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This forum is meant for discussing and sharing ideas of the Level II challenges. Do not post any complete solutions or codewords for any of the challenges. In case of posting solutions your post will be deleted and your account will be banned immediately.



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 Post subject: Challenge "BCR code (Book-Caesar-RSA)"
PostPosted: Wed Sep 12, 2012 18:42 

Joined: Tue Oct 19, 2010 19:30
Posts: 65
Help Alice and Bob to find a treasure on the island Mallorca. For this purpose, a three-stage cipher needs to be broken.
Read more...


Last edited by admin on Wed Jul 31, 2013 15:14, edited 1 time in total.

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 Post subject: Re: Challenge "BCR code (Book-Caesar-RSA)"
PostPosted: Thu Sep 13, 2012 14:28 

Joined: Mon May 23, 2011 21:21
Posts: 31
is it possible, that the evaluation of the solution does not work correctly?
i have a solution and i am almost sure that it is correct (i checked it some times), but unfortunately the solution is not accepted.

best regards,
jomandi


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 Post subject: Re: Challenge "BCR code (Book-Caesar-RSA)"
PostPosted: Thu Sep 13, 2012 15:08 

Joined: Wed Jul 27, 2011 17:13
Posts: 247
Use spaces in the solution.
The solution without spaces is not accepted, but it is nowhere mentioned, that we have to use spaces. (I had the same problem trying to figure out the desired format)


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 Post subject: Re: Challenge "BCR code (Book-Caesar-RSA)"
PostPosted: Thu Sep 13, 2012 15:43 

Joined: Mon May 23, 2011 21:21
Posts: 31
the solution is now accepted with the additional spaces. thanks for the help.

best regards,
jomandi


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 Post subject: Challenge "BCR code (Book-Caesar-RSA)"
PostPosted: Thu Sep 13, 2012 17:32 

Joined: Sun Dec 18, 2011 14:41
Posts: 39
Hello

your observations are correct about having to add spaces so that the solution is accepted
As i am the author of this challenge In the first versions i used the expression with spaces which increased the message and thus the RSA number n. In this case the time to factor this number was too big for a Level 2 challenge.
So in the last and final version of this challenge we agreed to use the "strange" text as a solution where no spaces where inserted, as it is mentioned in the example as well.
I believe somewhere during the process something was misunderstood and we came to this frustrating event.

I have already contacted to a member of the MTC3 team to
- either add a comment to add additional spaces in order that the solution to be accepted or
- to alter the procedure in order to accept the text that is revealed after the RSA deciphering (without the additional spaces) - which is more appropriate

Either way you will be informed
Sorry for any inconvenience
George Theofanidis


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 Post subject: Re: Challenge "BCR code (Book-Caesar-RSA)"
PostPosted: Mon Sep 17, 2012 16:09 

Joined: Tue Mar 01, 2011 11:56
Posts: 53
We updated the PDF files. Now the information regarding the spaces is included.

We apologize for the inconvenience!


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 Post subject: Re: Challenge
PostPosted: Tue Feb 11, 2014 11:37 

Joined: Sat Aug 18, 2012 13:48
Posts: 4
Is it possible, that the example for RSA encryption in the text doesn't actually work?
I checked it with Wolfram Mathematica. Correct me if I'm wrong, but wouldn't I have to calculate
PowerMod[c,e,n]? If I enter PowerMod[11118972545543347912460760023455,17,23733023782520878059756093771613] I get an entirely different result:16954639647529558846119482491199.
Did I make a mistake?


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 Post subject: BCR code (Book-Caesar-RSA)
PostPosted: Tue Feb 11, 2014 17:35 

Joined: Sun Dec 18, 2011 14:41
Posts: 39
Dear Trismegistos

1. As for the data of the example, they are correct

2. As for Powermod in Wolfram Mathematica :

The syntax is

PowerMod[a, b, m], which gives a^b mod m

so you should have used PowerMod[m, e, N] to find the ciphertext :

This way PowerMod[065083049048069048053068048051,17,23733023782520878059756093771613]

should give 11118972545543347912460760023455

and PowerMod[c, d, N] to find the plaintext :

PowerMod[11118972545543347912460760023455,16752722670014729874339333912641,23733023782520878059756093771613]

should give 065083049048069048053068048051

by the way d = 16752722670014729874339333912641 is not given in the example, but it is calculated when you factor n . . .

3. As for how can you delete a topic :
Some time ago you could delete your own topic because a small icon with the symbol x was next to your own topic, next to the exclamation mark "!"
Nowdays this symbol has disappeared so i believe you cannot delete it by your own. Maybe MTC3 team can clarify this

Best Regards
George Theofanidis


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 Post subject: Re: Challenge
PostPosted: Thu Feb 13, 2014 16:51 

Joined: Sat Aug 18, 2012 13:48
Posts: 4
I'm terribly sorry. I obviously confused e and d. Oh dear. I'm sorry.


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 Post subject: Re: Challenge
PostPosted: Wed Apr 08, 2015 11:40 

Joined: Thu Feb 19, 2015 19:18
Posts: 14
Hello,

if have a problem by the RSA-chiffre. I think i have found the other solutions but i don't know whether they are correkt. Can someone perhaps check my solutions?

Thank you!

Best regards
kiekuk


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