Rosanne Gingold

DNS is the foundational component of the internet yet it has no strong security mechanism to assure data integrity and authentication. Domain Name System Security Extensions (DNSSEC) provide these services to security-aware resolvers or applications using cryptographic signatures. DNSSEC is designed to thwart the most common attacks on DNS, such as DNS hijacking, DNS amplification, and DNS poisoning.

Despite being introduced two decades ago, the adoption of DNSSEC is very slow, especially in the second-level domains where the adoption rate remains steady at roughly 5%. The primary reasons for slow adoptions are complexities in the initial setup and ongoing maintenance.

The Domain Name System (DNS)[1], [2] is a crucial component of the Internet. It enables communication using domain names that are easier to remember than numerical IP addresses. In essence, DNS is a distributed database for looking up data, based on domain name and query type, that maps human-readable hostnames to IP addresses.

Modern DNS is not only useful to end-users but also essential to other core network technologies, including telephone number mapping, SIP, email, spam filtering, and directory services. The beginnings of the DNS were a lot more modest. Its original design from 1983 focused on scalability and did not include any security considerations. As it originally did, DNS continues to rely on plain text files and unencrypted UDP-based communication.

Flaws in DNS were identified and discussed in the early 1990s[3]. The Domain Name System Security Extensions (DNSSEC) was published in 1997 and further refined in 2005.[4] The Domain Name System (DNS) security extensions provide origin authentication and integrity assurance services for DNS data, including mechanisms for authenticated denial of the existence of DNS data[4]. To ensure authentic replies, DNSSEC relies on cryptographic keys. Private keys are used for digital signatures generated for resources and can be verified by their public counterparts.

Initially, DNSSEC adoption was very slow. It picked up around 2011 and reached its peak in 2014. Ever since then, DNSSEC adoption has been going down. In this paper, we will attempt to understand why.

DNS, DNSSEC, Datagram, DNS Zone, RRSIG, DNSKEY

DNS was born out of an observation, made in 1982, that the ‘HOSTS.TXT’ text file-based system for mapping between hostnames and IP addresses was not scalable. As the number of computers connected to the Internet was rapidly growing this issue became very apparent. On the modern *nix systems, the file is still present and is located at /etc/hosts. The file structure is fairly straightforward as shown in Fig. 1

Fig.1 Structure of /etc/hosts used for local DNS resolution

As Fig.1 demonstrates, to set up a translation for the small number of places that were available at the beginning of the Internet, a network address followed by a space and followed by the name entry was all that was needed.

The HOSTS.TXT was centrally maintained on a computer at the Stanford Research Institute Network Information Center (SRI-NIC) and distributed to all computers on the Internet via file transfers[1]. That model did not fit the trend towards more of the distributed management of the Internet. At the time, the internet was transforming rapidly, moving away from the original ARPANET to the TCP/IP-based network. The net result of this transition was that the number of hosts, which originally was roughly equal to the number of the connected organization, grew rapidly and became roughly equal to the number of workstations (users).

That increase directly affected the size of the HOSTS.TXT and the number of transfers. As a result, the costs associated with managing the system grew exponentially and organizations were forced to invest significant resources into managing network addresses, names, etc. It became apparent and quite logical that some sort of a partitioning system was needed to allow local control of the local names and address space.

RFC 882 and RFC 883 specify the original design of the DNS. [5], [6]. Although DNS went through several transformations, the current specifications and usage are quite similar to the original design. [7], [8]. DNS design base assumptions were and are:

As one can notice, no security assumptions were made in any shape or form. [1]

There are three major components used for DNS: the namespace, Name Servers (NS), and Resolvers.

-The namespace is a tree-structured entity, where each branch of the tree is called a domain. Each domain is a collection of resource records (RRs) that maps hostnames to IP addresses and other information. DNS queries are attempts to retrieve specific resource records from a particular domain.

-Name Servers(NS) are repositories of information and answer DNS queries based on the information they possess. Name Servers host the namespace.

