DNS Extensions H. Rafiee INTERNET-DRAFT Hasso Plattner Institute Updates RFC 2845 (if approved) M. v. Loewis Intended Status: Standards Track Hasso Plattner Institute C. Meinel Hasso Plattner Institute Expires: August 24, 2013 February 24, 2013 Transaction SIGnature (TSIG) using CGA Algorithm in IPv6 Abstract The first step in the Transaction SIGnature (TSIG) (RFC 2845) process is the generation of a shared secret to be used between a DNS server and a host. The second step consists of modifying the DNS configuration so that the DNS server will know what key to use with which host, because this shared secret is only valid between a pair of hosts. This document, CGA-TSIG, proposes a possible way to eliminate the human intervention needed for the generation and exchange of keys between a DNS server and a host when SEcure Neighbor Discovery (SEND) (RFC 3971) is used. CGA-TSIG will facilitate the authentication process of a host with a DNS server and will reduce the time needed to accomplish DNS Updates. It will also provide a means for securing the authentication process between resolvers and clients. CGA-TSIG will be added, as an extension, to TSIG in order to provide data integrity and proof of IP address ownership. The current signature generation and verification process used in TSIG will be substituted with the use of the same parameters as are used in generating a secure address in IPv6 networks, i.e., Cryptographically Generated Addresses (CGA) (RFC 3972). Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering 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." Rafiee, et al. Expires August 24, 2013 [Page 1] INTERNET DRAFT TSIG using CGA in IPv6 February 24, 2013 This Internet-Draft will expire on May 20, 2013. Copyright Notice Copyright (c) 2012 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. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Conventions used in this document . . . . . . . . . . . . . . 3 3. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 3 3.1. IP Spoofing and Reflector Attacks . . . . . . . . . . . . 5 3.2. DNS Dynamic Update Spoofing . . . . . . . . . . . . . . . 5 3.3. Resolver Configuration Attack . . . . . . . . . . . . . . 5 3.4. Exposing Shared Secret (key pairs) . . . . . . . . . . . 5 3.5. Replay attack . . . . . . . . . . . . . . . . . . . . . . 5 4. Algorithm Overview . . . . . . . . . . . . . . . . . . . . . 6 4.1. Modification to the TSIG Record . . . . . . . . . . . . . 6 4.2. Generation of CGA-TSIG DATA . . . . . . . . . . . . . . . 9 4.3. Verification of the CGA-TSIG DATA for DNS update messages 11 4.4. Verification of the CGA-TSIG DATA for DNS Query Response 13 5. Security Considerations . . . . . . . . . . . . . . . . . . . 14 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 7. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 16 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16 9.1. Normative . . . . . . . . . . . . . . . . . . . . . . . . 16 9.2. Informative . . . . . . . . . . . . . . . . . . . . . . . 17 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18 Rafiee, et al. Expires August 24, 2013 [Page 2] INTERNET DRAFT TSIG using CGA in IPv6 February 24, 2013 1. Introduction Transaction SIGnature (TSIG) [RFC2845] is a protocol that provides endpoint authentication and data integrity by the use of one-way hashing and shared secret keys in order to establish a trust relationship between two hosts which can be either a client and a server, or two servers. The TSIG keys, which are manually exchanged between these two hosts, need to be maintained in a secure manner. This protocol is used to secure a Dynamic Update, or to give assurance to the slave name server, that the zone transfer is from the original master name server and that it has not been spoofed by hackers. It does this by verifying the signature using a cryptographic key that is shared with the receiver. It is possible to extend the TSIG protocol with the use of newly defined algorithms. This document proposes the use of Cryptographically Generated Addresses (CGA) [RFC3972] for use as a new algorithm in the TSIG Resource Record (RR). CGA is an important option available in SEcure Neighbor Discovery (SEND) [RFC3971] which provides nodes with the necessary proof of IP address ownership by providing a cryptographic binding between a host and its IP address without the need for the introduction of a new infrastructure. CGA is a one-way hashing algorithm used to generate Interface IDs for IPv6 addresses in a secure manner. An