是否有可能使用散列和簽名散列來簽署PDF文檔？

Question

我可以使用帶有外部簽名的itextpdf庫簽署文檔。

但問題是最終用戶不想發送他的文檔，因爲它可能包含任何敏感數據。因此，我要求最終用戶提供文檔散列以便用外部服務對散列進行簽名，並將簽名散列發送回去。

但是，這裏問題來了，當他們試圖簽下使用itextpdf與給定的簽署哈希文檔（PdfSignatureAppearance）PDF文檔是越來越簽名。但是在驗證簽名時顯示簽名無效。

我在這裏看到過同樣的問題 Sign PDF using an external service and iText。

因此，問題發生的原因是每次我們使用PdfSignatureAppearance（itextpdf庫）打開文檔時散列都會失效。

誰能告訴我是否有可能與先前產生的散列簽署PDF文件，並簽署哈希使用itextpdf庫（這是我從外部服務獲得），這樣的哈希不應該獲得失效？

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); 

    }