Decrypts the Storable instance using a passcode

get_raw_byte_key.kt

/**
 * Decrypts the [Storable] instance using the [passcode].
 *
 * @pararm passcode the user's passcode
 * @param storable the storable instance previously saved with [saveToPrefs]
 * @return the raw byte key previously generated with [generateRandomKey]
 */
fun getRawByteKey(passcode: CharArray, storable: Storable): ByteArray {
    val aesWrappedKey = Base64.decode(storable.key, Base64.DEFAULT)
    val iv = Base64.decode(storable.iv, Base64.DEFAULT)
    val salt = Base64.decode(storable.salt, Base64.DEFAULT)
    val secret: SecretKey = generateSecretKey(passcode, salt)
    val cipher = Cipher.getInstance("AES/GCM/NoPadding")
    cipher.init(Cipher.DECRYPT_MODE, secret, IvParameterSpec(iv))
    return cipher.doFinal(aesWrappedKey)
}