-Resolvers interface with client programs and implement routines needed to find the correct NS that holds the information needed by the client.

Note: Name servers and resolvers can be combined into a single entity.

DNS RRs are organized into what is known as the zone file. Like the original HOSTS.TXT, the zone file is also just a specially formatted plain text file. Name Servers for the same domain have the same copy of the zone file distributed to them. Changes to the zone file are typically what triggers zone transfers, i.e zone file distributions.

Every zone file has what is called an SOA record, also known as the Start of Authority. There could be only one SOA record per zone. However, there are multiple Resource Records (RRs) of various types per zone. Fig. 2 provides an example of the complete zone file for the fictional example.com domain.

Fig. 2 example.com very basic zone file

To speed up the name resolution process and reduce congestion, DNS uses UDP protocol as its transport by default, with TCP being used as a failback. Failback to TCP occurs when the request or the response is greater than a single packet.

The iPv4 standard specifies that every host must be prepared to reassemble packets of 576 bytes or less [9]. IPv4 header, when using options might be as large as 60 bytes. UDP header is 8 bytes. Total DNS UDP packet size is normally 512 bytes[10],[8]. Once IPv6 adoption completes globally, the minimum size of the UDP payload for DNS messages would become 1232 bytes[10].

DNS namespace is a very hierarchical tree-structured system as illustrated in Fig. 3

Fig. 3 DNS Namespace hierarchy.

At the very top of the tree sits the root domain “.”. The first level below is referred to as Top-Level Domains, with their subdomains known as Second-level domains. The deeper into the tree, the more partitions the DNS database splits into. Overall, 13 Name Servers are serving the root zone[11]. The Root Zone file provides delegation information for top-level domains. Fig. 4 illustrates the section of the root zone file responsible for the microsoft.com domain delegation.

Fig. 4 Microsoft.com delegation information from the root zone file (http://www.internic.net/domain/root.zone)

As original DNS design assumptions did not include any security considerations, DNS is inherently not secure. In the early 1990s, Steve Bellovin of AT&T Bell Laboratories wrote a paper titled “Using Domain Name System for System Break-ins”. However, he did not publish it until 1995. In his paper, he described several attacks that relied on DNS. His work only underscored DNS’s susceptibility to attacks like hijacking and cache poisoning. However, the formal Threat Analysis of the Domain Name System (DNS) was only published 9 years later in RFC 3833 [12].

According to RFC3833, members of the DNS working group had a meeting in November of 1993 which is recognized as the earliest organized work on Domain Name System Security Extensions (DNSSEC). As a result of this meeting, outlines of the DNSSEC design considerations became apparent [12]:

In addition, during this meeting, the team made an explicit decision that DNS data is to remain publicly available and ruled out data disclosure threats explicitly out of scope for DNSSEC.

The first DNSSEC RFC, RFC2065, was published in 1997. In that document, DNSSEC was defined as a mechanism to assure data integrity, authentication, and storage of authenticated public keys. The stored keys enabled security-enabled resolvers to learn the authenticating keys of zones in addition to the zones that they are configured for. The keys associated with DNS names can be used for the support of other protocols as well.

There are 3 distinct services provided by DNSSEC:

DNSSEC is very explicitly designed to provide the same answers to all inquirers. Therefore, no attempts have been made to differentiate inquirers using access control lists or other means. DNSSEC does not provide any confidentiality for queries and responses as well.

DNSSEC relies on cryptographic mechanisms to verify the integrity and authenticity of DNS records. Each zone needs to provide three record types to achieve the said goals [13]:

A typical DNS query sequence is illustrated in Fig. 5

Fig. 5 Traditional DNS request sequence

A DNSSEC enabled DNS query sequence is illustrated in Fig. 6

Fig. 6 DNSSEC-enabled DNS query sequence

As seen in the illustrations, DNSSEC adds 14 additional steps compared to the traditional DNS request sequence. These extra steps are derived from the DNSSEC hierarchical public key infrastructure, which establishes a chain of trust to mirror the structure of the DNS hierarchy, where the root of trust is in the DNS root zone[13]. The overall process of trust verification is very similar to the x509 trust chaining.

