DNS Extensions H. Rafiee INTERNET-DRAFT Huawei TECHNOLOGIES Duesseldorf GmbH Updates RFC 2845 (if approved) M. v. Loewis Intended Status: Standards Track C. Meinel Hasso Plattner Institute Expires: April 24, 2015 October 24, 2014 CGA-TSIG/e: Algorithms for Secure DNS Authentication and Optional DNS Confidentiality Abstract This document describes a new mechanism for secure DNS authentication and DNS data confidentiality in various scenarios. The purpose of this document is to reduce human interaction during different DNS scenarios such as the communications of resolvers to stub resolvers, recursive resolvers to Authoritative Name Server, Dynamic DNS updates, (especially updating PTR and FQDN records). The aim of this document is to assist DNSSEC to protect the last miles of Internet easier. This document supports both IPv4 and IPv6 enabled networks. 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 April 24, 2015. Copyright Notice Copyright (c) 2014 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to Rafiee, et al. Expires April 24, 2015 [Page 1] INTERNET DRAFT New algorithms in TSIG October 24, 2014 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. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 2.1. Overview of CGA-TSIG/e Mechanisms . . . . . . . . . . . . 5 2.2. Problem Statement . . . . . . . . . . . . . . . . . . . . 7 2.2.1. Transaction SIGnature (TSIG) . . . . . . . . . . . . 7 2.2.2. DNS Security Extension (DNSSEC) . . . . . . . . . . . 7 2.2.3. SIG0 . . . . . . . . . . . . . . . . . . . . . . . . 8 2.2.4. Pros and Cons with DNS privacy proposals . . . . . . 8 2.2.4.1. Private DNS (JSON): . . . . . . . . . . . . . . . 8 2.2.4.2. DNS over DTLS (DNSoD): . . . . . . . . . . . . . 9 2.2.4.3. DNS using TLS (DTLS): . . . . . . . . . . . . . . 9 2.2.4.4. DNS over TLS: . . . . . . . . . . . . . . . . . . 9 3. Conventions Used In This Document . . . . . . . . . . . . . . 10 4. Algorithm Overview . . . . . . . . . . . . . . . . . . . . . 10 4.1. CGA-TSIG . . . . . . . . . . . . . . . . . . . . . . . . 10 4.1.1. The CGA-TSIG DATA Structure . . . . . . . . . . . . 10 4.1.2. CGA-TSIG DATA . . . . . . . . . . . . . . . . . . . 12 4.1.2.1. IPv6 Specific Data . . . . . . . . . . . . . . . 13 4.1.2.2. IPv4 Specific Data . . . . . . . . . . . . . . . 13 4.1.3. Generation of CGA-TSIG DATA . . . . . . . . . . . . 14 4.2. CGA-TSIGe . . . . . . . . . . . . . . . . . . . . . . . . 15 4.2.1. The CGA-TSIGe DATA Structure . . . . . . . . . . . . 15 4.2.1.1. Public Key Request . . . . . . . . . . . . . . . 17 4.2.1.2. Public Key Response . . . . . . . . . . . . . . . 17 4.2.2. Generation of CGA-TSIGe DATA . . . . . . . . . . . . 18 4.2.2.1. IPv6 Specifics . . . . . . . . . . . . . . . . . 18 4.2.2.1.1. Generation of Query Request Message . . . . . 18 4.2.2.1.2. Generation of Query Response Message . . . . 20 4.2.2.2. IPv4 Scenario . . . . . . . . . . . . . . . . . . 21 4.2.2.2.1. Generation of Query Request Message . . . . . 21 4.2.2.2.2. Generation of Query Response Message . . . . 22 4.2.3. Process of Public Key Response Message . . . . . . . 22 4.2.3.1. IPv6 only Scenarios . . . . . . . . . . . . . . . 22 4.2.3.2. IPv4 only Scenarios . . . . . . . . . . . . . . . 22 4.2.4. Process of Encrypted Query Request Message . . . . . 22 4.2.5. Process of Encrypted Query Response Message . . . . . 23 5. General Verification Steps . . . . . . . . . . . . . . . . . 23 6. CGA-TSIG/CGA-TSIGe Use Case Scenarios . . . . . . . . . . . . 25 6.1. The FQDN Or PTR Update (IPv6 only) . . . . . . . . . . . 25 6.1.1. Verification Process . . . . . . . . . . . . . . . . 26 Rafiee, et al. Expires April 24, 2015 [Page 2] INTERNET DRAFT New algorithms in TSIG October 24, 2014 6.2. DNS Resolving Scenario (stub to recursive) . . . . . . . 26 6.2.1. Client Verification Process (CGA-TSIGe only) . . . . 27 6.2.2. Resolver Verification Process . . . . . . . . . . . . 28 6.3. DNS Resolving Scenario (Authoritative NS to Recursive NS) 29 7. SeND Is Not Supported (IPv6 only) . . . . . . . . . . . . . . 29 8. CGA-TSIG/e Attack Protections . . . . . . . . . . . . . . . . 30 8.1. IP Spoofing . . . . . . . . . . . . . . . . . . . . . . 30 8.2. Resolver Configuration Attack . . . . . . . . . . . . . . 30 8.3. Exposing A Shared Secret . . . . . . . . . . . . . . . . 30 8.4. Replay Attack . . . . . . . . . . . . . . . . . . . . . 30 8.5. Data Confidentiality . . . . . . . . . . . . . . . . . . 31 9. Update to TSIG Specification . . . . . . . . . . . . . . . . 31 10. Security Considerations . . . . . . . . . . . . . . . . . . . 31 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 32 12. Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . 32 12.1. A Sample Key Storage For CGA-TSIG . . . . . . . . . . . 32 12.2. Stored parameters in the node . . . . . . . . . . . . . 33 12.3. CGA Generation Script . . . . . . . . . . . . . . . . . 33 12.4. Other Optional Use case scenarios . . . . . . . . . . . 35 12.5. DNS Zone Transfer . . . . . . . . . . . . . . . . . . . 35 12.5.1. Verification Process . . . . . . . . . . . . . . . . 36 13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 36 14. References . . . . . . . . . . . . . . . . . . . . . . . . . 36 14.1. Normative . . . . . . . . . . . . . . . . . . . . . . . . 36 14.2. Informative . . . . . . . . . . . . . . . . . . . . . . . 37 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 39 Rafiee, et al. Expires April 24, 2015 [Page 3] INTERNET DRAFT New algorithms in TSIG October 24, 2014 1. Terminology The terms used in this document have the following standard meaning: - Bot: a malicious program that is installed on a node and allows an attacker to control some functions of that node to send malicious messages. - Name Server: A server that supports DNS service. - Recursive Name Server: A Name Server that responds to all queries. - Stub Resolver: A DNS resolver that is unable to resolve queries recursively, and relies on a Recursive DNS Server to resolve queries. - Authoritative Name Server: Provides answers to DNS queries that it contains in its system configuration. There are two types of Authoritative Name Servers: 1. Master Server (Primary): A Master Server stores the original copies of all 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): A Slave Server is an exact replica of the master server. - Root Name Server: An Authoritative Name Server for the root domain (i.e., '.' (dot)) - 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 2. Introduction Protecting stub resolvers (clients) from spoofed DNS messages and fake DNS resolvers requires manual configuration of each stub resolvers with a list of trusted anchors so that DNSSEC can be used and work to protect the nodes. Introducing a list of trusted anchors to the clients is not easy and requires human interaction, especially, when the clients are dynamic in the network or in public networks where clients are anonymous. Furthermore, protecting DNS servers from unauthorized update during Rafiee, et al. Expires April 24, 2015 [Page 4] INTERNET DRAFT New algorithms in TSIG October 24, 2014 dynamic DNS update (DDNS) is another scenario that requires human interactions for the configuration of each node for a secure authentication during DNS update. Manual configuration only increases overheads on domain administrators. This is because nodes join and leave the networks or frequently change their IP addresses. Therefore, they want to update their PTR or FQDN records on DNS servers accordingly. 