Develop Reference

Reading a stored SecretKey from file

with this below code i can store SecretKey into file:
public static SecretKey generateKey() throws NoSuchAlgorithmException {
// Generate a 256-bit key
final int outputKeyLength = 256;
SecureRandom secureRandom = new SecureRandom();
// Do *not* seed secureRandom! Automatically seeded from system entropy.
KeyGenerator keyGenerator = KeyGenerator.getInstance("AES");
keyGenerator.init(outputKeyLength, secureRandom);
yourKey = keyGenerator.generateKey();
return yourKey;
}
yourKey = generateKey();
File file = new File(Environment.getExternalStorageDirectory() + File.separator + "encrypt" + File.separator, "config.xml");
BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream(file));
byte[] filesBytes = yourKey.getEncoded();
bos.write(filesBytes);
bos.flush();
bos.close();
now how can i read this file and pass bytes[] into SecretKey variable? for example:
File file = new File(Environment.getExternalStorageDirectory() + File.separator + "convert" + File.separator, "config.xml");
BufferedInputStream buf = new BufferedInputStream(
new FileInputStream(file));
int length = (int) file.length();
byte[] audio_data = new byte[length];
int bytesRead;
ByteArrayOutputStream output = new ByteArrayOutputStream();
while ((bytesRead = buf.read(audio_data)) != -1) {
output.write(audio_data, 0, bytesRead);
}
byte[] inarry = output.toByteArray();
yourKey=inarry;
problem is yourKey=inarry; and pass bytes into yourKey variable, how can i resolve that?

Even though I never do this myself, if you want to write SecretKey into a file and read it later, you can use ObjectOutputStream and ObjectInputStream.
SecretKey is Serializable, so you can use with those 2 funtions.
write like:
FileOutputStream fout = new FileOutputStream("G:\\address.ser");
ObjectOutputStream oos = new ObjectOutputStream(fout);
oos.writeObject(yourKey);
oos.close();
fout.close();
read like:
FileInputStream fin = new FileInputStream("G:\\address.ser");
ObjectInputStream ois = new ObjectInputStream(fin);
SecretKey yourKey = (SecretKey) ois.readObject();
ois.close();
fin.close();
But as I told, you should normally never do it like this. If you want to just store your key, you need to use KeyStore. If you need to save it for sending, you need to save it encrypted. Key is the most important part of a cryptography algorithm, so you should never save it like this in a file.

How can I make pdf file readable only by my app?

Is it possible to download a PDF from server and save in format that only my application can read?