interface ID consists of the rightmost 64 bits of the 128 bit IPv6 address. CGA verifies the ownership of the sender's IP address by finding a relationship between the sender's IP address and his public key [1,2]. +------------------------------------------------+ | Subnet Prefix | Interface ID | | (8 octets) | (8 octets) | +------------------------------------------------+ Figure 1 IPv6 addresses 2. Conventions used in this document 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 RFC-2119 [RFC2119]. In this document, these words will appear with that interpretation only when in ALL CAPS. Lower case uses of these words are not to be interpreted as carrying RFC-2119 significance. 3. Problem Statement Rafiee, et al. Expires August 24, 2013 [Page 3] INTERNET DRAFT TSIG using CGA in IPv6 February 24, 2013 This document addresses the authentication problems associated with the need for hosts to change their IP addresses frequently in order to maintain privacy. This problem is present in two different situations: the authentication of a resolver with a client and the authentication of two hosts (a client and a DNS server and two DNS servers) during the DNS Update process. The DNS Update process is vulnerable to several types of spoofing attacks -- man in the middle, reflector , source IP spoofing, etc. TSIG secures this process by providing the transaction level authentication necessary by use of a shared secret. The problem is that this protocol is not widely used. The current problem with the use of TSIG is the need for manual processing required to generate and exchange the shared secrets. For each paired host there needs to be one shared secret and the administrator needs to add it manually to the DNS configuration file for each of these hosts. So, whenever these two hosts change their IP addresses, because of privacy issues as explained in RFC-4941 [RFC4941] or when moving to another subnet within the same network, this manual process will need to be invoked. The purpose of CGA-TSIG is to minimize the amount of human intervention required to accomplish this exchange and, as a byproduct, to reduce the process's vulnerability to attacks introduced by human errors when SEcure Neighbor Discovery (SEND) is used for addressing purposes. This same problem exists between a client and a DNS resolver. When a client sends a DNS query to a resolver, an attacker can send a response to this client with the spoofed source IP address of this resolver. The client checks the resolver's source IP address for authentication. If the attacker spoofed the resolver's IP address and if the attacker responds faster than the legitimate resolver, then the client's cache will be updated with the attacker's response. The client does not have any way to authenticate the resolver. In the above scenario, the resolver SHOULD add the TSIG Resource Record (RR) to the DNS query response and use the CGA-TSIG Algorithm. CGA-TSIG assures the client that the query response comes from the true originator and not from an attacker. Currently there is no consideration for the use of the TSIG RR for resolver authentication with clients. One reason is that resolvers respond to anonymous queries and can be located in any part of the network. A second reason is that the manual TSIG process makes it hard to configure each new client with the shared secret of the resolver. There are several types of attack that CGA-TSIG can prevent. Here we will evaluate some of them. The use of CGA-TSIG will also reduce the number of messages needed in exchange between a client and a server in order to establish a secure channel. Normally, to initiate a secure DNS Update process between a DNS server and a host (another DNS server or a client), a minimum of four messages are required for the establishment of a secure channel (especially for another secure DNS Update mechanism, DNSSEC). Modifying RFC-2845 to use CGA-TSIG will decrease the number of messages needed in the exchange. The Rafiee, et al. Expires August 24, 2013 [Page 4] INTERNET DRAFT TSIG using CGA in IPv6 February 24, 2013 messages used in RFC-2930 (TKEY RR) are not needed when CGA-TSIG is used. 3.1. IP Spoofing and Reflector Attacks During the DNS Update process it is important that both communicating parties know that the one that they are communicating with is the actual owner of that IP address and that the messages are not being sent from a spoofed IP address. This can be accomplished by the use of the CGA algorithm that utilizes the node for IP address verification of other nodes. The reflector attack is a kind of distributed Denial of Service attack. It uses the IP address of the victim as a source of the DNS message and sends several queries to the DNS server, which then redirects this traffic to the victim, thus keeping the victim busy processing these packets. Using the CGA signature and authentication approach will prevent this type of attack. 