Re: Arcfour in Ada

["Julian Morrison" <julian@extropy.demon.co.uk>]

"Thomas Boschloo" <nospam@multiweb.nl> wrote:

> But I figure that Arcfour has some overhead because of the extra keys
> you have to send :-)

You don't send extra keys, you send one partial key, you complete it with
a new IV each time it's used, and prepend the IV to the message.
 
> Funny that DoD doesn't have Rijndael in Ada, as they developed Ada in
> the first place :-P I had a large interest in Ada because the design
> philosophy appealed to me, but I figured it would be largely 'dead' by
> now and replaced by C++ and Java :-( I don't like C++, it's a mess.

There is Rijndael in Ada, available from the Adapower site. Unlikely to be
guv'mint code - bureaucrats are born with "security through obscurity"
hardwired into the soul.
 
> To Julian (if he still frequents this newsgroup, my reply is a bit
> overtime)

I do :-)

> , I figured you could just use one of those 16 bytes as a
> 'length' field. You would even keep 4 bits of that 'octet' for other
> purposes or future additions! The overhead doesn't seem as bad as you
> presented at first (I seem to remember somehow that you thought it was
> 64 bytes, I might be mistaken).

I can switch to Rijndael easily, since there's Ada code for it, but it's
fiddly and more bother than I care for, and the potential gain isn't great
enough to justify the hassle.
 
> And you wouldn't have the 'key' overhead in Arcfour (no idea how big
> that would be in the long run).

There isn't any, really, at least not any I wouln't need just as bad with
Rijndael.

> Here are some RFC's you might consider reading (if you hadn't done so
> already):
> 
> RFC 793 (TCP), 1122 (fixes), 1323 (extensions) => TCP protocol RFC 768
> => UDP (very easy and simple to understand) RFC 791 => IP version 4 RFC
> 1883 => IP version 6 (longer addresses for the future)
> 
> Protocols like TCP/UDP are layered on IP and the RFC's can tell you the
> sizes of the datagrams you can send with them.

Thanks for that info :-)