Every digital interaction, from sending an email to completing an online payment, relies on trust. But how is trust built online, and how can users be certain their communication is private and authentic? The answer is public key cryptography, the backbone of secure digital communications.
Unlike traditional encryption methods that depend on a single shared secret, public key cryptography uses two mathematically linked keys: one public and one private. This system enables confidentiality, integrity, and authentication at scale, forming the basis for technologies that protect everything from online banking sessions to the Domain Name System (DNS).
By understanding how public key cryptography works, organizations and individuals can better appreciate why it remains central to internet security, and why it underpins critical protocols like SSL/TLS and Domain Name System Security Extensions (DNSSEC).
What is Public Key Encryption Cryptography?
PKI is a form of asymmetric cryptography that uses a pair of mathematically related keys to encrypt and decrypt data. This stands in stark contrast to its predecessor, symmetric cryptography, such as the Advanced Encryption Standard (AES), which uses a single, shared key for both locking and unlocking information. The challenge with symmetric key algorithms is distribution: how do you securely share the secret key with the intended recipient without someone else intercepting it first?
Asymmetric cryptography solves this problem by creating two distinct keys: a public key and a private key. The public key can be shared freely with anyone, while the private key must be kept secret by its owner.
Think of it like a personal mailbox. Your mailbox has a public mail slot (the public key) that anyone can use to deposit letters. However, only you possess the unique physical key (the private key) to open the mailbox and retrieve the contents. In this analogy, anyone can send you a secure message, but only you can read it. This two-key system is the cornerstone of modern key cryptography.
How Does Public Key Encryption Work?
The PKI process involves a precise sequence of steps that ensures the confidentiality, authenticity, and integrity of data in transit. While the underlying mathematics are complex, the workflow can be broken down into key stages, from key creation to final decryption.
Key Generation
The entire security of the system begins with the creation of a strong key pair. This is not a random process but is governed by proven cryptographic algorithms. Two of the most prominent key encryption algorithms are the Rivest–Shamir–Adleman (RSA) algorithm, named for its inventors, and Elliptic Curve Cryptography (ECC). ECC has gained popularity, especially in mobile and Internet of Things (IoT) infrastructure, because it can provide the same level of security as RSA but with much smaller key sizes, making it more efficient.
During generation, the algorithm produces a public and private key that are intrinsically linked. The strength of this pair depends on key length, which is measured in bits, and the quality of the randomness used in its creation. The private key must remain secret at all times, since its confidentiality underpins the entire trust model of public key cryptography. Modern standards typically demand keys of at least 2048-bit or 4096-bit length for RSA. A weak or predictable key generation process can undermine the entire security framework.
Key Exchange
Once a key pair is generated, the public key must be shared with anyone who wants to send encrypted data. This exchange, however, must be handled carefully to prevent man-in-the-middle attacks, where an attacker secretly intercepts and replaces a public key with their own.
This is where a Public Key Infrastructure (PKI) becomes essential. A PKI is a framework of policies, standards, and systems that manages the distribution and validation of public keys. At the heart of a PKI is the certificate authority (CA), a trusted third party that issues digital certificates to bind a public key to a verified identity, usually an individual or a website domain. PKI frameworks are designed to ensure that only the verified owner holds the private key associated with the certificate, preventing attackers from substituting their own. When you receive someone’s public key via a certificate issued by a trusted CA, you can be confident it’s legitimate. This entire process is often managed by a PKI server, which handles certificate issuance, revocation, and storage.
Encryption
With a trusted public key in hand, the sender can now encrypt their message. The sender takes the plaintext data and applies the recipient’s public key using an encryption algorithm. This transforms the data into unreadable ciphertext.
The core principle here is confidentiality. The mathematical relationship between the keys ensures that once data is encrypted with a public key, it can only be decrypted by its corresponding private key. In many systems, this process is paired with digital signatures to not only protect the confidentiality of the data but also verify the sender’s identity and ensure the message has not been altered. If the private key is ever exposed, however, encrypted data can be compromised, which is why secure storage and lifecycle management of private keys are critical best practices. This one-way function is easy to compute in one direction (encryption) but computationally infeasible to reverse (decrypt) without the secret private key. This is fundamental to securing sensitive information like financial transactions, login credentials, and DNS data.
Sending Encryption
The encrypted ciphertext is then transmitted over an open, untrusted network. Because the data is scrambled, it is resilient to eavesdropping. Even if an attacker intercepts the transmission, without the recipient’s private key, they only see meaningless ciphertext, making the data useless.
This secure transit is what enables protocols like Transport Layer Security (TLS), the successor to SSL, which secures web traffic (HTTPS), and DNSSEC, which secures DNS queries. Public key cryptography provides a secure channel through which information can travel safely, protected from snooping or tampering. It’s important to note that DNSSEC differs from DNS-over-TLS (DoT) and DNS-over-HTTPS (DoH). While DoT and DoH encrypt DNS queries during transmission, DNSSEC authenticates the data at its source to prevent tampering or cache poisoning. When used together, they address different aspects of DNS security.
Decryption
Public key cryptography also extends beyond secrecy to enable authenticity and integrity through digital signatures. A sender can generate a unique signature by encrypting a hash of the message with their private key. Anyone with the sender’s public key can then verify that signature. If the signature matches, it proves two things:
- The message truly came from the claimed sender (authenticity).
