小程序數據簽名校驗-Java端

JDK內置的簽名算法不包含小程序須要的（對稱解密使用的算法爲 AES-128-CBC，數據採用PKCS#7填充），因此須要引用第三方jar。

    compile group: 'org.bouncycastle', name: 'bcprov-jdk15on', version: '1.54'

如下是具體的代碼：

  //自行在構造函數中賦值
   String sessionKey;

 /**
     * AES-128-CBC解密
     * 使用PKCS填充
     * @param encryptedData
     * @param iv
     * @return
     * @throws Exception
     */
    public String decryptAesPkcData(String encryptedData, String iv) throws Exception {
        //檢查sessionKey的長度
        if (this.sessionKey.length() != 24) {
            throw new AesException(AesException.IllegalAesKey);
        }
        //檢查iv的長度
        if (iv.length() != 24) {
            throw new AesException(AesException.IllegalAesKey);
        }
        byte[] aesKey = Base64.decodeBase64(this.sessionKey);
        byte[] aesIV = Base64.decodeBase64(iv);
        byte[] aesCipher = Base64.decodeBase64(encryptedData);
        Security.addProvider(new org.bouncycastle.jce.provider.BouncyCastleProvider());
        Cipher cipher = Cipher.getInstance("AES/CBC/PKCS7Padding");
        Key sKeySpec = new SecretKeySpec(aesKey, "AES");
        AlgorithmParameters params = AlgorithmParameters.getInstance("AES");
        params.init(new IvParameterSpec(aesIV));
        cipher.init(Cipher.DECRYPT_MODE, sKeySpec, params);
        return new String(cipher.doFinal(aesCipher), "utf-8");
    }