Java mcrypt_create_iv

Question

Is there an equivalent mcrypt_create_iv function for Java?

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Answer 1

There is no single call to create a random IV, and if you leave the IV out then the Oracle implementation will default to a zero IV (an IV consisting of N bytes set to 00 value, where N is the block size). Also note that in Java the getBlockSize() method returns the amount of bytes, not bits.

Cipher enCipher = Cipher.getInstance("AES/CBC/PKCS5Padding");

// create IV array of the correct size
final byte[] ivData = new byte[enCipher.getBlockSize()];
// create (or retrieve) a cryptographic secure random implementation (auto-seeded)
final SecureRandom rng = new SecureRandom();
// fill the IV array with random data
rng.nextBytes(ivData);
// generate the ParameterSpec (to create a general parameter for Cipher.init())
IvParameterSpec iv = new IvParameterSpec(ivData);
// and initialize with the new IV
enCipher.init(Cipher.ENCRYPT_MODE, key, iv);