The challenge tells us that ‘sharing is caring!’ and it was just hinting that the challenge was about a secret sharing scheme. The goal was to recover the secret under certain conditions, the most basic one is that we can only get up to threshold-1 shares (otherwise the challenge would be about doing calculations), however, we were able to find an additional free share and thus recover the secret really easily.

Original writeup (https://www.ayoub-benaissa.com/blog/csaw-final19-sharing-is-caring/).