Every secure website begins with a certificate. But before a trusted Certificate Authority (CA) can issue one, the process starts with a Certificate Signing Request (CSR certificate), the digital application that proves an organization’s identity and helps establish the trust chain that browsers rely on to keep users safe.
Every day, sensitive information is exchanged online, everything from financial to business data, which makes the integrity of SSL/TLS certificates non-negotiable. CSRs provide the foundation for these certificates by binding together an organization’s information, a public key, and cryptographic details in a way that can be verified and trusted. By understanding how CSRs improve security, organizations can better manage certificate lifecycles and continue to provide superior customer experiences.
What Is a Certificate Signing Request (CSR)?
A CSR is essentially a digital application form used to request an SSL/TLS certificate, also called a digital certificate. This encoded block of text contains information that will be embedded in the certificate, making it the critical first step in receiving a new or renewed certificate.
The CSR includes the public key that will be part of the certificate, as well as identifying information such as the organization name, domain name, and location details. A CA, the trusted third party in this process, uses this data to verify the requester’s identity. Once validation is complete, the CA issues a signed digital certificate that browsers and systems can trust.
It’s important to note that the phrase “CSR certificate” is a common misnomer. A CSR is not the certificate itself, but rather the formal request used to obtain one.
What Information Is Included in a CSR?
A CSR bundles several key pieces of information into a standardized format known as PKCS #10, the Public Key Cryptography Standards specification that defines how certificate requests are structured, and ensures that the request can be recognized and processed by any CA. The data inside is collectively known as the Distinguished Name (DN), and it identifies the organization requesting the certificate. A CSR also includes the applicant’s public key and a digital signature created with the private key, which proves possession of that key. The CA uses this information to validate the request and issue a digital certificate.
Business Information
Accuracy is paramount when providing business information. During the validation process, a CA cross-references these details with public records to confirm an organization’s legitimacy, and any discrepancies can delay or prevent certificate issuance.
The key fields include:
- Organization Name (O): The full, legally registered name of the organization
- Organizational Unit (OU): The specific department within the organization
- Locality (L): The city or town where the organization is located
- State/Province (ST): The full name of the state or province
- Country (C): The two-letter ISO country code (e.g., US for the United States)
- Common Name (CN): The most critical field, representing the fully qualified domain name (FQDN) being secured. For multi-domain certificates, additional domains are specified as Subject Alternative Names (SANs).
Public Key
The CSR is fundamentally built around your public key. When a CSR is generated, a cryptographic key pair is created: a public key and a private key.
- The public key is embedded in the CSR and shared with the CA. Browsers and clients use this key to encrypt data sent to the server.
- The private key remains on the server and must be kept confidential. It is the only key capable of decrypting information encrypted with the public key.
- To prove possession of the private key, the CSR is digitally signed with it. This signature confirms that the requester controls the key pair and prevents attackers from submitting fraudulent requests with only a copied public key.
If the private key is compromised, the certificate becomes invalid, and any communication secured by it is at risk. The overall security of an SSL/TLS implementation depends on safeguarding the private key.
Key Type and Length
The strength of your encryption is determined by the type and length of the keys generated, which is specified during CSR creation. The two primary key types are:
- RSA (Rivest-Shamir-Adleman): The long-standing industry standard. A key size of RSA 2048 bits is the current minimum requirement for security, with many organizations moving toward RSA 3072 for enhanced protection.
- ECC (Elliptic Curve Cryptography): A more modern and efficient alternative. ECC keys provide equivalent security to RSA with much smaller key sizes, which reduces computational overhead and improves performance, especially on mobile devices.
Choosing a stronger key size significantly increases the computational effort required for an attacker to break the encryption. As computing power advances, minimum key length standards evolve to stay ahead of potential threats, making it essential to use currently recommended sizes.
The Certificate Signing Request Process
Obtaining a trusted TLS/SSL certificate is a structured process involving three main stages: creating the request, undergoing validation, and receiving the signed certificate from the CA.
Creating and Submitting the Request
The CSR generation process must be performed on the server or system where the certificate will ultimately be installed. This is because the process creates the private key, which should never leave its origin server. Administrators typically use command-line tools such as OpenSSL or built-in server software like Microsoft Internet Information Services (IIS) or Apache.
Once executed, the process produces two files:
- CSR File: This file commonly has a .csr or .pem extension, which is a block of Base64-encoded text submitted to the CA.
- Private Key File: This must remain secure and protected on the server.
Certificate Signing Authorization
After submitting a CSR, the CA begins the validation process. The CA’s role is to confirm the organization’s identity and verify that the entity requesting the certificate controls the domain specified in the CN through a process called domain control validation (DCV). For many organizations, demonstrating control over digital assets can be complex. Several DCV methods are available, and the choice depends on which approach best aligns with existing workflows and infrastructure.
The most common DCV validation methods include:
- Email-based validation: The CA sends an approval request to a pre-approved, domain-based email address.
- HTTP/HTTPS file upload: A validation file is placed on the organization’s web server, and the CA checks it to confirm domain ownership.
- DNS TXT or CNAME record validation: A unique token is added to the domain’s DNS TXT record or DNS CNAME record Once detected, this serves as proof of administrative control.
