SECURITY & LEGAL

How to Validate Digital Signatures Long-Term (LTV) in PDF

January 5, 2025 • 10 min read • Security

Digital signatures in PDF documents can expire due to certificate revocation or time-stamping authority changes. Long-Term Validation (LTV) ensures signatures remain valid for decades.

What is LTV?

Long-Term Validation (LTV) is a method to preserve the validity of digital signatures over long periods by embedding all necessary validation materials into the PDF itself.

Why LTV Matters for Legal Documents

  • Contract validity: 10+ year contracts need valid signatures
  • Legal compliance: eIDAS regulation requirements
  • Audit trails: Long-term document retention
  • Certificate expiration: Signing certificates have limited lifetimes

How LTV Works

LTV embeds three critical components into the PDF:

  1. Certificate Revocation Lists (CRLs) or OCSP responses
  2. Time-stamp tokens from trusted authorities
  3. Certificate chains for validation

Checking LTV Status

You can check if a PDF has LTV enabled:

Using Adobe Acrobat:

  1. Open PDF with signatures
  2. Open Signature Panel (Ctrl+Shift+I)
  3. Right-click signature → Validate Signature
  4. Check "Document revision includes long-term validation"

Common LTV Issues

  • Missing revocation information: CRL/OCSP data not embedded
  • Time-stamp issues: TSA certificate expired
  • Chain problems: Intermediate certificates missing
  • PDF/A incompatibility: LTV data can conflict with PDF/A

Free LTV Validation Tool

Try our free signature validator to check LTV status:

Best Practices for LTV

  1. Use qualified time-stamping authorities (TSA)
  2. Embed all validation materials during signing
  3. Regularly re-validate long-term documents
  4. Keep certificate trust lists updated
  5. Consider PDF/A-3 for archival with signatures

Conclusion

LTV is essential for any document requiring long-term legal validity. Regular validation and proper signing practices ensure signatures withstand the test of time.