DNS Extensions H. Rafiee INTERNET-DRAFT Ciber AG Updates RFC 2845 (if approved) M. v. Loewis Intended Status: Standards Track C. Meinel Hasso Plattner Institute Expires: August 15, 2014 February 15, 2014 Secure DNS Authentication using CGA/SSAS Algorithm in IPv6 <draft-rafiee-intarea-cga-tsig-07.txt> Abstract This document describes a new mechanism that can be used to reduce the need for human intervention during DNS authentication and secure DNS authentication in various scenarios such as the DNS authentication of resolvers to stub resolvers, authentication during zone transfers, authentication of root DNS servers to recursive DNS servers, and authentication during the FQDN (RFC 4703) update. Especially in the last scenario, i.e., FQDN, if the node uses the Neighbor Discovery Protocol (NDP) (RFC 4861, RFC 4862), unlike the Dynamic Host Configuration Protocol (DHCP) (RFC 3315), the node has no way of updating his FQDN records on the DNS and has no means for a secure authentication with the DNS server. While this is a major problem in NDP-enabled networks, this is a minor problem in DHCPv6. This is because the DHCP server updates the FQDN records on behalf of the nodes on the network. This document also introduces a possible algorithm for DNS data confidentiality. 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." This Internet-Draft will expire on August 15, 2014. Rafiee, et al. Expires August 15, 2014 [Page 1]
INTERNET DRAFT TSIG using CGA in IPv6 February 15, 2014 Copyright Notice Copyright (c) 2014 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 . . . . . . . . . . . . . . . . . . . . . . . . 4 1.1. Problem Statement . . . . . . . . . . . . . . . . . . . . 4 2. Conventions used in this document . . . . . . . . . . . . . . 5 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6 4. Algorithm overview . . . . . . . . . . . . . . . . . . . . . 7 4.1. The CGA-TSIG DATA structure . . . . . . . . . . . . . . 7 4.2. Generation of CGA-TSIG DATA . . . . . . . . . . . . . . . 9 5. Authentication during Zone Transfer . . . . . . . . . . . . . 12 5.1. Verification process . . . . . . . . . . . . . . . . . . 13 6. Authentication during the FQDN or PTR Update . . . . . . . . 14 6.1. Verification Process . . . . . . . . . . . . . . . . . . 15 7. Authentication during Query Resolving (stub to recursive) . . 15 7.1. Verification process . . . . . . . . . . . . . . . . . . 15 8. Authentication during Query Resolving (Auth. to recursive) . 17 9. No cache parameters available or SeND is not supported . . . 17 10. How to obtain the IP address of resolvers . . . . . . . . . 17 11. CGA-TSIG Data confidentiality . . . . . . . . . . . . . . . 17 11.1. Generation of secret key . . . . . . . . . . . . . . . . 18 11.2. DNS message generation . . . . . . . . . . . . . . . . . 18 11.3. CGA-TSIGe DATA generation . . . . . . . . . . . . . . . 18 11.4. Process of encrypted DNS message . . . . . . . . . . . . 18 12. CGA-TSIG/CGA-TSIGe Applications . . . . . . . . . . . . . . 19 12.1. IP Spoofing . . . . . . . . . . . . . . . . . . . . . . 20 12.2. DNS Dynamic Update Spoofing . . . . . . . . . . . . . . 20 12.3. Resolver Configuration Attack . . . . . . . . . . . . . 20 12.4. Exposing Shared Secret . . . . . . . . . . . . . . . . . 20 12.5. Replay attack . . . . . . . . . . . . . . . . . . . . . 20 12.6. Data confidentiality . . . . . . . . . . . . . . . . . . 21 13. Security Considerations . . . . . . . . . . . . . . . . . . . 21 14. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22 15. Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Rafiee, et al. Expires August 15, 2014 [Page 2]
INTERNET DRAFT TSIG using CGA in IPv6 February 15, 2014 16. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 24 17. References . . . . . . . . . . . . . . . . . . . . . . . . . 24 17.1. Normative . . . . . . . . . . . . . . . . . . . . . . . . 24 17.2. Informative . . . . . . . . . . . . . . . . . . . . . . . 25 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 26 Rafiee, et al. Expires August 15, 2014 [Page 3]
INTERNET DRAFT TSIG using CGA in IPv6 February 15, 2014 1. Introduction Transaction SIGnature (TSIG) [RFC2845] is a protocol that provides endpoint authentication and data integrity through the use of one-way hashing and shared secret keys in order to establish a trust relationship between two/group of hosts, which can be either a client and a server, or two servers. The TSIG keys, which are manually exchanged between a group of hosts, need to be maintained in a secure manner. This protocol is today mostly 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. But, handling this shared secret in a secure manner and exchanging it, does not seem to be easy. This is especially true if the IP addresses are dynamic due to privacy reasons or the shared secret is exposed to attacker. To address the existing problems with TSIG, this document proposes the use