3.2. DNS Dynamic Update Spoofing Dynamic Update Spoofing is eliminated because the signature contains both the CGA parameters and the DNS update message. This will offer proof of the sender's IP address ownership (CGA parameters) and the validity of the update message. 3.3. Resolver Configuration Attack In CGA-TSIG, the DNS server, or the client, would not need further configuration. This would reduce the possibility of human errors being inserted into the DNS configuration file. Since this type of attack is predicated on human error, the chances of it occurring, when our proposed extension is used, are minimized. 3.4. Exposing Shared Secret (key pairs) In order to decrease the chances of attackers gaining unauthorized access to private keys on a node, it is recommended that key pairs be generated "on-the-fly". 3.5. Replay attack Using the Time Signed value in the signature modifies the content of the signature each time the node generates it and sends it to the DNS Rafiee, et al. Expires August 24, 2013 [Page 5] INTERNET DRAFT TSIG using CGA in IPv6 February 24, 2013 server. This value is the node's current time in UTC. If the attacker tries to spoof this value with another timestamp, to show that the update message is current, the DNS server checks this message by verifying and regenerating the signature (when the private key of the other DNS server is manually set in this DNS server). In this case steps 2 and 8 of verification process will fail and thus the replay attack will also be prevented. 4. Algorithm Overview The following sections explain the use of CGA, or other future algorithms used in place of CGA, for securing the DNS process when using the TSIG Resource Record (RR). 4.1. Modification to the TSIG Record The modified TSIG Resource Record (RR) will use the same format as the other RRs in use in the DNS field. The DNS RR format is explained in section 3.2.1 RFC-1035 [RFC1035], where the algorithm type must be set to TSIG. The RDATA field is also extended in order to provide a place to store the CGA-TSIG DATA (see figures 2 and 3). The RDATA Algorithm type must be set to CGA-TSIG. A detailed explanation of the RDATA standard fields can be found in section 2.3 RFC-2845. This document focuses only on the new extensions added to the RDATA field. These new fields are CGA-TSIG Len and CGA-TSIG DATA. TSIG RR is added to an additional section of the DNS messages. The general format for DNS messages is explained in RFC1035 [section 4.1 RFC-1035]. If another algorithm is used in place of CGA for SEND, such as SSAS [4], then CGA-TSIG Len will be the length for the parameters of this algorithm and CGA-TSIG DATA will consist of the parameters required for verification of that algorithm, like signature, public key, etc. +---------------------------------------+ | Algorithm type | | (CGA-TSIG) | +---------------------------------------+ | Time Signed | | | +---------------------------------------+ | Fudge | | | +---------------------------------------+ | MAC Size | | | +---------------------------------------+ | Mac | | | +---------------------------------------+ Rafiee, et al. Expires August 24, 2013 [Page 6] INTERNET DRAFT TSIG using CGA in IPv6 February 24, 2013 | Original ID | | | +---------------------------------------+ | Error | | | +---------------------------------------+ | OTHER LEN | | | +---------------------------------------+ | OTHER DATA | | | +---------------------------------------+ Figure 2 Modified TSIG RDATA CGA-TSIG DATA Field and CGA-TSIG Len will occupy the first two slots of Other DATA. Figure 3 shows the layout. +---------------------------------------+ | CGA-TSIG Len | | | +---------------------------------------+ | CGA-TSIG DATA | | | +---------------------------------------+ | Other Options | | | +---------------------------------------+ Figure 3 Other DATA section of RDATA field CGA-TSIG DATA Field Name Data Type Notes -------------------------------------------------------------- Algorithm type u_int16_t Name of the algorithm [RFC3972] RSA (by default) CGA type u_int16_t Name of the algorithm used in SEND IP tag 16 octet the tag used