[RC5] 40 bit encryption

Don Cohen cohen at maine.rr.com
Fri Mar 15 18:59:32 EST 2002


On Friday 15 March 2002 04:45 pm, I wrote:
> On Friday 15 March 2002 09:19 am, you wrote:
> > If you assume only one computer
> > 1.4*10^9 = 1,400,000,000 cycles per sec
> > I think someone said on here recently that the RC5 core takes 250 cycles
> > per key.
> > so 5,600,000 keys per sec
> > 196,341.36210285714285714285714286 sec for key space
>
> Not quit,  you chose 2^40 as the number of keys in forty bit encription
> (which would be a 1 followed by 39 0's).  The correct number of keys is
> 2^41 - 1

Oops I forgot the rightmost bit is 2^0 not 2^1 so 40 bit encription does have 
2^40 -1 possible keys.

> Divide this by the 5,600,000 k/s you get 392,682.72420554 seconds for
> keyspace
>
> about 4.5 days.
>
> > about 2 - 3 days.
> > Though dnet could do it in less than a second.
> >
> > Orthanc.
> >
> >
> > ----- Original Message -----
> > From: "Brad T." <bradtod at rocketmail.com>
> > To: <rc5 at lists.distributed.net>
> > Sent: Saturday, March 16, 2002 2:16 AM
> > Subject: [RC5] 40 bit encryption
> >
> > > how long would it take to crack 40bit encryption? Assuming a Athlon TB
> > > 1.4ghz computer was used. Some web sites still use this level of
> > > security so how safe are they?
> > >
> > > =====
> > > Take care,
> > > Check out my site @
> > > http://members.tripod.com/~Rambo_21/
> > >
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-- 
Don Cohen
cohen at maine.rr.com
http://usmcug.usm.maine.edu/~cohen
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