LastPass encryption scheme is recently changed to use more PBKDF2 rounds, specifically 100100. This seems like a really weird number choose. From what I understand brute force time scales linearly with rounds because more rounds simply mean that each hash takes longer/more memory to compute. Being just over 100k, it feels like there could be some weird prime number tricks that they are trying to avoid, but I honestly can't come up with anything, and it doesn't seem to be for backward compatibility with un-upgraded vaults either because those used to be 5k rounds IIRC, which would make it 105000 if they just slapped the extra 100k rounds on top.
So, why did they pick such a weirdly specific number instead of just straight up 100k? I don't get it.