Security

/ˌsiː-ɛs-ˈpiː/

n. “Trust nothing by default. Especially the browser.”

CSP, short for Content Security Policy, is a defensive security mechanism built into modern browsers to reduce the damage caused by malicious or unintended content execution. It does not fix broken code. It does not sanitize input. What it does instead is draw very explicit boundaries around what a web page is allowed to load, execute, embed, or communicate with — and then enforces those boundaries with extreme prejudice.

At its core, CSP is a browser-enforced rulebook delivered by a server, usually via HTTP headers, sometimes via meta tags. That rulebook answers questions browsers used to shrug at: Where can scripts come from? Are inline scripts allowed? Can this page embed frames? Can it talk to third-party APIs? If an instruction isn’t explicitly allowed, it is blocked. Silence becomes denial.

The policy exists largely because of XSS. Cross-site scripting thrives in environments where browsers eagerly execute whatever JavaScript they encounter. For years, the web operated on a naive assumption: if the server sent it, the browser should probably run it. CSP replaces that assumption with a whitelist model. Scripts must come from approved origins. Stylesheets must come from approved origins. Inline execution becomes suspicious by default.

This matters because many real-world attacks don’t inject entire applications — they inject tiny fragments. A single inline script. A rogue image tag with an onerror handler. A compromised third-party analytics file. With CSP enabled and properly configured, those fragments simply fail to execute. The browser refuses them before your application logic ever sees the mess.

CSP is especially effective when paired with modern authentication and session handling. Even if an attacker manages to reflect or store malicious input, the policy can prevent that payload from loading external scripts, exfiltrating data, or escalating its reach. This makes CSP one of the few mitigations that still holds value when other layers have already failed.

Policies are expressed through directives. These directives describe allowed sources for different content types: scripts, styles, images, fonts, connections, frames, workers, and more. A policy might state that scripts are only allowed from the same origin, that images may load from a CDN, and that inline scripts are forbidden entirely. Browsers enforce each rule independently, creating a layered denial system rather than a single brittle gate.

Importantly, CSP can operate in reporting mode. This allows a site to observe violations without enforcing them, collecting reports about what would have been blocked. This feature turns deployment into a learning process rather than a blind leap. Teams can tune policies gradually, tightening restrictions as they understand their own dependency graph.

CSP does not replace input validation. It does not replace output encoding. It does not make unsafe frameworks safe. What it does is drastically limit the blast radius when something slips through. In that sense, it behaves more like a containment field than a shield — assuming compromise will happen, then making that compromise far less useful.

Modern frameworks and platforms increasingly assume the presence of CSP. Applications built with strict policies tend to avoid inline scripts, favor explicit imports, and document their dependencies more clearly. This side effect alone often leads to cleaner architectures and fewer accidental couplings.

CSP is not magic. Misconfigured policies can break applications. Overly permissive policies can provide a false sense of safety. But when treated as a first-class security control — alongside transport protections like TLS and authentication mechanisms — it becomes one of the most effective browser-side defenses available.

In a hostile web, CSP doesn’t ask whether content is trustworthy. It asks whether it was invited. Anything else stays outside.

/ˈnæ-t/

n. “Your private world, masquerading on the public internet.”

NAT, short for Network Address Translation, is a method used by routers and firewalls to map private, internal IP addresses to public IP addresses, enabling multiple devices on a local network to share a single public-facing IP. It hides internal network structure from the outside world while allowing outbound and inbound traffic to flow securely.

Without NAT, every device would need a unique public IP, which is increasingly impractical given the limited availability of IPv4 addresses. By translating addresses and port numbers, NAT conserves IP space and provides a layer of isolation, effectively acting as a firewall by making internal devices unreachable directly from the internet.

There are several types of NAT configurations. Static NAT maps one private IP to one public IP, useful for servers that need consistent external accessibility. Dynamic NAT maps private IPs to a pool of public IPs on demand. Port Address Translation (PAT), also called overloading, allows many devices to share a single public IP by differentiating connections via port numbers — this is the most common NAT in home routers.

