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Challenge "BCR code (Book-Caesar-RSA)"  

  By: Javex on Sept. 12, 2012, 6:42 p.m.

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 Oct. 31, 2021, 2:55 a.m., edited 1 time in total.

Re: Challenge "BCR code (Book-Caesar-RSA)"  

  By: jomandi on Sept. 13, 2012, 2:28 p.m.

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

Re: Challenge "BCR code (Book-Caesar-RSA)"  

  By: Veselovský on Sept. 13, 2012, 3:08 p.m.

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)

Re: Challenge "BCR code (Book-Caesar-RSA)"  

  By: jomandi on Sept. 13, 2012, 3:43 p.m.

the solution is now accepted with the additional spaces. thanks for the help.

best regards,
jomandi

Challenge "BCR code (Book-Caesar-RSA)"  

  By: Theofanidis on Sept. 13, 2012, 5:32 p.m.

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

Re: Challenge "BCR code (Book-Caesar-RSA)"  

  By: aurelie on Sept. 17, 2012, 4:09 p.m.

We updated the PDF files. Now the information regarding the spaces is included.

We apologize for the inconvenience!

Re: Challenge  

  By: Trismegistos on Feb. 11, 2014, 10:37 a.m.

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?

BCR code (Book-Caesar-RSA)  

  By: Theofanidis on Feb. 11, 2014, 4:35 p.m.

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 . . .

  1. 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

Re: Challenge  

  By: Trismegistos on Feb. 13, 2014, 3:51 p.m.

I'm terribly sorry. I obviously confused e and d. Oh dear. I'm sorry.

Re: Challenge  

  By: kiekuk on April 8, 2015, 11:40 a.m.

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

Re: Challenge  

  By: Theofanidis on April 8, 2015, 7:53 p.m.

Dear kiekuk

Since i am the author of this challenge, please send me a PM (private message with your findings, in order to assist you

Best Regards
George Theofanidis

Re: Challenge  

  By: Ossili on April 9, 2015, 7:29 a.m.

Hello Mr. Theofanidis

i think that in the example on page 9 the letters are shifted 4 positions to left
or 22 to right, right ?

Kind regards
Ossili

Re: Challenge  

  By: Ossili on April 9, 2015, 3:02 p.m.

And the plaintext m on page 11 (in the german doc) has a wrong value.

Kind regards
Ossili

Re: Challenge  

  By: Theofanidis on April 9, 2015, 8:22 p.m.

Dear Ossili :

You are absolutely "right" for both of your points

  1. "i think that in the example on page 9 the letters are shifted 4 positions to left
    or 22 to right, right ?". Indeed the phrase right or left or up or down could be misleading and indeed it is wrong. It should be written as "4 positions to the left or 22 to the right". The fact is that if one understands the example, one has to convert I to E, then E to A and so on. Also the fact that 41 members have solved it up to know it means that they have understand this mistake.

  2. "And the plaintext m on page 11 (in the german doc) has a wrong value.". Also this observation is correct. The value of m in the German doc is wrong while in the English version is correct. Again one can see the fault if he factors the RSA digits, but again one is not supposed to do so in order to verify an example. Since my German is at all good for understanding i did not compare the text and the relevant digits . . .

I will be more consistent when being an author to new challenges.

Thanks again for your observations.

Anyway, sorry for any inconvenience. I will propose to the MTC3 team to correct this mistake

Best Regards
George Theofanidis

Re: Challenge  

  By: Scatha on April 27, 2015, 3:57 p.m.

Hello,

the bcr challenge has been updated according to the issues Ossili pointed out in his post.

@Ossili
Thank you for finding those faults.

Best regards,
Scatha


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