This is my working example used in my app ....hope this help you
Is it possible to download pdf from server and save
Yes i have use retrofit library to download pdf file from server you can use Volly or Loopj AsyncTask as well
After downloading pdf file you will get InputeStream object of file than encrypt that and store in app private folder (so no other application can able to use it)
public static File encryptAndSaveFileInPrivateFolder(
Context context, String albumName, InputStream inputStream, String fullFileName) {
File file = null;
try {
// Get the directory for the app's private pictures directory.
File fileDirectory = new File(context.getExternalFilesDir(
Environment.DIRECTORY_PICTURES),""+albumName);
if (!fileDirectory.exists()) {
fileDirectory.mkdirs();
}
file = new File(fileDirectory,""+fullFileName);
if (file.exists()) {
file.delete();
}
FileOutputStream output = new FileOutputStream(file);
encrypt(inputStream,output);
inputStream.close();
} catch (Exception e) {
e.printStackTrace();
}
return file;
}
This method encrypt your file
public static void encrypt(InputStream fis,FileOutputStream fos ) throws IOException, NoSuchAlgorithmException
, NoSuchPaddingException, InvalidKeyException {
// Here you read the cleartext.
//FileInputStream fis = new FileInputStream("data/cleartext");
// This stream write the encrypted text. This stream will be wrapped by another stream.
// FileOutputStream fos = new FileOutputStream("data/encrypted");
String password ="passwordProtectd";
// Length is 16 byte
byte[] inputByte = password.getBytes("UTF-8");
SecretKeySpec sks = new SecretKeySpec(inputByte, "AES");
// SecretKeySpec sks = new SecretKeySpec(password.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();
}
Than show pdf using intent
public void decryptFileAndShow(Context context,File mFile) {
try{
if (null != mFile) {
String parentPath = mFile.getAbsoluteFile().getParent();//Actual encrypted file path
File tempFile = new File(parentPath, "report.pdf"); //Created new file that decrypted format after view we will delete this
//tempFile =File.createTempFile("prefix","TestMyPDF.pdf", context.getExternalFilesDir(""));
Utilities.decrypt( new FileInputStream(mFile), new FileOutputStream(tempFile));
Intent intent = new Intent(Intent.ACTION_VIEW);
intent.setDataAndType(Uri.fromFile(tempFile), "application/pdf");
intent.setFlags(Intent.FLAG_ACTIVITY_NO_HISTORY);
context.startActivity(intent);
tempFile.deleteOnExit();
}
}catch (Exception e){
e.printStackTrace();
}
}
Last the method used for decryption
public static void decrypt(FileInputStream fis,FileOutputStream fos ) throws IOException, NoSuchAlgorithmException,
NoSuchPaddingException, InvalidKeyException {
// FileInputStream fis = new FileInputStream("data/encrypted");
// FileOutputStream fos = new FileOutputStream("data/decrypted");
String password ="passwordProtectd";
byte[] inputByte = password.getBytes("UTF-8");
SecretKeySpec sks = new SecretKeySpec(inputByte, "AES");
Cipher cipher = Cipher.getInstance("AES");
cipher.init(Cipher.DECRYPT_MODE, sks);
CipherInputStream cis = new CipherInputStream(fis, cipher);
int b;
byte[] d = new byte[8];
while((b = cis.read(d)) != -1) {
fos.write(d, 0, b);
}
fos.flush();
fos.close();
cis.close();
}

Is it possible to download pdf from server.
Yes, it is possible. Download your pdf and encrypt and decrypt your file accordingly.
You can try like this using CipherOuputStream and CipherInputStream:
byte[] buf = new byte[1024];
Encryption:
public void encrypt(InputStream in, OutputStream out) {
try {
// Bytes written to out will be encrypted
out = new CipherOutputStream(out, ecipher);
// Read in the cleartext bytes and write to out to encrypt
int numRead = 0;
while ((numRead = in.read(buf)) >= 0) {
out.write(buf, 0, numRead);
}
out.close();
} catch (java.io.IOException e) {
}
}
Decryption:
public void decrypt(InputStream in, OutputStream out) {
try {
// Bytes read from in will be decrypted
in = new CipherInputStream(in, dcipher);
// Read in the decrypted bytes and write the cleartext to out
int numRead = 0;
while ((numRead = in.read(buf)) >= 0) {
out.write(buf, 0, numRead);
}
out.close();
} catch (java.io.IOException e) {
}
}

If I understand your question correctly, you want your application to be the only application that reads this particular PDF files. You want to know how you can ensure that you do that.
Since your requirement is not genuine(hacky), the solution also has to be a bit hacky.
You can download the file and store it with your own custom extension (eg. file.mypdf)
Have an intent filter, that supports mimetypes matching .mypdf files

You could have the server encrypt the download and your client side app decrypt it using a public/private key pair. This would prevent anyone with a snooping proxy from observing and saving your content, but it wouldn't deter the most determined users from stealing these documents as they would eventually exist in decrypted form somewhere. To achieve that you'd probably ave to create your own PDF viewer and damage the bytes of the PDF in a way that your viewer can do, but no other viewer can recover