DNSSEC is ultimately invisible to the end-user as DNS resolution occurs before a user ever interacts with an application. In cases of the hijacked DNS, the user may end up interacting with an impostor instead. Therefore, even if the endpoint is protected by the strongest firewall, end-users data is at risk if DNS architecture is not protected. In the future, DNSSEC may join TLS in becoming an implicit requirement, expected by the end-users and digital services.

Despite the importance, DNSSEC adoption is not yet at 100%. Fig. 7 illustrates the current trend of DNSSEC adoption [14]. As one can observe from the data, despite being introduced in 1997, adoption didn’t really start until the second half of 2010. It remained below 200 signed Top Level Domains (TLDs) up until 2014. In 2014 the adoption rate rapidly accelerated, peaking in 2017. Ever since the trend remained constant if not sloping downward slightly.

Fig.7 Current DNS adoption trend.

Internet Societies report on the state of DNSSEC deployment in 2016 [15] indicated that only 89% of top-level domain zones signed with only around 47% of country-code TLDs.

4 years later, as of January 2020, the % of TLDs signed in root is still at 90% and only 4% of second-level domains signed [14]. The current statistics are shown in Fig. 8 below.

Fig. 8 % of signed domains as of January 2020.

What makes DNSSEC adoption so challenging? Turns out, it almost has nothing to do with a query latency or performance. In our test comparing name resolution for DNSSEC-enabled domain vs. not-enabled one, the latency penalty was negligible compared to the overall length of the transaction. Fig. 9 shows DNS resolution time for the DNSSEC-enabled and properly-configured domain ‘internetsociety.com’ with DNSSEC (+dnssec flag) and without it. Although the real-time for the DNSSEC-enabled query is 2x of the not DNSSEC-enabled one, 254ms vs. 122ms, the overall perceived impact on a typical web transaction remains negligible.

Fig. 9 DNSSEC vs DNS name resolution times.

If performance is not a real factor, then challenges must be attributed to other aspects of the system like initial configuration complexity and ongoing maintenance and support.

To begin, 512 bytes afforded by the default DNS specified maximum UDP message size is no longer enough due to the added burden of added digital signatures in each response while performing trust validation [16]. In some extreme cases, the response could be so large that it gets fragmented. Many firewalls are configured to block fragments, effectively blocking name resolution. This issue is especially apparent when RSA-based signatures are used.

The complexity of DNSSEC implementation very often results in misconfigurations. A misconfiguration of DNSSEC deployment can result in a broken chain of trust. There are 6 most common misconfigurations [17]:

DS Mismatch: if the child zone DNSKEY does not match DS RRs in the parent zone, the chain of trust will be broken and RRs in the child zone and below are deemed bogus.

DNSKEY Missing: if a DNSKEY referenced in RRSIG or DS is needed to complete the chain of trust but it is missing, the chain of trust is broken.

RRSIG Missing: If an authoritative server is missing RRSIGs for a given RRset, the chain of trust is broken.

RRSIG Mismatch: results in a broken chain of trust.

RRSIG Validity Period Mismatch: If RRSIG is presented outside of its validity dates, the chain of trust is broken.

NSEC Missing: NSEC is needed to confirm the non-existent domain. It is critical to insecure delegations for proving that no DS RRs exist for the child zone, thus the chain of trust is broken and it will fail validation.

Uploading a DS record to the parent zone requires it to be passed to the registry. However, domain owners are not allowed to interact with the registry directly: only a registrar, an organization certified by ICANN to sell domains, has the authority to access the registry. The registrar must provide the NS and the DS record set. The situation becomes even more complicated for the organization that outsources DNS hosting to a third party.

In their paper, Van Andrichem et al performed a detailed analysis on DNSSEC misconfiguration [18].

