Preventing Headaches: Generate CSR on Windows & Troubleshoot Common TLS Errors in IIS

Securing your IIS websites with SSL/TLS is essential, but sometimes things go wrong, resulting in frustrating TLS errors for your users. Often, these errors trace back to issues with the SSL certificate itself, and the foundation for that certificate is the request you create. Properly learning how to Generate CSR on Windows using IIS tools is the first critical step in preventing many common certificate-related connection problems.

This guide covers the correct procedure for creating a Certificate Signing Request (CSR) on your Windows Server and provides insights into diagnosing and fixing frequent TLS errors that might arise if something is amiss with your certificate setup.

Key Takeaways

• Accurate CSR is Crucial: Generating a CSR with precise and correct information (especially the Common Name) is vital to prevent future TLS errors like name mismatches.
• CSR Generation Process: Use the “Create Certificate Request…” wizard in IIS Manager on the specific server where the certificate will reside. This also creates the private key.
• Common TLS Errors: Frequent browser errors like “NET::ERR_CERT_COMMON_NAME_INVALID” (Name Mismatch), “SEC_ERROR_EXPIRED_CERTIFICATE” (Expired), or “ERR_CERT_AUTHORITY_INVALID” (Untrusted Chain) often relate directly to certificate issues.
• Troubleshooting Steps: Diagnosing TLS errors involves checking certificate details (CN, SANs, expiration), verifying the correct certificate is bound in IIS, ensuring the intermediate chain is complete, and using external validation tools.
• Installation & Binding Matter: Even with a perfect CSR, errors can occur if the certificate isn’t installed correctly or bound to the right site/port in IIS.

Part 1: How to Generate CSR on Windows (Focus on Accuracy)

Generating the CSR correctly is your first line of defense against certificate-related TLS errors.

Information Needed (Distinguished Name – DN):

Accuracy here is paramount, especially for the Common Name.

1. Common Name (CN): The exact Fully Qualified Domain Name (FQDN) users will type to access your site (e.g., www.yourdomain.com, portal.yourcompany.net). For Wildcards: *.yourdomain.com. A mismatch here is a primary cause of NET::ERR_CERT_COMMON_NAME_INVALID errors.
2. Organization (O): Your registered legal business name (for OV/EV certs).
3. Organizational Unit (OU): Your division or department (e.g., “IT Department”).
4. City/Locality (L): Full city name (no abbreviations).
5. State/Province (S): Full state/province name (no abbreviations).
6. Country/Region (C): Two-letter ISO country code (e.g., US, GB, FR).

Step-by-Step CSR Generation in IIS:

1. Launch IIS Manager: Type inetmgr in the Run dialog (Win + R) or find it via Server Manager.
2. Select Server: Click your server’s name in the left Connections pane.
3. Navigate to Certificates: Double-click Server Certificates in the central pane.
4. Start Wizard: Click Create Certificate Request… in the right Actions pane.
5. Enter DN Details: Fill in the information gathered above with extreme care. Double-check the Common Name. Click Next.
6. Configure Cryptography:
   • Keep Microsoft RSA SChannel Cryptographic Provider.
   • Set Bit length to 2048 or higher (current industry standard). ^^[NIST SP 800-57 Pt 1 Rev 5 recommends minimum 2048-bit RSA keys]^^
   • Click Next.
7. Save CSR File: Specify a location and filename (e.g., C:\CSR_Requests\yourdomain_csr.txt). Click Finish.

Important Outcomes:

• You have a .txt file containing the CSR text.
• A private key corresponding to this CSR is now stored securely on this server, linked to a pending request in IIS. Do not delete this pending request before installing the certificate.
• Submit the CSR text to your Certificate Authority (like SSLRepo).

Part 2: Understanding Common TLS Errors Related to Certificates

Even after you Generate CSR on Windows correctly and install the certificate, users might encounter TLS errors. Here are common ones linked to certificate issues:

1. Certificate Name Mismatch Error
   • Browser Examples: NET::ERR_CERT_COMMON_NAME_INVALID, SSL_ERROR_BAD_CERT_DOMAIN
   • Meaning: The domain name in the browser’s address bar doesn’t match the Common Name (CN) or any Subject Alternative Names (SANs) listed in the SSL certificate.
   • Possible Certificate/CSR Causes:
     • Incorrect Common Name provided during CSR generation.
     • Accessing the site via a different subdomain (e.g., yourdomain.com instead of www.yourdomain.com) not covered by the certificate or its SANs.
     • Wrong certificate selected in the IIS binding.
2. Expired Certificate Error
   • Browser Examples: NET::ERR_CERT_DATE_INVALID, SEC_ERROR_EXPIRED_CERTIFICATE
   • Meaning: The current date is outside the certificate’s validity period (past the “Valid To” date).
   • Possible Certificate/CSR Causes:
     • The certificate wasn’t renewed and updated in IIS before expiring. (CSR generation is the first step of renewal).
     • Server’s clock is significantly incorrect.
3. Untrusted Certificate Authority (CA) Error
   • Browser Examples: NET::ERR_CERT_AUTHORITY_INVALID, MOZILLA_PKIX_ERROR_MITM_DETECTED (can sometimes relate), SEC_ERROR_UNKNOWN_ISSUER
   • Meaning: The browser doesn’t trust the Certificate Authority that issued the SSL certificate, or it cannot verify the chain of trust back to a trusted root CA.
   • Possible Certificate/CSR Causes:
     • Using a self-signed certificate (generated directly on the server without a public CA – only suitable for testing).
     • Intermediate CA certificate(s) are missing or not installed correctly on the server. The CA provides these; they must be installed to link your server certificate back to the trusted root. (Not directly a CSR issue, but part of the installation process after the CSR).
     • Using a certificate from an untrusted or disreputable CA.
4. Revoked Certificate Error
   • Browser Examples: NET::ERR_CERT_REVOKED, SEC_ERROR_REVOKED_CERTIFICATE
   • Meaning: The Certificate Authority has explicitly invalidated the certificate before its expiration date (e.g., due to key compromise or issuance problems).
   • Possible Certificate/CSR Causes:
     • The specific certificate serial number is listed on a Certificate Revocation List (CRL) or OCSP responder managed by the CA. (Usually initiated by the certificate owner or CA, not directly tied to the generation of the CSR itself, but invalidates the cert derived from it).