Example: A home network with devices on the 192.168.1.0/24 range accesses the internet. Outbound requests are translated to the router’s public IP, each with a unique source port. Responses from external servers are mapped back to the correct internal device by the router, making this entire process transparent to users.

NAT interacts with many other networking concepts. VPNs, for example, often require special configuration (like NAT traversal) to ensure encrypted tunnels function correctly across NAT boundaries. Similarly, protocols that embed IP addresses in payloads, such as FTP or SIP, can face challenges unless NAT helpers or Application Layer Gateways are used.

While NAT is not a security mechanism by design, it provides incidental protection by concealing internal IP addresses. However, it should not replace firewalls or other security measures. Its primary function is address conservation and routing flexibility, critical in IPv4 networks and still relevant even as IPv6 adoption grows.

In short, NAT is the bridge between private and public networks: it translates, conceals, and allows multiple devices to coexist under a single IP, making modern networking feasible and scalable.

/ˌɛks-ɛs-ˈɛs/

n. “Sneaky scripts slipping where they shouldn’t.”

XSS, short for Cross-Site Scripting, is a class of web security vulnerability that allows attackers to inject malicious scripts into web pages viewed by other users. Unlike server-side attacks, XSS exploits the trust a user has in a website, executing code in their browser without their consent or knowledge.

There are three main types of XSS: Reflected, Stored, and DOM-based. Reflected XSS occurs when malicious input is immediately echoed by a web page, such as through a search query or URL parameter. Stored XSS involves the attacker saving the payload in a database or message forum so it executes for anyone viewing that content. DOM-based XSS happens when client-side JavaScript processes untrusted data without proper validation.

A classic example: a user clicks on a seemingly normal link that contains JavaScript in the query string. If the website fails to sanitize or escape the input, the script runs in the victim’s browser, potentially stealing cookies, session tokens, or manipulating the page content. XSS attacks can escalate into full account takeover, phishing, or delivering malware.

Preventing XSS relies on a combination of techniques: input validation, output encoding, and content security policies. Frameworks often include built-in escaping functions to ensure that user input does not become executable code. For example, in HTML, characters like < and > are encoded to prevent interpretation as tags. In modern web development, using libraries that automatically sanitize data, alongside Content Security Policy, greatly reduces risk.

XSS remains one of the most common vulnerabilities in web applications, making awareness critical. Even large, popular sites can fall victim if validation and sanitization practices are inconsistent. Testing tools, such as automated scanners, penetration tests, and bug bounty programs, often prioritize XSS detection due to its prevalence and impact.

In essence, XSS is about trust and control. Users trust a website to deliver content safely; attackers exploit that trust to execute unauthorized scripts. Proper sanitization, rigorous coding practices, and security policies are the antidotes, turning a website from a potential playground for malicious scripts into a secure, trustworthy environment.

/ˈdʌbəljuː-ˈeɪ-ɛf/

n. “A gatekeeper that filters the bad, lets the good pass, and occasionally throws tantrums.”

WAF, short for Web Application Firewall, is a specialized security system designed to monitor, filter, and block HTTP traffic to and from a web application. Unlike traditional network firewalls that focus on ports and protocols, a WAF operates at the application layer, understanding web-specific threats like SQL injection, cross-site scripting (XSS), and other attacks targeting the logic of web applications.

A WAF sits between the client and the server, inspecting requests and responses. It applies a set of rules or signatures to detect malicious activity and can respond in several ways: block the request, challenge the client with a CAPTCHA, log the attempt, or even modify the request to neutralize threats. Modern WAF solutions often include learning algorithms to adapt to the traffic patterns of the specific application they protect.

Consider an example: a user submits a form on a website. Without a WAF, an attacker could inject SQL commands into input fields, potentially exposing databases. With a WAF, the request is inspected, recognized as suspicious, and blocked before it reaches the backend, preventing exploitation.