DNS-based DCV is generally the most scalable and efficient option, particularly for organizations managing many domains. However, this process intersects with the broader challenge of DNS hygiene. Misconfigured or inactive records, also called DNS “debt,” can increase the risk of DNS-based cyberattacks such asas subdomain hijacking, disrupt certificate renewals, or even result in expired certificates that undermine compliance and customer trust. Using a DNS service provider helps ensure records propagate quickly, reduce errors, and streamline certificate lifecycle management.
Review by the Signer (CA)
The CA acts as a trusted anchor within the public key infrastructure. It reviews all the information in your CSR and the results of its validation checks. A Registration Authority (RA) may act as an intermediary to perform some of these checks on behalf of the CA.
If the data is accurate and validation is successful, the CA uses its private key to sign the new certificate, affirming its authenticity. The outcome is either approval, resulting in the issuance of your SSL/TLS certificate, or rejection if there are discrepancies that need to be corrected.
Explaining the Certificate Trust Chain
A digital certificate is not inherently trusted on its own; its legitimacy is established through a hierarchical structure known as the certificate trust chain. This chain links an end-user SSL/TLS certificate back to a universally trusted root.
Root Certificate
A root certificate belongs to a CA and is pre-installed in operating systems and web browsers. Because root certificates are self-signed and serve as the foundation of trust, their protection is critical. They are stored offline in highly secure hardware security modules (HSMs) to minimize exposure and reduce risk.
Intermediate Certificate
To safeguard the root, CAs issue intermediate certificates that act as delegated authorities. Each intermediate is signed by the root and authorized to issue end-user certificates on its behalf. This structure improves scalability and creates an added layer of protection; if an intermediate is compromised, the CA can revoke it without impacting the root certificate.
End-User Certificate
The end-user digital certificate is issued to the requesting domain and contains the public key and identity details included in the original CSR certificate request. When a browser receives this certificate, it validates the chain of signatures, from end-user to intermediate to root, before establishing trust.
How Browsers Authenticate SSL/TLS Certificates
When a browser connects to a website, it performs automated checks on the site’s SSL/TLS certificate. It verifies the digital signature by tracing the certificate trust chain back to a trusted root. The browser also confirms that the CN or one of the SANs matches the domain visited, that the certificate is currently valid (not expired), that the certificate has appropriate usage fields, and that it has not been revoked.
If the trust chain is valid and all checks pass, the browser displays a padlock icon in the address bar and establishes a secure HTTPS connection; an indicator users have come to expect as a sign of security and trustworthiness. Suppose the certificate is self-signed (not issued by a trusted CA), expired, or the chain is broken. In that case, the browser will display a prominent security warning, discouraging users from proceeding and eroding confidence in the site.
Unfortunately, misconfigurations remain a common problem: in a 2024 survey, nearly 29% of websites failed SSL/TLS best practices, often due to incomplete trust chains or weak configurations—issues that directly trigger these browser errors.
Why CSR Certificates Are Foundational to Digital Trust
Users today have options. There are millions of active websites vying for their attention, and they expect a performant, secure, trustworthy digital experience. The CSR process is the foundational step in establishing verifiable digital identity and enabling secure communications online, thereby continuing to deliver an optimal user experience. With over 88% of websites using HTTPS, the integrity of this process underpins the security of the modern internet. Each CSR initiates a validation sequence that confirms domain ownership and organizational identity, transforming a simple request into a trusted credential.
This framework allows users to confidently exchange sensitive data, knowing it is protected from interception and tampering. By providing a standardized, interoperable method for requesting certificates, the CSR certificate ensures that the principles of digital security are applied consistently, making it a cornerstone of the public key infrastructure (PKI) ecosystem.
Strengthen Your Certificate Management Strategy
A CSR is the starting point, not the destination. In an era of shrinking certificate lifespans and growing operational complexity, automated certificate lifecycle management is no longer optional. Manual processes for generating CSRs, validating domains, and managing renewals are error-prone and unable to scale to modern demands.
Organizations that adopt a purpose-built approach to certificate management gain resilience, reduce risk, and ensure continuity of trust for customers. A DNS service provider can streamline record management and strengthen DNS security. But forward-looking organizations should select a provider that also integrates DNS and certificate lifecycle management (CLM). This combined approach centralizes certificate issuance, validation, and renewal within a single platform, creating automated workflows that track expiration dates, notify personnel, and update DNS records whenever new certificates are issued. The result: fewer manual errors, reduced risk of DNS debt, and a reduced burden on internal teams, ensuring uninterrupted security.
Next Step: Build Trust with Authoritative DNS and Simplified Certificate Management
Securing today’s digital ecosystem requires more than generating a CSR certificate; it demands a holistic, automated approach to certificate lifecycle management. CSR certificate best practices are directly tied to DNS security, where automated domain control validation ensures faster, more reliable certificate issuance and renewal. This integration forms the foundation of modern certificate lifecycle management and protects against downtime, DNS hygiene errors, and compliance failures.
UltraDNS provides the authoritative DNS backbone organizations need for scale, reliability, and security. When combined with DigiCert’s certificate lifecycle management solutions, businesses can automate issuance, validation, and renewal, while ensuring DNS records propagate quickly and accurately across the internet. This synergy simplifies operations, reduces risk, and keeps digital trust intact across every connection.
Learn more about UltraDNS and how UltraDNS and DigiCert CLM work together to strengthen certificate management from the very first CSR.