Part 3: Troubleshooting TLS Errors in IIS

If users report TLS errors, follow these steps, focusing on certificate aspects:

1. Verify Certificate Details:
   • In IIS: Go to Server Certificates, double-click the certificate bound to the site. Check:
     • Issued To (CN): Does it exactly match the URL users are accessing?
     • Valid From/To: Is the current date within this range?
     • Details Tab > Subject Alternative Name: Are all required hostnames listed here if different from the CN?
   • Using a Browser: Navigate to the https:// site, click the padlock, view certificate details. Cross-reference CN, SANs, and expiration dates.
2. Confirm IIS Binding:
   • Go to IIS Manager > Sites > [Your Site] > Bindings….
   • Select the https binding (port 443). Click Edit….
   • Check the SSL certificate dropdown. Is the correct certificate (matching the one verified in step 1) selected? If you have multiple certs (e.g., old and new), ensure the current, valid one is chosen.
3. Check Intermediate Certificates:
   • This is a common cause of “Untrusted” errors. Your CA provides intermediate certs. If you didn’t use a P7B bundle for installation, you might need to install them manually.
   • Use certlm.msc (Manage Computer Certificates), navigate to Intermediate Certification Authorities > Certificates. Ensure the issuer(s) of your server certificate are listed here. If not, import the intermediate .crt files provided by your CA.
   • Use Online Tools: An SSL checker (like Qualys SSL Labs) is excellent for diagnosing chain issues.
4. Test with External Tools: Use online SSL validation tools. They check for expiration, name mismatches, chain completeness, revocation status, and common configuration issues from an external perspective.
5. Review CSR Details (If Renewing/Replacing): If you recently renewed or replaced the certificate, double-check the information you submitted in the new CSR against the details of the old certificate or your intended configuration. Simple typos in the CSR are easy mistakes.
6. Check Server Clock: Ensure the server’s date, time, and timezone are accurate.
7. Firewall Rules: Verify that TCP port 443 is open on all relevant firewalls between clients and the server.

Wrapping It Up

While TLS errors can stem from various server configuration issues, problems with the SSL certificate itself are frequent culprits. Ensuring you Generate CSR on Windows with meticulous accuracy is the foundational step. When errors do occur, systematically checking the certificate’s details, its binding in IIS, and the integrity of the trust chain will often lead you directly to the root cause.

Need a trusted SSL certificate after generating your CSR? Visit SSLRepo for reliable options from leading Certificate Authorities.

Frequently Asked Questions (FAQ)

Q1: Can the CSR file itself cause TLS errors after the certificate is issued?
A: Indirectly. The CSR file itself isn’t used by the live server. However, incorrect information submitted within the CSR (like the wrong Common Name) directly leads to the issued certificate having incorrect details, which then causes TLS errors (like Name Mismatch).

Q2: What if I generated the CSR but deleted the pending request in IIS before installing the certificate?
A: You cannot install the certificate. The pending request holds the private key. You must generate a new CSR (creating a new private key and pending request), and then request your CA to reissue the certificate using this new CSR.

Q3: Does the CSR contain my private key?
A: No. The CSR only contains the public key and the distinguished name information you provided. The corresponding private key is generated simultaneously but stored securely and separately on the server where you ran the CSR wizard.

Q4: What are Subject Alternative Names (SANs) and how do they relate to CSRs?
A: SANs are additional hostnames (besides the main Common Name) that the certificate should be valid for (e.g., yourdomain.com, www.yourdomain.com, mail.yourdomain.com all on one cert). You typically specify required SANs during the ordering process with the CA, often after submitting the initial CSR based on the primary Common Name. Incorrect SAN configuration can also lead to name mismatch errors.

Q5: How can I easily check if intermediate certificates are installed correctly?
A: Besides using certlm.msc on the server, the easiest way is often using an online SSL checker tool (like Qualys SSL Labs). These tools specifically test the certificate chain and will report if intermediate certificates are missing or incorrect.