Thanks Geremy,
That has been an absolute bump........... GOD i cant sit on my chair, it has
worked even on 512 bit number and with no time..........
superb i would say.
lastly, i am using the code below to calculate Largest Prime factor of a number:
print
('''==============================================================================='''
''' CALCULATE HIGHEST PRIME FACTOR
'''
'''===============================================================================''')
#!/usr/bin/env python
def highest_prime_factor(n):
if isprime(n):
return n
for x in xrange(2,n ** 0.5 + 1):
if not n % x:
return highest_prime_factor(n/x)
def isprime(n):
for x in xrange(2,n ** 0.5 + 1):
if not n % x:
return False
return True
if __name__ == "__main__":
import time
start = time.time()
print highest_prime_factor(1238162376372637826)
print time.time() - start
the code works with a bit of delay on the number : "1238162376372637826" but
extending it to
(109026109913291424366305511581086089650628117463925776754560048454991130443047109026109913291424366305511581086089650628117463925776754560048454991130443047)
makes python go crazy. Is there any way just like above, i can have it
calculated it in no time.
thanks for the support.
> Date: Sun, 7 Mar 2010 15:40:59 -0500
> Subject: Re: Calculating very large exponents in python
> From: debat...@gmail.com
> To: miracles...@hotmail.com
> CC: python-list@python.org
>
> On Sun, Mar 7, 2010 at 1:55 PM, Fahad Ahmad <miracles...@hotmail.com> wrote:
> > Dear All,
> >
> > i am writing my crytographic scheme in python, i am just a new user to it.
> > I have written the complete code, the only point i am stuck it is that i am
> > using 256 exponentiation which is normal in crytography but python just
> > hangs on it.
> >
> > g**x [where both g and x are 256 bit numbers , in decimal they are around
> > 77]
> >
> > after reading several forums, i just come to know it can be done using
> > numpy, i have installed python(x,y) has has both numpy and scipy installed
> > but i am not able to make it happen.
> >
> > any idea which library, module, or piece of code can solve this mystery :S
> >
> > sorry for bad english
>
> A couple of things:
>
> 1) if you're working with modular exponentiation, remember that pow() takes
> three arguments, ie:
>
> a = 222222222222222222222222222
> b = 5555555555555555555555555555
> pow(a, b, 1200)
>
> will calculate the correct answer (768) very quickly, while
>
> a**b % 1200
>
> has not terminated in the time it took me to compose this
> email.
>
> 2) sage has a lot of excellent tools for crypto/cryptanalysis that you
> may want to take a look at.
>
> 3) not saying you don't know what you're doing, but be careful when
> rolling your own cryptosystems- even very good cryptographers make
> implementation mistakes!
>
> Geremy Condra
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