This challenge gives a remote server, a binary file, and the following description.

Am incercat sa ghicesc raspunsul, insa nu am reusit:( Care sunt sansele…depinde de tine

I tried to guess the answer, but I couldn’t 🙁 What are the chances … it’s up to you

Opening the file in IDA we immediately see that the main function just calls another function called predict:

Looking at the predict function we can see that this is the function that outputs the flag after a series of questions:

But looking at the start of the function we can see some calls to the srand and rand , we can also see that the return value is stored in some variable.

Add breakpoints when the values are stored and reading the value from eax gives us the response to the 3 questions.

After debugging we get this values:

653FDDCB = 1698684363

D5AE3203 = 3584963075

4E435224 = 1313034788

Sending them to the remote server and we get the flag: abso-tech{PRNG_m4st3r_und3r7t4nd1ng_:O}

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