When encrypting data with the Cipher Block Chaining (CBC) mode an Initialization Vector (IV) is used to randomize the encryption, ie under a given key the same plaintext doesn’t always produce the same ciphertext. The IV doesn’t need to be secret but should be unpredictable to avoid "Chosen-Plaintext Attack".

To generate Initialization Vectors, NIST recommends to use a secure random number generator.

Noncompliant Code Example

val bytesIV = "7cVgr5cbdCZVw5WY".toByteArray(charset("UTF-8")) // Predictable / hardcoded IV

val iv = IvParameterSpec(bytesIV)
val skeySpec = SecretKeySpec(secretKey.toByteArray(), "AES")

val cipher: Cipher = Cipher.getInstance("AES/CBC/PKCS5PADDING")
cipher.init(Cipher.ENCRYPT_MODE, skeySpec, iv) // Noncompliant (s3329)

val encryptedBytes: ByteArray = cipher.doFinal("foo".toByteArray())

Compliant Solution

val random: SecureRandom = SecureRandom()

val bytesIV: ByteArray = ByteArray(16)
random.nextBytes(bytesIV); // Unpredictable / random IV

val iv = IvParameterSpec(bytesIV)
val skeySpec = SecretKeySpec(secretKey.toByteArray(), "AES")

val cipher: Cipher = Cipher.getInstance("AES/CBC/PKCS5PADDING")
cipher.init(Cipher.ENCRYPT_MODE, skeySpec, iv) //Compliant (s3329)

val encryptedBytes: ByteArray = cipher.doFinal("foo".toByteArray())

See