Why do multiple algos make it more secure? Isn't it basically as secure as the weakest link, i.e. the algo with (relatively) least mining power?
since the algos are independent one algo compromised means only 20% of the blockchains is compromised. unlike chained algos like x11 where the algos are sequential and if one link is broken the chain is broken.
myr ftw.
With a single blockchain secured by five algos (with independent difficulties), what does it mean for "20% of the blockchains" to be compromised? Surely a blockchain is either compromised or it's not. Can you expand please?
It's only a metaphorical picture. If a malicious attacker would gain leverage over 1 algo (20% of the blockchain) there are 4 other algos that will secure the blockchain, thus the blockchain will remain unaffected. We only use the percentages to give a better idea of what a 51% attack would look like to myr. There was a 51% accident on scrypt last week about the same time it happened on AUR. You know what happened ? Nothing. The pool with 51% of scrypt forked and that's about it, the blockchain had no reaction whatsover to the fork created and ignored it like business as usual. Like it was explained above 51% in one algo is only about 11% of the whole hash power. It's like cutting off a reptile's limb, the rest of the body remains unaffected and it will grow back the said limb imediately.
Well, I still don't get your point, sorry.
If a malicious attacker gains leverage over one algo, what is to stop him launching a double spending attack using that algo, and reversing several transactions from other algos (no matter how much mining power is put onto them)? Done correctly, a double spending attack could potentially net a malicious attacker substantial funds; more than legitimate mining at least.
It also isn't clear to me how a node calculates the best chain. If it is cumulative difficulty, without any normalisation, then what is to stop someone reversing a sequence of low difficulty blocks (e.g. Scrypt or Qubit ones, currently) by means of a single high difficulty block (SHA256D, currently)?
Perhaps these points are just me being dumb. The technical study on 51% attacks that you have put the bounty out for will be most welcome. In the meantime feel fee to point out my mistakes (in technical terms, without harming reptiles, plz).
What you're missing in there is that the speed of the other algo's acts as a rate limiter as far as i know. as the retarget works to ensure there is an even distribution of 30 second blocks per algo.
