How to encrypt and decrypt a file using “AES” algorithm in Android?

This is a simple example showing how to encrypt and decrypt a file in android.
1. Generate a key for encrypting our data.
2. Create a file and save data using ENCRYPTION with our generated key to the SDCARD.
3. With  the help of the key DECRYPT  the file and show the contents.
This complete program does this.
Please check the Logcat for the output.

package com.smr.encryptfile;

import java.io.BufferedInputStream;

import java.io.BufferedOutputStream;

import java.io.File;

import java.io.FileInputStream;

import java.io.FileNotFoundException;

import java.io.FileOutputStream;

import java.io.IOException;

import java.<span id="IL_AD3" class="IL_AD">security</span>.NoSuchAlgorithmException;

import java.security.SecureRandom;

import java.security.spec.InvalidKeySpecException;

import java.security.spec.KeySpec;

import javax.crypto.Cipher;

import javax.crypto.KeyGenerator;

import javax.crypto.SecretKey;

import javax.crypto.SecretKeyFactory;

import javax.crypto.spec.IvParameterSpec;

import javax.crypto.spec.PBEKeySpec;

import javax.crypto.spec.SecretKeySpec;

import android.app.Activity;

import android.os.Bundle;

import android.os.Environment;

<span id="IL_AD7" class="IL_AD">public</span> class MainActivity extends Activity {

    private String encryptedFileName = "Enc_File.txt";

    private static String <span id="IL_AD2" class="IL_AD">algorithm</span> = "AES";

    static SecretKey yourKey = null;

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        saveFile("Hello From CoderzHeaven asaksjalksjals");

        decodeFile();

    }

     

    public static SecretKey generateKey(char[] passphraseOrPin, byte[] salt) throws NoSuchAlgorithmException, InvalidKeySpecException {

        // Number of PBKDF2 hardening rounds to use. Larger values increase

        // computation time. You should select a value that causes computation

        // to take >100ms.

        final int iterations = 1000;

        // Generate a 256-bit key

        final int outputKeyLength = 256;

        SecretKeyFactory secretKeyFactory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA1");

        KeySpec keySpec = new PBEKeySpec(passphraseOrPin, salt, iterations, outputKeyLength);

        SecretKey secretKey = secretKeyFactory.generateSecret(keySpec);

        return secretKey;

    }

    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;

    }

    public static byte[] encodeFile(SecretKey yourKey, byte[] fileData)

            throws Exception {

        byte[] encrypted = null;

        byte[] data = yourKey.getEncoded();

        SecretKeySpec skeySpec = new SecretKeySpec(data, 0, data.length,

                algorithm);

        Cipher cipher = Cipher.getInstance(algorithm);

        cipher.init(Cipher.ENCRYPT_MODE, skeySpec, new IvParameterSpec(

                new byte[cipher.getBlockSize()]));

        encrypted = cipher.doFinal(fileData);

        return encrypted;

    }

    public static byte[] decodeFile(SecretKey yourKey, byte[] fileData)

            throws Exception {

        byte[] decrypted = null;

        Cipher cipher = Cipher.getInstance(algorithm);

        cipher.init(Cipher.DECRYPT_MODE, yourKey, new IvParameterSpec(

                new byte[cipher.getBlockSize()]));

        decrypted = cipher.doFinal(fileData);

        return decrypted;

    }

    void saveFile(String stringToSave) {

        try {

            File file = new File(Environment.getExternalStorageDirectory()

                    + File.separator, encryptedFileName);

            BufferedOutputStream bos = new BufferedOutputStream(

                    new FileOutputStream(file));

            yourKey = generateKey();

            byte[] filesBytes = encodeFile(yourKey, stringToSave.getBytes());

            bos.write(filesBytes);

            bos.flush();

            bos.close();

        } catch (FileNotFoundException e) {

            e.printStackTrace();

        } catch (IOException e) {

            e.printStackTrace();

        } catch (Exception e) {

            e.printStackTrace();

        }

    }

    void decodeFile() {

        try {

            byte[] decodedData = decodeFile(yourKey, readFile());

            String str = new String(decodedData);

            System.out.println("DECODED FILE CONTENTS : " + str);

        } catch (Exception e) {

            e.printStackTrace();

        }

    }

    public byte[] readFile() {

        byte[] contents = null;

        File file = new File(Environment.getExternalStorageDirectory()

                + File.separator, encryptedFileName);

        int size = (int) file.length();

        contents = new byte[size];

        try {

            BufferedInputStream buf = new BufferedInputStream(

                    new FileInputStream(file));

            try {

                buf.read(contents);

                buf.close();

            } catch (IOException e) {

                e.printStackTrace();

            }

        } catch (FileNotFoundException e) {

            e.printStackTrace();

        }

        return contents;

    }

}