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Challenge "Alice's Birthday Party (Part 1)"  

  By: admin on May 7, 2010, 2:28 p.m.

Alice sends encrypted invitations for her birthday party to her friends. As it turns out, two of her friends use the same RSA parameter N. This fact allows an adversary Eve to decrypt the encrypted message without knowing the corresponding secret key.

Where does Alice's party take place? The codeword for this challenge is the location of Alice's party.
Read more...

 Last edited by: admin on May 19, 2022, 11:10 a.m., edited 2 times in total.

Re: Challenge "Alice's birthday party (Part 1)"  

  By: wittiger on Oct. 16, 2010, 10:37 p.m.

I'm having problems entering my solution. I very sure I got it correctly, yet I#m told it is wrong and to try again.

(I'm sure because I can clearly read the two sentences the answer is comprised of)

Can you be more specific on what to enter into the textbox in order for it to count?

Martin

Re: Challenge "Alice's birthday party (Part 1)"  

  By: wackerao on Oct. 17, 2010, 12:51 a.m.

If you can already read the text, then the solution to your problem is probably hidden in the description of challenge. On the website description you find:

"Where does Alice's party take place? The codeword for this challenge is the location of Alice's party."

I agree this can be overlooked, since it is not specified inside the challenge-pdf.

Cheers,
Arno

Re: Challenge "Alice's birthday party (Part 1)"  

  By: unknown on Oct. 22, 2010, 8:20 p.m.

is it on purpose that in the example in the description an 'a' is appended at the end of the base64hex string?

Re: Challenge "Alice's birthday party (Part 1)"  

  By: mazze on Oct. 23, 2010, 7:07 p.m.

no, sorry, thats a mistake and not intended.
Openssl was used to encode the string in base64 and it appended a "new line" at the end. Nevertheless, even then it is wrong because then is should be 0a at the end.

Sorry for the confusion. I will fix it.

Cheers,
Mazze

Re: Challenge "Alice's Birthday Party (Part 1)"  

  By: accepted_rush on Aug. 24, 2011, 6:25 p.m.

—-8><——
MTC3-Team Edit:

This post gave away big parts of the solution (or the approach). Therefore we will investigate if this posting was in violation of the forum rules and delete it, if it was (or reactivate it if we come to the conlcusion that the challenge was not harmed by the information given). Until then, please refrain from re-posting such infos.
—-8><——

 Last edited by: wackerao on Aug. 25, 2011, 12:02 a.m., edited 1 time in total.
Reason: Post might be in violation of forum rules!

Re: Challenge "Alice's Birthday Party (Part 1)"  

  By: fretty on Aug. 24, 2011, 6:55 p.m.

Please can the moderators delete the post before this…it blatantly gives an full solution to the challenge.

Re: Challenge "Alice's Birthday Party (Part 1)"  

  By: accepted_rush on Aug. 25, 2011, 12:47 a.m.

I am very sorry. I just mentioned the Number Theory's approach behind the problem, since it's different from the level 1 problems and it has no chance to be solved with only pencil and paper. I gave no tips on programming implementation or whatever.
So, maybe I could just say "Diophantine Equation rocks…" ? [HTML_REMOVED]

Re: Challenge "Alice's Birthday Party (Part 1)"  

  By: fretty on Aug. 25, 2011, 1:01 a.m.

The idea of this forum is more to help people that need it by giving brief hints…after all what use is it to just be given the solution.

With this challenge…and a few others, the entire solution revolves around the method rather than the "programming". In fact, once you know how to do this challenge you don't even need to program at all since it boils down to a routine calculation.

Re: Challenge "Alice's Birthday Party (Part 1)"  

  By: fretty on Aug. 25, 2011, 1:03 a.m.

Basically, in your post you told people exactly how to do it, leaving any potential readers in the position of only needing a big number calculator (which CrypTool and and many other websites/programs have)

Re: Challenge "Alice's Birthday Party (Part 1)"  

  By: ljuhrich on Nov. 1, 2012, 7:46 p.m.

I've got a little question:
I know the mathematical context behind this problem and I just jave to calculate to get the plaintext. But there's a big potency in it, so My question: how long does it take for a computer (Athlon XP@2GHz) to potence a x10^300-number with a 10^4 Exponent?

Re: Challenge "Alice's Birthday Party (Part 1)"  

  By: ljuhrich on Nov. 4, 2012, 3:50 p.m.

Solved, didnt take much time…

Re: Challenge "Alice's birthday party (Part 1)"  

  By: arvindsraj on July 14, 2013, 7:04 a.m.

no, sorry, thats a mistake and not intended.
Openssl was used to encode the string in base64 and it appended a "new line" at the end. Nevertheless, even then it is wrong because then is should be 0a at the end.

Sorry for the confusion. I will fix it.

Cheers,
Mazze

The example hasn't been corrected yet right? Because Base64("Beispieltext) is "QmVpc3BpZWx0ZXh0" while Base64("Beispieltext\n") is "QmVpc3BpZWx0ZXh0Cg==". I guess a newline got appended before base64 encoding?

Re: Challenge  

  By: cruachan on Sept. 27, 2013, 2:07 a.m.

Is the same plaintext message used to create the ciphertexts c1 and c2? Quite important to know, which algorithms work or work not.

Re: Challenge  

  By: veered on Dec. 28, 2013, 1:10 a.m.

Is the same plaintext message used to create the ciphertexts c1 and c2? Quite important to know, which algorithms work or work not.

Yes the same plaintext message is used to create both c1 and c2.


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