to identify the IP address Parameters Len Octet the length of CGA parameters Parameters variable CGA parameters Section 3 RFC-3972 Signature Len Octet the length of CGA signature Signature variable Section 3.2.1 This document old pubkey Len variable the length of old public key field old pubkey variable Old public key old Signature Len variable the length of old signature field old Signature variable Old signature generated by old public key. Rafiee, et al. Expires August 24, 2013 [Page 7] INTERNET DRAFT TSIG using CGA in IPv6 February 24, 2013 +---------------------------------------+ | Algorithm type | | | +---------------------------------------+ | Type | | | +---------------------------------------+ | IP tag | | (16 bytes) | +---------------------------------------+ | Parameter Len | | (1 byte) | +---------------------------------------+ | Parameters | | (variable) | +---------------------------------------+ | Signature Len | | (1 byte) | +---------------------------------------+ | Signature | | (variable) | +---------------------------------------+ | old pubkey Len | | (1 byte) | +---------------------------------------+ | old pubkey | | (variable) | +---------------------------------------+ | old Signature Len | | (1 byte) | +---------------------------------------+ | old Signature | | (variable) | +---------------------------------------+ Figure 4 CGA-TSIG DATA Field Type indicates the Interface ID generation algorithm that was used in SEND. This field allows for the use of future algorithms in place of CGA. The default value for CGA is 1. Other algorithms would be assigned a new number sequentially. For example, a new algorithm called SSAS could be assigned a value of 2. The IP tag is a node's old IP address. It is only used during the DNS update process and not for resolving a query. A client's public key can be associated with several IP addresses on a server. The DNS server, or the DNS message verifier node, SHOULD store the IP addresses and the public keys so as to indicate their association to each other. An example of how to store this formated data in mysql is shown in figure 5. If a client wants to add RRs to the server by using a new IP address, then the IP tag field will be set to binary zeros. The server will then store the new IP address that was passed to it in storage. (Figure 5 shows how to store it in the CGATSIGIPs table.) If the client wants to replace Rafiee, et al. Expires August 24, 2013 [Page 8] INTERNET DRAFT TSIG using CGA in IPv6 February 24, 2013 an existing IP address in a DNS server with a new one, then the IP tag field will be populated with the IP address which is to be replaced. The DNS server will then look for the IP address referenced by the IP tag stored in its storage and replace that IP address with the new one. This enables the client to update his own RRs using multiple IP addresses while, at the same time, giving him the ability to change IP addresses. If a node changes its public key in order to maintaining privacy, then it SHOULD add the old public key to the old pubkey field. It SHOULD also retrieve the current time from Time signed field, sign it using the old private key, and add the digest (signature) to the old signature field. This enables the verifier node to authenticate a host with a new public key. The detailed verification steps are explained in section 4.3. and section 4.4. Note: When a host sends a DNS message to a DNS server or a client for the first time, the verifier host SHOULD save the public key for this client/resolver in a storage. (Figure 5 table CGATSIGkeys shows an example.) create table cgatsigkeys ( id INT auto_increment, pubkey VARCHAR(300), primary key(id) ); create table cgatsigips ( id INT auto_increment, idkey INT, IP VARCHAR(20), FOREIGN KEY (idkey) REFERENCES cgatsigkeys(id) primary key(id) ); Figure 5 CGA-TSIG tables on mysql backend database 4.2. Generation of CGA-TSIG DATA All DNS messages, except those from a client resolving a query, need to contain the CGA-TSIG option. To generate the CGA-TSIG DATA, a host must execute the following steps. Figure 6 shows what parameters SHOULD be cached by a host for further usage by the CGA-TSIG algorithm. If the Type (section 4.1) is CGA, then the parameters that SHOULD be cached are the modifier, algorithm type, location of the public/private keys and the IP addresses of this host. For example, the modifier is stored as bytes and each byte should be separated by a comma (for example : 284,25,14,...). Algorithmtype is the algorithm used in signing the message. Zero is the default algorithm for RSA. Secval is the CGA Sec value that is, by default, one. GIP is the global IP address of this node (for example: 2001:abc:def:1234:567:89a). oGIP is the old IP address of this node, Rafiee, et al. Expires August 24, 2013 [Page 9] INTERNET DRAFT TSIG using CGA in IPv6 February 24, 2013 before the generation of the new IP address. Keys contains the path where the CGA-TSIG algorithm can find the PEM format used for the public/private keys (for example: /home/myuser/keys.pem ).