The group analyzed 122,779 signed domains from .bg, .br, .co, .com, .nl and .se domains and their findings were quite revealing. Fig. 10 illustrates the data they’ve collected on misconfigurations found in those TLDs.

Fig.10 DNSSEC misconfiguration distribution.

As one can observe, almost 30% of the domains in those zones had their DNSKEY missing and 10% had failed DNSKEY validation by the DS. 25% had their Zone Signing Key (ZSK) invalidated by the Key Signing Key(KSK), indicating an unsuccessful key rollover attempt that has not been noticed by the domain owner yet.

Fig. 11 Shows the effect of these misconfigurations caused in the said domains' reachability where only 26% of domains were reachable [18].

Fig. 11 Availability of DNSSEC misconfigured domains.

RRSIGs have a limited time span and must be periodically updated. Updating RRSIG requires re-signing of RRsets they cover as RRSIG is added to the zone for each of the resource records that were present before zone signing.

DNSKEYs technically do not expire. However, it is a good security practice to periodically replace them. To ensure disruption-free service, it is recommended to maintain at least 2 DNSKEYs. Rolling over a DNSKEY involves coordination with the owners of the parent zone [19], [20].

Despite the shortcoming identified here in the DNSSEC CHALLENGES section, DNSSEC has the support needed to become the de facto mechanism to provide key distribution, data origin authentication, and transaction and request authentication. However, 23 years since its introduction, it faces the same set of challenges as it did on day one. Cryptographic bootstrapping and key rollover problems remain critical open questions.

The issues outlined here have been noticed by the DNSSEC community. The work to improve and accelerate DNSSEC adoption, especially for the second-level domains, is ongoing. Only real security in the internetworking environment can be achieved with cryptography [3]. DNSSEC directly addresses that by designing a hierarchical PKI. However, current complexities in deployment and ongoing maintenance are the primary factors affecting the widespread DNSSEC adoption.

The main focus of future work should be on reducing complexity and reducing maintenance costs. Adopting IPv6 should help with the issues caused by packet fragmentation [21].

[1] P. V. Mockapetris and K. J. Dunlap, “Development of the Domain Name System,” p. 11.

[2] P. V. Mockapetris, “Domain names - implementation and specification.” [Online]. Available: https://tools.ietf.org/html/rfc1035. [Accessed: 08-Mar-2020].

[3] S. M. Bellovin and T. B. Laboratories, “Using the Domain Name System for System Break-ins,” p. 11.

[4] M. Larson, D. Massey, S. Rose, R. Arends, and R. Austein, “DNS Security Introduction and Requirements.” [Online]. Available: https://tools.ietf.org/html/rfc4033. [Accessed: 08-Mar-2020].

[5] “RFC 882 - Domain names: Concepts and facilities.” [Online]. Available: https://tools.ietf.org/html/rfc882. [Accessed: 13-Mar-2020].

[6] “RFC 883 - Domain names: Implementation specification.” [Online]. Available: https://tools.ietf.org/html/rfc883. [Accessed: 13-Mar-2020].

[7] “RFC 1034 - Domain names - concepts and facilities.” [Online]. Available: https://tools.ietf.org/html/rfc1034. [Accessed: 13-Mar-2020].

[8] “RFC 1035 - Domain names - implementation and specification.” [Online]. Available: https://tools.ietf.org/html/rfc1035. [Accessed: 13-Mar-2020].

[9] “RFC 791 - Internet Protocol.” [Online]. Available: https://tools.ietf.org/html/rfc791#section-2.2. [Accessed: 13-Mar-2020].

[10] “UDP payload size for DNS messages.” [Online]. Available: https://tools.ietf.org/id/draft-madi-dnsop-udp4dns-00.html. [Accessed: 13-Mar-2020].

[11] “IANA — Root Servers.” [Online]. Available: https://www.iana.org/domains/root/servers. [Accessed: 13-Mar-2020].

