75 lines
3.6 KiB
Markdown
75 lines
3.6 KiB
Markdown
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---
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title: Validate Signature
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description: Verify digital signatures in PDF files. Check certificate validity, signer identity, document integrity, and trust chain status.
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---
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# Validate Signature
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Upload a signed PDF and this tool extracts every digital signature, identifies the signer, checks certificate validity, and reports whether the document has been modified since signing. You can also provide a trusted certificate to verify the signature chain.
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## How It Works
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1. Upload a signed PDF file. Validation starts automatically.
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2. The tool displays a summary: number of signatures found, how many are valid.
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3. Each signature gets a detailed card showing signer name, issuer, dates, and status.
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4. Optionally upload a **trusted certificate** (.pem, .crt, .cer, .der) to verify the signature against a specific trust anchor. Re-validation runs automatically.
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## What Gets Checked
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### Signature Parsing
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The tool extracts PKCS#7 signature objects from the PDF, decodes the ASN.1 structure, and pulls out the signer's X.509 certificate along with any certificate chain embedded in the signature.
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### Certificate Validity
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- **Expiration**: Is the certificate currently within its valid date range?
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- **Self-signed detection**: Is the certificate its own issuer?
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- **Trust chain**: When a trusted certificate is provided, does the signer's certificate chain back to it?
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### Document Coverage
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- **Full coverage**: The signature covers the entire PDF file, meaning no bytes were added or changed after signing.
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- **Partial coverage**: The signature covers only part of the file. This can indicate modifications were made after signing (not necessarily malicious -- incremental saves produce partial coverage).
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## Signature Details
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Each signature card shows:
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- **Signed By**: Common name, organization, and email from the signer's certificate
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- **Issuer**: The Certificate Authority that issued the signer's certificate
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- **Signed On**: The timestamp embedded in the signature
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- **Valid From / Valid Until**: The certificate's validity period
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- **Reason**: Why the document was signed (if provided)
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- **Location**: Where it was signed (if provided)
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- **Coverage Status**: Full or Partial
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- **Trust Badge**: Trusted or Not in trust chain (only when a custom certificate is provided)
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### Technical Details
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Expand the technical details section for:
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- Serial number of the signer's certificate
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- Digest algorithm (SHA-256, SHA-512, etc.)
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- Signature algorithm (RSA with SHA-256, ECDSA with SHA-256, etc.)
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- Error messages for invalid signatures
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## Use Cases
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- Verifying a digitally signed contract before countersigning
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- Auditing signed documents to confirm they have not been tampered with
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- Checking whether a certificate has expired since the document was signed
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- Validating signatures against your organization's root certificate
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- Inspecting the signing details of government or legal documents
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## Tips
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- A self-signed certificate does not mean the signature is invalid -- it means the signer's identity cannot be verified through a trusted third party. This is common for internal documents.
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- Partial coverage does not always indicate tampering. Many PDF workflows add incremental updates (like a second signature) that create partial coverage.
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- Upload your organization's root or intermediate certificate as the trusted certificate to get trust chain verification.
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## Related Tools
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- [Digital Signature](./digital-sign-pdf) -- sign PDFs with your own certificate
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- [Flatten PDF](./flatten-pdf) -- flatten a PDF before signing to prevent post-signature modifications
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- [Remove Metadata](./remove-metadata) -- clean a PDF before applying a signature
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