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. However, DHCP alone cannot provide the necessary secure authentication for the nodes and other monitoring approaches are needed. When Neighbor Discovery Protocol (NDP) is in use, there is no feature available that allows the host process a secure update for its own FQDN or PTR. Using a shared secret which is shared between many nodes for secure authentication during DDNS process, similar to TSIG mechanism requires the exchange of this shared secret manually between these nodes. This results in repeating the key exchange between many nodes (This process involves human interaction) where one of these nodes are compromised due to virus or other problems. Besides, there are recently a lot of concerns about DNS privacy and hiding the data exchanges between stub resolvers? and DNS server from prying eyes (either in active or passive attacks). To address these existing problems with TSIG, as well as considering DNS data protection where it is needed (Data confidentiality), considering different factors such ? automation (minimizing human interaction); secure authentication; performance; encryption, and to secure the last miles of Internet where DNSSEC cannot easily handle this protection, this document proposes two algorithms -- one is for secure authentication that is called CGA-TSIG and one for both secure authentication and DNS data encryption (DNS privacy) that is called CGA-TSIGe. In DNS privacy, this document uses both asymmetric and symmetric cryptography. Asymmetric cryptography is used for encrypting the 16 byte secret key. This secret key then can be used as a key for the symmetric encryption algorithm in order to encrypt the whole DNS message. This process will increase the DNS performance by avoiding the encryption of a large DNS message using a public key cryptography. These algorithms support both IPv4 and IPv6 enabled network and considered as new algorithms in the TSIG Resource Record (RR). 2.1. Overview of CGA-TSIG/e Mechanisms The purpose of CGA-TSIG and CGA-TSIGe is to minimize the human intervention required to accomplish a shared secret or key exchange (automation as much as possible), secure authentication, with the end result of providing data confidentiality to prevent DNS spoofing. Minimizing the amount of human intervention reduces the vulnerability to attacks introduced by human errors. As explained earlier, CGA-TSIG/e can be used to assist DNSSEC server in last mile of Rafiee, et al. Expires April 24, 2015 [Page 5] INTERNET DRAFT New algorithms in TSIG October 24, 2014 Internet. CGA-TSIG/e supports both IPv4 and IPv6 scenarios. In the IPv6 scenario, the algorithms use Cryptographically Generated Addresses (CGA) [RFC3972] or Secure Simple Addressing Scheme for IPv6 Autoconfiguration (SSAS) [4, 5]. Both CGA and SSAS provide the 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 infrastructure. For example, in DNS stub resolver to resolver scenario, CGA-TSIG provides this secure authentication by receiving the IP address of a DNS resolver via an option from a secure Router Advertisement (RA) or from DHCPv6 server that is protected via SAVI approaches [savi-dhcp]. When it (client) wants to resolve a query, it sends a DNS query message by only setting algorithm type to ?CGA-TSIG? without signing this message or adding any more information. This is because resolver does not need to verify the client and a client can be anonymous. If resolvers supports CGA-TSIG algorithm, then it sends a DNS query response message by setting algorithm type to ?CGA-TSIG?, include required parameters such as its public key in CGA-TSIG data (to be verifiable on client), sign this message and submit it. When the client receives this message, since there is a binding between this public key and the IP address of the resolver, by verifying the signature, the client makes sure that this public key belongs to the target resolver. In other word, public key of the resolver is sent in a same message as a DNS query (no separate message is required). In case of DNS confidentiality (CGA-TSIGe), if this client haven?t already cached the public key of the resolver, it sends an empty DNS query message by only setting the algorithm type to ?CGA-TSIGe?. Then the resolver knows that it should submit its public key to the client. Since this binding exists, client can use the public key of the DNS resolver to exchange a random value (called shared key). Then DNS resolver uses AES or other secure symmetric algorithm to encrypt all DNS message with this random value received from this client. In case the network is not secure, user can easily introduce the IP address of trusted resolver (or select home resolver from the list of trusted resolvers in its computer). In IPv4 scenarios, the algorithms use the hash of public key as an authentication approach. For example, in resolver scenario, the client receives the DNS resolver?s hash of (IPv4 + public key) from a DHCPv4 server that is protected by SAVI approaches or other monitoring approaches. If the network is not reliable, then this hash value can be introduced once manually to the stub resolver. The other option is that when the client receives the IP address or hash of (IPv4 + public key) securely from a secure DHCP server or an option in RA message, it caches this value in a list of trusted resolver (called trusted list). Whenever there is no trusted resolver available (like public network), the implementation can provide a way for the user to select one of the trusted resolver stored in this trusted list or it can be some random selection mechanisms. This will avoid any manual configuration for the user. However, if this trusted list is empty and the network is not reliable, the only way to provide this reliability is to introduce the DNS server?s IP address Rafiee, et al. Expires April 24, 2015 [Page 6] INTERNET DRAFT New algorithms in TSIG October 24, 2014 manually. Similar to IPv6 scenario, the public key is sent by the resolver in a DNS query response message. When this client resolves any query response, it compare the hash of (resolver?s source IP address + public key) with what is available on its own and if there is a match, it verifies the resolver and accepts the message. In case of DNS confidentiality (CGA-TSIGe), the same approach that is explained in the prior paragraph can be in use. The detail steps for these scenarios are explained in next sections. 2.2. Problem Statement There are several different methods where DNS records (during DDNS processes) on a DNS server can become compromised. Two examples of methods are DNS Spoofing; Unauthorized DNS Update. There are also several different methods where harm user?s privacy or poison user?s devices caches (Stub resolver?s cache). Some examples of methods are Resolver Source IP Spoofing; User Privacy Attack; and Human Intervention. The following sections only focus on the problem with current available solutions. 2.2.1. Transaction SIGnature (TSIG) - No protection against IP spoofing and DNS amplification - Not scalable and applicable for specific scenarios. 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. - Offline exchange of shared secrets. 