Hello, Good question, I'm the author of Yilacoin and Kylacoin, I used SHA3 algorithm for PoW hash, block hash and transaction hash including witness transaction hashes. SHA3 is secure against length extension attacks, you can research more about it on the web. SHA3 algorithm was used by a coin created in 2019 called BSHA3 but the project looks like abandoned so I created Yilacoin with an active development, I created Kylacoin because Yilacoin has premine and some people don't like it, tend to have better value in the future. Also these coins have the block time of 60 seconds not 10 minutes which means transaction are confirmed very faster than bitcoin, makes it even usable in fast food stores for example. One more problem bitcoin has, is if one node goes down, if won't be notified of new transactions in the meanwhile, I altered the client so each node asks for the full mempool once per connection, which now no transaction will be left behind. I also am a computer programmer like every other programmers like new challenges you can't just call it an experiment. can I ask you what's your purpose of asking the question?