From a conversation on Komodo Telegram:
Regnar: The reason why Komodo notarizes to Bitcoin is because of the huge amount of hash power Bitcoin has that makes 51% attacks very unlikely. Komodo uses [Equihash] Proof of Work for it’s own mining algorithm for transactions, what we use Bitcoin for is to essentially store a fingerprint (notarization) of the Komodo blockchain to Bitcoin every 10 minutes. This means if someone tries to 51% attack Komodo they can’t change anything that was in that fingerprint on Bitcoin, unless they 51% attack Bitcoin as well and specifically alter that fingerprint (to the new one they need for the attack to work).
So technically if someone were able to 51% attack Bitcoin, it wouldn’t affect Komodo because we only store these fingerprints there. Komodo still mines just like any other blockchain and we can actually switch where we store fingerprints to the next strongest chain to keep dPoW security up (if Bitcoin is attacked we could store it on Ethereum or Litecoin or Bitcoin Cash or whatever works best.)
So to attack Komodo they need to gain 51% of Komodo hashrate, as well as 51% of Bitcoin hashrate (to change the notarizations) at the same time. If they JUST attack Bitcoin, Komodo can notarize to a different blockchain and run fine on its own mining. If they JUST attack Komodo they won’t be able to change past notarizations and if their “double spend” transaction gets notarized while they are performing their attack, they won’t be able to reverse it by releasing their malicious blocks.
Yorklab: Bottom line is that nobody is going to attack Bitcoin just to get to Komodo. The hashrate on Bitcoin is so high now it’s almost impossible to attack Bitcoin; so ultimately it’s almost impossible, and most definitely impractical to attack Komodo. There’s a reason other coins are starting to use Komodo’s dPoW system, or trying to come up with something similar on their own.