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. When this shared secret is leaked, it makes it necessary to repeat this manual share key exchange process. It will also have to be invoked in the case where any of these hosts needs to change their IP addresses, such as privacy issues explained in RFC4941 [RFC4941], or when moving networks, etc. The manual TSIG process for the exchange of shared secrets makes it difficult to configure each new client with the shared secret of a DNS server like a resolver. - Does not easily protect DNS data confidentiality. TSIG provides the node with transaction level authentication and it is not used for encrypting the content of DNS messages. 2.2.2. DNS Security Extension (DNSSEC) - Offline generation of the signature and no support for DNS privacy Rafiee, et al. Expires April 24, 2015 [Page 7] INTERNET DRAFT New algorithms in TSIG October 24, 2014 DNSSEC [RFC6840] needs manual step for the configuration. For instance, in case a DNSSEC needs to sign the zone offline (However there are new efforts to automate this process). It is also needed that the DNSSEC verifier node to be configured with the list of root trusted anchors. Therefore, it is not scalable to end users since it is not easy to do this configuration and checkup. This makes it difficult to use it for the authentication of stub resolver to recursive resolver scenarios (last miles of Internet) where anonymous nodes need to verify a resolver. (This is what this draft aims to address and assists DNSSEC in this step) 2.2.3. SIG0 - Not scalable and does not support automation (key management problem) - No protection against IP spoofing and DNS amplification - Does not support DNS privacy 2.2.4. Pros and Cons with DNS privacy proposals To address DNS privacy, there are currently some proposals available. This section only compares CGA-TSIGe with these proposals by considering some factors ? change on DNS protocol, performance, Attacks (MITM), automation and authentication. This is because most of these proposals need to change DNS protocol. But CGA-TSIGe kept this change in a minimal level. In other words, for using the CGA-TSIGe, one only needs to register these algorithms with IANA. 2.2.4.1. Private DNS (JSON): Private DNS [private-dns] is one of privacy approaches that uses TLS and consider using JSON. To establish a secure communications, many messages needs to back and forth because the assumption is that a node itself needs to verify the TLS certificate. - Might not have good performance (number of messages exchanged to establish this secure communication) - Needs a change on DNS protocol since it uses TLS and JSON - IP spoofing and MITM might be possible only when there is no CA or predefined Trusted Anchors (TA) so that it makes it possible for an attacker intercepts this communication at the beginning of TLS establishment. This approach is supposed to provide protection for a recursive resolver. Certificate is usually provided for a domain name but there is no binding between this domain and the IP address of this resolver. If this certificates was signed by a CA, this binding is not necessary as an attacker does not have the private key of a Rafiee, et al. Expires April 24, 2015 [Page 8] INTERNET DRAFT New algorithms in TSIG October 24, 2014 node. When this CA is not available or a node was not pre-reconfigured with a list of TAs, an attacker has a chance to intercept this communication at the beginning of establishment and forge the identity of this DNS resolver. 2.2.4.2. DNS over DTLS (DNSoD): DNSoD [dnsod] uses DTLS [RFC6347]. DTLS is quite similar to TLS but works on UDP. The disadvantages of this approach are as follows: - IP spoofing and MITM might be possible only when the attacker intercepts this communication at the beginning of TLS establishment (as explained in private DNS section). The document suggests having a list of IP addresses and domain names of trusted nodes. But there is no binding between these IP addresses and trusted node?s domain name. So, if an attacker is inside this network, he can spoof the IP address of one of these trustees. When there is no trusted server available, then there is no solution offered while CGA-TSIG does not have this problem. 2.2.4.3. DNS using TLS (DTLS): DNS using TLS (DTLS) [dtls] is another proposal that uses TLS for a secure communication. The disadvantages of this approach are as follows: - Need to change on DNS protocol since it uses TLS as an encryption mechanism. However there is explanation of how to handle this process in case DNS server or client does not support it. - IP spoofing and MITM might be possible only when the attacker intercepts this communication at the beginning of TLS establishment (as explained in private DNS section). 2.2.4.4. DNS over TLS: Stub resolver to resolver authentication [dnstlsstub] is another proposal that uses opportunistic encryption and similar to DTLS, uses TLS for secure communications. The disadvantages of this approach are as follows: - Use different port than DNS port that is 443. So it needs to change DNS protocol - IP spoofing and MITM might be possible only when the attacker intercepts this communication at the beginning of TLS establishment (as explained in private DNS section. - There is no practical authentication approach offered by this mechanisms and the assumption is that the other services provide this Rafiee, et al. Expires April 24, 2015 [Page 9] INTERNET DRAFT New algorithms in TSIG October 24, 2014 authentication. So, it is vulnerable to active attacks. It also cannot protect the node against passive attacks. It is because a surveillance actor has access to the whole traffic and can sniff the traffic initiated from certain network or node. So the content of that encrypted message is not hidden. This actor already knows the content and encryption wasn?t helpful. 3. 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. => This sign in the document should be interpreted as "change to". IPv6 only: this indicates that the explained approach can be used only in IPv6 scenario IPv4 only: this indicates that the explained approach can be used only in IPv4 scenario IPv4 and IPv6: This indicates that the explained approach can be used in both IPv4 and IPv6 scenario and there are no differences. | This sign in this document should be interpreted as ?concatenation?. Note: This document uses the names CGA-TSIG and CGA-TSIGe. But it does not mean that the algorithm in use in this document is only CGA. The "CGA" name was taken from the first versions of this draft and continued to be appeared in the latest versions of this draft. This draft also uses TSIG as a carrier protocol to avoid changing the current DNS protocol. 4. Algorithm Overview The following sections explain the CGA-TSIG data structure in IPv4 and IPv6 scenarios. A CGA-TSIG data structure is an option to the TSIG Resource Record (RR). 4.1. CGA-TSIG 4.1.1. The CGA-TSIG DATA Structure The CGA-TSIG data structure SHOULD be added to the Other DATA section Rafiee, et al. Expires April 24, 2015 [Page 10] INTERNET DRAFT New algorithms in TSIG October 24, 2014 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 CGA-TSIG name is used when there is no need for DNS data confidentiality. The CGA-TSIGe (Please refer to section 4.2) is used when all parts of a DNS message should be encrypted to provide data confidentiality. 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 when the Algorithm Name is CGA-TSIG. A detailed explanation of the standard RDATA fields can be found in section 2.3 [RFC2845]. 