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Challenge "Factorization Cipher — Part 2"  

  By: admin on Dec. 1, 2011, 9:07 p.m.

After making yourself familiar with the idea of this cipher in part 1 it is now time to attack a larger plaintext. The monoalphabetic cipher that has been applied on the plaintext before should be the least problem.
Read more...

 Last edited by: admin on Oct. 31, 2021, 2:54 a.m., edited 1 time in total.

Re: Challenge  

  By: Witten on Dec. 7, 2011, 9:49 p.m.

Is there any more clever way to solve it than brutally using a library for large integers (i used gmp) and really compute the factorization of a 12mb integer ???

Re: Challenge  

  By: Veselovský on Dec. 7, 2011, 10:57 p.m.

You have solved it - no comments needed.

Re: Challenge  

  By: jacobian1729 on Dec. 28, 2011, 3:03 p.m.

How to partition the exponents which are very large???

Re: Challenge  

  By: be on Dec. 28, 2011, 3:43 p.m.

How to partition the exponents which are very large???

Do you want to know, how big the exponents are? In the opposite of the bases the exponents can become quite large (up to 7,000,000).

Re: Challenge  

  By: jacobian1729 on Dec. 28, 2011, 4:09 p.m.

No I did not mean that.Yes the exponent are very large but how do you break it to make sentence…

Re: Challenge  

  By: Veselovský on Dec. 28, 2011, 4:39 p.m.

how do you break it to make sentence…

Same way as you did in part one of this challenge.
Maybe you did not fully spot "the logic of exponents" in the cipher, so it may be useful for you to return to part one of the challenge and try to explain for yourself how specifically the exponents relate to the plaintext…

Re: Challenge  

  By: mmisc on March 30, 2012, 3:40 p.m.

i'm stuck at the mono alphabetic substitution, are there some hints? :)

Re: Challenge  

  By: Veselovský on March 30, 2012, 3:54 p.m.

Hints for substitution part are at the end of PDF:

"The monoalphabetic substitution that has been used is involutoric (the keys for en- and decryption are identical, i.e. if A maps to Q then Q maps to A).
In addition, letters that do not appear in the plaintext map to themselves."

Re: Challenge: How to read such a big number in Sage  

  By: Veselovský on Oct. 21, 2012, 11:17 p.m.

I was asked several times how to read such a big number in Sage.
While Sage is a great free open-source mathematics software, its documentation is poor.

Here is a code to read the number into variable "n":

f=open(DATA+'factcipher.txt');
n=Integer(f.read());

…but first you have to upload factcipher.txt file into DATA directory.
There is a "Data" button in Sage notebook. Click it and then click "Upload or create file…"
Select factcipher.txt in your location and then click on "Upload or Create a Data File"

Re: Challenge: How to read such a big number in Sage  

  By: be on Oct. 22, 2012, midnight

I was asked several times…

Victor, Thanks a lot for your ongoing and valuable support to all the users. I really appreciate that. Best regards, be

Re: Challenge  

  By: ThunderArmy on Feb. 11, 2019, 11:46 a.m.

Is there no other way like splitting the large number into parts or do i really need to calculate the prime numbers? The largest Prime Number has twice the size, how should i handle a 13 million length number?

Re: Challenge  

  By: Veselovský on Feb. 11, 2019, 12:57 p.m.

No, there is no other way. You can see how to handle such a big number in my previous comment in this thread. A common mistake is to use "copy and paste" to insert such a big number into some software which may make your PC stop responding. Instead read the number straight from file into memory without displaying it.

Re: Challenge  

  By: ThunderArmy on Feb. 11, 2019, 1:46 p.m.

No, there is no other way. You can see how to handle such a big number in my previous comment in this thread. A common mistake is to use "copy and paste" to insert such a big number into some software which may make your PC stop responding. Instead read the number straight from file into memory without displaying it.

Okay but then, how long (on average) would it take to compute such a big number?

Re: Challenge  

  By: Veselovský on Feb. 11, 2019, 5:02 p.m.

A second if you do it wisely.


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