Java读取PKCS8格式私钥文件

        byte[] buffer = Base64.getDecoder().decode(readRsaFileBody("pkcs8_rsa_private_key.pem"));
        PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(buffer);
        KeyFactory keyFactory = KeyFactory.getInstance("RSA");
        PrivateKey privateKey = keyFactory.generatePrivate(keySpec);
        System.out.println(String.format(
                "算法:%s\n" +
                        "格式:%s\n",
                privateKey.getAlgorithm(),
                privateKey.getFormat()
        ));

Java读取X509格式公钥文件

        byte[] buffer = Base64.getDecoder().decode(readRsaFileBody("rsa_public_key.pem"));
        KeyFactory keyFactory = KeyFactory.getInstance("RSA");
        X509EncodedKeySpec keySpec = new X509EncodedKeySpec(buffer);
        PublicKey publicKey = keyFactory.generatePublic(keySpec);
        System.out.println(String.format(
                "算法:%s\n" +
                        "格式:%s\n",
                publicKey.getAlgorithm(),
                publicKey.getFormat()
        ));

公钥加密输出Base64编码

        byte[] buffer = Base64.getDecoder().decode(readRsaFileBody("rsa_public_key.pem"));
        KeyFactory keyFactory = KeyFactory.getInstance("RSA");
        X509EncodedKeySpec keySpec = new X509EncodedKeySpec(buffer);
        PublicKey publicKey = keyFactory.generatePublic(keySpec);

        Cipher cipher = Cipher.getInstance("RSA");
        //私钥加密同理,将 publicKey 替换成 privateKey
        cipher.init(Cipher.ENCRYPT_MODE, publicKey);
        String data = "12345678";
        byte[] output = cipher.doFinal(data.getBytes());
        String encryptData = Base64.getEncoder().encodeToString(output);
        System.out.println(String.format("%s\n=>ENCRYPT,Base64=>\n%s", data, encryptData));

私钥解密

        byte[] buffer = Base64.getDecoder().decode(readRsaFileBody("pkcs8_rsa_private_key.pem"));
        PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(buffer);
        KeyFactory keyFactory = KeyFactory.getInstance("RSA");
        PrivateKey privateKey = keyFactory.generatePrivate(keySpec);

        Cipher cipher = Cipher.getInstance("RSA");
        //公钥解密同理,将 privateKey 替换成 publicKey
        cipher.init(Cipher.DECRYPT_MODE, privateKey);
        //12345678
        String encryptData = "UF8CW4ovruUM9ot+G3tG5DFGtDs2h3x6YOuUnK9WIz39w5W9/i7aUyi5kmMISharTg7YV9DNBzD/Zv29CZFA0acN5fejz9vXKeR4Dn50WU0ZU3yF9RuVbi2tqvpjShF6sM88ETblt9cdDty0agYBN+p0eWX1kvF/2m+TEGw4IXI=";
        byte[] output = cipher.doFinal(Base64.getDecoder().decode(encryptData));
        String data = new String(output);
        System.out.println(String.format("%s\n=>DECRYPT=>\n%s", encryptData, data));

其他相关代码示例

    public static byte[] file2bytes(String path) throws Exception {
        URL resource = SslTest.class.getClassLoader().getResource(path);
        return Files.readAllBytes(Paths.get(resource.toURI()));
    }

    public static String file2str(String path) throws Exception {
        return new String(file2bytes(path));
    }

    /**
     * 返回body去掉首尾行和换行字符
     *
     * @param name
     * @return
     * @throws Exception
     */
    public static String readRsaFileBody(String name) throws Exception {
        String content = file2str(name);
        //tip: Base64.getDecoder() and Base64.getEncoder() 编码字符串中不包含换行字符
        //tip: Base64.getMimeDecoder() and Base64.getMimeEncoder() 支持编码字符串中包含换行字符
        return Arrays.stream(content.split("\r\n|\n")).filter(line -> !line.startsWith("-----")).collect(Collectors.joining(""));
    }

    public static InputStream file2Stream(String name) throws Exception {
        return SslTest.class.getClassLoader().getResourceAsStream(name);
    }

    @Test
    public void _read_file() throws Exception {
        System.out.println(readRsaFileBody("rsa_private_key.pem"));
        byte[] encode = Base64.getEncoder().encode("123456".getBytes());
        byte[] decode = Base64.getMimeDecoder().decode(readRsaFileBody("rsa_private_key.pem"));
        System.out.println(decode.length);
    }

Reference

openssl-and-keytool-example