证书类型的Android问题

我需要在Android应用程序中签署PDF文件的证书。似乎我只能使用pfx或p12类型（在iText中）对它们进行签名。 我现在所拥有的：

Android应用向服务器生成证书签名请求

服务器以以下格式返回证书数据：

-----开始证书----- -----结束证书-----

服务器返回X509证书，我无法使用该证书签署PDF。有没有办法将cer（由上述数据构成）转换为p12？如有任何信息，将不胜感激。

我已找到。希望能有帮助

        String password = "password";
        String text = "545048";
        KeyStore keyStore = KeyStore.getInstance("pkcs12");
        InputStream inputStream = activity.getResources().openRawResource(R.raw.am_client);
        keyStore.load(inputStream, password.toCharArray());

        String alias = keyStore.aliases().nextElement();
        PrivateKey privateKey = (PrivateKey)keyStore.getKey(alias, password.toCharArray());
        X509Certificate certificate = (X509Certificate)keyStore.getCertificate(alias);

        //Sign Data
        byte[] dataToSign = text.getBytes("UTF-8"); //change to UTF-16 if needed
        Signature signature1 = Signature.getInstance("SHA1WithRSA");
        signature1.initSign(privateKey);
        signature1.update(dataToSign);
        byte[] signedData = signature1.sign();
        String signed = new String(signedData, "UTF-8"); //change to UTF-16 if needed
        Log.d("MESSAGE", "string = " + signed);

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一般来说，要对文档进行数字签名，您需要一个私钥和一个证书（可能还有证书链），并且您有：

• 私钥用于对发送到服务器的证书签名请求进行签名（其中包括一些证书数据，如

  CN

  和公钥）

• 服务器返回证书（可能还有链）

我不擅长itext，但您可以看到签名是用私钥和链完成的。pkcs12密钥库仅用于提取密钥和链

public void signPdfFirstTime(String src, String dest)
    throws IOException, DocumentException, GeneralSecurityException {
    String path = properties.getProperty("PRIVATE");
    String keystore_password = properties.getProperty("PASSWORD");
    String key_password = properties.getProperty("PASSWORD");
    KeyStore ks = KeyStore.getInstance("pkcs12", "BC");
    ks.load(new FileInputStream(path), keystore_password.toCharArray());
    String alias = (String)ks.aliases().nextElement();
    PrivateKey pk = (PrivateKey) ks.getKey(alias, key_password.toCharArray());
    Certificate[] chain = ks.getCertificateChain(alias);
    // reader and stamper
    PdfReader reader = new PdfReader(src);
    FileOutputStream os = new FileOutputStream(dest);
    PdfStamper stamper = PdfStamper.createSignature(reader, os, '\0');
    // appearance
    PdfSignatureAppearance appearance = stamper .getSignatureAppearance();
    appearance.setImage(Image.getInstance(RESOURCE));
    appearance.setReason("I've written this.");
    appearance.setLocation("Foobar");
    appearance.setVisibleSignature(new Rectangle(72, 732, 144, 780), 1,    "first");
    // digital signature
    ExternalSignature es = new PrivateKeySignature(pk, "SHA-256", "BC");
    ExternalDigest digest = new BouncyCastleDigest();
    MakeSignature.signDetached(appearance, digest, es, chain, null, null, null, 0, CryptoStandard.CMS);
}

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您好，写证书是指公共部分，即.cer？是的，证书是公共部分。.cer文件包含一个证书