RSA 非对称加解密 公私钥的生成

    /**
     *  生成RSA随机密钥对（公钥和私钥）
     * @return
     */
    public static Map<String, String> createKeyPair() throws Exception {
        Map<String,String> keyPairMap = new HashMap<>();
        // 密钥生成器，基于RSA算法
        KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("RSA");
        // 初始化密钥生成器，密钥大小为96-1024位
        keyPairGenerator.initialize(1024, SecureRandom.getInstance("SHA1PRNG"));
        // 生成一个密钥对，保存在KeyPair中
        KeyPair keyPair = keyPairGenerator.generateKeyPair();
        // 获取公钥及公钥字节数组
        PublicKey publicKey = keyPair.getPublic();
        byte[] publicKeyBytes = publicKey.getEncoded();
        // 获取私钥及私钥字节数组
        PrivateKey privateKey = keyPair.getPrivate();
        byte[] privateKeyBytes = privateKey.getEncoded();
        // 转换成16进制字符保存在map中
        keyPairMap.put(PUBLIC_KEY, byte2Hex(publicKeyBytes));
        keyPairMap.put(PRIVATE_KEY, byte2Hex(privateKeyBytes));
        return keyPairMap;
    }

    /**
     *  RSA公钥加密。RSA加密算法对于加密数据长度是有要求的，一般来说，明文长度大小小于等于密钥长度(bytes)-11.
     *   解决这个问题要对较长的明文进行分段加解密(这里不做实现)
     * @param contents
     * @param publicKeyString
     * @return
     */
    public static String encryptWithPublicKey(String contents, String publicKeyString) throws Exception {
        // 判断入参非空
        // 获取公钥
        PublicKey publicKey = KeyFactory.getInstance("RSA").generatePublic(new X509EncodedKeySpec(hex2Byte(publicKeyString)));
        // RSA公钥加密
        Cipher cipher = Cipher.getInstance("RSA");
        cipher.init(Cipher.ENCRYPT_MODE, publicKey);
        byte[] encryptBytes = cipher.doFinal(contents.getBytes("UTF-8"));
        return byte2Hex(encryptBytes);
    }

    /**
     * RSA私钥解密。同样这里不做分段实现
     * @param encryptContents
     * @param privateKeyString
     * @return
     */
    public static String decryptWithPrivateKey(String encryptContents, String privateKeyString) throws Exception {
        // 判断非空
        // 获取私钥
        PrivateKey privateKey = KeyFactory.getInstance("RSA").generatePrivate(new PKCS8EncodedKeySpec(hex2Byte(privateKeyString)));
        // RSA解密
        Cipher cipher = Cipher.getInstance("RSA");
        cipher.init(Cipher.DECRYPT_MODE, privateKey);
        byte[] decryptBytes = cipher.doFinal(hex2Byte(encryptContents));
        return new String(decryptBytes, "UTF-8");
    }

    /**
     *  RSA私钥加密（用于签名）
     * @param contents
     * @param privateKeyString
     * @return
     */
    public static String encryptWithPrivateKey(String contents, String privateKeyString) throws Exception {
        // 判断非空
        // 获取私钥
        PrivateKey privateKey = KeyFactory.getInstance("RSA").generatePrivate(new PKCS8EncodedKeySpec(hex2Byte(privateKeyString)));
        // RSA加密
        Cipher cipher = Cipher.getInstance("RSA");
        cipher.init(Cipher.ENCRYPT_MODE, privateKey);
        byte[] encryptBytes = cipher.doFinal(contents.getBytes("UTF-8"));
        return byte2Hex(encryptBytes);
    }

    /**
     *  RSA公钥解密，用于验证签名
     * @param encryptContents
     * @param publicKeyString
     * @return
     */
    public static String decryptWithPublicKey(String encryptContents, String publicKeyString) throws Exception {
        // 判断非空
        // 获取公钥
        PublicKey publicKey = KeyFactory.getInstance("RSA").generatePublic(new X509EncodedKeySpec(hex2Byte(publicKeyString)));
        // RSA解密
        Cipher cipher = Cipher.getInstance("RSA");
        cipher.init(Cipher.DECRYPT_MODE, publicKey);
        byte[] decryptBytes = cipher.doFinal(hex2Byte(encryptContents));
        return new String(decryptBytes, "UTF-8");
    }

    /**
     *  将byte[]数组转换成16进制字符。一个byte生成两个字符，长度对应1:2
     * @param bytes，输入byte[]数组
     * @return 16进制字符
     */
    public static String byte2Hex(byte[] bytes) {
        if (bytes == null) {
            return null;
        }
        StringBuilder builder = new StringBuilder();
        // 遍历byte[]数组，将每个byte数字转换成16进制字符，再拼接起来成字符串
        for (int i = 0; i < bytes.length; i++) {
            // 每个byte转换成16进制字符时，bytes[i] & 0xff如果高位是0，输出将会去掉，所以+0x100(在更高位加1)，再截取后两位字符
            builder.append(Integer.toString((bytes[i] & 0xff) + 0x100, 16).substring(1));
        }
        return builder.toString();
    }

    /**
     *  将16进制字符转换成byte[]数组。与byte2Hex功能相反。
     * @param string 16进制字符串
     * @return byte[]数组
     */
    public static byte[] hex2Byte(String string) {
        if (string == null || string.length() < 1) {
            return null;
        }
        // 因为一个byte生成两个字符，长度对应1:2，所以byte[]数组长度是字符串长度一半
        byte[] bytes = new byte[string.length() / 2];
        // 遍历byte[]数组，遍历次数是字符串长度一半
        for (int i = 0; i < string.length() / 2; i++) {
            // 截取没两个字符的前一个，将其转为int数值
            int high = Integer.parseInt(string.substring(i * 2, i * 2 + 1), 16);
            // 截取没两个字符的后一个，将其转为int数值
            int low = Integer.parseInt(string.substring(i * 2 + 1, i * 2 + 2), 16);
            // 高位字符对应的int值*16+低位的int值，强转成byte数值即可
            // 如dd，高位13*16+低位13=221(强转成byte二进制11011101，对应十进制-35)
            bytes[i] = (byte) (high * 16 + low);
        }
        return bytes;
    }