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Verify Digital Signatures ​

Verifying a digital signature consists of signature validity and certificate trustworthiness. Signature validity indicates that the document has not been tampered with. Certificate trustworthiness confirms that the signer is trustworthy.

Generally, a signature is verified only when both the signature is valid and the certificate is trustworthy.

This example shows how to verify digital signatures：

java
CPDFDocument document = new CPDFDocument(context);
document.open(FileUtils.getAssetsTempFile(context, "Signed.pdf"));
// Iterate through all digital signatures.
for (int i = 0; i < document.getSignatureCount(); i++) {
  CPDFSignature signature = document.getPdfSignature(i);
  // Check if the signer array exists and is not empty.
  if (signature.getSignerArr() != null && signature.getSignerArr().length > 0) {
    CPDFSigner signer = signature.getSignerArr()[0];

    // Verify the validity of the signature.
    boolean verifyValid = signature.verify(document);

    // Verify if the document has not been modified.
    boolean unmodified = signature.verifyDocument(document);

    // Determine if the signature is valid and the document is unmodified.
    boolean isSignVerified = verifyValid && unmodified;

    // Check if the certificate is trusted.
    boolean certChainTrusted = signer.getCert().verifyGetChain(document.getContext(), signature);
    boolean certificateIsTrusted = signer.getCert().checkCertificateIsTrusted(document.getContext());
    boolean certIsTrusted = certChainTrusted || certificateIsTrusted;

    // Check if the certificate has expired.
    boolean isExpired = signer.getCert().isExpired();

    // Take appropriate actions based on the verification results.
    if (isSignVerified && certIsTrusted) {
      // Signature is valid and the certificate is trusted.
      // Perform the corresponding actions.
    } else if (isSignVerified && !certIsTrusted) {
      // Signature is valid but the certificate is not trusted.
      // Perform the corresponding actions.
    } else {
      // Signature is invalid.
      // Perform the corresponding actions.
    }
  }
}
kotlin
val document = CPDFDocument(context)
document.open(FileUtils.getAssetsTempFile(context, "Signed.pdf"))
// Iterate through all digital signatures.
for (i in 0 until document.signatureCount) {
  val signature = document.getPdfSignature(i)
  // Check if the signer array exists and is not empty.
  if (signature.signerArr != null && signature.signerArr.isNotEmpty()) {
    val signer = signature.signerArr[0]

    // Verify the validity of the signature.
    val verifyValid = signature.verify(document)

    // Verify if the document has not been modified.
    val unmodified = signature.verifyDocument(document)

     // Determine if the signature is valid and the document is unmodified.
    val isSignVerified = verifyValid && unmodified

    // Check if the certificate is trusted.
    val certChainTrusted = signer.cert.verifyGetChain(document.context, signature)
    val certificateIsTrusted = signer.cert.checkCertificateIsTrusted(document.context)
    val certIsTrusted = certChainTrusted || certificateIsTrusted

    // Check if the certificate has expired.
    val isExpired = signer.cert.isExpired

    // Take appropriate actions based on the verification results.
    if (isSignVerified && certIsTrusted) {
      // Signature is valid and the certificate is trusted.
      // Perform the corresponding actions.
    } else if (isSignVerified && !certIsTrusted) {
      // Signature is valid but the certificate is not trusted.
      // Perform the corresponding actions.
    } else {
      // Signature is invalid.
      // Perform the corresponding actions.。
    }
  }
}