AES-GCM Encryption Support

Over the years, encryption in PDF has been strengthened again and again. With the release of iText 9.0, we’ve now added support for AES-GCM encryption which was specified in ISO-32003 as an extension for PDF 2.0.

The Galois/Counter Mode (GCM) is a block cipher mode of operation standardized for use with the Advanced Encryption Standard (AES). AES-GCM is a big improvement over the previous AES-CBC (Cipher-Block Chaining) methods introduced with PDF 1.6. Not only is it more secure, it also allows for higher-speed encryption and decryption.

First, here is an overview of the individual PDF versions and their corresponding encryption.

PDF and Acrobat version	encryption algorithm and key length	max. password length and password encoding	iText Encryption Constants
PDF 1.1 - 1.3 (Acrobat 2-4)	RC4 40-bit (weak, should not be used)	32 characters (Latin-1)	STANDARD_ENCRYPTION_40
PDF 1.4 (Acrobat 5)	RC4 128-bit (weak, should not be used)	32 characters (Latin-1)	STANDARD_ENCRYPTION_128
PDF 1.5 (Acrobat 6)	same as PDF 1.4, but different application of encryption method (weak, should not be used)	32 characters (Latin-1)	STANDARD_ENCRYPTION_128
PDF 1.6 (Acrobat 7) and PDF 1.7 = ISO 32000-1 (Acrobat 8)	AES-128	32 characters (Latin-1)	ENCRYPTION_AES_128
PDF 1.7 Adobe Extension Level 3 (Acrobat 9)	AES-256 with shortcomings in password handling (weak; deprecated in PDF 2.0)	127 UTF-8 bytes (Unicode)	ENCRYPTION_AES_256
PDF 1.7 Adobe Extension Level 8 (Acrobat X/XI/DC) and PDF 2.0 = ISO 32000-2	AES-256 with improved password handling	127 UTF-8 bytes (Unicode)	ENCRYPTION_AES_256
ISO 32003 extension PDF 2.0	AES-256 in Galois Counter Mode (GCM)	127 UTF-8 bytes (Unicode)	ENCRYPTION_AES_GCM

Please note that many PDF consumers, such as Acrobat, do not currently support GCM encryption at the time of writing. ISO/TS 32003 is a very recent specification, and so is not yet widely-supported.

Here is a simple code snippet, which shows how you can setup the WriterProperties (Java/.NET) to create a PDF file with the new encryption.

JAVA

import java.security.Security;

import com.itextpdf.bouncycastleconnector.BouncyCastleFactoryCreator;
import com.itextpdf.kernel.pdf.EncryptionConstants;
import com.itextpdf.kernel.pdf.PdfDocument;
import com.itextpdf.kernel.pdf.PdfVersion;
import com.itextpdf.kernel.pdf.PdfWriter;
import com.itextpdf.kernel.pdf.WriterProperties;

...
        Security.addProvider(BouncyCastleFactoryCreator.getFactory().getProvider());
        WriterProperties writerProperties = new WriterProperties().setPdfVersion(PdfVersion.PDF_2_0).setStandardEncryption(
            userpassword, 
            masterpassword, 
            0, 
            EncryptionConstants.ENCRYPTION_AES_GCM);
        PdfWriter writer = new PdfWriter(filename  , writerProperties);

C#

using iText.Kernel.Pdf;
using System.Text;

...
        WriterProperties writerProperties = 
            new WriterProperties().SetPdfVersion(PdfVersion.PDF_2_0).SetStandardEncryption(
                userpassword, 
                masterpassword, 
                0,
                EncryptionConstants.ENCRYPTION_AES_GCM);

        PdfWriter writer = new PdfWriter(filename, writerProperties);