/**
 * MD5加密
 * @param byteStr 需要加密的内容
 * @return 返回 byteStr的md5值
 */
public static String encryptionMD5(byte[] byteStr) {
  MessageDigest messageDigest = null;
  StringBuffer md5StrBuff = new StringBuffer();
  try {
    messageDigest = MessageDigest.getInstance("MD5");
    messageDigest.reset();
    messageDigest.update(byteStr);
    byte[] byteArray = messageDigest.digest();
    for (int i = 0; i < byteArray.length; i++) {
      if (Integer.toHexString(0xFF & byteArray[i]).length() == 1) {
        md5StrBuff.append("0").append(Integer.toHexString(0xFF & byteArray[i]));
      } else {
        md5StrBuff.append(Integer.toHexString(0xFF & byteArray[i]));
      }
    }
  } catch (NoSuchAlgorithmException e) {
    e.printStackTrace();
  }
  return md5StrBuff.toString();
}

/**
 * 获取app签名md5值
 */
public String getSignMd5Str() {
  try {
    PackageInfo packageInfo = mActivity.getPackageManager().getPackageInfo(mActivity.getPackageName(), PackageManager.GET_SIGNATURES);
    Signature[] signs = packageInfo.signatures;
    Signature sign = signs[0];
    String signStr = encryptionMD5(sign.toByteArray());
    return signStr;
  } catch (PackageManager.NameNotFoundException e) {
    e.printStackTrace();
  }
  return "";
}