iTextSharp Password Protected PDF

Question

The following question and answer on StackOverflow show how to generate a PDF that cannot be opened without the appropriate password.

Password protected PDF using

Answer 1

Another implementation:

public static void Common_PassWordProtectPDF_Static_WithoutEmail(FileInfo[] filteredfiles, string strAgentName, string strAgentCode, string strpassword, string strEmailID, string sourcefolder, string strdestfolder, string strdestinationFileName)
{
    foreach (FileInfo file in filteredfiles)
    {
        //string sourcePdf = Convert.ToString(ConfigurationManager.AppSettings["SourceFolder"]) + "\\" + file.Name;
        //string strdestPdf = Convert.ToString(ConfigurationManager.AppSettings["DestinationFolder"]) + file.Name;

    string sourcePdf = sourcefolder + "\\" + file.Name;
    string strdestPdf = strdestfolder + strdestinationFileName;

    using (Stream input = new FileStream(sourcePdf, FileMode.Open, FileAccess.Read, FileShare.Read))
    {
        //sourcePdf  unsecured PDF file
        //destPdf secured PDF file

        using (Stream output = new FileStream(strdestPdf, FileMode.Create, FileAccess.Write, FileShare.None))
        {
            PdfReader pdfReader = new PdfReader(input);
            X509Store store = new X509Store("My");
            store.Open(OpenFlags.ReadOnly);

            X509Certificate2 cert = new X509Certificate2();
            RSACryptoServiceProvider csp = null;
            AcroFields fields = pdfReader.AcroFields;

            foreach (X509Certificate2 mCert in store.Certificates)
            {
                //TODO's
                string strresult = mCert.GetName();
                bool str123 = false;
                if (strresult.Contains("Certificate name") == true)
                {
                    csp = (RSACryptoServiceProvider)mCert.PrivateKey;

                    SHA1Managed sha1 = new SHA1Managed();
                    UnicodeEncoding encoding = new UnicodeEncoding();
                    byte[] data = encoding.GetBytes(file.Name);
                    byte[] hash = sha1.ComputeHash(data);

                    // Sign the hash

                    byte[] signature = csp.SignHash(hash, CryptoConfig.MapNameToOID("SHA1"));

                    if (Verify(file.Name, signature, mCert))
                    {
                        char s = pdfReader.PdfVersion;
                        //var pdfStamper = PdfStamper.(pdfReader, output, s, @"\0", true);
                        //csp.SignData(signature, true);
                        pdfReader.Appendable = false;

                        Org.BouncyCastle.X509.X509CertificateParser cp = new Org.BouncyCastle.X509.X509CertificateParser();
                        Org.BouncyCastle.X509.X509Certificate[] chain = new Org.BouncyCastle.X509.X509Certificate[] {
    cp.ReadCertificate(mCert.RawData)};

                        IExternalSignature externalSignature = new X509Certificate2Signature(mCert, "SHA-1");


                        // var signedPdf = new FileStream(output, FileMode.Create);
                        // var signedPdf = PdfEncryptor.Encrypt(pdfReader, output, true, strpassword, strpassword, PdfWriter.ALLOW_PRINTING);
                        //char s = pdfReader.PdfVersion;
                        var pdfStamper = PdfStamper.CreateSignature(pdfReader, output, s, @"\", false);
                        PdfSignatureAppearance signatureAppearance = pdfStamper.SignatureAppearance;

                        byte[] USER = Encoding.ASCII.GetBytes("userpwd");
                        byte[] OWNER = Encoding.ASCII.GetBytes(strpassword);

                        Rectangle cropBox = pdfReader.GetCropBox(1);
                        float width = 108;
                        float height = 32;

                        // signatureAppearance.SignatureGraphic = Image.GetInstance("C:\\logo.png");
                        //signatureAppearance.Layer4Text = "document certified by";
                        //signatureAppearance.Reason = "Because I can";
                        //signatureAppearance.Location = "My location";
                        //signatureAppearance.SetVisibleSignature(new Rectangle(100, 100, 250, 150), pdfReader.NumberOfPages, "Signature");