of Cryptographically Generated Addresses (CGA) [RFC3972] or Secure Simple Addressing Scheme for IPv6 Authoconfiguration (SSAS) 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?s public key and its IP address without the need for the introduction of a new infrastructure. This document also addresses the DNS data confidentiality by using both asymmetric and symmetric cryptography as well as data integrity. This document updates the following sections in TSIG document - section 4.2: The server MUST not generate a signed response to an unsigned request => The server MUST not generate a signed response to an unsigned request, unless the Algorithm Name filed contains CGA-TSIG. - Section 4.5.2: It MUST include the client's current time in the time signed field, the server's current time (a u_int48_t) in the other data field, and 6 in the other data length field => It MUST include the client's current time in the time signed field, the server's current time (a u_int48_t) in the other data field, and if the Algorithm Name is CGA-TSIG, then add the length of this client?s current time to the total length of Other DATA field. The client?s current time in this case will be placed after the CGA-TSIG Data. 1.1. Problem Statement The authentication during any DNS query process is solely based on the source IP address when no secure mechanism is in use either Rafiee, et al. Expires August 15, 2014 [Page 4]
INTERNET DRAFT TSIG using CGA in IPv6 February 15, 2014 during the DNS update (zone transfer, FQDN update) or during the DNS query resolving process. This makes the DNS query process vulnerable to several types of spoofing attacks -- man in the middle, source IP spoofing, etc. One example is the problem that 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 containing the spoofed source IP address for 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. If DNSSEC (RFC 6840) or TSIG, as a security mechanism is in use, then the problem would be the manual step required for the configuration. For instance, when a DNSSEC needs to sign the zone offline. The public key verification in DNSSEC creates chicken and eggs situation. In other words, the key for verifying messages should be obtained from DNSSEC server itself. This is why the query requestor needed to ask other DNS servers up to top level in root to be able to verify the key. If this does not happen, DNSSEC is vulnerable to IP spoofing attack. This problem could easily be handled by the use of CGA-TSIG as a means of providing the proof of IP address ownership. If TSIG is in use, the shared secret exchange is done offline. Currently there is little deployment of TSIG 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 difficult to configure each new client with the shared secret of the resolver. Another catastrophic problem with TSIG would be when this shared secret, that is shared between a group of hosts, leaks and makes it necessary to repeat this manual step. The reason is, that for each group of hosts there needs to be one shared secret and the administrator will need to manually add it to the DNS configuration file for each of these hosts. This manual process will need to be invoked in the case where one of these hosts is compromised and the shared secret is well known to the attacker. It will also have to be invoked in the case where any of these hosts needs to change their IP addresses, because of different reasons such as privacy issues, as explained in RFC 4941 [RFC4941], or when moving to another subnet within the same network, etc. Therefore, the problem that exists today with the authentication processes used in different scenarios is what this document addresses. The various scenarios include authentication during zone transfer, authentication of the nodes during DNS query resolving and authentication during updating PTR and FQDN (RFC 4703). 2. Conventions used in this document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", Rafiee, et al. Expires August 15, 2014 [Page 5]
INTERNET DRAFT TSIG using CGA in IPv6 February 15, 2014 "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. => This sign in the document should be interpreted as "change to". 