Question

感谢您的帮助，我已经测试了建议的解决方案，但是问题是，当我调用getrangestream（）时，会引发NullPointerException。代码如下：

 public byte[] presign(string src,string dest){
 PdfReader reader=new PdfReader(src);  
 FileStream os=File.OpenWrite(dest);
 PdfStamper stamper = 
 PdfStamper.CreateSignature(reader, os, '\0'); 
 sap = stamper.SignatureAppearance; 
 Stream data=sap.GetRangeStream();
 hash = DigestAlgorithms.Digest(data, "SHA256");
 return hash;
 }//returns the hash to signing application on the server 
 public void postsign(byte[] signed_bytes){ 
IExternalSignature mysig=new MySignature(); 
 mysig.Sign(signed_bytes);//the signed_hash is returned from the server 
 MakeSignature.SignDetached(sap,mysig,final_chain,crlList,null, 
 null,8192,CryptoStandard.CMS)}

/// crllist和final_chain分别是通过读取pem文件生成的“ crl信息”和“证书链”信息

Answer 1

使用外部签名服务或设备使用iText 5.5.x实现PDF签名的直接方法是使用IExternalSignature或IExternalSignatureContainer实现，其中分别使用Sign方法调用外部签名服务或代码，以使用该设备的自变量对该数据进行签名，并返回结果签名。

为简单起见，我们假设您的签名服务/设备可用于返回完整的CMS签名容器。在这种情况下，可以使用IExternalSignatureContainer这样的实现：

PdfReader reader = new PdfReader(SRC);
FileStream os = new FileStream(DEST, FileMode.Create);
PdfStamper stamper = PdfStamper.CreateSignature(reader, os, '\0');
// Creating the appearance
PdfSignatureAppearance appearance = stamper.SignatureAppearance;
appearance.Reason = "For a reason surely";
appearance.Location = "Positively somewhere";
appearance.SetVisibleSignature(new Rectangle(36, 748, 144, 780), 1, "sig");
IExternalSignatureContainer externalSignatureContainer = new ExternalServiceContainerSigner();
// Creating the signature
MakeSignature.SignExternalContainer(appearance, externalSignatureContainer, 8192);

使用

class ExternalServiceContainerSigner : IExternalSignatureContainer
{
    public void ModifySigningDictionary(PdfDictionary signDic)
    {
        signDic.Put(PdfName.FILTER, PdfName.ADOBE_PPKLITE);
        signDic.Put(PdfName.SUBFILTER, PdfName.ADBE_PKCS7_DETACHED);
    }

    public byte[] Sign(Stream data)
    {
        String hashAlgorithm = "SHA256";
        byte[] hash = DigestAlgorithms.Digest(data, hashAlgorithm);
        // call your external signature service to create a CMS signature
        // container for the given document hash and return the bytes of
        // that signature container.
        return CALL_YOUR_EXTERNAL_SIGNATURE_SERVICE_TO_CREATE_A_CMS_SIGNATURE_CONTAINER_FOR(hash);
    }
}

如果您的签名服务/设备不提供创建CMS签名容器的功能，而是仅提供裸签名字节或PKCS＃1样式的签名，则可以

使用您自己的代码替换上面的CALL_YOUR_EXTERNAL_SIGNATURE_SERVICE_TO_CREATE_A_CMS_SIGNATURE_CONTAINER_FOR调用，并使用外部服务/设备为给定文档哈希准备并签名签名容器，或者
使用IExternalSignature实现来调用您的服务，并使用MakeSignature.SignDetached使用该实现。

使用itextsharp和令牌对PDF签名：错误正确嵌入签名

1 个答案: