Speed up android DES encryption/decryption

Question

I've got to encrypt and decrypt a file on android. To do this, I wrote the following class:

package blabla.fileencrypter;

import alotofclasses;

/**
 * The FileEncoder class provides an interface to allow for easy encrypting and decrypting of files. To use this class, first call both {@link #setSalts(String, String)} and {@link #setFolders(String, String)}.
 * @author Daniël van den Berg
 * @since Nov 26, 2015
 *
 */
public class FileEncrypter {
    private static String encryptedFolder = "";
    private static String decryptedFolder = "";
    private static byte[] salt = null;
    private static IvParameterSpec iv = null;
    private static String encryptedPostfix = "";

    /**
     * Sets the folders the documents have to be placed in.
     * @param encryptedFolder The folder encrypted files have to be placed in.
     * @param decryptedFolder The folder decrypted files have to be placed in.
     */
    public static void setFolders(String encryptedFolder, String decryptedFolder){
        FileEncrypter.encryptedFolder = encryptedFolder;
        FileEncrypter.decryptedFolder = decryptedFolder;
    }

    /**
     * A postfix to give to encrypted files. Can be "" for no postfix.
     * @param extension The postfix to append to encrypted files.
     */
    public static void setEncryptedPostfix(String extension){
        if (extension != null){
            FileEncrypter.encryptedPostfix = extension;
        }else{
            FileEncrypter.encryptedPostfix = "";
        }
    }

    /**
     * The salts to use when encrypting/decrypting files.
     * @param salt The salt to use.
     * @param ivParameterSpec The buffer with the IV.
     * @throws FileEncryptingException When the ivParameterSpec is smaller than 16 bytes.
     */
    public static void setSalts(String salt, String ivParameterSpec) throws FileEncryptingException{
        FileEncrypter.salt = salt.getBytes();
        if (ivParameterSpec.length() < 16){
            throw new FileEncryptingException("ivParameterSpec not long enough. Should be at least 16 bytes.");
        }
        FileEncrypter.iv = new IvParameterSpec(ivParameterSpec.getBytes(),0,16);
    }

    /**
     * Encode the given inputFile with the given key.
     * @param inputFile The file to encrypt.
     * @param key The key to use for encrypting the file.
     * @return The encrypted file.
     * @throws FileEncryptingException
     * @throws NoSuchAlgorithmException
     * @throws NoSuchPaddingException
     * @throws InvalidKeyException
     * @throws IOException
     * @throws InvalidKeySpecException
     * @throws InvalidAlgorithmParameterException
     */
    public static File encrypt(File inputFile, String key) throws FileEncryptingException, NoSuchAlgorithmException, NoSuchPaddingException, InvalidKeyException, IOException, InvalidKeySpecException, InvalidAlgorithmParameterException{
        if (isEncrypted(inputFile)){
            throw new FileEncryptingException("File not decrypted: "+inputFile.getAbsolutePath());
        }

        FileInputStream inputStream = new FileInputStream(inputFile);

        File outputFile = new File(inputFile.getAbsolutePath().replace(decryptedFolder,encryptedFolder) + encryptedPostfix);
        outputFile.getParentFile().mkdirs();
        FileOutputStream outputStream = new FileOutputStream(outputFile);
        processStream(Cipher.ENCRYPT_MODE,key,inputStream,outputStream);
        inputStream.close();
        outputStream.close();
        return outputFile;
    }

    /**
     * Decrypt the given inputFile with the given key.
     * @param inputFile The file to decrypt.
     * @param key The key to use for decrypting the file.
     * @return The decrypted file.
     * @throws FileEncryptingException
     * @throws IOException
     * @throws NoSuchAlgorithmException
     * @throws NoSuchPaddingException
     * @throws InvalidKeyException
     * @throws InvalidKeySpecException
     * @throws InvalidAlgorithmParameterException
     */
    public static File decrypt(File inputFile, String key) throws FileEncryptingException, IOException, NoSuchAlgorithmException, NoSuchPaddingException, InvalidKeyException, InvalidKeySpecException, InvalidAlgorithmParameterException{
        if (!isEncrypted(inputFile)){
            throw new FileEncryptingException("File not encrypted: "+inputFile.getAbsolutePath());
        }

        if (!inputFile.exists() && !inputFile.getAbsolutePath().contains(encryptedPostfix)){
            inputFile = new File(inputFile.getAbsolutePath()+encryptedPostfix);
        }

        FileInputStream inputStream = new FileInputStream(inputFile);