Figure 6 XML file contains the cached DATA 1.Obtain required parameters from cache. The CGA-TSIG algorithm obtains the old IP address, modifier, subnet prefix, public key from the cache (XML file). It concatenates the old IP address with the CGA parameters, i.e., modifier, subnet prefix, public key and collision count (the order of CGA parameters are shown in section 3 RFC-3972). If the old IP address is not available, CGA-TSIG must set the old IP address (IP tag) to zero. In the case of processing a DNS update for multiple DNS servers (authentication of two DNS servers), there are three possible scenarios with regard to the authentication process, which differs from that of the authentication of a node (client) with one DNS server, because of the need for human intervention. These scenarios do not apply to the authentication of a resolver to a client. a. Add the DNS servers' IP address to a slave configuration file A DNS server administrator should only manually add the IP address of the master DNS server to the configuration file of the slave DNS server. When the DNS update message is processed, the slave DNS server can authenticate the master DNS server based on the source IP address and then, prove the ownership of this address by using the CGA-TSIG option from the TSIG RR. This scenario will be valid until the IP address in any of these DNS servers changes. To automate this step's process, the DNS Update message sender's public key must be saved on the other DNS server, after the source IP address has been successfully verified for the first time. In this case, when the sender generates a new IP address by executing the CGA algorithm using the same public key, the other DNS server can still verify it and add its new IP address to the DNS configuration file automatically. Rafiee, et al. Expires August 24, 2013 [Page 10] INTERNET DRAFT TSIG using CGA in IPv6 February 24, 2013 b. Retrieve public/private keys from a third party Trusted Authority (TA) The message exchange option of SEND [RFC3971] may be used for the retrieval of the third party certificate. This may be done automatically from the TA by using the Certificate Path Solicitation and the Certificate Path Advertisement messages. Like in scenario b, saving the certificate on the DNS server for later use in the generation of its address or in the DNS update process. In this case, whenever any of these servers want to generate a new IP address, the DNS update process can still be done automatically without the need for human intervention. 2. Generate signature For signature generation, all CGA parameters (modifier, public key, collision count and subnet prefix), that are concatenated with the DNS update message, IP tag and the Time Signed field, are signed by using a RSA algorithm, the default, or any future algorithm used in place of RSA, and the private key which was obtained from cache in the first step. This signature must be added to the signature field of the CGA-TSIG DATA. Time Signed is the same timestamp as is used in RDATA. This value is the UTC date and time value obtained from the signature generator. This approach will prevent replay attacks by changing the content of the signature each time a node wants to send a DNS message. The format of DNS messages is explained in section 4.1.2 RFC-1035 [RFC1035]. +-----------------------------------------------------------+ | Modifier | Subnet Prefix |collision count | Public key | | (128 bits)| (64 bits) | (8 bit) | (variable) | +-----------------------------------------------------------+ | IP tag |Time Signed | DNS Update Message | | (128 bits)| | | +-----------------------------------------------------------+ Figure 7 CGA-TSIG Signature 3. Generate old signature If the nodes generated new key pairs, then they need to add the old public key and messag,e signed by the old private key, to the CGA-TSIG DATA. A node will retrieve the timestamp from Time Signed, will use the old private key to sign it, and then will add the content of this signature to old signature field of the CGA-TSIG DATA. This step MUST be skipped when the node did not generate new key pairs. 