                        Rectangle rect = new Rectangle(600, 100, 300, 150);
                        Chunk c = new Chunk("A chunk represents an isolated string. ");
                        rect.Chunks.Add(c);
                        //signatureAppearance.SetVisibleSignature(new Rectangle(100, 100, 600, 150), pdfReader.NumberOfPages, "Signature");

                        signatureAppearance.SetVisibleSignature(rect, pdfReader.NumberOfPages, "Signature");

                        // signatureAppearance.SetVisibleSignature(new Rectangle(cropBox.GetLeft(0), cropBox.GetBottom(0), cropBox.GetLeft(width), cropBox.GetLeft(height)), pdfReader.NumberOfPages, "Signature");

                        signatureAppearance.SignatureRenderingMode = PdfSignatureAppearance.RenderingMode.DESCRIPTION;
                        pdfStamper.SetEncryption(USER, OWNER, PdfWriter.AllowPrinting, PdfWriter.ENCRYPTION_AES_128);
                        MakeSignature.SignDetached(signatureAppearance, externalSignature, chain, null, null, null, 0, CryptoStandard.CMS);

                        pdfStamper.Close();


                        // PdfEncryptor.Encrypt(pdfReader, output, true, strpassword, strpassword, PdfWriter.SIGNATURE_EXISTS);
                    }
                    else
                    {
                        Console.WriteLine("ERROR: Signature not valid!");
                    }
                }
            }

            string Password = strpassword;

        }
    }
}




public static byte[] Sign(string text, string certSubject)
{

    // Access Personal (MY) certificate store of current user

    X509Store my = new X509Store(StoreName.My, StoreLocation.CurrentUser);

    my.Open(OpenFlags.ReadOnly);

    // Find the certificate we’ll use to sign

    RSACryptoServiceProvider csp = null;

    foreach (X509Certificate2 cert in my.Certificates)
    {

        if (cert.Subject.Contains(certSubject))
        {
            // We found it.

            // Get its associated CSP and private key
            csp = (RSACryptoServiceProvider)cert.PrivateKey;
        }

    }

    if (csp == null)
    {
        throw new Exception("No valid cert was found");
    }

    // Hash the data

    SHA1Managed sha1 = new SHA1Managed();

    UnicodeEncoding encoding = new UnicodeEncoding();

    byte[] data = encoding.GetBytes(text);

    byte[] hash = sha1.ComputeHash(data);

    // Sign the hash

    return csp.SignHash(hash, CryptoConfig.MapNameToOID("SHA1"));

}

    static bool Verify(string text, byte[] signature, X509Certificate2 cert)
    {

        // Load the certificate we’ll use to verify the signature from a file

        //  X509Certificate2 cert = new X509Certificate2(certPath);

        // Note:

        // If we want to use the client cert in an ASP.NET app, we may use something like this instead:

        // X509Certificate2 cert = new X509Certificate2(Request.ClientCertificate.Certificate);

        // Get its associated CSP and public key

        RSACryptoServiceProvider csp = (RSACryptoServiceProvider)cert.PublicKey.Key;

        // Hash the data

        SHA1Managed sha1 = new SHA1Managed();

        UnicodeEncoding encoding = new UnicodeEncoding();

        byte[] data = encoding.GetBytes(text);

        byte[] hash = sha1.ComputeHash(data);

        // Verify the signature with the hash

        return csp.VerifyHash(hash, CryptoConfig.MapNameToOID("SHA1"), signature);
}

Answer 2

Yes, there are two passwords that you can pass to PdfEncryptor.Encrypt(), userPassword and ownerPassword. Just pass null to the userPassword and people will be able to open it without specify a password.

        string WorkingFolder = Environment.GetFolderPath(Environment.SpecialFolder.Desktop);
        string InputFile = Path.Combine(WorkingFolder, "Test.pdf");
        string OutputFile = Path.Combine(WorkingFolder, "Test_enc.pdf");

        using (Stream input = new FileStream(InputFile, FileMode.Open, FileAccess.Read, FileShare.Read))
        {
            using (Stream output = new FileStream(OutputFile, FileMode.Create, FileAccess.Write, FileShare.None))
            {
                PdfReader reader = new PdfReader(input);
                PdfEncryptor.Encrypt(reader, output, true, null, "secret", PdfWriter.ALLOW_SCREENREADERS);
            }
        }