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.
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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...
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
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)
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 way you will be informed
Sorry for any inconvenience
George Theofanidis
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?
By: Theofanidis on Feb. 11, 2014, 4:35 p.m.
Dear Trismegistos
As for the data of the example, they are correct
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 . . .
Best Regards
George Theofanidis
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.
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
By: Theofanidis on April 9, 2015, 8:22 p.m.
Dear Ossili :
You are absolutely "right" for both of your points
"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.
"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