WAFs can be deployed as hardware appliances, software running on a server, or cloud-based services. Popular cloud-based offerings integrate seamlessly with CDNs and CDN services, combining traffic acceleration with security filtering. Rulesets may follow well-known standards, such as the OWASP Top Ten, ensuring coverage against the most common web vulnerabilities.

While a WAF provides strong protection, it is not a panacea. It cannot fix insecure code or prevent all attacks, especially those that exploit logical flaws not covered by its rules. However, combined with secure coding practices, HTTPS, proper authentication mechanisms like OAuth or SSO, and monitoring, a WAF significantly raises the bar for attackers.

Modern WAF features often include rate limiting, bot management, and integration with SIEM systems, providing visibility and automated response to threats. They are particularly valuable for high-traffic applications or services exposed to the public internet, where the volume and diversity of requests make manual inspection impossible.

In short, a WAF is a critical component in web application security: it enforces rules, blocks known attack patterns, and adds a layer of defense to protect sensitive data, infrastructure, and user trust. It does not replace secure design but complements it, catching threats that slip past traditional defenses.

/ˈɛn-ɛs-siː-θriː/

n. “Proof of nothing — without revealing the map.”

NSEC3 is a record type in DNSSEC designed to provide authenticated denial of existence while mitigating the privacy concern inherent in the original NSEC records. Unlike NSEC, which directly reveals the next valid domain name in a zone, NSEC3 hashes domain names so that the zone structure cannot be trivially enumerated, making it more resistant to zone-walking attacks.

The fundamental purpose of NSEC3 is the same as NSEC: to cryptographically prove that a requested DNS name does not exist. When a resolver queries a non-existent domain, the authoritative server responds with an NSEC3 record. The resolver uses the hash and the associated RRSIG signature to verify that the non-existence claim is authentic, without seeing the actual names in the zone.

Hashing is the key feature. Each domain name in the zone is processed with a cryptographic hash function, often with multiple iterations, producing a pseudo-random label. NSEC3 records then link these hashed labels in canonical order. When a resolver queries a name, it is hashed the same way, and the resolver checks the hashed interval against the NSEC3 record to confirm the name’s absence.

This approach solves a significant problem with plain NSEC. Original NSEC records, while providing proof of non-existence, inadvertently exposed the zone’s structure — every non-existent query returned the next valid domain. With NSEC3, attackers cannot easily enumerate all names in the zone, increasing security for sensitive domains while retaining cryptographic proof.

Consider a domain example.com with hashed labels in NSEC3. A client queries secret.example.com. The server responds with an NSEC3 record showing that the hash of secret.example.com falls between two hashed domain names, confirming non-existence. The actual names remain concealed, protecting internal structure.

NSEC3 is fully compatible with DNSSEC’s chain of trust. Resolvers use the parent zone’s DS record, the zone’s DNSKEY, and the RRSIG on the NSEC3 to verify authenticity. If any signature verification fails, the response is discarded, preventing spoofed negative responses.

While NSEC3 increases security and privacy, it also adds computational overhead. Each query requires hashing and comparison operations, and zone signing becomes slightly more complex. Despite this, the trade-off is widely accepted, and many modern DNSSEC-enabled zones use NSEC3 by default to prevent zone enumeration without sacrificing cryptographic assurances.

In short, NSEC3 is the evolution of negative proof in DNSSEC: it preserves the integrity and authenticity of non-existent domain answers while preventing attackers from easily mapping the zone, enhancing both security and privacy in the domain name system.

/ˈɛn-ɛs-siː/

n. “Proof of nothing — and everything in between.”

NSEC, short for Next Secure, is a record type used in DNSSEC to provide authenticated denial of existence. In plain terms, it proves that a queried DNS record does not exist while maintaining cryptographic integrity. When a resolver asks for a domain or record that isn’t present, NSEC ensures that the response cannot be forged or tampered with by an attacker.

