// ------------------------ ValidateSignatures ------------------------
/// <summary>
///   Validates all the digital signatures of a given package.</summary>
/// <param name="package">
///   The package for validating digital signatures.</param>
/// <returns>
///   true if all digital signatures are valid; otherwise false if the
///   package is unsigned or any of the signatures are invalid.</returns>
private static bool ValidateSignatures(Package package)
{
    if (package == null)
        throw new ArgumentNullException("ValidateSignatures(package)");

    // Create a PackageDigitalSignatureManager for the given Package.
    PackageDigitalSignatureManager dsm =
        new PackageDigitalSignatureManager(package);

    // Check to see if the package contains any signatures.
    if (!dsm.IsSigned)
        return false;   // The package is not signed.

    // Verify that all signatures are valid.
    VerifyResult result = dsm.VerifySignatures(false);
    if (result != VerifyResult.Success)
        return false;   // One or more digital signatures are invalid.

    // else if (result == VerifyResult.Success)
    return true;        // All signatures are valid.
}// end:ValidateSignatures()