In a multi threaded Java application, we are using AES-256 for encryption and decryption of files to the disk. Please note that multiple threads can make concurrent calls to the encryption and decryption methods for different files.
Encryption:
Cipher encrypter = Cipher.getInstance(algorithm, new BouncyCastleProvider());
IvParameterSpec ivSpec = getIvParamSpec(encrypter.getBlockSize());
encrypter.init(Cipher.ENCRYPT_MODE, key, ivSpec);
//..encrypt the data
Decryption:
Cipher decrypter = Cipher.getInstance(algorithm, new BouncyCastleProvider());
IvParameterSpec ivSpec = readIvParamSpec(decrypter.getBlockSize(), is);
decrypter.init(Cipher.DECRYPT_MODE, key, ivSpec);
//.. decrypt the data
In our understanding, it is better to use random IV for encryption instead of static/fixed IV. For this purpose, we are using SecureRandom API to generate the IV. The random IV is persisted in the encrypted file at the start.
SecureRandom random = new SecureRandom();
byte[] iv = new byte[ivSizeBytes];
random.nextBytes(iv);
new IvParameterSpec(iv);
My question is, since I am using random IV for each encryption, do I need to call Cipher.getInstance() and Cipher.Init() for all the calls? For performance improvement, can these be called only once during the class initialization and then reuse the individual cipher instances to encrypt and decrypt the data?
Thanks in advance!