[Micro] development platform open letter to decrypt data

background:

Micro-channel fast login, obtain the user's phone number.

Micro-channel public platform to explain:

For security reasons, open micro-channel data transmitted to the encryption server via a server developer, the developer then needs to open the data obtained by the decryption.

The micro-channel public internet applet explained, as follows:
1, the distal end need to call wx.login () , Get code;
2, using the micro-code calling channel interface to obtain session_key of: https://developers.weixin.qq.com/miniprogram/dev /api/open-api/login/code2Session.html
. 3, the encrypted data provided by the front end and iv encryptedData
reference: Gets phone number
4, obtained by the above encryptedData, session_key of, iv decrypting

	/**
     * 解密获取信息
     */
    public static JSONObject getUserInfo(String encryptedData,String sessionkey,String iv) {
        // 被加密的数据
        byte[] dataByte = Base64.decode(encryptedData);
        // 加密秘钥
        byte[] keyByte = Base64.decode(sessionkey);
        // 偏移量
        byte[] ivByte = Base64.decode(iv);
        try {
            // 如果密钥不足16位，那么就补足.  这个if 中的内容很重要
            int base = 16;
            if (keyByte.length % base != 0) {
                int groups = keyByte.length / base + (keyByte.length % base != 0 ? 1 : 0);
                byte[] temp = new byte[groups * base];
                Arrays.fill(temp, (byte) 0);
                System.arraycopy(keyByte, 0, temp, 0, keyByte.length);
                keyByte = temp;
            }
            // 初始化
            Security.addProvider(new BouncyCastleProvider());
            Cipher cipher = Cipher.getInstance("AES/CBC/PKCS7Padding", "BC");
            SecretKeySpec spec = new SecretKeySpec(keyByte, "AES");
            AlgorithmParameters parameters = AlgorithmParameters.getInstance("AES");
            parameters.init(new IvParameterSpec(ivByte));
            cipher.init(Cipher.DECRYPT_MODE, spec, parameters);// 初始化
            byte[] resultByte = cipher.doFinal(dataByte);
            if (null != resultByte && resultByte.length > 0) {
                String result = new String(resultByte, "UTF-8");
                return JSONObject.parseObject(result);
            }
        } catch (NoSuchAlgorithmException e) {
            e.printStackTrace();
        } catch (NoSuchPaddingException e) {
            e.printStackTrace();
        } catch (InvalidParameterSpecException e) {
            e.printStackTrace();
        } catch (IllegalBlockSizeException e) {
            e.printStackTrace();
        } catch (BadPaddingException e) {
            e.printStackTrace();
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        } catch (InvalidKeyException e) {
            e.printStackTrace();
        } catch (InvalidAlgorithmParameterException e) {
            e.printStackTrace();
        } catch (NoSuchProviderException e) {
            e.printStackTrace();
        }
        return null;
    }

problem

1, need to be buffered acquired sessionkey tip call wx.login () code acquired acquiring sessionkey holding the rear end code; if acquired with the repetition code, error code been used.
2, decryption method common mistakes:
①ValueError: IV the MUST BE 16 bytes Long
resolve: to fight binary
②pad block corrupted
Solution: The reason is sessionkey date and needs to reacquire

Reference:
get the phone number