根据文件摘要创建pkcs7签名

Question

目前，我有一个客户机-服务器应用程序，给定一个PDF文件，它对其进行签名（使用服务器证书），将签名附加到原始文件，并将输出返回给客户机（所有这些都是通过PDFBox实现的）。
我有一个签名处理程序，它是我的外部签名支持（其中的内容是PDF文件）

    public byte[] sign(InputStream content) throws IOException {
    try {
        System.out.println("Generating CMS signed data");
        CMSSignedDataGenerator generator = new CMSSignedDataGenerator();
        ContentSigner sha1Signer = new JcaContentSignerBuilder("Sha1WithRSA").build(privateKey);
        generator.addSignerInfoGenerator(
                new JcaSignerInfoGeneratorBuilder(new JcaDigestCalculatorProviderBuilder().build())
                        .build(sha1Signer, new X509CertificateHolder(certificate.getEncoded())));
        CMSTypedData cmsData = new CMSProcessableByteArray(IOUtils.toByteArray(content));
        CMSSignedData signedData = generator.generate(cmsData, false);

        return signedData.getEncoded();
    } catch (GeneralSecurityException e) {
        throw new IOException(e);
    } catch (CMSException e) {
        throw new IOException(e);
    } catch (OperatorCreationException e) {
        throw new IOException(e);
    }
}

它工作得很好，但我在想--如果PDF文件太大无法上传怎么办？例如：100MB...这会花上很长时间的！鉴于此，我试图弄清楚，如果不签署PDF文件，是否可能只是签署该文件的散列（如SHA1)，然后客户机最终把它放在一起？

更新：

    @Override
public byte[] sign(InputStream content) throws IOException {
    // testSHA1WithRSAAndAttributeTable
    try {
        MessageDigest md = MessageDigest.getInstance("SHA1", "BC");
        List<Certificate> certList = new ArrayList<Certificate>();
        CMSTypedData msg = new CMSProcessableByteArray(IOUtils.toByteArray(content));

        certList.add(certificate);

        Store certs = new JcaCertStore(certList);

        CMSSignedDataGenerator gen = new CMSSignedDataGenerator();

        Attribute attr = new Attribute(CMSAttributes.messageDigest,
                new DERSet(new DEROctetString(md.digest(IOUtils.toByteArray(content)))));

        ASN1EncodableVector v = new ASN1EncodableVector();

        v.add(attr);

        SignerInfoGeneratorBuilder builder = new SignerInfoGeneratorBuilder(new BcDigestCalculatorProvider())
                .setSignedAttributeGenerator(new DefaultSignedAttributeTableGenerator(new AttributeTable(v)));

        AlgorithmIdentifier sha1withRSA = new DefaultSignatureAlgorithmIdentifierFinder().find("SHA1withRSA");

        CertificateFactory certFactory = CertificateFactory.getInstance("X.509");
        InputStream in = new ByteArrayInputStream(certificate.getEncoded());
        X509Certificate cert = (X509Certificate) certFactory.generateCertificate(in);

        gen.addSignerInfoGenerator(builder.build(
                new BcRSAContentSignerBuilder(sha1withRSA,
                        new DefaultDigestAlgorithmIdentifierFinder().find(sha1withRSA))
                                .build(PrivateKeyFactory.createKey(privateKey.getEncoded())),
                new JcaX509CertificateHolder(cert)));

        gen.addCertificates(certs);

        CMSSignedData s = gen.generate(new CMSAbsentContent(), false);
        return new CMSSignedData(msg, s.getEncoded()).getEncoded();

    } catch (Exception e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
        throw new IOException(e);
    }

}

            ExternalSigningSupport externalSigning = document.saveIncrementalForExternalSigning(output);
        byte[] cmsSignature = sign(externalSigning.getContent());
        externalSigning.setSignature(cmsSignature);

问题是Adobe说签名是无效的，因为“文档在签名后已经被更改或损坏”。有人能帮忙吗？

Answer 1

在他的更新操作几乎是正确的，只有两个错误：

>

他尝试读取InputStream参数内容两次：

CMSTypedData msg = new CMSProcessableByteArray(IOUtils.toByteArray(content));
[...]
Attribute attr = new Attribute(CMSAttributes.messageDigest,
        new DERSet(new DEROctetString(md.digest(IOUtils.toByteArray(content)))));

因此，在第二次尝试之前，所有数据都已从流中读取，因此返回一个空的字节[]。因此消息摘要属性包含错误的哈希值。

return new CMSSignedData(msg, s.getEncoded()).getEncoded();

// Digest generation step
MessageDigest md = MessageDigest.getInstance("SHA256", "BC");
byte[] digest = md.digest(IOUtils.toByteArray(content));

// Separate signature container creation step
List<Certificate> certList = Arrays.asList(chain);
JcaCertStore certs = new JcaCertStore(certList);

CMSSignedDataGenerator gen = new CMSSignedDataGenerator();

Attribute attr = new Attribute(CMSAttributes.messageDigest,
        new DERSet(new DEROctetString(digest)));

ASN1EncodableVector v = new ASN1EncodableVector();

v.add(attr);

SignerInfoGeneratorBuilder builder = new SignerInfoGeneratorBuilder(new BcDigestCalculatorProvider())
        .setSignedAttributeGenerator(new DefaultSignedAttributeTableGenerator(new AttributeTable(v)));

AlgorithmIdentifier sha256withRSA = new DefaultSignatureAlgorithmIdentifierFinder().find("SHA256withRSA");

CertificateFactory certFactory = CertificateFactory.getInstance("X.509");
InputStream in = new ByteArrayInputStream(chain[0].getEncoded());
X509Certificate cert = (X509Certificate) certFactory.generateCertificate(in);

gen.addSignerInfoGenerator(builder.build(
        new BcRSAContentSignerBuilder(sha256withRSA,
                new DefaultDigestAlgorithmIdentifierFinder().find(sha256withRSA))
                        .build(PrivateKeyFactory.createKey(pk.getEncoded())),
        new JcaX509CertificateHolder(cert)));

gen.addCertificates(certs);

CMSSignedData s = gen.generate(new CMSAbsentContent(), false);
return s.getEncoded();

void sign(PDDocument document, OutputStream output, SignatureInterface signatureInterface) throws IOException
{
    PDSignature signature = new PDSignature();
    signature.setFilter(PDSignature.FILTER_ADOBE_PPKLITE);
    signature.setSubFilter(PDSignature.SUBFILTER_ADBE_PKCS7_DETACHED);
    signature.setName("Example User");
    signature.setLocation("Los Angeles, CA");
    signature.setReason("Testing");
    signature.setSignDate(Calendar.getInstance());
    document.addSignature(signature);
    ExternalSigningSupport externalSigning =
            document.saveIncrementalForExternalSigning(output);
    byte[] cmsSignature = signatureInterface.sign(externalSigning.getContent());
    externalSigning.setSignature(cmsSignature);
}

（CreateSignature方法符号)

像这样

try (   InputStream resource = getClass().getResourceAsStream("test.pdf");
        OutputStream result = new FileOutputStream(new File(RESULT_FOLDER, "testSignedWithSeparatedHashing.pdf"));
        PDDocument pdDocument = PDDocument.load(resource)   )
{
    sign(pdDocument, result, data -> signWithSeparatedHashing(data));
}

（CreateSignature测试方法TestSignwithSeparatedHashing)