3. Terminology The terms used in this document have the following standard meaning: - Name server: A server that supports DNS service. - Resolver/recursive DNS server: A resolver/recursive name server responds to queries where the query does not contain an entry for the node in its database. It first checks its own records and cache for the answer to the query and then, if it cannot find an answer there, it may recursively query name servers higher up in the hierarchy and then pass the response back to the originator of the query. This is known as a recursive query or recursive lookup. - Stub resolver: A specific kind of DNS resolver that is unable to resolve the queries recursively. So, it relies on a recursive DNS resolver to resolve the queries. - Authoritative: An authoritative name server provides the answers to DNS queries. For example, it would respond to a query about a mail server IP address or website IP address. It provides original, first-hand, definitive answers (authoritative answers) to DNS queries. It does not provide 'just cached' answers that were obtained from another name server. Therefore it only returns answers to queries about domain names that are installed in its system configuration. There are two types of Authoritative Name Servers: 1. Master server (primary name server): A master server stores the original master copies of all zone records. A host master is only allowed to change the master server?s zone records. Each slave server gets updated via a special automatic updating mechanism within the DNS protocol. All slave servers maintain identical copies of the master records. 2. Slave server (secondary name server): A slave server is an exact replica of the master server. It is used to share the DNS server's load and to improve DNS zone availability in cases where the master server fails. It is recommended that there be at least 2 slave servers and one master server for each domain name. Rafiee, et al. Expires August 15, 2014 [Page 6]
INTERNET DRAFT TSIG using CGA in IPv6 February 15, 2014 - Root DNS server: An authoritative DNS server for a specific root domain. For example, .com - Client: a client can be any computer (server, laptop, etc) that only supports stub DNS servers and not other DNS services. It can be a mail server, web server or a laptop computer. - Node: a node can be anything such as a client, a DNS server (resolver, authoritative) or a router. - Host: all nodes except routers 4. Algorithm overview The following sections explain the use of CGA or any other future algorithm in place of CGA for securing the DNS process by adding a CGA-TSIG data structure as an option to the TSIG Resource Record (RR). 4.1. The CGA-TSIG DATA structure The CGA-TSIG data structure SHOULD be added to the Other DATA section of the RDATA field in the TSIG Resource Record (RR) (see figures 1 and 2). The DNS RRTYPE MUST be set to TSIG [RFC2845]. The RDATA Algorithm Name MUST be set to CGA-TSIG. The Name MUST be set to root (.).This is the smallest possible value that can be used. The MAC Size MUST be set to 0. A detailed explanation of the standard RDATA fields can be found in section 2.3 RFC 2845. This document focuses only on the new structure added to the Other DATA section. These new fields are CGA-TSIG Len and CGA-TSIG DATA. The TSIG RR is added to an additional section of the DNS message. If another algorithm is used in place of CGA for SeND, such as SSAS [4 , 5], then the 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 Name | | (CGA-TSIG) | +---------------------------------------+ | Time Signed | | | +---------------------------------------+ | Fudge | | | +---------------------------------------+ | MAC Size | | | Rafiee, et al. Expires August 15, 2014 [Page 7]
INTERNET DRAFT TSIG using CGA in IPv6 February 15, 2014 +---------------------------------------+ | Mac | | | +---------------------------------------+ | Original ID | | | +---------------------------------------+ | Error | | | +---------------------------------------+ | OTHER LEN | | | +---------------------------------------+ | OTHER DATA | | | +---------------------------------------+ Figure 1 Modified TSIG RDATA The CGA-TSIG DATA Field and the CGA-TSIG Len will occupy the first two slots of Other DATA. Figure 2 shows the layout. Any extra options/data should be placed after CGA-TSIG field. CGA-TSIG Len is the length of CGA-TSIG DATA in byte. This value is multiple of 8. +---------------------------------------+ | CGA-TSIG Len | | (1 byte) | +---------------------------------------+ | CGA-TSIG DATA | | | +---------------------------------------+ | Other Options | | | +---------------------------------------+ Figure 2 Other DATA section of RDATA field CGA-TSIG DATA Field Name Data Type Notes -------------------------------------------------------------- Algorithm type u_int16_t IANA numeric value of the algorithm for RSA 1.2.840.113549.1.1.1 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 Rafiee, et al. Expires August 15, 2014 [Page 8]