        File outputFile = new File(inputFile.getAbsolutePath().replace(encryptedPostfix, "").replace(encryptedFolder,decryptedFolder));
        outputFile.getParentFile().mkdirs();
        FileOutputStream outputStream = new FileOutputStream(outputFile);
        processStream(Cipher.DECRYPT_MODE,key,inputStream,outputStream);
        inputStream.close();
        outputStream.close();
        return outputFile;
    }

    /**
     * Used for generating a cipher.
     * @param cipherMode The cipher mode to use. Either <code>Cipher.DECRYPT_MODE</code> or <code>Cipher.ENCRYPT_MODE</code>
     * @param key The key to generate the cipher with.
     * @return The generated cipher.
     * @throws NoSuchAlgorithmException
     * @throws InvalidKeySpecException
     * @throws NoSuchPaddingException
     * @throws InvalidKeyException
     * @throws InvalidAlgorithmParameterException
     */
    private static Cipher getCipher(int cipherMode, String key) throws NoSuchAlgorithmException, InvalidKeySpecException, NoSuchPaddingException, InvalidKeyException, InvalidAlgorithmParameterException {
        SecretKeyFactory factory = SecretKeyFactory.getInstance("DES");
        KeySpec spec;
        try {
            spec = new DESKeySpec((key+salt).getBytes("UTF8"));
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
            return null;
        }
        SecretKey secret = factory.generateSecret(spec);

        Cipher c = Cipher.getInstance("DES");
        c.init(cipherMode, secret,iv);
        return c;
    }

    /**
     * Process a stream. This will encrypt or decrypt the stream, depending on the given cipherMode. The output will be available in the given {@link OutputStream}.
     * @param cipherMode The cipher mode to use. Either <code>Cipher.DECRYPT_MODE</code> or <code>Cipher.ENCRYPT_MODE</code>
     * @param key The key to use for decryption/encryption.
     * @param inputStream The stream to read from.
     * @param outputStream The stream to write the encrypted/decrypted result to.
     * @throws InvalidKeyException
     * @throws NoSuchAlgorithmException
     * @throws InvalidKeySpecException
     * @throws NoSuchPaddingException
     * @throws InvalidAlgorithmParameterException
     * @throws IOException
     */
    public static void processStream(int cipherMode, String key, InputStream inputStream, OutputStream outputStream) throws InvalidKeyException, NoSuchAlgorithmException, InvalidKeySpecException, NoSuchPaddingException, InvalidAlgorithmParameterException, IOException{
        Cipher c = getCipher(cipherMode,key);
        CipherOutputStream cipherOutputStream = new CipherOutputStream(outputStream, c);
        int b = 0;
        while ((b = inputStream.read()) !=-1){
            cipherOutputStream.write(b);
        }
        cipherOutputStream.close();
    }

    /**
     * Returns a file, no matter whether it's encrypted or not. See {@link #isEncrypted(File)} to detect if the file is encrypted.
     * @param filenameDecrypted The filename the decrypted file would have.
     * @return The file that corresponds with the given filename.
     */
    public static File getFile(String filenameDecrypted){
        if (!filenameDecrypted.contains(decryptedFolder) && !filenameDecrypted.contains(encryptedFolder)){
            filenameDecrypted = decryptedFolder + filenameDecrypted;
        }
        File file = new File(filenameDecrypted);
        if (!file.exists()){
            file = new File(filenameDecrypted.replace(decryptedFolder, encryptedFolder)+encryptedPostfix);
        }
        return file;
    }

    /**
     * Checks if the file is encrypted or not.
     * @param file The file to check.
     * @return True if the file is encrypted, false otherwise.
     */
    public static boolean isEncrypted(File file){
        return file.getAbsolutePath().contains(encryptedFolder) || (!encryptedPostfix.isEmpty() && file.getAbsolutePath().contains(encryptedPostfix));
    }
}

At first I implemented this class using AES for encryption and decryption. However, the speed of this was too slow, so we switched to using DES. However, this still seems to be terribly slow. A file of about 1MB takes about half a minute to encrypt.

Is there any way to speed this up significantly?

Answer 1

Credits to Wagner Tsuchiya for helping out on this one.

The solution laid mostly in two things.

1. Using a BufferedReader/Writer, as can be seen in the functions encrypt() and decrypt. This changed the speed from 3MB/2:16 minutes to about 3MB/0:59 minutes.
2. Using a different encryption algorithm. DES turned out to be even slower than AES, but for my current requirements a much simpler algorythm, RC4, is sufficient. This about halved the time it took for encryption and decryption again. A comparison of the different algorythms can be found on http://www.javamex.com/tutorials/cryptography/ciphers.shtml.

