有可能用哈希和签名哈希签署PDF文档吗？

Question

我可以通过外部签名使用itextpdf库对文档进行签名。

但问题是，最终用户不想发送他的文档，因为它可能包含任何敏感数据。因此，我要求最终用户给出文档哈希，以便与外部服务签署哈希，并将签署后的哈希发回。

但是，问题来了，当他们试图使用itextpdf(PDFSignatureOutcome)用给定的签名散列对文档进行签名时，PDF文档被签名了。但在验证签名时,表明签名是无效的。

因此，问题的发生是因为每次使用pdfsignatureappeating(itextpdf库）打开文档时，散列会失效。

有没有人可以告诉我，是否可以使用itextpdf库，用以前生成的哈希和签名的哈希（我从外部服务获得的）来签名PDF文档，这样哈希就不会失效？

Answer 1

class MyExternalSignatureContainer implements ExternalSignatureContainer {
    protected byte[] sig;
    protected Certificate[] chain;
    protected PrivateKey pk;
    public MyExternalSignatureContainer(byte[] sig,Certificate[] chain,PrivateKey pk) {
        this.sig = sig;
        this.chain=chain;
        this.pk=pk;
    }
    public byte[] sign(InputStream is)throws GeneralSecurityException  {

        return sig;

    }
    public void modifySigningDictionary(PdfDictionary signDic) {
    }
}

 public byte[] emptySignature_hash(String src, String dest, String fieldname, Certificate[] chain) throws IOException, DocumentException, GeneralSecurityException {
        PdfReader reader = new PdfReader(src);
        FileOutputStream os = new FileOutputStream(dest);
        PdfStamper stamper = PdfStamper.createSignature(reader, os, '\0');
        PdfSignatureAppearance appearance = stamper.getSignatureAppearance();
        appearance.setVisibleSignature(new Rectangle(36, 748, 144, 780), 1, fieldname);
        appearance.setCertificate(chain[0]);
        ExternalSignatureContainer external = new ExternalBlankSignatureContainer(PdfName.ADOBE_PPKLITE, PdfName.ADBE_PKCS7_DETACHED);
        MakeSignature.signExternalContainer(appearance, external, 8192);



        InputStream inp = appearance.getRangeStream();  

        BouncyCastleDigest digest = new BouncyCastleDigest();


         byte[] hash = DigestAlgorithms.digest(inp, digest.getMessageDigest("SHA256"));
         return hash;


    }


public byte[] signed_hash(byte[] hash, PrivateKey pk, Certificate[] chain)throws GeneralSecurityException{
        PrivateKeySignature signature = new PrivateKeySignature(pk, "SHA256", "SunPKCS11-eToken");

        //return extSignature;
       BouncyCastleDigest digest = new BouncyCastleDigest();
        Calendar cal = Calendar.getInstance();
        String hashAlgorithm = signature.getHashAlgorithm();
        System.out.println(hashAlgorithm);
        PdfPKCS7 sgn = new PdfPKCS7(null, chain, "SHA256", null, digest, false);

        byte[] sh = sgn.getAuthenticatedAttributeBytes(hash, cal, null, null, CryptoStandard.CMS);
        byte[] extSignature = signature.sign(sh);

        System.out.println(signature.getEncryptionAlgorithm());

       // Calendar cal = Calendar.getInstance();
        sgn.setExternalDigest(extSignature, null, signature.getEncryptionAlgorithm());
    return sgn.getEncodedPKCS7(hash, cal, null, null, null, CryptoStandard.CMS);

        }
    public void createSignature(String src, String dest, String fieldname,byte[] hash, PrivateKey pk, Certificate[] chain) throws IOException, DocumentException, GeneralSecurityException {

    PdfReader reader = new PdfReader(src);
    FileOutputStream os = new FileOutputStream(dest);
    ExternalSignatureContainer external = new MyExternalSignatureContainer(hash,chain,pk);
    MakeSignature.signDeferred(reader, fieldname, os, external);
}


public static void main(String[] args) throws IOException, GeneralSecurityException, DocumentException {
 byte[] hh = app.emptySignature_hash(SRC, TEMP, "sig1", chain);
 byte[] hh_sign = (app.signed_hash(hh,  pk,  chain));

 app.createSignature(TEMP, DEST1, "sig1",hh_sign, pk, chain);

    }