INTERNET DRAFT TSIG using CGA in IPv6 February 15, 2014 field old pubkey variable Old public key in ASN.1 DER format (the same format as public key) old Signature Len variable the length of old signature field old Signature variable Old signature generated by old public key. Type indicates the Interface ID generation algorithm that was used in SeND (An Interface ID is the 64 leftmost bits of an IPv6 address.). This field allows for the use of future, optional algorithms in SeND. The default value for CGA is 1. The IP tag is a node's old IP address. 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. 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 zeroes. The server will then store the new IP address that was passed to it in storage. If the client wants to replace 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 maintain privacy, then it MUST add the old public key to the old pubkey field. It MUST also retrieve the current time from Time Signed field, sign it using the old private key, and then 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 sections 5.1, 6.1 and 7.1. 4.2. Generation of CGA-TSIG DATA In order to use CGA-TSIG as an authentication approach, some of the parameters need to be cached during IP address generation. If no parameters are available in cache, please see section 8. 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 generated by the use of CGA. 1. Obtain required parameters from cache. The CGA-TSIG algorithm obtains the old IP address, modifier, subnet prefix, collision count and public key from cache. It concatenates the old IP address with the CGA parameters, i.e., modifier, subnet prefix, collision count, public key (the order of CGA parameters are shown in section 3 RFC 3972). If the old IP address is not available, then CGA-TSIG must set the old IP address (IP tag) to zero. Rafiee, et al. Expires August 15, 2014 [Page 9]
INTERNET DRAFT TSIG using CGA in IPv6 February 15, 2014 Note: If the node is a DNS server (resolver or authoritative DNS server) which does not support SeND, but wants to use CGA-TSIG algorithm, then it is possible to use a script to generate the CGA parameters, which are needed to manually configure this server's IP address. Then this server can make use these parameters for authentication purposes. +---------------------------------------+ | Algorithm Name | | | +---------------------------------------+ | 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 3 CGA-TSIG DATA Field 2. Generate signature For signature generation, The 128-bit CGA Message Type tag value for SeND that is 0x086F CA5E 10B2 00C9 9C8C E001 6427 7C08, is concatenated with the whole DNS message from Type to additional data sections (Please refer to figure 4 and figure 5) excluding the signature fields itself in the CGA-TSIG DATA is signed by using a RSA algorithm, by default, or any future algorithm used in place of RSA, Rafiee, et al. Expires August 15, 2014 [Page 10]
INTERNET DRAFT TSIG using CGA in IPv6 February 15, 2014 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 number of seconds since 1 January 1970 in UTC 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 4.1.3 RFC 1035 [RFC1035]. Figure 6 shows this signature. +-----+------+--------+ |Type |Length|Reserved| |1byte|1 byte| 1 byte | +---------------------+ | Header | | 12 bytes | +---------------------+ | Zone section | | variable length | +---------------------+ | prerequisite | | variable length | +---------------------+ | Update section | | variable length | +---------------------+ | Additional Data | | variable length | +---------------------+ Figure 4 DNS update message +-----+------+--------+ |Type |Length|Reserved| |1byte|1 byte| 1 byte | +---------------------+ | Header | | 12 bytes | +---------------------+ | Question | | variable length | +---------------------+ | Answer | | variable length | +---------------------+ | Authority | | variable length | +---------------------+ | Additional Data | | variable length | +---------------------+ Figure 5 DNS Query message (section 4.1 RFC 1035) Rafiee, et al. Expires August 15, 2014 [Page 11]
INTERNET DRAFT TSIG using CGA in IPv6 February 15, 2014 +------------------+ | CGA message tag | | 16 bytes | +------------------+ | DNS message | | (excluding | | signature fields | |in CGA-TSIG DATA) | +------------------+ Figure 6 CGA-TSIG Signature content 3. Generate old signature If the nodes generated new key pairs, then they need to add the old public key and message, signed by the old private key, to 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 the old signature field of CGA-TSIG DATA. This step MUST be skipped when the node did not generate new key pairs. 5. Authentication during Zone Transfer This section discusses the use of CGA-TSIG for the authentication of two DNS servers (a master and a slave). In the case of processing a DNS update for multiple DNS servers (authentication of two DNS servers), there are two possible scenarios with regard to the authentication process, which differs from that of the authentication of a node (client) with one DNS server. This is because of the need for human intervention. 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 use of 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 process, the sender's public key of the DNS Update message 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 15, 2014 [Page 12]