The way NSEC works is deceptively simple. Each NSEC record links one domain name in a zone to the “next” domain name in canonical order, along with the list of record types present at that name. If a resolver queries a name that isn’t present, the authoritative server returns an NSEC proving the non-existence: the requested name falls between the current name and the “next” name listed in the record. The resolver can cryptographically verify the NSEC using the corresponding RRSIG and DNSKEY records.

This mechanism prevents attackers from silently fabricating negative responses. Without NSEC, a man-in-the-middle could claim that any nonexistent domain exists or does not exist, undermining the authenticity of DNSSEC validation. NSEC ensures that negative answers are just as verifiable as positive ones.

There are nuances. The original NSEC design exposes zone structure because it reveals the next valid domain in the zone. For sensitive zones, this can be considered an information leak, potentially aiding enumeration attacks. Later enhancements, like NSEC3, mitigate this by hashing the domain names while preserving the proof of non-existence.

An example of NSEC in action: suppose a resolver queries nonexistent.example.com. The authoritative server responds with an NSEC showing alpha.example.com → zeta.example.com. The resolver sees that nonexistent.example.com falls between alpha and zeta, confirming that it truly does not exist.

NSEC does not encrypt DNS traffic. It only guarantees that absence can be proven securely. When combined with DNSSEC’s chain of trust, NSEC ensures that both presence and absence of records are authentic, making the DNS resistant to spoofing, cache poisoning, and other attacks that rely on falsifying non-existent entries.

In modern DNSSEC deployments, NSEC and its variants are indispensable. They complete the story: every “yes” or “no” answer can be trusted, leaving no room for silent forgery in the system.

/ˈdiː-ɛs/

n. “The chain that links the trust.”

DS, short for Delegation Signer, is a special type of DNS record used in DNSSEC to create a secure chain of trust between a parent zone and a child zone. It essentially tells resolvers: “The key in the child zone is legitimate, signed by authority, and you can trust it.”

In DNSSEC, every zone signs its own data with its private key, producing RRSIG records. But a validating resolver needs to know whether that signature itself is trustworthy. That’s where DS comes in — it links the child’s DNSKEY to a hash stored in the parent zone.

When a resolver looks up a domain in a child zone, it starts at the parent zone, retrieves the DS record, and uses it to verify the child’s DNSKEY. Once the public key is verified against the DS, the resolver can check the RRSIG on the actual records. This process builds the chain of trust from the root down to the leaf domains.

Without DS, a child zone’s signatures would be isolated. They could prove internal integrity but wouldn’t be anchored to the larger DNS hierarchy. DS provides the glue that allows validators to trust a signed zone without needing to manually install its keys.

Consider a hypothetical domain, example.com. The .com parent zone publishes a DS record pointing to the hash of the DNSKEY used by example.com. When a client queries example.com with DNSSEC validation, the resolver fetches the DS from .com, confirms the hash matches the child DNSKEY, then trusts the RRSIGs within example.com. If the hash doesn’t match, the resolver discards the response, preventing tampered or forged data from being accepted.

DS records do not encrypt data or prevent eavesdropping. They only provide a verifiable link in the chain of trust. If an attacker can manipulate the parent zone or inject a fraudulent DS, security fails — highlighting why operational security at registries is critical.

In short, DS is the handshake between parent and child in DNSSEC, establishing that the child’s keys are legitimate and forming the backbone of secure, authenticated DNS resolution. It transforms the DNS from a fragile trust-on-first-use system into one where the chain of signatures can be validated cryptographically at every step.

/ˈɑːr-ɑːr-sɪɡ/

n. “Signed. Sealed. Verifiable.”

RRSIG, short for Resource Record Signature, is a record type used by DNSSEC to cryptographically sign DNS data. It is the proof attached to an answer — evidence that a DNS record is authentic, unmodified, and published by the rightful owner of the zone.