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. +---------------------------------------+ | Algorithm Name | | (CGA-TSIG) | +---------------------------------------+ | Time Signed | | | +---------------------------------------+ | Fudge | | | +---------------------------------------+ | MAC Size | | | +---------------------------------------+ | 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. +---------------------------------------+ | CGA-TSIG Len | | (2 bytes) | Rafiee, et al. Expires April 24, 2015 [Page 11] INTERNET DRAFT New algorithms in TSIG October 24, 2014 +---------------------------------------+ | CGA-TSIG DATA | | | +---------------------------------------+ | Other Options | | | +---------------------------------------+ Figure 2: Other DATA section of RDATA field 4.1.2. CGA-TSIG DATA Figure 3 explains detail structure of CGA-TSIG DATA section. Fields that are marked (*) are different depending on IPv6 or IPv4. +---------------------------------------+ | AsyAlgorithm | | (15 bytes) | +---------------------------------------+ | Type * | | (u_int16_t) | +---------------------------------------+ | IP Tag * | | (variable) | +---------------------------------------+ | Parameters Len | | (1 byte) | +---------------------------------------+ | Parameters * | | (variable) | +---------------------------------------+ | Signature Len | | (1 bytes) | +---------------------------------------+ | Signature | | (variable) | +---------------------------------------+ | Old Pubkey Len | | (1 byte) | +---------------------------------------+ | old Pubkey | | (variable) | +---------------------------------------+ | Old Signature Len | | (1 byte) | +---------------------------------------+ | Old Signature | | (variable) | +---------------------------------------+ Figure 3: structure of CGA-TSIG DATA section - AsyAlgorithm: Asymmetric algorithm. IANA numeric value for RSA algorithm 1.2.840.113549.1.1.1[RFC4055]. For ECC, IANA needs to define a new number. Rafiee, et al. Expires April 24, 2015 [Page 12] INTERNET DRAFT New algorithms in TSIG October 24, 2014 - Type: Name of algorithm - IP Tag: Tag used to identify the IP address - Parameters Len: Length of parameters - Signature Len: Length of public key cryptography signature - Signature: Please refer to section 4.1.3 of this document - Old Pubkey Len: Length of old public key field - Old Pubkey: Old public key in ASN.1 DER format (same format as public key) - Old Signature Len: Length of old signature field - Old Signature: Old signature generated by old public key. The IP Tag is one of the old IP addresses of the Node. A client's public key can be associated with several IP addresses on a server. The DNS server SHOULD store the IP addresses and the public keys to indicate their association. If a client wants to add RRs by using a new IP address, then the IP tag field will be zeroed out. 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 and replace it 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, then it MUST add the old public key to the Old Pubkey field. It MUST also retrieve the current time from the Time Signed field, sign it using the old private key, and then add the signature to the old signature field. This enables the verifier node to authenticate a host with a new public key. The verification steps are explained in detail in sections 5, 6.1.1, 6.2.1 and 6.2.2. 4.1.2.1. IPv6 Specific Data For IPv6, the Type field indicates the Interface ID generation algorithm that is used in SeND (An Interface ID is the 64 rightmost bits of an IPv6 address). The field allows for future development. The default value for CGA is 1 and for SSAS is 2. IP Tag for IPv6 is 16 octets. 4.1.2.2. IPv4 Specific Data Rafiee, et al. Expires April 24, 2015 [Page 13] INTERNET DRAFT New algorithms in TSIG October 24, 2014 For IPv4, the Type field indicates the hashing function used to generate the hash of (public key + IPv4). By default, it is SHA256. This value SHOULD be set to 1 for SHA256 and other numeric incremental value for other hashing algorithms. This allows for future hashing functions. 4.1.3. 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 the cache, please see section 7. 1. Obtain Require Parameters From Cache. For IPv6, if the Type Field above 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 the host. For IPv4, the location to the key pairs needs to be cached in order to generate the signature. If this node changes its IP address, it also needs to cache the old IP address. Note: If the node is a DNS server (resolver or Authoritative Name Server) that does not support SeND but wants to use the CGA-TSIG algorithm, a script can be used to generate the CGA parameters. (Please refer to the section 12.2. appendix) 2. Generate Signature The signature is generated by concatenation of the following values where Type is the 128-bit Message Type tag value. This value for CGA (SeND) is 0x086F CA5E 10B2 00C9 9C8C E001 6427 7C08. Plain text= Type | Entire DNS message (Please refer to figure 4 and figure 5) Then the node uses its own private key obtained from the cache as explained in last step to sign the plain text. This signature MUST be added to the signature field of the CGA-TSIG DATA record. The Time Signed field uses the same timestamp in RDATA. This will prevent replay attacks by changing the signature each time a Node sends a DNS message. The format of DNS messages is explained in section 4.1.3 [RFC1035]. +-----+------+--------+ |Type |Length|Reserved| |1byte|1 byte| 1 byte | +---------------------+ | Header | | 12 bytes | +---------------------+ | Zone section | | variable length | Rafiee, et al. Expires April 24, 2015 [Page 14] INTERNET DRAFT New algorithms in TSIG October 24, 2014 +---------------------+ | 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.) 3. Generate Old Signature If the nodes generated new key pairs, they need to add the old public key, signed by the old private key, to the CGA-TSIG DATA. A node will sign the new public key with the old private key, and then will add the contents 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. 4.2. CGA-TSIGe One possible solution to provide the DNS server with data confidentiality during DNS update or other DNS query processes is the use of symmetric encryption with CGA-TSIG that is called CGA-TSIGe. 4.2.1. The CGA-TSIGe DATA Structure The node MUST set the Algorithm Type in TSIG RDATA to CGA-TSIGe. Other sections of CGA-TSIGe DATA are similar to CGA-TSIG DATA. This Rafiee, et al. Expires April 24, 2015 [Page 15] INTERNET DRAFT New algorithms in TSIG October 24, 2014 section only explains the differences between CGA-TSIG and CGA-TSIGe. Figure 6 shows CGA-TSIGe DATA structure. - Message Hash = 3-bit hashing algorithm identifier | hash (whole DNS message) The value of Message Hash is the concatenation of the 3 bits hashing algorithm identifier with the hash of the whole DNS message (see figure 4 and 5 for the whole DNS message). This is used for data integrity of the packet. For SHA256, the value of hashing algorithm SHOULD set to 1. For other hashing algorithms, this 3 bits SHOULD set to sequential value after one. The field Message Hash Len is the length of Message Hash. - digest_secret_key len: Length of digest_secret_key (encrypted secret key) - digest_secret_key = encryption of a 16 byte random number using DNS server?s public key +---------------------------------------+ | AsyAlgorithm | | | +---------------------------------------+ | 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) | Rafiee, et al. Expires April 24, 2015 [Page 16] INTERNET DRAFT New algorithms in TSIG October 24, 2014 +---------------------------------------+ | Message Hash Len | | (1 byte) | +---------------------------------------+ | Message Hash | | (variable) | +---------------------------------------+ | digest_secret_key Len | | (1 byte) | +---------------------------------------+ | digest_secret_key | | (variable) | +---------------------------------------+ Figure 6 CGA-TSIGe DATA Field 4.2.1.1. Public Key Request In the TSIG RDATA section, the Algorithm Name MUST be set to 'CGA-TSIGe', and the CGA-TSIGe Len field MUST be set to zero. This alerts the DNS server that the other Node needs its public key for encryption purposes. This format is used if a Node does not want to use DNSKEY RR [RFC3757] to retrieve the public key of the DNS server. 