4.3. Verification of the CGA-TSIG DATA for DNS update messages Sender authentication is necessary in order to prevent attackers from Rafiee, et al. Expires August 24, 2013 [Page 11] INTERNET DRAFT TSIG using CGA in IPv6 February 24, 2013 making unauthorized modifications to DNS servers through the use of spoofed DNS messages. The verification process uses the following steps: 1. Execute the CGA verification These steps are found in section 5 RFC-3972. If the sender of the DNS message uses another algorithm instead of CGA, then this step becomes the verification step for that algorithm. If the verification process is successfu,l then step 2 will be executed. Otherwise the message will be discarded without further action. 2. Check the Time Signed The Time Signed value is obtained from the TSIG RDATA and is called t1. The current system time is then obtained and converted to UTC time and is called t2. If t1 is in the range of t2 and t2 minus x minutes (see formula 1, x minutes may vary according to the transmission lag time) then step 3 will be executed, otherwise, the message will be considered a spoofed message and the message should be discarded without further action. The range is used in consideration of the delays that can occur during its transmission over TCP or UDP. Both times must use UTC time in order to avoid differences in time based on different geographical locations. t2-x <= t1 <= t2 (1) 3. Verify the signature The signature contained in the CGA-TSIG DATA should be verified. This can be done by retrieving the public key and signature from the CGA-TSIG DATA and using this public key to verify the signature. If the verification process is successful and the node does not want to update another node's RR, then the Update Message will be processed. If the signature verification is successful and the node wants to update another node's RRs, then step 4 will be executed. If the verification fails, then the message should be discarded without further action. 4. Verify the Source IP address If a node wants to update a/many RR(s) on another DNS server, like a master DNS server wanting to update RRs on the slave DNS server, then the requester source IP address must be checked against the one contained in the DNS configuration file. If it is the same, then the Update Message should be processed, otherwise, step 5 will be executed. 5. Verify the public key The DNS server checks whether or not the public key retrieved from the CGA-TSIG DATA is the same as what was available in the storage where the public keys and IP addresses were saved. If it is the same, Rafiee, et al. Expires August 24, 2013 [Page 12] INTERNET DRAFT TSIG using CGA in IPv6 February 24, 2013 then the Update Message should be processed, otherwise step 6 will be executed. 6. Verify the old public key If the old public key length is zero, then skip this step and discard the DNS update message without further action. If the old public key length is not zero, then the DNS server will retrieve the old public key from the CGA-TSIG DATA and will check whether or not it is the same as what was saved in the DNS server's storage where the public keys and IP addresses are stored. If it is the same, then step 7 will be executed, otherwise the message should be discarded without further action. 7. Verify the old signature The old signature contained in the CGA-TSIG DATA should be verified. This can be done by retrieving the old public key and old signature from the CGA-TSIG DATA and using this old public key to verify the old signature. If the verification is successful, then the Update Message should be processed and the new public key should be replaced with the old public key in the DNS server. If the verification process fails, then the message should be discarded without further action. 4.4. Verification of the CGA-TSIG DATA for DNS Query Response A DNS query request sent by a host, such as a client or a mail server, does not need to include the CGA-TSIG DATA because the resolver responds to anonymous queries. But the resolver's response SHOULD contain the CGA-TSIG DATA field in order to enable this client to verify him. When a resolver responds to the host's query request for the first time, the client saves its public key in a file. This allows the client to verify this resolver when it changes its IP address due to privacy or security issues. The first 2 steps in the verification process are the same as the similar steps explained in section 4.3. These steps are as follows: 1. Execute the CGA verification 2. Check the Time Signed 3. Verify the Source IP address If the resolver's source IP address is the same as that which is known for the host, then step 4 will be executed. Otherwise the message SHOULD be discarded without further action. 