9 CSR Mistakes to Avoid in TLS Setup

9 CSR Mistakes to Avoid in TLS Setup

Your certificate is only as strong as its Certificate Signing Request (CSR). TLS rarely fails in production. It fails at the CSR.  

One typo or weak key and the whole thing wobbles. Browsers complain. Auditors stall - revenue pauses. The CSR looks like a harmless text block. It isn't.  

It holds the details that decide trust, uptime, and compliance. Nail it and nobody notices.  

Miss and you pay in re-issues, warnings, and late nights.  

Below are nine traps and the quick fixes. 

Choosing the Wrong Key Size or Algorithm 

A certificate's strength depends on its key size and algorithm. Weak keys or unsupported algorithms result in CA rejections or vulnerable certificates. 

To ensure strong, compliant keys: 

• Use RSA with at least 2048-bit keys or ECC P-256 for efficiency and security.  

• Verify the CA's list of accepted algorithms before generating the CSR.  

• Test PQC-ready or hybrid key options to prepare for quantum migration.  

• Selecting the correct key prevents delays, costly re-issuance, and credibility damage from stalled projects.  

Misconfiguring the Common Name (CN) 

The CN must exactly match the domain the certificate secures. A typo or omission (e.g., "example.com" instead of "www.example.com”) triggers browser "Not Secure" warnings. 

To configure the CN accurately: 

• Use the fully qualified domain name (FQDN) in the CSR. 

• Apply the correct format for wildcard coverage, such as *.example.com. 

• Double-check spelling, as a single misplaced character invalidates the certificate. 

• A mismatched CN erodes user confidence. Visitors see your site as unsafe, requiring you to restart the validation process. 

Omitting Subject Alternative Names (SANs) 

SANs extend coverage to multiple domains or subdomains. Excluding them leaves services beyond the CN unprotected, causing security warnings for users. 

To cover all necessary domains: 

• List all relevant variations, such as example.com, www.example.com, and mail.example.com. 

• Include internal hostnames if your infrastructure relies on them. 

• Review SANs carefully before submission to avoid costly re-issuance. 

• Missing SANs leads to service disruptions and wasted budgets. A single oversight may require additional certificates. 

Providing Inaccurate Organization Data 

CAs verify CSR organization details against legal records. Inconsistencies in company name, address, or unit information delay validation and may require extra documentation. 

To ensure accurate organizational details: 

• Use the official legal name as it appears in records. 

• Confirm address fields are consistent and correct across documents. 

• Standardize department or unit fields for repeated requests. 

• Inaccurate data causes delays. It may trigger compliance reviews in regulated industries, significantly slowing certificate issuance. 

Using Weak or Unsupported Hash Algorithms 

Hashing algorithms secure the CSR. Modern CAs and browsers reject outdated hashes like SHA-1, rendering certificates unusable or insecure. 

To ensure trusted CSR hashes: 

• Generate CSRs with SHA-256 or stronger algorithms.  

• Check the CA's accepted hash standards before starting.  

• Audit automation scripts to avoid defaulting to deprecated hashes.  

• Weak hashes undermine trust. Even if issued, browsers may block such certificates, causing outages and urgent replacements.  

Failing to Secure the Private Key 

The CSR includes a public key, paired with a private key. Attackers who access the private key can impersonate your site or decrypt sensitive traffic. 

To protect private keys: 

• Generate CSRs on the server or HSM hosting the key.  

• Restrict file access to authorized administrators only.  

• Never share private keys via email or other insecure methods.  

• A compromised private key requires revocation and replacement, leading to downtime, costs, and reputational damage.  

Neglecting Certificate Extensions 

Extensions define usage, policies, and constraints. Incorrect or missing extensions can produce certificates that fail to meet technical or compliance requirements. 

To configure extensions correctly: 

• Include key usage and extended key usage fields consistently. 

• Specify certificate policies if required by regulations. 

• Validate extensions against technical and compliance needs. 

• Skipping extensions risks audit failures or operational issues, exposing you to technical and regulatory risks. 

Generating CSRs on Unsupported Platforms 

CSRs created on outdated or incompatible platforms often fail during deployment. Using old tools or local machines introduces compatibility issues. 

To ensure reliable CSR generation: 

• Create CSRs on the target system or a supported HSM. 

• Use CA-recommended tools and syntax for generation. 

• Test CSRs in staging environments before production deployment. 

• A CSR from an unsupported platform delays rollouts, requiring rework and hindering critical deployments. 

Skipping Validation Before Submission 

Rushing the CSR submission increases errors. Without validation, issues like typos, missing SANs, or deprecated algorithms go unnoticed, leading to rejections. 

To validate CSRs before submission: 

• Use CSR linting tools to check formatting and fields. 

• Verify CN, SANs, key sizes, and hash algorithms. 

• Involve a second reviewer to catch oversights. 

A quick validation prevents weeks of rework, reduces costs, and avoids audit complications. 

NEXT STEPS 

CSRs are foundations. Crack them, and everything above suffers. The fix is simple: Pick the right keys, match CN and SANs, use modern hashes, guard the private key, and validate before you submit.

Do this, and you'll cut re-issues, avoid outages, and pass audits. 

Futurex automates CSR intake, protects keys in HSMs, and manages lifecycles. Want a clean, repeatable process? Learn more https://www.futurex.com/blog/what-is-a-certificate-signing-request  

Watch this on-demand webinar

Frequently Asked Questions 

What is a CSR in TLS certificates? 

A certificate signing request (CSR) is a file generated during TLS setup, containing your domain, organization details, and public key. It's submitted to a certificate authority (CA) for validation. Accuracy is critical, as errors delay approvals or cause rejections. 

How do I choose the right key size for a CSR? 

Use at least a 2048-bit RSA key or ECC P-256 for security. Avoid outdated 1024-bit keys, which browsers reject. Stronger keys protect against brute-force attacks and future threats, including quantum risks. 

Why does my TLS certificate show "Not Secure" after installation? 

This often results from a CN mismatch or missing SANs. Browsers require exact matches between the certificate and domains. Verify CN and SAN entries during CSR creation to prevent warnings and disruptions. 

Do I need Subject Alternative Names (SANs) in a CSR? 

Yes. SANs cover multiple domains or subdomains, protecting services beyond the CN. Including all relevant SANs prevents browser errors, reduces costs for extra certificates, and simplifies multi-domain management. 

Why did my CA reject my CSR? 

Rejections occur due to weak algorithms (e.g., RSA 1024-bit), outdated hashes (e.g., SHA-1), or incorrect organization details. Missing SANs or unsupported platforms also cause issues. Validate all fields before submission to avoid delays. 

How do I secure the private key generated with a CSR? 

Generate CSRs on the deployment server or HSM. Restrict access to authorized administrators, avoid sharing keys, and monitor access. A compromised key requires revocation, causing downtime and certificate replacement. 

Can I reuse the same CSR for multiple certificates? 

Reusing CSRs is discouraged. Each certificate should have a unique CSR and key pair to enhance security, simplify revocation, and reduce compromise risks. Reused keys amplify damage if exposed. 

How can I check if my CSR is valid before submission? 

Use CSR validation or linting tools from CAs or open-source platforms. Verify key size, hash algorithm, CN, and SANs. A second reviewer ensures accuracy, preventing rejections and saving time.