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Challenge "Trendy Messenger"

Challenge "Trendy Messenger"  

  By: admin on June 12, 2018, 1:26 p.m.

Sniffing on the WiFi, you notice an ElGamal encrypted message. Are you able to compute it?
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Re: Challenge  

  By: madness on April 21, 2020, 9:34 p.m.

I tried brute-forcing r < 2^32, but no match.
Am I missing something?

Re: Challenge  

  By: tryone144 on April 26, 2020, 4:46 p.m.

Hey madness,

the used r is definitely in the range (0, 2^32). But there are significantly faster methods than brute-force. ;)

If you still struggle with this challenge, you can write me a PM with your approach and I'll take a look.

Greetings, BB

Re: Challenge  

  By: madness on April 27, 2020, 9:18 p.m.

Admins would like me to tell what happened. It turns out that I had miscopied one of the numbers from the PDF file. Once that was corrected, I tried a faster method (not brute-forcing) and found the correct exponent.

Regarding beta value  

  By: vinay27 on Sept. 7, 2020, 10:42 p.m.

why is delta smaller than beta?

Re: Regarding beta value  

  By: tryone144 on Sept. 11, 2020, 9:09 p.m.

Hey vinay27,

i've moved your question to the corresponding challenge thread. ;)

To answer your question:
The value of gamma can be smaller than beta since gamma is an element in Z_p as well — and therefore gamma = m * beta^r mod p.

Greetings, BB


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