In classic DNS, answers arrive naked. No signatures. No verification. A resolver asks a question and trusts the response by default. DNSSEC replaces that blind trust with math, and RRSIG is where the math lives.

An RRSIG record accompanies one or more DNS records of the same type — for example, A, AAAA, MX, or TXT. It contains a digital signature generated using the zone’s private key. That signature covers the record data, the record type, and a defined validity window. Change even a single bit, and verification fails.

When a validating resolver receives DNS data protected by DNSSEC, it also receives the corresponding RRSIG. The resolver retrieves the zone’s public key from a DNSKEY record and checks the signature. If the cryptographic check passes, the data is accepted as authentic. If it fails, the response is rejected — no fallback, no warning page, no partial trust.

RRSIG records are time-bound. Each signature has an inception time and an expiration time. This prevents replay attacks where old but valid data is resent indefinitely. It also means signatures must be refreshed regularly. Let them expire, and the zone effectively disappears for validating clients.

This time sensitivity is one of the reasons DNSSEC is unforgiving. Clock skew, stale signatures, or broken automation can all result in immediate resolution failures. The system assumes that if authenticity cannot be proven, the answer must not be used.

RRSIG does not exist in isolation. It works in concert with DNSKEY to prove signatures and with DS records to link zones together into a chain of trust. From the DNS root, through TLD operators, and down to the individual domain, each layer signs the next. RRSIG is the visible artifact of that trust at every step.

Without RRSIG, DNSSEC would be little more than a promise. With it, DNS answers become verifiable statements rather than suggestions. Cache poisoning attacks, forged responses, and silent redirections lose their power when signatures are enforced.

Consider an attacker attempting to redirect traffic to a fake server. Without DNSSEC, a forged response might succeed if delivered quickly enough. With RRSIG validation enabled, the forged data lacks a valid signature and is discarded before it can do damage.

Like the rest of DNSSEC, RRSIG does not encrypt DNS traffic. Anyone can still observe queries and responses. What it guarantees is that the answers cannot be altered without detection.

RRSIG is quiet when correct and catastrophic when wrong. It either proves the data is real or ensures it is not used at all. There is no middle ground.

In a system once built entirely on trust, RRSIG is the moment DNS learned how to sign its name.

/ˈdiː-ɛn-ɛs-kiː/

n. “This is the key — literally.”

DNSKEY is a record type used by DNSSEC to publish the public cryptographic keys for a DNS zone. It is the anchor point for trust inside a signed domain. Without it, nothing can be verified, and every signature becomes meaningless noise.

In traditional DNS, records are answers with no proof attached. A resolver asks a question and accepts the first response that looks plausible. DNSSEC changes that by requiring cryptographic validation, and DNSKEY is where that validation begins.

A DNSKEY record contains a public key along with metadata describing how that key is meant to be used. Private keys never appear in DNS. They remain securely stored by the zone operator and are used to generate digital signatures over DNS records. The corresponding public keys are published via DNSKEY so resolvers can verify those signatures.

There are typically two categories of DNSKEY records in a zone. One is used to sign individual DNS records, and the other is used to sign the key set itself. This separation allows keys to be rotated safely without breaking the chain of trust. The details are deliberately strict — mistakes here are not tolerated.

When a resolver receives a signed DNS response, it also receives one or more RRSIG records. These signatures are checked against the public keys published in DNSKEY. If the math checks out, the data is authentic. If it does not, the response is rejected, even if the data itself looks valid.

Trust does not stop at the zone boundary. A parent zone publishes a reference to the child’s key using a DS record. This creates the DNSSEC chain of trust, starting at the root and flowing downward through TLD operators, registrars, and finally the domain itself. DNSKEY is the endpoint where that trust becomes actionable.

