Documentation Worksheet for Determining Certificate Validity

When working with digital certificateswhether for TLS/SSL, code signing, S/MIME, or internal PKIaccurate and consistent documentation is essential. The Certificate Validity Worksheet provides a structured way to capture all relevant information and make a clear determination about a certificates current status.

Why a Worksheet Is Needed

• Regulatory compliance: Auditors often require evidence of how certificates are managed.
• Operational continuity: Knowing expiration dates prevents unexpected service outages.
• Risk mitigation: Early identification of revocations or weakened algorithms reduces exposure.
• Stakeholder communication: A shared worksheet creates a single source of truth for IT, security, and business teams.

Core Sections of the Worksheet

1. Certificate Identification

2. Validity Period

3. Usage & Extensions

• Key Usage: Digital Signature, Key Encipherment, etc.
• Extended Key Usage (EKU): Server Authentication, Client Authentication, Code Signing, etc.
• Subject Alternative Names (SANs): Additional DNS names, IP addresses, URIs.

4. Cryptographic Strength

5. Revocation Status

• CRL Check: Date of last CRL download and result (present/absent).
• OCSP Check: URL, response status, and timestamp.
• Manual Revocation List: Internal list if the organization maintains one.

6. Environmental Context

• Associated Service: Web server, API gateway, VPN, email system, etc.
• Impact if Invalid: Description of business impact (downtime, compliance breach, loss of trust).
• Replacement Plan: Owner, target renewal date, and migration steps.

StepbyStep Process to Fill the Worksheet

1. Gather the certificate. Export the PEM/DER file or use a platformspecific command (e.g., openssl x509 -in cert.pem -text -noout).
2. Record identification data. Copy the fields from the certificate header into Section1.
3. Calculate validity dates. Use the Not Before and Not After values to compute remaining days. Highlight any certificate with less than 30 days remaining.
4. Verify usage constraints. Confirm that the EKU matches the intended service (e.g., a web server must have Server Authentication).
5. Assess cryptographic strength. Identify any weak algorithms; mark them for replacement.
6. Check revocation. Query the CAs CRL and OCSP responder. Document the responses and timestamps.
7. Determine validity. Based on the collected data, answer the worksheets final question: Is the certificate currently valid for its intended purpose?
8. Document next steps. If the certificate is near expiration, revoked, or fails any requirement, outline a remediation plan.

Sample Decision Matrix

The worksheet includes a simple matrix to help determine the final status:

Best Practices for Ongoing Management

• Automate extraction. Use scripts to pull certificate data nightly and populate the worksheet automatically.
• Integrate with CMDB. Link each certificate record to the configurationmanagement database for asset tracking.
• Set alerts. Configure monitoring tools to trigger when Days Until Expiration falls below a threshold.
• Regular audits. Perform a quarterly review of all worksheets to ensure compliance with corporate policy.
• Maintain a change log. Record every renewal, revocation, or reissue event with date, responsible party, and justification.

Downloadable Template

A readytouse Excel/GoogleSheets template is available for download. It contains the sections described above, builtin formulas for date calculations, and dropdowns for status selections.

Download Certificate Validity Worksheet (XLSX)

References & Further Reading

• RFC 5280 Internet X.509 Public Key Infrastructure Certificate and CRL Profile
• National Institute of Standards and Technology (NIST) SP 80057 Part1 Recommendation for Key Management
• Microsoft Docs Certificate Lifecycle Management
• OpenSSL Documentation openssl x509 command reference

By consistently completing the Documentation Worksheet for Determining Certificate Validity, organizations can reduce the risk of certificaterelated incidents, stay auditready, and keep their digital services trustworthy.