c#微信小程序解密接口返回的數據

微信小程序中，由於有些數據比較隱私（openid，手機號等），所以你請求微信對應的接口返回的數據是加密的，這就需要解密了，具體可以看https://developers.weixin.qq.com/miniprogram/dev/framework/open-ability/getPhoneNumber.html

而微信又沒有提供c#demo,所以在網上找了一下，總結出來：

首先要解密數據，需要幾個參數：①sessionKey ②encryptedData ③iv

sessionKey：在js頁面調用wx.login方法返回code然後通過後端請求

https://api.weixin.qq.com/sns/jscode2session?appid=APPID&secret=SECRET&js_code=JSCODE&grant_type=authorization_code

就會得到了。

 encryptedData：微信返回的解密數據

iv：加密算法的初始向量

/// <summary>
/// WXBizDataCrypt 的摘要說明
/// 微信小程序解密類
/// </summary>
public class WXBizDataCrypt
{
    private string _appid;
    private string _sessionKey;

    /// <summary>
    /// 
    /// </summary>
    /// <param name="sessionKey">sessionKey用戶在小程序登錄後獲取的會話密鑰</param>
    public WXBizDataCrypt(string sessionKey)
    {
        _appid = AppSettingUtil.AppSettings["appid"];
        _sessionKey = sessionKey;
    }

    /// <summary>
    /// 檢驗數據的真實性，並且獲取解密後的明文.
    /// </summary>
    /// <param name="encryptedData">加密的用戶數據</param>
    /// <param name="iv">與用戶數據一同返回的初始向量</param>
    /// <param name="data">解密後的原文</param>
    /// <returns>成功0，失敗返回對應的錯誤碼</returns>
    /**
     * error code 說明.
     * <ul>

     *    <li>-41001: encodingAesKey 非法</li>
     *    <li>-41003: aes 解密失敗</li>
     *    <li>-41004: 解密後得到的buffer非法</li>
     *    <li>-41005: base64加密失敗</li>
     *    <li>-41016: base64解密失敗</li>
     * </ul>
     */
    public int decryptData(string encryptedData, string iv, out string data)
    {
        data = string.Empty;
        if (this._sessionKey.Length != 24)
        {
            return -41001;
        }
        if (iv.Length != 24)
        {
            return -41002;
        }
        try
        {
            data = AESDecrypt(encryptedData, this._sessionKey, iv);
        }
        catch (Exception ex)
        {
            return -41004;
        }
        return 0;
    }

    public static string AESDecrypt(string encryptedDatatxt, string AesKey, string AesIV)
    {
        try
        {
            byte[] encryptedData = Convert.FromBase64String(encryptedDatatxt);
            RijndaelManaged rijndaelCipher = new RijndaelManaged();
            rijndaelCipher.Key = Convert.FromBase64String(AesKey);
            rijndaelCipher.IV = Convert.FromBase64String(AesIV);
            rijndaelCipher.Mode = CipherMode.CBC;
            rijndaelCipher.Padding = PaddingMode.PKCS7;
            ICryptoTransform transform = rijndaelCipher.CreateDecryptor();
            byte[] plainText = transform.TransformFinalBlock(encryptedData, 0, encryptedData.Length);
            string result = Encoding.Default.GetString(plainText);
            return result;
        }
        catch (Exception ex)
        {
            throw ex;

        }
    }
}

這個是c#的解密類，然後調用解密方法可以這樣：

new WXBizDataCrypt(session_key).decryptData(encryptedData, iv, out data);