INTERNET DRAFT TSIG using CGA in IPv6 February 15, 2014 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, the certificate should be saved on the DNS server for later use for the generation of its address or for the DNS update process. In this case, whenever any of these servers want to generate a new IP address, then the DNS update process can be accomplished automatically without the need for human intervention. 5.1. Verification process Sender authentication is necessary in order to prevent attackers from making unauthorized modifications to DNS servers through the use of spoofed DNS messages. The verification process executes the following steps: 1. Verify the signature The signature contained in CGA-TSIG DATA should be verified. This can be done by retrieving the public key and signature from CGA-TSIG DATA and using this public key to verify the signature. If the verification process is successful, then step 2 will be executed. If the verification fails, then the message should be discarded without further action. 2. Check the Time Signed The Time Signed value is obtained from TSIG RDATA and is called t1. The current system time is then obtained and converted to UTC time and is called t2. Fudge time is obtained from TSIG RDATA. If t1 is in the range of t2 and t2 minus/plus fudge (see formula 1) 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. (t1 - fudge) <= t2 <=(t1 + fudge) (1) 3. 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 successful, then step 4 will be executed. Otherwise the message will be discarded without further action. Rafiee, et al. Expires August 15, 2014 [Page 13]
INTERNET DRAFT TSIG using CGA in IPv6 February 15, 2014 4. Verify the source IP address The source IP address of the Update requester 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 CGA-TSIG DATA is the same as what was available in the storage where the public keys and IP addresses were saved. If no entry is found in storage for this public key, then the update will be rejected without further action. Otherwise, when the old public key length is not zero go to step 6. 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 CGA-TSIG DATA and will check to see 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 6 will be executed, otherwise the message should be discarded without further action. 7. Verify the old signature The old signature contained in CGA-TSIG DATA should be verified. This can be done by retrieving the old public key and the old signature from CGA-TSIG DATA and then 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. 6. Authentication during the FQDN or PTR Update Normally the DHCPv6 server will update the client's RRs on their behalf in the scenario where SeND is used as a secure NDP, the nodes will need to do this process themselves unless there is stateless DHCPv6 server available. CGA-TSIG can be used to give nodes the ability of doing this process themselves. In this case the clients need to include the CGA-TSIG option in order to allow the DNS server to verify them. The verification process is the same as that explained in section except for step 4. Rafiee, et al. Expires August 15, 2014 [Page 14]
INTERNET DRAFT TSIG using CGA in IPv6 February 15, 2014 6.1. Verification Process The verification steps are the same as those is explained in section 5.1, but removing step 4 and modifying step 5. 1- Verify the signature 2- Check the Time Signed 3- Execute the CGA verification 4. Verify the public key The DNS server checks whether or not the public key retrieved from CGA-TSIG DATA is the same as what was available in the storage where the public keys and IP addresses were saved. If no entry is found in storage for this public key, and the FQDN or PTR is also not available in the DNS server, then the DNS server will store the public key of this node in his database and add this node's PTR and FQDN. Otherwise if any PTR is available, and the node IP tag is empty, or there is currently another public key associated with the node's FQDN, then the update will be rejected without further action. Otherwise go to step 5 when the old public key length is not zero. 5- Verify the public key 6- Verify the old public key 7- Verify the old signature 7. Authentication during Query Resolving (stub to recursive) A DNS query request sent by a host, such as a client or a mail server, does not need to generate 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. However, the client needs to include the TSIG RDATA and set the Algorithm type to CGA-TSIG. It MUST set the CGA-TSIG Len to zero. This allows the resolver to know when to include CGA-TSIG for verification process in client. In generation of the CGA-TSIG for a resolver, there is no need to include the IP tag. This is because resolvers do not usually have several IP addresses so the client does not need to keep several IP addresses for the same resolver. 7.1. Verification process Rafiee, et al. Expires August 15, 2014 [Page 15]