4.2.1.2. Public Key Response The DATA structure is similar to CGA-TSIG. There is only a flag field which indicates that it is a response to the public key request message. +---------------------------------------+ | AsyAlgorithm | | | +---------------------------------------+ | Type | | | +---------------------------------------+ | Parameter Len | | (1 byte) | +---------------------------------------+ | Parameters | | (variable) | +---------------------------------------+ | Signature | | (variable) | +---------------------------------------+ | Signature Len | | (1 byte) | +---------------------------------------+ | Signature | | (variable) | +---------------------------------------+ | Flag | Rafiee, et al. Expires April 24, 2015 [Page 17] INTERNET DRAFT New algorithms in TSIG October 24, 2014 | (1 bit) | +---------------------------------------+ Figure 7 CGA-TSIGe DATA Field (public key response) 4.2.2. Generation of CGA-TSIGe DATA 4.2.2.1. IPv6 Specifics Nodes can securely obtain the IP address of DNS resolvers from the DHCPv6 server (use SAVI-DHCP [savi-dhcp]); or from a DNS option of Router Advertisement message [RFC6106] after authenticating with the router via a trusted authority. The IP addresses can be generated using CGA, SSAS or other mechanisms. This is the same approach that a node can use for obtaining a DNS server IP address during a Dynamic DNS update. In case this approach is used for zone transfer, to avoid any malicious update to DNS server, it is RECOMMENDED that this IP address is set manually on the DNS server for the first time or cache the IP address of trusted resolvers in a trusted list and randomly select them in a unsecure network. 4.2.2.1.1. Generation of Query Request Message 1. Retrieve Public Key of DNS Server 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 [RFC3757] 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 asking for the public key of the DNS Server. The DNS Server then answers this query and includes the public key contained in the DNSKEY RR with the SEP flag set to zero (0). This indicates that it is not the zone key. It is also possible to use the RR format explained in sections 4.2.1.1 and 4.2.1.2 of this document. The DNS server SHOULD include CGA-TSIGe DATA so that the client can verify its IP address. In this case, there will be a binding between a DNS Server's public key and its IP address. If the Node can verify the DNS Server public key (explained below), it goes to step 2. Otherwise it discards the DNS message without further action. 2. Obtain Required Parameters From Cache. This step is the same as what is explained in section 5.1.3. 3. Generation of Secret Key After a successful verification, the Node generates a 16 byte random number called a secret key. The Node can use any algorithm explained Rafiee, et al. Expires April 24, 2015 [Page 18] INTERNET DRAFT New algorithms in TSIG October 24, 2014 in [RFC4086] to generate a good randomized value. It encrypts the secret key using the DNS Server?s public key. Then, the Node sets the digest_secret_key in CGA-TSIGe DATA structure to this encrypted secret key and set the digest_secret_key len to the length of this encrypted value. Similar to CGA-TSIG, MAC Size in TSIG RDATA MUST set to 0. The DNS Server knows what to do with MAC field from the Algorithm Type in TSIG. 4. Encryption of DNS message The Node uses the secret key generated in the previous step to encrypt the header, zone section, prerequisite, and update section for the DNS update message (see figure 8) or encrypt header, question, answer, authority of a DNS Query (see figure 9). It then calculates the length of a digest as a number of bytes in multiples of 8. For example, if the digest is 242 bytes then 242 = (30 * 8) + 2. Therefore, 6 bytes are added as padding, and then 31 is placed at the beginning of digest (see figure 10). If there is no padding for the digest then one zero-filled byte will be added at the end of digest. This allows the DNS Server to interpret this digest as a long string. +-----+------+--------+ |Type |Length|Reserved| |1byte|1 byte| 1 byte | +---------------------+ | Header | | 12 bytes | +---------------------+ | Encrypted sections | | variable length | +---------------------+ | Additional Data | | variable length | +---------------------+ Figure 8 Encrypted DNS update message +-----+------+--------+ |Type |Length|Reserved| |1byte|1 byte| 1 byte | +---------------------+ | Header | | 12 bytes | +---------------------+ | Encrypted sections | | variable length | +---------------------+ | Additional Data | | variable length | +---------------------+ Figure 9 Encrypted DNS Query message +---------------------+ Rafiee, et al. Expires April 24, 2015 [Page 19] INTERNET DRAFT New algorithms in TSIG October 24, 2014 | Len of digest | | (1 byte) | +---------------------+ | digest | | variable length | +---------------------+ Figure 10 Digest format in DNS question section The Node then adds a new header with the following data. This will allow the DNS Server to process this message. CGA-TSIGe actually uses the whole encrypted section as one single question followed by additional data. Field Sub-field Value Intrepretation ------------------------------------------------------- ID 0xdb42 Response should have ID 0xdb42 Flags 0x0100 QR 0 It's a query OPCODE 0 Standard query TC 0 Not truncated RD 1 Recursion requested RA 0 Not meaningful for query Z 0 Reserved RCODE 0 Not meaningful for query QDCOUNT 0x0001 One question follows ANCOUNT 0x0000 No answers follow NSCOUNT 0x0000 No records follow ARCOUNT 0x0001 No additional records follow The digest will be interpreted like the following table. Data Intrepretation ------------------------------------------ 0x1f String of length 248 follows 0x777777.. String is xxxxxx 0x00 End of this string 5. Generation of Message Hash In a case where a DNS Server responds to anonymous queries, as in a DNS Resolver scenario, the Node executes SHA256 by default on the whole DNS message. This includes the additional section and the TSIG RR as a part of additional section of DNS message. It then computes the Message Hash Len. In this case the message does not need to be signed by the Node (stub resolver) using its private key. This is because the DNS Server does not expect to verify the Node and it only checks for the message integrity and confidentiality. In the case a message contains Message Hash, the Node MUST set the Parameters Len , Signature Len, Old Pubkey Len and Old Signature Len to zero (0) and it SHOULD skips steps 6 and 7. 