Fast file encryption in android

Hi i am creating a sample to lock file or folder in android. I have a issue when i encrypt or decrypt large size (more than 1 GB) file it takes too much time.
Please help me to encrypt and decrypt file fastly.
Here i am attaching code which i am using on below
if (!isEncrypted) {
FileInputStream fis = new FileInputStream(path);
// This stream write the encrypted text. This stream will be wrapped by another stream.
FileOutputStream fos = new FileOutputStream(path + ".abcd");
// Length is 16 byte
SecretKeySpec sks = new SecretKeySpec("abcdefghijklmnop".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[1024];
try {
while ((b = fis.read(d)) != -1) {
cos.write(d, 0, b);
}
// Flush and close streams.
cos.flush();
cos.close();
fis.close();
new File(path).deleteOnExit();
isEncrypted = true;
runOnUiThread(new Runnable() {
#Override
public void run() {
btnEncrypt.setText("Decrypt Path");
deleteMyFile(path);
}
});
} catch (Exception ex) {
ex.printStackTrace();
}
} else {
FileInputStream fis = new FileInputStream(path + ".abcd");
FileOutputStream fos = new FileOutputStream(path);
SecretKeySpec sks = new SecretKeySpec("abcdefghijklmnop".getBytes(), "AES");
Cipher cipher = Cipher.getInstance("AES");
cipher.init(Cipher.DECRYPT_MODE, sks);
CipherInputStream cis = new CipherInputStream(fis, cipher);
int b;
byte[] d = new byte[1024];
while ((b = cis.read(d)) != -1) {
fos.write(d, 0, b);
}
fos.flush();
fos.close();
cis.close();
isEncrypted = false;
runOnUiThread(new Runnable() {
#Override
public void run() {
deleteMyFile(path + ".abcd");
btnEncrypt.setText("Encrypt Path");
}
});
}
} catch (final Exception e) {
runOnUiThread(new Runnable() {
#Override
public void run() {
progressDialog.setMessage(e.getMessage());
}
});

I hope you found a way to do this. But, here is how I do it.
I realized that writing our own AES classes in java Or C is not recommendable way if you are especially just focused on the end result. Java is pretty slow in comparison with C, but in java you can use multithreading whereas in C you can't. Of course there are aes c programs which do a better job. But using them is difficult. You said you want to encrypt 1GB file under a minute. So, do this.
Install Userland Or Termux and install openssl. Next cd to your file storage location and try aes encrypt command. To automate it, write a bash script and run it. Openssl can easily do 23 MBps to 68 MBps.

Android AES-128 encryption/decryption of file is very slow. How can I increase the speed

I am developing an android app that secures images and videos like Vaulty and Keep safe. I am trying to use AES-128 encryption/decryption technique to store images and videos. I tried it by taking 3 sample images of size 5.13, 4.76 and 5.31 respectively. But the time it is consuming to encrypt is 25s, 22s, 27s respectively and time to decrypt is 31s, 30s, 34s respectively. I am testing it on HTC One X.
Such speed wont be feasible for my app as users will scroll and view images quickly without interruption. Can you please suggest me how can I improve the performance(speed) or should i switch to other algorithms? Can you please suggest me any other techniques through which i can encrypt/decrypt images and videos quickly without compromising security too much.
I tried Vaulty and Keep safe, and they are very quick. Vaulty is said to be using AES-256, but it is still very fast and responsive in terms of encrypting and viewing images. How is it possible that vaulty is that quick using AES-256?
Code I am using is:
static void encrypt(String filename) throws IOException, NoSuchAlgorithmException,
NoSuchPaddingException, InvalidKeyException {
// Here you read the cleartext.
File extStore = Environment.getExternalStorageDirectory();
startTime = System.currentTimeMillis();
Log.i("Encryption Started",extStore + "/5mbtest/"+filename);
FileInputStream fis = new FileInputStream(extStore + "/5mbtest/"+filename);
// This stream write the encrypted text. This stream will be wrapped by
// another stream.
FileOutputStream fos = new FileOutputStream(extStore + "/5mbtest/"+filename+".aes", false);
// Length is 16 byte
SecretKeySpec sks = new SecretKeySpec("MyDifficultPassw".getBytes(),
"AES");
// Create cipher
Cipher cipher = Cipher.getInstance("AES/CBC/PKCS7Padding");
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();
stopTime = System.currentTimeMillis();
Log.i("Encryption Ended",extStore + "/5mbtest/"+filename+".aes");
Log.i("Time Elapsed", ((stopTime - startTime)/1000.0)+"");
}
static void decrypt(String filename) throws IOException, NoSuchAlgorithmException,
NoSuchPaddingException, InvalidKeyException {
File extStore = Environment.getExternalStorageDirectory();
Log.i("Decryption Started",extStore + "/5mbtest/"+filename+".aes");
FileInputStream fis = new FileInputStream(extStore + "/5mbtest/"+filename+".aes");
FileOutputStream fos = new FileOutputStream(extStore + "/5mbtest/"+"decrypted"+filename,false);
SecretKeySpec sks = new SecretKeySpec("MyDifficultPassw".getBytes(),
"AES");
// Create cipher
Cipher cipher = Cipher.getInstance("AES/CBC/PKCS7Padding");
cipher.init(Cipher.DECRYPT_MODE, sks);
startTime = System.currentTimeMillis();
CipherInputStream cis = new CipherInputStream(fis, cipher);
int b;
byte[] d = new byte[8];
while ((b = cis.read(d)) != -1) {
fos.write(d, 0, b);
}
stopTime = System.currentTimeMillis();
Log.i("Decryption Ended",extStore + "/5mbtest/"+"decrypted"+filename);
Log.i("Time Elapsed", ((stopTime - startTime)/1000.0)+"");
fos.flush();
fos.close();
cis.close();
}

