[英]How to encrypt and decrypt a pdf/doc file in Android
我是 Android 新手,我正在嘗試加密和解密文件,並希望在解密后在 Android 設備中顯示。
在這里,我從 URL 下載文件並存儲在 SD 卡中,我現在不知道如何加密文件然后存儲在 SD 卡中,文件大小可能超過 20MB。
代碼:
File downloadFile(String dwnload_file_path) {
File file = null;
try {
String extStorageDirectory = Environment.getExternalStorageDirectory().toString();
File folder = new File(extStorageDirectory, "SampleFolder");
folder.mkdir();
file = new File(folder, dest_file_path);
try{
file.createNewFile();
}catch (IOException e){
e.printStackTrace();
}
URL url = new URL(dwnload_file_path);
HttpURLConnection urlConnection = (HttpURLConnection)url.openConnection();
urlConnection.connect();
InputStream inputStream = urlConnection.getInputStream();
FileOutputStream fileOutputStream = new FileOutputStream(file);
int totalSize = urlConnection.getContentLength();
byte[] buffer = new byte[MEGABYTE];
int bufferLength = 0;
while((bufferLength = inputStream.read(buffer))>0 ){
fileOutputStream.write(buffer, 0, bufferLength);
}
fileOutputStream.close();
//ToastManager.toast(this, "Download Complete. Open PDF Application installed in the device.");
} catch (final MalformedURLException e) {
//ToastManager.toast(this, "Some error occured. Press try again.");
} catch (final IOException e) {
//ToastManager.toast(this, "Some error occured. Press try again.");
} catch (final Exception e) {
//ToastManager.toast(this, "Failed to download image. Please check your internet connection.");
}
return file;
}
在這里,我在 Android 設備中顯示文件,但在解密文件后,如何顯示它?
代碼:
File pdfFile = new File(Environment.getExternalStorageDirectory() + "/SampleFolder/" + "Sample."pref.getString(Constants.PrefConstants.PATH_NAME));
File f = new File(pdfFile.toString());
if(f.exists()) {
Uri path = Uri.fromFile(pdfFile);
Intent pdfIntent = new Intent(Intent.ACTION_VIEW);
pdfIntent.setDataAndType(path, pref.getString(Constants.PrefConstants.PATH_NAME_APP));
//pdfIntent.setFlags(Intent. FLAG_ACTIVITY_CLEAR_TOP);
pdfIntent.setFlags(Intent.FLAG_ACTIVITY_NO_HISTORY);
startActivity(pdfIntent);
} else {
//uiManager.execute(Constants.Commands.REQGET_INSTRUCTIONS_SCREEN,null);
ToastManager.toast(getApplicationContext(), "No data available...");
}
我該如何解決這個問題?
您需要使用 SecretKeySpec 庫。 加密方法示例
static void encrypt() throws IOException, NoSuchAlgorithmException, NoSuchPaddingException, InvalidKeyException {
// Here you read the cleartext.
FileInputStream fis = new FileInputStream("SampleFolder/yourfilename");
// This stream write the encrypted text. This stream will be wrapped by another stream.
FileOutputStream fos = new FileOutputStream("SampleFolder/yourencryptedfilename");
// Length is 16 byte
// Careful when taking user input!!! https://stackoverflow.com/a/3452620/1188357
SecretKeySpec sks = new SecretKeySpec("MyDifficultPassw".getBytes(), "AES");
// Create cipher
Cipher cipher = Cipher.getInstance("AES");
cipher.init(Cipher.ENCRYPT_MODE, sks);
// Wrap the output stream
CipherOutputStream cos = new CipherOutputStream(fos, cipher);
// Write bytes
int b;
byte[] d = new byte[8];
while((b = fis.read(d)) != -1) {
cos.write(d, 0, b);
}
// Flush and close streams.
cos.flush();
cos.close();
fis.close();
}
有關解密方法,請參閱下面的鏈接。 更多詳細信息: 如何在 Android 中使用 AES 從 SD 卡加密文件?
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