INTERNET DRAFT TSIG using CGA in IPv6 February 15, 2014 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 concerns. The steps 2 and 3 of the verification process are the same as those steps explained in section 5.1. These steps are as follows: 1. Verify the signature The signature contained in CGA-TSIG DATA should be verified. This can be done by retrieving the public key and signature from CGA-TSIG DATA and using this public key to verify the signature. If the verification process is successful, then step 2 will be executed. If the verification fails, then the message should be discarded without further action. 2. Check the Time Signed 3. Execute the CGA verification 4. 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 5 will be executed. Otherwise the message SHOULD be discarded without further action. 5. Verify the public key The host checks whether or not the public key retrieved from CGA-TSIG DATA matches any public key that was previously saved in the storage where the public keys and IP addresses of resolvers are saved. If there is a match, 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 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 CGA-TSIG DATA should be verified. This can be done by retrieving the old public key and old signature from CGA-TSIG DATA and then 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 Rafiee, et al. Expires August 15, 2014 [Page 16]
INTERNET DRAFT TSIG using CGA in IPv6 February 15, 2014 process fails, then the message should be discarded without further action. 8. Authentication during Query Resolving (Auth. to recursive) This verification step in the authentication of authoritative to recursive DNS server is the same as that explained in section 7.1. In this case the recursive DNS server does not need to generate CGA-TSIG DATA, but the root DNS server does need to include it in order to enable the recursive DNS server to verify it. The recursive DNS server needs to include the TSIG RDATA and set the Algorithm type to CGA-TSIG. It MUST set the CGA-TSIG Len to zero. This allows the root DNS server to know when to include CGA-TSIG for verification process in client. 9. No cache parameters available or SeND is not supported In the case where there are no cache parameters available during the IP address generation, there are then two scenarios that come into play here. In the first scenario there is the case where the sender of a DNS message needs to generate a key pair and generate the CGA-TSIG data structure as explained in section 4. The node SHOULD skip the first section of the verification processes explained in section 5.1 , section 6.1 and section 7.1. In the second scenario, as explained in section 4.2 (step 1), it is not necessary for the server to support the SeND or CGA algorithm. The DNS administrator can make a one-time use of a CGA script to generate the CGA parameters and then manually configure the IP address of this DNS server. Then later, this DNS server can use those values as a means for authenticating other nodes. The verifier nodes also do not necessarily need to support SeND. They only need to support CGA-TSIG. 10. How to obtain the IP address of resolvers Nodes can obtain the IP address of resolvers from the DHCPv6 server (that will not be secure) or from a DNS option of Router Advertisement message [RFC6106] after authenticating the router via a trusted authority. The IP addresses can be generated using CGA, SSAS or other mechanisms. 11. CGA-TSIG Data confidentiality One possible solution to provide the DNS server with data Rafiee, et al. Expires August 15, 2014 [Page 17]
INTERNET DRAFT TSIG using CGA in IPv6 February 15, 2014 confidentiality during DNS update or other DNS query processes is the use of symmetric encryption with CGA-TSIG that is called CGA-TSIGe. In this case, the node MUST set the Algorithm type in TSIG RDATA to CGA-TSIGe. 11.1. Generation of secret key To encrypt the DNS message using a symmetric algorithm for performance purposes, first, a node needs to retrieve the public key of the DNS server. It is possible to use the current DNSKEY RR (RFC 3757) to send the public key of the DNS server. When the client wants to update any records on the DNS server, it first sends a DNS message and asks for the public key of the DNS server. DNS server then answers to this query and includes the public key contained in the DNSKEY RR with the SEP flag set to zero. This is done to indicate that it is not the zone key. The DNS server SHOULD include CGA-TSIG DATA so that the client can verify its IP address. In this case, there will be a binding between DNS server?s public key and its IP address. After a successful verification, the node then generates a 16 byte random number and calls it a secret key. It encrypts this secret key using the DNS server public key. This allows only the DNS server to decrypt this secret key. In this case, the node sets the MAC in TSIG RDATA to the digest of secret key and set the MAC Size to the length of this digest. The DNS server knows what to do with MAC field from the Algorithm type in TSIG. If it is CGA-TSIGe, then it looks for an encrypted secret key. 11.2. DNS message generation The node MUST encrypt all DNS message sections that required protections using the secret key generated in last section and AES symmetric algorithm. It excludes TSIG RDATA (That usually added in the additional section of the DNS messages) from the encryption text. They are explained in figure 4 and figure 5 of section 4.2 of this document. 