Re: M4 project

In message <1141752631.29473.69.camel-00BgfDGvnxGoHq8ECNvGLUEOCMrvLtNR@public.gmane.org>, Steve
Hosgood <steve-ZMQM5VTtYHJ+cjeuK/[email protected]> writes

>Yeah, but they apparently did *10* walks through the whole M4 keyspace
>with the middle ring at 'A' if I understood it right. Surely if the
>first walk failed, there's no point in doing it again? And certainly not
>without changing the mid wheel ring.

If the first walk failed it may be because the hill climb failed to
start rather than the correct wheel setting was not there. I don't know
how Stefan defines 'walks' but he knows what he is doing, so the other 9
walks would, I guess be some variation on the hill-climb. Hill-climbs
don't come with a guarantee.

>> Wrong fast ring is not always fatal. See todays break. 
>
>OK. Apart from middle ring just 1 or two letters out either way, I'd
>have thought the garbles would break the stats. Evidently not.

No, not if the plain-text contains stuff like:
NEUNACHTSECHSDREIYZWONUL....

>
>Presumably one of the optimisations in the system is to try only every 5
>fast wheel ring positions on the grounds that you'll hillclimb OK even
>if you slightly miss the correct ring position.

...but if the plain-text is not as rich in high frequency trigrams as
the above sample then skipping rings is very risky. Who bother with
risks in a distributed computer project - plenty of processing
available. Plenty of hungry clients out there, apparently.


>
>Was there even a ring on the thin rotors at all?
>
Yes, I believe so.

Regards,

Geoff