4.2.2.1.2. Generation of Query Response Message This is similar to generation of query request message as explained Rafiee, et al. Expires April 24, 2015 [Page 20] INTERNET DRAFT New algorithms in TSIG October 24, 2014 in section 4.2.2.1.1. of this document. However, steps 1, 3 and 5 should be skipped. 1. Obtain Required Parameters From Cache. 2. Encryption of DNS message Query response needs to be encrypted using a shared secret obtain from the Query Request message explained in section 4.2.4. 3. Generation of Signature This step is the same as what is explained in section 4.1.3. 4. Generation of Old Signature This step is the same as what is explained in section 4.1.3. 4.2.2.2. IPv4 Scenario The key pairs needs to be cached in order to generate a signature. If this Node changes its IP address, it also needs to cache the old IP address. Similar to the IPv6 scenario, the Node can obtain the hash of (public key + IPv4) and the IPv4 address of the DNS server from a DHCPv4 server. It can use [savi-dhcp]. If this Node is in unsecured environment, it can manually add the hash of (public key + IPv4 address) of its trusted DNS server. This is especially true in the Resolver scenario. The implementers SHOULD define a possibility for users to change the default value for CGA-TSIGe. 4.2.2.2.1. Generation of Query Request Message 1. Retrieves Public Key of DNS server This is similar to IPv6 scenario. 2. Obtain Required Parameters From Cache. This step is the same as what is explained in section 4.1.3. 3. Generation of Secret Key 4. Encryption of DNS Message 5. Generation of Message Hash All Three are similar to IPv6 scenario. 6. Generation of Signature This step is the same as what is explained in section 4.1.3. Rafiee, et al. Expires April 24, 2015 [Page 21] INTERNET DRAFT New algorithms in TSIG October 24, 2014 7. Generation of Old Signature This step is the same as what is explained in section 4.1.3. 4.2.2.2.2. Generation of Query Response Message This is similar to IPv6 scenario. 2. Obtain Required Parameters From Cache. This step is the same as what is explained in section 4.1.3. 1. Obtain Required Parameters From Cache. 2. Encryption of DNS message Query response needs to be encrypted using a shared secret obtain from the Query Request message explained in section 4.2.4. 3. Generation of Signature This step is the same as what is explained in section 4.1.3. 4. Generation of Old Signature This step is the same as what is explained in section 4.1.3. 4.2.3. Process of Public Key Response Message This section explains the verification needed for the process of public key response (The format of this message was explained in section 4.2.1.2) 4.2.3.1. IPv6 only Scenarios Depends on the algorithm used by the DNS server, CGA or SSAS verification process MUST be executed. 4.2.3.2. IPv4 only Scenarios The verifier node MUST execute hashing function on (public key + IPv4 address) and compare this value with the value exists on its cache or the value retrieved from a DNS server in a secure manner. 4.2.4. Process of Encrypted Query Request Message When the DNS server receives the message from any node with TSIG Rafiee, et al. Expires April 24, 2015 [Page 22] INTERNET DRAFT New algorithms in TSIG October 24, 2014 RDATA Algorithm type set to CGA-TSIGe, it executes the following steps: 1- Retrieves The Secret Key The DNS server retrieves the secret key from digest_secret_key field. Secret key is a random value generated by the node (such as a stub resolver) and encrypted using the public key of this DNS server (section 4.2.2.1.1 explains the steps to generate and encrypt this value). DNS server then decrypts this secret key using its own private key. 2- Decrypts the DNS Message The DNS server decrypts the DNS server message using this secret key and the symmetric algorithm, which by default is AES. The DNS server can then start the verification process explained in the next section. 4.2.5. Process of Encrypted Query Response Message When the node (like a client) receives a query response message from any node with TSIG RDATA Algorithm type set to CGA-TSIGe, it executes the following steps: 1- Retrieves The Secret Key This node, itself, generated this secret key. It fetches this secret key from its memory. 2- Decrypts the DNS Message The node decrypts the query response message using this secret key and the symmetric algorithm, which by default is AES. The node can then start the verification process explained in the next sections. 5. General Verification Steps This section explains general verification steps and can be used as a reference for verification in different scenarios. The modification of these steps is possible according the use case scenarios (next section). 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 uses the following steps: 1. Verify The Signature (IPv4 and IPv6) The Signature contained in CGA-TSIGe DATA should be verified. This Rafiee, et al. Expires April 24, 2015 [Page 23] INTERNET DRAFT New algorithms in TSIG October 24, 2014 can be done by retrieving the public key and signature from CGA-TSIGe DATA and using this public key to verify the signature. If the verification process is successful, then execute step 2. Otherwise, the message should be discarded. 2. Check The Time Signed (IPv4 and IPv6) The Time Signed value is obtained from TSIG RDATA and is called t(1). The current system time is then obtained and converted to UTC time and is called t(2). Fudge time is obtained from TSIG RDATA and is called t(fudge). If t(1) is in the range of t(2) and t(2) minus/plus t(fudge) (see formula 1), then step 3 will be executed. Otherwise, the message will be considered spoofed and discarded. 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. (t(1) - t(fudge)) <= t(2) <=(t(1) + t(fudge)) Formula: (1) 3. Execute The CGA Verification (IPv6 only) These steps are in section 5 of [RFC3972]. 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 6 will be executed. Otherwise the message will be discarded without further action. 4. Generate The Hash of (public key | IP address) (IPv4 only) The DNS server retrieves the hashing Algorithm Type from the CGA-TSIGe DATA structure. It then uses the following concatenations. Digest = hash(public key | IP address of the update requester) Where hash is SHA256 algorithm (by default) or another algorithm identified in Type section of CGA-TSIG DATA structure. It then compares digest with the hash value available in the DNS configuration. If they are the same, the Update Message should be processed, otherwise, go to step 5. 5. Generate The Hash of (Old Public Key + IPv4 Address) (IPv4 only) If the Old Public Key Length is zero, then skip this step and discard the DNS update message. If the Old Public Key Length is not zero, then the DNS server retrieves the hashing algorithm Type from the CGA-TSIGe DATA structure. It then concatenates the following values: Digest_old = hash (Old Public Key | IP address of the update requester) Rafiee, et al. Expires April 24, 2015 [Page 24] INTERNET DRAFT New algorithms in TSIG October 24, 2014 Where hash is the SHA256 algorithm (by default) or another algorithm identified in Type section of CGA-TSIGe DATA. It then compares digest_old with the hash value available in the DNS configuration. If they are the same, the Update Message should be processed, otherwise, go to step 8. 