11.3. CGA-TSIGe DATA generation The CGA-TSIGe generation is the same as that explained in section 4.2 of this document. But only the Algorithm type MUST be set to CGA-TSIGe. 11.4. Process of encrypted DNS message When the DNS server receives the message from any node with TSIG Rafiee, et al. Expires August 15, 2014 [Page 18]
INTERNET DRAFT TSIG using CGA in IPv6 February 15, 2014 RDATA Algorithm type set to CGA-TSIGe, it execute the following steps: 1- Retrieve the secret key The DNS server retrieves the secret key from MAC field. It then decrypts this secret key using its own private key. 2- Decrypt the DNS message The DNS server decrypts the DNS server message using this secret key and the symmetric algorithm, which by default is AES. Then the DNS server can starts the verification process as explained in section 5.1, 6.1, 7.1 of this document. 12. CGA-TSIG/CGA-TSIGe Applications The purpose of CGA-TSIG [7] is to minimize the amount of human intervention required to accomplish shared secret or key exchange and, as a byproduct, to reduce the process's vulnerability to attacks introduced by human errors (during changing the DNS configuration) when Secure Neighbor Discovery (SeND) is used for addressing purposes or when SeND is not available for use. As explained in a prior section, CGA-TSIG can be used in different scenarios. For the FQDN update scenario CGA-TSIG is useful in dynamic networks where the nodes want to change their IP addresses frequently in order to maintain privacy. If the Dynamic Host Configuration Protocol (DHCP) is in use, then the DHCP server can do this update on behalf of the nodes in this network on a DNS server but in Neighbor Discovery Protocol (NDP), there is no feature available that allows the host security update process for its own FQDN. CGA-TSIG can be a solution. For the resolver scenario, usually the resolver can add the TSIG Resource Record (RR) to the DNS query response and use the CGA-TSIG algorithm in order to permit a useful authentication of the result. CGA-TSIG assures the client that the query response comes from the true originator and not from an attacker. It also ensures the integrity of the data by signing the data. 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. To exchange the shared secret between a DNS resolver and a client, when TSIG is used, a minimum of four messages are required for the establishment of a secure channel. Modifying RFC 2845 to use CGA-TSIG will decrease the number of messages needed in this exchange. The messages used in RFC 2930 (TKEY RR) are not needed when CGA-TSIG is used. Rafiee, et al. Expires August 15, 2014 [Page 19]
INTERNET DRAFT TSIG using CGA in IPv6 February 15, 2014 12.1. IP Spoofing During the DNS Update process or the query resolving 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 which utilizes the node for IP address verification of other nodes. 12.2. 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. 12.3. Resolver Configuration Attack When using CGA-TSIG, the DNS server, or the client, would not need further configuration. This would reduce the possibility of human errors being introduced into the DNS configuration file. Since this type of attack is predicated on human error, the chances of it occurring, when this extension is used, are minimized. 12.4. Exposing Shared Secret Using CGA-TSIG will decrease the number of manual steps required in generating the new shared secret and in exchanging it among the hosts where the old shared secret was shared between them for updating purposes. This manual step is required after a leakage has occurred of the shared secret to an attacker via any of these hosts. 12.5. Replay attack Using the Time Signed value in the signature modifies the content of the signature each time the node generates and sends it to the DNS server. 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 the signature. In this case, the verification process will fail thus also preventing the replay attack. Rafiee, et al. Expires August 15, 2014 [Page 20]