This both resulted in the following code:

package blabla.fileencrypter;

import lots;

/**
 * The FileEncoder class provides an interface to allow for easy encrypting and decrypting of files. To use this class, first call both {@link #setSalts(String, String)} and {@link #setFolders(String, String)}.
 * @author Daniël van den Berg
 * @since Nov 26, 2015
 *
 */
public class FileEncrypter {
    private static String encryptedFolder = "";
    private static String decryptedFolder = "";
    private static byte[] salt = null;
    private static String encryptedPostfix = "";
    private static final HashMap<Integer, HashMap<String,Cipher>> ciphers = new HashMap<Integer, HashMap<String, Cipher>>();

    /**
     * Sets the folders the documents have to be placed in.
     * @param encryptedFolder The folder encrypted files have to be placed in.
     * @param decryptedFolder The folder decrypted files have to be placed in.
     */
    public static void setFolders(String encryptedFolder, String decryptedFolder){
        FileEncrypter.encryptedFolder = encryptedFolder;
        FileEncrypter.decryptedFolder = decryptedFolder;
    }

    /**
     * A postfix to give to encrypted files. Can be "" for no postfix.
     * @param extension The postfix to append to encrypted files.
     */
    public static void setEncryptedPostfix(String extension){
        if (extension != null){
            FileEncrypter.encryptedPostfix = extension;
        }else{
            FileEncrypter.encryptedPostfix = "";
        }
    }

    /**
     * The salts to use when encrypting/decrypting files.
     * @param salt The salt to use.
     * @param ivParameterSpec The buffer with the IV.
     * @throws FileEncryptingException When the ivParameterSpec is smaller than 16 bytes.
     */
    public static void setSalts(String salt) throws FileEncryptingException{
        FileEncrypter.salt = salt.getBytes();
    }

    /**
     * Encode the given inputFile with the given key.
     * @param inputFile The file to encrypt.
     * @param key The key to use for encrypting the file.
     * @return The encrypted file.
     * @throws FileEncryptingException
     * @throws NoSuchAlgorithmException
     * @throws NoSuchPaddingException
     * @throws InvalidKeyException
     * @throws IOException
     * @throws InvalidKeySpecException
     * @throws InvalidAlgorithmParameterException
     */
    public static File encrypt(File inputFile, String key) throws FileEncryptingException, NoSuchAlgorithmException, NoSuchPaddingException, InvalidKeyException, IOException, InvalidKeySpecException, InvalidAlgorithmParameterException{
        if (isEncrypted(inputFile)){
            throw new FileEncryptingException("File not decrypted: "+inputFile.getAbsolutePath());
        }

        FileInputStream inputStream = new FileInputStream(inputFile);
        BufferedInputStream bufferedInputStream = new BufferedInputStream(inputStream);

        File outputFile = new File(inputFile.getAbsolutePath().replace(decryptedFolder,encryptedFolder) + encryptedPostfix);
        outputFile.getParentFile().mkdirs();
        FileOutputStream outputStream = new FileOutputStream(outputFile);
        BufferedOutputStream bufferedOutputStream = new BufferedOutputStream(outputStream);
        processStream(Cipher.ENCRYPT_MODE,key,bufferedInputStream,bufferedOutputStream);
        inputStream.close();
        outputStream.close();
        bufferedInputStream.close();
        bufferedOutputStream.close();
        return outputFile;
    }

    /**
     * Decrypt the given inputFile with the given key.
     * @param inputFile The file to decrypt.
     * @param key The key to use for decrypting the file.
     * @return The decrypted file.
     * @throws FileEncryptingException
     * @throws IOException
     * @throws NoSuchAlgorithmException
     * @throws NoSuchPaddingException
     * @throws InvalidKeyException
     * @throws InvalidKeySpecException
     * @throws InvalidAlgorithmParameterException
     */
    public static File decrypt(File inputFile, String key) throws FileEncryptingException, IOException, NoSuchAlgorithmException, NoSuchPaddingException, InvalidKeyException, InvalidKeySpecException, InvalidAlgorithmParameterException{
        if (!isEncrypted(inputFile)){
            throw new FileEncryptingException("File not encrypted: "+inputFile.getAbsolutePath());
        }

        if (!inputFile.exists() && !inputFile.getAbsolutePath().contains(encryptedPostfix)){
            inputFile = new File(inputFile.getAbsolutePath()+encryptedPostfix);
        }

        FileInputStream inputStream = new FileInputStream(inputFile);
        BufferedInputStream bufferedInputStream = new BufferedInputStream(inputStream);

