They may not need it, but source code will allow them to read it faster and with a higher chance of getting it right. It will also make it easier to re-run the

They may not need it, but source code will allow them to read it faster and with a higher chance of getting it right. It will also make it easier to re-run the decryption routine to get the original file/verify a cracking attempt instead of having to reimplement it correctly (possibly without having known-good test vectors to check if they got it right).