Large Prime

Agnishom · 2013-09-21 14:30:45

Is there a effective quick way to generate a large prime of a given length?

bobbym · 2013-09-21 20:48:32

I know where you are going with this and it is not necessary.

To answer your question, there is no extremely quick way.

Agnishom · 2013-09-21 21:14:34

Where am I going?

while True:
    randomnumber = random.randrange(2**(length-1),(2**(length))-1)
    if primep(randomnumber):
        print randomnumber
        break

Thats all I got from stackoverflow

Last edited by Agnishom (2013-09-21 21:16:47)

bobbym · 2013-09-21 21:27:06

You think you need a large prime to learn Diffie- Hellman. I can denmonstrate the procedure using a small one.

Thats all I got from stackoverflow

Hohohohohohohahahaha, they are always good for a laugh. To think that such brilliant people can still have a wonderful sense of humor gives me much hope for the human race.

Agnishom · 2013-09-22 00:53:29

bobbym wrote:

You think you need a large prime to learn Diffie- Hellman. I can denmonstrate the procedure using a small one.

I can too. But that is not secure enough.

Sorry, I did not get the humor

bobbym · 2013-09-22 03:49:36

I agree. But I thought you wanted to see how it worked?

anonimnystefy · 2013-09-22 04:04:58

I think the only problem is - after Alice and Bob have the shared secret, how do they exchange messages using it?

bobbym · 2013-09-22 04:13:47

I have been waiting to answer that one since yesterday. But it seems I have missed Agnishom today.

Agnishom · 2013-09-22 13:43:16

anonimnystefy wrote:

I think the only problem is - after Alice and Bob have the shared secret, how do they exchange messages using it?

They use a symmetric cypher, like RC4 with the key.

Agnishom · 2013-09-22 14:48:10

Let us take the generally accepted p from http://tools.ietf.org/html/rfc2409#section-6.2

179769313486231590770839156793787453197860296048756011706444423684197180216158519368947833795864925541502180565485980503646440548199239100050792877003355816639229553136239076508735759914822574862575007425302077447712589550957937778424442426617334727629299387668709205606050270810842907692932019128194467627007

The generator g is

anonimnystefy · 2013-09-22 14:52:04

Hi Agnishom

My number:

170889576082067697731054176601909874828559452754928289693960008087616417613737398548717155229171096112124599345710842437121675819339812482513978573388985033018038377053945453188374711735023121936105534290646082341664680937820085667262891263915428892361981765346083422852575547729295502827704976423861860303103

Agnishom · 2013-09-22 16:25:55

Hi anonymnesty,

g[sup]b[/sup] (mod p)

173419298906489863864646388281941306843742681293608592957943679413527102401811311961611828206757391788738800024670641247258673805804085888390828078173388181181530749311360724611386280929348614725682444473741887149211776384725911058474047582365359321545094524307293842804350322782081718297375589621859722244791

Last edited by Agnishom (2013-09-22 16:34:05)

anonimnystefy · 2013-09-22 17:36:04

Hm, just call me Stefy. It's easier for everybody that way.

Agnishom · 2013-09-23 00:55:52

Hi Stefy,

Sorry for the typo. Is what you posted in #11 g[sup]a[/sup] (mod p) ?

How should I use the secret key to message you now? What about RC4?

auyeungyat · 2013-09-23 01:47:39

I have tested on my computer(Mac on Terminal).That doesn't generate any numbers!

Agnishom · 2013-09-23 02:43:32

auyeungyat wrote:

I have tested on my computer(Mac on Terminal).That doesn't generate any numbers!

I am sorry, primep is defined externally. Do you want the full working code?

Last edited by Agnishom (2013-09-23 03:02:37)

anonimnystefy · 2013-09-23 06:33:03

Agnishom wrote:

Hi Stefy,
Sorry for the typo. Is what you posted in #11 g[sup]a[/sup] (mod p) ?
How should I use the secret key to message you now? What about RC4?

It is.

Is there something more simple we could try first?

bobbym · 2013-09-23 08:22:28

I have a nice tut on this if you need to see how it is done.

anonimnystefy · 2013-09-23 08:23:01

Hi bobbym

You can post them, if you want.

bobbym · 2013-09-23 08:29:01

It uses baby sized numbers but maybe that is best for an example.

anonimnystefy · 2013-09-23 08:39:11

Sure. Any example would suffice, seeing how I am not sure at all how to use the shared secret.

bobbym · 2013-09-23 08:44:43

Neither am I. How about we try to follow their example?

anonimnystefy · 2013-09-23 09:35:07

Their?

bobbym · 2013-09-23 09:53:22

The video I have. They use an example. They go through the technique step by step. Should be easy to do with a real problem later on.

anonimnystefy · 2013-09-23 12:38:11

Could you post the link to the video?

Math Is Fun Forum

#1 2013-09-21 14:30:45

Large Prime

#2 2013-09-21 20:48:32

Re: Large Prime

#3 2013-09-21 21:14:34

Re: Large Prime

#4 2013-09-21 21:27:06

Re: Large Prime

#5 2013-09-22 00:53:29

Re: Large Prime

#6 2013-09-22 03:49:36

Re: Large Prime

#7 2013-09-22 04:04:58

Re: Large Prime

#8 2013-09-22 04:13:47

Re: Large Prime

#9 2013-09-22 13:43:16

Re: Large Prime

#10 2013-09-22 14:48:10

Re: Large Prime

#11 2013-09-22 14:52:04

Re: Large Prime

#12 2013-09-22 16:25:55

Re: Large Prime

#13 2013-09-22 17:36:04

Re: Large Prime

#14 2013-09-23 00:55:52

Re: Large Prime

#15 2013-09-23 01:47:39

Re: Large Prime

#16 2013-09-23 02:43:32

Re: Large Prime

#17 2013-09-23 06:33:03

Re: Large Prime

#18 2013-09-23 08:22:28

Re: Large Prime

#19 2013-09-23 08:23:01

Re: Large Prime

#20 2013-09-23 08:29:01

Re: Large Prime

#21 2013-09-23 08:39:11

Re: Large Prime

#22 2013-09-23 08:44:43

Re: Large Prime

#23 2013-09-23 09:35:07

Re: Large Prime

#24 2013-09-23 09:53:22

Re: Large Prime

#25 2013-09-23 12:38:11

Re: Large Prime

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