6. Verify The Source IP Address (IPv6 only) The source IP Address of the Update requester MUST be checked against the one contained in the DNS configuration. If they are the same, the Update Message should be processed, otherwise, proceed to step 7. 7. Verify The Public Key (IPv6 only) The DNS server checks whether or not the public key retrieved from CGA-TSIGe DATA is the same as what is available in the cache where the public keys and IP addresses are saved. If this Public Key is not found in the cache, then the update will be rejected. Otherwise, when the Old Public Key Length is not zero go to step 8. 8. Verify The Old Public Key (IPv4 and IPv6) If the Old Public Key Length is zero, skip this step and discard the DNS update message. If the Old Public Key Length is not zero, then the DNS server will retrieve the Old Public Key from CGA-TSIGe DATA and check to see if it is the same as what was saved in the DNS server's cache. If they are the same, execute step 6, otherwise discard the message. 7. Verify The Old Signature (IPv4 and IPv6) The Old Signature contained in CGA-TSIGe DATA should be verified. This can be done by retrieving the Old Public Key and the Old Signature from CGA-TSIGe DATA and then using this Old Public Key to verify the Old Signature. If the verification is successful, 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, discard the message. 6. CGA-TSIG/CGA-TSIGe Use Case Scenarios 6.1. The FQDN Or PTR Update (IPv6 only) 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 unless a stateless DHCPv6 server is available. CGA-TSIG/CGA-TSIGe can be used to give Nodes the ability of doing this process themselves. In this case the clients need to include the CGA-TSIG/CGA-TSIGe option to allow the DNS server to verify them. The verification process is as following. Rafiee, et al. Expires April 24, 2015 [Page 25] INTERNET DRAFT New algorithms in TSIG October 24, 2014 6.1.1. Verification Process The verification steps are the same as those is explained in section 5, 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 if the public key retrieved from CGA-TSIG/CGA-TSIGe DATA is the same as what was available in cache. If no entry is found 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 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 skipped. Otherwise, if the Old Public Key Length is not zero, go to step 5. 5. Verify The Public Key 6. Verify The Old Public Key 7. Verify The Old Signature 6.2. DNS Resolving Scenario (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. The Resolver's response SHOULD contain the CGA-TSIG DATA field in order to verify him. However, the client needs to include the TSIG RDATA and set the Algorithm Type to CGA-TSIG, and it MUST set the CGA-TSIG Len to zero (0). This allows the resolver to include CGA-TSIG in the client. If the Node needs to deploy DNS data confidentiality, then it needs to set the Algorithm Type to CGA-TSIGe and follows the step explained in section 4.2.2. In this particular scenario, the Node MUST set Message Hash in CGA-TSIGe. This allows the DNS server to ensure data integrity without going to the process of message decryption. In the generation of the CGA-TSIG/CGA-TSIGe for a Resolver, there is no need to include the IP Tag. This is because the Resolvers do not usually have several IP addresses so the client does not need to keep several IP addresses for the same resolver. +----------------+ +----------------+ Rafiee, et al. Expires April 24, 2015 [Page 26] INTERNET DRAFT New algorithms in TSIG October 24, 2014 | DNS Resolver | | DNS client | | | Ask for public key | | | | <------------------- | | | | Here you are | | | | -------------------> | | | | | Verification | | | | explained in | | | | section 4.2.3 | | | | | | | | Generation of | | | | Query request | | | |set message hash| | | |explained in | | | |section 4.2.2 | | | Encrypted DNS message| | | | <------------------- | | | Verification | | | | explained in | | | | section 6.2.1| | | | | | | | DNS message | | | | decryption | | | | explained in | | | | section 4.2.4| | | | Encrypt Query| | | | response | | | | explained in | | | | section 4.2.2| | | | |Encrypted Query response| | | | -------------------> | | | | | Verification | | | | explained in | | | | section 6.2.2 | | | | | | | | DNS message | | | | decryption | | | | explained in | | | | section 4.2.5 | +----------------+ +----------------+ Figure 11. DNS resolving scenario using CGA-TSIGe (Data confidentiality and secure authentication) 6.2.1. Client Verification Process (CGA-TSIGe only) 1. Retrieves Hashing Algorithm From CGA-TSIGe The resolver retrieves the hashing algorithm from CGA-TSIGe Type field. 2. Executes Hashing Algorithm on DNS Message The Resolver computes the SHA algorithm on the whole DNS message. It compares this with the value obtained from Message Hash of CGA-TSIGe. Rafiee, et al. Expires April 24, 2015 [Page 27] INTERNET DRAFT New algorithms in TSIG October 24, 2014 If they are the same, it decrypts the message using the shared secret obtained from the digest_secret_key section of the Other DATA section of TSIG RRType. 6.2.2. Resolver Verification Process When a Resolver responds to the client'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. These steps are as follows: 1. Verify The Hash of Public Key (IPv4 only) The client retrieves the SHA Algorithm Type from the Type section of CGA-TSIG/CGA-TSIGe, concatenates the following values: digest= hash(Resolver's Public Key | the Resolver's IP address) Where hash is a hash function (by default; SHA256). The client compares the digest with the value in its cache (received securely from a DHCP server or manually set by client). If they are the same, it stores its Public Key in its cache, and continues onto the next step. Otherwise the message will be discarded. 2. Verify The Signature (IPv4 and IPv6) The Signature contained in CGA-TSIG/CGA-TSIGe DATA can be verified by retrieving the Public Key and Signature from the CGA-TSIG/CGA-TSIGe DATA. If the verification process is successful, continue onto step 3, otherwise the message will be discarded. 3. Check The Time Signed (IPv4 and IPv6) 4. Execute The CGA Verification (IPv6 only) 5. Verify The Source IP Address (IPv6 only) If the Resolver's source IP address is the same as that which is known for the host or the length of Old Public Key is not zero (0), then step 6 will be executed. Otherwise the message SHOULD be discarded without further action. 6. Verify The Public Key (IPv6 only) The client checks whether or not the Public Key retrieved from CGA-TSIG/CGA-TSIGe DATA matches any Public Key that was previously saved in the storage where the Public Key and IP addresses of Resolvers are saved. If there is a match, then the message is processed. If not, then step 7 will be executed. Rafiee, et al. Expires April 24, 2015 [Page 28] INTERNET DRAFT New algorithms in TSIG October 24, 2014 7. Verify The Old Public Key (IPv4 and IPv6) If the Old Public Key Length is zero (0), discard this message without further action. If the Old Public Key Length is not zero(0), then the host will retrieve the Old Public Key from CGA-TSIG/CGA-TSIGe 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 8 will be executed. 8. Verify The Old Signature (IPv4 and IPv6) The Old Signature contained in CGA-TSIG/CGA-TSIGe DATA can be verified by retrieving the Old Public Key and Old Signature from CGA-TSIG/CGA-TSIGe DATA and then using this Old Public Key to verify the Old Signature. If the verification is successful, 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 will be discarded. 