4. Verify the signature The signature contained in the CGA-TSIG DATA should be verified. This Rafiee, et al. Expires August 24, 2013 [Page 13] INTERNET DRAFT TSIG using CGA in IPv6 February 24, 2013 can be done by retrieving the public key and signature from the CGA-TSIG DATA and using this public key to verify the signature. If the verification process is successful, then step 4 will be executed. If the verification fails, then the message should be discarded without further action. 5. Verify the public key The host checks whether or not the public key retrieved from the CGA-TSIG DATA is the same as what was available in the storage where the public keys and IP addresses of resolvers are saved. If it is the same, then the message is processed. If not, then step 5 will be executed. 5. Verify the old public key If the old public key length is zero, then skip this step and discard the DNS query response without further action. If the old public key length is not zero, then the host will retrieve the old public key from the CGA-TSIG DATA and will check whether or not it is the same as what was saved in the host's storage where the public keys and IP addresses are stored. If it is the same, then step 6 will be executed, otherwise the message should be discarded without further action. 6. Verify the old signature The old signature contained in the CGA-TSIG DATA should be verified. This can be done by retrieving the old public key and old signature from the CGA-TSIG DATA and using this old public key to verify the old signature. If the verification is successful, then the DNS Message should be processed and the new public key should be replaced with the old public key of the resolver in the host. If the verification process fails, then the message should be discarded without further action. 5. Security Considerations Rafiee, et al. Expires August 24, 2013 [Page 14] INTERNET DRAFT TSIG using CGA in IPv6 February 24, 2013 The solution explained in this draft, CGA-TSIG, is an approach that can secure DNS messages from spoofing type attacks as explained in section 3. Note: If a host does not support CGA-TSIG, the CGA-TSIG DATA Field SHOULD be ignored. It is RECOMMENDED that both communicating nodes support this option in order to diminish the possibility for the occurrence of the attacks explained in section 3. The problem that can arise here are attacks against the CGA algorithm. In this section we explain the possibility of attacks against CGA [5] itself, and explain the available solutions that we considered in this draft. a) Discover an Alternative Key Pair Hashing of the Victim's Node Address In this case an attacker would have to find an alternate key pair hashing of the victim?s address. The success of this attack will rely on the security properties of the underlying hash function, i.e., an attacker will need to break the second pre-image resistance of that hash function. The attacker will perform a second pre-image attack on a specific address in order to match other CGA parameters with Hash1 and Hash2. The cost of doing so is (2^59+1) * 2^(16?1). If the user uses a sufficient security level, it will be not feasible for an attacker to carry out this attack due to the cost involved. Changing the IP address frequently will also decrease the chance for this attack. b) DoS to Kill a CGA Node Sending a valid or invalid CGA signed message with high frequency across the network can keep the destination node(s) busy with the verification process. This type of DoS attack is not specific to CGA, but it can be applied to any request-response protocol. One possible solution to mitigate this attack is to add a controller at the verifier side to determine the maximum number of messages that the receiver can accept within a certain period of time from a specific node. If this threshold rate is exceeded, the receiver drops any new incoming messages from that node. c) CGA Privacy Implication Due to the high computational complexity necessary for the creation of a CGA, it is likely that once a node generates an acceptable CGA it will continue its use at that subnet. The result is that nodes using CGAs are still susceptible to privacy related attacks. One solution to these types of attacks is setting a lifetime for the address as explained in RFC-4941. Rafiee, et al. Expires August 24, 2013 [Page 15] INTERNET DRAFT TSIG using CGA in IPv6 February 24, 2013 6. IANA Considerations The IANA has allowed for choosing new algorithm(s) for use in the TSIG Algorithm name. Algorithm name refers to the algorithm described in this document. The requirement to have this name registered with IANA is specified. 