如何使用带有 PKCS1 签名的 iText 签署 pdf

Question

我需要使用将返回 PKCS1 签名的外部服务签署 pdf 文档。这意味着我必须在 IExternalSignatureContainer 实例中添加公钥。我在整个签名过程中使用 iText 7。

iText website 上有一个很好的例子说明这种方法

我确实实现了这个示例，但我没有使用服务来签署哈希值，而是使用 X509 证书来实现。问题是签名在某种程度上无效（它说文件在签名后被更改）。证书似乎是正确集成的。

我在一个文件中创建了整个唱歌过程的示例。 所需参考资料：

• BouncyCastle.Crypto
• itext.kernel
• itext.sign

可以在此处下载（自签名）公钥、私钥和已签名 pdf 文档的示例：http://www.filedropper.com/pdfsignfiles

知道我在这里做错了什么吗？

示例代码（一个文件中的两个类准备用于控制台应用程序）：

using System;
using System.Collections.Generic;
using System.IO;
using System.Security.Cryptography;
using System.Security.Cryptography.X509Certificates;
using System.Text;
using iText.Kernel.Pdf;
using iText.Signatures;
using Org.BouncyCastle.X509;
using X509Certificate = Org.BouncyCastle.X509.X509Certificate;

namespace SignExternalTestManuel
{
    class Program
    {
        public static void Main(String[] args)
        {
            string filePath = @"c:\temp\pdfsign\";
            string pdfToSign = Path.Combine(filePath, @"test.pdf");
            string destinationFile = Path.Combine(filePath, "test_signed.pdf");
            string userCertificatePublicKey = Path.Combine(filePath, "BITSignTestManuel5Base64.cer");
            string caCertificatePublicKey = Path.Combine(filePath, "BITRoot5Base64.cer");
            string privateKeyFile = Path.Combine(filePath, "BITSignTestManuel5.pfx");
            string privateKeyPassword =  "test";

            PdfReader reader = new PdfReader(pdfToSign);
            using (FileStream os = new FileStream(destinationFile, FileMode.OpenOrCreate))
            {
                StampingProperties stampingProperties = new StampingProperties();
                //For any signature in the Pdf  but the first one, you need to use appendMode
                //        stampingProperties.useAppendMode();
                stampingProperties.UseAppendMode();
                PdfSigner pdfSigner = new PdfSigner(reader, os, stampingProperties);
                pdfSigner.SetCertificationLevel(PdfSigner.CERTIFIED_NO_CHANGES_ALLOWED);

                IExternalSignatureContainer external = new GsSignatureContainer(
                    PdfName.Adobe_PPKLite,
                    PdfName.Adbe_pkcs7_detached,
                    userCertificatePublicKey,
                    caCertificatePublicKey,
                    privateKeyFile,
                    privateKeyPassword);
                pdfSigner.SignExternalContainer(external, 32000);
            }

        }
    }
    public class GsSignatureContainer : IExternalSignatureContainer
    {
        private PdfDictionary sigDic;
        private string userCertificatePublicKey;
        private string caCertificatePublicKey;
        private string privateKeyFile;
        private string privateKeyPassword;

        public GsSignatureContainer(PdfName filter, PdfName subFilter, string userCertificatePublicKey, string caCertificatePublicKey, string privateKeyFile, string privateKeyPassword)
        {
            sigDic = new PdfDictionary();
            sigDic.Put(PdfName.Filter, filter);
            sigDic.Put(PdfName.SubFilter, subFilter);
            this.userCertificatePublicKey = userCertificatePublicKey;
            this.caCertificatePublicKey = caCertificatePublicKey;
            this.privateKeyFile = privateKeyFile;
            this.privateKeyPassword = privateKeyPassword;
        }

