iText-生成没有证书链的PDF哈希

Question

我试图构建一个应用程序，其中会发生以下情况：

null

public byte[] simplePresign(String src, String digestAlgorithm) throws IOException, DocumentException, GeneralSecurityException {
    this.digestAlgorithm = digestAlgorithm;
    tsaClient = new CustomTSAClient();

    PdfReader reader = new PdfReader(src);
    os = new ByteArrayOutputStream();
    PdfAStamper stamper = PdfAStamper.createSignature(reader, os, '\0', PdfAConformanceLevel.PDF_A_1B);
    appearance = stamper.getSignatureAppearance();

    PdfSignature dic = new PdfSignature(PdfName.ADOBE_PPKLITE, PdfName.ADBE_PKCS7_DETACHED);
    appearance.setCryptoDictionary(dic);

    HashMap<PdfName, Integer> exc = new HashMap<PdfName, Integer>();
    exc.put(PdfName.CONTENTS, getEstimatedSize(null, tsaClient) * 2 + 2);
    appearance.preClose(exc);

    InputStream data = appearance.getRangeStream();
    MessageDigest mDigest = DigestAlgorithms.getMessageDigest(digestAlgorithm, null);

    return DigestAlgorithms.digest(data, mDigest);

}

不幸的是，这个散列似乎不正确，签名这个散列并根据签名的散列生成签名的文档会导致无效签名。

如果有人能帮助我改进这个代码片段，或者给我一些关于签名需要消化的数据的见解，我将非常感激。

Answer 1

您似乎忽略了DeferredSigning示例。

在本例中，我们首先创建一个带有空签名的PDF：

public void emptySignature(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);
}

当然，公共证书链[0]被传递给外观。在本例中，它用于创建可视外观和创建PDFPKCS7对象。

BouncyCastleDigest digest = new BouncyCastleDigest();
PdfPKCS7 sgn = new PdfPKCS7(null, chain, hashAlgorithm, null, digest, false);
byte[] hash = DigestAlgorithms.digest(is, digest.getMessageDigest(hashAlgorithm));
Calendar cal = Calendar.getInstance();
byte[] sh = sgn.getAuthenticatedAttributeBytes(hash, cal, null, null, CryptoStandard.CMS);

您的外部签名容器可以保持非常简单：它只需要返回签名字节：

class MyExternalSignatureContainer implements ExternalSignatureContainer {
    protected byte[] sig;
    public MyExternalSignatureContainer(byte[] sig) {
        this.sig = sig;
    }
    public byte[] sign(InputStream is) throws Exception {
        return sig;
    }
    public void modifySigningDictionary(PdfDictionary signDic) {
    }
}

现在可以在服务器上使用createsignature()方法：

public void createSignature(String src, String dest, String fieldname, PrivateKey pk, Certificate[] chain) throws IOException, DocumentException, GeneralSecurityException {
    
    PdfReader reader = new PdfReader(src);
    FileOutputStream os = new FileOutputStream(dest);
    ExternalSignatureContainer external = new MyExternalSignatureContainer(sig);
    MakeSignature.signDeferred(reader, fieldname, os, external);
}