INTERNET DRAFT TSIG using CGA in IPv6 February 15, 2014 12.6. Data confidentiality Encrypting the whole DNS message will avoid the attacker to know the content of DNS messages. This will avoid zone walking and many other attacks on DNS RRs. This also provides the higher privacy for hosts that has DNS records. 13. Security Considerations The approach explained in this draft, CGA-TSIG, is a solution for securing DNS messages from spoofing type attacks like those explained in section 3. A problem that may arise here concerns attacks against the CGA algorithm. In this section we will explain the possibility of such attacks against CGA [5] 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 probability for success of this type of 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 using Hash1 and Hash2. The cost of doing this 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 type of attack due to the cost involved. Changing the IP address frequently will also decrease the chance for this type of attack succeeding. 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 Rafiee, et al. Expires August 15, 2014 [Page 21]
INTERNET DRAFT TSIG using CGA in IPv6 February 15, 2014 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 to the verifier side of the process to determine how many messages a node has received over a certain period of time from a specific node. If a determined threshold rate is exceeded, then the node will stop further receipt of 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. 14. 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. In section 4.1, Type should allow for the use of future optional algorithms with regard to SeND. The default value for CGA might be 1. Other algorithms would be assigned a new number sequentially. For example, a new algorithm called SSAS [4,5] could be assigned a value of 2. IANA also needs to define a numeric algorithm number for ECC. The similar way that is defined for RSA. 15. Appendix - A sample key storage for CGA-TSIG create table cgatsigkeys ( id INT auto_increment, pubkey VARCHAR(300), primary key(id) ); Rafiee, et al. Expires August 15, 2014 [Page 22]
INTERNET DRAFT TSIG using CGA in IPv6 February 15, 2014 create table cgatsigips ( id INT auto_increment, idkey INT, IP VARCHAR(20), FOREIGN KEY (idkey) REFERENCES cgatsigkeys(id) primary key(id) ); CGA-TSIG tables on mysql backend database - a sample format of stored parameters in the node For example, the modifier is stored as bytes and each byte might 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, 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 ). <?xml version="1.0" encoding="UTF-8"?> <Details> <CGATSIG> <modifier value=""/> <algorithmtype value="1.2.840.113549.1.1.1"/> <secval value="1"/> <GIP value=""/> <oGIP value=""/> <Keys value=""/> </CGATSIG> </Details> Rafiee, et al. Expires August 15, 2014 [Page 23]
INTERNET DRAFT TSIG using CGA in IPv6 February 15, 2014 XML file contains the cached DATA 16. Acknowledgements The continual improvement of this document is as a result of the helps and assistance of its supporters. The authors would like to thank all those people who directly helped in improving this draft and all supporters of this draft, especially Ralph Droms, Andrew Sullivan, Ted Lemon, Brian Haberman. The authors would like also to special acknowledge the supports of NLnet Labs director and researchers; Olaf Kolkman, Matthijs Mekking and their master student Marc Buijsman. 17. References 17.1. 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. [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. [RFC2845] Vixie, P., Gudmundsson, O. , Eastlake 3rd, D., Wellington, B., " Secret Key Transaction Authentication for DNS (TSIG)", RFC 2845, May 2000. [RFC6106] Jeong, J., Park, S., Beloeil, L., Madanapalli, S.,"IPv6 Router Advertisement Options for DNS Rafiee, et al. Expires August 15, 2014 [Page 24]
INTERNET DRAFT TSIG using CGA in IPv6 February 15, 2014 Configuration",RFC 6106, November 2010. 17.2. 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, 2013. [5] Rafiee, H., Meinel, C., "A Simple Secure Addressing Scheme for IPv6 AutoConfiguration (SSAS)", 11th International conference on Privacy, Security and Trust (IEEE PST), 2013. [6] AlSa'deh, A., Rafiee, H., Meinel, C., "Cryptographically Generated Addresses (CGAs): Possible Attacks and Proposed Mitigation Approaches," in proceedings of 12th IEEE International Conference on Computer and Information Technology (IEEE CIT'12), pp.332-339, 2012. [7] Rafiee, H., Meinel, C., "A Secure, Flexible Framework for DNS Authentication in IPv6 Autoconfiguration" in proceedings of The 12th IEEE International Symposium on Network Computing and Applications (IEEE NCA13), 2013. Rafiee, et al. Expires August 15, 2014 [Page 25]
INTERNET DRAFT TSIG using CGA in IPv6 February 15, 2014 Authors' Addresses Hosnieh Rafiee Ciber AG KoelnTurm Im Mediapark 8 50670, Cologne http://www.ciber.com Phone: +49 (0221) 272 67- 122 Email: ietf@rozanak.com Christoph Meinel Hasso-Plattner-Institute Prof.-Dr.-Helmert-Str. 2-3 Potsdam, Germany Email: meinel@hpi.uni-potsdam.de Martin von Loewis Hasso-Plattner-Institute Prof.-Dr.-Helmert-Str. 2-3 Potsdam, Germany Rafiee, et al. Expires August 15, 2014 [Page 26]