write-ups-challenges-2021-2022/rng_farm/SOLUTION.md

Difficulty

Hard. It requires knowledge on websocket networking, encoding and decoding, and naturally random number generation. 120 points

How To Solve

The greenies can be expressed in 2 bits each, and in total they form 18 bytes. The seed is XORed with a random bitstring, which forms the first set of greenies. This value is then used in place of the seed to be XORed by the same random bitstring, but bit-shifted by one to the right. Simply find this random bit-string by analysing the random outcomes by reverse XOR-ing, shift it one to the left, and XOR that with the first harvest. This will give you the seed in binary, convert it to ascii to uncover the string!

Flag

IGCTF{oLdMcDoNaLd}