- The content has not been altered in transit (integrity).
This mechanism also provides non-repudiation, meaning the sender cannot later deny having sent the signed message. Common digital signature algorithms include:
- RSA: The most widely used algorithm in TLS/SSL certificates, RSA relies on the difficulty of factoring large prime numbers. It remains highly secure when modern key lengths (2048-bit or 4096-bit) are used.
- Elliptic Curve Digital Signature Algorithm (ECDSA): Built on ECC, this approach offers equivalent security with smaller key sizes, making it faster and more efficient. Common in DNSSEC and in mobile/IoT environments.
- Digital Signature Algorithm (DSA): Once standardized for U.S. government use, DSA is now largely deprecated due to reliance on weaker key sizes and the outdated SHA-1 hash function.
How does Public Key Encryption Relate to DNS and Website Security?
Public key cryptography does more than secure individual messages. From browsing a website to resolving a DNS query, it ensures that users connect to the right destination and that data exchanged in transit is authentic and untampered. When public key cryptography is absent or mismanaged, attackers gain opportunities to impersonate sites, poison DNS caches, or intercept sensitive information.
SSL/TLS Certificates
When you visit a website with HTTPS in the address bar, you are using a connection secured by TLS. This protocol relies heavily on public key cryptography. The website’s server presents your browser with its digital certificate, which contains its public key and has been signed by a trusted Certificate Authority. Your browser verifies the certificate’s authenticity, and then a secure channel is established. The global market for SSL certificates reflects this importance, valued at $5 billion as of 2025, and projected to grow significantly.
However, the padlock icon isn’t a silver bullet. Attackers can also obtain basic certificates, which is why more than 90% of phishing sites use HTTPS to appear legitimate. This underscores the importance of robust certificate lifecycle management (CLM), wherein organizations actively manage every certificate from issuance to renewal or revocation. Advanced practices include using mark certificates, a method of tagging or classifying certificates based on their purpose, owner, or risk level, which simplifies auditing and management within a large infrastructure.
DNSSEC
Despite being the cornerstone of internet navigation, DNS was not designed with security in mind. This leaves it vulnerable to attacks, such as DNS spoofing and cache poisoning, where attackers quietly redirect users to malicious websites under their control.
DNSSEC addresses this security gap by applying public key cryptography to DNS. Instead of encrypting data, DNSSEC uses digital signatures to verify that responses come from a legitimate source and have not been altered in transit, guaranteeing that users connect to the correct server.
The system establishes a chain of trust that begins at the root zone, extends through top-level domains (TLDs), and reaches down to individual domains. Each DNS zone owner signs their records with a private key, while validating resolvers use the corresponding public key (published in the DNS) to authenticate the response. This ensures the integrity of the DNS hierarchy, prevents cache poisoning and forged zones, and protects users from unauthorized redirection to fraudulent websites.
Best Practices for Configuring DNSSEC
Implementing DNSSEC is a critical step in securing your domain’s integrity. Rolling out any new security control or configuration should be done carefully to avoid misconfigurations. To maximize effectiveness, organizations should follow these best practices:
Establish a Complete Chain of Trust:
Ensure there is an unbroken sequence of signed zones, starting from the root zone down to your domain. This requires proper handling of DNSSEC record types, including:
- Resource Record Sets (RRSIG) – contains the digital signatures that validate DNS data.
- DNSKEY – holds the public keys used to verify signatures.
- DS – establishes trust between parent and child zones by pointing to the child zone’s DNSKEY.
- NSEC / NSEC3 – provide authenticated denial of existence, confirming that a queried record does not exist.
Choose Strong Cryptographic Algorithms
The choice of cryptographic algorithm is key to DNSSEC’s security. Algorithm 13, specified as ECDSA with a P-256 curve using SHA-256, is effective in securing DNS records. Each algorithm has a specific number for identification, which is crucial for ensuring seamless interaction and verification. Constant evaluation of these algorithms ensures they stay effective against cyber threats.
Implement Robust Key Management
Effective DNSSEC depends on disciplined key management. Both the Key Signing Key (KSK) and Zone Signing Key (ZSK) should be rotated on a regular schedule to reduce exposure and maintain compliance with cryptographic standards. Private keys must be stored securely, ideally in a hardware security module (HSM), to prevent theft or tampering. Automating rollover processes helps avoid outages or broken chains of trust, while monitoring for unexpected key changes ensures that any compromise can be detected and addressed quickly.
Leverage a DNS Service Provider
Deploying DNSSEC can feel complex, especially for organizations without dedicated DNS expertise. A DNS service provider can simplify the process by automating key management and record signing, eliminating much of the manual work that often leads to errors. Providers also streamline DS record coordination by generating and, in some cases, automatically submitting DS records to registrars, ensuring the chain of trust is properly established. Many also supply configuration tools and monitoring capabilities, giving organizations confidence that their DNSSEC deployment is not only seamless but continuously validated for integrity and availability.
Strengthen Your DNS Security with Proven Public Key Cryptography
Public key cryptography is the foundation of digital trust, but managing it effectively requires the right partner. UltraDNS delivers enterprise-grade DNS security solutions that combine DNSSEC, advanced DDoS mitigation and protection, and certificate lifecycle management into a unified platform.
Whether you’re securing domains, validating DNS queries, or preparing for evolving cryptographic standards, UltraDNS provides the expertise and automation needed to protect your organization at scale.