One thing that is making your code run slow is the size of your buffer:
byte[] d = new byte[8];
You should bump it up by a few orders of magnitude if you want it to run fast. Given the size of your files I would suggest using at least 1 MB but nowadays you can realistically set it to a few MBs, even on Android. Try changing it to:
byte[] d = new byte[1024 * 1024];
and let us know how much did that improve the speed by.

Use a larger buffer as suggested by #MikeLaren, and also wrap the FileOutputStream in a BufferedOutputStream. When decrypting, wrap the FileInputStream in a BufferedInputStream. Or do both in both cases: no harm done.
No need for heroic buffer sizes like a megabyte: 8k or 32k is sufficient.

How to encrypt file from SD card using AES in Android?

I want to encrypt image from the sd card and store it again in SD card again using AES. The main idea is the application browse an image, then encrypt it when I push a button, then store it in sd card. so my image would be secure.
I already succeed do string encryption using AES from this tutorial http://www.androidsnippets.com/encryptdecrypt-strings, but I don't have idea how to do this with an image, not string.
This is how I do it with a string:
public static String encrypt(String seed, String cleartext) throws Exception
{
byte[] rawKey = getRawKey(seed.getBytes());
byte[] result = encrypt(rawKey, cleartext.getBytes());
return toHex(result);
}
private static byte[] encrypt(byte[] raw, byte[] clear) throws Exception
{
SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES");
Cipher cipher = Cipher.getInstance("AES");
cipher.init(Cipher.ENCRYPT_MODE, skeySpec);
byte[] encrypted = cipher.doFinal(clear);
return encrypted;
}
Can anyone help me give example code how to encrypt an image with AES?
maybe it must using I/O file stream but I don't have an idea how to implement with this code.