[12] “RFC 3833 - Threat Analysis of the Domain Name System (DNS).” [Online]. Available: https://tools.ietf.org/html/rfc3833. [Accessed: 13-Mar-2020].

[13] T. Chung et al., “Understanding the role of registrars in DNSSEC deployment,” in Proceedings of the 2017 Internet Measurement Conference, London, United Kingdom, 2017, pp. 369–383, DOI: 10.1145/3131365.3131373.

[14] R. Lamb, “DNSSEC Deployment Report.” [Online]. Available: http://rick.eng.br/dnssecstat/. [Accessed: 15-Mar-2020].

[15] “State of DNSSEC Deployment 2016,” Internet Society. [Online]. Available: https://www.internetsociety.org/resources/doc/2016/state-of-dnssec-deployment-2016/. [Accessed: 15-Mar-2020].

[16] Gijs van den Broek, Roland van Rijswijk-Deij, Anna Sperotto, and Aiko Pras, “DNSSEC Meets Real World: Dealing with Unreachability Caused by Fragmentation.” [Online]. Available: https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=6828880. [Accessed: 22-Feb-2020].

[17] C. Deccio, “Maintenance, mishaps and mending in deployments of the domain name system security extensions (DNSSEC),” International Journal of Critical Infrastructure Protection, vol. 5, no. 2, pp. 98–103, Jul. 2012, DOI: 10.1016/j.ijcip.2012.05.002.

[18] N. L. M. van Adrichem et al., “A measurement study of DNSSEC misconfigurations,” Security Informatics, vol. 4, no. 1, p. 8, Oct. 2015, DOI: 10.1186/s13388-015-0023-y.

[19] J. Ihren, J. Dickinson, and S. Morris, “DNSSEC Key Rollover Timing Considerations.” [Online]. Available: https://tools.ietf.org/html/rfc7583. [Accessed: 15-Mar-2020].

[20] W. (Matthijs) Mekking and O. M. Kolkman, “DNSSEC Operational Practices, Version 2.” [Online]. Available: https://tools.ietf.org/html/rfc6781. [Accessed: 15-Mar-2020].

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In the Philippines, Tagalog is the most spoken language. It is in the western branch of the Malayo-Polynesian family. The capital of the island is located in the central and southern parts. If the data for second language speakers are added, the figure reaches more than 100 million.

The United States and Canada have many communities of Tagalog speakers due to the increasing emigration of Filipinos to other parts of the world. It is in the ninth position of the most spoken languages in the US.

It is spoken by more than 23 million Filipinos as their first language and by more than 80 million as a second language.

It is the basis of the national language. Fray de Totanés was a Franciscan friar who was born in Totano in 1688.

The National Language Institute was created by the first Philippine National Assembly in 1937 to create a new language. In 1961, the language became known as Pilipino.

The national language of the Philippines has been the subject of controversy and misunderstandings.

Many Filipinos have thoughts about the Filipino language.

Most of the Filipino people think that Filipino is almost identical to Tagalog. One Filipino asked another if he spoke "Tagalog" or "Filipino". Adherents to the second opinion maintain that Tagalog does not include words like 'beautiful', and that they are not used in Tagalog-speaking areas.

Some people believe that the Philippine language should include English terms, which Tagalog does not. This position is criticized by the most respected linguists in the country and also by the people who call the language they speak "Taglish" due to the mixture that is made of both languages.

Filipino is strictly based on Tagalog and attempts to replace words of English or Spanish origin with Tagalog root terms.

There are people in academia who think that the Philippine language is an amalgam of the languages spoken in the Philippines, and there are people who think that English should be included in the lexicon. The Philippine languages are not dialects of the same language, but true languages per se, unintelligible from each other.

The purpose of achieving a true lingua Franca is not achieved if vocabulary and grammar are included.

Perhaps Filipino is the only language spoken in Metro Manila. The native Manileo speech has words from the other Filipino languages. The Tagalog used in the capital is difficult to serve as a standard. There are no dictionaries or guides that tell you which words are part of the official language.