        File outputFile = new File(inputFile.getAbsolutePath().replace(encryptedPostfix, "").replace(encryptedFolder,decryptedFolder));
        outputFile.getParentFile().mkdirs();
        FileOutputStream outputStream = new FileOutputStream(outputFile);
        BufferedOutputStream bufferedOutputStream = new BufferedOutputStream(outputStream);
        processStream(Cipher.DECRYPT_MODE,key,bufferedInputStream,bufferedOutputStream);
        inputStream.close();
        outputStream.close();
        bufferedInputStream.close();
        bufferedOutputStream.close();
        return outputFile;
    }

    /**
     * Used for generating a cipher.
     * @param cipherMode The cipher mode to use. Either <code>Cipher.DECRYPT_MODE</code> or <code>Cipher.ENCRYPT_MODE</code>
     * @param key The key to generate the cipher with.
     * @return The generated cipher.
     * @throws NoSuchAlgorithmException
     * @throws InvalidKeySpecException
     * @throws NoSuchPaddingException
     * @throws InvalidKeyException
     * @throws InvalidAlgorithmParameterException
     */
    private static Cipher getCipher(int cipherMode, String key) throws NoSuchAlgorithmException, InvalidKeySpecException, NoSuchPaddingException, InvalidKeyException, InvalidAlgorithmParameterException {
        if (!ciphers.containsKey(cipherMode)){
            synchronized (ciphers){
                if (!ciphers.containsKey(cipherMode)){
                    ciphers.put(cipherMode, new HashMap<String,Cipher>());
                }
            }
        }
        HashMap<String, Cipher> hashMap = ciphers.get(cipherMode);
        if (!hashMap.containsKey(key)){
            synchronized (hashMap) {
                if (!hashMap.containsKey(key)){
                    SecretKeyFactory factory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA1");
                    KeySpec spec = new PBEKeySpec(key.toCharArray(), salt, 65536, 128);
                    SecretKey tmp = factory.generateSecret(spec);
                    SecretKey secret = new SecretKeySpec(tmp.getEncoded(), "RC4");

                    Cipher c = Cipher.getInstance("RC4");
                    c.init(cipherMode, secret);
                    hashMap.put(key, c);
                }
            }
        }
        return hashMap.get(key);
    }

    /**
     * Process a stream. This will encrypt or decrypt the stream, depending on the given cipherMode. The output will be available in the given {@link OutputStream}.
     * @param cipherMode The cipher mode to use. Either <code>Cipher.DECRYPT_MODE</code> or <code>Cipher.ENCRYPT_MODE</code>
     * @param key The key to use for decryption/encryption.
     * @param inputStream The stream to read from.
     * @param outputStream The stream to write the encrypted/decrypted result to.
     * @throws InvalidKeyException
     * @throws NoSuchAlgorithmException
     * @throws InvalidKeySpecException
     * @throws NoSuchPaddingException
     * @throws InvalidAlgorithmParameterException
     * @throws IOException
     */
    public static void processStream(int cipherMode, String key, InputStream inputStream, OutputStream outputStream) throws InvalidKeyException, NoSuchAlgorithmException, InvalidKeySpecException, NoSuchPaddingException, InvalidAlgorithmParameterException, IOException{
        Cipher c = getCipher(cipherMode,key);
        CipherOutputStream cipherOutputStream = new CipherOutputStream(outputStream, c);
        int b = 0;
        while ((b = inputStream.read()) !=-1){
            cipherOutputStream.write(b);
        }
        cipherOutputStream.close();
    }

    /**
     * Returns a file, no matter whether it's encrypted or not. See {@link #isEncrypted(File)} to detect if the file is encrypted.
     * @param filenameDecrypted The filename the decrypted file would have.
     * @return The file that corresponds with the given filename.
     */
    public static File getFile(String filenameDecrypted){
        if (!filenameDecrypted.contains(decryptedFolder) && !filenameDecrypted.contains(encryptedFolder)){
            filenameDecrypted = decryptedFolder + filenameDecrypted;
        }
        File file = new File(filenameDecrypted);
        if (!file.exists()){
            file = new File(filenameDecrypted.replace(decryptedFolder, encryptedFolder)+encryptedPostfix);
        }
        return file;
    }

    /**
     * Checks if the file is encrypted or not.
     * @param file The file to check.
     * @return True if the file is encrypted, false otherwise.
     */
    public static boolean isEncrypted(File file){
        return file.getAbsolutePath().contains(encryptedFolder) || (!encryptedPostfix.isEmpty() && file.getAbsolutePath().contains(encryptedPostfix));
    }
}