        /// <summary>
        /// Implementation based on https://kb.itextpdf.com/home/it7kb/examples/how-to-use-a-digital-signing-service-dss-such-as-globalsign-with-itext-7#HowtouseaDigitalSigningService(DSS)suchasGlobalSign,withiText7-Examplecode
        /// </summary>
        /// <param name="pdfStream"></param>
        /// <returns></returns>
        public byte[] Sign(Stream pdfStream)
        {
            //Create the certificate chaing since the signature is just a PKCS1, the certificates must be added to the signature
            string cert = System.IO.File.ReadAllText(userCertificatePublicKey);
            string ca = System.IO.File.ReadAllText(caCertificatePublicKey);
            X509Certificate[] chain = CreateChain(cert, ca);

            String hashAlgorithm = DigestAlgorithms.SHA256;
            PdfPKCS7 pkcs7Signature = new PdfPKCS7(null, chain, hashAlgorithm, false);

            //Create the hash of of the pdf document
            byte[] hash = DigestAlgorithms.Digest(pdfStream, DigestAlgorithms.GetMessageDigest(hashAlgorithm));


            //TODO: Unclear whether i need to use this. It is from the example, but maybe only required for 
            //byte[] sh = pkcs7Signature.GetAuthenticatedAttributeBytes(hash, null, null, PdfSigner.CryptoStandard.CMS);
            //using (SHA256 sha256 = SHA256.Create())
            //{
            //    sh = sha256.ComputeHash(hash);
            //}

            //Create the actual signautre (This will be done via Service)
            byte[] signature = CreateSignature(hash, privateKeyFile, privateKeyPassword);

            pkcs7Signature.SetExternalDigest(signature, null, "RSA");

            return pkcs7Signature.GetEncodedPKCS7(hash, null, null, null, PdfSigner.CryptoStandard.CMS);
        }

        public void ModifySigningDictionary(PdfDictionary signDic)
        {
            signDic.PutAll(sigDic);
        }

        private static X509Certificate[] CreateChain(String cert, String ca)
        {
            //Note: The root certificate could be omitted and it would still work
            X509Certificate[] chainy = new X509Certificate[2];
            X509CertificateParser parser = new X509CertificateParser();
            chainy[0] = new X509Certificate(parser.ReadCertificate(Encoding.UTF8.GetBytes(cert))
                .CertificateStructure);
            chainy[1] = new X509Certificate(parser.ReadCertificate(Encoding.UTF8.GetBytes(ca))
                .CertificateStructure);
            return chainy;
        }

        #region "Create signature, will be done by an actual service"
        private byte[] CreateSignature(byte[] hash, string privateKeyFile, string privateKeyPassword)
        {
            X509Certificate2 rootCertificateWithPrivateKey = new X509Certificate2();
            byte[] rawData = System.IO.File.ReadAllBytes(privateKeyFile);
            rootCertificateWithPrivateKey.Import(rawData, privateKeyPassword, X509KeyStorageFlags.Exportable);
            using (var key = rootCertificateWithPrivateKey.GetRSAPrivateKey())
            {
                return key.SignData(hash, HashAlgorithmName.SHA256, RSASignaturePadding.Pkcs1);
            }
        }

        #endregion


    }
}

Answer 1

我想我在我的代码中发现了问题。 我没有使用 GetAuthenticatedAttributeBytes 直接对哈希值进行签名。只要我添加以下代码，签名就会生效，然后签名 sh 而不是哈希：

            //Create the hash based on the document hash which is suitable for pdf siging
            X509Certificate2 rootCertificateWithoutPrivateKey = new X509Certificate2();
            rootCertificateWithoutPrivateKey.Import(caCertificatePublicKey);
            X509Certificate rootCertBouncy = DotNetUtilities.FromX509Certificate(rootCertificateWithoutPrivateKey);
            List<X509Certificate> c = new List<X509Certificate>();
            c.Add(rootCertBouncy);
            PdfPKCS7 sgn = new PdfPKCS7(null, c.ToArray(), hashAlgorithm, false);
            byte[] sh = sgn.GetAuthenticatedAttributeBytes(hash, null, null, PdfSigner.CryptoStandard.CMS);