Many Filipinos who speak two or more languages, with English predominating among them, are now using Taglish as their everyday language. Implementation of this language in formal and written communications is difficult even when it's suitable for informal communication.

The southern parts of central Luzon are home to many Tagalog dialects. The following dialects are identified in the Ethnologue Language Database.

The Spanish conquistadores brought with them three vowels: /a/, /i/ and /u/. The number of vowels in Spanish increased to five, each of which has a long version. The vowels of modern Tagalog are shown in the table.

There are six diphthongs in Tagalog: /a/, //, //, /i/, and /ei/.

It is written in Spanish and Tagalog and was written in the year 1593 in the printing house of San Miguel, Manila.

There is a The questions are first in Romce and then in Tanogang.

The Spanish language had an influence on Tagalog.

One third of the words in the language are Spanish. The Tagalog phrase 'Kumusta?' is a classic example. This sentence came from a question.

Spanish-influenced Tagalog words refer to objects that were unknown to the indigenous inhabitants before the Spanish arrived. The table, silya or kutsara are examples. The names of the days of the week and the months are foreign concepts that are used in many of the adopted words.

The curious phenomenon of two or more words referring to the same concept is recreated by this adoption of words.

For example, the word for chair in Tagalog may be native upuan or Spanish silya, or the word for city may be native lungsod or Spanish Siyudad.

Can you turn on the window fan? "Pwede mo ba buksan ang bentilador na malapit sa bintana?" is what it is in Tagalog.

Other words of Hispanic origin.

The meaning of certain words has changed, for example, which means "of course" in Tagalog.

Seguro means perhaps.

Spanish had more sounds than pre-colonial Tagalog. The original vowels of Tagalog were /a/, /i/ and/u/. The vowels /e/ and /o/ weren't distinguishable but were allophones. The number of Spanish words that have these distinctions increased to five.

Baybayin was the abugida where Tagalog was written before the Spanish colonial period in the Philippines. The writing system was composed of symbols that represented vowels and consonants.

It is believed to be descended from the script used by the Bugis in Sulawesi and is a member of the Brahmic family.

Baybayin fell out of favor in favor of using the Latin alphabet because of its high level of literacy.

Baybayin is an abugida, or alphasyllabary, rather than an alphabet, and has caused confusion.

The Baybayin alphasyllabary doesn't represent all of the letters of the Latin alphabet. Baybayin uses symbols instead of letters to make sounds.

A "kudlit" resembling an apostrophe is used to change the sound of the vowels. The vowels are "E" or "I" if the kudlit is used. The vowels are "O" or "U" if the kudlit is used below.

Spanish missionaries added a cross to the symbol to make it sound like a letter instead of a letter. Previously, the reader was forced to use context when reading words with no following vowels.

The example is:

The Spanish orthography of 32 letters called "AbecedARIO" was used to create a variety of forms for Tagalog. The letters are ch, ll, ng,, ng/g and rr.

The Old Spanish spelling of the spelling had different rules, such as using H for J, and Y for I, descending from it.

A new alphabet consisting of 20 letters called "ABAKADA" was introduced in school books.

The rules are unique to Abakada and the 20 letters are based on the old Baybayin script. Removed unnecessary letters (C, Q, V, Z), letters that did not have an exact baybayin character (F, J, Ñ, X), and spelling rules like C (k) for A, O and U vowels, Qu (k ) for vowels I and E, etc.

The Department of Education released a memo in 1987 stating that the Philippine alphabet had changed to a new 28-letter alphabet.

The English alphabet has 26 letters.

There are two sets of numbers, one native and one Spanish. Tagalog speakers use numbers in English, as they are better able to say dates in English.

In Spanish, months and days are also called months and days.

"Month" in the Philippines is "buwn", which means "month" or "archaic", and "day" is "araw", which means sun. Tagalog months and days are capitalized.

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