Mismanaging DNSKEY records is one of the fastest ways to make a domain vanish from the Internet. An expired signature, a missing key, or a mismatched parent reference causes validating resolvers to fail closed. The domain does not partially work. It simply stops resolving.

This harsh behavior is intentional. DNSSEC assumes that authenticity is more important than availability in the presence of tampering. If a resolver cannot prove the answer is correct, it prefers silence over deception.

In practical terms, DNSKEY enables protection against DNS cache poisoning, man-in-the-middle attacks, and malicious redirection. Without it, attackers can reroute traffic, intercept email, or downgrade security protocols long before TLS ever gets a chance to object.

Modern DNS tooling often automates DNSKEY generation and rotation, but the underlying mechanics remain unforgiving. Keys expire. Algorithms deprecate. Cryptographic strength must evolve. DNSKEY records must evolve with it or the zone will fail validation.

DNSKEY does not encrypt data. It does not hide queries. It exists for one purpose only: to make DNS answers provably authentic.

When DNSKEY is present and correct, DNS becomes verifiable instead of hopeful. When it is wrong, the Internet reminds you immediately — and without sympathy.

/ˈdiː-ɛn-ɛs-sɛk/

n. “Proves the answer wasn’t forged.”

DNSSEC, short for Domain Name System Security Extensions, is a set of cryptographic mechanisms designed to protect the DNS from lying to you. Not from spying. Not from tracking. From quietly, efficiently, and convincingly giving you the wrong answer.

The traditional DNS was built on trust. Ask a question, get an answer, move on. There was no built-in way to verify that the response actually came from the authoritative source or that it wasn’t altered in transit. If an attacker could inject a response faster than the legitimate server, the client would believe it. This class of attack — cache poisoning — was not theoretical. It happened. A lot.

DNSSEC fixes this by adding cryptographic signatures to DNS records. When a domain is signed, each critical record is accompanied by a digital signature generated using public-key cryptography. The resolver validating the response checks that signature against a known public key. If the signature matches, the data is authentic. If it does not, the response is rejected outright.

This creates a chain of trust that starts at the DNS root, flows through ICANN and IANA, continues through TLD operators, and ends at the domain itself. Each layer vouches for the next. Break the chain anywhere, and validation fails.

Importantly, DNSSEC does not encrypt DNS data. Queries and responses are still visible on the network. What it provides is authenticity and integrity — proof that the answer you received is the same answer the authoritative server intended to give. Confidentiality is handled elsewhere, often by protocols like DNS over HTTPS or DNS over TLS.

The cryptographic machinery behind DNSSEC includes key pairs, signatures, and carefully structured record types. DNSKEY records publish public keys. RRSIG records contain signatures. DS records link child zones to parent zones. Each component is boring on its own. Together, they form a system that makes silent tampering extremely difficult.

Without DNSSEC, an attacker who poisons DNS can redirect traffic to malicious servers, intercept email, downgrade security, or impersonate entire services. With DNSSEC properly deployed and validated, those attacks fail loudly instead of succeeding quietly.

Consider a user attempting to reach a secure website. Even with TLS enabled, DNS remains a weak link. If DNS is compromised, the user may never reach the real server to begin with. DNSSEC ensures the name resolution step itself is trustworthy, reducing the attack surface before encryption even begins.

Adoption of DNSSEC has been slow, partly because it requires coordination across registries, registrars, operators, and resolvers. Misconfigurations can cause domains to disappear instead of merely degrade. The system is unforgiving by design. Incorrect signatures do not limp along — they fail.

Modern validating resolvers increasingly treat DNSSEC as expected rather than optional. Many CDN providers and large platforms sign their zones by default. The Internet has learned, repeatedly, that unauthenticated infrastructure eventually becomes hostile terrain.

DNSSEC does not make the Internet safe. It makes it honest. It ensures that when the Internet answers a question about names, the answer can be proven — not merely trusted.

It is invisible when it works, merciless when it does not, and foundational in a world where the first lie is often the most damaging one.