6.3. DNS Resolving Scenario (Authoritative NS to Recursive NS) This verification step of Authoritative Name Server to Recursive Name Server is the same as that explained in section 5. In this case the Recursive Name Server does not need to generate CGA-TSIG DATA, but the Root Name Server does need to include it in order to enable the Recursive Name Server to verify it. The Recursive Name Server needs to include the TSIG RDATA and set the Algorithm Type to CGA-TSIG. It MUST set the CGA-TSIG Len to zero (0). This allows the Root Name Server to know when to include CGA-TSIG for verification process in client. In case the node needs to use DNS data confidentiality, then it needs to set the Algorithm Type to CGA-TSIGe and follows the step explained in section 4.2.2. In this particular scenario, the Node MUST set the Message Hash in CGA-TSIGe. This allows the DNS server to ensure the data integrity of this message without going to the process of message decryption. 7. SeND Is Not Supported (IPv6 only) In the case where there are no cache parameters available during the IP Address generation, there are then three 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 or CGA-TSIGe data structure as explained in section 4.1 or section 4.2. The Node SHOULD skip the first section of the verification processes explained in section 5, section 6.1.1, section 6.2.1, and section 6.2.2. In the second scenario, as explained in section 4.1.3 (step 1), it is Rafiee, et al. Expires April 24, 2015 [Page 29] INTERNET DRAFT New algorithms in TSIG October 24, 2014 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 the DNS server. Later, the 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. In the third scenario, as explained in section 4.1.2.2., the Node can use the same approach used for IPv4 and retrieve the hash of (Public Key + IPv6 Address) from the DHCPv6 server. 8. CGA-TSIG/e Attack Protections There are several types of attacks that CGA-TSIG/CGA-TSIGe can prevent. The use of CGA-TSIG will reduce the number of messages needed 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 (4) messages are required. By modifying [RFC2845] to use CGA-TSIG, this will decrease the number of messages needed . The messages used in [RFC2930] (TKEY RR) are not needed when CGA-TSIG is used. 8.1. IP Spoofing This prevents the attack by finding a binding between the IP address and the Public Key for both IPv4 and IPv6 , with different approaches. 8.2. Resolver Configuration Attack When using CGA-TSIG/CGA-TSIGe, the DNS server (or client), would not need further configuration. This reduces the possibility of human errors being introduced into the DNS configurations. Since this type of attack is predicated on human error, the chances of it occurring are minimized. 8.3. Exposing A Shared Secret Using CGA-TSIG/CGA-TSIGe will decrease the number of manual steps required in generating the new shared secret and in exchanging it among the hosts to update the old shared secret. This manual step is required after a shared secret is leaked. 8.4. 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 Rafiee, et al. Expires April 24, 2015 [Page 30] INTERNET DRAFT New algorithms in TSIG October 24, 2014 server. If the attacker attempts to spoof the timestamp, the DNS server will check this message by verifying the signature. In this case, the verification process will fail preventing the replay attack. 8.5. Data Confidentiality Encrypting the whole DNS message will deny the attacker from knowing the content of DNS messages. This will avoid zone walking and many other attacks on DNS RRs. 9. Update to TSIG Specification To support CGA-TSIG/e as a new algorithm in TSIG, updates needs to be made in the following sections of TSIG specification. In case any node does not support CGA-TSIG/e, it only ignores these new algorithms. - 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 or CGA-TSIGe. - 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 or CGA-TSIGe, 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/CGA-TSIGe Data. 10. 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 1.1. 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 Rafiee, et al. Expires April 24, 2015 [Page 31] INTERNET DRAFT New algorithms in TSIG October 24, 2014 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 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. 11. 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 5.1, Type should allow for the use of future optional algorithms with regard to SeND. The default value is CGA. For this algorithm and other algorithms, (such as SSAS [4, 5], there needs to be a new number sequentially. IANA also needs to define a numeric algorithm number for ECC. The similar way that is defined for RSA. 12. Appendix 12.1. A Sample Key Storage For CGA-TSIG Rafiee, et al. Expires April 24, 2015 [Page 32] INTERNET DRAFT New algorithms in TSIG October 24, 2014 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) ); CGA-TSIG tables on mysql backend database 12.2. Stored parameters in the node Here is 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 file contains the cached DATA 12.3. CGA Generation Script Here introduces a sample CGA generation script for the nodes that does not support SeND. byte[] modifier; typedef int bool; #define true 1 #define false 0 // length_of_digest : 8 leftmost bytes of digest. //this function sets sec value on the first byte of digest //since interface ID is only 8 bytes, it returns only 8 leftmost bytes of digest Rafiee, et al. Expires April 24, 2015 [Page 33] INTERNET DRAFT New algorithms in TSIG October 24, 2014 byte[] set_secvalue(byte[] digest,int length_of_digest); //this function compares the 16 by cga_sec_value bits of digest to zero bool compare(byte[] digest, int cga_sec_value); //this function executes hashing function on cga_parameters byte[] sha1(byte[] cga_parameters); //this function reads public key from a file byte[] read_public_key(char[] public_key_path); //this function increments the modifier by one increment(byte[] modifier); //this function concatenates the input values. byte[] concat(byte[], byte[],....); //Write in a file CacheCGAparameters(byte[] ipv6_address, byte[] modifier, char[] public_key_path, int cga_sec_value, byte[] public_key_algorithm); //--------------main function ------------------------ int main(char[] interface_name) { byte[] cga=cgagen("\\xxx\key.pub",prefix); byte[] ipv6_address=concat(prefix,cga); //set the CGA address on a desired interface setIP(ipv6_address,"eth0\0"); CacheCGAparameters(ipv6_address,modifier,public_key_path, cga_sec_value, '1.2.840.113549.1.1.1'); } //------------------sample function for CGA Generation-------------- byte[] cgagen(char[] public_key_path, byte[] prefix, int cga_sec_value) { bool flag=true; byte[] cga; byte[] public_key=read_public_key(public_key_path); modifier= randomnumber(16); while(flag) { //concatinate all values byte[] cgaparameters=concat(modifier,prefix,0,public_key); byte[] digest=sha1(cgaparameters); if(compare(digest,cga_sec_value)==false) increment(modifier); else flag=false; } cga=set_secvalue(digest,8); return cga; } //-------------Sample function for random number generator---- //random generator explained in ra_privacy draft byte[] randomnumber(int length_byte) { byte[] num=new byte[length_byte]; srand(time(NULL)); for(int i=0;i