What is DNSSEC and why is it important?

DNSSEC stands for Domain Name System Security Extensions, a suite of extension specifications by the Internet Engineering Task Force (IETF) for securing data exchanged in the Domain Name System (DNS) in Internet Protocol (IP) networks. DNS is a critical component of the Internet, as it translates human-friendly domain names (such as example.com) to the IP addresses (such as 192.0.2.1) needed by servers, routers, and other network devices to route traffic across the Internet to the proper destination.

However, DNS was designed in the 1980s when security was not a primary consideration in its design. As a result, DNS data can be easily forged or manipulated by attackers, leading to various types of attacks, such as DNS cache poisoning, where an attacker redirects users to malicious websites by altering the DNS records in a cache server.

DNSSEC aims to protect applications using DNS from accepting forged or manipulated DNS data by providing cryptographic authentication of data, authenticated denial of existence, and data integrity. With DNSSEC, every DNS zone has a public/private key pair, and every DNS record in the zone is digitally signed by the zone owner using the private key. When a DNS resolver receives a response from an authoritative name server, it can verify the digital signature using the public key and check if the data is identical (i.e., unmodified and complete) to the data published by the zone owner.

DNSSEC can protect any data published in the DNS, including text records (TXT), mail exchange records (MX), and references to cryptographic certificates stored in the DNS such as Certificate Records (CERT), SSH fingerprints (SSHFP), IPSec public keys (IPSECKEY), TLS Trust Anchors (TLSA), or Encrypted Client Hello (SVCB/HTTPS records for ECH). This can enable various security applications that rely on DNS data, such as secure email, secure web browsing, secure file transfer, and secure voice over IP.

DNSSEC does not provide confidentiality of data; it only ensures that the data is authentic and has not been tampered with. DNSSEC also does not protect against denial-of-service attacks directly, though it may provide some indirect benefit by allowing the use of potentially untrustworthy parties for caching or forwarding. Other standards are used to secure bulk data sent between DNS servers, such as TSIG or SIG(0).

DNSSEC is an important technology for enhancing the security and trustworthiness of the Internet. By deploying DNSSEC on your domains and servers, you can help protect your users and customers from various types of attacks that exploit the vulnerabilities of the DNS protocol.

How does DNSSEC work?

DNSSEC works by adding cryptographic signatures to existing DNS records to establish a secure DNS. The signatures are stored in DNS name servers alongside common record types, such as A, AAAA, MX, CNAME, etc. By checking the signature, a DNS resolver can verify that the data is authentic and has not been altered en-route.

DNSSEC uses public key cryptography to create and verify the signatures. Every DNS zone has a zone-signing key pair (ZSK): the private portion of the key digitally signs each RRset (a group of records with the same type) in the zone, while the public portion verifies the signature. The public ZSK is stored as a DNSKEY record in the zone.

To enable DNSSEC validation across different zones, there is also a key-signing key pair (KSK) for each zone. The KSK signs only the DNSKEY record that contains the ZSK, and its public portion is stored as another DNSKEY record in the zone. The KSK’s public key is also hashed and stored as a DS record in the parent zone. This creates a chain of trust from the root zone to the child zones.

When a DNS resolver receives a response from an authoritative name server, it can follow the chain of trust and verify the signatures using the public keys. For example, if a resolver queries for blog.example.com, it can check the signature of the A record using the public ZSK of example.com, which is signed by the KSK of example.com. Then it can check the signature of the KSK using the public DS record of example.com, which is stored in the .com zone and signed by the KSK of .com. Finally, it can check the signature of the KSK of .com using the public DS record of .com, which is stored in the root zone and signed by the KSK of the root.

DNSSEC also provides authenticated denial of existence, which means that if a record does not exist, the authoritative name server can prove it using either NSEC or NSEC3 records. These records indicate which records exist between two consecutive names in a zone, so if a resolver queries for a non-existent name, it can receive an NSEC or NSEC3 record that covers that name and proves its non-existence.

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