7. Conclusions In TSIG, not all processing is done automatically and some steps might even need to be done offline. To address this issue, and to automate this process when Secure Neighbor Discovery (SEND) (RFC3971) is used, this document introduces an extension to the TSIG protocol (CGA-TSIG) in order to take advantage of the use of CGA for the DNS Update authentication process of a node within a DNS server. CGA-TSIG also decreases the number of messages needed in the exchange between the DNS server and the DNS client during the update process. This enhances the performance of the DNS update process. Since CGA does not need Public Key Infrastructure (PKI) framework to verify the node's IP address ownerships, the authentication of a node with a DNS server in the DNS update process is automated. This document also makes use of SEND for the authentication of two DNS servers together when processing DNS Update messages. However ,the first step should be done manually, the first time it is used, to afford greater security for this process. This document also proposes an automatic process for authenticating a resolver in a client. This will help to eliminate the possibility of attacks against a client's DNS during the query request and responses processes. 8. Acknowledgements The author would like to thank all those who helped directly in improving of this draft and all supporters of this draft especially Ralph Droms, Andrew Sullivan and Brian Haberman. 9. References 9.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)," RFC 3972, March 2005. Rafiee, et al. Expires August 24, 2013 [Page 16] INTERNET DRAFT TSIG using CGA in IPv6 February 24, 2013 [RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure Neighbor Discovery (SEND)", RFC 3971, March 2005. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2930] Eastlake 3rd, D., "Secret Key Establishment for DNS (TKEY RR)", RFC 2930, September 2000. [RFC1035] Mockapetris, P., "Domain Names - Implementation And Specification", RFC 1035, November 1987. [RFC4941] Narten, T., Draves, R., Krishnan, S., "Privacy Extensions for Stateless Address Autoconfiguration in IPv6", RFC 4941, September 2007. [RFC2136] Vixie, P. (Editor), Thomson, S., Rekhter, Y., Bound, J., "Dynamic Updates in the Domain Name System (DNS UPDATE)", RFC 2136, April 1997. 9.2. Informative References [1] Aura, T., "Cryptographically Generated Addresses (CGA)", Lecture Notes in Computer Science, Springer, vol. 2851/2003, pp. 29-43, 2003. [2] Montenegro, G. and Castelluccia, C., "Statistically Unique and Cryptographically Verifiable (SUCV) Identifiers and Addresses," ISOC Symposium on Network and Distributed System Security (NDSS 2002), the Internet Society, 2002. [3] AlSa'deh, A., Rafiee, H., Meinel, C., "IPv6 Stateless Address Autoconfiguration: Balancing Between Security, Privacy and Usability". Lecture Notes in Computer Science, Springer(5th International Symposium on Foundations & Practice of Security (FPS). October 25 - 26, 2012 Montreal, QC, Canada), 2012. [4] Rafiee, H., Meinel, C., "A Simple Secure Addressing Generation Scheme for IPv6 AutoConfiguration (SSAS)". Work in progress, http://tools.ietf.org/html/draft-rafiee-6man-ssas-01, 2013. [5] AlSa'deh, A., Rafiee, H., Meinel, C., ?Cryptographically Generated Addresses (CGAs): Possible Attacks and Proposed Mitigation Approaches,? in 12th IEEE International Conference on Computer and Information Technology (IEEE CIT?12), pp.332-339, 2012. Rafiee, et al. Expires August 24, 2013 [Page 17] INTERNET DRAFT TSIG using CGA in IPv6 February 24, 2013 Authors' Addresses Hosnieh Rafiee Hasso-Plattner-Institute Prof.-Dr.-Helmert-Str. 2-3 Potsdam, Germany Phone: +49 (0)331-5509-546 Email: ietf@rozanak.com Dr. Christoph Meinel (Professor) Hasso-Plattner-Institute Prof.-Dr.-Helmert-Str. 2-3 Potsdam, Germany Email: meinel@hpi.uni-potsdam.de Dr. Martin von Loewis Hasso-Plattner-Institute Prof.-Dr.-Helmert-Str. 2-3 Potsdam, Germany Email: martin@v.loewis.de Rafiee, et al. Expires August 24, 2013 [Page 18]