Encrypted RandomAccessFile Wrapper

Wrapper around Java RandomAccessFile to allow encryption (and description) on fly in CTR mode

Usage

To read and wirte data one need to instantiate EncryptedRandomAccessFileWrapper with RandomAccessFile and use read() and write() methods:

	// Init with random keys and IV (file can be read only until ERAFW is available)
	EncryptedRandomAccessFileWrapper wrapper = new EncryptedRandomAccessFileWrapper( randomAccessFile );
	
	// Provide previously stored key and nonce+IV bytes
	// nonce+IV bytes should be 96 bytes long
	// see https://tools.ietf.org/html/rfc3686#section-4
	EncryptedRandomAccessFileWrapper wrapper = new EncryptedRandomAccessFileWrapper( randomAccessFile , key, nonceAndIvBytes);
	
	// write bytes at some position
	wrapper.write( position, bs );
	wrapper.write( position, bs, off, len );
	
	// read bytes from some position
	int read;
	read = wrapper.read( position, bs );
	read = wrapper.read( position, bs, off, len );
	read = wrapper.readFully( position, bs );
	read = wrapper.readFully( position, bs, off, len );
	
	// Create CipherInputStream to read data from file
	Cipher cipher = Cipher.getInstance(EncryptedRandomAccessFileWrapper.TRANSFORMATION);
	wrapper.initCipher(Cipher.DECRYPT_MODE, 0);
	try (FileInputStream fis = new FileInputStream(...);
	        CipherInputStream inputStream = new CipherInputStream(fis, cipher) ) {
	    // read data from inputStream
	}

Performance question

Would you need performance you should use Cipher objects pooling. The following example uses Apache commons-pool2:

	final GenericObjectPoolConfig config = new GenericObjectPoolConfig();
	
	final GenericObjectPool<Cipher> cipherPool = new GenericObjectPool<>(new BasePooledObjectFactory<Cipher>() {
		@Override
		public Cipher create() throws Exception {
			return Cipher.getInstance(EncryptedRandomAccessFileWrapper.TRANSFORMATION);
		}
	
		@Override
		public PooledObject<Cipher> wrap(Cipher cipher) {
			return new DefaultPooledObject<>(cipher);
		}
	}, new GenericObjectPoolConfig());
	
	EncryptedRandomAccessFileWrapper wrapper = new EncryptedRandomAccessFileWrapper(
					new RandomAccessFile(testFile, "rw")) {
		@Override
		protected Cipher borrowCipher() {
			try {
				return cipherPool.borrowObject();
			} catch (Exception e) {
				throw new RuntimeException(e);
			}
		}
	
		@Override
		protected void returnCipher(Cipher cipher) {
			cipherPool.returnObject(cipher);
		};
	}