If you take user input for the password make sure to read this answer.
You should take a look at:
CipherInputStream and CipherOutputStream. They are used to encrypt and decrypt byte streams.
I have a file named cleartext. The file contains:
Hi, I'm a clear text.
How are you?
That's awesome!
Now, you have an encrypt() function:
static void encrypt() throws IOException, NoSuchAlgorithmException, NoSuchPaddingException, InvalidKeyException {
// Here you read the cleartext.
FileInputStream fis = new FileInputStream("data/cleartext");
// This stream write the encrypted text. This stream will be wrapped by another stream.
FileOutputStream fos = new FileOutputStream("data/encrypted");
// 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();
}
After you execute this function, there should be a file names encrypted. The file contains the encrypted characters.
For decryption you have the decrypt function:
static void decrypt() throws IOException, NoSuchAlgorithmException, NoSuchPaddingException, InvalidKeyException {
FileInputStream fis = new FileInputStream("data/encrypted");
FileOutputStream fos = new FileOutputStream("data/decrypted");
SecretKeySpec sks = new SecretKeySpec("MyDifficultPassw".getBytes(), "AES");
Cipher cipher = Cipher.getInstance("AES");
cipher.init(Cipher.DECRYPT_MODE, sks);
CipherInputStream cis = new CipherInputStream(fis, cipher);
int b;
byte[] d = new byte[8];
while((b = cis.read(d)) != -1) {
fos.write(d, 0, b);
}
fos.flush();
fos.close();
cis.close();
}
After the execution of decrypt, there should be a file named decrypted. This file contains the free text.
You write you're a "noob" but depending on the use-case of encryption you could do a lot of harm if you're not doing it the right way. Know your tools!
Usage of CipherOutputStream Oracle documentation:
SecretKeySpec skeySpec = new SecretKeySpec(y.getBytes(), "AES");
FileInputStream fis;
FileOutputStream fos;
CipherOutputStream cos;
// File you are reading from
fis = new FileInputStream("/tmp/a.txt");
// File output
fos = new FileOutputStream("/tmp/b.txt");
// Here the file is encrypted. The cipher1 has to be created.
// Key Length should be 128, 192 or 256 bit => i.e. 16 byte
SecretKeySpec skeySpec = new SecretKeySpec("MyDifficultPassw".getBytes(), "AES");
Cipher cipher1 = Cipher.getInstance("AES");
cipher1.init(Cipher.ENCRYPT_MODE, skeySpec);
cos = new CipherOutputStream(fos, cipher1);
// Here you read from the file in fis and write to cos.
byte[] b = new byte[8];
int i = fis.read(b);
while (i != -1) {
cos.write(b, 0, i);
i = fis.read(b);
}
cos.flush();
Thus, the encryption should work. When you reverse the process, you should be able to read the decrypted bytes.

Starting android 10, there have been huge storage restrictions, so DocumentFile is going to be common compared to File class. So I am also providing answer using Uri.
fun Activity.encrypt(curLocUri: Uri, newLocUri: Uri, password: String, salt: String) : Boolean{
// opening file input/outputStreams
val fis = contentResolver.openInputStream(curLocUri) ?: return false
val fos = contentResolver.openOutputStream(newLocUri) ?: return false
try {
var key: ByteArray = ("$salt$password").toByteArray(Charsets.UTF_8)
val sha: MessageDigest = MessageDigest.getInstance("SHA-1")
key = sha.digest(key)
key = key.copyOf(16)
val sks = SecretKeySpec(key, "AES")
val cipher: Cipher = Cipher.getInstance("AES")
cipher.init(Cipher.ENCRYPT_MODE, sks)
val cos = CipherOutputStream(fos, cipher)
var b: Int
val d = ByteArray(8)
while (fis.read(d).also { b = it } != -1) {
cos.write(d, 0, b)
}
cos.flush()
cos.close()
return true
} catch (e: Throwable){
fis.close()
fos.close()
return false
}
}
fun Activity.decrypt(curLocUri: Uri, newLocUri: Uri, password: String, salt: String): Boolean {
// opening file input/outputStreams
val fis = contentResolver.openInputStream(curLocUri) ?: return false
val fos = contentResolver.openOutputStream(newLocUri) ?: return false
try {
var key: ByteArray = ("$salt$password").toByteArray(Charsets.UTF_8)
val sha = MessageDigest.getInstance("SHA-1")
key = sha.digest(key)
key = Arrays.copyOf(key, 16)
val sks = SecretKeySpec(key, "AES")
val cipher = Cipher.getInstance("AES")
cipher.init(Cipher.DECRYPT_MODE, sks)
val cis = CipherInputStream(fis, cipher)
var b: Int
val d = ByteArray(8)
while (cis.read(d).also { b = it } != -1) {
fos.write(d, 0, b)
}
fos.flush()
fos.close()
cis.close()
return true
} catch (e: Throwable){
fos.flush()
fos.close()
return false
}
}
Here Uri s are the one received from file picker from onActivityResult.
For examples, you can find it here