Conceal

Quick start

If you're using BUCK, you can grab the repo from Github and build it. 

buck build :crypto
The resulting binaries will be in buck-out/

If you're not using BUCK, you can just grab the binaries from

Add a dependency to libconceal.jar as well as conceal_android.jar from java code using your favorite dependency management system, and drop the .so files in libs.zip into your jniLibs/ folder located at src/main/jniLibs

Encrypting content

// Creates a new Crypto object with default implementations of 
// a key chain as well as native library.
Crypto crypto = new Crypto(
  new SharedPrefsBackedKeyChain(context),
  new SystemNativeCryptoLibrary());

// Check for whether the crypto functionality is available
// This might fail if android does not load libaries correctly.
if (!crypto.isAvailable()) {
  return;
}

OutputStream fileStream = new BufferedOutputStream(
  new FileOutputStream(file));

// Creates an output stream which encrypts the data as
// it is written to it and writes it out to the file.
OutputStream outputStream = crypto.getCipherOutputStream(
  fileStream,
  entity);

// Write plaintext to it.
outputStream.write(plainTextBytes);
outputStream.close();

Decrypting content

// Get the file to which ciphertext has been written.
FileInputStream fileStream = new FileInputStream(file);

// Creates an input stream which decrypts the data as
// it is read from it.
InputStream inputStream = crypto.getCipherInputStream(
  fileStream,
  entity);

// Read into a byte array.
int read;
byte[] buffer = new byte[1024];

// You must read the entire stream to completion.
// The verification is done at the end of the stream.
// Thus not reading till the end of the stream will cause
// a security bug. 
while ((read = inputStream.read(buffer)) != -1) {
  out.write(buffer, 0, read);
}

inputStream.close();

Creating a new keychain

The default KeyChain stores it's data into shared preferences. You might want to implement your own KeyChain to persist key material somewhere else. 
public class CustomKeyChain implements KeyChain {
  ...
}