 5: HA-id List Field
The Certificate option carries the certificate of the client/server, which is contained in the Reply message. 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | EA-id | SA-id | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | . Certificate . | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: Certificate Option
It should be noticed that the scenario where the values of EA-id and SA-id are both 0 makes no sense and the client MUST discard a message with such values.
The Signature option contains a signature that is signed by the private key to be attached to the Reply message. The Signature option could be in any place within the DHCPv6 message while it is logically created after the entire DHCPv6 header and options. It protects the entire DHCPv6 header and options, including itself. 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SA-id | HA-id | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | . Signature (variable length) . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: Signature Option
Note: If Secure DHCPv6 is used, the DHCPv6 message is encrypted in a way that the authentication mechanism defined in RFC3315 does not understand. So the Authentication option SHOULD NOT be used if Secure DHCPv6 is applied.
The Increasing-number option carries the strictly increasing number for anti-replay protection, which is contained in the Reply message and the encrypted DHCPv6 message. 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_INCREASING_NUM | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Increasing-Num (64-bit) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
option-code OPTION_INCREASING_NUM (TBA4).
option-len 8, in octets.
Increasing-Num A strictly increasing number for the replay attack detection
which is more than the local stored number.
Figure 8: Increasing-number Option
The Encryption-Key-Tag option carries the key identifier which is calculated from the public key data. The Encrypted-Query message MUST contain the Encryption-Key-Tag option to identify the used public/private key pair.
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_ENCRYPTION_KEY_TAG | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. encryption key tag .
. (variable) .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9: Encryption-Key-Tag Option
The Encrypted-message option carries the encrypted DHCPv6 message, which is calculated with the recipient's public key. The Encrypted-message option is contained in the Encrypted-Query message or the Encrypted-Response message.
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 10: Encrypted-message Option
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 11: The format of Encrypted-Query and Encrypted-Response Messages
The following new status codes, see Section 5.4 of [RFC3315] are defined.
This document provides the authentication and encryption mechanisms for DHCPv6.
[RFC6273] has analyzed possible threats to the hash algorithms used in SEND. Since 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 Secure DHCPv6.
There are some mandatory algorithm for encryption algorithm in this document. It may be at some point that the mandatory algorithm is no longer safe to use.
A server or a client, whose local policy accepts messages without a Increasing-number option, may have to face the risk of replay attacks.
If the client tries more than one cert for client authentication, the server can easily get a client that implements this to enumerate its entire cert list and probably learn a lot about a client that way. For this security item, It is RECOMMENDED that client certificates could be tied to specific server certificates by configuration.
This document defines six new DHCPv6 [RFC3315] options. The IANA is requested to assign values for these six options from the DHCPv6 Option Codes table of the DHCPv6 Parameters registry maintained in http://www.iana.org/assignments/dhcpv6-parameters. The six options are:
The IANA is also requested to assign value for these two messages from the DHCPv6 Message Types table of the DHCPv6 Parameters registry maintained in http://www.iana.org/assignments/dhcpv6-parameters. The two messages are:
The IANA is also requested to add three new registry tables to the DHCPv6 Parameters registry maintained in http://www.iana.org/assignments/dhcpv6-parameters. The three tables are the Hash Algorithm for Secure DHCPv6 table, the Signature Algorithm for Secure DHCPv6 table and 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.
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
-------------------+---------+--------------
SigAlg-Combined | ox00 | this document
SHA-256 | 0x01 | this document
SHA-512 | 0x02 | this document
Name | Value | RFCs
-------------------+---------+--------------
Non-SigAlg | 0x00 | this document
RSASSA-PKCS1-v1_5 | 0x01 | this document
Name | Value | RFCs
-------------------+---------+--------------
Non-EncryAlg | 0x00 | this document
RSA | 0x01 | this document
IANA is requested to assign the following new DHCPv6 Status Codes, defined in Section 10.3, in the DHCPv6 Parameters registry maintained in http://www.iana.org/assignments/dhcpv6-parameters:
Code | Name | Reference
---------+-----------------------+--------------
TBD9 | AuthenticationFail | this document
TBD10 | ReplayDetected | this document
TBD11 | SignatureFail | this document
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, Zilong Liu and other members of the IETF DHC working group for their valuable comments.
This document was produced using the xml2rfc tool [RFC2629].
| [RFC2629] | Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629, DOI 10.17487/RFC2629, June 1999. |
| [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. |
| [RFC6273] | Kukec, A., Krishnan, S. and S. Jiang, "The Secure Neighbor Discovery (SEND) Hash Threat Analysis", RFC 6273, DOI 10.17487/RFC6273, June 2011. |
| [RFC7258] | Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May 2014. |
| [RSA] | RSA Laboratories, "RSA Encryption Standard, Version 2.1, PKCS 1", November 2002. |