从 CMSSignedDataGenerator 获取消息摘要以登录外部服务器

如何解决从 CMSSignedDataGenerator 获取消息摘要以登录外部服务器

目前我有一个类，我可以在本地正确生成 CMS 签名（可以访问私钥）。 我需要调整它，以便签名操作在异步响应请求的外部服务器（我只能访问公共证书）上完成，因此我想找到一种方法来获取必须签名的摘要，将其发送到服务器并退出。

收到响应后，我将构建 CMS 容器并将其插入。

我知道我可以创建一个不对数据进行签名而是返回已签名数据的 ContentSigner。但是我怎样才能得到实际上必须签名的摘要？

我有这个执行签名的类

public class MyContentSigner implements ContentSigner {

    private final Signature sign;
    private final ByteArrayOutputStream byteArrayOutputStream;
    private final AlgorithmIdentifier sha256withRSA;

    public MyContentSigner(PrivateKey privateKey,AlgorithmIdentifier sha256withRSA) throws NoSuchAlgorithmException,InvalidKeyException {
        this.sha256withRSA = sha256withRSA;

        sign = Signature.getInstance("SHA256withRSA",new BouncyCastleProvider());
        sign.initSign(privateKey);

        byteArrayOutputStream = new ByteArrayOutputStream();

    }

    @Override
    public AlgorithmIdentifier getAlgorithmIdentifier() {
        return sha256withRSA;
    }

    @Override
    public OutputStream getOutputStream() {
        return byteArrayOutputStream;
    }

    @Override
    public byte[] getSignature() {
        try {

            byte[] input = byteArrayOutputStream.toByteArray();

            this.sign.update(input);

            byteArrayOutputStream.reset();

            return this.sign.sign();

        } catch (SignatureException e) {
            e.printStackTrace();
        }
        return null;
    }
}

然后是这个创建 CMS Container 并将前一个类设置为 ContentSigner 的类。

public class SignServiceWithMyContentSigner {


    private final PrivateKey privateKey;
    private final X509Certificate certificate;

    public static final String SIGNATURE_ALGORITHM = "SHA256withRSA";
    private final Certificate[] chain;

    public SignServiceWithMyContentSigner(KeyStore ks) throws NoSuchAlgorithmException,KeyStoreException,UnrecoverableKeyException {
        privateKey = (PrivateKey) ks.getKey("....","".toCharArray());
        certificate = (X509Certificate) ks.getCertificate("....");
        chain = ks.getCertificateChain(".....");
    }

    public byte[] signDocument(byte[] digestInfo) {

        try {

            List<Certificate> certificateList = Arrays.asList(chain);
            JcaCertStore jcaCertStore = new JcaCertStore(certificateList);

            CMSSignedDataGenerator generator = new CMSSignedDataGenerator();

            Attribute attribute = new Attribute(CMSAttributes.messageDigest,new DERSet(new DEROctetString(digestInfo)));

            ASN1EncodableVector asn1EncodableVector = new ASN1EncodableVector();

            asn1EncodableVector.add(attribute);

            SignerInfoGeneratorBuilder builder =
                    new SignerInfoGeneratorBuilder(
                            new BcDigestCalculatorProvider()
                    ).setSignedAttributeGenerator(
                            new DefaultSignedAttributeTableGenerator(
                                    new AttributeTable(asn1EncodableVector)
                            )
                    );

            AlgorithmIdentifier sha256withRSA = new DefaultSignatureAlgorithmIdentifierFinder().find(SIGNATURE_ALGORITHM);


            generator.addSignerInfoGenerator(
                    builder.build(
                            // Here is the my previous class 
                            new MyContentSigner(privateKey,sha256withRSA),new JcaX509CertificateHolder(certificate)
                    )
            );

            generator.addCertificates(jcaCertStore);


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

        } catch (IOException | CertificateEncodingException | OperatorCreationException | CMSException | NoSuchPaddingException | NoSuchAlgorithmException | InvalidKeyException e) {
            e.printStackTrace();
        }

        return new byte[0];
    }
}