How to set ENCRYPTION_AES_128? - iText 7.1.0 for Java - itext7

Question

At the moment I'm writing a couple of evaluatuation programs with iText.
I have an issue with AES Encryption.
STANDARD_ENCRYPTION_128 is working fine but ENCRYPTION_AES_128 produces a runtime error.
I tried a lot but nothing worked. Has anybody a clue what's wrong here?
Thanks, Dirk
import java.awt.Desktop;
import java.io.File;
import java.io.IOException;
import com.itextpdf.kernel.pdf.EncryptionConstants;
import com.itextpdf.kernel.pdf.PdfDocument;
import com.itextpdf.kernel.pdf.PdfWriter;
import com.itextpdf.kernel.pdf.WriterProperties;
import com.itextpdf.layout.Document;
import com.itextpdf.layout.element.Paragraph;
public class problem3 {
public static void main(String[] args) throws IOException {
String fnPdf = "results/problem3.pdf";
WriterProperties properties = new WriterProperties();
// ENCRYPTION_AES_128 produces an runtime error, STANDARD_ENCRYPTION_128 is working.
properties.setStandardEncryption("Hello".getBytes(), "World".getBytes(), EncryptionConstants.ALLOW_PRINTING,
EncryptionConstants.ENCRYPTION_AES_128);
PdfWriter writer = new PdfWriter(fnPdf, properties);
PdfDocument pdf = new PdfDocument(writer);
Document document = new Document(pdf);
Paragraph paragraph = new Paragraph("Hello AES-128!");
document.add(paragraph);
document.close();
pdf.close();
Desktop.getDesktop().open(new File(fnPdf));
}
}

Answer 1

Your error at runtime is probably
java.lang.NoClassDefFoundError: org/bouncycastle/crypto/BlockCipher
This is because iText uses BouncyCastle library for providing some of the encryption capabilities. The dependency is optional which means you have to add it manually if you need it.
If you use Maven for building, then make sure that you have the following dependencies:
<dependency>
<groupId>org.bouncycastle</groupId>
<artifactId>bcpkix-jdk15on</artifactId>
<version>1.49</version>
</dependency>
<dependency>
<groupId>org.bouncycastle</groupId>
<artifactId>bcprov-jdk15on</artifactId>
<version>1.49</version>
</dependency>
If you are adding jars to the classpath manually, which is not recommended, then you can go to Maven Central and download the necessary artifact jars manually.